IMPROVING THE BANDWIDTH OF 1-3 CONNECTIVITY COMPOSITE RECEIVERS USINGMODE-COUPLING

Temporal resolution in an ultrasonic system may be enhanced by the app lication of mechanical damping to the transducer rear face, thereby re ducing internal reverberation and increasing effective bandwidth. Howe ver, for thickness drive transducers, this is accompanied inevitably b y a reduction in sensitivity and, moreover, manufacture of suitable da mping blocks can be difficult, particularly for lower frequency, small signal applications such as the detection of gas coupled ultrasound. This work describes an interesting alternative approach that utilizes the relatively strong coupling between the fundamental thickness mode and first lateral mode in 1-3 connectivity piezocomposite transducers. Finite element modeling is used to evaluate the influence of mode int eraction on electromechanical coupling efficiency, surface displacemen t, sensitivity, and bandwidth as functions of the ceramic pillar dimen sions for operation into both water and air load media. A range of com posite devices was constructed and close agreement between theory and experiment is demonstrated, with a measured device bandwidth of 130% c entered at 1.15 MHz. An example of using such a device within a gas-co upled ultrasonic system is presented and the response is shown to comp are favorably with alternative transducer configurations. (C) 1998 Aco ustical Society of America.