Research News

Op-ed: World War II technology still with us today

Dennis Hall
Dennis Hall, professor of physics and professor of electrical engineering (Vanderbilt University)

The code-breaker movie The Imitation Game opened in theaters on Dec. 25. It centers on mathematician Alan Turing, the legendary pioneer of computer science and artificial intelligence. Turing’s work during World War II let the British unscramble messages encrypted by the German Enigma machines, shortening the war in Europe, perhaps by years.

The movie reminds us that the urgencies of World War II hastened a number of advances in science and technology that continue to benefit us today. But not every such story becomes a movie. In particular, one less familiar story tells of the radar breakthrough that led unexpectedly to the microwave oven. Here are a few highlights of that story.

In 1914, the young physicist Albert Hull joined the General Electric Research Laboratory in Schenectady, New York. Hull is best remembered for his 1920 invention of the magnetron tube, novel for using a magnet to help control the electric current within an evacuated electron tube, or vacuum tube. However intriguing it was conceptually, his magnetron found only limited use.

Now jump ahead 20 years to World War II England and a secret effort to create a higher-frequency radar technology for the war effort. Radar, an acronym for radio detection and ranging, locates distant objects by bouncing radio waves off of them and then analyzing the reflections.

The goal was a radar system based on electromagnetic waves in the microwave region of the radio spectrum. Such a system would require smaller antennas and detect smaller objects than lower-frequency, longer-wavelength radars. Coming up with a compact, high-power source of microwave radiation was the challenge.

In 1940, John Turton Randall and Harry Boot, two young physicists working in England at the University of Birmingham, found a way to modify Hull’s original magnetron tube to make it produce microwaves with high enough power. The British government shared the new tube design, called a cavity magnetron tube, with the U.S. radar effort. It quickly became the heart of the Allies’ advanced radar systems that were so essential, perhaps decisive, to the overall Allied victory in World War II.

During the war years, under government contract, the Massachusetts-based Raytheon Manufacturing Company became a major producer of the new cavity magnetron tubes and radar systems. Raytheon’s Percy Spencer, a self-taught engineer and ham-radio hobbyist with a deep interest in radio technology, became a leading authority on magnetron tube design.

One day, Spencer noticed that candy bars melted when placed too close to radar units. His investigations confirmed that the microwaves produced by a cavity-magnetron tube reliably heated food and popped popcorn. In 1945, Raytheon filed a patent, granted in 1950, on the method behind what first became known commercially as the Radar Range oven, a more compact version of which we know today as the microwave oven. The cavity magnetron tube that generates microwave-frequency radio waves in every microwave oven uses the same basic tube design harnessed so effectively for WWII radar.

January 2015 marks the 65th anniversary of the awarding of the original microwave oven patent, U.S. #2,495,429, to Percy Spencer and Raytheon. When you use your microwave oven to heat up a few leftovers or pop some popcorn, show it a little respect. Its core technology has quite a history.

by Dennis G. Hall, professor of physics and professor of electrical engineering at Vanderbilt University