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Cakes Baked in 90 Seconds - Early Microwave "Oven"
November 1951 Radio & Television News

November 1951 Radio & TV News
November 1951 Radio & Television News Cover - RF Cafe[Table of Contents]

Wax nostalgic about and learn from the history of early electronics. See articles from Radio & Television News, published 1919-1959. All copyrights hereby acknowledged.

Little known to most people (including moi until recently), De Forest Training School was started by DeVry University's founder Herman A. DeVry. DeVry and De Forest were DeGood DeFriends, leading DeVry to name his electronics school after De Forest. It was re-named DeVry Technical Institute in 1953. Research at De Forest Training School produced one of the first RF / microwave food baking "oven." The prototype reported in this 1951 Radio & Television News magazine article was not at all like modern microwave ovens. There was no enclosure into which baking bowls, pans, and dishes can be inserted. Rather, electrodes were arranged at the perimeters of the special pan that in this demonstration contained cake batter. It was adapted from a process originally developed for RF induction heating of industrial materials (a major source of RF interference in the early days). A 10 MHz signal from a 1 kW generator provided the energy needed to bake an off-the-grocery-shelf cake mix in just 90 seconds.

Cakes Baked in 90 Seconds - Early Microwave Oven

Cakes Baked in 90 Seconds - Early Micowave Oven, November 1951 Radio & Television News - RF CafeBy George Petchel

Industrial Electronics Dept., DeForest's Training. Inc.

"Sounds fantastic, doesn't it? - well, it is!"

So stated a newspaper reporter at the scene of a 90-second cake baking demonstration conducted in the laboratories of DeForest's Training, Inc., 2735 N. Ashland Ave., Chicago, Illinois.

A batter made from a nationally-known cake mix plus plain water was poured into an ordinary Pyrex baking dish. This was placed between two vertical electrodes fastened to a polystyrene base and mounted on top of a kitchen table. The electrodes were connected by means of copper tubing to a radio frequency generator located nearby.

The batter turned into the kind of cake Mother used to make, not in 45 minutes, not in 10 minutes, but in 90 seconds! However, this feat was not accomplished without some measure of research and toil by students and instructors.

Flat aluminum electrodes were first used, but difficulty was encountered in obtaining the correct concentration of electric field and were later supplemented with ordinary aluminum foil. The foil was affixed to two opposite sides of the baking dish and then cut and shaped to form a field which gave best results.

Thickness of the batter also determined the quality of the cake. A thick batter baked more slowly and caused arcing between batter and electrodes. This cake was heavy and had burned spots. A batter which was quite fluid gave fine results and produced a cake that was light and tender with excellent texture and flavor qualities. With this type of batter little or no arcing was encountered and baking time was reduced to a minimum.

The demonstration was performed with a Westinghouse 1 kilowatt radio frequency generator designed especially for schools and laboratories. The unit has two radio frequency outputs. Its low frequency is at 300 kilocycles per second, suitable for experiments in induction heating. Its high frequency output at 10 megacycles per second is for experiment and study in dielectric heating. The latter is the frequency at which the cake baking was done.

Materials suitable for radio frequency heating are determined by their electrical properties. If the material is an electrical conductor, either magnetic or non-magnetic, it can be heated by means of its own I2R losses due to currents induced in the material when it is placed in a varying magnetic field. On the other hand, if the material is nominally insulating, it is placed in a varying electric field and will be heated due to its own dielectric losses generated due to the field.

Dielectric heating, a comparatively new technique, employs higher frequencies than induction heating and is commercially applied to plastics, ceramics, rubber, wood-bonded products such as plywood, and similar non-conducting materials.

The materials available to the student at DeForest's Training, Inc., are limited only by his imagination. Electronics' challenge to convention captures his fancy. Under the stimulation and guidance of the instructors he is encouraged and directed in the development of his ideas. Students who come to the school from far flung sections of the country suggest original applications of this new technique. The drying of hay and corn, curing tobacco, vulcanizing rubber, or cooking and baking various foods are subjects of experimentation.

What has been done in hours can now be done in minutes - even seconds! To the unexpected guest it can now be said, "I didn't know you were coming, but I'll bake a cake anyhow!"

Test setup used to bake cake with r.f.



Posted September 24, 2020

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    Kirt Blattenberger,


RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

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