Multimode Ceramic Transducers

Abstract

Cylindrical transducers of poled piezoelectric ceramic, magnetostrictive, and similar materials can be excited electrically or mechanically in any one of the modes of the cylinder or a special combination of modes. Plane wave signals which can be expressed as the mathematical sum of an infinite series of cylindrical waves with their origin at the center of the cylinder and a reference axis at 0° azimuth provide multimode mechanical excitation. The multimode ceramic transducer is designed to respond to the conventional fundamental radial mode and also to the two orthogonal components of the first-order circumferential mode simultaneously. These three modal components with beam patterns described by the functions P=const, P=sinθ, and P=cosθ are sufficient to determine unambiguously the direction of propagation of the plane wave signal. These signals can be combined in a manner similar to that used for the radio direction finder. Measurements were made in the Raytheon test tank using cathode follower summing circuitry and an oscilloscope to indicate azimuth. Over the entire 360° rotation of the transducer the bearing measured on the oscilloscope was within ±7° of the mechanical orientation of the transducer.