"cavity walls to prevent inefficient modes of oscillation. This is called pi-strapping because the two straps lock the phase difference between adjacent cavities at pi radians (180°). The modern magnetron is a fairly efficient device. In a microwave oven, for instance, a 1.1-kilowatt input will generally create about 700 watts of microwave power, an efficiency of around 65%. (The high-voltage and the properties of the cathode determine the power of a magnetron.) Large S band magnetrons can produce up to 2.5 megawatts peak power with an average power of 3.75 kW. Some large magnetrons are water cooled. The magnetron remains"
"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"". Contracts were awarded to Raytheon and other companies for mass production of the magnetron. In 1945, the specific heating effect of a high-power microwave beam was accidentally discovered by Percy Spencer, an American self-taught engineer from Howland, Maine. Employed by Raytheon at the time, he noticed that microwaves from an active radar set he was working on started to melt a chocolate bar he had in his pocket. The first food deliberately cooked with"
"by instruments aboard the Explorer 1 satellite. If one of the poles in the magnetic bottle is reversed, it becomes a biconic cusp, which can also hold charged particles. Biconic cusps were first studied by Harold Grad at the Courant Institute, studies reveal the presence of different types of particles inside a biconic cusp. Magnetic mirror A magnetic mirror, known as a magnetic trap (магнитный захват) in Russia and briefly as a pyrotron in the US, is a type of magnetic confinement device used in fusion power to trap high temperature plasma using magnetic fields. The mirror was one of"
"egg was placed in a tea kettle, and the magnetron was placed directly above it. The result was the egg exploding in the face of one of his co-workers, who was looking in the kettle to observe. Spencer then created the first true microwave oven by attaching a high density electromagnetic field generator to an enclosed metal box. The magnetron emitted microwaves into the metal box blocking any escape, allowing for controlled and safe experimentation. He then placed various food items in the box, while observing effects and monitoring temperatures. Raytheon filed a patent on October 8, 1945 for a"
"Refrigerator magnet A refrigerator magnet or fridge magnet is an ornament, often whimsical, attached to a small magnet, which is used to post items such as shopping lists, child art or reminders on a refrigerator door, or which simply serves as decoration. Refrigerator magnets come in a wide variety of shapes and sizes, and may have promotional messages placed on them. Refrigerator magnets are popular souvenir and collectible objects. The first fridge magnets were cylindrical or solid rectangular magnets. Later, a flexible magnet was developed, composed of a high-coercivity ferromagnetic compound (usually ferric oxide) mixed with a plastic binder. This"
"human carcinogen by the IARC; therefore, broken ceramic insulators or magnetrons should not be directly handled. All magnetrons contain a small amount of thorium mixed with tungsten in their filament. While this is a radioactive metal, the risk of cancer is low as it never gets airborne in normal usage. Only if the filament is taken out of the magnetron, finely crushed, and inhaled can it pose a health hazard. Cavity magnetron The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series"
"Magnet A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets. A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called"
"fridge magnets in Europe at that time, over 2000. As of January 2016 he had a collection of over 4500. He was again interviewed by the BBC and ITV during 2017. In February 2018, whilst on holiday in Sri Lanka, his 104th country, Tony's collection surpassed 5,000 magnets. Refrigerator magnets are also popular as crafts projects. Refrigerator magnet A refrigerator magnet or fridge magnet is an ornament, often whimsical, attached to a small magnet, which is used to post items such as shopping lists, child art or reminders on a refrigerator door, or which simply serves as decoration. Refrigerator magnets"
"at a former girls' school, Leeson House, outside Langton Matravers. A new lab had to be constructed on-site causing further delays, but by the late summer of 1940 the magnetron system was effectively operational at the new site. Meanwhile, the Army had been very impressed with the performance of the 25 cm experimental sets and became interested in using it as a range finder in a Gun Laying radar. Operators would point the radar at targets indicated to them by search radars, and from then on the radar information would be fed to the analogue computers that aimed the guns."
"he had invented. During his career in electronics he was the author or coauthor of 72 technical publications and was awarded 94 patents. Albert W. Hull Albert Wallace Hull (19 April 1880 – 22 January 1966) is an American physicist and electrical engineer who made contributions to the development of vacuum tubes, and invented the magnetron. He was a member of the National Academy of Sciences. He was born on 19 April 1880 in Southington, Connecticut. He majored in Greek and after taking one undergraduate course in physics, graduated from Yale University. He taught languages at The Albany Academy before"
"perhaps a meter across, or smaller. Initially, most work with the magnetron was focused on airborne roles, where it's small size was an enormous advantage. However, as the winds of war changed, there was increasing demand for a new anti-aircraft radar that could replace the existing GL's with something that was far more practical, and in particular, much more mobile. In November 1940 the magnetron had been demonstrated to Canadian and US researchers, both of whom had begun developing their own versions. After some initial work, the three countries agreed that Canada and the UK would work on a simple"
"copper. If an aircraft carrying one were shot down and recovered, there was a very good chance the block would survive, at which point the secret would be revealed to anyone familiar with microwave techniques. This is precisely what occurred on the night of 2/3 March 1943, when the second mission to attempt to use H2S led to one of the Short Stirling bombers carrying it being shot down near Rotterdam. The magnetron was recovered and this ""Rotterdam Gerät"" (gadget, or device) led to the rapid formation of a study group to exploit it. The group first met at the"
"and found the Germans were using pulse modulation at VHF with great success. When he returned to Japan, he produced a prototype pulse magnetron with 2 kW in October 1941. This was then widely deployed. In the post-war era the magnetron became less widely used in the radar role. This was because the magnetron's output changes from pulse to pulse, both in frequency and phase. This makes the signal unsuitable for pulse-to-pulse comparisons, which is widely used for detecting and removing ""clutter"" from the radar display. The magnetron remains in use in some radars, but has become much more common"
"Magnetic mirror A magnetic mirror, known as a magnetic trap (магнитный захват) in Russia and briefly as a pyrotron in the US, is a type of magnetic confinement device used in fusion power to trap high temperature plasma using magnetic fields. The mirror was one of the earliest major approaches to fusion power, along with the stellarator and z-pinch machines. In a magnetic mirror, a configuration of electromagnets is used to create an area with an increasing density of magnetic field lines at either end of the confinement area. Particles approaching the ends experience an increasing force that eventually causes"
"provides the microwave field that is passed through a waveguide to the lighting cavity containing the light-emitting substance (e.g., sulfur, metal halides, etc.). Although efficient, these lamps are much more complex than other methods of lighting and therefore not commonly used. More modern variants use HEMTs or GaN-on-SiC power semiconductors to generate the microwaves, which are substantially less complex and can be adjusted to maximize light output using a PID system. In 1910 Hans Gerdien of the Siemens corporation invented a magnetron. In 1912, Swiss physicist Heinrich Greinacher was looking for new ways to calculate the electron mass. He settled"
"A more high-powered microwave generator that worked at shorter wavelengths was needed, and in 1940, at the University of Birmingham in England, Randall and Harry Boot produced a working prototype. They invented a valve that could spit out pulses of microwave radio energy on a wavelength of 10 cm, an unprecedented discovery. 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). An early 6 kW version, built in England by the General Electric Company Research Laboratories, Wembley, London, was given to the U.S."
"Robert N. Hall Robert Noel Hall (December 25, 1919 – November 7, 2016) was an American engineer and applied physicist. He demonstrated the first semiconductor laser and invented a type of magnetron commonly used in microwave ovens. He also contributed to the development of rectifiers for power transmission. Robert N. Hall was born on December 25, 1919 in New Haven, Connecticut. He was first inspired by his inventor uncle, who showed him the wonders of small inventions and experimentation. After long studies at his local library, Hall decided to attempt controlled experiments of his own with his mother's approval. He"
"participants test them using a meter that measures magnetism. They were not able to tell which one had the magnets and which one had the jelly beans through the mattress - the results were the same. This trial was telecast on Channel Nine, and their journalist suggested the name ""Jelly Bean Lady"" which Marron stayed with. Her conclusion that the magnets were just as effective as jelly beans, was an effective way to communicate the results accurately to a non-technical audience, without using jargon about topics such as controls and blinding. She further developed this persona of ""the Jellybean Lady"","
"and Harry Boot developed the cavity magnetron, which made ten-centimetre ( wavelength ) radar a reality. This device, the size of a small dinner plate, could be carried easily on aircraft and the short wavelength meant the antenna would also be small and hence suitable for mounting on aircraft. The short wavelength and high power made it very effective at spotting submarines from the air. To aid Chain Home in making height calculations, at Dowding's request, the Electrical Calculator Type Q (commonly called the ""Fruit Machine"") was introduced in 1940. The solution to night intercepts would be provided by Dr."
"Vacuum tubes can be tested outside of their circuitry using a vacuum tube tester. Most small signal vacuum tube devices have been superseded by semiconductors, but some vacuum tube electronic devices are still in common use. The magnetron is the type of tube used in all microwave ovens. In spite of the advancing state of the art in power semiconductor technology, the vacuum tube still has reliability and cost advantages for high-frequency RF power generation. Some tubes, such as magnetrons, traveling-wave tubes, carcinotrons, and klystrons, combine magnetic and electrostatic effects. These are efficient (usually narrow-band) RF generators and still find"
"University in early 1940 marked a major advance in radar capability. The resulting magnetron was a small device that generated high-power microwave frequencies and allowed the development of practical centimetric radar that operated in the SHF radio frequency band from 3 to 30 GHz (wavelengths of 10 to 1 cm). Centimetric radar enables the detection of much smaller objects and the use of much smaller antennas than the earlier, lower frequency radars. A radar with a wavelength of 2 meters cannot detect objects that are much smaller than 2 meters and requires an antenna whose size is on the order"
"magnetron or a Penning source. A magnetron consists of a central cylindrical cathode surrounded by an anode. The discharge voltage is typically greater than 150 V and the current drain is around 40 A. A magnetic field of about 0.2 tesla is parallel to the cathode axis. Hydrogen gas is introduced by a pulsed gas valve. Caesium is often used to lower the work function of the cathode, enhancing the amount of ions that are produced. For a Penning source, a strong magnetic field parallel to the electric field of the sheath guides electrons and ions on cyclotron spirals from"
"Cavity magnetron The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field while moving past a series of open metal cavities (cavity resonators). Electrons pass by the openings to these cavities and cause radio waves to oscillate within, similar to the way a whistle produces a tone when excited by an air stream blown past its opening. The frequency of the microwaves produced, the resonant frequency, is determined by the cavities' physical dimensions. Unlike other vacuum tubes such as a klystron or a traveling-wave tube (TWT), the"
"magnetron cannot function as an amplifier in order to increase the intensity of an applied microwave signal; the magnetron serves solely as an oscillator, generating a microwave signal from direct current electricity supplied to the vacuum tube. An early form of magnetron was invented by H. Gerdien in 1910. Another form of magnetron tube, the split-anode magnetron, was invented by Albert Hull of General Electric Research Laboratory in 1920, but it achieved only a frequency of 30 kHz. Similar devices were experimented with by many teams through the 1920s and 1930s. Hans Erich Hollmann filed a patent on a design"
"1933 Chicago World's Fair demonstrated cooking meals with a 60 MHz radio transmitter. In 1945 Percy Spencer, an engineer working on radar at Raytheon, noticed that microwave radiation from a magnetron oscillator melted a candy bar in his pocket. He investigated cooking with microwaves and invented the microwave oven, consisting of a magnetron feeding microwaves into a closed metal cavity containing food, which was patented by Raytheon on 8 October 1945. Microwave heating became widely used as an industrial process in industries such as plastics fabrication, and as a medical therapy to kill cancer cells in microwave hyperthermy. The traveling"
"the course of the next few years. His improvements were among those that increased magnetron production to 2,600 per day. For his work, he was awarded the Distinguished Public Service Award by the U.S. Navy. One day while building magnetrons, Spencer was standing in front of an active radar set when he noticed the candy bar he had in his pocket had melted. Spencer was not the first to notice this phenomenon, but he was the first to investigate it. He decided to experiment using food, including popcorn kernels, which became the world’s first microwaved popcorn. In another experiment, an"
"the lamp. The second issue - long life, low cost RF generation has been solved using a combination of a magnetron with a specialized controller. Magnetrons are manufactured in large volumes for use in microwave ovens. They are able to produce RF power at a cost of less than $0.02/W(RF). This is far below any expected solid state chip price for the foreseeable future. Historically, the problem with magnetrons has been their short life. A microwave magnetron has a typical life of approximately 2,000 hours. In cooperation with Dipolar of Sweden, Ceravision has developed a method of extending the life"
"include iron ore (magnetite or lodestone), cobalt and nickel, as well as the rare earth metals gadolinium and dysprosium (when at a very low temperature). Such naturally occurring ferromagnets were used in the first experiments with magnetism. Technology has since expanded the availability of magnetic materials to include various man-made products, all based, however, on naturally magnetic elements. Ceramic, or ferrite, magnets are made of a sintered composite of powdered iron oxide and barium/strontium carbonate ceramic. Given the low cost of the materials and manufacturing methods, inexpensive magnets (or non-magnetized ferromagnetic cores, for use in electronic components such as portable"
"less. There are three main types of magnetometer used to measure magnetic anomalies: In ground-based surveys, measurements are made at a series of stations, typically 15 to 60 m apart. Usually a proton precession magnetometer is used and it is often mounted on a pole. Raising the magnetometer reduces the influence of small ferrous objects that were discarded by humans. To further reduce unwanted signals, they do not carry objects such as keys, knives or compasses. In addition, objects such as motor vehicles, railway lines, and barbed wire fences are avoided. If some such contaminant is overlooked, it often shows"
"summer of 1940, the Tizard Mission brought to America one of the first of the new magnetrons. On October 6, Edward George Bowen, a key developer of RDF at the Telecommunications Research Establishment (TRE) and a member of the mission, demonstrated the magnetron, producing some 15,000 watts (15 kW) of power at 3 GHz, i.e. a wavelength of 10cm. American researchers and officials were amazed at the magnetron, and the NDRC immediately started plans for manufacturing and incorporating the devices. Alfred Lee Loomis, who headed the NDRC Microwave Committee, led in establishing the Radiation Laboratory at MIT as a joint"
"the klystron, a beam of electrons was passed through a metal disk known as a resonator. The mechanical layout of the copper resonator caused it to influence the electrons, speeding them up and slowing them down, releasing microwaves. This was reasonably efficient, and power was limited by the guns. In the case of the magnetron, the resonator was replaced by two metal plates held at opposite charges to cause the alternating acceleration, and the electrons were forced to travel between them using a magnet. There was no real limit to the number of electrons this could accelerate, but the microwave"
"the similarly named American company General Electric), was given to the US government in September 1940. The British magnetron was a thousand times more powerful than the best American transmitter at the time and produced accurate pulses. At the time the most powerful equivalent microwave producer available in the US (a klystron) had a power of only ten watts. The cavity magnetron was widely used during World War II in microwave radar equipment and is often credited with giving Allied radar a considerable performance advantage over German and Japanese radars, thus directly influencing the outcome of the war. It was"
"radar systems, particularly for submarine detection. Raytheon ranked 71st among United States corporations in the value of World War II military production contracts. Raytheon's research on the magnetron tube revealed the potential of microwaves to cook food. In 1945, Raytheon's Percy Spencer invented the microwave oven by discovering that the magnetron could rapidly heat food. In 1947, the company demonstrated the Radarange microwave oven for commercial use. In 1945, the company expanded its electronics capability through acquisitions that included the Submarine Signal Company (founded in 1901), a leading manufacturer of maritime safety equipment. With its broadened capabilities, Raytheon developed the"