A trimodal directional transducer

• Published in: The Journal of the Acoustical Society of America 2001-05, Vol.109 (5_Supplement), p.2363-2363
• Main Authors: Butler, Alexander L., Butler, John L., Rice, Joe
• Format: Article
• Language: English
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4744314

A cylindrical transducer, which achieves a directional horizontal beam through the addition of the first three extensional modes of radial vibration is presented. The three modes are the omni, dipole, and quadrupole modes, related in resonant frequency by the formula fn=f0(1+n)1/2, where ∫n=0, 1, and 2, respectively. The addition of the quadrupole mode to the omni and dipole modes yields a frequency independent horizontal beam that has greater directionality than the commonly used two-mode scheme, first described by S. L. Ehrlich and P. D. Frelich [U. S. Patent 3,290,646 (1966)]. Theoretical and measured beam pattern results on two different trimodal cylindrical transducer designs are presented and compared. One of the transducers, fabricated from rings of the same diameter, operates in the vicinity of 20 kHz and combines modes with three different resonant frequencies. The second transducer, fabricated from rings of different diameters, operates in the vicinity of 10 kHz and combines modes with the same resonant frequency. It is shown that steered beamwidths of 90° and front to back ratios of 10 dB can be readily obtained from comparatively small diameter transducers. [SBIR work supported by ONR and SPAWAR.]