Design, Fabrication and Evaluation of an Underwater Acoustic Imaging Sensor Array

Acoustic imaging array systems generate an image by processing the acoustic waves backscattered from an underwater object. Generally these systems operate at higher frequencies and provide shorter imaging ranges. The lateral resolution is determined by the ultrasound beam width which is a function of aperture diameter and frequency. The diffraction pattern of an array accounts for all linear effects, such as, transducer size, side and grating lobes, focusing, and beam steering. Angular resolution enhance with increase in the number of elements or the frequency. The side lobes appear as a background noise in the image. The ability and usefulness of the algorithms depend on the quality (Sensitivity, bandwidth, and dynamic range) of the original echo signal, making the transducer the most critical component of ultrasound imaging systems. The present paper presents the design of a 128 element underwater acoustic imaging sensor linear array that operates at 500 kHz and with a horizontal beam width less than 1°. There are several sound field parameters that are critical in designing an ultrasonic transducer array, which have been discussed in the paper. The array evaluated underwater at 500 kHz shows a source level of 184 dB and a receiving sensitivity of -192 dB re V/μPa @1 m. The acoustic cross-talk and other acoustical parameters are also discussed.