The history
160 years from a physicist's equations and wartime radar to the humming box that reheats dinner in two minutes.
In the 1860s a Scottish physicist predicted invisible waves of electricity and magnetism, and soon scientists in Germany and India were making them. Engineers in the US, Europe and Japan then built tubes called magnetrons that could pump out short waves, and in 1940 two scientists in Birmingham made one powerful enough for radar. After the war, a radar engineer noticed that the same waves could cook food. It took Japanese factories, cheap magnetrons and new safety rules to shrink a fridge-sized machine into a box on almost every kitchen counter.
1886–1888
Electromagnetic waves made and detected on purpose
Heinrich Hertz, Germany
1895
Millimetre-wave experiments (about 60 GHz)
Jagadish Chandra Bose, India
1926
Split-anode magnetron
Kinjiro Okabe, Japan
1940
High-power cavity magnetron
John Randall and Harry Boot, England
1945
Patent for microwave cooking filed
Percy Spencer, Raytheon, USA
1947
Microwave oven for sale
Raytheon Radarange, USA
1962
Mass-produced microwave oven
Sharp R-10, Japan
1967
Popular countertop home microwave
Amana Radarange, USA
1975
Microprocessor-controlled microwave
Amana RR-6, USA
1988
Inverter microwave oven
Panasonic, Japan
1865 – 1939
Scientists predict and then make electromagnetic waves. Inventors in the US, Europe and Japan build the first magnetrons, tubes that turn electricity into radio waves.
1865
Maxwell, a Scottish physicist, wrote down a set of equations that tie electricity and magnetism together. They showed that the two could travel through space as a wave, and that light itself is one of these waves. His equations also said there should be waves much longer than light, which no one had seen yet.
Why it mattered. Microwaves are one of the invisible waves Maxwell's equations predicted.
1887
1886–1888
Hertz made sparks jump across a gap and found that a small loop of wire across the room sparked too. Invisible waves were crossing the room. He showed they bounce and bend like light, just as Maxwell had predicted.
Why it mattered. It proved electromagnetic waves were real, and the unit of frequency, the hertz, is named after him.
1895
Bose built his own transmitter, horn antennas and detectors for waves only millimetres long, at about 60 GHz. In a public demonstration he sent them 23 m, through two walls, to ring a bell and set off a little gunpowder. An IEEE Milestone plaque now honours the work.
Why it mattered. He showed that very short radio waves could be made, aimed and detected, decades before radar.
1921
Hull studied a vacuum tube with a wire in the middle, a metal cylinder around it and a magnet outside. The magnet bends the electrons flying from the wire so they curl round instead of reaching the cylinder. He published papers and patents on this tube, now called a magnetron.
Why it mattered. Electrons spinning in a magnetic field are still the heart of every microwave oven's magnetron.
1924
Working separately, the Czech physicist Žáček and the German physicist Habann found that a magnetron could do more than switch. It could oscillate and send out radio waves between about 100 MHz and 1 GHz. Žáček published first, but in a small journal that few people read.
Why it mattered. It turned the magnetron from a curiosity into a source of short radio waves.
1926
1926–1929
Okabe, one of Yagi's first doctoral students, split the magnetron's metal cylinder into halves. This let it make much shorter waves, and he won a US patent for it in 1929. Later, in Osaka, he reached waves about 12 cm long, close to the waves in a kitchen microwave today.
Why it mattered. Japan's early magnetron research started worldwide interest in centimetre waves.
1933
Westinghouse cooked food between two metal plates connected to a 10 kW shortwave radio transmitter. The waves were about 5 m long, at 60 MHz, far longer than a modern microwave oven's.
Why it mattered. It showed that radio energy could heat food, years before anyone had a small, powerful source of shorter waves.
1935
Hollmann patented a magnetron with several resonant cavities, an early version of the design that would later change radar. The German military turned it down because its frequency drifted, and built radar with a different tube instead.
Why it mattered. Good ideas need the right moment: the cavity idea only took off five years later in England.
1939 – 1945
A powerful new magnetron from Birmingham makes short-wave radar possible. It crosses the Atlantic in secret, and American factories make it by the thousand.
1940
21 February 1940
Randall and Boot drilled holes around a solid copper block so it rang with microwaves, a bit like blowing across a bottle. When they switched it on, it made about 400 W at a wavelength of about 10 cm, around a hundred times more than earlier tubes at that wavelength. Within weeks, engineers pushed it past 1 kW.
Why it mattered. Every microwave oven's magnetron is a descendant of this copper block.
1940
September 1940
Britain sent a team of scientists to share its war secrets with the United States. The Welsh physicist Bowen carried cavity magnetron number 12 in a box. On 19 September it was shown working to astonished American scientists, whose best tubes made far less power at those wavelengths.
Why it mattered. An American historian later called it “the most valuable cargo ever brought to our shores”.
1940
October 1940
Within weeks of the demonstration, the Radiation Laboratory opened at MIT to build microwave radar around the magnetron. Bell Telephone made its first 30 magnetrons that October. By the end of the war, almost every Allied radar used one.
Why it mattered. Thousands of scientists and engineers learned to work with microwaves, and some later brought that knowledge to the kitchen.
1943
1942–1945
Carving each magnetron from solid copper was slow. Spencer, Raytheon's self-taught chief engineer, found a way to stamp out thin copper pieces and join them, and output rose to about 2,600 a day. By 1945 Raytheon had built about 80% of all the magnetrons made.
Why it mattered. Mass production made magnetrons cheap and familiar, the first step toward one in every home.
1945 – 1966
A radar engineer finds that microwaves cook food. The first ovens are as big as fridges and cost as much as a car, so they go to restaurants, ships and trains.
1945
c. 1945 (attributed)
The famous story says Spencer was standing near a working radar magnetron when a candy bar in his pocket melted. No reliable first-hand record of it exists. He then tried popcorn kernels, which popped, and an egg, which exploded, reportedly in a colleague's face.
Why it mattered. Whatever really happened, Spencer saw that microwaves could cook, and Raytheon decided to sell ovens.
1945
8 October 1945 (granted 24 January 1950)
Raytheon filed Spencer's patent, ‘Method of Treating Foodstuffs’, for cooking with waves about 10 cm long. It said an egg could be hard-boiled with about 2 kilowatt-seconds of energy, compared with 36 on a normal stove. It was granted in 1950 as US patent 2,495,429.
Why it mattered. It described cooking with microwaves from a magnetron, the idea inside every microwave oven.
1947
December 1946 and 1947
On 30 December 1946 the US Federal Communications Commission approved 2,450 MHz for microwave cooking. In 1947 an international radio conference in Atlantic City set aside bands for industrial, scientific and medical use, and the American delegation proposed 2.4 GHz for microwave heating. Kitchen ovens still use 2.45 GHz, with waves about 12 cm long.
Why it mattered. Ovens got their own slice of the radio spectrum, which Wi-Fi and Bluetooth now share.
1947
The first microwave oven for sale was almost 1.8 m tall and weighed about 340 kg. It used 3 kW of power, about three times a modern oven, and its magnetron was cooled with water. It cost about $5,000, and went to restaurants, ships and railway dining cars. Its name won a Raytheon staff contest.
Why it mattered. It proved microwave cooking worked, even if no family could fit or afford one.
1955
1955–1956
Tappan licensed Raytheon's patents in 1952 and showed an ‘Electronic Oven’ for homes in New York on 27 October 1955. It sold for about $1,300, and few families bought one.
Why it mattered. The home microwave was possible, but it was still too big and costly.
1962
1961–1962
Sharp developed Japan's first microwave oven, the R-10, in 1961, and in 1962 began making them in large numbers. Toshiba also began production in 1962. Sharp sold them to businesses first, because people doubted they would ever cook without a flame at home.
Why it mattered. Japan began to become the centre of microwave oven making.
By the numbers
Launch prices in the dollars of the day, not adjusted for inflation: in 25 years the microwave went from the price of a small house to that of a fancy TV.
1966 – 1990
Ovens shrink onto the countertop, Japanese factories make cheap magnetrons, safety rules calm people's fears, and microwave food fills the shops.
1966
Sharp's R-600 put the food on a spinning plate. Microwaves bounce around the box and leave hot and cold spots, so turning the food spreads the heat more evenly. American ovens instead used a spinning metal stirrer in the roof.
Why it mattered. The turntable became the standard design found in most microwave ovens today.
1967
Raytheon bought the appliance maker Amana in 1965, and in 1967 it launched a Radarange small enough for the kitchen counter that plugged into an ordinary wall socket. It cost $495, still a lot of money. A cheap magnetron, developed with Raytheon's Japanese partner New Japan Radio, helped bring the price down.
Why it mattered. It is widely considered the first popular home microwave oven.
1971
18 October 1968 and 6 October 1971
The Radiation Control for Health and Safety Act of 1968 let the US government set limits for products that give off radiation. From 6 October 1971, new ovens could leak no more than 1 mW per square centimetre, measured 5 cm away, and 5 mW over their whole life. Every door needs two separate interlocks that stop the microwaves the moment it opens.
Why it mattered. Clear, strict limits helped calm fears and let the microwave into millions of homes.
1971
1969–1970s
After Raytheon's basic magnetron patent ran out, several Japanese companies began making magnetrons for ovens, and Japan sold 380,000 ovens in 1969 alone. In 1971 Toshiba magnetrons went into Litton ovens in the US. Over the next decade the American magnetron makers stopped, and a few Japanese firms supplied almost the whole world.
Why it mattered. Cheap, reliable Japanese magnetrons made the home microwave affordable everywhere.
1975
1974–1975
Amana added an automatic defrost setting in 1974. In 1975 its RR-6 model became the first microwave with a microprocessor and a digital touch panel instead of a turning dial.
Why it mattered. The beeping number pad on today's microwaves began here.
1984
1981 and 1984
In 1981 a General Mills patent by Brastad described a very thin metal coating on film that turns microwaves into heat to brown food, now called a susceptor. In 1984 Golden Valley Microwave Foods launched Act II, the first mass-marketed microwave popcorn that could sit on a shelf, in a bag invented by the former Pillsbury engineer James Watkins.
Why it mattered. Popcorn, Spencer's first test food, became the snack most linked with the microwave.
1987
Kafka, a food writer who had not used a microwave until 1984, published ‘Microwave Gourmet’. It showed serious cooks that the oven could do much more than reheat leftovers, even though many food lovers were horrified.
Why it mattered. It helped turn the microwave from a reheating box into a cooking tool.
By the numbers
US government household surveys show the microwave going from rare to almost everywhere in about 30 years.
1985 – today
Smarter electronics give ovens gentler power, China becomes the world's microwave factory, and the appliance spreads to new kitchens in Asia and beyond.
1988
Most ovens make ‘half power’ by switching the magnetron fully on and off every few seconds. Panasonic's inverter used electronics to run the magnetron at a steady lower power instead. The first model gave up to 700 W.
Why it mattered. Steady, gentle power heats food more evenly, and many ovens now work this way.
1998
1992–1998
Galanz, a company that began in 1978 making other goods, started making microwave ovens in 1992. By 1998 it was the biggest microwave maker in the world, with about 40% of the global market. By 2019 it was making about half of the world's microwaves.
Why it mattered. Huge factories in China made microwave ovens cheap enough for families around the world.
2025
2013–2025
Only about 5% of Indian households owned a microwave oven in 2013, far fewer than owned a fridge. Sales are growing as cities grow, and one market research firm valued India's microwave market at about US$572 million in 2025. Convection models that can also bake and grill are popular.
Why it mattered. The microwave is still spreading, and much of its next growth is in Asia.
Did you know?
Percy Spencer reportedly got a bonus of just $2 for his microwave cooking patent.
Kitchen microwaves use waves about 12 cm long. Melt a plate of chocolate with the turntable removed, measure the gap between melted spots (half a wave), and you can estimate the speed of light.
The metal mesh in the oven door has holes far smaller than the 12 cm microwaves, so light gets out and microwaves do not.
Microwave ovens and Wi-Fi share the same 2.4 GHz band, which is why a running microwave can slow down nearby Wi-Fi.
By 2019 one Chinese company, Galanz, was making about half of all the world's microwave ovens.
The people
1831 – 1879 · Physicist · Scotland
Predicted that electricity and magnetism travel together as waves, including ones we cannot see.
1857 – 1894 · Physicist · Germany
First to make and detect electromagnetic waves on purpose.
1858 – 1937 · Physicist and biologist · India
Made and detected millimetre waves in Calcutta in the 1890s, with antennas and detectors he built himself.
1880 – 1966 · Physicist · USA
Studied the magnetron at General Electric in 1921.
1886 – 1961 · Physicist · Czechoslovakia
Found in 1924 that a magnetron could make radio waves, and patented his design.
1896 – 1984 · Engineer · Japan
Invented the split-anode magnetron and reached waves about 12 cm long.
1886 – 1976 · Engineer and teacher · Japan
Led the Tohoku lab where Okabe did his magnetron work; best known for the Yagi-Uda antenna.
1905 – 1984 · Physicist · England
Co-invented the cavity magnetron; later led the King's College lab where Rosalind Franklin studied DNA.
1917 – 1983 · Physicist · England
Co-invented the cavity magnetron with Randall as a young researcher.
1894 – 1970 · Engineer and inventor · USA
Left school early, taught himself, sped up magnetron production and patented microwave cooking.
1933 – 2018 · Food writer · USA
Her 1987 ‘Microwave Gourmet’ showed that microwaves could really cook.
Where it happened
Sources
Dates marked “c.” are approximate, and historians sometimes disagree about who was first. If you spot a mistake, tell us.
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