Microwave refers to the frequency of300MHz-300GHz[4-5]Betweenelectromagnetic wave。It is easy to gather into bundles, highly oriented andRectilinear propagationIt can be used in unobstructed line of sightfree spacetransmissionHigh frequency signal。[2]microwaveFrequency ratioGeneralradio wavesHigh frequency, often called“UHFelectromagnetic wave”。As an electromagnetic wave, microwave also hasWave particle duality。The basic properties of microwave are usually characterized by penetration, reflection and absorption.For glass, plastic and porcelain, microwave almost passes through without being absorbed.For water and food, it will absorb microwave and make itselffever。And rightMetalThings like this will reflect microwaves.
onephysicsNouns.Refers to electromagnetic wave with shorter wavelength.Refers to radio communication with a wavelength between 1 mm and 1 melectromagnetic wave。
2. Tiny waves.Liu Xiang of the Han Dynasty, in his New Preface, Miscellaneous II, said, "Lead the fiber to pay, raise the microwave, and break the breeze and die." Tang Xuhun, in his poem "Pan Wu Yun Xi", said, "The rapid wrasse chirps its axle, and the microwave ripples its fishing tube
3. Remaining waves.Sima Xiangru of the Han Dynasty, in his "Fengchan Wen", said, "Let all the people in the world enjoy a clear flow, raise the microwave, become famous among the elites, and be vigorous." In the volume of the "Poetry" by Liang Zhongrong of the Southern Dynasty, "In Yongjia, you value the old and the yellow, and you still talk a little. In the time of writing, you can sort out the words, which are less than tasteful, so you can reach the surface of the river, and the microwave is still popular." In the volume of Preface to "A Collection of Records of Sheltered Cottage", "you can look up at the scenery and stop, and you can only express your thoughts on the microwave."
4. It refers to the eye wave of a woman.The Ode to Luoshen by Cao Zhi of Wei of the Three Kingdoms Period: "The unscrupulous media use the microwave to communicate with each other." Huang Zunxian of the Qing Dynasty wrote Duyou Song: "Some people use the microwave to communicate with each other, and the lotus! I can bring my hairpin phoenix to my emerald snail, and the lotus!" Gao Xu wrote in his poem "Gives Shen Xiaoze": "A melancholy beauty leaves a picture, and is willing to trust the microwave with her thoughts."
Microwave wavelength
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The frequency of microwave is between 300MHz and 300GHz, and the wavelength is between 1mm and 1mDecimeter wave, centimeter wave and millimeter wave.microwaveFrequency ratioGeneralradio wavesHigh frequency, often called“UHFRadio Waves ".As an electromagnetic wave, microwave also hasWave particle duality。The energy of microwave quantum is 1.99 × 10-25～ 1.99×10-22joule。[3]
Microwave properties
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The basic properties of microwave are usually characterized by penetration, reflection and absorption.For example, for glass, plastic and porcelain, microwave almost passes through without being absorbed.For water and food, it will absorb microwave and make itselffever。For metal objects, microwave will be reflected.
Microwave is used forRadiant heatingOfelectromagnetic wave, such asinfrared、Far infraredThe equal wavelength is longer, so it has better penetrability.When microwave penetrates into the medium, due to certain interaction between microwave energy and the mediumhertzIt makes the molecules of the medium produce 2.45 billion vibrations every second, and the molecules of the medium produce friction with each other, which causes the rise of the medium temperature, so that the internal and external parts of the medium materials are heated almost simultaneously, forming a body heat source state, greatly reducing the heat in conventional heatingConduction time, and if the condition isDielectric loss factorIt is similar to the medium temperatureNegative correlationThe internal and external heating of the material is uniform.
Selective heating
The ability of a substance to absorb microwaves is mainly determined by its mediumLoss factorTo decide.The material with a large dielectric loss factor has a strong ability to absorb microwave, on the contrary, the material with a small dielectric loss factor has a weak ability to absorb microwave.Due to the difference in the loss factors of various substances,microwave heating It shows the characteristics of selective heating.Different substances produce different thermal effects.Water MoleculesPolar molecule，Dielectric constantLarge, its dielectric loss factor is also large, and it has strong microwave absorption ability.andprotein、carbohydrateWaitingDielectric constantRelatively small, its microwave absorption capacity is much smaller than that of water.Therefore, for food,water contentThe amount of microwave heating has a great influence on the effect of microwave heating.
Low thermal inertia
Microwave pairmediumThe material is heated instantaneously, and the heating speed is fast.On the other hand, microwaveoutput powerAdjustable at any time, mediumtemperature riseIt can be changed without inertia and does not exist“waste heat”Phenomenon, which is very conducive to automatic control andContinuityProduction needs.
Photomimetic
The microwave wavelength is shorter than that of ordinary objects on the earth (such as aircraft,warship, automobile buildings, etc.) are much smaller or on the same scale.The characteristics of microwavegeometrical optics Similarity is the so-called photolike property.Therefore, working with microwave can makeCircuit elementSize reduction;Make the system more compact;It can be made into small size and narrow beamdirectionalVery strong, high gainantenna system, receiving the reflection from various objects on the ground or in spaceweak signal So as to determine the orientation and distance of the object and analyze the characteristics of the target.
Because the microwave wavelength and the size of the object (wireless equipment in the laboratory) have the same order of magnitude, the characteristics of the microwave are similar to the longer wave, namely the so-called quasi long wave.for exampleMicrowave waveguideSimilar to that in radioreceiver；Horn antennaandSlot antennaSimilar to transmitter in radio;Microwave resonatorSimilar to a radio resonator.
Nonionization
The quantum energy of microwave is not large enough to change the internal structure of material molecules or destroy the bonds between molecules (except for some substances: for example, microwave can regenerate waste rubber, which is to change waste rubber through microwaveMolecular bond）。Another way of physics, moleculesNucleusPluselectromagnetic fieldUnder the action of the periodic force ofresonanceAll phenomena occur in the microwave range, so microwave provides an effective research means for exploring the internal structure and basic characteristics of materials.On the other hand, using this feature, you can also make manyMicrowave device。
Informational
Because of the high microwave frequencyRelative bandwidthNext, its availablefrequency bandVery wide, up to hundreds or even gigahertz.This is low frequencyradio wavesIncomparable.This means that the microwaveInformation capacityLarge, so modern multiplexcommunication system , includingsatellite communication system(On Earthouter spaceexistencethe ionosphereFor short wave, almost all of them are reflected, which is short waveSkywavecommunication mode 。In the microwave band, there are several "cosmic windows" passing through the ionosphere, so microwave is a unique universeMeans of communication[6]）, almost without exception, they work in the microwave band.In addition, microwave signal can also provide phase information, polarization information and Doppler frequency information.This isobject detection ，remote sensingTarget feature analysis is very important in application.
Microwave generation
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Microwave energy usually consists ofDCOr 50Hzalternating currentObtained by a special device.There are many kinds of devices that can generate microwave, but they are mainly divided into two categories: semiconductor devices and electric vacuum devices.The electric vacuum device is a device that uses the movement of electrons in vacuum to complete energy conversion, or calledElectronic tube。Among the electric vacuum devices that can generate high-power microwave energy areMagnetron, multicavityKlystron. Microwave 3Tetrode、Traveling wave tubeEtc.In the field of microwave heating, especiallyIndustrial applicationsMainly used inMagnetronandKlystron。
It is a new technology that uses microwave energy to improve the extraction rate.Its principle is that in the microwave field, the difference in microwave absorption ability makes some areas of the matrix material orExtraction systemSome components in are selectively heated, so that the extracted substances are separated from the matrix or system and enterDielectric constantSmall, microwaveAbsorptive capacityRelatively poorExtractantMedium;Microwave extractionSimple equipment, wide application rangeExtraction efficiencyHighReproducibilityGood, time-saving, reagent saving, less pollution and other characteristics.Except mainly forPretreatment of environmental samplesIn addition, it is also used forbiochemistry、food、Industrial analysisandnatural productExtraction and other fields.In China, there are few reports on the application of microwave extraction technology in the extraction of Chinese herbal medicines.
The mechanism of microwave extraction can be analyzed from the following three aspects: ①microwave radiationThe process isHigh frequency electromagnetic waveThe process of penetrating the extraction medium to the microtubule bundles and gland cell system inside the material.As microwave energy is absorbed, the temperature inside the cell will rise rapidly, so that the pressure inside the cell will exceedcell wallThe ability of expansion to withstand, resulting in cell ruptureActive ingredientIt flows out freely and dissolves in the extraction medium at a lower temperature.The required extract can be obtained through further filtration and separation. ②Microwave generatedelectromagnetic fieldMolecules that can accelerate the extraction of components from the interior of solids to solid-liquidInterfaceThe rate of diffusion.For example, towaterWhen used as solvent, under the action of microwave field, water molecule changes from high-speed rotation state toexcited stateThis is an unstable state with high energy.At this time, water molecules may be vaporized to enhance the extraction of componentsdrive, or release its own surplus energy back toground state, the released energy will be transferred to the molecules of other substances to accelerate theirThermal movementSo as to shorten the time for the molecules of the extracted components to diffuse from the interior of the solid to the solid-liquid interface, so as to increase the extraction rate several times, reduce the extraction temperature, and maximize the quality of the extract. ③Since the frequency of microwave is related to the frequency of molecular rotation, microwave energy isIon migrationanddipoleCaused by rotationMolecular motionDeionization ofradiant energyWhen it acts on the molecule, it can promote the rotational movement of the molecule. If the molecule has a certain polarity, it can produce instantaneous polarization under the action of the microwave field and operate at a speed of 2.45 billion times/sPolarity transformationMovement, thus producing the vibration and tearing of bonds, friction and collision between particles, and rapidly generating a large amount of heat energy, promoting the cell to breakCytosolSpill and diffuse to solvent.In microwave extraction, the difference in microwave absorption ability can make certain areas of the matrix material or some components in the extraction system be selectively heated, so that the extracted material can be separated from the matrix or system into the extraction solvent with small dielectric constant and relatively poor microwave absorption ability.
heat effect
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The effect of microwave on organismheat effectIt refers to organisms caused by microwaveorganizationOr physiological effects on organisms caused by heating of the system.Thermal effects are mainly in vivoPolar moleculeUnder the action of microwave high frequency electric field, it rotates rapidly and repeatedlyfriction generates heat；The vibration of ions in the body under the action of microwave will also convert the vibration energy into heat;Generally, molecules will absorb microwave energyThermal movementEnergy increase.If the biological tissue absorbs less microwave energy, it can pass through theBlood circulationRadiate absorbed microwave energy (heat) to the whole body or outside the body.If the microwave power is very strong, and the microwave energy absorbed by the biological tissue is more than the energy emitted by the organism, the temperature of the part will rise.Local tissue temperature rise will produce a series ofPhysiological response, such as expanding local blood vessels, accelerating blood circulation and enhancing tissue metabolism through the thermal regulation system,white blood cellPhagocytosisEnhancementPathological productAbsorption and dissipation, etc.
Non thermal effect
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Microwave nonheat effectIt refers to other effects except thermal effects, such asElectric effect、Magnetic effectandChemical effectEtc.Under the action of microwave electromagnetic field, some molecules in the organism will deform and vibratecell membraneThe function is affected, which changes the electrical status of the fluid inside and outside the cell membrane, causing changes in biological effects, which can affect the central nervous system.Microwave interferenceBioelectricity(e.gECGEEG, EMGnerve conductionPotential and cell activityMembrane potential) will lead to cardiac activityCerebral nerveActivities and endocrine activities and a series of obstacles.MicrowaveNon thermal effectPeople don't know much about it.When the organism is exposed to high power microwave, the thermal effect is the main (it is generally believed that,power density At 10mW/cmtwoMost of them produce slight heat effect.And the higher the frequency, the thermal effectThreshold intensityLower);Long term low power density (1mW/cmtwoBelow)microwave radiationIt mainly causes non thermal effects
Heating principle
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Microwave is a radio wave with a frequency between 300MHz and 300GHzwaterThe molecule isPolar molecule。It's inRapid changeUnder the action of high-frequency electromagnetic field (microwave), its polarity orientation will change with the change of external electric field.The effect of causing the spin motion of water moleculesField energyIt is converted into heat energy in the medium, which increases the temperature of the material and generates a series of physical and chemical processes such as heatingmicrowave heating The purpose of drying.
The wavelength orfrequency range Is a traditional agreement.From the development of modern microwave technology, it is generally believed thatelectromagnetic wave(i.e. millimeter wave above 100GHz) belongs to the microwave range and is an important field of modern microwave research.
From the point of view of electronics and physics, microwaveElectromagnetic spectrumIt has some characteristics different from other bands.The characteristic of microwave in electronics is that its wavelength is much smaller than that of many objects on the earth and commonly used devices in the laboratory, or at the same order of magnitude.This is as common as people are already familiar withradio wavesDifferent, because the wavelength of ordinary radio wavesMuch greater thanThe size of general objects on the earth.When the wave length is smaller than the size of objects (such as aircraft, ships, rockets, buildings, etc.), the characteristics of microwave are similar to those of geometric optics.This feature can be used to make highdirectionalSystem (e.gParabolic reflector）。When wavelength and object (such asradio set）When the size of the microwave has the same order of magnitude, the characteristics of the microwave are similar to the longer wave, for example, the microwave waveguide is similar to the receiver in the radio;Horn antennaandSlot antennaSimilar to transmitter in radio;Microwave resonators are similar to radio resonators.The characteristics of wavelength and object size at the same level provide a series of typical electromagnetic fieldsBoundary value problem。
In physics, many resonance phenomena of molecules, atoms and nuclear systems occur in the range of microwave, so microwave provides an effective research means for exploring the basic properties of matter.
Because of these characteristics, a series of technologies such as generation, amplification, transmission, reception, transmission, control and measurement of microwave are different from those of other wavebands (seeMicrowave tube、Microwave measurementEtc.).
Microwave becomes a doorTechnical science, began in the 1930s.The formation of microwave technologyWaveguideThe actual application of is its mark.Several forms of microwave tubes（Klystron、Magnetron、Traveling wave tubeThe invention of is another symbol.
Microwave sensor
staythe Second World WarMedium,Microwave technologyIt has achieved rapid development.Because of the need of war, the focus of microwave research is on radar, which has led toMicrowave elementAnd devices, high powerMicrowave tube, microwave circuit and microwave measurementresearch and development 。Until today, microwave technology has become a very mature discipline both in theory and technology, and it is also a discipline that continues to develop in depth.
It is still a major trend of microwave research and development to continuously promote the frequency to a higher range.In the 1960s, the research and development of laser has passedSubmillimeter wave（Far-infrared）Andinfra-redThe gap betweenvisible lightThe electromagnetic spectrum of.Using conventional microwave technology andQuantum electronicsThe method can generate the whole electromagnetic spectrum from microwave to lightRadiant power。However, at some frequencies and frequency bands in the millimeter wave infrared gap, the coherent radiation power for practical systems cannot be obtained.
Design industrial microwave device according to GMP microwave schematic diagram
Microwave and other disciplines infiltrate each other to form several importantMarginal discipline, such as microwave astronomy, microwavemeteorology、Microwave spectroscopy、Quantum electrodynamicsMicrowave semiconductor electronics, microwaveSuperconducting electronicsIt is quite mature.Microwave opticsThe research and application of GIS has become an active field.Microwave opticsThe development of optical fiber technology, especially since the 1970s, has the significance of technological transformation (see microwave and radio frequency spectroscopy).
master controlguided wavesTube mounted transmitter.electromagnetApplicator（cavity）The inner waveguide structure is derived from energy coupling.The reflected electromagnetic energy depends on the size andDielectric heatingHeating products.through the use oftunerThe amount of reflected electromagnetic energy can be minimized to improve efficiency and optimize heating effect.
