A balanced, centrally stiffened design for PVDF hydrophone arrays

Abstract

As PVDF thick films become more readily available, there has been a growing interest in the development of a large-area hydrophone for passive sonar applications. These new PVDF materials offer the advantages of having a lower density, greater mechanical strength and flexibility, and better impedance match to water than conventional piezoelectric ceramics. Furthermore, they are now available in large sheets, from which arrays can be developed for acoustic detection covering large surface areas. Prototype PVDF hydrophone arrays were fabricated and tested to show that in-plane flexural motion greatly affected hydrophone responses due to the in-plane anisotropy of the piezoelectric properties of PVDF. To circumvent this difficulty, a balanced, centrally stiffened configuration was adapted by sandwiching two pieces of PVDF to a common damped plate, while aligning in parallel the stretched “3—1” directions of the PVDF sheets. With this design, constant receiving sensitivity and directivity patterns in agreement with theoretical predictions were obtained. Further refinement of this design was also achieved through mathematical modeling. [Work supported by ONR.]