The exploitation of high-frequency radio waves for heating substances was made possible by the development of vacuum tube radio transmitters around 1920. By 1930 the application of short waves to heat human tissue had developed into the medical therapy of diathermy. 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.[3] The Westinghouse team, led by I. F. Mouromtseff, found that foods like steaks and potatoes could be cooked in minutes.
If your primary concern is cooking speed, you need a microwave with higher wattage. The unit has to be large enough for your family's needs but not too large to fit in your kitchen. It is desirable to have quick keys, multi-stage cooking, and true variable power. Easy cleaning is a must because, at some point, you will need to wipe up after a cooking job.
When you add in the competent wattage and the internal space, which is large enough for the bigger plates in your home, it’s tough to see what this Panasonic model doesn’t do right. This 2.2 cu ft microwave is a winner. Even the design is pleasantly modern and easy to clean in case of grease or stains. This microwave really does impress on every level…but it’s not an over the range model, which may limit your options.
Like the 0.9-cubic-foot model, this Toshiba has one-touch start buttons from 1 to 6 minutes, a plus-30-seconds button, and a child-lock function. This model also shares several other features with the smaller Toshiba, such as a memory function and a multistage cooking function—but, realistically, we don’t think most people will use these controls often.
If your microwave is broken, do not attempt to repair it yourself. Microwaves are dangerous to tamper with and should be serviced by professionals because the magnetron can retain a hazardous charge even when it isn’t plugged in. Most microwave manufacturers discourage people from even changing the light bulbs. But realistically, it’s probably cheaper and less of a hassle to buy a new microwave than to have it repaired.

Our microwave oven tests found big differences in overall performance among models. To test heating we warm up mashed potatoes, and we use frozen ground beef to test defrosting. We also test speed of heating, noise, and ease of use. We measure usable capacity, too. (Manufacturers often include space you can't use.) Plus we test how well the over-the-range models vent.

If you want a smaller microwave that still offers plenty of power, then this 1.1-cubic-feet, 1000-watt option from Samsung is a great pick. Customers love the modern black color scheme and the brushed stainless steel handle. The design of the control panel is also unique because it combines digital controls with a metal dial. The ceramic enamel interior is designed to wipe clean easily and resist grease, oil, and scratches. Online reviewers appreciate the unique LED display and say that one of the microwave's highlights is Eco mode, which allows you to turn the digital display off to conserve energy. One downside is that the microwave can be quite loud, according to current owners.

In most ovens, the magnetron is driven by a linear transformer which can only feasibly be switched completely on or off. (One variant of the GE Spacemaker had two taps on the transformer primary, for high and low power modes.) Usually choice of power level doesn't affect intensity of the microwave radiation; instead, the magnetron is cycled on and off every few seconds, thus altering the large scale duty cycle. Newer models use inverter power supplies that use pulse-width modulation to provide effectively continuous heating at reduced power settings, so that foods are heated more evenly at a given power level and can be heated more quickly without being damaged by uneven heating.[33][34][35]
The defrost options (varying by type or weight) are ideal if you want to warm something up with the microwave before cooking with the convection setting. If you have a busy kitchen and want multiple ways to cook foods (instead of just nuking the occasional popcorn bag), Cuisinart delivers. About the only thing that it’s missing is the ability to set power levels, but with all these other features, that’s a minor quibble to be had.
Any object containing pointed metal can create an electric arc (sparks) when microwaved. This includes cutlery, crumpled aluminium foil (though some foil used in microwaves is safe, see below), twist-ties containing metal wire, the metal wire carry-handles in paper Chinese take-out food containers, or almost any metal formed into a poorly conductive foil or thin wire, or into a pointed shape.[57] Forks are a good example: the tines of the fork respond to the electric field by producing high concentrations of electric charge at the tips. This has the effect of exceeding the dielectric breakdown of air, about 3 megavolts per meter (3×106 V/m). The air forms a conductive plasma, which is visible as a spark. The plasma and the tines may then form a conductive loop, which may be a more effective antenna, resulting in a longer lived spark. When dielectric breakdown occurs in air, some ozone and nitrogen oxides are formed, both of which are unhealthy in large quantities.

One touch buttons take care of all the work for you. We particularly like the buttons that combine sensors with a preprogrammed cooking time to automatically adjust based on the food you put inside the microwave. One touch buttons for common foods like popcorn, potatoes, hot dogs and more are also a plus – as are time-saving buttons for immediate reheating, melting, defrosting, and so on.

Countertop microwaves are some of the most popular models, and there are many options to choose from. They are quick and easy to install—just plug them in—and you can move them around as needed, making them a top choice for renters. The main downside of countertop microwaves is that they take up valuable counter space, which can be frustrating if you have a small kitchen. 
Food and cookware taken out of a microwave oven are rarely much hotter than 100 °C (212 °F). Cookware used in a microwave oven is often much cooler than the food because the cookware is transparent to microwaves; the microwaves heat the food directly and the cookware is indirectly heated by the food. Food and cookware from a conventional oven, on the other hand, are the same temperature as the rest of the oven; a typical cooking temperature is 180 °C (356 °F). That means that conventional stoves and ovens can cause more serious burns.
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. ... 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.