Ferroelectric nylon dielectric and electromechanical properties and ultrasonic transducer performance

Ferroelectric (odd-numbered) nylons have gained recent interest for their electromechanical properties which are competitive with PVDF and its copolymers for some sensor applications. Nylon-5, -7, and -11 films were prepared by melt quenching and cold drawing to impart three-dimensional molecular orientation. Their thickness-mode high frequency dielectric and electromechanical properties were characterized over a temperature range of 0-160°C using a piezoelectric resonance technique. These tests yielded electromechanical coupling coefficients, k_t, and mechanical quality factors, Q_m, which are competitive with PVDF. Measurements of the ultrasonic pulse-echo performance of ferroelectric nylon-7 were conducted and compared with PVDF and P(VDF-TrFE) copolymer with the use of a simple contact transducer test fixture. Comparisons were made of the pulse-echo insertion loss, pulse-width, and bandwidth performance. The effects of water absorption on nylon-7 properties and ultrasonic transducer performance are also reported