Increased Usable Frequency Band for Underwater Transducers with Single Crystal

In the increasing market of transducers for small underwater platforms, each transducer should be used for several purposes, hence cover as large frequency range as possible. Bandwidth is commonly defined as the -3dB limit of the electromechanical transfer function. Many applications can utilize information from the transducer far beyond this limit. However, another relevant restriction for underwater transducers confined in a small space is the maximum reactive power, limited by the heating and size of electronic components. The higher electromechanical coupling coefficients of piezoelectric single crystals compared to PZTs enable a wider frequency band with acceptable electrical power factor. In this paper we use a 1D model to find the usable frequency band for two water loaded 1-3 composite transducers, restricted by electrical power factor and electromechanical transfer function . The transducers have air backing and three numerically optimized matching layers. One transducer has PZT as the active material. The effective electromechanical coupling coefficient of this transducer is 0.69 and the usable bandwidth is calculated to 120 %, referred to the center of the band. The second transducer has single crystal as the active material and an effective electromechanical coupling coefficient of 0.87. For the single crystal transducer, the usable bandwidth is calculated to 150 %.