electromagnetic wave

[diàn cí bō]

Physical concepts

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synonym air waves (radio wave) generally refers to electromagnetic wave

Electromagnetic wave Is created by in-phase oscillation^[1] And perpendicular to each other electric field And magnetic field Oscillating particle waves derived and emitted in space are propagated in the form of waves electromagnetic field , with Wave particle duality , which Particle morphology be called photon The relationship between electromagnetic waves and photons is not black or white, but two aspects of their properties according to different actual research. The electric and magnetic fields, which oscillate in phase and are perpendicular to each other, move in the form of waves in space, and their propagation direction is perpendicular to the plane formed by the electric and magnetic fields. The speed of electromagnetic wave in vacuum is fixed, and the speed is light speed 。 see Maxwell's equations 。

Electromagnetic wave concomitant Electric field direction The magnetic field direction and the propagation direction are perpendicular to each other, so the electromagnetic wave is transverse wave 。 Electromagnetic waves are actually divided into radio waves and Magnetic wave , is the general name of the two, but because the electric field and magnetic field always appear at the same time, disappear at the same time, and convert each other, they are commonly referred to as electromagnetic waves, sometimes directly referred to as radio waves.

stay quantum mechanics In terms of angle, the energy of electromagnetic wave is presented as photons one by one. Photons are essentially wave packet That is, the wave presented as local energy. The energy of electromagnetic wave is quantized, when its energy level step transitions over radiation critical point , then radiates outward in the form of photons. At this stage, the wave body is photons, and photons belong to Boson 。

certain frequency range The electromagnetic wave of visible light , or simply light, sunlight It is a visible radiation form of electromagnetic wave. Electromagnetic waves propagate independently of the medium.

electromagnetic radiation Generally, it refers to electromagnetic waves with all electromagnetic radiation characteristics, Nonionizing radiation Means radio waves , microwave infrared , visible light ultraviolet rays 。 and X-ray and Gamma ray Usually considered as radioactivity Radiation. call ionizing radiation^[2] 。

It is important to note that electromagnetic waves are not Mechanical wave The same vibration occurred in space, but propagation path The change of electric field and magnetic field properties at different points on the.

Chinese name: electromagnetic wave
Foreign name: Electromagnetic wave
Alias: air waves 、 electromagnetic radiation
expression: Propagation: c=λ f Energy: S=E × H
Presenter: James Clerk Maxwell

Proposed time: 1865
Applicable fields: Communication, microwave oven, remote control, telescope
Applied discipline: Physics
Verifier: hertz
Particle morphology: photon
Hazards: Thermal effect, non thermal effect and accumulation effect

catalog

▪ example
four find
▪ theory
▪ confirm
five produce
six nature
seven Electromagnetic spectrum
eight Radio spectrum
nine Penetration of electromagnetic waves

ten application
▪ radio communication
▪ medical care
▪ other
eleven electromagnetic radiation
▪ Definition of electromagnetic radiation
▪ type
▪ Human injury
▪ performance
▪ Recognize hazards
twelve Electromagnetic pollution

definition

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From a scientific point of view, electromagnetic wave is a kind of energy, belonging to a kind of wave, just like Mechanical wave ， Gravitational wave and Matter wave （ Probability wave ）Same as above Absolute zero The higher the temperature, the higher the frequency and the shorter the wavelength of the electromagnetic wave. This kind of electromagnetic wave is called Blackbody radiation 。 Just as people have been living in the air but can't see the air with their eyes, they can't see other electromagnetic waves everywhere except light waves.

electromagnetic field Including electric field and magnetic field, respectively electric field intensity E (or Electric displacement D) And Magnetic flux density B (or magnetic field intensity H) Indicates its properties. According to Maxwell's Electromagnetic field theory These two parts are closely related. The time-varying electric field will cause the magnetic field, and the time-varying magnetic field will also cause the electric field. When the source of the electromagnetic field changes with time, its electric field and magnetic field excite each other to cause the movement of the electromagnetic field and form electromagnetic waves. Electromagnetic propagation velocity Equal to the speed of light at free space In, c=299792458m/s ≈ 3 × 10 eight m/s。 The travel of electromagnetic waves is accompanied by the transmission of power.

electromagnetism Radiation Temperature related, usually higher than Absolute zero Of substances or particles electromagnetic radiation The higher the temperature, the greater the radiation, the higher the frequency, and the shorter the wavelength, but most of them cannot be observed by the naked eye.

attribute

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Basic Attributes

Electromagnetic waves have three properties , i.e amplitude (strength light intensity ）, frequency (wavelength) and waveform (spectrum distribution), for visible light The three correspond to Lightness , hue and chroma For electromagnetic waves with single frequency Initial phase The waveform is Sine curve (cosine curve), called sine wave （ Cosine wave ）, the closer the waveform of electromagnetic wave is sine wave The purer its spectrum is, the better its monochromaticity is. A typical example is laser.

An important attribute of electromagnetic waves is Frequency, which can determine various properties of electromagnetic wave, but describing the frequency of electromagnetic wave is not necessarily based on the frequency itself, but also related to the frequency physical quantity , wavelength is commonly used (if no description is given, then Default refers to vacuum Wavelength in , is the only corresponding relationship with frequency, and is inversely proportional) Photon energy (proportional to frequency) wave number (The reciprocal of the wavelength, which is proportional to the frequency, defaults to the wavelength in the vacuum) and the period (which is inversely proportional to the frequency).

Physical quantity symbol

Frequency → f or ν（ Greek alphabet New, no English letter v， be chiefly used in quantum mechanics ）, wavelength → λ, photon energy → E, wave number → k（ spectroscopy σ and ν), period → T, speed of light → c (in vacuum) or v (in medium) (wavelength λ, wave number k, speed of light c Default refers to ）

Definitional expression ：f=1/T，λ=c/f(=c/ν)，E=hf(=hν)，k=1/λ

Conversion between physical quantities related to electromagnetic waves

f(=ν)=c/λ=1/T=E/h=ck

λ=c/f(=c/ν)=cT=hc/E=1/k

E=hf(=hν)=hc/λ=hck=h/T

k=1/λ=f/c(=ν/c)=E/hc=1/cT

T=1/f(=1/ν)=λ/c=1/ck=h/E

Propagation velocity of electromagnetic wave in vacuum（ wave velocity ）Is a certain value, that is, the speed of light (in vacuum), which is recorded as c, c=299792458m/s. Electromagnetic waves can propagate in both vacuum and medium, but the wave speed in the medium will decrease. Generally, the wave speed of electromagnetic waves in gas, liquid and solid will decrease in turn. The effect of a medium on an electromagnetic wave Refractive index N is equal to the speed of light c in vacuum divided by the speed v of the electromagnetic wave in the medium. The refractive index of vacuum is 1, the refractive index of gas is slightly greater than 1, and the refractive index of liquid and solid is greater than 1. The greater the refractive index, the smaller the wave speed in the medium. Generally, in the same medium, the higher the frequency of electromagnetic wave (the shorter the wavelength), the greater the refractive index and the lower the wave speed. For example, in the same medium, the refractive index of purple light is larger than that of red light (purple light Frequency ratio Red light is high and its wavelength is shorter than red light).

Wave particle duality

All electromagnetic waves have Wave particle duality , which Particle morphology It is called photon. The relationship between electromagnetic wave and photon is not black or white, but two sides reflected by their properties according to different actual research. They coexist. about Mechanical wave and Gravitational wave In terms of particle morphology—— phonon and Graviton Where phonons are quasi particles, requiring the existence of media, while gravitons may be the same as photons Boson , but it has not been observed yet, belonging to a kind of Hypothetical particle 。 according to quantum mechanics Theory, Physical particle There are also Volatility , this wave is called Matter wave , or de Broglie wave.

Volatility and Particle property The strength of depends on the frequency and wavelength, radio waves It is dominated by fluctuation, and the particle property is extremely weak; Microwave waves are strong, and there are also some particles; infrared 、 visible light and ultraviolet rays Both fluctuation and particle characteristics are obvious, and they are in the transition zone between fluctuation and particle characteristics; X-ray Although it can happen Diffraction phenomenon （ X-ray microscope ）, but the fluctuation is weak and the particle property is obvious（ Compton effect ）, strong ionization capacity; Gamma ray It is mainly particle, with strong ionization ability and weak fluctuation.

electromagnetic field

Electromagnetic field is a special form of matter, which has the main properties of general matter, such as mass, energy, momentum, etc. Objectively, there is always a unified electromagnetic field that has nothing to do with the observation conditions. To divide it into electric field and magnetic field is relative and related to the test conditions.

spherical wave 、 cylinder Wave and plane wave For electromagnetic waves that change sinusoidally with time Isophase surface (That is, the front of the wave) is spherical, cylindrical or planar, and electromagnetic waves are spherical Cylindrical wave And plane wave.

Transverse electromagnetic wave 、 Transverse wave And Transverse magnetic wave The electromagnetic wave whose electric field and magnetic field are both in the plane perpendicular to the propagation direction is called transverse electromagnetic wave TEM wave 。 The electromagnetic wave with only electric field on the plane perpendicular to the propagation direction of the wave is called transverse wave, or TE wave for short. The electromagnetic wave with only magnetic field on the plane perpendicular to the propagation direction of the wave is called transverse magnetic wave, or TM wave for short.

frequency range

Electromagnetic wave length and frequency

electromagnetism spectrum According to the wavelength λ or frequency f (λ f=c=299792458m/s ≈ 3 × 10) of the sinusoidal electromagnetic wave in the free space eight M/s) Sequential arrangement The resulting table is called Electromagnetic wave spectrum 。 For convenience, the spectrum is often divided into frequency bands or bands, as shown in the table. Above 300GHz, enter in sequence Far-infrared , visible light, x-ray and Gamma ray Area.

Electromagnetic wave length and frequency

Electromagnetic frequency range Can be accessed from Infinite approach At 0Hz (the wavelength is close to infinity, considering Observable universe The minimum frequency is about 3.4 × 10 -19 Hz， The corresponding wavelength is about 93 billion light years), and the Planck frequency is 1.85 × 10 forty-three Hz (wavelength equal to Planck length ）The frequency range that human technology can detect is 10 -2 ~10 thirty-five Hz, from ELF (pole long wave , for ground exploration) -2 Hz (0.01Hz) to Extremely high frequency (Very short wave, ultra-high energy cosmic rays ）10 of thirty-five Hz。 Electromagnetic waves are divided by frequency and wavelength. From low to high frequency (from long to short wavelength), they can be divided into radio waves , microwave infrared 、 visible light 、 ultraviolet rays 、 X-ray and Gamma ray The electromagnetic wave visible light that can be seen by human eyes is only a small part of it. Electromagnetic frequency International unit yes hertz (Hz), and millihertz (mHz, 10 -3 Hz）、 Kilohertz Z (kHz, 10 three Hz）、 Megahertz（ MHz ，10 six Hz）、 Gigahertz（ GHz ，10 nine Hz）、 Terahertz （THz，10 twelve Hz）、 Beat Hz (PHz, 10 fifteen Hz）、 EHz, 10 eighteen Hz）、 Zehertz (ZHz, 10 twenty-one Hz) and YaoHz (YHz, 10 twenty-four Hz), etc. The electromagnetic wave frequency used for broadcasting is 10 five ～10 eight Hz, the electromagnetic wave frequency used by TV is 10 seven ～10 eight Hz magnitude, mobile phone wireless network The electromagnetic wave frequency used is 10 eight ～10 nine Hz magnitude, Optical fiber communication The electromagnetic wave frequency used is 10 fourteen Hz magnitude.

calculation

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And Mechanical wave (such as sound wave, water wave and rope wave) and Gravitational wave Similarly, electromagnetic waves have the nature of waves. Refraction and other phenomena can occur. Its speed, wavelength and frequency meet the relationship:

propagation velocity =Wavelength × frequency.

The propagation speed of electromagnetic wave in the air is the speed of light, and the wavelength λ=299.792458/frequency F（ GHz ）Mm ≈ 300/frequency F (GHz) mm. from Geostationary satellite Earthbound Propagation time About 1/8 second.

formula

Electromagnetic waves in sunlight

c=λf

c： wave velocity (The speed of light is a constant, equal to 299792458m/s in vacuum, Approximately equal to 3×10 eight M/s) Unit: m/s

f: Frequency (unit: Hz, 1MHz=1000kHz=1 × 10 six Hz）

λ: Wavelength (unit: m)

The wave velocity of electromagnetic wave in vacuum is c, which is equal to the product of wavelength λ and frequency f

In vacuum Electromagnetic wave propagation The speed c is about 300000 kilometers per second Material movement The fastest speed of. C is a very important constant in physics, and the accepted values are:

c=299792.458km/s≈3×10 eight m/s

The unit of electromagnetic wave frequency is also hertz （Hz）。 But the common unit is Kilohertz (KHz) and Megahertz （ MHz ）。

energy

Electromagnetic wave has energy. Electromagnetic wave is a kind of substance, which is composed of electric field and magnetic field, but has no mass.

Poynting vector

The energy of electromagnetic wave is determined by Poynting vector Decide that S = E × H , where S Is Poynting vector, E by electric field intensity ， H by magnetic field intensity 。 E 、 H 、 S Constitute vertically with each other Right-hand spiral Relationship; That is S That represents the unit time flowing through the unit area perpendicular to it Electromagnetic energy ， Unit: W/m two 。

Intensity and amplitude

Electric and magnetic field components of electromagnetic waves

Electromagnetic waves are generated by electric field Component E And magnetic field Component H The direction of the electric field component and the magnetic field component is always perpendicular to each other, and the phase is the same. The electric field component of the electromagnetic wave is called radio wave, and the magnetic field component is called Magnetic wave However, sometimes electromagnetic waves can be simply called radio waves. For single frequency electromagnetic wave, its waveform is Sine curve (cosine curve), called sine wave （ Cosine wave ）, so sine Function is a basic tool for studying electromagnetic waves, which can greatly simplify formula calculation. Any electromagnetic wave with complex spectrum can be superimposed by sinusoidal electromagnetic waves with different frequencies. The common method for decomposing complex electromagnetic waves into electromagnetic waves with different frequencies or wavelengths is Fourier transform 。

The energy of electric field component and magnetic field component is always converted to each other, so the energy of electromagnetic wave（ Electromagnetic energy ）Actually Electric field energy (electric energy) and Magnetic field energy （ Magnetic energy ）They are composed together, and their energy is equal at any time, which is half of the total energy. The energy transmitted by electromagnetic wave in unit time is called power, and the derivative of electric energy and magnetic energy with respect to time is electric field and magnetic field instantaneous power The electric field power is proportional to the square of the electric field strength, and the magnetic field power is proportional to the square of the magnetic field strength. The magnitude of both conforms to the change of the sine function, except that the change frequency is twice the frequency of the electromagnetic wave itself. The instantaneous power of the electromagnetic wave is the sum of the instantaneous power of the electric field and the instantaneous power of the magnetic field, which is always twice the instantaneous power of the electric field or the instantaneous power of the magnetic field. Generally, the power is integrated on a cycle and average value The power thus obtained is called Average power 。

Electromagnetic Electric field intensity E and Magnetic field strength H The maximum that can be reached absolute value Called electromagnetic wave Maximum or amplitude , the amplitude of electromagnetic wave is divided into electric field amplitude and magnetic field amplitude, and the units are V/m and A/m Both of them can characterize the intensity of electromagnetic waves, but in practical applications, electric field intensity is more used as the expression method of electromagnetic wave amplitude. In addition, there is a potential shift（ induction Strength) D and Magnetic induction B is used to represent the amplitude of electromagnetic wave, and the units are C/m two and T (i.e Wb/m two ）。 Electromagnetic strength Usage (average) Energy flux density S (or I, energy transmitted per unit area in unit time) W/m two , the vector corresponding to the energy flow density is called Poynting vector S ， S Direction of and E 、 H It is vertical and forms a right-hand spiral relationship, with the size of E and H The product of sizes. The square of energy current density and electric field strength or magnetic field strength Proportional Therefore, amplitude (electric field strength and magnetic field strength) can also be used to describe the strength of electromagnetic waves, but it is similar to its actual strength square root Proportional relationship.

In order to simplify the calculation, the electric field strength and magnetic field strength are often used as equivalent power DC component Intensity, which is called Valid values , effective value E of electric field strength and magnetic field strength r And H r Is 1/√ 2 times of its maximum value (amplitude), i.e. E r =E/√2，H r =H/√2。

remember electric field intensity Is E, magnetic field intensity Is H, Electric displacement (electric induction strength) is D, Magnetic induction B (the maximum value is distinguished by subscript 0), Angular frequency (2 π times the frequency) is ω, Initial phase Is φ zero , there are:

(1)，

(2) Where ε is the dielectric Permittivity , μ is dielectric Permeability 。

Wave speed of electromagnetic wave:

Sorted out:

, i.e

，

(3)，

(4)

Mark Z as medium characteristic impedance , there is

In Ω 。

(5)，

(6)

Therefore, in a given medium (ε and μ are known), as long as one of the four quantities E, H, D, and B is known, the values of the other three quantities can be derived from the three formulas related to the known quantity in the six formulas (1), (2), (3), (4), (5) and (6). In other words, in a certain medium, as long as one of the four quantities E, H, D and B is determined, the other three quantities will be determined. For example, if E is known, there are:

，

。

The energy flow density of electromagnetic wave is derived as follows Calculation formula ：

Electric field intensity change function:

Magnetic field intensity change function:

Electric field transient energy density Calculation formula:

(ε is dielectric Permittivity ， Vacuum permittivity ε zero =1/(4πc two )×10 seven F/m≈8.854188×10 -12 F/m）

Calculation formula of instantaneous energy density of magnetic field:

(μ is dielectric Permeability ， Vacuum permeability μ zero =4π×10 -7 H/m≈1.256637×10 -6 H/m）

among

electromagnetic field The energy density of is electric field and Magnetic field energy density And, the instantaneous energy density of the electromagnetic field is:

Calculation formula of average energy density of electric field:

Calculation formula of average energy density of magnetic field:

Average energy density of electromagnetic field:

remember

Is in the direction of Poynting vector Unit vector , then Poynting vector of electromagnetic wave（ Energy flow density vector ）：

(Z is the characteristic impedance , vacuum characteristic impedance Z zero =119.9169832πΩ≈376.7303Ω）

Finally, we can get the relationship between the (average) energy flow density S of the electromagnetic wave, that is, the intensity I, and the amplitude. First, remember that the maximum value of Poynting vector size is S zero , the average value of energy flow density

Then remember that the effective values of electric field strength, magnetic field strength, potential shift (electric induction strength) and magnetic induction strength are E, H, D and B respectively. The following gives the strength of electromagnetic wave and four amplitudes of electric field strength, magnetic field strength, potential shift (electric induction strength) and magnetic induction strength (with subscript 0) and four valid values (without subscript 0):

The relationship between the energy flow density S (intensity I) of electromagnetic wave and the electric field intensity E:

, and its valid value:

The relationship between the energy flow density S (intensity I) of electromagnetic wave and the magnetic field intensity H:

, and its valid value:

The relationship between the energy current density S (intensity I) of electromagnetic wave and the potential shift (electric induction intensity) D:

, and its valid value:

The relationship between the energy flow density S (intensity I) of electromagnetic wave and the magnetic induction intensity B:

, and its valid value:

Since the electric field strength E is used to represent the amplitude, the relationship between the intensity and the amplitude can be simpler (because only one parameter, namely the characteristic impedance Z, is needed to be introduced, and the characteristic impedance is an important attribute of the medium, which is more significant), and the electric field is easier to study than the magnetic field. In addition, the electric field component plays a leading role in most electromagnetic wave phenomena, Instead of the magnetic field component, the electric field strength is the most concise way to describe the electric field component, so most scientists will use the electric field strength E as the characterization quantity of electromagnetic wave amplitude to calculate the relationship between electromagnetic wave strength and amplitude. In physics, without any explanation, The amplitude of electromagnetic wave usually refers to the amplitude of electric field strength E 。 When using the above formula, use International System of Units Calculate, then the amplitude of the electromagnetic wave, that is, the electric field strength E zero (or effective value E of electric field intensity) V/m , the unit of electromagnetic wave strength S (I) is W/m two , the unit of dielectric characteristic impedance Z is Ω 。

example

Problem: The intensity of an electromagnetic wave in vacuum is

Find its electric field intensity amplitude, magnetic field intensity amplitude, electric displacement (electric induction intensity) amplitude and magnetic induction intensity amplitude.

Solution: known electromagnetic wave strength

, vacuum permittivity

, vacuum permeability

, speed of light in vacuum

。

Vacuum characteristic impedance

Then the amplitude of electric field strength of electromagnetic wave

Magnetic field intensity amplitude of electromagnetic wave

Electric displacement (electric induction intensity) amplitude of electromagnetic wave

Magnetic induction amplitude of electromagnetic wave

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theory

In 1864, British scientist maxwell Summarizing previous studies Electromagnetic phenomenon The complete electromagnetic wave theory is established on the basis of. He concluded the existence of electromagnetic waves and deduced that electromagnetic waves have the same propagation speed as light.

confirm

In 1887, German physicist hertz The existence of electromagnetic waves is confirmed by experiments. Later, in 1898, Marconi carried out many experiments, which not only proved that light is an electromagnetic wave, but also found more forms of electromagnetic waves. Their essence is identical, but the wavelength and frequency are very different.

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Electromagnetic wave is electromagnetic field A form of movement of. Electricity and magnetism It can be said that there are two sides of one body. The changing electric field will produce a magnetic field (that is, the current will produce a magnetic field), and the changing magnetic field will produce an electric field. The changing electric field and the changing magnetic field form an inseparable unified field, which is the electromagnetic field. The propagation of the changing electromagnetic field in space forms electromagnetic waves. The electromagnetic changes are like the water waves generated by the gentle wind blowing on the water surface. Therefore, they are called electromagnetic waves, also known as electric waves.

Electromagnetic waves are first generated by James Clerk Maxwell It was predicted in 1865 by German physicists Heinrich Hertz It was confirmed in experiments between 1887 and 1888. Maxwell derived the electromagnetic wave equation, a wave equation This clearly shows the fluctuating nature of electric and magnetic fields. Because the electromagnetic wave speed predicted by the electromagnetic wave equation is equal to the measured value of the speed of light, maxwell It is inferred that light waves are also electromagnetic waves.

nature

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When the current frequency is low, it mainly depends on the tangible Conductor To transmit electromagnetic waves. The reason is that at low frequencies Electric oscillation In, the mutual change between magnetoelectricity is relatively slow, and almost all of its energy returns to the original circuit without energy radiation; Current frequency When the height is high, the electromagnetic wave can be free space Internal transmission can also be bound in the tangible conductive body for transmission. The reason for the transmission in free space is that in the high frequency electrical oscillation, the magneto electric mutual change is very fast, and it is impossible to return all the energy to the original Oscillating circuit Then electric energy and magnetic energy spread out to space in the form of electromagnetic wave with the periodic change of electric field and magnetic field, and energy can be transferred out without medium, which is a kind of radiation. For example, the distance between the sun and the earth is very far, but when we are outdoors, we can still feel the light and heat of the warm sunshine, which is like“ electromagnetic radiation The principle of energy transfer by radiation phenomenon is the same.

Electromagnetic waves can be blocked and reflected by metal materials 。 The metal plate can block and reflect electromagnetic waves whose frequency is lower than X-ray Greater than or equal to In X-ray, the electromagnetic wave energy is high, and it will directly penetrate through. The metal mesh can also block and reflect electromagnetic waves, but only for electromagnetic waves with longer wavelength. For long wavelength electromagnetic waves When the aperture of the metal mesh is less than 1/4 of the wavelength (d ＜λ/4), it can block electromagnetic waves. For example, the metal mesh can shield the radiation of the microwave oven, and the metal plate of the elevator can shield Mobile signal Etc. For electromagnetic waves with short wavelength but frequency not greater than ultraviolet ray (The shorter wavelength here means that the wavelength scale is far smaller than the object pore scale, generally at or below the micron level), such as infrared, visible light and ultraviolet light. At this time, electromagnetic waves can pass through the mesh (the mesh scale is larger than the wave), but will still be blocked and reflected by the metal plate, This explains why all metal materials can strongly reflect visible light, which is also the fundamental reason why metal materials have luster. For example, light can pass through the wire mesh, but not through the iron plate. In addition, the iron plate has excellent reflective ability. For electromagnetic waves with shorter wavelength , cannot be blocked by metal plate, Such as X-rays and gamma rays , because its frequency (energy) is too high, Particle property Significant, resulting in Penetrability It is strong, so it can ignore the metal material and penetrate it directly.

Electromagnetic wave is transverse wave 。 The magnetic field, electric field and travel direction of electromagnetic wave are perpendicular to each other. amplitude Periodically alternating along the vertical direction of the propagation direction, its intensity is inversely proportional to the square of the distance, the wave itself drives the energy, and the energy power at any position is proportional to the square of the amplitude. Its speed is equal to the speed of light c (299792458m/s ≈ 3 × 10 eight m/s）。 For the electromagnetic wave propagating in space, the direction of the nearest electric field (magnetic field) intensity is the same, and the distance between the two points with the largest value is the wavelength λ of the electromagnetic wave, and the frequency f is the number of electromagnetic changes per second. The relationship between the three can be determined by the formula c=λ f.

Electromagnetic wave propagation does not require medium Electromagnetic waves with the same frequency have different velocities in different media. When electromagnetic waves with different frequencies propagate in the same medium, the higher the frequency is Refractive index The higher the speed, the lower the speed. And the electromagnetic wave is only in the same type Homogeneous medium Middle edge Rectilinear propagation If the same medium is uneven, the refractive index of electromagnetic wave in it is different, and it propagates along a curve in such a medium. When passing through different media, refraction, reflection, diffraction, scattering and absorption will occur. The propagation of electromagnetic waves has edges Ground propagation Of Surface wave , air waves propagating from the air and Skywave 。 The longer the wavelength is, the less the attenuation is. The longer the wavelength is, the easier it is for the electromagnetic wave to bypass the obstacles and continue to propagate. Mechanical wave , electromagnetic wave and Gravitational wave Can be refracted, reflected, diffracted and interfered, because all waves have Volatility 。 Diffraction, refraction, reflection and interference belong to Volatility 。

The electric field (or magnetic field) of electromagnetic wave changes with time and is periodic 。 In a Oscillation period The distance of propagation in is called wavelength. The reciprocal of the oscillation period, that is, the number of vibrations (changes) per second, is called frequency.

The product of wavelength and frequency is the propagation distance per second, that is wave velocity 。 Let the wavelength be λ, the frequency be f, and the speed be V. The result is: λ=V/f The unit of wavelength input is meters (m), the unit of speed is meters/second (m/sec), and the unit of frequency is Hertz (Hz) Electromagnetic spectrum , including the collection of various waves, lights, and rays from extremely low frequency radio waves to extremely high frequency gamma cosmic rays. The sections with different frequencies are respectively named as extremely long wave electromagnetic wave (radio wave below 3KHz), radio wave (3KHz-300GHz), infrared ray, visible light, ultraviolet ray, X-ray, gamma ray (gamma ray) and cosmic ray (ultra-high energy gamma ray).

Electromagnetic spectrum

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Arranging these electromagnetic waves in the order of wavelength or frequency is Electromagnetic spectrum 。 If the frequencies of each wave band are arranged from low to high, they are power frequency electromagnetic waves radio waves (divided into long wave 、 Medium wave , short wave, microwave) infrared 、 visible light 、 ultraviolet rays 、 X-ray and Gamma ray 。 The wavelength of radio is the longest, cosmic rays (X-rays, gamma rays and shorter wavelength rays) have the shortest wavelength.

First, radio waves are used for communication, and microwave is used for Microwave Oven , infrared for remote control, Thermal imager ， Infrared guided missile Visible light is the basis for most organisms to observe things, and ultraviolet light is used for medical disinfection and verification counterfeit banknote , Measuring distance , engineering flaw detection, X-ray is used for CT photograph, gamma ray Used to cure, make atoms happen transition So as to generate new rays, etc.^[3]

Electromagnetic spectrum

radio waves 1mm~3km (microwave 1 μ m~1m)

infrared 0.76 μ m~1mm (including: Near infrared Short wave is 0.76-1.1 μ m, Near infrared Long wave is 1.1 ～ 2.5 μ m, Mid infrared 2.5 ～ 6 μ m, Far-infrared 6 ～ 15 μ m, 15 μ m ～ 1mm for ultra far infrared)

visible light 0.38～0.76μm

ultraviolet rays 10nm～0.38μm

X-ray 1pm～10nm

Gamma ray 0.1～1pm

High energy ray is less than 1pm

The wavelength used for fax (TV) is 3-6m

The wavelength used for radar ranges from 3 meters to several millimeters.

Abbreviation of electromagnetic radiation classification:

γ = Gamma ray

X-ray:

HX = Hard X-ray

SX = Soft X-ray

ultraviolet rays:

EUV=Extreme UV

NUV = Near ultraviolet Line

infrared:

NIR = Near infrared Line

MIR = Mid infrared Line

FIR = Far infrared

Microwave:

EHF = Extremely high frequency

SHF = UHF

UHF = extra-high frequency

radio waves:

VHF = VHF

HF=High Frequency

MF = intermediate frequency

LF = Low frequency

VLF = VLF

ULF = Ultra-low frequency

ELF = ELF

Corresponding Table of Electromagnetic Spectrum Frequency and Wavelength
Electromagnetic wave name		frequency range		Wavelength range		Photon energy range		Cycle range
(The lowest frequency electromagnetic wave that may exist)		3.4×10 -19 Hz		8.8×10 twenty-six m		1.4×10 -33 eV		2.9×10 eighteen s
radio waves		<300MHz		>1m		<1.24μeV		>3.33ns
microwave		300MHz~300GHz		1mm~1m		1.24μeV~1.24meV		3.33ps~3.33ns
infrared		300GHz~400THz		750nm~1mm		1.24meV~1.65eV		2.5fs~3.33ps
visible light	Red light	400THz~750THz	400THz~480THz	400nm~750nm	620nm~750nm	1.65eV~3.1eV	1.65eV~2eV	1.33fs~2.5fs	2.07fs~2.5fs
	Orange glow		480THz~505THz		595nm~620nm		2eV~2.09eV		1.98fs~2.07fs
	Yellow light		505THz~520THz		575nm~595nm		2.09eV~2.16eV		1.92fs~1.98fs
	Green light		520THz~600THz		500nm~575nm		2.16eV~2.48eV		1.67fs~1.92fs
	Blue light		600THz~700THz		430nm~500nm		2.48eV~2.89eV		1.43fs~1.67fs
	Purple light		700THz~750THz		400nm~430nm		2.89eV~3.1eV		1.33fs~1.43fs
ultraviolet rays		750THz~30PHz		10nm~400nm		3.1eV~124eV		33.3as~1.33fs
X-ray		30PHz~30EHz		10pm~10nm		124~124keV		33.3zs~33.3as
Gamma ray		>30EHz		<10pm		>124keV		<33.3zs
(Highest possible electromagnetic wave)		1.85×10 forty-three Hz		1.62×10 -35 m		7.67×10 twenty-eight eV		5.39×10 -44 s

Radio spectrum

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At the end of the 19th century, the Italians Marconi And Russian Popov in 1895 radio communication Test. In the next 100 years, the spectrum from 3KHz to 300GHz was recognized, developed and gradually used. With the development of technology, extremely long wave electromagnetic waves below 3KHz can be generated, and optical bands (infrared) above 300GHz can also be used gradually Electronic oscillation Technology came into being, not just stay Quantum transition Generated (e.g Laser ）At the level of.

According to different propagation characteristics, different use services Radio spectrum It is divided into 13 sections: to low frequency (TLF) ELF (ELF)、 ultra-low frequency (SLF)、 Ultra-low frequency (ULF)、 VLF (VLF), LF, IF（ MF ）, high frequency（ HF )、 VHF (VHF)、 extra-high frequency (UHF)、 UHF (SHF)、 Extremely high frequency (EHF) and to high frequency (THF), plus Jimmy wave and Humi wave, the corresponding bands are from Jimmy wave, to long wave (100 megameter wave), extremely long wave (10 megameter wave), ultra long wave (megameter wave), ultra long wave (100000 meter wave) Very long wave (10000 meter wave) long wave (kilometre wave) Medium wave ( 100 meter wave ）, short wave (10 meter wave), very short wave (meter wave), ultra short wave（ Decimeter wave )、 ultrashort wave ( Centimeter wave ）, very short wave（ Millimeter wave ）, to short wave (Simi wave) and Humi wave (from Decimeter wave reach Millimeter wave The three kinds of are collectively called microwave). See the table below.

Radio spectrum and band division
Segment No	Band name	Frequency band range (including upper limit but excluding lower limit)	Band name 1	Band name 2	Wavelength range (including lower limit and excluding upper limit)	remarks
-1	-	0.03～0.3Hz	-	Jimmy Bo	10～1Gm	/
zero	To low frequency	0.3～3Hz	Longest wave	100M wave	1000～100Mm	/
one	ELF	3～30Hz	Extremely long wave	10 megameter wave	100～10Mm	/
two	ultra-low frequency	30～300Hz	Ultralong wave	Megameter wave	10～1Mm	/
three	Ultra-low frequency	300～3000Hz	Extra long wave	100000 meter wave	1000～100km	/
four	VLF	3～30kHz	Very long wave	10000 meter wave	100～10km	/
five	Low frequency	30～300kHz	long wave	Kilometre wave	10～1km	/
six	intermediate frequency	300～3000kHz	Medium wave	100 meter wave	1000～100m	/
seven	high frequency	3～30MHz	shortwave	10m wave	100～10m	/
eight	VHF	30～300MHz	Very short wave	Mibo	10～1m	/
nine	extra-high frequency	300～3000MHz	Ultrashort wave	Decimeter wave	10～1dm	microwave
ten	UHF	3～30GHz	ultrashort wave	Centimeter wave	10～1cm
eleven	Extremely high frequency	30～300GHz	Very short wave	Millimeter wave	10～1mm
twelve	To high frequency	300～3000GHz	To short wave	Simibo	1～0.1mm	/
thirteen	-	3～30THz	-	Humi wave	100～10μm	/

Penetration of electromagnetic waves

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Because electromagnetic waves have Wave particle duality The wavelength is inversely proportional to the photon energy. When the wavelength is shorter Photon energy The larger, the Penetrability The stronger. Such as high energy X-ray It can penetrate almost all non-metallic objects, even thin aluminum; and Gamma ray Can penetrate most metals. Some heavy metals, such as lead, can block the penetration of electromagnetic waves. For electromagnetic waves with long wavelength and low energy, the penetrability generally refers to the diffraction ability. At this time, the longer the wavelength, the stronger the penetrability, such as 2.4G Wi-Fi The signal penetration is stronger than 5G Wi Fi signal.

application

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Microwave radar

radio waves For communication, etc

microwave For microwave ovens satellite communication etc.

infrared Used for remote control, thermal imager, infrared guided missile, etc

visible light It is the basis for all creatures to observe things

ultraviolet rays Used for medical disinfection, verification of counterfeit banknotes, distance measurement, engineering flaw detection, etc

X-ray be used for CT photograph

gamma ray It is used for treatment, making atoms transition to generate new rays, etc

radio communication

Both radio and television use electromagnetic waves. In radio broadcasting, people first transmit sound signals（ Mechanical wave Signal) into electrical signal Then these signals are carried by high-frequency electromagnetic waves to the surrounding space. In another place, people use Receiver After receiving these electromagnetic waves, the electrical signals in them are restored to acoustic signals, which is air cast In television, in addition to processing the acoustic signal as in radio broadcasting, the optical signal of the image should be converted into an electrical signal, and then the two signals should be carried together by high-frequency electromagnetic waves to the surrounding space television receiver After receiving these electromagnetic waves, the electrical signals in them will be restored to acoustic signals and optical signals, so as to display the picture of the TV and the sound in the loudspeaker.^[4]

medical care

TDP

“ Specific electromagnetic spectrum ”(TDP) is defined by heater For the treatment plate Wavelength range The specific electromagnetic wave distributed in the range of 2-25 μ m and intensity (28-35mw/cm2) is generated with the same substance contained in the cells in the body when the human body is matched to receive it resonance Therefore, it can enhance microcirculation, promote metabolism, and repair human lesions, so that patients can recover quickly, and non patients can improve their resistance.^[2]

example

For example, Guoren TDP, based on a large number of clinical trials, confirmed that the radiation of specific electromagnetic spectrum can be used for treatment cervical spondylopathy ， Lumbar intervertebral disc Protrusion, low back pain, lumbar muscles strain ， rheumatism arthritis, sciatica ， Facial nerve paralysis , postoperative wound healing ， trauma Infected ， chilblains ， gastritis 、 Diaphragm Spasm Neurodermatitis 、 eczema ， migraine 、 headache 、 dysmenorrhea ， hemorrhoids Etc. Widely used Surgery 、 internal medicine 、 gynaecology 、 pediatrics 、 Neurology And other diseases. At the same time, through the country metering The precise determination by the Academy of Sciences and other institutions has confirmed that it has no side effects on the human body.

other

In addition, electromagnetic waves are also applied to mobile phone Communication, satellite signal Navigation 、 remote control 、 location , household appliances (microwave ovens Electromagnetic furnace ）Infrared wave, industry, medical equipment, etc.

From December 15, 2021 to January 20, 2022, Guangxi Mobile Widely carry out "scientific cognition" in the whole district Base station radiation Enjoy mobility 5G network ”Base station electromagnetic radiation environmental protection publicity campaign with the theme of "correct electromagnetic radiation" popular science knowledge 。^[5]

electromagnetic radiation

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Definition of electromagnetic radiation

Generalized electromagnetic radiation Usually refers to Electromagnetic wave spectrum In terms of, including radio waves, visible light, gamma rays and other electromagnetic waves. Narrowly defined electromagnetic radiation It refers to the radiation waves generated by electrical equipment. The wave band of these radiation waves is usually below the infrared ray (longer wavelength).

type

Electromagnetic radiation is a way to transfer energy. There are three types of radiation^{[6 ]} ：

Ionizing radiation

yes heat effect Nonionizing radiation

Non ionizing radiation without thermal effect

Base platform Electromagnetic waves are by no means free radiation waves

Human injury

Main mechanism

Electromagnetic radiation hazard The mechanism of human body is mainly heat effect 、 Non thermal effect and Cumulative effect Etc.

heat effect

The human body is a conductor. Like all conductors, the human body receives wireless current and microwave radiation After that, current will be generated, which will cause Human fever 。 Generally speaking, the radio waves and microwaves in the space where we live are relatively weak fever Very small, completely negligible.

The infrared and visible light emitted by the sun is the strongest electromagnetic radiation in nature, and also the strongest in our environment Electromagnetic radiation source Infrared and visible light can cause heat on the surface of human body.

Non thermal effect

There are weak electromagnetic fields in organs and tissues of the human body, which are stable and orderly. Once disturbed by electromagnetic waves of certain frequencies from outside, the weak electromagnetic fields in equilibrium may be damaged, thus affecting the human body's function.

What frequencies of electromagnetic waves can produce interference, and how much impact these interference has on the human body, all need further research.

Cumulative effect

In addition to radiating infrared and visible light, the sun also radiates a large amount of high-energy ultraviolet rays, which are also beneficial to the human body, but too strong ultraviolet rays can burn the skin and may induce Skin cancer 。

X-ray and gamma ray belong to high-energy electromagnetic radiation, which can directly destroy molecules in human body molecular structure , including protein DNA And so on, which will cause human body diseases and various cancer 。

If the damage of high-energy electromagnetic radiation to human body is radiated again before self repair, the damage will accumulate and become Permanent Sick or life threatening. For groups exposed to high-energy electromagnetic wave radiation for a long time, even if the power is small and the frequency is low, it may induce unexpected diseases, so we should be alert!

After long-term research, some scientists have proved that long-term exposure to electromagnetic radiation will cause the decline of human immunity, metabolic disorder Memory loss , premature aging Arrhythmia , decreased vision, hearing, abnormal blood pressure, skin spots, roughness, and even various cancer Etc; Decreased male and female reproductive capacity and women's vulnerability Menstrual disorder , abortion Teratology Etc. However, it has not been proved by experiments and there is no large-scale data statistics Verify that there is an inevitable connection

The foods with electromagnetic wave radiation hazards include: Green Tea 、 Kelp , seaweed, skirt vegetable, Va, Vc, Vb1 lecithin 、 Pig blood , milk Turtle , crabs and other animals High-quality protein Etc.

performance

1. Yes central nervous system Hazards of

The nervous system is very sensitive to electromagnetic radiation and is affected by its low intensity Repeated action After that, the function of central nervous system changes Neurasthenia Syndrome , mainly including headache ， dizzy , weakness, memory loss, Sleep disorders (Insomnia, abnormal sweating or Lethargy ）, dozing in the daytime, hotbed ， hyperhidrosis , palpitations, chest tightness, hair loss, etc., especially difficulty in falling asleep, weakness, sweating and memory loss are more prominent, which indicates that the brain is dominant in the inhibition process, so in addition to the above symptoms, the victim also shows short-term memory loss, vision Motor response Time value Minghao extension; The coordination of hand and brain is poor, showing that the speed of number writing is slow, and there are many errors

2. Harm to immune function

Make the body Resistance Down Animal experiment And the research and investigation of the radiation effect on the population show that white corpuscle Bacteriophagous percentage And the number of bacteria ingested by the human body Antibody formation Is significantly inhibited

3. Impact on cardiovascular system

People exposed to electromagnetic radiation, often Hemodynamics imbalance, Vascular permeability And reduced tension due to plants Neuromodulation The function is affected, people often Bradycardia Symptoms appear, a few appear Tachycardia The victim's blood pressure fluctuates, starts to rise, then returns to normal, and finally has low blood pressure; electrocardiogram There is a voltage drop of R T wave, which is vagus Of Anaphylactic reaction Is also the heart muscle Nutritional disorders Results; P? Q extension, P-wave Widening, description Atrioventricular conduction In addition, people who have been exposed to electromagnetic radiation for a long time will be more likely to suffer from cardiovascular diseases earlier and more easily

4. Yes Blood system Impact of

Under the effect of electromagnetic radiation, the peripheral blood picture may appear white blood cell instability, mainly falling tendency, white blood cell reduction red blood cell In addition, when radio waves and Radiation When acting on the human body at the same time, the effect on the blood system is more obvious than that of a single factor

5. Yes reproductive system And genetic influence

Long term exposure to ultrashort wave Generator Men's sexual function may decline, Impotence , women appear menstruation Cyclic disorder. Because of testicular blood circulation Bad, very sensitive to electromagnetic radiation, spermatogenesis is inhibited and fertility is affected; send Egg cell It is denatured and damaged Ovulation process And make women lose their fertility.

High intensity electromagnetic radiation can produce genetic effect , causing testicular chromosome aberration and mitosis Abnormal, pregnant women received shortwave in the early or pre pregnancy period Diathermy As a result, their offspring appear congenital birth defect (deformed infants)

6. Yes vision system Impact of

Eye tissue contains a large amount of water, easy to absorb electromagnetic radiation power, and blood flow Less, so under the action of electromagnetic radiation, the temperature of the eyeball is easy to rise, which is caused by cataract The main conditions of the rose guide eye Lens It is self-evident that protein coagulation, visible light and ultraviolet ray damage human eyes. In addition, most scholars believe that the long-term effect of low intensity microwave can accelerate the aging and turbidity of the lens, leading to yellow vision, and possibly color Reduced vision and Dark adaptation Prolonged time, resulting in some Visual impairment In addition, long-term low-intensity electromagnetic radiation can promote Visual fatigue ， Eye sensation Uncomfortable and dry eyes

7. Electromagnetic radiation Carcinogenesis

Most experimental animal After microwave treatment, it can incidence rate The experiments of some microwave biologists show that electromagnetic radiation can（ genetic genes ）Chromosome mutation and mitosis abnormality of microparticle cells cause some tissues to appear Pathological hyperplasia Process, making normal cells Becomes cancer cell . The United States is stationed abroad embassy Personnel have been exposed to the high electromagnetic radiation emitted by microwave eavesdropping for a long time, which has led to an increase in the number of white blood cells of embassy personnel and a higher incidence of cancer than normal people Microwave radar According to the investigation in the affected areas, the rapid increase of local cancer patients and the pyrogenic effect of microwave on human tissues can not only be used for physical therapy, but also can be used to treat cancer, so that the temperature in the center of cancer tissue rises, and the proliferation of cancer cells is destroyed

In addition to the above hazards of electromagnetic radiation to health endocrine system , vision, hearing, Material metabolism ， Tissue and organ The change of morphology of can produce adverse effects.

Recognize hazards

At security level electromagnetic environment Next, if you have a long-term fantasy that electromagnetic waves will cause damage to your health, you will inevitably have anxiety, fear, boredom, etc. due to excessive mental pressure Psychological problems , and then affect the endocrine, until affecting their own health. Therefore, it is necessary to correctly understand the causes of electromagnetic waves and their possible hazards, and master how to reduce or avoid the impact of common electromagnetic waves in life.

As long as it is not at absolute zero（ Celsius scale Minus 273.15 centigrade ）All objects in the world radiate electromagnetic waves. Absolute zero is impossible in nature, so electromagnetic waves are everywhere. Therefore, in general environment, electromagnetic wave (electromagnetic wave energy level does not exceed the corresponding frequency Limits ）It will not harm our health, but long-term exposure to high-energy electromagnetic waves (electromagnetic wave energy level exceeds the limit of corresponding frequency) will cause damage to our health.

Electromagnetic radiation exceeds the standard a burglar alarm (with certain Frequency response range ）, can measure the strength of electromagnetic wave in a certain frequency range, as long as it exceeds the specified Electromagnetic radiation intensity The standard will send out an alarm, and the user should stay away from the tested object until the alarm disappears (the location where the alarm disappears and the electromagnetic wave Launch facilities The distance of the equipment can be regarded as safe distance ）。

Electromagnetic wave protected Three principles ： Distance protection (Keep a relatively safe distance from electromagnetic wave transmitting facilities and equipment) Time protection (not entering a safe distance when the electromagnetic wave transmitting facilities and equipment are opened), shielding protection (depending on the influence of electromagnetic waves of shielding facilities). Relying on the three principles can effectively reduce or avoid the impact of the common electromagnetic waves in life.

There are also different ways to prevent household appliances. Current mainstream TV graphoscope All have been adopted lcd The energy level of the electromagnetic wave generated by itself, except for visible light, is very low, and there is a certain distance between the electromagnetic wave and the human body when it is used, without taking additional protective measures; And the old-fashioned Kinescope The TV and monitor shall be set with a safe distance of at least 1 to 2 meters. At present, mobile phones are commonly used in our lives. When dialing and answering mobile phones, they should be handheld or placed 50 cm away from the human body, and try to use the hands-free way to answer. The induction cooker and microwave oven should be as far away as possible (at least more than 1m) when they are used. After heating, the electric blanket should be turned off before going to bed. Do not stay on the electric blanket that is powered on for a long time. Currently commonly used WIFI When the equipment is opened, it can be more than 1m away from the human body. radio Due to its working principle, it only receives useful electromagnetic waves, and does not emit useful electromagnetic waves. Moreover, the energy level of electromagnetic waves generated by its own components and circuits is very small, so it is unnecessary to set a safety distance. hair drier Equidependence motor drive Due to the short service time, there is no need to set a special safety distance for small household appliances. For use in cold weather Electric heating Household appliances (such as Heater ）A safe use distance of more than 0.5m should be set to avoid Scald And electromagnetic radiation.

When purchasing residential buildings, they should be far away from the incoming and outgoing lines of outdoor high-voltage substations（ Voltage level Except for substations at 35kV and below; Indoor substation and Underground substation Except), high voltage Overhead line (except for overhead lines with voltage level of 35kV and below; except for underground cables), Antenna polarization mode by Vertical polarization And mainly rely on Ground wave propagation Of the tower (e.g Medium wave station ）, or the height difference with the building is relatively small Radio and television tower Station (under the radio and television tower with large height difference from the building, there is a signal blind zone).

To reduce the adverse effects of electromagnetic waves, we must develop the habit of self prevention. General electrical appliances stores sell "electromagnetic wave test pens", which can easily measure the strength of electromagnetic waves. As long as the strength exceeds the standard, an alarm will be issued. Users should stay away from the tested object until the alarm disappears.

To detect whether the electrical products have radiation or electromagnetic waves, a relatively simple way can also be adopted, that is, to use household, small and accessible AM（ amplitude modulation ）When the radio of channel is turned on, turn the channel to a place where there is no radio and close to the household appliances such as TV, refrigerator, microwave oven or computer to be measured. If the volume from the radio suddenly increases, it indicates that there is strong electromagnetic radiation around the appliance. After a certain distance, the volume will return to the original low state; In this way, the "safe" distance can be measured.

Different electrical appliances also have different prevention methods. For example, it is better to turn off the screen rather than turn off the computer when the computer is used. The computer screen is replaced by a LCD screen; When answering the phone, it is better not to put it in the waist or pants pocket, but to hold it in hand or place it 50 cm away from the human body; Buying a house is far away Substation equipment And the location of the base station.

1993 Sweden Northern Europe Three countries' research and investigation revealed that the patient suffered from electromagnetic radiation of more than 2mG leukemia Is 2.1 times more likely to suffer from brain Abscess The chance is 1.5 times that of normal people. The above information is extracted from Japan Published SAPIO magazine in March 1996.

use Computer radiation Eraser

The method of shaping, oscillating interference, derivation and absorption of the electronic shielding waveform of the computer radiation eliminator through the power supply; Make the computer and accessory equipment Of alternating current , which can dynamically discover and track computer motherboards CPU , hard disk, display, keyboard, mouse and the radiation generated by the equipment connected to the computer Smart chip The module absorbs, converts and eliminates, effectively eliminating the hidden killer that affects our health - computer radiation from the root!

Expert advice

10 Countermeasures for Preventing Electromagnetic Waves	Reason description
1. Keep away from electrochemical products as far as possible	The farther the distance is, the smaller the strength of the electromagnetic wave is, and the less harm to the human body will be caused.
2. Shorten the use time as much as possible when it is impossible to stay away	The stronger the electromagnetic wave, the shorter the time, the smaller the impact.
3. Select products with low electromagnetic radiation	The electric bulb is smaller than the fluorescent lamp, the energy-saving lamp is larger, the LED lamp is smaller, and the fixed telephone is smaller than the wireless telephone.
4. Instead of using large ones, try to use small ones	The same kind of household appliances, large ones not only consume Electricity High, strong electromagnetic wave.
5. Young people should pay special attention	Young people with vigorous cell division are vulnerable, so pregnant women should pay special attention.
6. Determine the safety distance	The manufacturer's data will not be too accurate, so it is better to measure clearly.
7. Pay attention to the rear and both sides	The electromagnetic wave emitted from the rear and both sides of the LCD TV and personal computer is strong.
8. Unplug the plug when not in use	When the plug is plugged in, most electromagnetic waves will be released.
9. Pay special attention when sleeping	Sleeping time is usually very long. Do not expose to electromagnetic waves of higher energy levels for a long time.
10. Change the mentality of relying on electricity	The life surrounded by electrochemical products has greatly increased the chance of exposure to electromagnetic waves.

In fact, not all electromagnetic radiation has an impact on the human body. As long as the intensity is small, there is little harm to the human body. As for the anti electromagnetic radiation products sold on the market, most of them have no effect. Don't be fooled. Remember that the method of shielding electromagnetic waves can be grounded Metal mesh Or metal plate, or use thick concrete or soil to absorb. If you can't shield strong electromagnetic waves, the only way to keep you unaffected is to stay away radiation source Because the strength of the electromagnetic wave is inversely proportional to the square of the distance, that is, the distance is twice as long as the original, and the strength is reduced to one quarter of the original.

Electromagnetic pollution

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Electromagnetic wave pollution, also known as Electromagnetic pollution Or called RF radiation Pollution. It is based on the electromagnetic field Field force It is closely related to the nature, power, density and frequency of electromagnetic waves. Due to the wide application of electronic technology, radio broadcast The rapid development and popularization of mobile phones, TV and microwave technology, the power of RF equipment has doubled electromagnetic radiation Substantial increase. It has reached the level of direct threat human health The degree of. Electromagnetic pollution is an invisible pollution, which has become a great concern Public nuisance , for human society The impact has attracted the attention of countries all over the world and has been listed as one of the environmental protection projects.

Natural pollution

The natural electromagnetic wave pollution is natural phenomena Caused by. The most common is thunder and lightning. In addition to the direct harm to electrical equipment, aircraft, buildings, etc., thunder and lightning can also produce extremely wide areas from thousands of Hz to hundreds of MHz frequency range Severe within electromagnetic interference 。 Volcano eruption , earthquakes and magnetic explosions caused by sunspot activities will produce electromagnetic interference. Natural electromagnetic wave pollution Shortwave communication The interference of is extremely serious.

Anthropogenic pollution

Artificial electromagnetic wave pollution Including:

one Pulse discharge 。 For example, when cutting off a high current circuit Spark discharge Its transient current is very large, which will produce strong electromagnetic. It is essentially the same as lightning, but its influence area is small.

2. Power frequency Alternating electromagnetic field 。 For example, the electromagnetic field near high-power motors, transformers and transmission lines does not radiate outward in the form of electromagnetic waves, but Near-field region Serious electromagnetic interference will be generated.

3. RF electromagnetic radiation 。 Such as radio, television microwave communication The radiation of various RF equipment, such as, has a wide frequency range and a large impact area, which can harm the workers in the near-field area. RF electromagnetic radiation It has become the main factor of electromagnetic wave pollution.

Communication mode

one radio and television Transmitting equipment, mainly for radio broadcasting and communication Launching pad and Transfer desk And other departments.

2 Communication radar and navigation transmitting equipment communication, including shortwave transmitting station, microwave Communication station , Ground Satellite communication station Mobile communication station.

3. Industry, scientific research and medical treatment High frequency equipment 。 Such equipment converts electric energy into heat energy or other energy for use, but electromagnetic radiation Produce and leak out, causing Workplace environmental pollution.

Industrial electromagnetic radiation equipment: mainly High frequency induction heating equipment , for example High frequency quenching 、 High frequency welding and High frequency furnace , high-frequency smelting equipment, and high-frequency medium heating equipment , e.g. plastic Heat sealing machine High frequency drying processor High frequency dielectric heating Interlocking machine Etc.

Medical electromagnetic radiation equipment: mainly short wave ultrashort wave physiotherapy Equipment, such as high frequency Physiotherapy machine , ultrashort wave physiotherapy machine ultraviolet rays Physiotherapy machine, etc.

Scientific research on electromagnetic radiation equipment: mainly Electron accelerator And various radiation devices Electromagnetic stove Etc.

four traffic system Electromagnetic radiation interference, including: Electrified railway , light rail and electric railway , trams, trolley buses, etc.

five Power system Electromagnetic radiation, high-voltage transmission lines including overhead transmission lines and Underground cable Substation includes power plant and transformer station.

6 Electromagnetic radiation of household appliances, including microwave heating And transmitting equipment, including computers, monitors, televisions Microwave Oven 、 wireless telephone Etc.

The electromagnetic wave pollution in family life closely related to people's daily life refers to various electronic life products, including air conditioners, computers, televisions, refrigerators, microwave ovens Karaoke machine , VCD, display Electric blanket , mobile phones, etc., interference, impact and harm to people caused by various electromagnetic waves of different wavelengths and frequencies during normal operation.

Main hazards

Electromagnetic pollution endangers human health

Because electromagnetic waves are colorless, tasteless, invisible and traceless, and pollution is neither felt nor ubiquitous, they are called“ E-waste ”Or "Electronic Radiation contamination ”The harm it brings to people cannot be underestimated. It is mainly manifested in the following four aspects:

1. Impact Electronic equipment Normal operation

Modern technology is increasingly inclined to use large-scale and vlsi ， Circuit element The density is extremely high, and the current used is micro current, so that the signal power and noise power Similar, parasitic radiation may cause Electronic system Or electronic equipment Misoperation Or obstacles. On the other hand, with the rapid development of modern wireless communication industry Launching tower It makes the air waves crowded and seriously affects the normal business of all aspects. Since September 1996, Beijing capital airport Aviation above 1.30 MHz Communication frequency Be wireless paging center Interference events occur frequently. At 8:15 a.m. on February 20, 1996, the air to air channel was seriously disturbed, and 10 aircraft had to circle and wait in the air, resulting in the departure of the aircraft had to open for 5 to 15 minutes flight time 。 The same incident happened frequently in other parts of the country. Where people are used to thinking that the sky is high enough for birds to fly, the interference of electromagnetic waves has brought great harm to people.

two scientific research And facts show that electromagnetic waves are also very harmful to human body. Harm of electromagnetic radiation to human body It is caused by the energy of electromagnetic waves. According to relevant experts, the mobile phones used in China Transmission frequency 800~1000 Megahertz Between radiation dosage Up to 600 microwatts, exceeding national standard More than 10 times, but excessive electromagnetic radiation Can cause human body Neurasthenia , loss of appetite palpitation Chest tightness 、 dizzy Dazzle, etc“ Electrical Hypersensitivity ”, or even cause brain tumor 。 There are many examples of electromagnetic wave pollution harm to human body, but the degree of its impact and the radiation intensity It has something to do with the time of accumulation, which has not been reflected in a large scale at present, so it has not attracted people's attention. Relevant research shows that the pathogenic effect of electromagnetic waves is accompanied by Vibration frequency The frequency is more than 100000 Hz, which may pose a potential threat to human body. Working and living in this environment for too long, the human body is disturbed by electromagnetic waves, which changes the original electric field of molecules in the body tissues, leading to the body ecological equilibrium Disorder. Some are subject to stronger or longer Electromagnetic wave radiation Of the people who have been sick, mainly reflected in nervous system and cardiovascular system aspect. Such as fatigue, memory decline, insomnia have a short fuse 、 menstruation Disorders, chest tightness, palpitations white blood cell And thrombocytopenia or low immunity Reduction, etc.

3. May cause explosive or Explosive mixture Danger of explosion. Under certain conditions, some tall metal structures High frequency induction Spark discharge will occur. This kind of discharge not only gives people different degrees of electric shock, but also may detonate Hazardous Substance , causing catastrophic consequences. This is a problem that needs to be paid great attention to for explosive production enterprises.

4. Electromagnetic radiation will affect human health. Electromagnetic radiation is Cardiovascular disease 、 diabetes One of the main inducements of cancer mutation. Electromagnetic radiation will Human reproductive system , nervous system and immune system Cause direct injury. Electromagnetic radiation causes abortion, infertility Teratology Etc. Excessive electromagnetic radiation directly affects the development of children's body tissues and bones, resulting in vision and liver Hematopoietic function Descending, which may lead to Retinal detachment 。 Electromagnetic radiation can Male sexual function Decline, female Endocrine disorder 。

Pollution pathway

Interference of electromagnetic wave Route of transmission There are two types:

One is conducted interference, which is the current along the power cord Interference caused by propagation;

The other is Radiated interference , is caused by the emission of electromagnetic wave source to the surrounding space.

In order to prevent and suppress electromagnetic interference, reasonable circuit design, filtering, shielding, etc. are mainly adopted technical method 。 Reasonable circuit design is to arrange components and lines reasonably in a narrow space, which can weaken parasitic electromagnetic coupling , suppress electromagnetic interference. wave filter It is a circuit composed of resistance, inductance and capacitance. This network can allow signals of some frequencies to pass through, but prevent signals of other frequencies from passing through. Correct design and installation of filters can reduce electromagnetic interference to Minimum 。 Shielding technology As a basic means of suppressing electromagnetic radiation, it has been widely used. The purpose of shielding is to Radiant energy It is restricted in a specific area, or it is to prevent radiant energy from entering another specific area. Shielding material yes Shielding efficiency Key to high and low, newly developed Wave absorbing material It has come out and will make contributions to opening up clean space for mankind. In addition to the above technical methods, other methods can also be used to reduce the harm of electromagnetic wave radiation pollution. For example, it is prohibited to set up high-power wireless paging stations around the airport, and good shielding can be taken for workers who often contact RF equipment Protective measures Etc.

In short, with the development of science and production, Electromagnetic radiation pollution It is of great practical significance to study the harm and protection of electromagnetic wave pollution.

Related cases

More than 20 years ago Microwave Oven After popularization in the United States, some were equipped with hearts pacemaker Of the patients, they often feel uncomfortable, and some pacemakers even fail to stop suddenly. Later, the research of scientists made it clear to the world that the reason was "electromagnetic wave pollution".

A few years ago, Russia famous Chess Master Nikolai Kedekov played chess with a computer. After winning three games in a row, he was suddenly knocked down by the strong current released by the computer. According to the investigation, this is not Computer hardware Electric leakage does not mean that the software has designed a killing procedure, and the cause of death is invisible electromagnetic waves.

It is reported that the staff who operate in front of the computer for more than 6 hours every day are vulnerable to a disease called "VOT". This symptom refers to long-term viewing Video terminal It is a general term for diseases that occur in some parts of the body. Its main symptoms are: visual impairment; Neck, shoulder and wrist dysfunction; Autonomic nerve dysfunction Etc; In addition, it can cause menstruation Misadjustment, abortion and other women's diseases and others skin disease 。 The reason is also caused by electromagnetic wave radiation.

Mobile phones and walkie-talkie It is also an emission source of high-frequency electromagnetic wave pollution. It emits electromagnetic waves every time you talk. Scientists believe that the electromagnetic wave radiation intensity of mobile phones is generally 4-6 times higher than the specified standard, and some types even exceed nearly 100 times. China Electromagnetic Radiation Test Center and Xiamen Evergreen Source Radiation Prevention After two years of Tracking detection It is confirmed that mobile phones will cause radiation hazards to human body at present.

Pollution prevention

There are many easy to operate measures to reduce the harm of electromagnetic wave pollution.

There are two general principles:

First, if it is necessary to stay away from the electromagnetic wave emission source Shielding protection Methods;

Second, try to increase the distance between the human body and the emission source.

Because the impact of electromagnetic waves on the human body is closely related to the size of the transmission power and the distance from the emission source, its harm is proportional to the transmission power and inversely proportional to the square of the distance. Take mobile phone for example. Although its transmission power is only a few watts Transmitting antenna Very close to the head of a person, the actual radiation intensity is equivalent to the radiation intensity received by the transmission antenna of a radio station with a distance of several hundred kilowatts. Fortunately, people use it for a short time, and will not show obvious harmful symptoms for a while; However, if used for a long time, the symptoms caused by radiation will gradually be exposed. Excessive radiation will cause abnormal cell activity and division, and may cause cancer.

In view of this, we should consciously take measures in daily life to reduce the harm of electromagnetic wave pollution. For example, personnel working in places with high electromagnetic wave intensity, such as the machine room, should pay special attention to the rest during the work, and can appropriately go to the outdoor far away from the electromagnetic field for activities; When using the mobile phone, keep the antenna away from the human body, especially the head, and try to reduce the time of each call; Household appliances should not be placed in a centralized manner. The distance to watch TV should be kept at 4-5 meters, and attention should be paid to opening windows for ventilation; Microwave ovens and refrigerators should not be used close to each other; Teenagers play as little as possible Video game machine ； After the electric blanket is preheated, the power supply should be cut off when sleeping. Children and pregnant women should not use the electric blanket; You should eat more fresh vegetables and fruits at ordinary times to enhance your body's ability to resist electromagnetic wave pollution.

1、 Keep your distance. The distance from the TV should be the size of the video screen multiplied by 6, and Microwave Oven The distance shall be 2.5~3m, and it is generally regarded as a safe area beyond 5000V/m of high-voltage transmission lines.

2、 Reduce exposure. People who often use computers should take a 15 minute break every hour of work, and work no more than 32 hours a week.

3、 Improve the environment. Pay attention to the air circulation, the temperature and humidity should be moderate, and household appliances should not be placed in the bedroom.

IV Individual protection 。 Pregnant women, children, weak and sickly people, people who are allergic to electromagnetic radiation, and people who have been in the environment with electromagnetic wave pollution exceeding the standard for a long time should choose to use their own Protective equipment 。

5、 Use less mobile phones. Try to reduce the use of mobile phones, walkie talkies and Cordless telephone If it is necessary to use it, make a long story short; Don't always hang your mobile phone on your body.

6、 Use less electric blankets. Electric blanket The electromagnetic wave pollution of is serious, and it is harmful to human body if it is used with power for a long time. If it is necessary to use it in cold weather, it is recommended to power on and dry it Warm bedclothes Then cut off the power supply immediately to reduce electromagnetic wave pollution.

7、 Shields are used to reduce electromagnetic wave pollution. To generate Electromagnetic pollution facilities can use shielding materials that shield, reflect or absorb electromagnetic waves, such as copper, aluminum, steel plate Polymer membrane Etc.

8、 According to the electromagnetic wave Distance attenuation In order to reduce the harm of electromagnetic waves to residents Electromagnetic power Large workplaces and facilities that may generate strong electromagnetic waves, such as television stations, radio stations, radars Communication station , microwave transmission stations, etc., should be located far away from residential areas in the outer suburbs, counties or high terrain areas. Facilities, such as substations, which must be set up in the city, adjacent residential areas and areas where residents often have activities, should be kept certain with the residential area Safety protection distance To ensure that its boundary conforms to the environmental electromagnetic wave hygienic standard Requirements. At the same time radiation source Copper, aluminum and steel that can shield, reflect or absorb electromagnetic waves shall be selected Wire Or polymer film and other materials, so as to limit the electromagnetic radiation energy within the specified space.

9、 High pressure, especially Ultrahigh pressure Transmission line It should be far away from residential, school, sports ground and other crowded areas. When using the computer, the low radiation display shall be selected, and the distance between the human body and the front of the display screen shall not be less than 75cm, and the side and back of the display screen shall not be less than 90cm. It is better to install shielding devices.

10、 Strictly control mobile communication base station To ensure the transmission of various mobile communications in urban areas Base station antenna If it is higher than the surrounding buildings, the transmitting antenna shall not be set up within a certain range around the kindergartens, school buildings, hospitals and other buildings.

11、 In order to reduce the electromagnetic pollution and Harmful effects The room should be ventilated frequently to keep the indoor air unblocked. Scientific use of household appliances: for example, watching TV or Home theater Keep a long distance and avoid all kinds of electrical appliances being turned on at the same time; The duration of using computer or video game machine should not be too long.

12、 Minimize the use of mobile phones Talk time ； Mobile phone antenna The top should be as far away from the head as possible, and the antenna should be lengthened as far as possible; Add to the mobile phone Isolation layer Etc.

13、 In addition, a certain amount of vitamin C Or eat more fresh vegetables rich in vitamin C, such as Pepper 、 Persimmon pepper 、 Chinese toon , cauliflower Spinach Etc; Eat more fresh fruits such as citrus , dates, etc. Pay attention to eating more rich foods vitamin A , C and protein Food, such as Tomatoes 、 lean meat , animal liver Bean sprout Etc; Drink green tea regularly. These dietary measures can, to a certain extent, actively prevent and reduce the harm caused by electromagnetic radiation to the human body.

14、 Electromagnetic radiation is a new kind of environmental pollution that has been recognized by people for nearly thirty or forty years. Now people are still in the stage of understanding and studying electromagnetic radiation. Because it is invisible, untouchable and imperceptible, it is easy to arouse people's doubts. In addition, some reports on electromagnetic radiation are not objective and lack of scientific nature, which leads to unnecessary misunderstanding and panic. Generally speaking, determine whether the electromagnetic radiation is correct Residential environment The pollution shall be comprehensively considered from the aspects of electromagnetic wave radiation intensity, main radiation direction, distance from radiation source, duration, etc. Therefore, while strengthening electromagnetic protection, we should also take a scientific attitude towards electromagnetic wave pollution, make objective analysis and take it seriously. We must not blindly exaggerate what others say, which will lead to confusion of people's understanding. Of course, with the development of science and technology, people's understanding of electromagnetic wave pollution and its harm will gradually deepen, and many mysteries will eventually be revealed.

Relevant regulations

electromagnetism Environmental standards And relevant regulations. In order to control the environmental pollution caused by electromagnetic waves in modern life and protect people's health Ministry of Health The Hygienic Standard for Environmental Electromagnetic Waves (GB9175-88) was promulgated, which stipulates that the limit value of environmental electromagnetic wave intensity in residential areas: long, medium and short waves should be less than 10V/m, ultrashort wave It should be less than 5V/m, and the microwave should be less than 10 μ W/cm two 。 The relevant departments of our country have also formulated the Radiation Health Protection Distance Standard for TV Towers, and the National Environmental Protection Agency has also promulgated《 Administrative Measures for Environmental Protection of Electromagnetic Radiation 》。

In view of the development of mobile communication, the Beijing Municipal Environmental Protection Bureau issued the Regulations on Environmental Protection Management of Mobile Communication Construction Projects in Beijing (for trial implementation), the first standardized management of electromagnetic pollution in China, on February 17, 2000, to standardize the construction and operation of mobile communication stations (stations) and prevent them from causing electromagnetic pollution to the environment. The regulations specify that mobile communication stations (stations) that can generate electromagnetic radiation must go through environmental protection approval procedures and go through formalities before construction Environmental protection acceptance Approved, monitored by the environmental protection department power density Conform to the country《 Electromagnetic radiation protection regulations 》The frequency in the range of 20 MHz to 3000 MHz Derived limits Power density of 40 μ W/cm two This standard can only be officially put into use, and those higher than this standard must be stopped or rectified; Users should be predicted before building cellular mobile communication base stations density distribution , using the best Frequency reuse mode Try to reduce the number of base stations; Build mobile communication stations (stations) on residential buildings realty management agency The opinions of the residents must be obtained; radio pagers Communication Trunking communication The minimum allowable height of antenna shall not be less than 40m, and Cellular mobile communication The outdoor antenna of the base station shall not be less than 25m generally, and hospitals, kindergartens, schools, residences and other buildings higher than the antenna shall not be built within 50m of the main radiation direction of the transmitting antenna and 30m of the non main radiation direction; Construction unit Electromagnetic radiation shall be set at the above antenna installation sites Warning sign 。

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