Side lobe level optimization and narrow beam design using spherical homogeneous liquid lens

Abstract

The theory for the focusing characteristics for an ideal homogeneous liquid lens is presented by C. A. Boyles [J. Acoust. Soc. Am. 38, 393–405) (1965)]. This paper considers the focusing characters of a lens with a limited aperture size which is controlled by the critical angle of a stiff acoustic window material. In addition, computed and measured for field beam patterns are presented for finite receivers located on the inner surface of the lens. The cases considered have d/λ >> 1 and an index of refraction between 1.85 ⩽ η ⩽ 2.17. The focused pressure distributions were obtained by brute force numerical integration over the aperture surface and the receive patterns were obtained by integrating this distribution over the surface of the receiver. Measurements were made on a 15 cm diameter lens with an ABS window material on circular and rectangular PZT‐5 receive elements. The results are presented along with normalized design curves for establishing the lens parameters for multiple narrow beam lens design. These curves show optimum index of refraction values and optimum receiver sizes and lens diameter for minimum side lobe levels for a given beam width and frequency.