An acoustic transducer system for long-distance ranging applications in air

Abstract

Transducers for long-distance pulse-echo ranging applications should combine high efficiency and directivity with a relatively wide bandwidth. Since the air has a very low acoustic impedance, the efficient transmission of sound from a solid transducer is one of the major problems. A means to improve the impedance matching between the source and the propagation medium is to increase the radiation impedance by using extensive vibrating plates as radiators. Nevertheless, these extensive radiators will vibrate at a flexural mode resonance, producing a poor directivity due to phase cancellation. In this paper we present a transducer system, based on a stepped-plate radiator, which is able to generate efficiently high-directional radiation in air. To be used for pulse-echo ranging applications, the stepped-plate radiator has been specially adapted in order to increase the bandwidth of the transducer system. In particular, three main features have been introduced: the development of very thin stepped plates; the addition of a matching layer; and the backing of the plate with a damping material. Electroacoustical and pulse-echo characterizations of the transducer system have shown its good performance for use as a level or distance sensor, specially for long-range applications (10–100 m).