Experiments showed that microwave heating could raise the internal temperature of many foods far more rapidly than a conventional oven1.
The first Raytheon commercial microwave oven was the 1161 Radarange, which was marketed in 1954. Rated at 1600 watts, it was so large and expensive that it was practical only for restaurant and institutional use.
In 1967, Amana, a division of Raytheon, introduced its domestic Radarange microwave oven, marking the beginning of the use of microwave ovens in home kitchens. Although sales were slow during the first few years, partially due to the oven's relatively expensive price tag, the concept of quick microwave cooking had arrived. In succeeding years, Litton and a number of other companies joined the countertop microwave oven market. By the end of 1971, the price of countertop units began to decrease and their capabilities were expanded2.
All electromagnetic energy can be characterized as waves with a specific wavelength and frequency distributed over a continuous range known as the electromagnetic spectrum. For example, some radio waves have a wavelength of 6 feet (2 meters) and a frequency of 50 million hertz (Hz-cycles per second). Visible light waves have a wavelength of 400 to 700 millimicrons, and typical X-rays have a length of 0.01 millimicrons and a frequency of 30 x 1012 millions.
Microwaves (short waves or high frequency radio waves) are the shortest of radio waves, with a length of 0.1 millimeter and a frequency of 3 x 101 Hz. They are found in the non-ionizing portion of the energy spectrum, between radio waves and visible light. "Non-ionizing" means that microwaves do not detach charged particles and produce atoms with an unbalanced plus or minus charge. Microwaves can therefore safely produce heat and not cause food to become radioactive.
Microwaves are reflected from most metals but they produce inductive resonance's in the atoms of many other substances. It was the discovery of their reaction to metals that led to the invention of radar. It was their ability to produce resonant coupling that led to the invention of the microwave oven3.
Microwave ovens use various combinations of electrical circuits and mechanical devices to produce and control an output of microwave energy for heating and cooking. Generally speaking the systems of a microwave oven can be divided into two fundamental sections, the control section and the high-voltage section .
The control section consists of a timer (electronic or electromechanical), a system to control or govern the power output, and various interlock and protection devices. The components in the high-voltage section serve to step up the house voltage to high voltage. The high voltage is then converted microwave energy.
Basically, here is how it works: As shown in Figure 1, electricity from the wall outlet travels through the power cord and enters the microwave oven through a series of fuse and safety protection circuits. These circuits include various fuses and thermal protectors that are designed to deactivate the oven in the event of an electrical short or if an overheating condition occurs4.
If all systems are normal, the electricity passes through to the interlock and timer circuits. When then oven door is closed, an electrical path is also established