Amin Hanafy

Characterization of Multielement Acoustic Arrays by Acousto-Optic Diffraction Methods

The characterization of multielement acoustic arrays for diagnostic ultrasound has always been a thorny problem. This paper describes optical techniques for determining the essential parameters of wideband multielement arrays. These parameters which are measured are the spatial frequency response of both the single element and full array, the acoustic cross-coupling between elements, the focusing properties of the array, and the acoustic field intensity.

Sensitivity Improvement by Step-Biasing in Holographic Interferometry

A technique of holographic interferometry yielding a one-order-of-magnitude increase in sensitivity over conventional techniques is described. The method, based on the superposition of a calibrated quarter-wavestep motion on the motion to be detected, is designated as step-biasing. The sensitivity improvements are due to a reversal of the brightness distribu-tion, so that vibrating points appear lighter, nodal points darker. A theoretical discussion of the technique, as applied to the detection of vibration by time-average holographic inter-ferometry, is offered and experimental verification with a 30A peak amplitude of vibration is presented, together with comparison with conventional techniques. The method was originally devised for application to real-time holographic interferometry. This is done easily, yielding the same sensitivity improvement.