Increasing piezoelectric effect in radially polarized soft piezoelectric cylinders by pressure treating and its practical applications.

Subjecting soft piezoelectric ceramics such as lead zirconate titanate (PZT)-5 to uniaxial stress in a direction perpendicular to the principal polarization axis is known to increase its transverse piezoelectric modulus [Krueger, J. Acoust. Soc. Am. 43 (3), 583-559 (1968)], however, practical transducer applications of this effect remain undeveloped. This study explores uniaxial pressure-treatment to develop experimental methods to realize practical pressure treatment, to use dynamic measurements of the electromechanical coupling coefficient k32, piezoelectric modulus, and dielectric constants, and to enhance piezoelectric properties and performance of underwater acoustic cylindrical transducer designs. The results of axial pressure treatment on parameters of the cylinders are shown to increase the coupling coefficient by about 20% and remained stable. The applicability of using pressure treated cylinders in transducer designs is investigated. The performance was analyzed under one-dimensional circumferential static compression and under the hydrostatic compression. When the improved piezoelectric cylinders are used in air-backed transducer designs, the benefit is only useful at shallow depths as it is observed that when subjected to increased hydrostatic pressure, the corresponding induced circumferential stress reduces the piezoelectric properties, namely, the coupling coefficient, to approximately its original pre-treated value. However, when the improved cylinders are used in transducers of the pressure-equalized design, such as liquid filled or free-flooded, the increase in coupling coefficient remains stable with environmental hydrostatic pressure.