Microwaves is descriptive term used to identify electromagnetic waves in the frequency spectrum ranging approximately from 1 GigaHertz to 30 GigaHertz..Sometimes higher frequencies (extending upto 600 GHz) are also called microwaves.
Microwaves have wavelengths that can be measured in centimeters.The longer microwaves, those closer to a foot in length, are the waves which heat our food in a microwave oven.
There are three types of waves:-
i>Mechanical Waves:These waves are most familiar because we encounter them almost constantly.example are water waves,sound waves.
ii>Electromagnetic waves:These waves are less familiar,but we can use them constantly.example are visible,ultraviolet light,radio waves,microwaves,x-rays.
iii>Matter waves:These waves are commonly used in modern technology,they are probably unfamiliar to us.
Electromagnetic waves are formed when an electric field (shown as blue arrows) couples with a magnetic field (shown as red arrows). The magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave.Â James Clerk Maxwell and Heinrich Hertz are two scientists who studied how electromagnetic waves are formed and how fast they travel.
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Radio waves, television waves, and microwaves are all types of electromagnetic waves. They differ from each other in wavelength. Wavelength is the distance between one wave crest to the next.
Waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short gamma-rays smaller than the size of the nucleus of an atom.
In electromagnetic radiation, the energy of the wave is related to both the frequency (nu) and wavelength (lambda) of the wave, in the following forms:
EÂ =Â h nuÂ =Â hcÂ /Â lambda.
The Electromagnetic Spectrum
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History of Microwaves
The discovery that a beam of light was actually an electromagnetic wave was made by J.C.Maxwell. Gradually, other types of electromagnetic waves were discovered.
As more discoveries were made, it was found that electromagnetic waves exist in a wide range of wavelengths, which is now called the Electromagnetic Spectrum, and visible light is only a small part of it. One of the first people to observe the spectrum was Issac Newton. He allowed sunlight coming through a small aperture to pass through a glass prism, which split it into its seven colours.
Microwaves have wavelengths more than that of infrared waves, but less than that of radio waves. Although they were first produced and studied in 1886 by Hertz, their practical application was not before the invention of suitable generators. The name "Microwave" is just a misnomer. The rays are not at all microwaves.
The reality of electromagnetic waves was predicted by James Clerk Maxwell in 1864 from his equations. In 1888, Heinrich Hertz was the first to express the reality of electromagnetic waves by constructing an apparatus that created and detected microwaves in the UHF region. In 1894 J. C. Bose publicly recognized radio control of a bell using millimeter wavelengths, and conducted research into the transmission of microwaves.
Possibly the first, documented, formal use of the term microwave occurred in 1931:
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Probably the first use of the word microwave in an astronomical framework occurred in 1946 in an editorial "Microwave Radiation from the Sun and Moon" by Robert Dicke and Robert Beringer.
Microwaves are basically extremely high frequency radio waves, and are made by various types of transmitter. In a mobile phone, they're made by a transmitter chip and an antenna, in a microwave oven they're made by a "magnetron".
Their wavelength is usually a couple of centimetres. Stars also give off microwaves.
Characteristics features of Microwaves
Microwaves present several interesting and unusual features not found in other portions of the electromagnetic frequency spectrum.
Microwave transmitters and receivers are parabolic dish antennas, which produce beams whose spreading angle depends upon their diameter, and can be directed like a searchlight.
Microwaves are the principal carriers of high-speed telegraphic data transmissions between Earth stations and with satellites and space probes. A system of synchronous satellites about 36,000 km above the Earth is used for international broadband telegraphy of all kinds of tele-communications.
Microwaves can penetrate clouds of smoke, but are scattered by water droplets, and hence can be used for mapping meteorologic disturbances and in weather forecasting.
The main characteristics features of microwaves originate from the small size of wavelengths(1 cm to 30 cm) in relation to the sizes of components or devices commonly used.Since the wavelengths are small ,the phase varies rapidly with distance;consequently the techniques of circuit analysis and design ,of measurements and of power generation,and amplification at these frequencies are distinct from those at lower frequencies.
For dealing with these small wavelengths,methods of circuit representation and analysis need to be modified.The phase difference caused by the interconnection between different various components or various parts of a single component is not negligible .Consequently ,analyses based on Kirchhoff's laws and voltage-current concepts are not adequate to describe the circuit behaviour at microwave frequencies.It is necessary to analyse the circuit or the component in terms of electric and magnetic fields associated with it.For this reason microwave engineering is also known as electromagnetic engineering or applied electromagnetics.A background of electromagnetic theory is a pre-requisite for understanding microwaves.Not only analytical techniques ,the methods of measurement also become specialized at microwave techniques,the methods of measurement also become specialized at microwave frequencies.Measurements are carried out in terms of field amplitudes,phase differences and powers carried by the waves.A very commonly used method of microwave measurement is based on the study of a standing wave pattern.
Ratio of the relationship between incident and reflected waves tell us about impedence characteristics of the components causing the reflection.Several other special techniques have been developed for use at microwave frequencies.
Microwave circuit components have a different look.Use of lumped elements at microwave frequencies becomes difficult because of small wavelengths involved.
The challenge of generation of microwaves has resulted in a variety of devices both in vacuum tube and in semiconductor device areas.When an attempt is made to use a lower frequency source at microwave frequencies,the operation is limited by the fact that transit time of the carriers through the device becomes comparable to the time period of the wave.This problem has been solved by technological innovations and by totally noval ideas (as in the case of klystrons,magnetrons,transferred electron devices and avalanche diode).
Application of Microwaves
Microwaves are characterized by small size of wavelengths,large bandwidth,propagation along the line -of-sight path transmission through ionosphere with negligible absorption and reflection ,small antenna size and reflection from metallic surfaces,microwave heating and microwave resonance in molecular ,atomic and nuclear systems.
These features have opened up new vistas of application in communication,in radar,in astronomy and remote sensing,in basic and applied research,in industry,in domestic sphear and in biomedical fields.
Basically we enumerate the various applications of microwaves without much account of them.The list is far from complete but does give an idea to the reader of the wide variety of uses to which this portion of radio-spectrum is put.
Communication and radar systems
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Microwave band is widely used for telephone networks ,in broadcast,in television systems,in long distance communication ,for microwave links,for space communication,in satellite communication and in several other communication applications by police,civil aviation,railways and services,etc.
Microwaves are extensively used for Radar(Radio detection and ranging)systems.Beside,high resolution radar capable of dectecting and locating enemy planes and ships there are varied forms of radars such as missile-tracking radar,early warning radar,air-port,traffic control radar,fire-control radar,fire -control radar,weather detecting radar,missile-guidance radar and Doppler radar.
The sub-nanosecond pulse are useful in several purpose radars for docking the pre-collision sensing etc.These pulses are being used in high speed logic circuits .Thus microwaves techniques are being introduced in extremely fast computer operations.
Recently (1999-2000) Jeffrey denials of Ohio state University reported in geographical physics letters that ground penetrating radar could be used in detecting subsurface hazardous waste.
Satellite as microwave relay station have been deployed for communication as well as for surveillance and collecting data on atmospheric and weather conditions.
The list is far from complete but represents a major use of microwave band for communication and radar systems.
Microwave radio is used in propagation and telecommunication transmissions because, due to their small wavelength, highly directional antennas are lesser and therefore more useful than they would be at longer wavelengths (lower frequencies). There is also extra bandwidth in the microwave spectrum than in the rest of the radio spectrum; the usable bandwidth below 300 MHz is less than 300 MHz while many GHz can be used above 300 MHz. Typically, microwaves are used in television news to convey a sign from a remote location to a television station from a specially prepared van.
Most satellite communications systems operate in the C, X, Ka, or Ku bands of the microwave spectrum. These frequencies allow huge bandwidth . Satellite TV either operates in the C band for the traditional large dish fixed satellite service or Ku band for direct-broadcast satellite. Military interactions run primarily over X or Ku-band links, with Ka band being used for Milstar.
Radio -astronomy and remote sensing application
Sensitive microwave receivers are used in radio-astronomy to detect and study the electromagnetic radiation,which lie in microwave region of radio spectrum.orginating from the sun and other astronomical objects.The microwave radiometers are used to map atmospheric temperature profiles,moisture conditions in soils and crops.and for other remote -sensing applications.
Basic and applied research
It is observed that the molecular ,atomic and nuclear systems display various resonance phenomena when subjected to electromagnetic fields and maby of these resonances occur in the microwave frequency range,hence microwaves have provided an experimental tool to study the basic properties of materials which led to the development of microwave spectroscopy.Later it also led to the development of non-reciprocal ferrite devices and solid -state microwave generators,e.g,masers and lasers.
Microwaves are used in linear accelerators to produce high-energy beams of charged particles for use in atomic and nuclear research.
Industrial and domestic applications
i>Microwaves are used extensively for non-destructive testing of materials,process controls such as moisture and thickness detectors,etc.
It is used to measure the concentration of different gases e.g. in exhaust chimneys,in order to control the emission of pollutants or in chemical processes in order to record continuously the concentration of gases evolved in the process.
ii>It is used for several industrial applications involving heating.This is used for industrial processing in Food,Plastic,Rubber,Chemicals,Forests products industries .
In mining it is used for breaking rocks and coal streams and in tunnel boring.It is also used for drying up concrete.It is also used for drying inks,textiles,leather,tobacco,grains etc.
iii>Microwave ovens are being increasingly used in domestic sphete for cooking and roasting.The microwave frequency used for this application is 2450 MHz with a power output of 500-1000 W.
iv> Microwave generators are commonly used in industry to cure chemical reactions, heat a part or seal a plastic seam. There are some estimates as many as five million people using some type of microwave source every day. Therefore, we are likely to encounter microwaves in just about every industry and manufacturing location we can imagine.
v> The first laser that was assembled in 1954 using a source of microwaves to energize or stimulate the electrons in a cloud of ammonia and form a coherent beam of light. It was called a MASER or microwave amplified by stimulated emission of radiation.
Microwave radiation has also been found useful for cancer therapy-hyperthermia.Electromagnetic techniques are used for medical diagnosis such as monitoring of heart-beat,lung water detection,etc.
Medical Linear Accelerators the mainstay of cancer treatment with their research in the 1940's, eclipsing the use of active Cobalt 60 radiation sources with a much more controllable and "power-off" safe radiation source. From the early 1970's to today the Medical LINAC has been the work horse of the medical cancer treatment industry.
Today Computed Tomography and Linear Accelerator technology has been married together into a single system with a common source to deliver the most precisely controlled radiation dose that has ever been delivered.
It has a potential lapplication in the field of energy
Satellites power stations have been proposed to harness solar energy.From these power station energy would be transported in form of microwaves.
The scope of microwaves applications in communication industry and basic and applied research is ever increasing.The extension of microwave techniques into the field of development of optical communication is an example of it.
Therefore, it is a fascinating field of study and research,which has vast opportunities in varied applications.As such large number of postgraduate students in physics and engineering as well as undergraduate students opt for specializing in microwave electronics/engineering.
Wireless energy transport or wireless power communication is the method that takes place in any system in which electrical energy is transferred from a power source to an electrical load devoid of any interconnecting wires. Wireless transmission is useful in cases where immediate or constant energy transfer is preferred but interconnecting wires are not convenient, risky, or unworkable.
Power transmission through radio waves can be completed further directional, allowing larger distance power beaming, with shorter wavelengths of electromagnetic emission, typically in the microwave range.
The microwave oven is now an essential part of most kitchens. During the summer or other hot times of the year, it's an excellent appliance to use because it won't heat up your kitchen the way an oven will. Unfortunately, most people still use the microwave to heat coffee, melt butter or make popcorn. That's just fine - but the appliance can do so much more!
It was invented to make cooking quicker and easier. Instead, microwaves were stumbled upon by scientists trying to invent magnetron, a tube that produces microwaves. Dr. Percy Spencer, an engineer with Raytheon Company was testing the magnetron in 1946. He had a chocolate bar in his pocket that suddenly melted out of the blue. This got Dr. Spencer excited and he placed popcorn kernels near the magnetron tube. To his amazement, the kernels began to pop!
This built up confidence in Dr. Spencer who bought an egg the next day. He placed the egg next to the magnetron. The egg began to tremble due to the temperature rising inside it. The egg exploded and the contents were showered all over his colleague. Another explosion took place in the mind of Dr. Spencer, who realized that he had stumbled upon a revolutionizing method of microwave cooking.
The early microwave ovens looked nothing like the sophisticated microwave ovens today. They were almost 6 feet high and weighed 750 pounds, approximately. the magnetron needed to be cooled by water.
Eventually, improvements were made and smaller units were manufactured. The plumbing units were done away with as magnetron in the smaller ovens could be cooled by air. In 1947, Raytheon introduced refrigerator sized Radarange, that could be used by commercial establishment not only for cooking food, but also for drying cork, paper and leather.. Soon, microwaves became a necessity more than a luxury. In today's time, it is difficult to find someone who does not own a microwave oven. But not many realize the dangers of microwaves they face with each push of a button.
In mobile phones
Mobile phones use microwaves, as they can be generated by a small antenna, which means that the phone doesn't need to be very big. The drawback is that, being small, they can't put out much power, and they also need a line of sight to the transmitter mobile phone. This means that companies need to have many transmitter towers if they're going to attract customers.
Advantages of Microwaves
Microwaves are easier to control (than longer wavelengths) because small antennas could direct the waves very well. One advantage of such control is that the energy could be easily confined to a tight beam (expressed as narrow beamwidth). This beam could be focused on another antenna dozens of miles away, making it very difficult for someone to intercept the conversation.
Because of their high frequency, greater amounts of information could be put on them (expressed as increased modulation bandwidth). These advantages (narow beamwidth and modulation bandwidth) make microwaves very
useful for RADAR as well as communications.
The ability to modulate with a wide bandwidth permitted so many conversations on just one signal, and the reduction in beamwidth made this reasonably secure.
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Disadvantages of Microwaves
i> Line-of-sight will be disrupted if any obstacle, such as new buildings, are in the way
ii> Signal absorption by the atmosphere. Microwaves suffer from attenuation due to atmospheric conditions.
Towers are expensive to build
People are supremely unaware of the dangers of microwaves. Microwaves are electromagnetic energy that travel at the speed of light. The magnetron in the microwave oven produces wave energy. This wave energy converts polarity of molecules from positive to negative. This polarity changes millions of times every second in the microwave oven. These microwaves bombard the food molecules and makes the polarized molecules to radiate at the same frequency millions of times every second. This friction heats up the food and also causes 'structural isomerism', that is, structural damage of the food molecules.
Microwaves significantly decrease the nutritional value of the foods up to 60 to 90% of the normal level. There is reduction in vitamin B 12, that is necessary for red blood cell formation and building up nervous system. The flavonoid content of the food decreases by 97% when cooked in microwave oven. Flavonoids contain anti cancer, anti-inflammatory and anti-microbial properties. There is significant decrease in vitamin C, vitamin E, essential mineral and lipotropic factors in food. Glucosides, nitrilosides, alkaloids present in the vegetables are damaged significantly.
Heating expressed breast milk in microwave oven destroys the enzymes that help digest food, absorb nutrients and protect babies from pathogens. Infant milk formulas also lose some of their vitamins when heated in microwaves. The amino acids in baby formulas are converted to synthetic isomers that are not active biologically. Amino acids like L-proline was converted to its d-isomer, that is found to be harmful for the nervous system and the kidneys.
The 19th issue of the Journal Franz Weber has an article which stated that microwave cooked food had cancerous effects on the blood. The violent deformations that can occur in human body when exposed to microwaves, are also seen in the food molecules cooked in microwaves. Studies have been conducted on food that have been thawed, cooked and heated in microwaves. The results showed that many food molecules were converted into carcinogens. The glucoside and galactoside present in frozen foods gets converted into carcinogenic substance. Plant alkaloids in vegetables were converted into carcinogens. Milk and cereals heated in microwaves also had some of their amino acids converted into carcinogens.
The Russians detected microwave sickness that had affected thousands of workers exposed to microwaves in the 1950s. The German, Swiss and Russian scientific studies have proven the dangers of microwave ovens.
The dangers of heating plastics in the microwave cannot be ignored. The cancer causing compounds in the plastic containers and plastic wraps percolate into the food cooked in microwave oven. Bisphenol A is a chemical toxin present in plastic bottles that can percolate into foods and cause cancer, early puberty, obesity and diabetes.
The radiations decrease the immune system of humans and regular eating of microwave cooked foods causes memory loss, emotional problems and decrease in IQ. Microwave cooked food also can lead to decrease in hormone production.
The use of microwave ovens had been banned in Soviet Russia in 1976. There is an ongoing debate regarding the dangers of microwaves as kitchen appliances as there is a fairly large group that claims otherwise. You have to carefully weigh the pros and cons of dangers of microwave ovens and apply your decision practically. You can always use conventional ovens to heat and cook food. The traditional methods, that is, cooking on gas stoves will always have an upper hand over all the other ways of cooking. You are the best judge regarding what is good and bad for yourself and your family. With proper research, take your stand in the debatable topic of the dangers of microwaves.
Prolonged exposure to microwaves is known to cause "cataracts" in your eyes, which is a clouding of the lens, preventing us from seeing clearly . So don't make a habit of pressing our face against the microwave oven door to see if your food's ready!
The microwave works when the high voltage is converted to waves of electromagnetic energy, which is a combination of electrical and magnetic energy. This energy is in the frequency band of radio waves, not x-rays.. When the door is opened or the timer reaches zero, the energy automatically stops, so no microwave radiation leaves the oven. All ovens also have two independent systems that ensure the electrical activity stops as soon as the door is opened.
Recent research indicates that microwaves from mobile phones can affect parts of our brain - after all, we are holding the transmitter right by our head. The advice is to keep calls short.
Microwave energy has proven to be a useful tool for enhancing slow and difficult chemical reactions.
Its application has been successfully applied to solid phase
1) peptide synthesis (SPPS) and shown useful for the synthesis of a range of difficult peptides [1-8]. The N-terminal amino group and peptide backbone are polar
and they constantly try to align with the alternating electric field of the microwave, this helps in breaking up the chain aggregation.
Previous studies have investigated the effects of microwave on aspartimide formation and
epimerization and offered optimized conditions for susceptible sequences to these well-known side reactions This study aims to build on previous work and offer
further improvements for routine microwave SPPS protocols.
Microwave energy interacts with molecular systems through both ionic conduction and dipole rotation that results in a kinetic excitation of the species. The kinetic
excitation is observed by standard measurement that observes the average temperature of the system.
Microwave energy interacts selectively with more polar components in a system which can lead to a wide range in molecular temperature at a given average system
temperature. Larger differences in polarity between the reactants and solvent in a system will increase this effect.