Size effects in capped ceramic underwater sound projectors

Cymbal transducers are small, thin Class V flextensional transducers. A single cymbal element consists of a piezoelectric disk sandwiched between two metal cymbal-shaped endcaps which serve as mechanical transformers, converting the low impedance, small extensional motion of the ceramic into high impedance, large flextensional motion of the endcap. A cymbal transducer element is very small, with a thin profile. A single element is characterized by high Q, low efficiency, and medium power capability. When comparing cymbals to other transducers, the designer should consider their use in large flexible, low cost arrays. This paper represents the work of eight researchers over a period of several years. The effects of changes in materials and dimensions on the cymbal-type flextensional transducers, in-air and water-loaded, were examined experimentally and through finite-element-analysis (FEA). Experimental and FEA calculated results matched quite well. After gaining experience and confidence in the FEA models, extensive parametric studies were performed using FEA to investigate the size and material effects on cymbal transducer characteristics. The scaling factor (i.e., overall size), endcap stiffness, and cavity design have the strongest influence on resonance frequency. Adjusting the dimensions and materials used for drivers and endcaps provides a range in the fundamental flexural frequency from about 5 to 150 kHz in water. These results also indicate trends that can be used to extend the ranges further. The scaling factor, cavity depth, and PZT thickness had the strongest effects on the projector/receiver performance (TVR/FFVS). Investigations are underway to combine and optimize some of these parameters for potentially significant improvements in bandwidth and efficiency.