Electromagnetic spectrum with light highlighted

Microwaves are electromagnetic waves with wavelengths ranging from 1 mm to 1 m, or frequencies between 300 MHz and 300 GHz. Electromagnetic radiation takes the form of self-propagating Waves in a Vacuum or in Matter. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. Frequency is a measure of the number of occurrences of a repeating event per unit Time. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second.

Apparatus and techniques may be described qualitatively as "microwave" when the wavelengths of signals are roughly the same as the dimensions of the equipment, so that lumped-element circuit theory is inaccurate. In general the lumped component model is a way of simplifying the behaviour of spatially distributed systems into a Topology consisting of discrete entities that approximate As a consequence, practical microwave technique tends to move away from the discrete resistors, capacitors, and inductors used with lower frequency radio waves. |- align = "center"| |width = "25"| | |- align = "center"| || Potentiometer |- align = "center"| | | |- align = "center"| Resistor| | A capacitor is a passive electrical component that can store Energy in the Electric field between a pair of conductors An inductor is a passive electrical component designed to provide Inductance in a circuit Radio waves are electromagnetic waves occurring on the Radio frequency portion of the Electromagnetic spectrum. Instead, distributed circuit elements and transmission-line theory are more useful methods for design, analysis. Open-wire and coaxial transmission lines give way to waveguides, and lumped-element tuned circuits are replaced by cavity resonators or resonant lines. A transmission line is the material medium or structure that forms all or part of a path from one place to another for directing the transmission of energy A waveguide is a structure which guides waves such as Electromagnetic waves Light, or Sound waves A resonator is a device or system that exhibits Resonance or resonant behavior that is it naturally oscillates at some frequencies, called its resonance Effects of reflection, polarization, scattering, diffraction, and atmospheric absorption usually associated with visible light are of practical significance in the study of microwave propagation. Polarization ( ''Brit'' polarisation) is a property of Waves that describes the orientation of their oscillations Scattering is a general physical process whereby some forms of Radiation, such as Light, Sound or moving particles for example are forced to deviate from Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle In Physics, absorption of electromagnetic radiation is the process by which the Energy of a Photon is taken up by matter typically the electrons of an Radio propagation is a term used to explain how Radio waves behave when they are Transmitted, or are propagated from one point on the Earth The same equations of electromagnetic theory apply at all frequencies. In Classical electromagnetism, Maxwell's equations are a set of four Partial differential equations that describe the properties of the electric

While the name may suggest a micrometer wavelength, it is better understood as indicating wavelengths very much smaller than those used in radio broadcasting. The boundaries between far infrared light, terahertz radiation, microwaves, and ultra-high-frequency radio waves are fairly arbitrary and are used variously between different fields of study. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Electromagnetic waves sent at terahertz frequencies, known as terahertz radiation, submillimeter radiation, terahertz waves, terahertz Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. A wave is a disturbance that propagates through Space and Time, usually with transference of Energy. The term microwave generally refers to "alternating current signals with frequencies between 300 MHz (3×10⁸ Hz) and 300 GHz (3×10¹¹ Hz). An alternating current ( AC) is an Electric current whose direction reverses cyclically as opposed to Direct current, whose direction remains constant "^[1] Both IEC standard 60050 and IEEE standard 100 define "microwave" frequencies starting at 1 GHz (30 cm wavelength). The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-e) is an international Non-profit, professional organization

Electromagnetic waves longer (lower frequency) than microwaves are called "radio waves". Electromagnetic radiation with shorter wavelengths may be called "millimeter waves", terahertz radiation or even T-rays. Electromagnetic waves sent at terahertz frequencies, known as terahertz radiation, submillimeter radiation, terahertz waves, terahertz Definitions differ for millimeter wave band, which the IEEE defines as 110 GHz to 300 GHz.

Discovery

The existence of electromagnetic waves, of which microwaves are part of the frequency spectrum, was predicted by James Clerk Maxwell in 1864 from his equations. James Clerk Maxwell (13 June 1831 &ndash 5 November 1879 was a Scottish mathematician and theoretical physicist. In Classical electromagnetism, Maxwell's equations are a set of four Partial differential equations that describe the properties of the electric In 1888, Heinrich Hertz was the first to demonstrate the existence of electromagnetic waves by building an apparatus that produced and detected microwaves in the UHF region. Heinrich Rudolf Hertz ( February 22, 1857 – January 1, 1894) was a German physicist who clarified and expanded the electromagnetic theory The design necessarily used horse-and-buggy materials, including a horse trough, a wrought iron point spark, Leyden jars, and a length of zinc gutter whose parabolic cross-section worked as a reflection antenna. The Leyden jar is a simple device that "stores" static electricity in large amounts In 1894 J. C. Bose publicly demonstrated radio control of a bell using millimetre wavelengths, and conducted research into the propagation of microwaves. Sir Jagadish Chandra Bose, CSI, CIE, FRS (জগদীশ চন্দ্র বসু Jôgodish Chôndro Boshu) ( November 30

Plot of the zenith atmospheric transmission on the summit of Mauna Kea throughout the entire gigahertz range of the electromagnetic spectrum at a precipitable water vapor level of 0. Mauna Kea is a Dormant volcano in the Hawaiian Islands, one of five volcanoes which together form the Island of Hawaii. 001 mm. (simulated)

Frequency range

The microwave range includes ultra-high frequency (UHF) (0. 3–3 GHz), super high frequency (SHF) (3–30 GHz), and extremely high frequency (EHF) (30–300 GHz) signals. Super high frequency (or SHF) refers to radio frequencies (RF in the range of 3  GHz and 30 GHz Extremely high frequency is the highest Radio frequency band.

Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that it is effectively opaque, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges. The meaning of this term depends on the context In Astronomy, the optical window is the optical portion of the Electromagnetic spectrum that passes through

Microwave Sources

Vacuum tube based devices operate on the ballistic motion of electrons in a vacuum under the influence of controlling electric or magnetic fields, and include the magnetron, klystron, travelling wave tube (TWT), and gyrotron. This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. A cavity magnetron is a high-powered Vacuum tube that generates coherent Microwaves They are commonly found in Microwave ovens as well as various A klystron is a specialized linear-beam Vacuum tube (evacuated electron tube A traveling-wave tube (TWT is an electronic device used to amplify Radio frequency signals to high power usually in an electronic assembly known as a traveling-wave Gyrotrons are high powered Vacuum tubes which emit Millimeter Wavelength beams by bunching Electrons with Cyclotron motion These devices work in the density modulated mode, rather than the current modulated mode. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different This means that they work on the basis of clumps of electrons flying ballistically through them, rather than using a continuous stream.

A maser is a device similar to a laser, except that it works at microwave frequencies. A maser is a device that produces coherent Electromagnetic waves through amplification due to Stimulated emission. A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission.

Solid-state sources include the field-effect transistor, at least at lower frequencies, tunnel diodes and Gunn diodes

Uses

A microwave telecommunications tower on Wrights Hill in Wellington, New Zealand

Communication

• Before the advent of fiber optic transmission, most long distance telephone calls were carried via microwave point-to-point links through sites like the AT&T Long Lines. The field-effect transistor (FET is a type of Transistor that relies on an Electric field to control the shape and hence the conductivity of a 'channel' A tunnel Diode or Esaki diode is a type of Semiconductor diode which is capable of very fast operation well into the Microwave frequency A Gunn diode, also known as a transferred electron device ( TED) is a form of Diode used in high-frequency Electronics. Wellington (ˈwælɪŋtən is the Capital of New Zealand, the country's second largest urban area, the New Zealand is an Island country in the south-western Pacific Ocean comprising two main landmasses (the North Island and the South Island An optical fiber (or fibre) is a Glass or Plastic fiber that carries Light along its length Long distance in Telecommunications, refers to Telephone calls made outside a certain area usually characterized by an Area code outside of a Local A telephone call is a connection over a Telephone network between the Calling party and the Called party. AT&T Communications Inc is a IXC / Long distance telephone company owned by AT&T. Starting in the early 1950's, frequency division multiplex was used to send up to 5,400 telephone channels on each microwave radio channel, with as many as ten radio channels combined into one antenna for the hop to the next site, up to 70 km away. Frequency-division multiplexing ( FDM) is a form of signal Multiplexing where multiple Baseband signals are Modulated on different frequency

• Wireless LAN protocols, such as Bluetooth and the IEEE 802.11 specifications, also use microwaves in the 2. A wireless LAN or WLAN is a Wireless Local area network, which is the linking of two or more computers or devices without using wires In computing, a protocol is a convention or standard that controls or enables the connection Communication, and Data transfer between two computing Bluetooth is a wireless protocol utilizing short-range communications technology facilitating data transmission over short distances from fixed and/or mobile devices creating wireless The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-e) is an international Non-profit, professional organization IEEE 80211 is a set of standards for wireless local area network (WLAN computer communication developed by the IEEE LAN/MAN Standards Committee ( IEEE 802 4 GHz ISM band, although 802.11a uses ISM band and U-NII frequencies in the 5 GHz range. The industrial scientific and medical (ISM Radio bands were originally reserved internationally for the use of RF electromagnetic fields for industrial scientific and medical IEEE 80211a-1999 or 80211a, is an amendment to the IEEE 80211 specification that added a higher throughput of up to 54 Mbit/s by using the 5 GHz The industrial scientific and medical (ISM Radio bands were originally reserved internationally for the use of RF electromagnetic fields for industrial scientific and medical The Unlicensed National Information Infrastructure ( U-NII) Radio band is part of the Radio frequency spectrum used by IEEE-802 Licensed long-range (up to about 25 km) Wireless Internet Access services can be found in many countries (but not the USA) in the 3. 5–4. 0 GHz range.

• Metropolitan Area Networks: MAN protocols, such as WiMAX (Worldwide Interoperability for Microwave Access) based in the IEEE 802.16 specification. Metropolitan area network s or MAN s are large Computer networks usually spanning a city WiMAX, an approximate acronym of Worldwide Interoperability for Microwave Access, is a Telecommunications technology that provides for the wireless transmission The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-e) is an international Non-profit, professional organization The IEEE 80216 Working Group on Broadband Wireless Access Standards, which was established by IEEE Standards Board in 1999 aims to prepare formal specifications The IEEE 802. 16 specification was designed to operate between 2 to 11 GHz. The commercial implementations are in the 2. 3GHz, 2. 5 GHz, 3. 5 GHz and 5. 8 GHz ranges.

• Wide Area Mobile Broadband Wireless Access: MBWA protocols based on standards specifications such as IEEE 802.20 or ATIS/ANSI HC-SDMA (e. Mobile broadband is the name used to describe various types of Wireless high-speed internet access through a portable Modem, Telephone or IEEE 80220 or Mobile Broadband Wireless Access (MBWA is an IEEE Standard to enable worldwide deployment of multi-vendor interoperable mobile broadband wireless access iBurst (or HC-SDMA, High Capacity Spatial Division Multiple Access is a wireless broadband technology developed by ArrayComm. g. iBurst) are designed to operate between 1. 6 and 2. 3 GHz to give mobility and in-building penetration characteristics similar to mobile phones but with vastly greater spectral efficiency.

• Cable TV and Internet access on coaxial cable as well as broadcast television use some of the lower microwave frequencies. The Internet is a global system of interconnected Computer networks Terrestrial television is a term which refers to modes of television broadcasting which do not involve satellite transmission Some mobile phone networks, like GSM, also use the lower microwave frequencies. GSM ( Global System for Mobile communications: originally from Groupe Spécial Mobile) is the most popular standard for Mobile phones in the

• Microwave radio is used in broadcasting and telecommunication transmissions because, due to their short wavelength, highly directive antennas are smaller and therefore more practical than they would be at longer wavelengths (lower frequencies). For the band see Broadcast (band Broadcasting is the distribution of audio and/or Video signals which transmit There is also more 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. Bandwidth is the difference between the upper and lower Cutoff frequencies of for example a filter, a Communication channel, or a Signal spectrum Typically, microwaves are used in television news to transmit a signal from a remote location to a television station from a specially equipped van. News broadcasting (also known as newscast or newsbreak) is the Broadcasting of various news events and other Information via

Remote Sensing

• Radar uses microwave radiation to detect the range, speed, and other characteristics of remote objects. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships Development of radar was accelerated during World War II due to its great military utility. Now radar is widely used for applications such as air traffic control, navigation of ships, and speed limit enforcement. Air traffic control ( ATC) is a service provided by ground-based controllers who direct Aircraft on the ground and in the air For a discussion of the maximum speed possible in the universe see Speed of light and Special relativity.

• A Gunn diode oscillator and waveguide are used as a motion detector for automatic door openers (although these are being replaced by ultrasonic devices). A Gunn diode, also known as a transferred electron device ( TED) is a form of Diode used in high-frequency Electronics.

• Most radio astronomy uses microwaves. Radio astronomy is a subfield of Astronomy that studies celestial objects at radio frequencies.

• Microwave imaging; see Photoacoustic imaging in biomedicine

Navigation

• Global Navigation Satellite Systems (GNSS) including the American Global Positioning System (GPS) and the Russian ГЛОбальная НАвигационная Спутниковая Система (GLONASS) broadcast navigational signals in various bands between about 1. Photoacoustic imaging, as a hybrid biomedical imaging modality is developed based on the photoacoustic effect. Global Navigation Satellite System (GNSS is the standard generic term for satellite navigation systems that provide autonomous geo-spatial positioning with global coverage Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth 2 GHz and 1. 6 GHz.

Power

• A microwave oven passes (non-ionizing) microwave radiation (at a frequency near 2. A microwave oven, or a microwave, is a Kitchen appliance that cooks or heats Food by Dielectric heating. 45 GHz) through food, causing dielectric heating by absorption of energy in the water, fats and sugar contained in the food. Dielectric heating (also known as electronic heating, RF heating, high-frequency heating) is the phenomenon in which Radiowave or Microwave Microwave ovens became common kitchen appliances in Western countries in the late 1970s, following development of inexpensive cavity magnetrons. A cavity magnetron is a high-powered Vacuum tube that generates coherent Microwaves They are commonly found in Microwave ovens as well as various

• Microwave heating is used in industrial processes for drying and curing products.

• Many semiconductor processing techniques use microwaves to generate plasma for such purposes as reactive ion etching and plasma-enhanced chemical vapor deposition (PECVD). Semiconductor device fabrication is the process used to create chips the Integrated circuits that are present in everyday Electrical and electronic In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound Reactive ion etching ( RIE) is an etching technology used in Microfabrication. Chemical vapor deposition (CVD is a Chemical process used to produce high-purity high-performance solid materials

• Microwaves can be used to transmit power over long distances, and post-World War II research was done to examine possibilities. Microwave power transmission ( MPT) is the use of Microwaves to transmit power through Outer space or the atmosphere without the need for World War II, or the Second World War, (often abbreviated WWII) was a global military conflict which involved a majority of the world's nations, including NASA worked in the 1970s and early 1980s to research the possibilities of using Solar power satellite (SPS) systems with large solar arrays that would beam power down to the Earth's surface via microwaves. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program A solar power satellite, or SPS or Powersat, as originally proposed would be a Satellite built in High Earth orbit that uses Microwave In the field of Photovoltaics, a photovoltaic module is a packaged interconnected assembly of photovoltaic cells also known as Solar cells An installation of

• Less-than-lethal weaponry exists that uses millimeter waves to heat a thin layer of human skin to an intolerable temperature so as to make the targeted person move away. Less-lethal weapons, less-than-lethal weapons, non-lethal weapons, non-deadly weapons, or more recently compliance weapons are weapons intended A two-second burst of the 95 GHz focused beam heats the skin to a temperature of 130 F (54 C) at a depth of 1/64th of an inch (0. 4 mm). The United States Air Force and Marines are currently using this type of Active Denial System. The Active Denial System (ADS is a Non-lethal, Directed-energy weapon developed by the U ^[2]

Microwave frequency bands

The microwave spectrum is usually defined as electromagnetic energy ranging from approximately 1 GHz to 1000 GHz in frequency, but older usage includes lower frequencies. Most common applications are within the 1 to 40 GHz range. Microwave frequency bands, as defined by the Radio Society of Great Britain (RSGB), are shown in the table below:

The term P band is sometimes used for Ku Band. The Q band of the Microwave part of the Electromagnetic spectrum and ranges from 33 to 50  GHz. The V band (vee-band of the Electromagnetic spectrum ranges from 40 to 75 GHz The NATO E band is the range of radio frequencies from 2  GHz to 3 GHz in the Electromagnetic spectrum. The W band of the Microwave part of the Electromagnetic spectrum ranges from 75 to 111  GHz. The F band is the range of radio frequencies from 3  GHz to 4 GHz in the Electromagnetic spectrum. D band is the range of radio frequencies from 1  GHz to 2 GHz in the Electromagnetic spectrum. The Ku band ( pronounced "kay-yoo") is a portion of the Electromagnetic spectrum in the Microwave range of frequencies For other definitions see Letter Designations of Microwave Bands

Health effects

Main article: Electromagnetic radiation and health

Microwaves contain insufficient energy to directly chemically change substances by ionization, and so are an example of nonionizing radiation. Electromagnetic radiation can be classified into ionizing radiation and Non-ionizing radiation, based on whether it is capable of ionizing atoms and breaking Non-ionizing radiation (or esp in British English, non-ionising radiation) refers to any type of Electromagnetic radiation that does not carry enough The word "radiation" refers to the fact that energy can radiate, and not to the different nature and effects of different kinds of energy. Specifically, the term in this context is not to be confused with radioactivity. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation.

A great number of studies have been undertaken in the last two decades, most concluding they are safe. It is understood that microwave radiation at a level that causes heating of living tissue is hazardous (due to the possibility of overheating and burns) and most countries have standards limiting exposure, such as the Federal Communications Commission RF safety regulations.

Synthetic reviews of literature indicate the predominance of their safety of use. ^[3][4]

History and research

Perhaps the first, documented, formal use of the term microwave occurred in 1931:

"When trials with wavelengths as low as 18 cm were made known, there was undisguised surprise that the problem of the micro-wave had been solved so soon. " Telegraph & Telephone Journal XVII. 179/1

Perhaps the first use of the word microwave in an astronomical context occurred in 1946 in an article "Microwave Radiation from the Sun and Moon" by Robert Dicke and Robert Beringer. Robert Henry Dicke ( May 6 1916 &ndash March 4 1997) was an American Physicist, who made important contributions to the fields of

For some of the history in the development of electromagnetic theory applicable to modern microwave applications see the following figures:

Specific significant areas of research and work developing microwaves and their applications:

See also

References

External links

• EM Talk, Microwave Engineering Tutorials and Tools
• Microwave Irradiation for Negative Refraction by using Metamaterials
• Microwaves101, web resource covering the fundamental principles of microwave design
• Applications of Microwaves in Medicine
• Microwave Technology Video
• Theory of Microwave Technology