SUMMARY

Recently, there has been an increased interest in wireless power transfer, energy harvesting and passive remote sensing with the emergence of implantable medical devices (IMDs), internet of things (IOT), wearable electronics and many other applications looking to eliminate wires and battery replacements. Piezoelectric transducers are typically preferred as the receiver element in acoustic sensors and transducers as they are completely passive devices that can be operated without the need for a power supply. However, various manufacturing, performance and integration challenges arise specially when using piezoelectric transducers in high frequency and implantable medical applications. As an alternative, capacitive or electrostatic transducers have been used for a variety of sensing and medical imaging applications as the can be realised with standard bulk and surface micromachining techniques, demonstrate high sensitivity with low power consumption and can be easily integrated with electronics via CMOS compatible processes. Despite these advantages, a DC bias or a permanent charge is required to operate a capacitive transducer, making them unsuitable for low power and remote sensing applications where a passive system is preferred. The objective of this research is to develop a new type of electromechanical transducer that operates based on the principle of parametric resonance. Such a transducer can potentially operate without the need for a DC bias or pre-charge and can be electronically integrated using industry compatible processes. Inspired by the original varactor-based parametric amplifier, the proposed capacitive parametric ultrasonic transducer or CPUT consists of a capacitive transducer coupled to an electrical RLC resonator. The electrical circuit can be driven into parametric resonance by mechanically pumping the capacitive transducer, thereby converting mechanical energy into electrical power without needing a DC bias. A lumped parameter mathematical model is developed to study the characteristics of the proposed transducer and with the help of numerical simulations and experimental demonstrations, it is shown that the CPUT can be operated as a highly efficient transducer for ultrasonic power transfer in both air and water. Deeper investigation into the operating characteristics of this class of parametrically excited capacitive transducers reveal tremendous utility in applications such as highly directional acoustic sensing, broadband vibration energy harvesting and passive vibration control. Finally, the transducer is used to generate phononic or acoustic frequency combs in a heavily damped medium for the first time. The development of these frequency combs enables a new scheme of mass measurement based on tracking the frequency shifts of high Q-factor acoustic resonances in fluid, which offers great promise in microfluidic sensing applications. Link: https://primetime.bluejeans.com/a2m/live-event/zagqcfae