![]() Nevertheless, the primary heating effect of all types of electromagnetic fields at both radio and microwave frequencies occurs via the dielectric heating effect, as polarized molecules are affected by a rapidly alternating electric field. Heating from microwaves that have a wavelength that is small relative to the cavity (as in a modern microwave oven) is due to "far-field" effects that are due to classical electromagnetic radiation that describes freely propagating light and microwaves suitably far from their source. This patent proposed radio frequency heating, at 10 to 20 megahertz (wavelength 30 to 15 meters, respectively). However, lower-frequency dielectric heating, as described in the aforementioned patent, is (like induction heating) an electromagnetic heating effect, the result of the so-called near-field effects that exist in an electromagnetic cavity that is small compared with the wavelength of the electromagnetic field. It has been proposed therefore to heat such materials simultaneously throughout their mass by means of the dielectric loss produced in them when they are subjected to a high voltage, high frequency field. This invention relates to heating systems for dielectric materials and the object of the invention is to heat such materials uniformly and substantially simultaneously throughout their mass. The 1937 United States patent application by Bell Laboratories states: ![]() Mouromtseff, found that foods like steaks and potatoes could be cooked in minutes. At the 1933 Chicago World's Fair, Westinghouse demonstrated the cooking of foods between two metal plates attached to a 10 kW, 60 MHz shortwave transmitter. By 1930 the application of short waves to heat human tissue had developed into the medical therapy of diathermy. The exploitation of high-frequency radio waves for heating substances was made possible by the development of vacuum tube radio transmitters around 1920. History Early developments ĭemonstration by Westinghouse of cooking sandwiches with a 60 MHz shortwave radio transmitter at the 1933 Chicago World's Fair However, such high heat sources can be added to microwave ovens in the form of a convection microwave oven. Microwave ovens have a limited role in professional cooking, because the boiling-range temperatures of a microwave oven does not produce the flavorful chemical reactions that frying, browning, or baking at a higher temperature produces. 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 usually do not directly brown or caramelize food, since they rarely attain the necessary temperature to produce Maillard reactions. 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 are a common kitchen appliance and are popular for reheating previously cooked foods and cooking a variety of foods. In addition to cooking food, microwave ovens are used for heating in many industrial processes. After microwave ovens became affordable for residential use in the late 1970s, their use spread into commercial and residential kitchens around the world, and prices fell rapidly during the 1980s. The countertop microwave oven was introduced in 1967 by the Amana Corporation. Sharp Corporation introduced the first microwave oven with a turntable between 19. 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. Named the "Radarange", it was first sold in 1946. American engineer Percy Spencer is generally credited with inventing the modern microwave oven after World War II from radar technology developed during the war. The development of the cavity magnetron in the United Kingdom made possible the production of electromagnetic waves of a small enough wavelength ( microwaves). 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. This induces polar molecules in the food to rotate and produce thermal energy in a process known as dielectric heating. A modern microwave oven (2022)Ī 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. For other uses of Microwave, see Microwaves (disambiguation). For the electromagnetic wave, see Microwave. ![]() ![]() This article is about the cooking appliance. ![]()
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