The study of long-term sensitivity changes in backplate electret type condenser microphones

Abstract

The estimation of the lifetime of a usual electret condenser microphone (ECM) using an electret foil as a diaphragm has already been reported by authors. On the other hand, backplate electret type condenser microphones (BECMs) used for mobile telephones, recently, and the backplate that is laminated with electret foil has been examined and studied concerning the estimation of sensitivity changes over a long time span. Heat acceleration tests for electret foil on the backplate were taken, and from the results, the surface charge decay of backplate electret was estimated. As the thickness of the diaphragm in a BECM is thinner than the usual ECM, sensitivity increasing because of looseness of diaphragm tension was expected to become larger than the usual ECM. Therefore, heat acceleration tests for the diaphragm only were taken and estimates of the levels of sensitivity increasing by the looseness of the results. The charge decay characteristics on the electret surface and the characteristics of tension looseness in the diaphragm had both results taken together. The long-term sensitivity changes of BECMs were estimated and compared with the sensitivity of BECM samples that were left for about 10 years at room temperature.