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The Microwave Oven:  Its History & How it Works

In very simple words, a microwave is a kitchen appliance that uses microwave radiation to heat food.

According to the literature, “a simple microwave system consists of four main components: a magnetron that converts electrical energy to microwave energy, a microwave cavity for holding and heating foods, waveguides that lead microwaves from the magnetron to the cavity, and a control system1.”

The history of microwave ovens

The history of microwaves is intertwined with world history, and as it happens with many cases when a war technology sees the end of the war, its developers need to find a new way to use it. Here is a summary timeline of the “invention” and history of the microwave oven1,5.

The Microwave Oven:  Its History & How it Works
  • 1937 to 1940Sir John Turton Randall, a British physicist, together with a team of British coworkers, developed a multi-cavity magnetron that allowed for the production of electromagnetic waves of a small enough wavelength (microwaves) and the development of radar.
  • September 1940 – Magnetron was given to the U.S. government in September 1940 in exchange for their financial and industrial help during the Second World War.
  • 1945Percy Spencer, an engineer from the company Raytheon, when working on a powered radar set, noticed that a chocolate bar that he had in his pocket was melting. He was not the first to notice this effect, but he was the first one to become curious enough to explore it. He later exposed corn to microwaves, and they popped, and a whole egg exploded. For controlled and safe experiments, he then attached a high-density electromagnetic field generator to an enclosed metal box and experimented on different foods.
  • October 8, 1945 – Percy L. Spencer of Raytheon Co. (Mass., U.S.A.) filed a patent application in which he described a device using electromagnetic (EM) energy with wavelengths of about 10 cm to heat foods (one of the first prototypes was placed at a Boston restaurant for testing).
  • January 1947 – First public microwave oven in a Speedy Weeny vending machine in Grand Central Terminal, selling “freshly cooked” hot dogs.
  • Later in 1947 – Radarange, the first commercially available microwave oven, made by Raytheon. It was 1.8 meters high and weighed 340 kilograms. The cost was approximately $5,000, which today would amount to around $52,000.
  • 1954 – New microwave oven model was released. This model consumed half the power of the first model and was sold for $2,000 to $3,000.
  • 1960s – Development of a new configuration of the microwave oven by Litton Company. This model already had the wide and short shape that is common nowadays. This model also held a magnetron feed that could survive a no-load condition (when there is nothing in the oven to absorb microwaves) which made the microwave oven safer.
  • 1970s – Prices fell between the 1960s and 1970s, and microwave ovens became a standard part of American households.
  • 1986 – Around 25% of households in the United States had a microwave oven.
  • 1997 – Over 90% of United States households had a microwave oven.
  • 2003 – In the U.S.A., microwaving is the 3rd most popular domestic heating method (after baking and grilling) for cooking and heating foods

How do microwaves heat up food?

As Tang describes it, “microwave heating involves complex multi-physics phenomena that include interaction between the heated materials and microwaves, conversion from electric energy into thermal energy, and heat transfer driven by temperature gradients1.”

Basically, the microwave oven turns electricity into high-frequency electromagnetic waves in the microwave frequency range2. Microwave frequencies range between 300 MHz and 300 GHz, corresponding to wavelengths ranging from about 1 m to 1 mm, respectively. Microwaves, besides being used in microwave ovens, “are used for air-traffic control, weather forecasting, global positioning, cellular video systems, and other telecommunication and remote ranging applications1.”

Microwave ovens generate radiation at a frequency of about 2,450 MHz by means of a magnetron, which is a kind of electron tube. These high-frequency electromagnetic waves induce polar molecules in the food to vibrate, rotate, spin, and clash with each other, turning electromagnetic wave energy into heat or thermal energy3. The magnetic component of microwaves does not interact with foods; only the electric component causes heating1. This mechanism is very distinct from the traditional conduction heating, as it is dependent on the dielectric properties (or electric permittivity) of foods “which are affected by food composition, in particular moisture content, salt, and fat contents,” but also temperature and frequency1,4. As described in a recent article, with dielectric heating “polar molecules and charged ions interaction with the alternative electromagnetic fields, resulting in fast and volumetric heating through their friction losses4.”

Microwaves mainly affect water because of its dipolar molecules, but they can also be absorbed by fats, sugars, and certain other molecules, whose consequent vibrations produce heat, and that is why the microwave oven only heats up food and not the surrounding air. The heating occurs due to the absorption of the microwaves by different food molecules, which explains why foods do not heat evenly but at different rates. Moist foods cook faster than dry foods, and the outer layers also tend to absorb more radiation and heat up faster than the inner layers, that may not be cooked1,2,4.

What about materials?

Certain materials that do not absorb microwaves, such as different types of glass, paper, polyethylene, and Styrofoam, do not heat up and should be avoided. Aluminum foil heats up very quickly and can start a fire. Metal containers block microwaves, and food will not heat up on those.

What are our conclusions?

Although microwave ovens have been on the market for over half a century and are common in most American households, it is interesting to realize that there are not many studies evaluating their effects on food and human health.

However, at An Oasis of Healing, we focus on a plant-rich diet, full of health-promoting foods. Therefore, we recommend that you eat a diet rich in fresh, raw, living foods and avoid, when possible, microwaving your meals and beverages.

References

  1. Tang J. Unlocking Potentials of Microwaves for Food Safety and Quality. J Food Sci. 2015 Aug;80(8):E1776-93. doi: 10.1111/1750-3841.12959. Epub 2015 Aug 4. PMID: 26242920; PMCID: PMC4657497.
  2. “Microwave Oven”. Encyclopedia Britannica. 26 October 2018. Retrieved 23 January 2023.
  3. Microwave Oven. https://en.wikipedia.org/wiki/Microwave_oven, accessed
  4. Jiang H, Liu Z, Wang S. Microwave processing: Effects and impacts on food components. Crit Rev Food Sci Nutr. 2018;58(14):2476-2489. doi: 10.1080/10408398.2017.1319322. Epub 2017 Aug 14. PMID: 28613917.
  5. History of Microwave. Facts and History of Microwave. http://www.historyofmicrowave.com/, accessed Jan 25, 2023.
  6. Özcan MM, Al Juhaimi F, Ahmed IAM, Uslu N, Babiker EE, Ghafoor K. Effect of microwave and oven drying processes on antioxidant activity, total phenol and phenolic compounds of kiwi and pepino fruits. J Food Sci Technol. 2020 Jan;57(1):233-242. doi: 10.1007/s13197-019-04052-6. Epub 2019 Aug 27. PMID: 31975726; PMCID: PMC6952493.
  7. Vallejo, F., Tomás-Barberán, F. and García-Viguera, C. (2003), Phenolic compound contents in edible parts of broccoli inflorescences after domestic cooking. J. Sci. Food Agric., 83: 1511-1516. https://doi.org/10.1002/jsfa.1585
  8. Géczi G, Horváth M, Kaszab T, Alemany GG. No major differences found between the effects of microwave-based and conventional heat treatment methods on two different liquid foods. PLoS One. 2013;8(1):e53720. doi: 10.1371/journal.pone.0053720. Epub 2013 Jan 16. PMID: 23341982; PMCID: PMC3547058.
  9. Regulska-llow B, Ilow R. Comparison of the effects of microwave cooking and conventional cooking methods on the composition of fatty acids and fat quality indicators in herring. Nahrung. 2002 Dec;46(6):383-8. doi: 10.1002/1521-3803(20021101)46:6<383::AID-FOOD383>3.0.CO;2-L. PMID: 12577584.
  10. Watanabe F, Abe K, Fujita T, Goto M, Hiemori M, Nakano Y. Effects of Microwave Heating on the Loss of Vitamin B(12) in Foods. J Agric Food Chem. 1998 Jan 19;46(1):206-210. doi: 10.1021/jf970670x. PMID: 10554220.
  11. Cross GA, Fung DY. The effect of microwaves on nutrient value of foods. Crit Rev Food Sci Nutr. 1982;16(4):355-81. doi: 10.1080/10408398209527340. PMID: 7047080.