Active and passive electronic interfaces adapted to a capacitive micromachined ultrasonic transducer (CMUT) used in acoustic energy transfer

Wireless power transfer is a key feature in the field of biomedical engineering. It allows a reduction of the energy storage devices in medical implants. An efficient way to safely transfer energy to medical implants is to convey ultrasounds through the body to a Capacitive Micromachined Ultrasonic Transducer (CMUT). For an application of ultrasonic energy transfer through skin, the present work compares the efficiency of two different electronic architectures to receive energy from an array of CMUT. The well known Synchronous Switch Harvesting on Inductor (SSHI) is compared in simulation to a simple impedance matching. Indeed, for an ultrasonic energy transfer, the high excitation frequency (1-8MHz) allows the use of an inductor matching the CMUT's clamped capacitor. The simplicity of an impedance matching circuit, its low volume and its efficiency makes it the best choice for an efficient energy transfer process to the targeted load. The CMUT model used in the simulations is a mason's model which component values are extracted from the impedance measurement of a real device. In the end, the impedance matching is experimentally tested on this same device and compared to the simulation. A maximum 4,5 mW power is transferred to an optimal load for an input ultrasound pressure of 90 kPa.