Progress in electroacoustic transducer research

Abstract

Manfred Schroeder always had a vivid interest in the field of electroacoustic transducers. During his time as Director of Acoustics Research at Bell Laboratories, work on electret transducers was started by Jim West and the author in 1962 and the activities were extended over the years to electret materials, directional microphones, and microphone signal processing. Schroeder himself made some interesting contributions to this field, such as the design of directional microphones based on gradients of various orders with toroidal and unidirectional directivity patterns. Some of these devices were implemented with electret transducers. Work on directional microphones at Bell Labs continued as the author went to the Darmstadt University of Technology. There, studies on silicon transducers were initiated, with the first silicon condenser microphone described in 1983. Recently, a completely new and promising variety of piezoelectric transducers was implemented, consisting of charged cellular polymers. This is a new modification of the electret transducer principle developed in the 1960s at Bell Laboratories.