Polymeric piezoelectric transducers for hydrophone applications

Conventional ceramic piezoelectric materials have been used in hydrophones for sonar applications since 1940′s. In the last few years since the discovery of polymeric piezoelectric hydrophones, the technology has matured, applications have emerged in extraordinary number of cases such as underwater navigation, biomedical applications, biomimetics, etc. Hydrophones are used underwater at high hydrostatic pressures. In the presence of hydrostatic pressures, the anisotropic piezoelectric response of ceramic materials is such that it has poor hydrophone performance characteristics whereas polymeric piezoelectric materials show enough hydrostatic piezoelectric coefficients. Moreover, piezoelectric polymers have low acoustic impedance, which is only 2–6 time that of water, whereas in piezoelectric ceramics, it is typically 11-time greater than that of water. A close impedance match permits efficient transduction of acoustic signals in water and tissues. Newly developed hydrostatic-mode polyvinylidene flouride (PVDF) hydrophones use a pressure-release system to achieve improved sensitivity. Recently, voided PVDF materials have been used for making hydrophones having higher sensitivity and figure of merit than unvoided PVDF materials.

FOM_m

Figure of merit for the raw piezoelectric material

Figure of merit for the finished piezoelectric hydrophones

Open circuit voltage sensitivity (volts per unit pressure)

Thickness

Piezoelectric stress constant for the 31 coupling mode

Piezoelectric stress constant for the 33 coupling mode

Hydrostatic mode piezoelectric stress constant (is the sum of the uniaxial stress constants)

Piezoelectric stress constant in the thickness mode

Stiffness constant is the stress-to-strain ratio in the thickness direction when the sides are clamped

Mechanical loss tangent

Dielectric loss tangent

Electromechanical coupling factor

Mechanical quality factor

Hydrostatic coefficient

Acoustic impedance