No abstract

We report a large electrostrictive strain in electron irradiated poly(vinylidene fluoride–trifluoroethylene) copolymer at a composition with 65 mol % vinylidene fluoride, which also exhibits a large ratio of strain to applied field (∼275 pm/V). The strain response is nearly independent of the external driving condition (unipolar or bipolar field) and does not change with temperature in about 20 °C temperature range near room temperature. Moreover, near room temperature, the material can reach a relatively high quasistatic longitudinal electromechanical coupling factor k33∼0.33.

A dilatometer based on the cantilever beam concept has been developed. The dilatometer is easy to use and capable of measuring transverse strain response of soft polymer films in a broad strain range ͑from 10 Ϫ7 to 10 Ϫ1 ͒ without mechanical constraining of the sample. It is capable of detecting strain over a relatively wide frequency range from mHz to above 100 Hz under different load and temperature. Using the setup, the electric field induced transverse strains of the electrostrictive poly͑vinylidene fluoride-trifluoroethylene͒ copolymer films were characterized which shows that a large transverse strain can be achieved in this class of polymer. In addition, the effect of mechanical tensile load on the transverse strain was also evaluated and the results show that the strain response will be affected by the load. However, depending on the load level, the strain response of the polymer film under a given electric field may increase or decrease with load. Based on the phenomenological theory, it is shown that for a ferroelectric based material, the mechanical load will shift the Curie temperature. Hence, to a large extent, the change of the strain response with load observed here can be understood by linking it to the strain change with temperature.

Most existing sonar transducer technologies that are capable of producing broadband, high power acoustic signals required for future Navy needs, are only conceptual in design, or very early into their development stage. A high power broadband 16 element array of Hybrid Magnetostrictive / Piezoelectric Tonpilz Transducer (MPT) projectors is currently being developed at Naval Undersea Warfare Center (NUWC), Newport, R. I. for these applications. The Hybrid Transducer combines the high strain magnetostrictive material, Terfenol-D, with that of Lead Zirconate Titanate piezoelectric ceramic, to create a double resonant, high power broadband device. This design provides a 1 kHz increase in bandwidth below the low end of the frequency band of a conventional piezoelectric Tonpilz transducers of the same size and weight. The theory of operation, fabrication technique and test results will be discussed for a single element and then compared with a conventional Tonpilz sonar transducer of same size and weight. Modeling and measurement data for the 16-element array will also be discussed

Investigations of the polarization versus electric field (P-E) and strain versus electric field (ε-E) responses for “hard” Pb(Zr1−xTix)O3 piezoelectric ceramics have been performed under various uniaxial stresses (σ) and ac electrical drive fields. Investigations revealed a significant decrease in the remanent polarization of specimens with increasing σ. Subsequent calculations of the longitudinal electromechanical coupling coefficient (k33) and acoustic power density revealed significant enhancements with increasing σ.