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Electricity
Published in Kevin Robinson, Practical Audio Electronics, 2020
There are also one or two places where static charge plays a key role in the operation of audio electronic components. There is a type of microphone capsule called an electret condenser microphone which depends for its operation on a small permanent static charge held by a piece of electret material within the microphone capsule. Electret material is just a particular type of substance capable of maintaining a static charge over a long period of time. It can be thought of as the electrical equivalent of a permanent magnet. Once an appropriate piece of iron has been magnetised it can stay that way indefinitely. Similarly once a piece of electret material has been charged up it can hold that charge for a very long time. The electret material inside an electret microphone can slowly lose its charge over time, and thus its ability to generate an audio signal, usually over the course of tens of years or more.
Instrumentation for Noise Measurement and Analysis
Published in David A. Bies, Colin H. Hansen, Carl Q. Howard, Engineering Noise Control, 2018
David A. Bies, Colin H. Hansen, Carl Q. Howard
A wide variety of transduction devices have been demonstrated over the years for converting sound pressure fluctuations to measurable electrical signals, but only two such devices are commonly used for precision measurement (Starr, 1988; Bruce, 1988). As this chapter is concerned with the precision measurement of sound pressure level, the discussion will be restricted to these two types of transducers. The most commonly used sound pressure transducer for precision measurement is the condenser microphone. To a lesser extent piezoelectric microphones are also used. Both microphones are used because of their very uniform frequency response and their long-term sensitivity stability. The condenser microphone generally gives the most accurate and consistent measure but it is much more expensive to construct than is the piezoelectric microphone. The condenser microphone is available in two forms, which are either externally polarised by application of a bias voltage in the power supply or pre-polarised internally by use of an electret. The externally polarised microphone is sensitive to dust and moisture on its diaphragm, but it is capable of reliable operation at elevated temperatures and generally has a lower electrical noise-floor than its electret counterpart. The pre-polarised type is not nearly as sensitive to dust and moisture and is the microphone of choice in current instrumentation for accurate measurement of sound. Low cost electret microphones are generally not temperature compensated and do not have a very flat frequency response. However, they are the most commonly used microphone in active noise control systems and headsets. Both forms of condenser microphone are relatively insensitive to vibration.
Sound Measurement and Analysis
Published in Lewis H. Bell, Douglas H. Bell, Industrial Noise Control, 2017
Lewis H. Bell, Douglas H. Bell
The electret microphone is also a condenser microphone. However, this type of microphone requires no polarizing voltage supply. The major difference lies in the construction of the capacitor. Here a permanently polarized polymer film, called an electret, is sandwiched between the diaphragm and the backplate. A schematic illustration is presented in Fig. 5.4. Electret microphones are often preferred for field instrumentation due to their more rugged construction and their ability to operate without a polarizing yoltage power supply.
Radon sampling methodologies: A case for accurate, accessible measurements using household instruments
Published in Journal of the Air & Waste Management Association, 2023
Rebecca A. Stern, Joy Lawrence, Jack M. Wolfson, Longxiang Li, Petros Koutrakis
The RadonEye and EcoQube are radon measurement devices using pulsed ionization chamber technology that provides continuous, hourly (60-minute moving average) measurements. Integrated radon measurements were made using the E-PERM, which is a passive electret-based method. The E-PERM consists of an electret (a dielectric material carrying an electrical charge) mounted on an ion chamber with a filtered diffusion barrier. The initially charged electret in the E-PERM is neutralized by ions generated from radon decay in the ion chamber, causing the electret voltage to drop. This voltage drop is proportional to the time-integrated progeny concentration (Copes and Scott 2007). After sample collection, the electret voltage drop was measured with a voltage reader, which was calibrated using references provided by the manufacturer. Other reference methods using charcoal canisters or charcoal liquid scintillation vials were not suitable because they are not reliable under conditions of elevated relative humidity expected in the test homes. The RAD7 is an active electronic radon detector that measures alpha particles by spectrometry using a passivated implanted planar silicon detector to measure the energy of each alpha particle.
Complexes of zinc halides with amide ligands having a high dipole moment
Published in Journal of Coordination Chemistry, 2022
Elena V. Savinkina, Natalia A. Efimova, Mikhail S. Grigoriev, Margarita N. Davydova, Valery V. Fomichev, Tatyana A. Ageeva
Complexes with a high dipole moment attract attention due to their potential application in new materials with promising electric properties, such as electret films [1]. Polymeric electrets can serve as generators of quasi-permanent electric fields [2]. The design of new electret materials based on polymer composites focusses on larger charge density and higher stability than that of the currently available materials. For this purpose, organometallic complexes with high dipole moment can be intercalated in a polymeric material during its polymerization under a permanent electric field. After removing the electric field, polar molecules should remain oriented in one direction, being fixed inside the polymer, and retain electric charge for a long time. Such design was realized by intercalation of porphyrin complexes with bismuth(III) iodide, titanyl, and vanadyl into a polyvinyl acetate framework [3]. We have proposed that effective electrets can form with the use of molecular tetrahedral complexes with two types of ligands, which should be polar due to their asymmetry. In such complexes, zinc can serve as a central metal ion, and halide ions and organic molecules, for example, amides, can serve as ligands.
Filtration efficiency, breathability, and reusability of improvised materials for face masks
Published in Aerosol Science and Technology, 2021
Morteza H. Bagheri, Iman Khalaji, Arad Azizi, Rebecca T. Loibl, Natalia Basualdo, Scott Manzo, Madhu L. Gorrepati, Shilpa Mehendale, Catherine Mohr, Scott N. Schiffres
Unscented dry floor wipes (Swiffers) are primarily polyethylene, as determined by FTIR (fourier-transform infrared spectroscopy), and develop an electrostatic charge upon rubbing on a dissimilar material like cellulose (e.g., the triboelectric effect) (Dyer et al. 2011; “Electrostatic Forces: The Secret to Swiffers’ Swiftness | Trent’s Physics” n.d.). The filtration efficiency of the dry floor wipes increased immediately and significantly after rubbing on a wood/cellulosic surface for about a minute, but all tests shown in the text are for wipes that have not been charged for at least 4 h. If there were a face mask design that could continually triboelectrically charge the Swiffer due to rubbing of a cotton liner with the Swiffer, the efficiency would further increase. The polymeric electrostatic HVAC filters performed very well, are made primarily of polypropylene (FTIR) and are thought to have an embedded electret from electrospraying the polymer or corona discharge treatments (Tsai, Schreuder-Gibson, and Gibson 2002; Tsai and Wadsworth 1995).