microwave oven (also commonly referred to as microwave ) is an electric oven that heats and cooks food by exposing it to electromagnetic radiation within the microwave frequency range. It induces polar molecules in the food to spin and generates heat energy in a process known as dielectric heating. Microwave heats food quickly and efficiently because excitation is fairly uniform beyond 25-38 mm (1-1.5 inches) from food items containing high and homogeneous water; food is more evenly distributed as is common in other cooking techniques.
The development of the cavity magnetron in the UK allows the production of electromagnetic waves of fairly small wavelengths (microwaves). American engineer Percy Spencer is generally credited with inventing modern microwave ovens after World War II from radar technology developed during the war. Named "Radarange", it was first sold in 1946. Raytheon then licensed its patent for a home microwave oven first introduced by Tappan in 1955, but these units are still too large and expensive for public home use. The desk microwave oven was first introduced in 1967 by Amana Corporation, and its use has spread to commercial and residential kitchens worldwide. In addition to its use in cooking food, this type of microwave oven is used for heating in many industrial processes.
Microwave ovens are common and popular kitchen utensils for reheating pre-cooked food and cooking a variety of foods. They are also useful for the rapid heating of groceries that are slowly prepared, which can be easily burned or turned back when cooked in a conventional skillet, such as hot butter, fat, chocolate or porridge. Unlike conventional ovens, microwave ovens are usually not directly chocolate or caramel foods, as they rarely reach the temperature required to produce Maillard reactions. Exceptions occur in rare cases where the oven is used to heat cooking oil and other very oily items (such as bacon), which reach a much higher temperature than boiling water.
Microwave ovens have a limited role in professional cooking, since the boiling-range temperature of the microwave will not produce scented chemical reactions that fry, brown, or grill at higher temperatures. However, additional heat sources may be added to the microwave oven.
Video Microwave oven
History
Initial development
Exploitation of high frequency radio waves for heating materials was made possible by the development of vacuum tube radio transmitters around 1920. In 1930 the application of shortwave for heating human tissue has evolved into diathermy medical therapy. At the 1933 Chicago World Show, Westinghouse demonstrated cooking meals between two metal plates connected to a 10 kW, 60 MHz shortwave transmitter. The Westinghouse team, led by I. F. Mouromtseff, found that foods such as steak and potatoes can be cooked in minutes.
The US patent application of 1937 by Bell Laboratories states:
"The present invention relates to a heating system for dielectric materials and the object of the present invention is to heat the materials uniformly and substantially simultaneously throughout their mass... It has been proposed therefore to heat the materials simultaneously throughout the mass they are using dielectrics, losses are generated in them when they experience high voltage, high frequency field. "
However, low-frequency dielectric heating, as described in the aforementioned patents, is (like induction heating) the electromagnetic heating effect, the result of so-called near field effects that exist in a small electromagnetic cavity compared to the wavelength of the electromagnetic field. This patent proposes radio frequency heating, at 10 to 20 megahertz (wavelength 15 to 30 meters). The warming of microwaves that have relatively small wavelengths to the cavities (as in modern microwave ovens) is due to the "far-field" effect caused by classical electromagnetic radiation which describes the free dissemination of light and microwave away from the source.. Nevertheless, the main heating effects of all types of electromagnetic fields on both radio and microwave frequencies occur through the dielectric heating effect, since the polarized molecules are affected by rapid alternating electric fields.
Magnetron cavity
The invention of the magnetron cavity allows the production of electromagnetic waves of fairly small wavelengths (microwaves). Magnetron was originally an important component in the development of short wavelength radar during World War II. In 1937-1940, a multi-cavity magnetron was built by British physicist Sir John Turton Randall, FRSE, along with a team of British colleagues, for the installation of British and American military radar in World War II. Higher-powered microwave generators working on shorter wavelengths are required, and in 1940, at the University of Birmingham in England, Randall and Harry Boot produced a working prototype. They found a valve that could spew microwave radio energy pulses at a wavelength of 10cm, an unprecedented discovery.
Sir Henry Tizard went to the US in late September 1940 to offer magnetrons in return for their financial and industrial assistance (see Tizard Mission). An early version of 6 kW, built in England by General Electric Company Research Laboratories, Wembley, London, was awarded to the US government in September 1940. The magnetron was later described by the American historian James Phinney Baxter III as "[t] he most precious cargo ever brought to our beach ". Contract awarded to Raytheon and other companies for mass production of magnetron.
Discovery
In 1945, a special heating effect of high-energy microwave rays was accidentally discovered by Percy Spencer, an American self-taught engineer from Howland, Maine. Hired by Raytheon at the time, he realized that the microwaves from the active radar he was working on began to melt the chocolate bars in his pocket. The first food cooked with Spencer's microwave was popcorn, and the second was an egg, which exploded on the faces of one of the experimenter. To verify its findings, Spencer invented a high-density electromagnetic field by powering the microwave from magnetrons into a non-removable metal box. When food is placed in boxes with microwave energy, food temperature rises rapidly. On October 8, 1945, Raytheon applied for a US patent for the microwave cooking process of Spencer, and an oven that heats food using microwave energy from a magnetron was immediately placed in a Boston restaurant for testing.
Commercial availability
In 1947, Raytheon built "Radarange", the first commercially available microwave oven. It's almost 1.8 meters (5Ã, ft. 11Ã), tall, weighs 340 kilograms (Â £ 750) and costs around US $ 5,000 ($ 55,000 in 2017 dollars) each. It consumes 3 kilowatts, about three times more than the current microwave oven, and is cooled with water. The name is the winning entry in the employee contest. The early Radarange was installed (and fixed) in the NS Savannah nuclear-powered passenger/cargo ship. The initial commercial model introduced in 1954 consumed 1.6 kilowatts and sold for US $ 2,000 to US $ 3,000 ($ 18,000 to $ 27,000 in dollars 2017). Raytheon licensed its technology to the Tappan Stove company in Mansfield, Ohio in 1952. They tried to market a large 220-volt wall unit as a home microwave oven in 1955 for US $ 1,295 ($ 12,000 in 2017 dollars), but did not sell well. In 1965, Raytheon acquired Amana. In 1967, they introduced the first popular home model, the Radarange table, for US $ 495 ($ 4,000 in 2017 dollars).
In the 1960s, Litton purchased the assets of Franklin Manufacturing Studebaker, which has produced magnetrons and built and sold microwave ovens similar to Radarange. Litton then developed a new configuration of the microwave: the short and wide shape that is now common. Magnetron feed is also unique. This produces an oven that can survive without a load condition: an empty microwave oven where nothing absorbs microwaves. The new oven is featured at a trade show in Chicago, and helps start a fast growth market for home microwave ovens. The sales volume of 40,000 units for the US industry in 1970 grew to one million in 1975. Rapid market penetration in Japan, because re-engineered magnetron allows cheaper units. Several other companies joined the market, and for the moment most of the systems were built by defense contractors, most familiar with magnetrons. Litton is very well known in the restaurant business.
Residential use
Previously only found in large industrial applications, microwave ovens are increasingly becoming standard housing kitchen fixtures in the developed world. By 1986, about 25% of households in the US had microwave ovens, up from only about 1% in 1971; The US Bureau of Labor Statistics reports that more than 90% of American households have microwave ovens in 1997. In Australia, a market research study in 2008 found that 95% of kitchens contained microwave ovens and 83% of them were used daily. In Canada less than 5% of households have microwave ovens in 1979, but more than 88% of households have one in 1998. In France, 40% of households have microwave ovens in 1994, but that number has increased to 65%. in 2004.
Adoption is slower in less developed countries, as households with disposable income concentrate on more important household appliances such as refrigerators and ovens. In India, for example, only about 5% of households have microwaves by 2013, well behind the fridge with 31% ownership. However, microwave ovens are gaining in popularity. In Russia, for example, the number of households with microwaves grew from nearly 24% in 2002 to nearly 40% in 2008. Nearly twice as many households in South Africa had microwaves in 2008 (38.7%) as in in 2002 (19.8%). Ownership of microwave in Vietnam reached 16% of households in 2008 - compared to 30% ownership of refrigerator; this rate rose significantly from the 6.7% ownership of the microwave in 2002, with 14% ownership for the refrigerator that year.
Maps Microwave oven
Principles
The microwave oven heats the food by passing microwave radiation through it. Microwaves are a form of non-ionizing electromagnetic radiation with a higher frequency than ordinary radio waves but lower than infrared light. Microwave ovens use frequencies in one of the ISM (industrial, scientific, medical) bands, provided for this use, so as not to interfere with other vital radio services. Consumer ovens typically use 2.45 gigahertz (GHz) - This is a 12.2 cm (4.80 inch) wavelength - while large industrial/commercial ovens often use 915 megahertz (MHz) - 32.8 centimeters (12.9 inches ). Water, fats, and other substances in food absorb energy from microwaves in a process called dielectric heating. Many molecules (such as those from water) are electric dipoles, meaning that they have a partial positive charge at one end and a partial negative charge on the other, and therefore rotate as they try to adjust to the alternating electric field of the microwaves. Spin molecules hit other molecules and make them move, thus spreading energy. This energy, dispersed as molecular rotation, vibration and/or translation in solids and liquids raises food temperature, in a process similar to heat transfer through contact with hotter bodies.
Microwave heating is more efficient in liquid water than in frozen water, where the molecular movement is more limited. Dielectric heating of liquid water is also dependent on temperature: At 0 ° C, the largest dielectric loss at the field frequency is about 10 GHz, and for higher water temperatures at higher terrain frequencies.
Compared with liquid water, microwave heating is less efficient in fats and sugars (which have smaller molecular dipole moments). Sugars and triglycerides (fats and oils) absorb microwaves due to the dipole moment of the hydroxyl group or ester group. However, due to lower specific heat capacities of fats and oils and higher evaporation temperatures, they often reach much higher temperatures in microwave ovens. This can cause temperatures in oils or fatty foods such as meat well above the boiling point of water, and high enough to induce browning reactions, many by conventional roasting (roasting), sweating, or deep fat frying. Foods high in water content and with less oil rarely exceed the temperature of boiling water.
Microwave heating can cause localized thermal runaway in some materials with low thermal conductivity which also has a dielectric constant that increases with temperature. An example is glass, which can show thermal runs in the microwave to the melting point when heated. In addition, microwaves can melt certain rock types, producing small amounts of molten rock. Some ceramics can also be melted, and can even become apparent after cooling. Thermal runaway is more common than electrically conductive liquids such as saltwater.
A common misconception is that microwave ovens cook food "from the inside out", which means from the center of the entire mass of food outwards. This idea arises from the observed warming behavior if the water absorbent layer lies below the absorbent absorbent layer on the food surface; in this case, the deposition of heat energy in the diet may exceed those on the surface. This can also occur if the inner layer has a lower heat capacity than the outer layer causing it to reach higher temperatures, or even if the inner layer is more thermally conductive than the outer layers so it feels hotter despite having lower temperatures. However, in many cases, with uniform or fairly homogeneous food items, microwaves are absorbed in the outer layer of goods at the same level as the inner layers. Depending on the moisture content, the depth of the initial heat deposition may be a few centimeters or more with a microwave oven, in contrast to grilling/baking (infrared) or heating convection - a method that stores thin heat on the food surface. Penetration of microwave depth depends on food composition and frequency, with lower microwave frequency (longer wavelength) penetrating further.
Heating efficiency
The microwave oven converts most of its electrical input into microwave energy. An average consumer microwave oven consumes 1100 W of electricity in generating 700 W of microwave power, an efficiency of 64%. Another 400 W is dissipated as heat, mostly in a magnetron tube. The wasted heat, along with the heat from the microwaveed product, runs out as warm air through the cooling vents. Additional power is used to operate the lamps, AC power transformers, magnetron cooling fans, food turntable motors and control circuits, although the power consumed by electronic control circuits from modern microwave ovens is negligible (1% of input power) during cooking.
Components
Microwave ovens consist of:
- High voltage power source, usually a simple transformer or an electronic power converter, which passes energy to a magnetron
- a high voltage capacitor connected to magnetron, transformer and through diode to chassis
- magnetron cavity, which converts high-voltage electrical energy into microwave radiation
- magnetron control circuit (usually with microcontroller)
- shortwave (to combine the microwave power of the magnetron into the cooking room)
- metal cooking room
- a swivel or metal waveguide that drives a fan.
- control panel
In most ovens, the magnetron is driven by a linear transformer that can only be fully activated or disabled. (One variant of GE Spacemaker has two taps on the primary transformer, for high and low power modes.) Usually the power level selection does not affect the intensity of microwave radiation; on the contrary, the magnetron is recycled and switched off every few seconds, thereby changing the large-scale duty cycle. The newer model uses an inverter power supply that uses pulse-width modulation to provide continuous heating effectively at reduced power settings, so that the food is heated more evenly at a given power level and can be heated more quickly without being damaged. with uneven heating.
The microwave frequencies used in microwave ovens are selected based on regulatory and cost restrictions. The first is that they must be in one of the industrial, scientific, and medical (ISM) frequency bands set aside for unlicensed purposes. For home use, 2.45 GHz has an advantage over 915 MHz because 915 MHz is only the ISM band in Region 2 ITU while 2.45 GHz is available worldwide. Three additional ISM bands are present in microwave frequency, but not used for microwave cooking. Two of them are centered on 5.8 GHz and 24.125 GHz, but are not used for microwave cooking because of the very high electricity generation costs of this frequency. The third, centered on 433.92 MHz, is a narrow band that will require expensive equipment to generate enough power without creating any outside interference bands, and is only available in some countries.
The cooking room is similar to Faraday's cage to prevent waves from coming out of the oven. Although there is no continuous metal-to-metal contact around the edges of the door, the choke connection on the edge of the door acts like a metal-to-metal contact, at microwave frequency, to prevent leakage. The oven door usually has a window for easy viewing, with a conductive mesh layer some distance away from the outer panel to keep the shield. Since the perforation size in the net is much less than the microwave wavelength (12.2 cm to the usual 2.45 GHz), microwave radiation can not pass through the door, while visible light (with a much shorter wavelength) can.
Control panel
Modern microwave ovens use either an analog dial-type timer or a digital control panel for operation. The control panel displays LEDs, liquid crystals or vacuum fluorescent displays, in 90s brands such as Panasonic and GE began offering models with rolling text display showing cooking instructions, numeric keypad to include cooking times, power level selection features, and other possible functions such as liquefaction arrangements and preprogrammed settings for different types of food, such as meat, fish, poultry, vegetables, frozen vegetables, frozen dinners, and popcorn. Warnings that sound like bells or pagers are usually there to indicate that the cooking is done.
Microwave control panels are often considered weird to use and are often used as examples for user interface design.
Variants and accessories
The variant of conventional microwave is microwave convection. Convection microwave ovens are a combination of standard microwave and convection ovens. This allows the food to be cooked quickly, but browned or crisp, as from a convection oven. Convection microwaves are more expensive than conventional microwave ovens. Some convective microwave waves - which have an open heating element - can generate smoke odor and burn when the food spatter from previous microwave usage is simply burned from the heating element.
In 2000, several manufacturers began offering high-power quartz halogen lamps to their convection microwave models, marketing them under names such as "Speedcook", "Advantium", "Lightwave" and "Optimawave" to emphasize their ability to cook food quickly and well. brownish. Bulbs heat up the food surface with infrared (IR) radiation, a brownish surface like in a conventional oven. Chocolate foods are also heated by microwave radiation and heated through conduction by contact with hot air. The IR energy that is sent to the outer surface of the food by the lamp is enough to start the caramelization of chocolate in the diet consisting mainly of carbohydrates and Maillard's reaction in the diet consists primarily of proteins. The reactions in these foods produce a texture and flavor similar to that usually expected from conventional cooking ovens rather than boiled and steamed flavors cooked in microwaves that tend to be made.
To help with browning, sometimes used trays of decorate accessories, usually consisting of glass or porcelain. It makes crispy food by oxidizing the top layer until it turns to brown. Ordinary plastic cookware is not suitable for this purpose because it can melt.
Frozen dinners, pies, and microwave popcorn bags often contain susceptor made of thin aluminum film in packaging or included on a small paper tray. Metallic films absorb microwave energy efficiently and consequently become very hot and radiating in the infrared, concentrating heating oil for popcorn or even brown frozen food surfaces. Heating or tray packs containing susceptor are designed to be disposable and then disposed of as waste.
Heating characteristics
Microwave ovens produce heat directly in the food, but apart from the common misconception that cooking microwave food from the inside out, 2.45 Ghz microwave can only penetrate about 1 centimeter (0.39 inches) into most food. The thicker inner parts of the food are mainly heated by heat from 1 centimeter (0.39 inches) outside.
Uneven warming in microwave foods can be partly due to uneven distribution of microwave energy in the oven, and partly because of the different energy absorption rates in different parts of the food. The first problem is reduced by the stirrer, a type of fan that reflects microwave energy to various parts of the oven as it rotates, or by a turntable or carousel that alters food; turntables, however, can still leave the premises, like the center of the oven, which receives an uneven energy distribution. The location of dead points and hot spots in the microwave can be mapped by placing a piece of wet thermal paper inside the oven. When the water-saturated paper is exposed to microwave radiation it becomes hot enough to cause the dye to be released which will provide a visual representation of the microwaves. If several layers of paper are built in the oven with sufficient distance between them, a three-dimensional map can be made. Many store receipts are printed on thermal paper that makes this easy to do at home.
The second problem is due to the composition of food and geometry, and must be handled by the cook, by regulating the food so as to absorb the energy evenly, and periodically testing and protecting the overheated food parts. In some materials with low thermal conductivity, where dielectric constant increases with temperature, microwave heating can cause local thermal runaway. Under certain conditions, the glass can show thermal runaway in the microwave to the melting point.
Because of this phenomenon, microwave ovens set at too high a power level may even start cooking the edges of frozen food while the inside of the food remains frozen. Other cases of uneven warming can be observed in baked goods containing berries. In this item, berries absorb more energy than the surrounding dry bread and can not dissipate heat due to the low thermal conductivity of the bread. Often this causes excessive heat relative to food scraps. The "Disbursement" oven setting uses a low power level designed to allow time for heat to be carried in frozen foods from areas that absorb heat more easily for those who are hotter slower. In an oven equipped with a turntable, more heating will occur by placing food outside the center on a turntable tray, rather than right in the middle, assuming the food items placed cover less than the "dead zone" center.
There is a microwave oven in the market that allows full power liquefaction. They do this by exploiting the properties of the LNO mode of electromagnetic radiation. The full liquefaction of NGOs may actually achieve more results than slow disbursements.
Microwave heating can be intentionally uneven by design. Some microwavable packages (especially pies) may include materials containing ceramic or aluminum flakes, which are designed to absorb microwaves and heats up, which helps in making bread or crust by storing more energy in this area. Ceramic patches affixed to cardboard are positioned next to food, and are usually blue or pale gray, usually making them easily identifiable; the cardboard sleeve included with Hot Pockets, which has a silver surface on the inside, is a good example for such packaging. The cardboard packaging with the microwave can also contain the above ceramic patch that works in the same way. The technical term for such a microwave-absorbent patch is susceptor.
Effects on food and nutrition
Any form of cooking will destroy some nutrients in the food, but the main variable is how much water is used in cooking, how long the food is cooked, and at what temperature. Nutrition is primarily lost due to leaching into boiling water, which tends to make microwave cooking healthier, given the shorter cooking times required. Like other heating methods, microwaves convert vitamin B 12 from active form to inactive; the number of conversions depends on the temperature reached, as well as the cooking time. Boiled food reaches a maximum of 100 Ã, Â ° C (212Ã, Â ° F) (boiling point of water), whereas microwaved food can become hotter locally than this, which causes faster damage than vitamin B 12 . The higher loss rate is partially offset by a shorter cooking time.
Spinach retains almost all of its folate when cooked in a microwave; in comparison, it loses about 77% when boiled, eliminating nutrients. Microwaved meats have lower carcinogenic nitrosamine levels than conventionally cooked flesh. Steamed vegetables tend to retain more nutrients when microwaved than when cooked on a stove. Microwave blanching is 3-4 times more effective than boiling boiling water in maintaining water soluble vitamin folic acid, thiamine and riboflavin, with the exception of ascorbic acid, which is 28.8% lost (vs. 16% with blanching water).
Microwaving human milk at high temperatures is not recommended as it causes a sharp decline in the activity of anti-infective factors.
Benefits and features of Satefy
All microwaves use a timer for cooking time, at the end of cooking time, the oven will turn itself off.
Microwave heats up hot food without becoming hot by themselves. Take a pot from the stove, except it is an induction cooker, leave a dangerous heating element or trivet that will remain hot for some time. Likewise, when taking a casserole from a conventional oven, one's arm is exposed to a very hot wall from the oven. Microwave ovens do not cause this problem.
Food and cookware taken from microwave ovens are rarely hotter than 100 Ã, Â ° C (212Ã, Â ° F). Cookware used in microwave ovens is often much colder than food because cookware is transparent to microwaves; microwave heats food directly and cookware indirectly heated by food. Food and cookware from a conventional oven, on the other hand, has the same temperature as the rest of the oven; the typical cooking temperature is 180 ° C (356 ° F). That means conventional stoves and ovens can cause more serious burns.
Lower cooking temperatures (boiling point of water) are a significant safety benefit compared to roasting in an oven or frying, as it eliminates the formation of tars and charcoal, which are carcinogenic. Microwave radiation also penetrates deeper than direct heat, so the food is heated by its own internal water content. Conversely, direct heat can burn the surface while the inside is still cold. Pre-heating food in a microwave oven before putting it into a grill or pot reduces the time it takes to heat the food and reduce the formation of carcinogenic char. Unlike frying and baking, microwaves do not produce acrylamide in potatoes, but unlike frying, it's only limited effectiveness in reducing glycoalkaloid levels (ie solanine). Acrylamide has been found in other microwave products such as popcorn.
Use kitchen sponge scrubber
The study has investigated the use of microwaves to clean the completely metallic non-metallic sponge that has been completely moistened. A 2006 study found that microwave-damped sponges for two minutes (at 1000 watts) produced 99% of coliform fistula, E. coli and MS2. Bacillus cereus spores are killed in 4 minutes of microwaves.
A 2017 study was less affirmative: about 60% of the germs were killed but the remaining quickly colonized the sponge.
Hazard
High temperature
Water and other homogeneous liquids can be heated when heated in a microwave oven in a container with a smooth surface. That is, the liquid reaches a temperature just above its normal boiling point without the bubbles formed in the liquid. The boiling process can be started explosively when the fluid is disturbed, such as when the user holds the container to remove it from the oven or while adding solid materials such as cream or powdered sugar. This can cause spontaneous boil (nucleation) which may be malignant enough to remove the boiling liquid from the container and cause severe burns.
Closed containers, such as eggs, can explode when heated in a microwave oven due to increased pressure from steam. Fresh egg yolk outside the shell will also explode, as a result of super warming. Isolation of plastic foams of all types generally contain closed air bags, and is generally not recommended for use in microwaves, because airbags explode and foam (which can be toxic if consumed) can melt. Not all plastics are microwave-safe, and some plastics absorb microwaves to the point that they can become dangerous heat.
Products that are heated for too long can burn. Although this is inherent in all forms of cooking, the quick and unattended cooking of microwave ovens produces additional hazards.
Metal objects
Any metal or conductive object placed into the microwave will act as an antenna to some degree, producing an electric current. This causes the object to act as a heating element. These effects vary with the shape and composition of the object, and are sometimes used for cooking.
Any object containing a pointed metal can make an electric arc (spark) during a microwave. These include cutlery, tangled aluminum foil (although some foils are used in microwave safely, see below), bonds containing metal wires, metal wire grips on paper, food containers taken out of China, or almost any metal molded into a poorly conductive foil or thin wire; or to a pointy shape. Forks are a good example: the fork tone responds to an electric field by generating a high concentration of electrical charge at the end. This has the effect of exceeding the air dielectric division, about 3 megavolts per meter (3ÃÆ' â € "10 6 V/m). Air forms a conductive plasma, which is seen as a spark. Plasmas and tines can form conductive loops, which may be more effective antennas, resulting in longer sparks. When dielectric damage occurs in the air, some ozone and nitrogen oxides are formed, both of which are unhealthy in large quantities.
It is possible for metal objects to be microwave-compatible ovens, although user experiments are not recommended. Conducting microwaves on individual fine metal objects without pointed tips, for example, a spoon or a shallow metal pans, usually does not produce sparks. Thick metal wire racks can be part of interior design in a microwave oven (see illustration). In the same way, the interior wall plates with holes that allow light and air into the oven, and allow the interior view through the oven door, all made of conductive metal formed in a safe form.
The effects of thin-metal microwave films can be seen clearly on Compact Discs or DVDs (especially types of pressed factories). Microwaves induce an electric current in a metal film, which heats up, melts the plastic inside the disk and leaves the scent pattern of concentric and visible scent. Similarly, porcelain with a thin metal film can also be destroyed or damaged by a microwave. Aluminum foil is thick enough to be used in a microwave oven as a shield against warming food parts, if the foil is not too curved. When wrinkles, aluminum foil is generally unsafe in the microwave, because foil manipulation causes sharp turns and gaps that invite sparks. The USDA recommends that aluminum foil be used as a partial food shield in a microwave cooking cover of no more than a quarter of the food object, and is carefully mashed to eliminate the dangers that trigger.
Another danger is the resonance of the magnetron tube itself. If the microwave is run without an object to absorb radiation, a standing wave will form. Energy is reflected back and forth between the tube and the cooking room. This can cause the tubes to burden and burn. High reflectivity can also cause magnetron curves, which may cause failure of primary power fuses, although such causal relationships are not easily formed. Thus, dry food, or food wrapped in non-stick metal, is problematic for excessive reasons, without being a fire hazard.
Certain foods such as wine, if properly arranged, can produce an electric arc. The prolonged array of foods carries the same risk to the arc from other sources as mentioned above.
Some other objects that can do splashes are holographic plastic/thermos prints (like new Starbuck cups) or cups with metal layers. If there is little metal exposed, all of the outermost shell will explode from the object or melt.
The high electric fields generated in the microwave can often be illustrated by placing a radiometer or neon glow-bulb inside the cooking room, creating a luminous plasma inside a low-pressure bulb in the device.
Direct microwave exposure
Direct microwave exposure is generally not possible, because the microwaves emitted by the source in the microwave oven are confined to the oven by the material from which the oven is constructed. Furthermore, the oven is equipped with an excess safety interlock, which removes power from the magnetron if the door is opened. This security mechanism is required by US federal regulations. Tests have demonstrated microwave confinement in commercially available ovens making it almost universal because making routine testing unnecessary. According to the US Center for Food and Drug Administration for Radiological Devices and Health, the US Federal Standard limits the number of microwaves that can leak from the oven throughout its lifetime to 5 milliwatts of microwave radiation per square centimeter around 5 cm (2 in) from the oven surface. This is far below the level of exposure that is currently considered harmful to human health.
The radiation produced by the microwave oven does not ionize. It therefore has no cancer risk associated with ionizing radiation such as X-rays and high-energy particles. Long-term rat studies to assess cancer risk have so far failed to identify any carcinogenicity of radiation radiation 2.45 GHz even with chronic exposure levels (fractions of life span) that are much greater than the possibility of humans to face from the oven that is leaking. However, with the oven door open, radiation can cause damage by heating. Every microwave oven sold has an interlock protector so it can not run when the door is open or unlocked properly.
Microwaves generated in a microwave oven are no longer present when the mains power is turned off. They do not remain in the food when the electricity is off, more than the light from the electric lights remain on the walls and the room furniture when the lights are off. They do not make food or radioactive ovens. Compared with conventional cooking, the nutritional content of some foods can be changed differently, but generally in a positive way by maintaining more micronutrients - see above. There is no indication of any adverse health problems associated with microwave food.
Nevertheless, some cases where people have been exposed to direct microwave radiation, either from accidental tool damage or acts. The common effect of this exposure is physical burns on the body, because human tissue, especially the fat and outer layers, has similar compositions to some foods normally cooked in a microwave oven so that they experience the same dielectric heating effect when exposed to a microwave. electromagnetic radiation.
Chemical exposure
Some magnetrons have ceramic insulators with beryllium oxide (berilia) added. Beryllium in the oxide is a serious chemical hazard if it is destroyed and then inhaled or digested. In addition, berilia are listed as human carcinogens confirmed by IARC; therefore, a broken ceramic insulator or magnetron should not be handled. It is dangerous if the microwave oven is physically damaged, if the insulator is cracked, or when the magnetron is opened and handled, but not during normal use.
The use of unscreened plastic for cooking with microwaves raises the problem of plastic softeners seeping into food, or chemically reacting plastic to microwave energy, by washing by the product into food, indicating that even plastic containers marked "microwave" can still coat plastic by-products into the food.
The plasticizers who receive the most attention are bisphenol A (BPA) and phthalates, although it is unclear whether other plastic components present the risk of toxicity. Other problems include melting and flammability. The issue of alleged release of dioxin into the diet has been rejected as a deliberate red herring disorder from a real security problem.
Some plastic containers and food wrappers are currently specially designed to withstand radiation from microwaves. Products can use the term "microwave safe", can carry microwave symbols (three wave lines, one above the other) or simply give instructions for proper microwave usage. All this is an indication that a product is suitable for microwaves when used in accordance with the instructions given.
Uneven heating
Microwave ovens are often used to heat food scraps, and bacterial contamination can not be suppressed if safe temperatures are not reached, resulting in foodborne diseases, as are all inadequate reheating methods. While microwaves can destroy bacteria and conventional ovens, they do not cook evenly, causing an increased risk that food parts will not reach the recommended temperature.
Interference
Microwave ovens, although protected for security purposes, still emit low microwave radiation. This is not harmful to humans, but can sometimes cause interference on Wi-Fi and Bluetooth and other devices that communicate on 2.45 GHz wavebands; especially from close range.
See also
- Induction cooker
- List of cooking utensils
- List of home appliances
- Microwave Chemicals
- Peryton (astronomy)
- Robert V. Decareau
- Thelma Pressman
References
External links
- AS. Patent 2,495,429 Genuine Percy Spencer patent
- Request a Chemical Archive, Argonne National Laboratory
- Further Reading on the History of Microwaves and Microwave Ovens
- Microwave oven history from American Heritage magazine
- Heat and Microwave Oven, University of New South Wales (including video)
- "Microwave Oven" A brief description of the microwave oven in terms of microwave cavities and waveguides, intended for use in the Electrical Engineering class
Source of the article : Wikipedia
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