Parametric array design and characterisation for underwater sonar and medical strain imaging applications

This paper reports potential contributions of parametric arrays in underwater sonar and biomedical imaging. The parametric array presents the opportunity to use a relatively small device made with high performance, high cost PMN-PT single crystal to produce a low frequency beam in underwater sonar. Additionally, the directional beam has potential applications in medical strain imaging used to detect pathological tissue changes indicative of cancer. The paper also aims to help address the relative lack of published data regarding the technique of parametric generation since its inception in the 1950s. An outline of the design, fabrication and characterisation process required to develop devices for parametric array generation is presented, together with a performance evaluation of two such devices, one with a flat radiating surface and one focused. The ease with which this technique can be employed with modern instrumentation suggests that it is viable for commercial implementation with PMN-PT single crystal material even in the highly cost-competitive underwater sonar market. Our findings also support the proposition that the parametric acoustic field mimics that of an end-fire array providing directional, low frequency excitation desirable in strain imaging.