No abstract

The accurate characterization of piezoelectric crystals should include the loss properties of the materials, which are represented as the imaginary parts of the material constants. The full complex properties of PMN-PT single crystals have never been evaluated. This paper proposes an automated iterative method to determine the complex material constants of PMN-28%PT single crystals. The PMN-28%PT single crystals were grown using the Bridgman method and were poled along the [001] direction to have 4mm effective symmetry. Five different resonators suitable for 4mm symmetry were used to analyze the impedance and admittance spectra of the distinctive resonant modes. The complex material constants were determined by the nonlinear regression of the impedance and admittance spectrum equations for each resonator through the iteration process to fit the measured spectra of the corresponding modes. The efficacy of the characterization method and the accuracy of the complex material constants determined using this method were verified by a comparison of the immittance spectra from the measurements with those from the calculation using the complex constants.

Typical underwater acoustic sensors can measure the magnitude of an incoming sound wave but cannot identify the direction. In this paper, a new simple method for detecting the direction of a sound wave with a piezoelectric ring hydrophone is proposed. This method divides the piezoceramic ring of the hydrophone into eight elements and distinguishes the direction of the sound wave by combining the output voltages of the elements in a particular manner. The validity of the design method was confirmed through the fabrication of an experimental prototype of the ring hydrophone with the proposed structure and a comparison of its performance with the design results. The method allows the ring vector hydrophone to operate over a very wide frequency range without being restricted to its structural resonant frequencies.

A piezoelectric artificial hair cell sensor was fabricated by the powder injection molding process in order to make an acoustic vector hydrophone. The entire process of powder injection molding was developed and optimized for PMN-PZT ceramic powder. The artificial hair cell sensor, which consists of high aspect ratio hair cell and three rectangular mechanoreceptors, was precisely fabricated through the developed powder injection molding process. The density and the dielectric property of the fabricated sensor shows 98% of the theoretical density and 85% of reference dielectric property of PMN-PZT ceramic powder. With regard to homogeneity, three rectangular mechanoreceptors have the same dimensions, with 3 μm of tolerance with 8% of deviation of dielectric property. Packaged vector hydrophones measure the underwater acoustic signals from 500 to 800 Hz with −212 dB of sensitivity. Directivity of vector hydrophone was acquired at 600 Hz as analyzing phase differences of electric signals.

In this paper, the resonant characteristic of a Tonpilz transducer with a fixed tail mass has been studied by means of an equivalent circuit approach. An equivalent circuit has been designed to describe the characteristic of a Tonpilz transducer that has an additional resonance because of its fixed tail mass. The transmitting voltage response of the transducer calculated by the designed circuit has been compared with that by the FEA (finite element analysis) to confirm the validity of the circuit. This equivalent circuit approach produces identical results with the FEA, in which the variation of resonant frequencies and TVR has been clearly figured out in relation to the stiffness of the mounting fixture and the mass of the tail mass. The suggested equivalent circuit can be utilized to figure out the characteristics of the Tonpilz transducer more efficiently than FEA that requires much calculation time and revision of the models in accordance with the variation of design variables.