Is a microwave oven dangerous to human health: truth or myth? The action of an electric field of ultrahigh frequency, microwave.
Section "Engineering and technology for processing hydrobionts and agricultural raw materials"
IMPACT OF ELECTROMAGNETIC MICROWAVE FIELD ON THE HUMAN BODY Kraev A.A. (Department of Physics, MSTU) It is almost impossible to calculate in advance the amount of radiant energy absorbed by the human body in a given area of electrical energy. magnetic field and converted into heat. The magnitude of this energy strongly depends on the basic electrical characteristics, the position, size and structure of muscle and fat tissues and the direction of incidence of the wave, i.e., in other words, this value depends on the input resistance of this complex structure. The direction of polarization of the incident wave relative to the body axis also plays a significant role. In each individual case, an accurate examination is required to establish symptoms existing conditions. The actual increase in body temperature depends on such parameters environment, like temperature and humidity, and from the body's cooling mechanism. Irradiation in microwave intense field living tissues leads to changes in their properties, which are associated with the thermal consequences of radiation absorption. To study these changes, living tissues can be divided into two classes: b) fabrics that do not contain blood vessels. By appropriately adjusting the output power of the microwave generator and the duration of irradiation, various tissues containing blood vessels can be heated to almost any temperature. The temperature of the tissue begins to rise immediately after microwave energy is supplied to it. This increase in temperature continues for 15-20 minutes and can increase the temperature of the tissue by 1-2 °C compared to the average body temperature, after which the temperature begins to fall. The temperature drop in the irradiated area occurs as a result of a sharp increase in blood flow in it, which leads to a corresponding heat removal. The lack of blood vessels in some parts of the body makes them particularly vulnerable to ultrahigh frequency radiation. In this case, heat can only be absorbed by the surrounding vascular tissues, to which it can only flow through thermal conduction. This is particularly true for eye tissues and such internal organs, like the gallbladder, urinary bladder and gastrointestinal tract. The small number of blood vessels in these tissues complicates the process of auto-regulation of temperature. In addition, reflections from the boundary surfaces of body cavities and areas of bone marrow under certain conditions lead to the formation of standing waves. Excessive temperature increases in certain areas of standing waves can cause tissue damage. Reflections of this kind are also caused by metal objects located inside or on the surface of the body. When these tissues are intensively irradiated with a microwave field, they overheat, leading to irreversible changes. At the same time, low-power microwave fields have a beneficial effect on the human body, which is used in medical practice. The brain and spinal cord are sensitive to changes in pressure, and therefore the increase in temperature resulting from radiation to the head can have serious consequences. The bones of the skull cause strong reflections, making it very difficult to estimate the absorbed energy. The increase in brain temperature occurs most rapidly when the head is irradiated from above or when the chest is irradiated, since heated blood from chest goes directly to the brain. Irradiation of the head causes a state of drowsiness followed by a transition to an unconscious state. With prolonged irradiation, convulsions appear, which then turn into paralysis. When the head is irradiated, death inevitably occurs if the brain temperature rises by 6 °C. The eye is one of the organs most sensitive to irradiation by microwave energy, because it has a weak thermoregulatory system and the generated heat cannot be removed quickly enough. After 10 minutes of irradiation with a power of 100 W at a frequency of 2450 MHz, the development of cataracts (clouding of the eye lens) is possible, as a result of which the lens protein coagulates and forms visible white inclusions. At this frequency, the highest temperature occurs near the back surface of the lens, which consists of a protein that is easily damaged by heat. Male genital organs in highest degree sensitive to thermal effects and therefore particularly vulnerable to irradiation. Safe radiation density expressed as maximum level 5 mW/cm2 is significantly lower than for other radiation-sensitive organs. As a result of irradiation of the testes, temporary or permanent infertility may occur. Damage to genital tissue is especially considered, since some geneticists believe that small doses of radiation do not lead to any physiological disorders, but at the same time can cause gene mutations that remain hidden for several generations.
The range of radio emission is opposite to gamma radiation and is also unlimited on one side - from long waves and low frequencies.
Engineers divide it into many sections. The shortest radio waves are used for wireless data transmission (Internet, cellular and satellite telephony); meter, decimeter and ultrashort waves (VHF) occupy local television and radio stations; short waves (HF) are used for global radio communications - they are reflected from the ionosphere and can circle the Earth; medium and long waves are used for regional radio broadcasting. Ultra-long waves (ELW) - from 1 km to thousands of kilometers - penetrate salt water and are used for communication with submarines, as well as for searching for minerals.
The energy of radio waves is extremely low, but they excite weak vibrations of electrons in a metal antenna. These vibrations are then amplified and recorded.
The atmosphere transmits radio waves with a length from 1 mm to 30 m. They make it possible to observe the nuclei of galaxies, neutron stars, and other planetary systems, but the most impressive achievement of radio astronomy is record-breaking detailed images of cosmic sources, the resolution of which exceeds a ten-thousandth of an arc second.
Microwave
Microwaves are a subband of radio emission adjacent to the infrared. It is also called ultra-high frequency (microwave) radiation because it has the highest frequency in the radio range.
The microwave range is of interest to astronomers because it records the remains of big bang cosmic microwave background radiation (another name is the microwave cosmic background). It was emitted 13.7 billion years ago, when the hot matter of the Universe became transparent to its own thermal radiation. As the Universe expanded, the CMB cooled and today its temperature is 2.7 K.
CMB radiation comes to Earth from all directions. Today, astrophysicists are interested in inhomogeneities in the sky glow in the microwave range. They are used to determine how clusters of galaxies began to form in the early Universe in order to test the correctness of cosmological theories.
But on Earth, microwaves are used for such mundane tasks as heating breakfast and talking on a cell phone.
The atmosphere is transparent to microwaves. They can be used to communicate with satellites. There are also projects for transmitting energy over a distance using microwave beams.
Sources
Sky Reviews
Microwave sky 1.9 mm(WMAP)
The cosmic microwave background, also called the cosmic microwave background radiation, is the cooled glow of the hot Universe. It was first discovered by A. Penzias and R. Wilson in 1965 ( Nobel Prize 1978) The first measurements showed that the radiation is completely uniform throughout the sky.
In 1992, the discovery of anisotropy (inhomogeneity) of the cosmic microwave background radiation was announced. This result was obtained by the Soviet satellite Relikt-1 and confirmed by the American COBE satellite (see Sky in the infrared). COBE also determined that the spectrum of the cosmic microwave background radiation is very close to that of the blackbody. The 2006 Nobel Prize was awarded for this result.
Variations in the brightness of the cosmic microwave background radiation across the sky do not exceed one hundredth of a percent, but their presence indicates subtle inhomogeneities in the distribution of matter that existed on early stage evolution of the Universe and served as the embryos of galaxies and their clusters.
However, the accuracy of the COBE and Relict data was not enough to test cosmological models, and therefore in 2001 a new, more accurate WMAP (Wilkinson Microwave Anisotropy Probe) apparatus was launched, which by 2003 had built a detailed map of the intensity distribution of the cosmic microwave background radiation across the celestial sphere. Based on these data, cosmological models and ideas about the evolution of galaxies are now being refined.
CMB arose when the age of the Universe was about 400 thousand years and, due to expansion and cooling, it became transparent to its own thermal radiation. Initially, the radiation had a Planck (blackbody) spectrum with a temperature of about 3000 K and accounted for the near-infrared and visible ranges of the spectrum.
As the Universe expanded, the cosmic microwave background radiation experienced a red shift, which led to a decrease in its temperature. Today the temperature of the cosmic microwave background radiation is 2.7 TO and it falls in the microwave and far-infrared (submillimeter) ranges of the spectrum. The graph shows an approximate view of the Planck spectrum for this temperature. The spectrum of the cosmic microwave background radiation was first measured by the COBE satellite (see Sky in the infrared), for which the Nobel Prize was awarded in 2006.
Radio sky on wave 21 cm, 1420 MHz(Dickey & Lockman)
Famous spectral line with wavelength 21.1 cm is another way to observe neutral atomic hydrogen in space. The line arises due to the so-called hyperfine splitting of the main energy level of the hydrogen atom.
The energy of an unexcited hydrogen atom depends on the relative orientation of the spins of the proton and electron. If they are parallel, the energy is slightly higher. Such atoms can spontaneously transform into a state with antiparallel spins, emitting a quantum of radio emission that carries away a tiny excess of energy. This happens to an individual atom on average once every 11 million years. But the huge distribution of hydrogen in the Universe makes it possible to observe gas clouds at this frequency.
Radio sky on wave 73.5 cm, 408 MHz(Bonn)
This is the longest wavelength of all sky surveys. It was performed at a wavelength at which a significant number of sources are observed in the Galaxy. In addition, the choice of wavelength was determined by technical reasons. To construct the survey, one of the world's largest full-rotating radio telescopes was used - the 100-meter Bonn radio telescope.
Terrestrial Application
The main advantage of a microwave oven is that over time the food is heated throughout the entire volume, and not just from the surface.
Microwave radiation, having a longer wavelength, penetrates deeper than infrared radiation under the surface of products. Inside food, electromagnetic vibrations excite rotational levels of water molecules, the movement of which mainly causes heating of food. In this way, microwave (microwave) drying of food, defrosting, cooking and heating takes place. Also, alternating electric currents excite high frequency currents. These currents can occur in substances where mobile charged particles are present.
But sharp and thin metal objects cannot be placed in a microwave oven (this especially applies to dishes with metal decorations coated with silver and gold). Even a thin ring of gold plating along the edge of the plate can cause a powerful electrical discharge that will damage the device that creates the electromagnetic wave in the furnace (magnetron, klystron).
The operating principle of cellular telephony is based on the use of a radio channel (in the microwave range) for communication between the subscriber and one of the base stations. Information is transmitted between base stations, as a rule, via digital cable networks.
The range of the base station - the size of the cell - is from several tens to several thousand meters. It depends on the landscape and on the signal strength, which is selected so that there are not too many active subscribers in one cell.
In the GSM standard, one base station can support no more than 8 telephone conversations simultaneously. At public events and natural disasters the number of calling subscribers increases sharply, this overloads base stations and leads to interruptions in service cellular communication. For such cases, cellular operators have mobile base stations that can be quickly delivered to areas with large crowds of people.
There is a lot of controversy about the possible harm of microwave radiation from cell phones. During a conversation, the transmitter is in close proximity to the person's head. Repeated studies have not yet been able to reliably register negative impact radio emissions from cell phones on health. Although the effects of weak microwave radiation on body tissue cannot be completely ruled out, there is no cause for serious concern.
Television images are transmitted on meter and decimeter waves. Each frame is divided into lines along which the brightness changes in a certain way.
The transmitter of a television station constantly broadcasts a radio signal of a strictly fixed frequency, it is called the carrier frequency. The receiving circuit of the TV is adjusted to it - a resonance arises in it at the desired frequency, which makes it possible to pick up weak electromagnetic oscillations. Information about the image is transmitted by the amplitude of the oscillations: large amplitude means high brightness, low amplitude means a dark area of the image. This principle is called amplitude modulation. Sound is transmitted similarly by radio stations (except FM stations).
With the transition to digital television, the rules for image encoding change, but the very principle of the carrier frequency and its modulation remains the same.
Parabolic antenna for receiving a signal from a geostationary satellite in the microwave and VHF ranges. The principle of operation is the same as that of a radio telescope, but the dish does not need to be made movable. At the time of installation, it is directed to the satellite, which always remains in one place relative to earthly structures.
This is achieved by placing the satellite into a geostationary orbit at an altitude of about 36 thousand. km above the Earth's equator. The period of revolution along this orbit is exactly equal to the period of rotation of the Earth around its axis relative to the stars - 23 hours 56 minutes 4 seconds. The size of the dish depends on the power of the satellite transmitter and its radiation pattern. Each satellite has a primary service area where its signals are received by a dish with a diameter of 50–100 cm, and the peripheral zone, where the signal quickly weakens and an antenna of up to 2–3 may be required to receive it. m.
The content of the article
ULTRA HIGH FREQUENCY RANGE, frequency range of electromagnetic radiation (100-300,000 million hertz), located in the spectrum between ultra-high television frequencies and frequencies of the far infrared region. This frequency range corresponds to wavelengths from 30 cm to 1 mm; therefore it is also called the decimeter and centimeter wave range. In English-speaking countries it is called the microwave band; This means that the wavelengths are very small compared to the wavelengths of conventional radio broadcasting, which are on the order of several hundred meters.
Since microwave radiation is intermediate in wavelength between light radiation and ordinary radio waves, it has some properties of both light and radio waves. For example, like light, it travels in a straight line and is blocked by almost all solid objects. Much like light, it is focused, spreads out as a beam, and reflected. Many radar antennas and other microwave devices are enlarged versions of optical elements such as mirrors and lenses.
At the same time, microwave radiation is similar to broadcast radio radiation in that it is generated by similar methods. The classical theory of radio waves applies to microwave radiation, and it can be used as a means of communication based on the same principles. But thanks to higher frequencies, it provides greater opportunities for transmitting information, which makes communication more efficient. For example, one microwave beam can carry several hundred telephone conversations simultaneously. The similarity of microwave radiation to light and the increased density of information it carries have proven to be very useful for radar and other fields of technology.
APPLICATION OF MICROWAVE RADIATION
Radar.
Waves in the decimeter-centimeter range remained a subject of purely scientific curiosity until the outbreak of World War II, when there was an urgent need for a new and effective electronic means of early detection. Only then did intensive research into microwave radar begin, although its fundamental possibility was demonstrated back in 1923 at the US Naval Research Laboratory. The essence of radar is that short, intense pulses of microwave radiation are emitted into space, and then part of this radiation is recorded, returning from the desired distant object - a sea vessel or aircraft.
Connection.
Microwave radio waves are widely used in communications technology. In addition to various military radio systems, there are numerous commercial microwave communication lines in all countries of the world. Since such radio waves do not follow the curvature earth's surface, and propagate in a straight line, these communication links typically consist of relay stations installed on hilltops or radio towers at intervals of approx. 50 km. Parabolic or horn antennas, mounted on towers, receive and transmit microwave signals. At each station, the signal is amplified by an electronic amplifier before retransmission. Since microwave radiation allows highly targeted reception and transmission, transmission does not require large amounts of electricity.
Although the system of towers, antennas, receivers and transmitters may seem very expensive, in the end it all more than pays off thanks to the large information capacity of microwave communication channels. Cities across the United States are connected by a complex network of more than 4,000 microwave relay links, forming a communications system that stretches from one ocean coast to the next. The channels of this network are capable of transmitting thousands of telephone conversations and numerous television programs simultaneously.
Communications satellites.
The system of radio relay towers necessary for transmitting microwave radiation over long distances can, of course, only be built on land. For intercontinental communication, a different relay method is required. Here, connected artificial earth satellites come to the rescue; launched into geostationary orbit, they can perform the functions of microwave communication relay stations.
An electronic device called an active-relay satellite receives, amplifies, and relays microwave signals transmitted by ground stations. The first experimental satellites of this type (Telstar, Relay and Syncom) successfully relayed television broadcasts from one continent to another in the early 1960s. Based on this experience, commercial intercontinental and domestic communications satellites were developed. Intelsat's latest intercontinental series satellites have been launched into different locations in geostationary orbit in such a way that their coverage areas overlap to provide service to subscribers around the world. Each Intelsat satellite of the latest modifications provides customers with thousands of high-quality communication channels for the simultaneous transmission of telephone, television, fax signals and digital data.
Heat treatment of food products.
Microwave radiation is used for heat treatment of food products at home and in the food industry. The energy generated by high-power vacuum tubes can be concentrated into a small volume for highly efficient thermal processing of products in the so-called. microwave or microwave ovens, characterized by cleanliness, noiselessness and compactness. Such devices are used in aircraft galleys, railway dining cars and vending machines, where quick food preparation and cooking are required. The industry also produces microwave ovens for household use.
Scientific research.
Microwave radiation played a role important role in studies of the electronic properties of solids. When such a body finds itself in a magnetic field, free electrons in it begin to rotate around magnetic field lines in a plane perpendicular to the direction of the magnetic field. The rotation frequency, called the cyclotron frequency, is directly proportional to the magnetic field strength and inversely proportional to the effective mass of the electron. (The effective mass determines the acceleration of an electron under the influence of some force in the crystal. It differs from the mass of a free electron, which determines the acceleration of the electron under the influence of some force in a vacuum. The difference is due to the presence of attractive and repulsive forces that act on the electron in the crystal surrounding atoms and other electrons.) If on solid, located in a magnetic field, microwave radiation falls, then this radiation is strongly absorbed when its frequency is equal to the cyclotron frequency of the electron. This phenomenon is called cyclotron resonance; it allows one to measure the effective mass of an electron. Such measurements have provided much valuable information about the electronic properties of semiconductors, metals, and metalloids.
Microwave radiation also plays an important role in space research. Astronomers have learned a lot about our Galaxy by studying the 21 cm wavelength emitted by hydrogen gas in interstellar space. It is now possible to measure the speed and direction of movement of the galaxy's arms, as well as the location and density of regions of hydrogen gas in space.
SOURCES OF MICROWAVE RADIATION
Rapid progress in the field of microwave technology is largely associated with the invention of special vacuum devices - magnetron and klystron, capable of generating large amounts of microwave energy. A generator based on a conventional vacuum triode, used at low frequencies, turns out to be very ineffective in the microwave range.
The two main disadvantages of the triode as a microwave generator are the finite time of flight of the electron and the interelectrode capacitance. The first is due to the fact that it takes an electron some (albeit short) time to fly between the electrodes of a vacuum tube. During this time, the microwave field manages to change its direction to the opposite direction, so that the electron is forced to turn back before reaching the other electrode. As a result, electrons oscillate inside the lamp without any benefit, without giving up their energy to the oscillatory circuit of the external circuit.
Magnetron.
The magnetron, invented in Great Britain before World War II, does not have these disadvantages, since it is based on a completely different approach to the generation of microwave radiation - the principle of a volumetric resonator. Just as an organ pipe of a given size has its own acoustic resonance frequencies, a cavity resonator has its own electromagnetic resonances. The walls of the resonator act as inductance, and the space between them acts as the capacitance of a certain resonant circuit. Thus, a cavity resonator is similar to a parallel resonant circuit of a low-frequency oscillator with a separate capacitor and inductor. The dimensions of the cavity resonator are chosen, of course, so that the desired resonant ultra-high frequency corresponds to a given combination of capacitance and inductance.
The magnetron (Fig. 1) has several volumetric resonators located symmetrically around the cathode located in the center. The device is placed between the poles of a strong magnet. In this case, the electrons emitted by the cathode are forced to move along circular trajectories under the influence of a magnetic field. Their speed is such that at a strictly defined time they cross the open grooves of the resonators at the periphery. At the same time, they give off their kinetic energy, exciting vibrations in the resonators. The electrons are then returned to the cathode and the process repeats. Thanks to this device, the time of flight and interelectrode capacitances do not interfere with the generation of microwave energy.
Magnetrons can be made big size, and then they give powerful pulses of microwave energy. But the magnetron has its drawbacks. For example, resonators for very high frequencies become so small that they are difficult to manufacture, and such a magnetron itself, due to its small size, cannot be powerful enough. In addition, a magnetron requires a heavy magnet, and the required magnet mass increases with increasing power of the device. Therefore, powerful magnetrons are not suitable for aircraft on-board installations.
Klystron.
This electric vacuum device, based on a slightly different principle, does not require an external magnetic field. In a klystron (Fig. 2), electrons move in a straight line from the cathode to the reflective plate, and then back. In doing so, they cross the open gap of the donut-shaped cavity resonator. The control grid and resonator grids group electrons into separate “clumps” so that electrons cross the resonator gap only at certain times. The gaps between the bunches are matched to the resonant frequency of the resonator in such a way that the kinetic energy of the electrons is transferred to the resonator, as a result of which powerful electromagnetic oscillations are established in it. This process can be compared to the rhythmic swinging of an initially motionless swing.
The first klystrons were rather low-power devices, but later they broke all records of magnetrons as high-power microwave generators. Klystrons were created that delivered up to 10 million watts of power per pulse and up to 100 thousand watts in continuous mode. The klystron system of the research linear particle accelerator produces 50 million watts of microwave power per pulse.
Klystrons can operate at frequencies up to 120 billion hertz; however, their output power, as a rule, does not exceed one watt. Design options for a klystron designed for high output powers in the millimeter range are being developed.
Klystrons can also serve as amplifiers for microwave signals. To do this, you need to apply an input signal to the grids of the cavity resonator, and then the density of the electron bunches will change in accordance with this signal.
Traveling wave lamp (TWT).
Another electrovacuum device for generating and amplifying electromagnetic waves in the microwave range is a traveling wave lamp. It consists of a thin evacuated tube inserted into a focusing magnetic coil. There is a retarding wire coil inside the tube. An electron beam passes along the axis of the spiral, and a wave of the amplified signal runs along the spiral itself. The diameter, length and pitch of the spiral, as well as the speed of the electrons, are selected in such a way that the electrons give up part of their kinetic energy to the traveling wave.
Radio waves travel at the speed of light, while the speed of electrons in the beam is much slower. However, since the microwave signal is forced to travel in a spiral, its speed along the tube axis is close to the speed of the electron beam. Therefore, the traveling wave interacts with electrons for a long time and is amplified, absorbing their energy.
If no external signal is applied to the lamp, then random electrical noise at a certain resonant frequency is amplified and the traveling wave TWT operates as a microwave generator rather than an amplifier.
The output power of a TWT is significantly less than that of magnetrons and klystrons at the same frequency. However, TWTs can be tuned over an unusually wide frequency range and can serve as very sensitive low-noise amplifiers. This combination of properties makes the TWT a very valuable device in microwave technology.
Flat vacuum triodes.
Although klystrons and magnetrons are preferred as microwave oscillators, improvements have somewhat restored the important role of vacuum triodes, especially as amplifiers at frequencies up to 3 billion hertz.
Difficulties associated with time of flight are eliminated due to the very short distances between the electrodes. Unwanted interelectrode capacitance is minimized because the electrodes are mesh and all external connections are made on large rings located outside the lamp. As is customary in microwave technology, a volumetric resonator is used. The resonator tightly encloses the lamp, and ring connectors provide contact along the entire circumference of the resonator.
Gunn diode generator.
Such a semiconductor microwave generator was proposed in 1963 by J. Gunn, an employee of the Watson Research Center of the IBM Corporation. Currently, such devices provide power of only the order of milliwatts at frequencies of no more than 24 billion hertz. But within these limits it has undoubted advantages over low-power klystrons.
Since the Gunn diode is a single crystal of gallium arsenide, it is in principle more stable and durable than a klystron, which must have a heated cathode to create a flow of electrons and requires a high vacuum. In addition, a Gunn diode operates at a relatively low supply voltage, whereas powering a klystron requires bulky and expensive power supplies with voltages ranging from 1000 to 5000 V.
CIRCUIT COMPONENTS
Coaxial cables and waveguides.
To transmit electromagnetic waves in the microwave range not through the ether, but through metal conductors, special methods and specially shaped conductors are needed. Conventional wires that carry electricity, suitable for transmitting low-frequency radio signals, are ineffective at ultra-high frequencies.
Any piece of wire has capacitance and inductance. These so-called distributed parameters become very important in microwave technology. The combination of the conductor's capacitance with its own inductance at ultra-high frequencies plays the role of a resonant circuit, almost completely blocking transmission. Since it is impossible to eliminate the influence of distributed parameters in wired transmission lines, we have to turn to other principles for transmitting microwave waves. These principles are embodied in coaxial cables and waveguides.
A coaxial cable consists of an inner conductor and a cylindrical outer conductor surrounding it. The gap between them is filled with a plastic dielectric, such as Teflon or polyethylene. At first glance, this may seem similar to a pair of ordinary wires, but at ultrahigh frequencies their function is different. A microwave signal introduced from one end of the cable actually propagates not through the metal of the conductors, but through the gap between them filled with insulating material.
Coaxial cables are good at transmitting microwave signals up to several billion hertz, but at higher frequencies their efficiency decreases and they are unsuitable for transmitting high powers.
Conventional channels for transmitting microwave waves are in the form of waveguides. A waveguide is a carefully machined metal tube with a rectangular or circular cross-section, inside which a microwave signal propagates. Simply put, the waveguide directs the wave, causing it to be reflected from the walls every now and then. But in fact, the propagation of a wave along a waveguide is the propagation of oscillations of the electric and magnetic fields of the wave, as in free space. Such propagation in a waveguide is possible only if its dimensions are in a certain relationship with the frequency of the transmitted signal. Therefore, the waveguide is precisely calculated, processed precisely and intended only for a narrow frequency range. It transmits other frequencies poorly or not at all. A typical distribution of electric and magnetic fields inside a waveguide is shown in Fig. 3.
The higher the wave frequency, the smaller sizes a corresponding rectangular waveguide; in the end, these dimensions turn out to be so small that its manufacture becomes excessively complicated and the maximum power transmitted by it is reduced. Therefore, the development of circular waveguides (circular cross-section) has begun, which can be quite large in size even at high frequencies in the microwave range. The use of a circular waveguide is hampered by some difficulties. For example, such a waveguide must be straight, otherwise its efficiency is reduced. Rectangular waveguides are easy to bend; they can be given the desired curvilinear shape, and this does not affect signal propagation in any way. Radar and other microwave installations usually look like intricate labyrinths of waveguide paths connecting different components and transmitting the signal from one device to another within the system.
Solid state components.
Solid-state components, such as semiconductors and ferrites, play an important role in microwave technology. Thus, germanium and silicon diodes are used to detect, switch, rectify, frequency convert and amplify microwave signals.
For amplification, special diodes are also used - varicaps (with controlled capacitance) - in a circuit called a parametric amplifier. Widespread amplifiers of this kind are used to amplify extremely small signals, since they introduce almost no noise or distortion of their own.
A ruby maser is also a solid-state microwave amplifier with a low noise level. Such a maser, whose operation is based on quantum mechanical principles, amplifies the microwave signal due to transitions between the internal energy levels of atoms in a ruby crystal. The ruby (or other suitable maser material) is immersed in liquid helium so that the amplifier operates at extremely low temperatures(only a few degrees above absolute zero temperature). Therefore, the thermal noise level in the circuit is very low, making the maser suitable for radio astronomy, ultra-sensitive radar and other measurements where extremely weak microwave signals need to be detected and amplified.
Ferrite materials such as magnesium iron oxide and yttrium iron garnet are widely used for the manufacture of microwave switches, filters and circulators. Ferrite devices are controlled by magnetic fields, and a weak magnetic field is sufficient to control the flow of a powerful microwave signal. Ferrite switches have the advantage over mechanical ones that they have no moving parts subject to wear, and switching is very fast. In Fig. Figure 4 shows a typical ferrite device - a circulator. Acting like a traffic circle, the circulator ensures that the signal travels only along certain paths connecting various components. Circulators and other ferrite switching devices are used when connecting multiple components of a microwave system to the same antenna. In Fig. 4, the circulator does not allow the transmitted signal to pass to the receiver, and the received signal to the transmitter.
The tunnel diode, a relatively new semiconductor device operating at frequencies up to 10 billion hertz, is also used in microwave technology. It is used in oscillators, amplifiers, frequency converters and switches. Its operating power is low, but it is the first semiconductor device capable of operating efficiently at such high frequencies.
Antennas.
Microwave antennas are very diverse unusual shapes. The size of the antenna is approximately proportional to the wavelength of the signal, and therefore designs that would be too bulky at lower frequencies are quite acceptable for the microwave range.
The designs of many antennas take into account those properties of microwave radiation that bring it closer to light. Typical examples include horn antennas, parabolic reflectors, metallic and dielectric lenses. Helical and spiral antennas are also used, often manufactured in the form of printed circuits.
Groups of slot waveguides can be arranged to produce the desired radiation pattern for the radiated energy. Dipoles like the well-known television antennas installed on roofs are also often used. Such antennas often have identical elements located at intervals equal to the wavelength, which increase directivity due to interference.
Microwave antennas are usually designed to be extremely directional, since in many microwave systems it is very important that energy is transmitted and received precisely. given direction. The directivity of the antenna increases with increasing its diameter. But you can make the antenna smaller while maintaining its directivity if you move to higher operating frequencies.
Many "mirror" antennas with a parabolic or spherical metal reflector are designed specifically to receive extremely weak signals coming, for example, from interplanetary spacecraft or from distant galaxies. In Arecibo (Puerto Rico) there is one of the largest radio telescopes with a metal reflector in the form of a spherical segment, the diameter of which is 300 m. The antenna has a fixed (“meridian”) base; its receiving radio beam moves across the sky due to the rotation of the Earth. The largest (76 m) fully movable antenna is located in Jodrell Bank (UK).
New in the field of antennas - an antenna with electronic directivity control; such an antenna does not need to be mechanically rotated. It consists of numerous elements - vibrators, which can be electronically connected to each other in different ways and thereby ensure the sensitivity of the “antenna array” in any desired direction.
I was very surprised when my simple homemade detector-indicator went off scale next to a working microwave oven in our work canteen. It’s all shielded, maybe there’s some kind of malfunction? I decided to check out my new stove; it had hardly been used. The indicator also deviated to the full scale!
I collect such a simple indicator for a short time every time I go to field tests of transmitting and receiving equipment. It helps a lot in work, you don’t have to carry a lot of equipment with you, it’s always easy to check the functionality of the transmitter with a simple homemade product (where the antenna connector is not fully screwed in, or you forgot to turn on the power). Customers really like this style of retro indicator and have to leave it as a gift.
The advantage is the simplicity of the design and the lack of power. Eternal device.
It’s easy to do, much simpler than the exact same “Detector from a network extension cord and a bowl of jam” in the mid-wave range. Instead of a network extension cord (inductor) - a piece of copper wire; by analogy, you can have several wires in parallel, it won’t be any worse. The wire itself in the form of a circle 17 cm long, at least 0.5 mm thick (for greater flexibility I use three such wires) is both an oscillating circuit at the bottom and a loop antenna for the upper part of the range, which ranges from 900 to 2450 MHz (I did not check the performance above ). It is possible to use a more complex directional antenna and input matching, but such a deviation would not correspond to the title of the topic. A variable, built-in or just a capacitor (aka a basin) is not needed, for a microwave there are two connections next to each other, already a capacitor.
There is no need to look for a germanium diode; it will be replaced by a PIN diode HSMP: 3880, 3802, 3810, 3812, etc., or HSHS 2812 (I used it). If you want to move above the frequency of the microwave oven (2450 MHz), choose diodes with a lower capacitance (0.2 pF), HSMP -3860 - 3864 diodes may be suitable. When installing, do not overheat. It is necessary to solder spot-quickly, in 1 second.
Instead of high-impedance headphones there is a dial indicator. The magnetoelectric system has the advantage of inertia. The filter capacitor (0.1 µF) helps the needle move smoothly. The higher the indicator resistance, the more sensitive the field meter (the resistance of my indicators ranges from 0.5 to 1.75 kOhm). The information contained in a deviating or twitching arrow has a magical effect on those present.
Such a field indicator, installed next to the head of a person talking on a mobile phone, will first cause amazement on the face, perhaps bring the person back to reality, and save him from possible diseases.
If you still have strength and health, be sure to point your mouse at one of these articles.
Instead of a pointer device, you can use a tester that will measure DC voltage at the most sensitive limit.
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| Microwave indicator circuit with LED. |
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| Microwave indicator with LED. |
Tried it LED as indicator. This design can be designed in the form of a keychain using a flat 3-volt battery, or inserted into an empty mobile phone case. The standby current of the device is 0.25 mA, the operating current directly depends on the brightness of the LED and will be about 5 mA. The voltage rectified by the diode is amplified by the operational amplifier, accumulated on the capacitor and opens the switching device on the transistor, which turns on the LED.
If the dial indicator without a battery deviated within a radius of 0.5 - 1 meter, then the color music on the diode moved up to 5 meters, as from cell phone, and from a microwave oven. I was not mistaken about color music, see for yourself that the maximum power will only be when talking on a mobile phone and in the presence of extraneous loud noise.
Adjustment.
I collected several such indicators, and they worked immediately. But there are still nuances. When turned on, the voltage on all pins of the microcircuit, except the fifth, should be equal to 0. If this condition is not met, connect the first pin of the microcircuit through a 39 kOhm resistor to minus (ground). It happens that the configuration of microwave diodes in the assembly does not coincide with the drawing, so you need to adhere to the electrical diagram, and before installation I would advise you to ring the diodes to ensure their compliance.
For ease of use, you can worsen the sensitivity by reducing the 1 mOhm resistor, or reducing the length of the wire turn. With the given field values, microwave base telephone stations can be sensed within a radius of 50 - 100 m.
With such an indicator, you can draw up an environmental map of your area and highlight places where you can’t hang out with strollers or stay with children for a long time.
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Be under base station antennas |
Analog level indicator.
I decided to try to make the microwave indicator a little more complex, for which I added an analog level meter to it. For convenience, I used the same element base. The circuit shows three DC operational amplifiers with different gains. In the layout, I settled on 3 stages, although you can plan a 4th one using the LMV 824 microcircuit (4th op-amp in one package). Having used power from 3, (3.7 telephone battery) and 4.5 volts, I came to the conclusion that it is possible to do without a key stage on a transistor. Thus, we got one microcircuit, a microwave diode and 4 LEDs. Taking into account the conditions of strong electromagnetic fields in which the indicator will operate, I used blocking and filtering capacitors for all inputs, feedback circuits and op-amp power supply.
Adjustment.
When turned on, the voltage on all pins of the microcircuit, except the fifth, should be equal to 0. If this condition is not met, connect the first pin of the microcircuit through a 39 kOhm resistor to minus (ground). It happens that the configuration of microwave diodes in the assembly does not coincide with the drawing, so you need to adhere to the electrical diagram, and before installation I would advise you to ring the diodes to ensure their compliance.
This prototype has already been tested.
The interval from 3 illuminated LEDs to completely extinguished ones is about 20 dB.
Power supply from 3 to 4.5 volts. Standby current from 0.65 to 0.75 mA. The operating current when the 1st LED lights up is from 3 to 5 mA.
This microwave field indicator on a chip with a 4th op amp was assembled by Nikolai.
Here is his diagram.
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| Dimensions and pin markings of the LMV824 microcircuit. |
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| Installation of microwave indicator on the LMV824 chip. |
The MC 33174D microcircuit, which has similar parameters and includes four operational amplifiers, is housed in a dip package and is larger in size and therefore more convenient for amateur radio installation. The electrical configuration of the pins completely coincides with the L MV 824 microcircuit. Using the MC 33174D microcircuit, I made a layout of a microwave indicator with four LEDs. A 9.1 kOhm resistor and a 0.1 μF capacitor in parallel with it are added between pins 6 and 7 of the microcircuit. The seventh pin of the microcircuit is connected through a 680 Ohm resistor to the 4th LED. The standard size of the parts is 06 03. The breadboard is powered by a lithium cell of 3.3 - 4.2 volts.
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| Indicator on the MC33174 chip. |
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| Reverse side. |
The original design of the economical field indicator is a souvenir made in China. This inexpensive toy contains: a radio, a clock with a date, a thermometer and, finally, a field indicator. The unframed, flooded microcircuit consumes negligibly little energy, since it operates in a timing mode; it reacts to turning on a mobile phone from a distance of 1 meter, simulating a few seconds of LED indication of an emergency alarm with headlights. Such circuits are implemented on programmable microprocessors with a minimum number of parts.
Addition to comments.
Selective field meters for the amateur band 430 - 440 MHz
and for the PMR band (446 MHz).
Indicators of microwave fields for amateur bands from 430 to 446 MHz can be made selective by adding an additional circuit L to SK, where L to is a turn of wire with a diameter of 0.5 mm and a length of 3 cm, and SK is a trimming capacitor with a nominal value of 2 - 6 pF . The turn of wire itself, as an option, can be made in the form of a 3-turn coil, with a pitch wound on a mandrel with a diameter of 2 mm with the same wire. An antenna in the form of a piece of wire 17 cm long must be connected to the circuit through a 3.3 pF coupling capacitor.
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| Range 430 - 446 MHz. Instead of a turn, there is a step-wound coil. |
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| Diagram for ranges 430 - 446 MHz. |
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| Frequency range mounting 430 - 446 MHz. |
By the way, if you are serious about microwave measurements of individual frequencies, you can use selective SAW filters instead of a circuit. In the capital's radio stores their assortment is currently more than sufficient. You will need to add an RF transformer to the circuit after the filter.
But this is another topic that does not correspond to the title of the post.
Who invented microwaves and how did it all end?
The first microwave ovens were invented by German scientists commissioned by the Nazis. This was done in order not to waste time on cooking and not to carry heavy fuel for stoves during the cold Russian winters. During operation, it turned out that food prepared in them had a negative effect on the health of soldiers and their use was abandoned.
In 1942-1943, these studies fell into the hands of the Americans and were classified.
At the same time, several microwave ovens fell into the hands of the Russians and were carefully studied by Soviet scientists in B Belarusian Radio Technological Institute and in closed research institutes of the Urals and Novosibirsk (Drs. Luria and Perov). In particular, their biological effect was studied, that is, the influence of microwave radiation on biological objects.
Result:
The Soviet Union passed a law prohibiting the use of microwave ovens due to their biological hazard! The Soviets have issued an international warning about the health and environmental hazards of microwave ovens and other similar electromagnetic devices.
These data are a little alarming, aren't they?
Continuing their work, Soviet scientists examined thousands of workers who worked with radar installations and received microwave radiation. The results were so severe that a strict radiation limit was set at 10 microwatts for workers and 1 microwatt for civilians.
Operating principle of a microwave oven:
Microwave radiation, Microwave radiation (microwave radiation)- electromagnetic radiation, including the centimeter and millimeter range of radio waves (from 30 cm - frequency 1 GHz to 1 mm - 300 GHz).
Microwaves are a form of electromagnetic energy, just like light waves or radio waves. These are very short electromagnetic waves that travel at the speed of light (299.79 thousand km per second). In modern technology, microwaves are used in microwave ovens, for long-distance and international telephone communications, transmission of television programs, and operation of the Internet on Earth and via satellites. But microwaves are best known to us as a source of energy for cooking - the microwave oven.
Every microwave oven contains a magnetron, which converts electrical energy into an ultra-high-frequency electric field with a frequency of 2450 MHz or 2.45 GHz, which interacts with water molecules in food. Microwaves attack water molecules in food, causing them to spin millions of times per second, creating molecular friction that heats the food.
What is the harm of a microwave?
For those who know about harmful influence mobile phones, it should be clear that a mobile phone operates on the same frequencies as a microwave oven. For those who are not familiar with this information, please read the information “The Impact of Mobile Phones on Humans”.
We will talk about four factors that indicate that microwaves are harmful.
Firstly, these are electromagnetic radiations themselves, or rather their information component. In science it is called a torsion field.
It has been experimentally established that electromagnetic radiation has a torsion (information) component. According to research by specialists from France, Russia, Ukraine and Switzerland, it is torsion fields, and not electromagnetic ones, that are the main factor negative influence on human health. Since it is the torsion field that transmits to a person all the negative information that causes headaches, irritation, insomnia, etc.
In addition, we must not forget about temperature. Of course, this applies to long periods of time and constant use of the microwave.
The most harmful to the human body, from a biological point of view, is high-frequency radiation in the centimeter range (microwave), which produces electromagnetic radiation of the highest intensity.
Microwave radiation directly heats the body, blood flow reduces heating (this applies to organs rich in blood vessels). But there are organs, such as the lens, that do not contain blood vessels. Therefore, microwave waves, i.e. significant thermal effects lead to clouding of the lens and its destruction. These changes are irreversible.
Electromagnetic radiation cannot be seen, heard or clearly felt. But it exists and affects the human body. The exact mechanism of action of electromagnetic study has not yet been studied. The influence of this radiation does not appear immediately, but as it accumulates, so it can be difficult to attribute a particular disease that suddenly appears in a person to the devices with which he was in contact.
Secondly, this is the effect of microwave radiation on food. As a result of the influence of electromagnetic radiation on a substance, ionization of molecules is possible, i.e. an atom can gain or lose an electron, and this changes the structure of the substance.
Radiation leads to the destruction and deformation of food molecules. Microwaves create new compounds that do not exist in nature, called radiolytics. Radiolytic compounds create molecular rot - as a direct consequence of radiation.
- Microwaved meats contain Nitrosodienthanolamines, a well-known carcinogen;
- Some amino acids in milk and cereals have become carcinogens;
- Defrosting frozen fruits in microwave ovens converts their glucosides and galactosides into particles containing carcinogenic elements;
- Even very short irradiation in a microwave oven raw vegetables converts their alkaloids into carcinogens;
- Carcinogenic free radicals are formed in microwaved plants, especially root vegetables;
- The value of food decreases from 60% to 90%;
- Disappears biological activity vitamin B (complex), vitamins C and E, also in many minerals;
- Destroyed in varying degrees in plants alkaloids, glucosides, galactosides and nitrilosides;
- Degradation of nucleoproteins in meat. Robert Becker in his book ‘Electricity of the Body’, citing research by Russian scientists, describes diseases associated with microwave ovens.
Data:
Some of the amino acids L-proline, which are part of mother's milk, as well as in infant formula, are converted under the influence of microwaves into d-isomers, which are considered neurotoxic (deform nervous system) and nephrotoxic (poisonous to the kidneys). It is a tragedy that many children are fed on artificial milk substitutes (baby formula), which are made even more toxic by microwave ovens.
A short-term study showed that people who ate microwaved milk and vegetables had changes in their blood composition, decreased hemoglobin and increased cholesterol, while people who ate the same food but cooked traditional way, the state of the body did not change.
Hospital patient Norma Levitt underwent simple knee surgery and then died from a blood transfusion. Usually the blood is warmed before a transfusion, but not in a microwave oven. This time, the nurse heated the blood in the microwave, unaware of the danger. Microwave-tainted blood killed Norma. The same thing happens with food that is heated and cooked in microwaves. Although the trial took place, newspapers and magazines did not talk about this case.
Researchers at the University of Vienna have found that heating with microwaves disrupts the atomic order of amino acids. According to the researchers, this is of concern because these amino acids are incorporated into proteins, which they then structurally, functionally and immunologically alter. Thus, proteins - the basis of life - are changed in food by microwaves.
Third, Microwave radiation leads to weakening of the cells of our body.
In genetic engineering, there is such a method: in order to penetrate a cell, it is lightly irradiated with electromagnetic waves and this weakens the cell membranes. Since the cells are practically broken, the cell membranes cannot protect the cell from the penetration of viruses, fungi and other microorganisms, and the natural self-healing mechanism is also suppressed.
Fourth, the microwave oven creates radioactive decay molecules with the subsequent formation of new alloys unknown to nature, as usual with radiation.
Doesn’t the harm of a microwave seem so unrealistic now?
The influence of microwave radiation on human health
As a result of eating microwaved food, the pulse and blood pressure first decrease, and then nervousness, high blood pressure, headaches, dizziness, eye pain, insomnia, irritability, nervousness, stomach pain, inability to concentrate, hair loss, increased incidence of appendicitis occur. , cataracts, reproductive problems, cancer. These chronic symptoms are exacerbated by stress and heart disease.
Consumption of food irradiated in a microwave oven contributes to the formation of an increased number of cancer cells in the blood serum.
According to statistics, in a large number of people, food irradiated in a microwave oven causes tumors resembling cancer in the stomach and digestive tract, in addition, a general degeneration of peripheral cellular tissue with permanent disruption of the functions of the digestive and excretory system.
Thus, food altered by microwaves harms the digestive tract and immune system humans and can ultimately cause cancer.
In addition, we must not forget about electromagnetic radiation itself. This is especially true for pregnant women and children.
Most susceptible to electromagnetic fields circulatory system, endocrine system, brain, eyes, immune and reproductive systems.
As for pregnant women, you need to be extremely careful. Unlimited “walks” through electromagnetic fields during pregnancy can lead to spontaneous abortions, premature births, and the appearance of congenital malformations in children.
Read more about the influence of electromagnetic fields in the section “The influence of electromagnetic radiation on humans”.
The purpose of this site is not to intimidate. We warn you.
Nobody says that tomorrow you will have mental disorders or, God forbid, they will discover something in your brain.
The harm of microwave radiation depends on its intensity and exposure time. Modern microwaves they won’t be able to kill you... tomorrow or in a year...
Scientists talk about the consequences in 10-15 years.
What does this mean?
1. If you are 20-25 today, then while still a young person (up to 35-40 years old), you risk remaining disabled, or giving birth to a disabled person, or not giving birth to one at all, significantly shortening the life span of yourself and your child.
2. If you are around 30-40, then you may not see your grandchildren or risk a painful old age. In addition, you influence the development and even the lives of your children.
3. If you are about 50 or older, refer to point 2. This applies to you too.
Do you need this?
Isn't it better to protect yourself from electromagnetic radiation and refuse to eat food from the microwave?
