The development of a piezoelectric hydrophone based on lead magnesium niobate-lead titanate [PbMg1/3Nb2/3O3-PbTiO3 (PMN-PT)] single-crystal piezoelectric as the hydrophone substrate is reported. Although PMN-PT can possess much higher piezoelectric sensitivity than traditional lead zirconate titanate (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, a composite hydrophone that maintains the optimal crystal axis around the hydrophone circumference has been developed. An 11.3 mm diameter 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 good agreement with the expected theoretical improvements of 10.1 and 4.5 dB, respectively.
This paper deals with the acoustic radiation from an unbaffled rotating disk. It is shown that when the disk is rotating, the natural modes are no longer stationary modes but are transformed into rotating waves. Using the concept of rotating waves instead of the retarded time potential method, rotation effects are taken into account in the vibratory part of the problem. Thus no assumption has to be made on the rotation speed and the near pressure field can be evaluated. A new collocation method is proposed to solve the double-layer potential problem which does not require evaluating double-surface integration as when using classical methods. A new analytical formula is established to evaluate the Hadamard finite part of the auto-influent terms. Radiation efficiencies of unbaffled rotating waves are calculated and charts are given which are useful for designing quiet circular disks such as saw blades or rotating wheels. Rotating waves are classified as radiating and nonradiating. The disk is not assumed to be baffled as it is the classical case; therefore, the charts given in this study can be used directly for real cases.
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