James Clerk Maxwell in his 1873 theory of electromagnetism, now called Maxwell's equations, had predicted that a coupled electric field and magnetic field could travel through space as an electromagnetic wave, and proposed that light consisted of electromagnetic waves of short wavelength.
In 1888, German physicist Heinrich Hertz was the first to demonstrate the existence of radio waves using a primitive spark gap radio transmitter.
She found no adverse health effects other than heat. == History == ===Hertzian optics=== Microwaves were first generated in the 1890s in some of the earliest radio experiments by physicists who thought of them as a form of "invisible light".
Independently in 1894, Oliver Lodge and Augusto Righi experimented with 1.5 and 12 GHz microwaves respectively, generated by small metal ball spark resonators.
Russian physicist Pyotr Lebedev in 1895 generated 50 GHz millimeter waves.
In 1897 Lord Rayleigh solved the mathematical boundary-value problem of electromagnetic waves propagating through conducting tubes and dielectric rods of arbitrary shape.
By the 1930s, the first low-power microwave vacuum tubes had been developed using new principles; the Barkhausen-Kurz tube and the split-anode magnetron.
The first modern silicon and germanium diodes were developed as microwave detectors in the 1930s, and the principles of semiconductor physics learned during their development led to semiconductor electronics after the war. Image:R&B Magnetron.jpg|thumb|Randall and Boot's prototype cavity magnetron tube at the University of Birmingham, 1940.
Radar and satellite communication motivated the development of modern microwave antennas; the parabolic antenna (the most common type), cassegrain antenna, lens antenna, slot antenna, and phased array. The ability of short waves to quickly heat materials and cook food had been investigated in the 1930s by I.
Barrow In 1931 an Anglo-French consortium headed by Andre C.
The first usage of the word micro-wave apparently occurred in 1931. ===Radar=== The development of radar, mainly in secrecy, before and during World War II, resulted in the technological advances which made microwaves practical.
Mouromtseff at Westinghouse, and at the 1933 Chicago World's Fair demonstrated cooking meals with a 60 MHz radio transmitter.
It was found that conventional transmission lines used to carry radio waves had excessive power losses at microwave frequencies, and George Southworth at Bell Labs and Wilmer Barrow at MIT independently invented waveguide in 1936.
Barrow invented the [antenna] in 1938 as a means to efficiently radiate microwaves into or out of a waveguide.
The first modern silicon and germanium diodes were developed as microwave detectors in the 1930s, and the principles of semiconductor physics learned during their development led to semiconductor electronics after the war. Image:R&B Magnetron.jpg|thumb|Randall and Boot's prototype cavity magnetron tube at the University of Birmingham, 1940.
Britain's 1940 decision to share its microwave technology with its US ally (the Tizard Mission) significantly shortened the war.
The MIT Radiation Laboratory established secretly at Massachusetts Institute of Technology in 1940 to research radar, produced much of the theoretical knowledge necessary to use microwaves.
In the new television broadcasting industry, from the 1940s microwave dishes were used to transmit backhaul video feeds from mobile production trucks back to the studio, allowing the first remote TV broadcasts.
Ten centimeter (3 GHz) microwave radar was in use on British warplanes in late 1941 and proved to be a game changer.
Microwave heating became widely used as an industrial process in industries such as plastics fabrication, and as a medical therapy to kill cancer cells in [hyperthermy]. The traveling wave tube (TWT) developed in 1943 by Rudolph Kompfner and John Pierce provided a high-power tunable source of microwaves up to 50 GHz, and became the most widely used microwave tube (besides the ubiquitous magnetron used in microwave ovens).
In 1945 Percy Spencer, an engineer working on radar at Raytheon, noticed that microwave radiation from a magnetron oscillator melted a candy bar in his pocket.
He investigated cooking with microwaves and invented the microwave oven, consisting of a magnetron feeding microwaves into a closed metal cavity containing food, which was patented by Raytheon on 8 October 1945.
Starting in the early 1950s, frequency-division multiplexing 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. Wireless LAN protocols, such as Bluetooth and the IEEE 802.11 specifications used for Wi-Fi, also use microwaves in the 2.4 GHz ISM band, although 802.11a uses ISM band and U-NII frequencies in the 5 GHz range.
In the 1950s and 60s transcontinental microwave relay networks were built in the US and Europe to exchange telephone calls between cities and distribute television programs.
Two low-noise solid state negative resistance microwave amplifiers were developed; the ruby maser invented in 1953 by Charles H.
Its invention set off a search for better negative resistance semiconductor devices for use as microwave oscillators, resulting in the invention of the IMPATT diode in 1956 by W.T.
Zeiger, and the varactor parametric amplifier developed in 1956 by Marion Hines.
The feedback oscillator and two-port amplifiers which were used at lower frequencies became unstable at microwave frequencies, and negative resistance oscillators and amplifiers based on one-port devices like diodes worked better. The tunnel diode invented in 1957 by Japanese physicist Leo Esaki could produce a few milliwatts of microwave power.
The first communications satellites were launched in the 1960s, which relayed telephone calls and television between widely separated points on Earth using microwave beams.
Johnston and the Gunn diode in 1962 by J.
The world's largest ground-based astronomy project to date, it consists of more than 66 dishes and was built in an international collaboration by Europe, North America, East Asia and Chile. A major recent focus of microwave radio astronomy has been mapping the cosmic microwave background radiation (CMBR) discovered in 1964 by radio astronomers Arno Penzias and Robert Wilson.
In 1964, Arno Penzias and Robert Woodrow Wilson while investigating noise in a satellite horn antenna at Bell Labs, Holmdel, New Jersey discovered cosmic microwave background radiation. Microwave radar became the central technology used in air traffic control, maritime navigation, anti-aircraft defense, ballistic missile detection, and later many other uses.
In 1969 Kurokawa derived mathematical conditions for stability in negative resistance circuits which formed the basis of microwave oscillator design. ===Microwave integrated circuits=== Prior to the 1970s microwave devices and circuits were bulky and expensive, so microwave frequencies were generally limited to the output stage of transmitters and the RF front end of receivers, and signals were [to a lower
Microwave ovens became common kitchen appliances in Western countries in the late 1970s, following the development of less expensive cavity magnetrons.
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. 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.
Research by NASA in the 1970s has shown this to be caused by thermal expansion in parts of the inner ear.
In 1969 Kurokawa derived mathematical conditions for stability in negative resistance circuits which formed the basis of microwave oscillator design. ===Microwave integrated circuits=== Prior to the 1970s microwave devices and circuits were bulky and expensive, so microwave frequencies were generally limited to the output stage of transmitters and the RF front end of receivers, and signals were [to a lower
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. 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.
Due to their expense microwave ovens were initially used in institutional kitchens, but by 1986 roughly 25% of households in the U.S.
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