A single-crystal acoustic hydrophone for increased sensitivity

This study describes the development of an underwater surveillance hydrophone based on next generation Lead Magnesium Niobate-Lead Titanate (PMN-PT) single-crystal piezoelectric as the hydrophone substrate. Although PMN-PT can possess much higher piezoelectric sensitivity than traditional PZT piezoelectrics, it is highly anisotropic and therefore there is a large gain in sensitivity only when the crystal structure is oriented in a specific direction. Because of this, simply replacing the PZT substrate with a PMN-PT cylinder is not an optimal solution because the crystal orientation does not uniformly align with the circumferential axis of the hydrophone. Therefore, we have developed a novel composite hydrophone that maintains the optimal crystal axis around the hydrophone circumference. An composite hydrophone cylinder was fabricated from a single <110> cut PMN-PT rectangular plate. Solid end caps were applied to the cylinder and the sensitivity was directly compared with a solid PZT-5A cylindrical hydrophone of equal dimensions in a hydrophone test tank. The charge sensitivity showed a 9.1 dB improvement over the PZT hydrophone and the voltage sensitivity showed a 3.5 dB improvement. This was in relatively good agreement with the theoretical improvements of 10.1 dB and 4.5 dB respectively.