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80-670: [REDACTED] Look up WPC in Wiktionary, the free dictionary. WPC may refer to: Events [ edit ] Microsoft Worldwide Partner Conference , an annual conference held by the Microsoft Corporation World Puzzle Championship , an annual international puzzle competition World Policy Conference , an annual conference on global governance Governmental organizations [ edit ] Weather Prediction Center , part of

160-412: A capacitor , with the intervening space as the dielectric . An alternating voltage generated by the transmitter is applied to the transmitting plate, and the oscillating electric field induces an alternating potential on the receiver plate by electrostatic induction , which causes an alternating current to flow in the load circuit. The amount of power transferred increases with the frequency

240-414: A mains power line, which converts the power to a time-varying electromagnetic field, and one or more "receiver" devices which receive the power and convert it back to DC or AC electric current which is used by an electrical load . At the transmitter the input power is converted to an oscillating electromagnetic field by some type of " antenna " device. The word "antenna" is used loosely here; it may be

320-434: A 10 km diameter area corresponds to 750 megawatts total power level. This is the power level found in many modern electric power plants. For comparison, a solar PV farm of similar size might easily exceed 10,000 megawatts (rounded) at best conditions during daytime. Following World War II, which saw the development of high-power microwave emitters known as cavity magnetrons , the idea of using microwaves to transfer power

400-452: A blue laser is diffracted less than a red one. The Rayleigh limit (also known as the Abbe diffraction limit ), although originally applied to image resolution, can be viewed in reverse, and dictates that the irradiance (or intensity ) of any electromagnetic wave (such as a microwave or laser beam) will be reduced as the beam diverges over distance at a minimum rate inversely proportional to

480-893: A charity based in Pittsburgh, Pennsylvania, United States Wildlife Preservation Canada , a wildlife conservation organization Wireless Power & Communication , a privately held company based in Norway Wireless Power Consortium , the business alliance that developed the Qi inductive power standard Women's Political Council , an Alabama-based organization that was part of the Civil Rights Movement Women's Press Collective, an all-woman publisher between 1969 and 1978 founded by Judy Grahn Workingmen's Party of California , an American labor organization World Parkinson Congress ,

560-617: A charity based in Pittsburgh, Pennsylvania, United States Wildlife Preservation Canada , a wildlife conservation organization Wireless Power & Communication , a privately held company based in Norway Wireless Power Consortium , the business alliance that developed the Qi inductive power standard Women's Political Council , an Alabama-based organization that was part of the Civil Rights Movement Women's Press Collective, an all-woman publisher between 1969 and 1978 founded by Judy Grahn Workingmen's Party of California , an American labor organization World Parkinson Congress ,

640-423: A coil of wire which generates a magnetic field , a metal plate which generates an electric field , an antenna which radiates radio waves, or a laser which generates light. A similar antenna or coupling device at the receiver converts the oscillating fields to an electric current. An important parameter that determines the type of waves is the frequency , which determines the wavelength. Wireless power uses

720-430: A commercial product out of his findings but his resonant inductive coupling method is now widely used in electronics and is currently being applied to short-range wireless power systems. Tesla went on to develop a wireless power distribution system that he hoped would be capable of transmitting power long distance directly into homes and factories. Early on he seemed to borrow from the ideas of Mahlon Loomis, proposing

800-472: A current in a conductor loop by a time-varying magnetic flux. Transmission of electrical energy without wires was observed by many inventors and experimenters, but lack of a coherent theory attributed these phenomena vaguely to electromagnetic induction . A concise explanation of these phenomena would come from the 1860s Maxwell's equations by James Clerk Maxwell , establishing a theory that unified electricity and magnetism to electromagnetism , predicting

880-513: A distant fork tuned to the same pitch. Nikola Tesla first discovered resonant coupling during his pioneering experiments in wireless power transfer around the turn of the 20th century, but the possibilities of using resonant coupling to increase transmission range has only recently been explored. In 2007 a team led by Marin Soljačić at MIT used two coupled tuned circuits each made of a 25 cm self-resonant coil of wire at 10 MHz to achieve

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960-399: A few times the diameter of the antenna device D ant . Unlike in a radiative system where the maximum radiation occurs when the dipole antennas are oriented transverse to the direction of propagation, with dipole fields the maximum coupling occurs when the dipoles are oriented longitudinally. In inductive coupling ( electromagnetic induction or inductive power transfer , IPT), power

1040-406: A garage floor or curb would turn a receiver armature in the underside of the vehicle to charge its batteries. It is claimed that this technique can transfer power over distances of 10 to 15 cm (4 to 6 inches) with high efficiency, over 90%. Also, the low frequency stray magnetic fields produced by the rotating magnets produce less electromagnetic interference to nearby electronic devices than

1120-459: A large coil operating in the megavolts range, as well as observations he made of the electronic noise of lightning strikes, led him to conclude incorrectly that he could use the entire globe of the Earth to conduct electrical energy. The theory included driving alternating current pulses into the Earth at its resonant frequency from a grounded Tesla coil working against an elevated capacitance to make

1200-487: A radius of up to 300 kilometers. Capacitive coupling also referred to as electric coupling, makes use of electric fields for the transmission of power between two electrodes (an anode and cathode ) forming a capacitance for the transfer of power. In capacitive coupling ( electrostatic induction ), the conjugate of inductive coupling , energy is transmitted by electric fields between electrodes such as metal plates. The transmitter and receiver electrodes form

1280-450: A receiver. The development of microwave technology during World War II, such as the klystron and magnetron tubes and parabolic antennas , made radiative ( far-field ) methods practical for the first time, and the first long-distance wireless power transmission was achieved in the 1960s by William C. Brown . In 1964, Brown invented the rectenna which could efficiently convert microwaves to DC power, and in 1964 demonstrated it with

1360-700: A set of circuit boards used in pinball machines throughout the 1990s Woman police constable, a former rank in the British police and other commonwealth countries, see History of the Metropolitan Police Service Wood-plastic composite , composite materials made of wood fiber and thermoplastics WPC 56 , a British television drama series A code given to numerous United States Coast Guard cutters William Patrick Corgan Jr. , an American musician and songwriter William Prideaux Courtney , biographer who contributed to

1440-546: A set of circuit boards used in pinball machines throughout the 1990s Woman police constable, a former rank in the British police and other commonwealth countries, see History of the Metropolitan Police Service Wood-plastic composite , composite materials made of wood fiber and thermoplastics WPC 56 , a British television drama series A code given to numerous United States Coast Guard cutters William Patrick Corgan Jr. , an American musician and songwriter William Prideaux Courtney , biographer who contributed to

1520-656: A support organization people with Parkinson's Disease World Peace Council , an anti-war organization based in Athens, Greece World Plumbing Council , an international organization concerned with plumbing standards World Policy Council , a think tank based in Washington, D.C., United States World Powerlifting Congress , an international sports federation World Press Cartoon , a cartoonist organization Other uses [ edit ] Whey concentrate , or whey protein concentrate Williams Pinball Controller ,

1600-544: A support organization people with Parkinson's Disease World Peace Council , an anti-war organization based in Athens, Greece World Plumbing Council , an international organization concerned with plumbing standards World Policy Council , a think tank based in Washington, D.C., United States World Powerlifting Congress , an international sports federation World Press Cartoon , a cartoonist organization Other uses [ edit ] Whey concentrate , or whey protein concentrate Williams Pinball Controller ,

1680-480: A system composed of balloons to suspend transmitting and receiving electrodes in the air above 30,000 feet (9,100 m) in altitude, where he thought the pressure would allow him to send high voltages (millions of volts) long distances. To further study the conductive nature of low pressure air he set up a test facility at high altitude in Colorado Springs during 1899. Experiments he conducted there with

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1760-454: A wire, create time-varying electric and magnetic fields in the space around them. These fields can exert oscillating forces on the electrons in a receiving "antenna", causing them to move back and forth. These represent alternating current which can be used to power a load. The oscillating electric and magnetic fields surrounding moving electric charges in an antenna device can be divided into two regions, depending on distance D range from

1840-441: A wireless lighting system based on near-field inductive and capacitive coupling and conducted a series of public demonstrations where he lit Geissler tubes and even incandescent light bulbs from across a stage. He found he could increase the distance at which he could light a lamp by using a receiving LC circuit tuned to resonance with the transmitter's LC circuit. using resonant inductive coupling . Tesla failed to make

1920-548: Is "transcutaneous" recharging of biomedical prosthetic devices implanted in the human body, such as cardiac pacemakers , to avoid having wires passing through the skin. It is also used to charge electric vehicles such as cars and to either charge or power transit vehicles like buses and trains. However the fastest growing use is wireless charging pads to recharge mobile and handheld wireless devices such as laptop and tablet computers , computer mouse , cellphones , digital media players , and video game controllers . In

2000-458: Is demonstrated to be a function of distance between the source and the receiver devices. In this method, power is transmitted between two rotating armatures , one in the transmitter and one in the receiver, which rotate synchronously, coupled together by a magnetic field generated by permanent magnets on the armatures. The transmitter armature is turned either by or as the rotor of an electric motor , and its magnetic field exerts torque on

2080-617: Is different from Wikidata All article disambiguation pages All disambiguation pages WPC [REDACTED] Look up WPC in Wiktionary, the free dictionary. WPC may refer to: Events [ edit ] Microsoft Worldwide Partner Conference , an annual conference held by the Microsoft Corporation World Puzzle Championship , an annual international puzzle competition World Policy Conference , an annual conference on global governance Governmental organizations [ edit ] Weather Prediction Center , part of

2160-488: Is different from Wikidata All article disambiguation pages All disambiguation pages Wireless-powered communication Wireless power techniques mainly fall into two categories: Near and far field . In near field or non-radiative techniques, power is transferred over short distances by magnetic fields using inductive coupling between coils of wire , or by electric fields using capacitive coupling between metal electrodes . Inductive coupling

2240-438: Is known as wireless powered communication (WPC). When the harvested power is used to supply the power of wireless information transmitters, the network is known as Simultaneous Wireless Information and Power Transfer (SWIPT); whereas when it is used to supply the power of wireless information receivers, it is known as a Wireless Powered Communication Network (WPCN). An important issue associated with all wireless power systems

2320-415: Is limiting the exposure of people and other living beings to potentially injurious electromagnetic fields . The 19th century saw many developments of theories, and counter-theories on how electrical energy might be transmitted. In 1826, André-Marie Ampère discovered a connection between current and magnets. Michael Faraday described in 1831 with his law of induction the electromotive force driving

2400-406: Is open circuited. If the two coils are on the same axis and close together so all the magnetic flux from L 1 {\displaystyle L1} passes through L 2 {\displaystyle L2} , k = 1 {\displaystyle k=1} and the link efficiency approaches 100%. The greater the separation between the coils, the more of the magnetic field from

2480-408: Is proportional to the square of the field strength, the power transferred decreases as ( D range / D ant ) . or 60 dB per decade. In other words, if far apart, increasing the distance between the two antennas tenfold causes the power received to decrease by a factor of 10 = 1000000. As a result, inductive and capacitive coupling can only be used for short-range power transfer, within

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2560-609: Is sufficient that the information can be received intelligibly. In wireless communication technologies only tiny amounts of power reach the receiver. In contrast, with wireless power transfer the amount of energy received is the important thing, so the efficiency (fraction of transmitted energy that is received) is the more significant parameter. For this reason, wireless power technologies are likely to be more limited by distance than wireless communication technologies. Wireless power transfer may be used to power up wireless information transmitters or receivers. This type of communication

2640-408: Is that resonant circuits interact with each other so much more strongly than they do with nonresonant objects that power losses due to absorption in stray nearby objects are negligible. A drawback of resonant coupling theory is that at close ranges when the two resonant circuits are tightly coupled, the resonant frequency of the system is no longer constant but "splits" into two resonant peaks, so

2720-424: Is the coupling coefficient k = M / L 1 L 2 {\displaystyle k\;=\;M/{\sqrt {L_{1}L_{2}}}} . This dimensionless parameter is equal to the fraction of magnetic flux through the transmitter coil L 1 {\displaystyle L1} that passes through the receiver coil L 2 {\displaystyle L2} when L2

2800-402: Is the most widely used wireless technology; its applications include charging handheld devices like phones and electric toothbrushes , RFID tags, induction cooking , and wirelessly charging or continuous wireless power transfer in implantable medical devices like artificial cardiac pacemakers , or electric vehicles . In far-field or radiative techniques, also called power beaming , power

2880-446: Is transferred between coils of wire by a magnetic field . The transmitter and receiver coils together form a transformer . An alternating current (AC) through the transmitter coil (L1) creates an oscillating magnetic field (B) by Ampere's law . The magnetic field passes through the receiving coil (L2) , where it induces an alternating EMF ( voltage ) by Faraday's law of induction , which creates an alternating current in

2960-468: Is transferred by beams of electromagnetic radiation , like microwaves or laser beams. These techniques can transport energy longer distances but must be aimed at the receiver. Proposed applications for this type include solar power satellites and wireless powered drone aircraft . Wireless power transfer is a generic term for a number of different technologies for transmitting energy by means of electromagnetic fields . The technologies differ in

3040-424: Is used, in which the efficiency is increased by using resonant circuits . This can achieve high efficiencies at greater distances than nonresonant inductive coupling. Resonant inductive coupling ( electrodynamic coupling , strongly coupled magnetic resonance ) is a form of inductive coupling in which power is transferred by magnetic fields (B, green) between two resonant circuits (tuned circuits), one in

3120-497: The Zenneck type waves was shown by Oruganti et al., where they demonstrated that it was possible to excite Zenneck wave type waves on flat metal-air interfaces and transmit power across metal obstacles. Here the idea is to excite a localized charge oscillation at the metal-air interface, the resulting modes propagate along the metal-air interface. Far field methods achieve longer ranges, often multiple kilometer ranges, where

3200-411: The microwave range. A rectenna may be used to convert the microwave energy back into electricity. Rectenna conversion efficiencies exceeding 95% have been realized. Power beaming using microwaves has been proposed for the transmission of energy from orbiting solar power satellites to Earth and the beaming of power to spacecraft leaving orbit has been considered. Power beaming by microwaves has

3280-405: The " thinned-array curse ", it is not possible to make a narrower beam by combining the beams of several smaller satellites. For earthbound applications, a large-area 10 km diameter receiving array allows large total power levels to be used while operating at the low power density suggested for human electromagnetic exposure safety. A human safe power density of 1 mW/cm distributed across

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3360-633: The Dictionary of National Biography as "W. P. C." Wireless-powered communication See also [ edit ] WPCS (disambiguation) Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title WPC . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=WPC&oldid=1153215575 " Category : Disambiguation pages Hidden categories: Short description

3440-574: The Dictionary of National Biography as "W. P. C." Wireless-powered communication See also [ edit ] WPCS (disambiguation) Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title WPC . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=WPC&oldid=1153215575 " Category : Disambiguation pages Hidden categories: Short description

3520-671: The U.S. National Weather Service Western Power Corporation , owned by the Government of Western Australia, the major electricity supplier from 1995 through 2006 Wireless Planning & Coordination Wing , an Indian government branch Other organizations [ edit ] West Penn Conference , intercollegiate athletic conference that operated from 1958 to 1969 in Western Pennsylvania Westminster Presbyterian Church (disambiguation) Western Pennsylvania Conservancy ,

3600-497: The U.S. National Weather Service Western Power Corporation , owned by the Government of Western Australia, the major electricity supplier from 1995 through 2006 Wireless Planning & Coordination Wing , an Indian government branch Other organizations [ edit ] West Penn Conference , intercollegiate athletic conference that operated from 1958 to 1969 in Western Pennsylvania Westminster Presbyterian Church (disambiguation) Western Pennsylvania Conservancy ,

3680-681: The United States, the Federal Communications Commission (FCC) provided its first certification for a wireless transmission charging system in December 2017. The power transferred increases with frequency and the mutual inductance M {\displaystyle M} between the coils, which depends on their geometry and the distance D range {\displaystyle D_{\text{range}}} between them. A widely used figure of merit

3760-441: The antenna. The boundary between the regions is somewhat vaguely defined. The fields have different characteristics in these regions, and different technologies are used for transferring power: At large relative distance, the near-field components of electric and magnetic fields are approximately quasi-static oscillating dipole fields. These fields decrease with the cube of distance: ( D range / D ant ) Since power

3840-405: The aperture size. The larger the ratio of a transmitting antenna's aperture or laser's exit aperture to the wavelength of radiation, the more can the radiation be concentrated in a compact beam . Microwave power beaming can be more efficient than lasers, and is less prone to atmospheric attenuation caused by dust or aerosols such as fog. Here, the power levels are calculated by combining

3920-572: The broadcasting and wireless telecommunications industries due to its excellent performance characteristics. Wireless high power transmission using microwaves is well proven. Experiments in the tens of kilowatts have been performed at the Goldstone Deep Space Communications Complex in California in 1975 and more recently (1997) at Grand Bassin on Reunion Island . These methods achieve distances on

4000-427: The coil, because transmission efficiency improves with frequency . Inductive coupling is the oldest and most widely used wireless power technology, and virtually the only one so far which is used in commercial products. It is used in inductive charging stands for cordless appliances used in wet environments such as electric toothbrushes and shavers, to reduce the risk of electric shock. Another application area

4080-492: The coils' axes aligned. Wide, flat coil shapes are usually used, to increase coupling. Ferrite "flux confinement" cores can confine the magnetic fields, improving coupling and reducing interference to nearby electronics, but they are heavy and bulky so small wireless devices often use air-core coils. Ordinary inductive coupling can only achieve high efficiency when the coils are very close together, usually adjacent. In most modern inductive systems resonant inductive coupling

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4160-540: The components may be dictated by the distance from transmitter to receiver , the wavelength and the Rayleigh criterion or diffraction limit, used in standard radio frequency antenna design, which also applies to lasers. Airy's diffraction limit is also frequently used to determine an approximate spot size at an arbitrary distance from the aperture . Electromagnetic radiation experiences less diffraction at shorter wavelengths (higher frequencies); so, for example,

4240-429: The critical coupled regime, the optimum voltage gain curve grows in magnitude (measured at the receiver) and peaks when k = k c r i t {\displaystyle k=k_{crit}} and then enters into the over-coupled regime where k > k c r i t {\displaystyle k>k_{crit}} and the peak splits into two. This critical coupling coefficient

4320-579: The difficulty that, for most space applications, the required aperture sizes are very large due to diffraction limiting antenna directionality. For example, the 1978 NASA study of solar power satellites required a 1-kilometre-diameter (0.62 mi) transmitting antenna and a 10-kilometre-diameter (6.2 mi) receiving rectenna for a microwave beam at 2.45 GHz . These sizes can be somewhat decreased by using shorter wavelengths, although short wavelengths may have difficulties with atmospheric absorption and beam blockage by rain or water droplets. Because of

4400-473: The distance is much greater than the diameter of the device(s). High- directivity antennas or well-collimated laser light produce a beam of energy that can be made to match the shape of the receiving area. The maximum directivity for antennas is physically limited by diffraction . In general, visible light (from lasers) and microwaves (from purpose-designed antennas) are the forms of electromagnetic radiation best suited to energy transfer. The dimensions of

4480-407: The distance over which they can transfer power efficiently, whether the transmitter must be aimed (directed) at the receiver, and in the type of electromagnetic energy they use: time varying electric fields , magnetic fields , radio waves , microwaves , infrared or visible light waves. In general a wireless power system consists of a "transmitter" device connected to a source of power such as

4560-463: The existence of electromagnetic waves as the "wireless" carrier of electromagnetic energy. Around 1884 John Henry Poynting defined the Poynting vector and gave Poynting's theorem , which describe the flow of power across an area within electromagnetic radiation and allow for a correct analysis of wireless power transfer systems. This was followed on by Heinrich Rudolf Hertz ' 1888 validation of

4640-514: The first coil misses the second, and the lower k {\displaystyle k} and the link efficiency are, approaching zero at large separations. The link efficiency and power transferred is roughly proportional to k 2 {\displaystyle k^{2}} . In order to achieve high efficiency, the coils must be very close together, a fraction of the coil diameter D ant {\displaystyle D_{\text{ant}}} , usually within centimeters, with

4720-604: The first wireless-powered aircraft, a model helicopter powered by microwaves beamed from the ground. Electric and magnetic fields are created by charged particles in matter such as electrons . A stationary charge creates an electrostatic field in the space around it. A steady current of charges ( direct current , DC) creates a static magnetic field around it. These fields contain energy , but cannot carry power because they are static. However time-varying fields can carry power. Accelerating electric charges, such as are found in an alternating current (AC) of electrons in

4800-415: The high frequency magnetic fields produced by inductive coupling systems. A prototype system charging electric vehicles has been in operation at University of British Columbia since 2012. Other researchers, however, claim that the two energy conversions (electrical to mechanical to electrical again) make the system less efficient than electrical systems like inductive coupling. A new kind of system using

4880-482: The human body, due to dielectric polarization . Intervening materials between or near the electrodes can absorb the energy, in the case of humans possibly causing excessive electromagnetic field exposure. However capacitive coupling has a few advantages over inductive coupling. The field is largely confined between the capacitor plates, reducing interference, which in inductive coupling requires heavy ferrite "flux confinement" cores. Also, alignment requirements between

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4960-575: The magnitude of power transfer is entirely dependent on critical coupling coefficient, denoted by k {\displaystyle k} , between the transmitter and receiver devices. For coupled resonators with same resonant frequencies, wireless power transfer between the transmitter and the receiver is spread over three regimes – under-coupled, critically coupled and over-coupled. As the critical coupling coefficient increases from an under-coupled regime ( k < k c r i t {\displaystyle k<k_{crit}} ) to

5040-457: The maximum power transfer no longer occurs at the original resonant frequency and the oscillator frequency must be tuned to the new resonance peak. Resonant technology is currently being widely incorporated in modern inductive wireless power systems. One of the possibilities envisioned for this technology is area wireless power coverage. A coil in the wall or ceiling of a room might be able to wirelessly power lights and mobile devices anywhere in

5120-407: The much weaker magnetic fields out in the peripheral regions ("tails") of the near fields. Resonant inductive coupling can achieve high efficiency at ranges of 4 to 10 times the coil diameter ( D ant ). This is called "mid-range" transfer, in contrast to the "short range" of nonresonant inductive transfer, which can achieve similar efficiencies only when the coils are adjacent. Another advantage

5200-407: The next year to propose a " World Wireless System " that was to broadcast both information and power worldwide. In 1901, at Shoreham, New York he attempted to construct a large high-voltage wireless power station, now called Wardenclyffe Tower , but by 1904 investment dried up and the facility was never completed. Before World War II, little progress was made in wireless power transmission. Radio

5280-417: The parameters together, and adding in the gains and losses due to the antenna characteristics and the transparency and dispersion of the medium through which the radiation passes. That process is known as calculating a link budget . Power transmission via radio waves can be made more directional, allowing longer-distance power beaming, with shorter wavelengths of electromagnetic radiation, typically in

5360-485: The potential of the Earth oscillate. Tesla thought this would allow alternating current to be received with a similar capacitive antenna tuned to resonance with it at any point on Earth with very little power loss. His observations also led him to believe a high voltage used in a coil at an elevation of a few hundred feet would "break the air stratum down", eliminating the need for miles of cable hanging on balloons to create his atmospheric return circuit. Tesla would go on

5440-939: The range. At the turn of the 20th century, Nikola Tesla did the first experiments with both resonant inductive and capacitive coupling. An electrodynamic wireless power transfer (EWPT) system utilizes a receiver with a mechanically resonating or rotating permanent magnet. When subjected to a time-varying magnetic field, the mechanical motion of the resonating magnet is converted into electricity by one or more electromechanical transduction schemes (e.g. electromagnetic/induction , piezoelectric , or capacitive ). In contrast to inductive coupling systems which usually use high frequency magnetic fields, EWPT uses low-frequency magnetic fields (<1 kHz), which safely pass through conductive media and have higher human field exposure limits (~2 mTrms at 1 kHz), showing promise for potential use in wirelessly recharging biomedical implants . For EWPT devices having identical resonant frequencies,

5520-445: The receiver armature, turning it. The magnetic field acts like a mechanical coupling between the armatures. The receiver armature produces power to drive the load, either by turning a separate electric generator or by using the receiver armature itself as the rotor in a generator. This device has been proposed as an alternative to inductive power transfer for noncontact charging of electric vehicles . A rotating armature embedded in

5600-432: The receiver. The induced alternating current may either drive the load directly, or be rectified to direct current (DC) by a rectifier in the receiver, which drives the load. A few systems, such as electric toothbrush charging stands, work at 50/60 Hz so AC mains current is applied directly to the transmitter coil, but in most systems an electronic oscillator generates a higher frequency AC current which drives

5680-536: The room, with reasonable efficiency. An environmental and economic benefit of wirelessly powering small devices such as clocks, radios, music players and remote controls is that it could drastically reduce the 6 billion batteries disposed of each year, a large source of toxic waste and groundwater contamination. A study for the Swedish military found that 85 kHz systems for dynamic wireless power transfer for vehicles can cause electromagnetic interference at

5760-413: The same fields and waves as wireless communication devices like radio , another familiar technology that involves electrical energy transmitted without wires by electromagnetic fields, used in cellphones , radio and television broadcasting , and WiFi . In radio communication the goal is the transmission of information, so the amount of power reaching the receiver is not so important, as long as it

5840-571: The square of the voltage, and the capacitance between the plates, which is proportional to the area of the smaller plate and (for short distances) inversely proportional to the separation. Capacitive coupling has only been used practically in a few low power applications, because the very high voltages on the electrodes required to transmit significant power can be hazardous, and can cause unpleasant side effects such as noxious ozone production. In addition, in contrast to magnetic fields, electric fields interact strongly with most materials, including

5920-655: The telegraph, doing away with artificial batteries, and could also be used for lighting, heat, and motive power. A more practical demonstration of wireless transmission via conduction came in Amos Dolbear 's 1879 magneto electric telephone that used ground conduction to transmit over a distance of a quarter of a mile. After 1890, inventor Nikola Tesla experimented with transmitting power by inductive and capacitive coupling using spark-excited radio frequency resonant transformers , now called Tesla coils , which generated high AC voltages. Early on he attempted to develop

6000-471: The theory, which included the evidence for radio waves . During the same period two schemes of wireless signaling were put forward by William Henry Ward (1871) and Mahlon Loomis (1872) that were based on the erroneous belief that there was an electrified atmospheric stratum accessible at low altitude. Both inventors' patents noted this layer connected with a return path using "Earth currents"' would allow for wireless telegraphy as well as supply power for

6080-419: The transmission of 60 W of power over a distance of 2 meters (6.6 ft) (8 times the coil diameter) at around 40% efficiency. The concept behind resonant inductive coupling systems is that high Q factor resonators exchange energy at a much higher rate than they lose energy due to internal damping . Therefore, by using resonance, the same amount of power can be transferred at greater distances, using

6160-429: The transmitter and one in the receiver. Each resonant circuit consists of a coil of wire connected to a capacitor , or a self-resonant coil or other resonator with internal capacitance. The two are tuned to resonate at the same resonant frequency . The resonance between the coils can greatly increase coupling and power transfer, analogously to the way a vibrating tuning fork can induce sympathetic vibration in

6240-437: The transmitter and receiver are less critical. Capacitive coupling has recently been applied to charging battery powered portable devices as well as charging or continuous wireless power transfer in biomedical implants, and is being considered as a means of transferring power between substrate layers in integrated circuits. Two types of circuit have been used: Resonance can also be used with capacitive coupling to extend

6320-487: Was developed for communication uses, but could not be used for power transmission since the relatively low- frequency radio waves spread out in all directions and little energy reached the receiver. In radio communication, at the receiver, an amplifier intensifies a weak signal using energy from another source. For power transmission, efficient transmission required transmitters that could generate higher-frequency microwaves , which can be focused in narrow beams towards

6400-572: Was researched. By 1964, a miniature helicopter propelled by microwave power had been demonstrated. Japanese researcher Hidetsugu Yagi also investigated wireless energy transmission using a directional array antenna that he designed. In February 1926, Yagi and his colleague Shintaro Uda published their first paper on the tuned high-gain directional array now known as the Yagi antenna . While it did not prove to be particularly useful for power transmission, this beam antenna has been widely adopted throughout

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