Principles of operation of condenser microphones

Abstract

Following a description of microphone cartridge construction, the topics to be discussed include: electrical and mechanical microphone sensitivities, effect of the polarization voltage, electrical and mechanical stability, membrane damping, electromechanical equivalent circuit, background noise, and response to infrasound. The discussion will be interspersed with little-known factoids on microphone performance which are not found in the traditional literature.

Performance Enhancement by Substrate Perforation for a Wafer-Level Encapsulated RF MEMS DC Shunt Switch

“…4um without holes 6um without holes 8um without holes lOum without hole -4um with holes -6um with holes 8um with holes lOumwith holes -= cosh!iarccosh V2f 1 (5) f1(x) = f2(x)[f2(x)-66]+3f3(26) (6) f2(x)=3x+26-1 (7) f3(X)=X2- (1) Coating & pattering of polymer, and cavity formation by DRIE backplate silicon (300 tm thick) is firstly spin-coated and patterned with a CYTOP bonding layer. A cavity with a depth of 150 tm is then generated by deep reactive ion etching (DRIE).…”

“…where T is the diaphragm tension, c is the angular velocity, and D is the air layer damping term (an dimensionless quantity) and is given by, terms, Zm is the diaphragm displacement function [7], z0 is the interim unknown diaphragm displacement in a trial expression [7], q is the number of holes, f, is the air velocity at the kh opening in the back-support, S, is the area of the kh opening in the back-support, Fm and Tm are numerical constants [7], am is the symmetric radical component of the scalar wave number, a, is the location of the kh opening in the back-support, 6(m) is a conditional function (6(m) = 1 when m =0; 6(m) = 0 otherwise), JO(Ka), J1 (Ka) and J2(Ka) are the zero, first-order and second-order Bessel functions of Ka, respectively. Here K is the wave number of sound in the diaphragm and can be expressed by…”

“…The damping coefficient (Ba), also termed as air resistance, of a diaphragm due to the viscous damping losses in the air gap and the damping holes is governed by following equation [5][6][7] (1)…”

Modified Škvor/Starr approach in the mechanical-thermal noise analysis of condenser microphone

“…The expression for the mechanical resistance of holes in the backplate only emphasizes the strong dependence on the total open area of holes, number of holes, and air gap thickness, while the positional effect of holes on the mechanical resistance is not considered and properly addressed. An accurate but more complicated modeling approach was described by Zuckerwar,18,19 and verified in Refs. 18-20 with very good accuracy.…”

An analytical-numerical method for determining the mechanical response of a condenser microphone

“…microphone is also included in Ref. 9. Tan and Miao 10 in 2006 reviewed the theory of condenser microphones and proposed a new analytical modeling method for the B&K MEMS condenser microphone.…”