First patent on foil electret microphone by G. M. Sessler et al. (pages 1 to 3) An electret microphone is a type of condenser microphone invented by Gerhard Sessler and Jim West at Bell laboratories in 1962. The externally applied charge used for a conventional condenser microphones is replaced by a permanent charge in an electret material. An electret is a ferroelectric material that has been permanently electrically charged or polarized.
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Though electret microphones were once considered low quality, the best ones can now rival traditional condenser microphones in every respect and can even offer the long-term stability and ultra-flat response needed for a measurement microphone. Only the best electret microphones rival good DC-polarized units in terms of noise level and quality; electret microphones lend themselves to inexpensive mass-production, while inherently expensive non-electret condenser microphones are made to higher quality.
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An electret (formed of electr- from "electricity" and -et from "magnet") is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet. Although Oliver Heaviside coined this term in 1885, materials with electret properties were already known to science and had been studied since the early 1700s. One particular example is the electrophorus, a device consisting of a slab with electret properties and a separate metal plate.
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They are mostly multi-layer. Filter material may be made of microfibers with an electrostatic charge; that is, the fibers are electrets. An electret filter increases the chances that smaller particles will veer and hit a fiber, rather than going straight through (electrostatic capture). While there is some development work on making electret filtering materials that can stand being washed and reused, current commercially produced electret filters are ruined by many forms of disinfection, including washing with soap and water or alcohol, which destroys the electric charge.
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Electrets, like magnets, are dipoles. Another similarity is the radiant fields: they produce an electrostatic field (as opposed to a magnetic field) around their perimeter. When a magnet and an electret are near one another, a rather unusual phenomenon occurs: while stationary, neither has any effect on one another. However, when an electret is moved with respect to a magnetic pole, a force is felt which acts perpendicular to the magnetic field, pushing the electret along a path 90 degrees to the expected direction of "push" as would be felt with another magnet.
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Along with Gerhard Sessler, West invented the foil electret microphone in 1962 while developing instruments for human hearing research. Compared to the previous condenser microphones, the electret microphone has higher capacitance and does not require a DC bias. West and Sessler optimized the mechanical and surface parameters of the system. Nearly 90 percent of more than two billion microphones produced annually are based on the principles of the foil-electret and are used in everyday items such as telephones, camcorders, hearing aids, baby monitors, and audio recording devices among others.
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He prepared the permanent photoelectret state of matter for the first time and published his paper in 1937 and 1938. He called the electret discovered by Mototaro Eguchi in 1919, thermoelectret and the electret discovered by him in 1937, photoelectret. Photoelectrets were the most notable achievement of Georgi Nadjakov. Its practical application led to the invention of the photocopier by Chester Carlson some years later.
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The name comes from electrostatic and magnet; a static charge is embedded in an electret by the alignment of the static charges in the material, much the way a permanent magnet is made by aligning the magnetic domains in a piece of iron. Due to their good performance and ease of manufacture, hence low cost, the vast majority of microphones made today are electret microphones; a semiconductor manufacturer estimates annual production at over one billion units. They are used in many applications, from high-quality recording and lavalier (lapel mic) use to built-in microphones in small sound recording devices and telephones. Prior to the proliferation of MEMS microphones, nearly all cell-phone, computer, PDA and headset microphones were electret types.
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Electret materials are quite common in nature. Quartz and other forms of silicon dioxide, for example, are naturally occurring electrets. Today, most electrets are made from synthetic polymers, e.g. fluoropolymers, polypropylene, polyethyleneterephthalate (PET), etc.
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There is a similarity between an electret and the dielectric layer used in capacitors; the difference is that dielectrics in capacitors have an induced polarisation that is only transient, dependent on the potential applied on the dielectric, while dielectrics with electret properties exhibit quasi-permanent charge storage or dipole polarisation in addition. Some materials also display ferroelectricity (i.e. they react to the external fields with a hysteresis of the polarisation). Ferroelectrics can retain the polarisation permanently because they are in thermodynamic equilibrium, and thus are used in ferroelectric capacitors.
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Mechanical filters can be made of a fine mesh of synthetic polymer fibers. The fibers are produced by melt blowing. The fibers are charged as they are blown to produce an electret, and then layered to form a nonwoven polypropylene fabric.
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NASA Langley has designed and developed an infrasonic detection system that can be used to make useful infrasound measurements at a location where it was not possible previously. The system comprises an electret condenser microphone PCB Model 377M06, having a 3-inch membrane diameter, and a small, compact windscreen.Development and installation of an infrasonic wake vortex detection system By Qamar A. Shams and Allan J. Zuckerwar, NASA Langley Research Center, Hampton VA USA, WakeNet-Europe 2014, Bretigny, France. Electret-based technology offers the lowest possible background noise, because Johnson noise generated in the supporting electronics (preamplifier) is minimized.
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Many players have a built-in electret microphone which allows recording. Usually recording quality is poor, suitable for speech but not music. There are also professional-quality recorders suitable for high-quality music recording with external microphones, at prices starting at a few hundred dollars.
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In recent years, alternatives to the cellular-foam ferroelectrets were developed. In the new polymer systems, the required cavities are formed by means of e.g. stamps, templates, laser cutting, etc. Thermo-forming of layer systems from electret films led to thermally more stable ferroelectrets.
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Although electrets are only in a metastable state, those fashioned from very low leakage materials can retain excess charge or polarisation for many years. An electret microphone is a type of condenser microphone that eliminates the need for a power supply by using a permanently charged material.
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This is the pyroelectric effect. All polar crystals are pyroelectric, so the 10 polar crystal classes are sometimes referred to as the pyroelectric classes. Pyroelectric materials can be used as infrared and millimeter wavelength radiation detectors. An electret is the electrical equivalent of a permanent magnet.
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All microphones made by Schoeps employ traditional (i.e. externally polarized, not electret) condenser transducers, and use small-diaphragm, single-diaphragm capsules, even in microphones which offer two or three different directional patterns. All models introduced since 1973, as well as some models from even earlier, have featured transformerless output circuitry.
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The corresponding face mask used in the European Union is the FFP2 respirator. Hard electret-filter masks like N95 and FFP masks must fit the face to provide full protection. Untrained users often get a reasonable fit, but fewer than one in four gets a perfect fit. Fit testing is thus standard.
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Busch-Vishniac received the ASA Silver Medal in Engineering Acoustics in 2001 for her work in developing novel electret microphones and of precision micro-electro- mechanical sensors and positioners. She was elected a Fellow of the Acoustical Society of America (ASA) in 1987, and also received the ASA R. Bruce Lindsay Award.
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Lambda Nova basic system Stax Ltd. (有限会社スタックス Yugen-gaisha SutakkusuSTAX Ltd home page) is a Japanese company that makes high-end-audio equipment. Stax is best known for their electrostatic and electret headphones, which they call “earspeakers.”STAX USA: History Electrostatic headphones work similarly to electrostatic loudspeakers, but on a smaller scale.
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TSC has been used to study traps in semi-insulating gallium arsenide (GaAs) substrates. It has also been applied to materials used for particle detectors or semiconductor detectors used in nuclear research, for example, high-resistivity silicon, cadmium telluride (CdTe), etc. TSC has also been applied to various organic insulators. TSC is useful for electret research.
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The most widely used transduction principles are electromagnetism, electrostatics and piezoelectricity. The transducers in most common loudspeakers (e.g. woofers and tweeters), are electromagnetic devices that generate waves using a suspended diaphragm driven by an electromagnetic voice coil, sending off pressure waves. Electret microphones and condenser microphones employ electrostatics—as the sound wave strikes the microphone's diaphragm, it moves and induces a voltage change.
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Electromechanical Film (EMFi) is a thin, flexible film that can function as a sensor or actuator. It is composed of a charged polymer coated with two conductive layers, making it an electret. It was first made by Finnish inventor Kari Kirjavainen. EMFi's voided internal structure and high resistivity allows it to hold a high electric charge and makes the film very sensitive to force.
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Electret was formed by combining carnauba wax, rosin and beeswax, and then cooling the solution while it is subject to an applied DC electrical bias. The mixture would then solidify into a polymeric material that exhibited a piezoelectric effect. Polymers that respond to environmental conditions, other than an applied electric current, have also been a large part of this area of study. In 1949 Katchalsky et al.
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Electrostatic Motors, Their History, Types, and Principles of Operation, Electret Scientific Company. pp. 22–45 The theoretical principle behind them, Coulomb's law, was discovered but not published, by Henry Cavendish in 1771. This law was discovered independently by Charles-Augustin de Coulomb in 1785, who published it so that it is now known with his name. The invention of the electrochemical battery by Alessandro Volta in 1799 made possible the production of persistent electric currents.
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In 2007 Chandler Bridges and Rob Chiarelli begin experimentation in loudspeaker and microphone design. In 2008 Gauge Precision Instruments introduces the ECM-87, their first cardioid condenser microphone. Gauge introduced the ECM-47 in 2009, their first multi-pattern Tube microphone. That year Gauge also introduced the USB-87, a Universal Serial Bus powered microphone designed specifically for use with the personal computer, and the ECM-84 and ECM-84SE, their first small diaphragm electret condenser microphone.
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The field of EAPs emerged back in 1880, when Wilhelm Röntgen designed an experiment in which he tested the effect of an electrostatic field on the mechanical properties of a stripe of natural rubber. The rubber stripe was fixed at one end and was attached to a mass at the other. Electric charges were then sprayed onto the rubber, and it was observed that the length changed. It was in 1925 that the first piezoelectric polymer was discovered (Electret).
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During the COVID-19 pandemic, public health authorities issued guidelines on how to save, disinfect and reuse electret-filter masks without damaging the filtration efficiency. Standard disposible surgical masks are not designed to be washed. A surgical mask, by design, does not filter or block very small particles in the air that may be transmitted by coughs, sneezes, or certain medical procedures. Surgical masks also do not provide complete protection from germs and other contaminants because of the loose fit between the surface of the face mask and the face.
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One of the earliest recipes consists of 45% carnauba wax, 45% white rosin, and 10% white beeswax, melted, mixed together, and left to cool in a static electric field of several kilovolts/cm. The thermo-dielectric effect, related to this process, was first described by Brazilian researcher Joaquim Costa Ribeiro. Electrets can also be manufactured by embedding excess negative charge within a dielectric using a particle accelerator, or by stranding charges on, or near, the surface using high voltage corona discharges, a process called corona charging. Excess charge within an electret decays exponentially.
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The H2 began shipping on August 21, 2007. This was delayed from the original May 2007 shipping date due as an additional microphone was added; the original three-microphone Mid-Side design was lacking in some respects, and was abandoned in favor of the four- microphone W-X/Y design. The built-in high-fidelity electret condenser microphone capsules are arranged to allow stereo recording and have user- selectable parameters to allow for either a 90- or 120-degree pickup angle. The H2 can also be used to record a 360-degree soundfield.
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First patent on foil electret microphone by G. M. Sessler and J. E. West (pages 1 to 3) West received a master's degree in Physics from Temple University in 1957. In 2001, West retired from Lucent Technologies after a distinguished 40-year career at Bell Laboratories where he received the organization's highest honor, being named a Bell Laboratories Fellow. West then joined the faculty of the Whiting School at Johns Hopkins University where he is currently a Professor in the Department of Electrical and Computer Engineering. In 2007, West received an honorary doctorate from NJIT.
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The electrophorus was originally invented by Johan Carl Wilcke in Sweden and again by Alessandro Volta in Italy. The name derives from "electron" and "magnet"; drawing analogy to the formation of a magnet by alignment of magnetic domains in a piece of iron. Historically, electrets were made by first melting a suitable dielectric material such as a polymer or wax that contains polar molecules, and then allowing it to re-solidify in a powerful electrostatic field. The polar molecules of the dielectric align themselves to the direction of the electrostatic field, producing a dipole electret with a permanent electrostatic bias.
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First patent on foil electret microphone by G. M. Sessler and J. E. West (pages 1 to 3) From 1950 to1959, Sessler studied physics at Universities of Freiburg, Munich, and Göttingen. He received his diploma in 1957 and his Ph.D. from the University of Göttingen in 1959. After working in the United States at Bell Labs until 1975, he returned to the academia in Germany. From 1975 to 2000, he worked as a professor of electrical engineering at the Department of Electrical Engineering and Information Technology of the Technische Universität Darmstadt where he invented the silicon microphone.
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Power is necessary for establishing the capacitor plate voltage and is also needed to power the microphone electronics (impedance conversion in the case of electret and DC- polarized microphones, demodulation or detection in the case of RF/HF microphones). Condenser microphones are also available with two diaphragms that can be electrically connected to provide a range of polar patterns (see below), such as cardioid, omnidirectional, and figure-eight. It is also possible to vary the pattern continuously with some microphones, for example, the Røde NT2000 or CAD M179. A valve microphone is a condenser microphone that uses a vacuum tube (valve) amplifier.
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They were difficult to match to early transistor equipment and were quickly supplanted by dynamic microphones for a time, and later small electret condenser devices. The high impedance of the crystal microphone made it very susceptible to handling noise, both from the microphone itself and from the connecting cable. Piezoelectric transducers are often used as contact microphones to amplify sound from acoustic musical instruments, to sense drum hits, for triggering electronic samples, and to record sound in challenging environments, such as underwater under high pressure. Saddle-mounted pickups on acoustic guitars are generally piezoelectric devices that contact the strings passing over the saddle.
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Condenser microphones have impedance converter (current amplifier) circuitry that requires powering; in addition, the capsule of any non-electret, non-RF condenser microphone requires a polarizing voltage to be applied. Since the mid- to late 1960s most balanced, professional condenser microphones for recording and broadcast have used phantom powering. It can be provided by outboard AC or battery supplies, but nowadays is most often built into the mixing console, recorder or microphone preamplifier to which the microphones are connected. By far the most common circuit uses +48 V DC fed through a matched pair of 6.8 kΩ resistors for each input channel.
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Unlike disposable masks, there are no legal standards for cloth masks. One study gives evidence that an improvised mask was better than nothing, but not as good as soft electret-filter surgical mask, for protecting health care workers while simulating treatment of an artificially infected patient. Another study had volunteers wear masks they made themselves, from cotton T-shirts and following the pattern of a standard tie behind the head surgical mask, and found the number of microscopic particles that leaked inside the homemade masks were twice that of commercial masks. The homemade mask also let a median average of three times as many microorganisms be expelled by the wearer.
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The static electrical charge on the microfibers (which attracts or repels particles passing through the mask, making them more likely to move sideways and hit and stick to a fiber; see electret) is destroyed by some cleaning methods. UVGI (ultraviolet light), boiling water vapour, and dry oven heating do not seem to reduce the filter efficiency, and these methods successfully decontaminate masks. UVGI (an ultraviolet method), ethylene oxide, dry oven heating and (highly toxic) vaporized hydrogen peroxide are currently the most-favoured methods in use in hospitals, but none have been properly tested. Where enough masks are available, cycling them and reusing a mask only after letting it sit unused for 5 days is preferred.
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This causes a force to be exerted on the charged diaphragm, and its resulting movement drives the air on either side of it. In virtually all electrostatic loudspeakers the diaphragm is driven by two grids, one on either side, because the force exerted on the diaphragm by a single grid will be unacceptably non-linear, thus causing harmonic distortion. Using grids on both sides cancels out voltage dependent part of non-linearity but leaves charge (attractive force) dependent part.The theory of electrostatic forces in a thin electret (MEMS) speaker Eino Jakku, Taisto Tinttunen and Terho Kutilainen, proceedings IMAPS Nordic 2008 Helsingør – 14–16 September The result is near complete absence of harmonic distortion.
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He worked at Bell Laboratories for 33 years before he joined Rutgers. He has worked in voice communications, computer techniques, and electroacoustic systems. At Bell Laboratories he was the department head of the Acoustics Research Department for many years, and managed and supported work such as James E. West's invention of the electret microphone, Bishnu S. Atal's work on speech coding, David Berkley and Gary Elko's work on acoustics, Jont Allen and Joe Hall's work on psychoacoustics, James D. Johnston's work on perceptual audio coding mp3, work on speech synthesis, and Lawrence Rabiner and Aaron Rosenberg (and others) work on speech recognition. Flanagan holds the patent on the modern artificial larynx design.
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3.5 mm jacks for microphone, audio out, and line-level audio in A 3.5 mm plug for computer audio A 3.5 mm headphone socket (TRS) on a computer Personal computer sound cards, such as Creative Labs' Sound Blaster line, use a 3.5 mm phone connector as a mono microphone input, and deliver a 5 V voltage on the ring to power electret microphones. Sometimes termed phantom power, this is not a suitable power source for microphones designed for true phantom power and is better termed bias voltage. (Note that this is not a polarizing voltage for the condenser, as electrets by definition have an intrinsic voltage; it is power for a FET preamplifier built into the microphone.) Compatibility between different manufacturers is unreliable. The Apple PlainTalk microphone jack used on some older Macintosh systems is designed to accept an extended 3.5 mm three-conductor phone connector; in this case, the tip carries power for a preamplifier inside the microphone.
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