A low-density extended acoustic sensor for low-frequency arrays

A novel PVDF hydrophone is described which has a sensitivity of -183 dBV/μPa or better and can be made in lengths from 4 cm to more than 1 m, and in diameters from 8 mm to >40 mm. It is based on a piezoelectric PVDF cable which allows considerable design freedom because of its very great mechanical flexibility and high longitudinal piezoelectric coefficient. The design centres on a helical structure which translates a hydrostatic pressure field into a longitudinal compressive strain in the cable and thus makes use of the very sensitive mode. Excellent pressure stability can be achieved, with devices showing a pressure dependency of 0.04 dB/MPa. The device has a flat frequency response from less than 1 Hz to several kHz and a density in the region of 1800 kg/m³, making it suitable for application in low-frequency sonar