Friday October 8, 2021’s Smile of the Day: The Microwave Oven

On this Day:

In 1945, the microwave oven was patented by US inventor Percy Spencer.

A microwave oven (commonly referred to as a microwave) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation in the microwave frequency range. This induces polar molecules in the food to rotate and produce thermal energy in a process known as dielectric heating. Microwave ovens heat foods quickly and efficiently because excitation is fairly uniform in the outer 25–38 mm (1–1.5 inches) of a homogeneous, high water content food item.

The development of the cavity magnetron in the UK made possible the production of electromagnetic waves of a small enough wavelength (microwaves). American engineer Percy Spencer is generally credited with inventing the modern microwave oven after World War II from radar technology developed during the war. Named the “Radarange”, it was first sold in 1946.

Raytheon later licensed its patents for a home-use microwave oven that was introduced by Tappan in 1955, but it was still too large and expensive for general home use. Sharp Corporation introduced the first microwave oven with a turntable between 1964 and 1966. The countertop microwave oven was introduced in 1967 by the Amana Corporation. After microwave ovens became affordable for residential use in the late 1970s, their use spread into commercial and residential kitchens around the world. In addition to cooking food, microwave ovens are used for heating in many industrial processes.

Microwave ovens are a common kitchen appliance and are popular for reheating previously cooked foods and cooking a variety of foods. They rapidly heat foods which can easily burn or turn lumpy if cooked in conventional pans, such as hot butter, fats, chocolate or porridge. Microwave ovens usually do not directly brown or caramelize food, since they rarely attain the necessary temperature to produce Maillard reactions. Exceptions occur in cases where the oven is used to heat frying-oil and other oily items (such as bacon), which attain far higher temperatures than that of boiling water.

Microwave ovens have a limited role in professional cooking, because the boiling-range temperatures of a microwave oven will not produce the flavorful chemical reactions that frying, browning, or baking at a higher temperature will. However, such high heat sources can be added to microwave ovens in the form of a convection microwave oven.

The invention of the cavity magnetron made possible the production of electromagnetic waves of a small enough wavelength (microwaves). The magnetron was a crucial component in the development of short wavelength radar during World War II. In 1937–1940, a multi-cavity magnetron was built by British physicist Sir John Turton Randall, FRSE and coworkers, for the British and American military radar installations in World War II. A higher-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 at a wavelength of 10 cm, an unprecedented discovery.

Sir Henry Tizard travelled to the U.S. in late September 1940 to offer the magnetron in exchange for their financial and industrial help (see Tizard Mission). 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.

In 1945, the heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer, an American self-taught engineer from Howland, Maine. Employed by Raytheon at the time, he noticed that microwaves from an active radar set he was working on started to melt a chocolate bar he had in his pocket. The first food deliberately cooked with Spencer’s microwave oven was popcorn, and the second was an egg, which exploded in the face of one of the experimenters.

To verify his finding, Spencer created a high density electromagnetic field by feeding microwave power from a magnetron into a metal box from which it had no way to escape. When food was placed in the box with the microwave energy, the temperature of the food rose rapidly. On 8 October 1945, Raytheon filed a United States patent application for Spencer’s microwave cooking process, and an oven that heated food using microwave energy from a magnetron was soon placed in a Boston restaurant for testing.

While uncommon today, combination microwave-ranges were offered by major appliance manufacturers through much of the 1970’s as a natural progression of the technology. Both Tappan and General Electric offered units that appeared to be conventional stove top/oven ranges, but included microwave capability in the conventional oven cavity. Such ranges were attractive to consumers since both microwave energy and conventional heating elements could be used simultaneously to speed cooking, and there was no loss of countertop space. The proposition was also attractive to manufacturers as the additional component cost could better be absorbed compared with countertop units where pricing was increasingly market-sensitive.

By 1972, Litton (Litton Atherton Division, Minneapolis) introduced two new microwave ovens, priced at $349 and $399, to tap into the market estimated at $750 million by 1976, according to Robert I Bruder, president of the division. While prices remained high, new features continued to be added to home models. Amana introduced automatic defrost in 1974 on their RR-4D model, and was the first to offer a microprocessor controlled digital control panel in 1975 with their RR-6 model.

The late 1970s saw an explosion of low-cost countertop models from many major manufacturers.

Formerly found only in large industrial applications, microwave ovens increasingly became a standard fixture of residential kitchens in developed countries. By 1986, roughly 25% of households in the U.S. owned a microwave oven, up from only about 1% in 1971; the U.S. Bureau of Labor Statistics reported that over 90% of American households owned a microwave oven in 1997. In Australia, a 2008 market research study found that 95% of kitchens contained a microwave oven and that 83% of them were used daily. In Canada, fewer than 5% of households had a microwave oven in 1979, but more than 88% of households owned one by 1998. In France, 40% of households owned a microwave oven in 1994, but that number had increased to 65% by 2004.

Adoption has been slower in less-developed countries, as households with disposable income concentrate on more important household appliances like refrigerators and ovens. 

Consumer household microwave ovens usually come with a cooking power of 600 watts and up (with 1000 or 1200 watts on some models). The size of household microwave ovens can vary, but usually have an internal volume of around 20 liters (1,200 cu in; 0.71 cu ft), and external dimensions of approximately 45–60 cm (1 ft 6 in–2 ft 0 in) wide, 35–40 cm (1 ft 2 in–1 ft 4 in) deep and 25–35 cm (9.8 in–1 ft 1.8 in) tall.

Microwaves can be turntable or flatbed. Turntable ovens include a glass plate or tray. Flatbed ones do not include a plate, so they have a flat and wider cavity.

By position and type, US DOE classifies them in (1) countertop or (2) over the range and built-in (wall oven for a cabinet or a drawer model).

Traditional microwaves rely on internal high voltage power from a line/mains transformer, but many newer models are powered by an inverter. Inverter microwaves can be useful for achieving more even cooking results, as they offer a seamless stream of cooking power.

A traditional microwave only has two heat settings, ON and OFF. Intermediate heat settings switch between full power and off every few seconds, with more time ON for higher settings.

An inverter type, however, can sustain lower temperatures for a lengthy duration without having to switch itself off and on repeatedly. Apart from offering superior cooking ability, these microwaves are generally more energy-efficient.

As of 2020, the majority of countertop microwave ovens (regardless of brand) sold in the United States were manufactured by the Midea Group (per Wikipedia).

First, a Story:

A hipster friend of mine insists on cooking everything in a microwave oven. He doesn’t like things that are conventional…

Second, a Song:

What happens if you microwave grapes? Well I am glad you asked that question…

Per Veritasium: “A bisected grape in the microwave makes plasma. But how does it work? A grape is the right size and refractive index to trap microwaves inside it. When you place two (or two halves) close together the fields interact with each other creating a maximum of electromagnetic energy where they touch. This creates heating, sparks, and plasma, which is further fed with energy directly by the microwaves.

Huge thanks to Hamza Khattak, Prof. Pablo Bianucci and Prof. Aaron Slepkov (unavailable for the call) for chatting to me and helping me understand the physics of this cool phenomenon.” (per

Veritasium states: “An element of truth – videos about science, education, and anything else I find interesting.”

Here is Veritasium’s video: “How Microwaving Grapes Makes Plasma”.  I hope you enjoy this!


Thought for the Day:

“The New Age? It’s just the old age stuck in a microwave oven for fifteen seconds.” – James Randi

Further to the Dark Side of the Moon Smile, Gerry Wahl of North Vancouver, BC writes:

“Very interesting!  Green cheese no doubt!!

Did you know that the earth has 3  ‘moons’ 2 of which are hidden. They are more like the ‘ingredients’ of moons rather than actual orbs.

The 5 km high tower on the dark side of the moon is intriguing – lots of speculation as to what it might be.”

Editor:  Yes there is lots of speculation over the web that aliens are indeed on the far side of the moon…perhaps they provided the inspiration for Pink Floyd’s Dark Side of the Moon Album…

Have a great day!

Dave & Colleen

© 2021 David J. Bilinsky and Colleen E. Bilinsky

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