Performance Evaluation of Cymbal Hydrophones for Underwater Applications

Abstract

This paper reports the performance differences in the receiving sensitivity and band width of Class V flex tensional transducers (Cymbals) both in-air and in-water by varying the design parameters. Cymbal elements with device diameter 8mm and 13mm with optimum designs achieved using finite element software ATILA is presented. The in-air and underwater characteristics of such transducers are described in this paper. The performance evaluation of the transducers both in air and water are also reported in this paper. It has been established that the resonance frequency shifts towards higher side while increasing the cavity depth retaining the cap diameter fixed. However, there exists a tradeoff between the choice of sensitivity and optimum cavity depth. A maximum Receiving Sensitivity (RS) of -203 dB re 1V/µPa @ 1m is obtained analytically for a single element with 13mm diameter and a cavity depth of 600 micron with a band of 2-20 kHz. Also a wide band of 1-30kHz is achieved with 8mm cymbal element having the same cavity depth with a Receiving Sensitivity -202.84 dB re 1V/µPa @ 1m. Effect of encapsulation on the performance of cymbal transducers is studied and analytical results are in agreement with experimental results. There exist critical fabrication factors that affect the performance of these elements while fabricated in bulk quantities for an array. Reliable production procedure has been developed for manufacturing of cymbal elements and its arrays. A 1×3 array of 13mm diameter cymbal transducer has been fabricated and tested for in-air and in-water performances. The RS showed a maximum value of -178 dB re 1V/µPa @ 1m in a frequency range of 2-20 kHz with an in-house developed preamplifier having a gain of 20dB for a single element using brass as cap material. An array gain of nearly 6 dB is obtained when connected in series. The procedure adopted for the fabrication of Cymbal elements is critical for obtaining a flat hydrophone array response over a wide frequency range.