Fabrication and Characterisation of a Nitinol Langevin Transducer

A new generation of ultrasonic transducer is emerging which incorporates advanced materials such as shape memory alloys. Recently, the flextensional cymbal transducer was fabricated using the shape memory alloy Nitinol to introduce tuneable frequency dynamics for applications including adaptive sensing. The elastic properties of Nitinol are highly dependent on modest temperature shifts, hence frequency tuneability of thousands of Hz was possible. However, this has not yet been achieved for the Langevin ultrasonic transducer, one of the most common power ultrasonic classes. To investigate the opportunities for a tuneable frequency, or adaptive, Langevin transducer, this study aims to explore the fabrication challenges in transducer construction and demonstrate the dynamic characteristics of a prototype. End-masses of the Nitinol Langevin transducer were fabricated by the electrical discharge machining, after which characterisations were conducted through laser Doppler vibrometry at ambient room temperature and impedance analysis at elevated temperatures towards 50°C. Results demonstrate the tuneability of the resonance and antiresonance frequencies, in the order of 1 kHz, and their electrical impedances. This research demonstrates the potential for adaptive ultrasonic Langevin transducers for a wide range of medical and industrial applications.