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).[7] 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 "[t]he most valuable cargo ever brought to our shores".[9] Contracts were awarded to Raytheon and other companies for mass production of the magnetron.
Another hazard is the resonance of the magnetron tube itself. If the microwave is run without an object to absorb the radiation, a standing wave will form. The energy is reflected back and forth between the tube and the cooking chamber. This may cause the tube to overload and burn out. High reflected power may also cause magnetron arcing, possibly resulting in primary power fuse failure, though such a causal relationship isn't easily established. Thus, dehydrated food, or food wrapped in metal which does not arc, is problematic for overload reasons, without necessarily being a fire hazard.
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Microwave ovens are a common kitchen appliance and are popular for reheating previously cooked foods and cooking a variety of foods. They are also useful for rapid heating of otherwise slowly prepared foodstuffs, which can easily burn or turn lumpy when cooked in conventional pans, such as hot butter, fats, chocolate or porridge. Unlike conventional ovens, microwave ovens usually do not directly brown or caramelize food, since they rarely attain the necessary temperatures to produce Maillard reactions. Exceptions occur in rare cases where the oven is used to heat frying-oil and other very oily items (such as bacon), which attain far higher temperatures than that of boiling water.
Some current plastic containers and food wraps are specifically designed to resist radiation from microwaves. Products may use the term "microwave safe", may carry a microwave symbol (three lines of waves, one above the other) or simply provide instructions for proper microwave use. Any of these is an indication that a product is suitable for microwaving when used in accordance with the directions provided.[71]
Microwave ovens come in a variety of styles to fit all your home decor needs. It doesn’t matter if we are talking about otr microwaves or countertop microwaves. Some are black stainless steel, others are shiny stainless steel finish for the modern kitchen. If you have retro decor, there is also a retro microwave for you. Many people prefer a stainless steel exterior. It is easy to find the right model that blends right into your kitchen and matches your, espresso machines, food processors, coffee makers, air fryers and other appliances. Many of today’s models can even work with other smart home devices if your home is a smart home.
All microwaves use this same core technology, but today, there are many models available that come with a variety of additional features. For instance, many products have pre-programmed settings to cook common foods, as well as various cooking methods, such as steaming and grilling. Depending on what size and features you want, you can spend anywhere from $20 to $2,000 on a new microwave. 
The second problem is due to food composition and geometry, and must be addressed by the cook, by arranging the food so that it absorbs energy evenly, and periodically testing and shielding any parts of the food that overheat. In some materials with low thermal conductivity, where dielectric constant increases with temperature, microwave heating can cause localized thermal runaway. Under certain conditions, glass can exhibit thermal runaway in a microwave to the point of melting.[41]
Wattage is not only about size, but also about how powerful the microwave is. If your microwave has 1,000 watts of power or more, it’s going to be very effective at heating. If it has a lower wattage, you may need to temper your expectations: the best way to microwave a potato, for example, may vary based on wattage, especially if you’re making a big change from your old model to the new one.
What is a microwave ovens role in your home? Do you need the best compact microwave to fit on a tiny counter and travel with you when you switch apartments? Do you need the best built in microwave that works with your oven range? No matter your kitchen appliance situation, if you’re stuck with a clunky, ugly microwave, it’s time to improve your cooking situation.
If you’re a fan of wall ovens, you may also like the look of built-in microwaves, which are designed to be installed flush with a wall or cabinet so you don't have to give up counter space. However, these microwaves are significantly more expensive than other options, starting at around $300. It’s worth noting that some countertop microwaves have optional kits that allow them to be installed as a built-in, so this may be a way to save some money. Additionally, it’s often complicated to install a built-in microwave, especially if you didn’t have one previously. 
Microwave ovens don’t actually deliver heat to a food item the way a conventional oven does (via heated air); they work by using microwave energy to cause the water and other simple molecules in food to rapidly vibrate, which generates internal friction at the molecular level, heating the food from within. That’s why microwave ovens can heat things so quickly, and why they’re so good at steaming vegetables in their own juices—they don’t rely on the slow and uneven process of transferring heat energy from the air, the way a conventional oven does. But the microwaves aren’t delivered evenly, the way heated air in a conventional oven is. That’s why microwave trays rotate: so that, ideally, every section of the food item gets equal treatment. But the world doesn’t operate on ideals, and neither do microwave ovens. Almost inevitably, you’ll get hotter spots near the center of the oven, which may or may not matter depending on the size of the thing you’re microwaving.
A new microwave can provide extra options that you may not have not – including sensors for more accurate cooking times, inverter technology that creates more accurate power levels, and customized cooking menus for the food you love. If you do a lot of cooking, a modern microwave can also serve as an able assistance, with programmable defrosting, butter melting, and warm-up functions that make your cooking projects that much easier. One of these new models may also provide faster cooking times, child locks for great safety, and more consistent cooking/thawing for a variety of foods.
Every microwave oven contains a magnetron, which generates microwaves. Those waves are then guided into the oven’s cavity, where they bounce around, rapidly swinging the polarity of charged molecules in foods (particularly water, fats, and sugars) and generating heat. Metal mesh on the door keeps those large-wavelength microwaves from escaping the metal box and cooking you. (This great video uses a disassembled model to explain further.)
To find the best microwave, we tested 10 microwaves in our Kitchen Appliances and Technology Lab, checking how well they melted cheese, "baked" potatoes, reheated food, defrosted frozen food, popped popcorn, and cooked vegetables. We also looked at their ease of use — controls, opening the doors, view-ability inside, cooking alerts, and cleaning. For models with convection and/or grill capabilities, we tested their ability to roast chicken, bake cake, and broil steak, then noted the surface temperatures. Based on our extensive tests, we've rounded up our top-rated microwaves:
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.[1] 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.
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