Electret microphone

Materials Photoacoustic measurements were made on a component-assembled PAS spectrometer consisting of a 9W argon ion laser (Spectra Physics), a 0.5 cc internal volume PAS cell equipped with a sensitive electret microphone (Radio Shack, 3.2 mV/Pa). Circular polarization modulation was achieved with a special low frequency (220 Hz) photoelastic modulator (15) (Hinds International). Signals were detected and processed with a vector tracking lock-in amplifier (PAR model 5204), and intensity modulation was done with a 30-slot blade mechanical chopper (Ortec). Syntheses of all compounds were by well established literature methods. 

As already pointed out, miniature electret microphones are in conunon use as detectors in resonant photoacoustic spectroscopy . Even these small devices may have a pronounced effect on the Q factor of the resonator. For example, the... 

Fig. 8. Cross section of a miniature electret microphone with a separate membrane. This type allows an independent optimization of the membrane and the electret material. Holes to a back chamber decrease the stiffness of the air gap...

Rychkov D, Altaflm RAP, Gerhard R (2014) Unipolar ferroelectrets - following the example of the electret microphone more closely. In Annual Report, IEEE Conference on Electrical Insulation and Dielectric Phenomena. IEEE, New York, pp 860-862. doi 10.1109/CEIDP.2014.6995907... 

Fig.1 Foil electret microphone (Sessler and West 1973) (Reproduced with permission from AIP)... 

For professional use, microphones with a push-pull electret structure are also employed. Unidirectional ECMs that deliver a faithful response at high sound-pressure levels over a wide dynamic range have also been developed. Structure of the push-pull electret microphone (Sakamoto et al. 1979) is depicted in Fig. 5. 

More recently, MEMS microphones based on a single wafer are proposed (Hagiwara et al. 2010). With the aid of a soft-X-ray charging method, Si02/Si3N4 thin-film electret inside the silicon structure is successfully charged. The practical use of the ultrasmall silicon electret microphone has also been studied (Goto etal. 2011). 

Hsieh WHetal (1997) A micromachinedthin-film Teflon electret microphone. IntConf Solid-State Sensors Actuators 1 425-428... 

After reducing the complex voided stmcture to a simplified three-layer system, the electret microphone theory can be applied. To demonstrate the relation between this theory and the ferroelectret model, the electric charged layered system, as shown in Fig. 2b, was considered. The eharged model represents the charges trapped on the inner void surfaces and the charges induced on the proximity of the electrodes, after the stmcture has been submitted to an external high electric field and dielectric barrier discharges had occiured inside the air cavities. 

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