What's new in electroacoustic transducers

About 15 years ago, the science and technology of electroacoustic transducers appeared to be mature fields, with only minor additions and improvements on the horizon. In the meantime, however, a number of unexpected and significant new developments have taken place in this area of acoustics. As a result, electroacoustic transducers present themselves today in a very new and different fashion. Some of the innovations were, not surprisingly, brought about by communications technology. Examples are the invention of fiber-optic and silicon transducers. Other changes originated directly within the field of electroacoustics. Most prominent among these are the introduction of piezoelectric polymer devices and the wide utilization of polymer-electret transducers. Within each of the above-mentioned groups, most of the attention has focused on microphones, nowadays often referred to as acoustic sensors. In comparison, progress in the field of sound-transmitting devices has been more gradual and, with the exception of some polymer devices, along the traditional lines of acoustic transduction. Another significant aspect of the progress in the transducer field is that many developments were only possible because of advances in the material sciences. This includes not only the introduction of new materials and the better characterization of existing ones, but also the emergence of vastly improved material-processing capabilities. In the present paper, some of the interesting work that originated from the conception of transducers of the fiber-optic, silicon, piezopolymer, and electret varieties is reviewed. In particular, typical representatives of each of these groups are described and their advantages and limitations are discussed. To make the causes for progress in the field of electroacoustic transduction more visible, a few of the corresponding innovations in the material sciences are also analyzed. At the end of each section, a brief outlook on the future of the particular kind of transducer is ventured.