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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.
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.
Microphones
Published in John Watkinson, The Art of Sound Reproduction, 2012
In the electret microphone a material is employed which can produce a constant electric field without power. It is the electrostatic equivalent of a permanent magnet. An electret is an extremely good insulator which has been heated in an intense electric field. A conductor moving in such a field will produce a high impedance output which will usually require to be locally amplified. The electret microphone can be made very light because no magnet is required. This is useful for hand-held and miniature designs.
Experimental study of the stack geometric parameters effect on the resonance frequency of a standing wave thermoacoustic refrigerator
Published in International Journal of Green Energy, 2019
For the temperature measurement, K-type thermocouples were used with an accuracy of ±0.1°C. The thermocouples were connected to a digital temperature recorder (Yokogawa R 180). For the oscillating pressure measurement, a microphone (LM 393 Electret Microphone) was used. The pressure signal from the resonator was sent to an oscilloscope (Velleman type) connected to a personal computer. The personal computer contained a built-in program called "PC lab 2000" to view the signal from the oscilloscope. The maximum measured drive ratio, D was observed to be 0.017 at frequency, f = 105 Hz, porosity, B = 0.8, normalized stack length, Lsn= 0.191, and normalized stack position, Xsn = 1.72.
Inverse problem solving in semiconductor photoacoustics by neural networks
Published in Inverse Problems in Science and Engineering, 2021
Katarina Lj. Djordjevic, Dragan D. Markushev, Žarko M. Ćojbašić, Slobodanka P. Galović
In order to validate our ANN choice, independent PA measurements were used with the same frequency step and the range of the parameter values as those used for the network training. The open photoacoustic cell OPC [12,13,28] experimental set-up was used, explained in detail elsewhere [12,13,28]. As a detector, standard electret microphone ECM30B was used together with a laser diode of 660 nm wavelength and 20 mW of power as a light source modulated with a current modulator in the frequency range of 20 Hz–20 kHz. All our measurements were performed using circular plates made of n-type silicon as a well-known material having the radius of and different thicknesses l: 830, 417 and 128 µm. Experimental signal (a) amplitudes A and (b) phases ϕ were obtained from these samples, (Figure 5, asterisks). Following signal correction procedure explained earlier, the rectified (‘true’) PA signal (a) amplitudes and (b) phases are obtained (Figure 5, solid lines), applying H(f) results from previous analysis [12,13]. Rectified signals presented in Figure 5 fairly represent the signals from the silicon sample having these parameters: thermal diffusivity DT = 9.0×10−5 m2s−1 and thermal expansion αT = 2.6×10−6 κ−1. In our further analysis, these parameters will be compared to the ANNs prediction.
The effects of biodiesel produced from waste cooking oils on vibroacoustic properties of a heavy-duty diesel engine
Published in Biofuels, 2023
Harun Yıldırım, Ahmet Necati Özsezen, Ali Çınar
In the test bench, a PCB (352C03) Piezotronics accelerometer transducer (z-direction vertical) with 1.02 mV/(m/s2) sensitivity was used. The accelerometer was mounted on the head of the engine’s first cylinder. A free field microphone of the type 01 dB MCE212 (Electret microphone 1/2", type 1, 50 mV/Pa) was used for monitoring noise emissions. The microphone was placed 1 m from the engine. Following the Nyquist theorem, by selecting a sampling frequency of 25.6 kHz, noise, vibration, and cylinder gas pressure values were collected synchronously with the NETdB12 data acquisition device.