Microwave heating can be deliberately uneven by design. Some microwavable packages (notably pies) may include materials that contain ceramic or aluminium flakes, which are designed to absorb microwaves and heat up, which aids in baking or crust preparation by depositing more energy shallowly in these areas. Such ceramic patches affixed to cardboard are positioned next to the food, and are typically smokey blue or gray in colour, usually making them easily identifiable; the cardboard sleeves included with Hot Pockets, which have a silver surface on the inside, are a good example of such packaging. Microwavable cardboard packaging may also contain overhead ceramic patches which function in the same way. The technical term for such a microwave-absorbing patch is a susceptor.[43]
Ever wondered how microwaves heat up food so quickly and efficiently? These appliances contain a part called a magnetron, which uses electricity to create high-powered radio waves. The waves are pushed into the microwave’s interior, where they bounce off the metal walls and penetrate whatever food you’re cooking. The turntable spins to help the waves hit the food from all angles, and this process makes the molecules in the food vibrate, warming them up. However, one of the downsides of microwave cooking is that radio waves can only travel a few centimeters into your food, so larger items don’t always cook evenly.
Microwaves generated in microwave ovens cease to exist once the electrical power is turned off. They do not remain in the food when the power is turned off, any more than light from an electric lamp remains in the walls and furnishings of a room when the lamp is turned off. They do not make the food or the oven radioactive. Compared to conventional cooking, the nutritional content of some foods may be altered differently, but generally in a positive way by preserving more micronutrients - see above. There is no indication of detrimental health issues associated with microwaved food.[66]
There’s no keypad, and you’ll have to twist a dial to program anything over 30 seconds. After some initial acquainting, we found those differences made programming simple. We weren’t completely ignoring presets and extra keys like we all do on our ordinary microwaves, instead we found ourselves able to specify exactly what we wanted done — without having to consult the user’s manual.
A microwave’s wattage tells you how much power it has, and more wattage means your food will cook faster and more evenly. You’ll typically see microwaves between 500 and 1,200 watts. Be aware that microwaves with fewer than 700 watts are generally underpowered and add time to the cooking process. These models are a good option for people limited by a budget, looking to save space, or willing to wait a few extra minutes. If you want a fully functional microwave to cook meat and vegetables, look for models with 1,000 watts or more.
Microwave ovens heat food without getting hot themselves. Taking a pot off a stove, unless it is an induction cooktop, leaves a potentially dangerous heating element or trivet that will stay hot for some time. Likewise, when taking a casserole out of a conventional oven, one's arms are exposed to the very hot walls of the oven. A microwave oven does not pose this problem.

In our heat map test, the Toshiba produced the most even heating pattern of all the microwaves we tested, perfectly browning the layer of marshmallows from edge to edge. It expertly cooked a baked potato in about 6 minutes, which was average for the microwaves we tried. It also reheated beverages well and perfectly cooked frozen macaroni and cheese. And it made tasty popcorn, with only 5 grams of kernels left unpopped, which was on a par with most of the models we tested. This model allows you to defrost by time or weight, but like most of the microwaves we tested, it didn’t defrost meat well.
^ "Efficient" here meaning more energy is deposited, not necessarily that the temperature rises more, because the latter also is a function of the specific heat capacity, which is often less than water for most substances. For a practical example, milk heats slightly faster than water in a microwave oven, but only because milk solids have less heat capacity than the water they replace.[citation needed]

A microwave with a convection function, like the Toshiba EC042A5C, offers multiple ways to cook your meals with one appliance. This 1,000-watt microwave has enough power to reheat food in microwave mode or cook, roast, and bake using the convection function between 170 and 425 degrees Fahrenheit. Featuring 1.5 cubic feet of space, it's large enough to microwave full-size dinner plates or accommodate a small chicken or pizza. A grill rack (for convection mode cooking) makes it easy to get a crispy exterior. People love this unit for its versatility, but others mention that it’s bigger and heavier than expected. It also may tack a few minutes onto recipe cook times when using convection mode.


We wanted to find microwaves that could cook a variety of foods, including frozen meals, popcorn, and whole potatoes, quickly and evenly. Some models have functions that cook food using preprogrammed time and power level settings. Others use built-in sensors that automatically adjust the cooking time based on the amount of steam emanating from the food. But regardless of the technology used, none of the microwaves we tested were perfect. Some microwaves had a more accurate baked-potato setting, while others were better at defrosting ground beef. We’d recommend choosing a microwave that excels at cooking the food you plan to prepare most often.

The radiation produced by a microwave oven is non-ionizing. It therefore does not have the cancer risks associated with ionizing radiation such as X-rays and high-energy particles. Long-term rodent studies to assess cancer risk have so far failed to identify any carcinogenicity from 2.45 GHz microwave radiation even with chronic exposure levels (i.e. large fraction of life span) far larger than humans are likely to encounter from any leaking ovens.[64][65] However, with the oven door open, the radiation may cause damage by heating. Every microwave oven sold has a protective interlock so that it cannot be run when the door is open or improperly latched.
Uneven heating in microwaved food can be partly due to the uneven distribution of microwave energy inside the oven, and partly due to the different rates of energy absorption in different parts of the food. The first problem is reduced by a stirrer, a type of fan that reflects microwave energy to different parts of the oven as it rotates, or by a turntable or carousel that turns the food; turntables, however, may still leave spots, such as the center of the oven, which receive uneven energy distribution. The location of dead spots and hot spots in a microwave can be mapped out by placing a damp piece of thermal paper in the oven. When the water saturated paper is subjected to the microwave radiation it becomes hot enough to cause the dye to be released which will provide a visual representation of the microwaves. If multiple layers of paper are constructed in the oven with a sufficient distance between them a three-dimensional map can be created. Many store receipts are printed on thermal paper which allows this to be easily done at home.[40]
From the late 1970s, Japanese companies such as Sharp Corporation manufactured low-cost microwave ovens that were affordable for residential use, leading to the rapid expansion of the microwave oven market in the 1980s. After Japanese dominance for much of the 1980s, with Sharp as market leader, South Korean manufacturers began entering the market in the late 1980s, with Samsung becoming a major microwave manufacturer.[18]

Another misconception is that microwave ovens cook food "from the inside out", meaning from the center of the entire mass of food outwards. This idea arises from heating behavior seen if an absorbent layer of water lies beneath a less absorbent drier layer at the surface of a food; in this case, the deposition of heat energy inside a food can exceed that on its surface. This can also occur if the inner layer has a lower heat capacity than the outer layer causing it to reach a higher temperature, or even if the inner layer is more thermally conductive than the outer layer making it feel hotter despite having a lower temperature. In most cases, however, with uniformly structured or reasonably homogenous food item, microwaves are absorbed in the outer layers of the item at a similar level to that of the inner layers. Depending on water content, the depth of initial heat deposition may be several centimetres or more with microwave ovens, in contrast to broiling/grilling (infrared) or convection heating—methods which deposit heat thinly at the food surface. Penetration depth of microwaves is dependent on food composition and the frequency, with lower microwave frequencies (longer wavelengths) penetrating further.[citation needed]


You’ve probably heard of a convection oven, but did you know that there are convection microwaves, too? These specialty appliances use the same technology as their oven counterparts: A fan blows and circulates hot air into the microwave, helping to cook food faster and more evenly. Convection microwaves can also brown or crisp food, similar to a traditional oven. 

There are, however, a few cases where people have been exposed to direct microwave radiation, either from appliance malfunction or deliberate action.[67][68] The general effect of this exposure will be physical burns to the body, as human tissue, particularly the outer fat and muscle layers, has similar composition to some foods that are typically cooked in microwave ovens and so experiences similar dielectric heating effects when exposed to microwave electromagnetic radiation.
Frozen dinners, pies, and microwave popcorn bags often contain a susceptor made from thin aluminium film in the packaging or included on a small paper tray. The metal film absorbs microwave energy efficiently and consequently becomes extremely hot and radiates in the infrared, concentrating the heating of oil for popcorn or even browning surfaces of frozen foods. Heating packages or trays containing susceptors are designed for a single use and are then discarded as waste.
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.
Consider both a microwave's dimensions and capacity as you shop. If you’re looking for an OTR or built-in model, it’s important to choose the proper size for the space, especially if you’re replacing an existing microwave. Also, make sure to check that the door has clearance to open. You have more leeway if you’re buying a countertop model, but it’s still important to measure that area in your kitchen.
When shopping for a new countertop microwave, make sure to look for a microwave with adjustable heat settings: while most microwave tasks are performed on “high,” lower power levels are usually built-in to defrost frozen foods or tackle delicate tasks like softening butter or melting chocolate (one of our favorite uses: it’s quicker and less likely to scorch if you look away for a second).
It’s a good idea to clean your microwave regularly, even if you clean up spills or splatters here and there. To clean the inside, heat a microwave-safe bowl filled with water and a tablespoon of vinegar (white or apple cider will work) for several minutes. You want the inside to get steamy without the bowl of water to boiling over. Let the mixture cool for a few minutes before opening the door. Then, wipe the inside clean with a paper towel or use an abrasive sponge for any stuck-on food. Remove the turntable and either wash it by hand or in the dishwasher. Use an all-purpose cleaner for the exterior, but spray onto a paper towel or sponge first—not directly onto the microwave—to avoid it getting into the venting system. You should also avoid using bleach in your microwave.
This GE microwave oven with a 16-inch turntable proves you don't need to spend a bundle to get perfectly "baked" potatoes, steamed broccoli, or evenly heated mac 'n cheese. Thanks to a smooth control panel with lettering that contrasts well with the background, it's super easy to read the display and wipe it clean. If stainless steel isn't your style, this model also comes in black and white. 
Due to this phenomenon, microwave ovens set at too-high power levels may even start to cook the edges of frozen food while the inside of the food remains frozen. Another case of uneven heating can be observed in baked goods containing berries. In these items, the berries absorb more energy than the drier surrounding bread and cannot dissipate the heat due to the low thermal conductivity of the bread. Often this results in overheating the berries relative to the rest of the food. "Defrost" oven settings either use low power levels or turn the power off and on repeatedly - designed to allow time for heat to be conducted within frozen foods from areas that absorb heat more readily to those which heat more slowly. In turntable-equipped ovens, more even heating will take place[citation needed] by placing food off-centre on the turntable tray instead of exactly in the centre, so that no part of the food item will be continuously unheated by the center "dead zone".
Microwaves generated in microwave ovens cease to exist once the electrical power is turned off. They do not remain in the food when the power is turned off, any more than light from an electric lamp remains in the walls and furnishings of a room when the lamp is turned off. They do not make the food or the oven radioactive. Compared to conventional cooking, the nutritional content of some foods may be altered differently, but generally in a positive way by preserving more micronutrients - see above. There is no indication of detrimental health issues associated with microwaved food.[66]
The most important way to ensure that your microwave lasts is to avoid slamming the door. That’s because microwaves have a dual kill switch in the latch to make it impossible for the microwave to turn on if the door is open or even compromised. That’s a good thing—but it means that the latch is a vulnerable point of potential failure. Do yourself a favor and be gentle with it.

It is possible for metal objects to be microwave-oven compatible, although experimentation by users is not encouraged. Microwaving an individual smooth metal object without pointed ends, for example, a spoon or shallow metal pan, usually does not produce sparking. Thick metal wire racks can be part of the interior design in microwave ovens (see illustration). In a similar way, the interior wall plates with perforating holes which allow light and air into the oven, and allow interior-viewing through the oven door, are all made of conductive metal formed in a safe shape.


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.
It’s a good idea to clean your microwave regularly, even if you clean up spills or splatters here and there. To clean the inside, heat a microwave-safe bowl filled with water and a tablespoon of vinegar (white or apple cider will work) for several minutes. You want the inside to get steamy without the bowl of water to boiling over. Let the mixture cool for a few minutes before opening the door. Then, wipe the inside clean with a paper towel or use an abrasive sponge for any stuck-on food. Remove the turntable and either wash it by hand or in the dishwasher. Use an all-purpose cleaner for the exterior, but spray onto a paper towel or sponge first—not directly onto the microwave—to avoid it getting into the venting system. You should also avoid using bleach in your microwave.

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.
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