A trimodal directional modem transducer

With suitable voltage distribution, higher order extensional modes of a piezoelectric cylinder can be excited which produce directional radiation patterns. These modal radiation patterns can then be combined to synthesize desired beam patterns which may be steered by incrementing the excitation. This paper describes a directional modem communication transducer which uses the combined acoustic response of the first three extensional modes of vibration of a piezoelectric ceramic cylinder, a method of synthesizing a desired radiation pattern and an experimental implementation of a two-ring directional modem transducer that uses these techniques. This trimodal transducer has a smooth response in the band from 15 kHz to 20 kHz, with a frequency-independent 90 degree beam width which may be steered in 45 degree increments from a coded input. The interior of the transducer contains the electronics and the unit may be deployed from a Type A launch tube. (Works supported by a Phase II, SBIR from ONR and SPAWAR).