New developments in the field of acoustic transducers

Abstract

New developments in the field of acoustic transducers based on the silicon, fiber-optic, and polymer technologies are reviewed. The silicon transducers are produced on silicon wafers with micromechanic methods utilizing anisotropic etching procedures. Subminiature transducers of this kind, based on the capacitive or piezoelectric principles, were made with membranes of about 1-mm2 area and less than 1-uμm thickness. Their use as “intelligent sensors” with on-chip signal-processing capability is presently under study. Fiber-optic sensors consist of glass fibers and detect modulations of either phase or amplitude of the transmitted light waves, caused by interaction of the sound waves with the fiber. Such transducers have initially been used as hydrophones and accelerometers but are now also under study as microphones. Polymer-electret transducers are finding widespread applications as microphones, earphones, and ultrasonic devices. New developments include the use of electret biasing in silicon transducers and the design of electret-microphone arrays and antennas. Piezoelectric polymer transducers were recently improved by the use of better materials and by innovative poling techniques, such as methods to produce single-film monomorphs and bimorphs.