75 Years Ago — Raytheon files US patent application for microwave cooking process (October 8, 1945)

“My grandfather was watching a microwave testing rig, and he realized that the peanut-cluster bar in his pocket started to melt — it got quite warm.”

Rod Spencer — Inventor and grandson of Percy Spencer
Percy Spencer — Inventor of microwave oven

October 8 2020 — The origins of the microwave oven can be traced to World War II. Scientists in Britain had developed the magnetron, a tube that produces microwaves, as part of a radar system to spot Nazi warplanes. Follow us on Twitter: @INTEL_TODAY

The technology was passed to the United States, and Raytheon was among the companies putting it to use for the military.

In early 1945, the Raytheon Company was looking for something to sell to civilians after World War II was over. The company’s head, Laurence Marshall, convened a team of technicians to come up with an answer.

One of these technicians, Percy Spencer, suggested that Raytheon should build on its radar expertise by making an oven. He had walked by a microwave tube one day and noticed that a candy bar in his pocket had melted. Intrigued, he placed some popcorn kernels near the tube and watched them pop all over his lab. The next morning, he exploded an egg for a colleague.

Earlier this year, I posted a story — On This Day — US Surgeon General Report Links Tobacco and Cancer (January 11 1964) [5G & Cancer] — that prompted the following comment:

“Microwaves have not been proven to cause cancer, in fact the Varian associates medical division actually uses microwaves to cure cancer.

Also there is no evidence the Havana syndrome has anything to do with microwaves, an urban vernacular to attribute just about every malady and malfunction to those mysterious microwaves. Not really mysterious, every kitchen has one.

The magnetron that powers these common devices is the same as the ones that spotted the Japanese aircraft flying towards Pearl Harbor at the start of WW2, been around a very long time.”

Edgar Gillham, team leader in advanced development, ALQ-131 electronic countermeasures for USA and allied aircraft.

First thing first… In 2018, the U.S. National Toxicology Program (NTP) concluded that microwave radiation causes cancer.

This year, the NTP will begin a systematic search for mechanisms to explain how and why the tumors developed. [NTP Turns to Mechanisms — DNA Breaks, Oxidative Stress and Gene Expression Are on the Agenda]

Second. The cavity magnetron was not yet used in RADAR at the time of Pearl harbor.

The invention of the cavity magnetron made possible the production of electromagnetic waves of a small enough wavelength (microwaves). The magnetron was originally a crucial component in the development of short wavelength radar during World War II.

In 1937–1940, a multi-cavity magnetron was built by the British physicist Sir John Turton Randall, FRSE, together with a team of British coworkers, for the British and American military radar installations in World War II. A more high-powered microwave generator that worked at shorter wavelengths was needed, and in 1940, at the University of Birmingham in England, Randall and Harry Boot produced a working prototype. They invented a valve that could produce pulses of microwave radio energy on a wavelength of 10 cm, an unprecedented discovery.

Sir Henry Tizard traveled to the U.S. in late September 1940 to offer the magnetron in exchange for their financial and industrial help. An early 6 kW version, built in England by the General Electric Company Research Laboratories, Wembley, London, was given to the U.S. government in September 1940. The magnetron was later described by American historian James Phinney Baxter III as the “most valuable cargo ever brought to our shores”. Contracts were awarded to Raytheon and other companies for the mass production of the magnetron. [Wikipedia]

In May 1939, a contract was awarded to RCA for production. Designated CXAM, deliveries started in May 1940. The acronym RADAR was coined from “Radio Detection And Ranging”.

One of the first CXAM systems was placed aboard the USS California, a battleship that was sunk in the Japanese attack on Pearl Harbor on December 7, 1941.

The CXAM radar system was the first production radar system deployed on United States Navy ships, operating in the mid-high VHF frequency band of 200 MHz, about a tenth of the frequency used by a microwave oven.

Of course, people were well aware of the advantages of microwaves for RADAR but without the cavity magnetron, this frequency band was simply not a option.


Microwave oven — Wikipedia


75 Years Ago — Raytheon files US patent application for microwave cooking process (October 8, 1945)

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1 Response to 75 Years Ago — Raytheon files US patent application for microwave cooking process (October 8, 1945)

  1. Edgar Gillham says:

    75 years ago there were no reliable ways to read microwave power. According to my engineering supervisor they used to put steel wool in a glass jar and hold it to the output wave-guide, power out was guessed at by how bright the steel wool glowed. Bob Graham helped Hewlett Packard develop the first thermistor power meter. they were difficult to read but light years ahead of glowing steel wool


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