Active Modal Coupling of a Nitinol Langevin Transducer

The Langevin transducer is widely adopted for power ultrasonic applications. Its basic configuration consists of a front mass, a back mass, lead zirconate titanate rings, electrodes, and a preloading bolt. Recent research of Langevin ultrasonic actuators is focused on modal coupling, such as utilising a bending-bending coupled mode and a longitudinal-bending coupled mode to generate complex output motions. However, one challenge is that there are often notable frequency differences between the modes to be coupled, normally due to assembly and machining inconsistencies. Therefore, an active modal coupling method is proposed to overcome this, using the shape memory alloy Nitinol. The elastic modulus of Nitinol is temperature dependent, which means that the dynamics of key parts of the Langevin transducer can be actively controlled by modest variations in temperature. In this study, a Nitinol Langevin transducer is manufactured, and its temperature-dependent dynamic properties studied. Admittance, conductance, and susceptance frequencies near the resonance frequency of two out-of-plane modes were investigated over a sufficiently wide temperature range around 100°C. The results show that the phase transformation of Nitinol can be used to promote active modal coupling in a Langevin transducer comprising this material.