Modal transducers and Stan Ehrlich

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There have been a number of transducer designs which use the dipole mode of a piezoelectric cylinder to obtain directionality since Stan Ehrlich’s early patent (with P.D. Frelich), [“Sonar Transducer,” U.S. Patent 3,290,646, December 6, 1966] was first published. There is now a whole class of transducers, called vector sensors or hydrophones, which use the dipole mode in one or more directions. In addition to this, other designs have emerged which use modes higher than the monopole and dipole modes. For example, the added use of the quadrupole mode has allowed beam patterns from cylinders which approximate patterns from piston transducers. Work on the dipole mode and higher modes of spherical transducers and arrays allow 3-D acoustical coverage from one transducer or array. This presenters interest in modal excitation from transducers and arrays began after reading Stan’s patent, and interest developed further after working with Stan at Raytheon. A review of some of the transducers and arrays which we worked on will be presented, along with more recent work based on these modal concepts.