Abstract
The theory of a broadband constant beamwidth transducer (CBT) which is based on Legendre function shading of a spherical cap was described in a previous report [P. H. Rogers and A. L. Van Buren, J. Acoust. Soc. Am. 64, 38–43 (1968)]. Theoretical calculations showed the CBT to have uniform acoustic loading, extremely low sidelobes, virtually no nearfield, an essentially constant beam pattern for all frequencies above a certain cutoff frequency, and a flat transmitting current response over a broad band for piezoelectric drive. In this paper we present experimental results obtained for a prototype CBT based on fifth‐order Legendre function shading. The transducer is a spherical cap with a diameter of 30.5 cm and a total cap angle of 50 degrees. The spherical cap is an aluminum plate in which 849 lead zirconate‐titanate disks, 0.635 cm in diameter and 0.318 cm thick, are arranged in 16 circular bands with each disk isolated from the plate by corprene. Measurements on the CBT showed it to possess very low sidelobes and a nearly constant beamwidth over the frequency range from 20 to 140 kHz and for ambient pressures up to 3.4 MPa.
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