title: On the forces in single-ended and push-pull electret transducers.
abstract: The equations for the electromechanical force conversion in single-ended and push-pull electret transducers are derived. Traditionally, the charge distribution has been modeled as a concentrated layer at an arbitrary distance from the surface of the dielectric. For the purpose of this analysis, a negative charge is assumed to be evenly distributed throughout the dielectric. The membrane has a conductive coating in which a positive charge is induced, giving an overall dipole charge. The resulting formulas are used to derive the voltage sensitivity of a microphone and the equivalent electrical circuit for the electromechanical transduction part of a microphone or loudspeaker. An equivalent external polarizing voltage is then derived that would produce the same driving force in a conventional electrostatic loudspeaker without a stored charge. The condition for the static stability of a circular electret membrane is also determined.
authors.affiliation: Nokia UK Ltd., Farnborough, Hants GU14 0NG, United Kingdom.
authors.forename: Tim
authors.initials: T
authors.lastname: Mellow
authors.forename: Leo
authors.initials: L
authors.lastname: Kärkkäinen
mesh_terms: D000162:Acoustics / Q000295:instrumentation*; D000669:Amplifiers, Electronic; D025802:Electric Capacitance; D055664:Electrochemical Techniques; D004867:Equipment Design; D008567:Membranes, Artificial; D008962:Models, Theoretical; D016062:Porosity; D011312:Pressure; D014160:Transducers, Pressure
chemical_list: D008567:Membranes, Artificial