The design of ultrasonic lead magnesium niobate-lead titanate (PMN-PT) composite transducers for power and signal delivery to implanted hearing aids

We present a system for efficiently powering implanted hearing aids by transmitting an ultrasonic signal across the skin. The use of ultrasound as method for power and signal transfer is known for embedded systems in industrial applications and has more recently been investigated for use with other medical implants. In our application, ultrasonic transducers are investigated as they offer substantially reduced size relative to traditional magnetic induction coil power delivery. The developed transducers use lead magnesium niobate-lead titanate (PMN-PT) piezoelectric material in a 1–3 composite formulation. PMN-PT offers an electromechanical coupling factor (kt, an indicator of maximum efficiency) that is up to 60% greater than traditional piezoceramics, while the use of composite transducers removes geometric constraints that can limit the achieved efficiency. The fabrication methods for the transducers are detailed. Experimental results are presented to show the composite transducers achieve a kt of 0.86 (out of 1.00), and a power transmission efficiency that is improved by 38% relative to a similar non-composite transducers. It is also demonstrated that these transducers offer sufficient bandwidth for amplitude or frequency modulation schemes to transmit data signals along the power carrier beam.