| Description |
Bioimplantable devices have been used to perform therapeutic functions such as drug delivery or diagnostic monitoring of physiological parameters. Proper operation of these devices depends on the continuous, reliable supply of power. Ultrasonic power transfer systems can wirelessly power bioimplantable devices. The power delivered to the implant should remain stable and reliable even with possible uncertainties in the location of the implant. Although commercial off-the-shelf (COTS) transducers are widely used in the literature, they may not be the best candidate for powering small implants since they may not be able to provide sufficient power in the presence of location uncertainties. In this work, a diaphragm-based structure, which uses piezoelectric materials (also known as piezoelectric micromachined ultrasonic transducers), is fabricated on a small scale suitable for implantable devices. The proposed process demonstrates a new method to fabricate ultrasonic power receivers for bio medical implants. For the first time, a MEMS scale ultrasonic power receiver suitable for bio implantable devices is designed and fabricated that enables the highest demonstrated power output to our knowledge. The pMUT is able to generate a power of 0.7 mW across an optimal resistive load of 4.3 kW when separated from the transmitter by a distance of 20 mm. The transmitter generates an input power intensity of 322 mW/cm2 at 88 kHz, less than Food and Drug Administration limit of 720 mW/cm2. A comparative study is performed between power generation capability of the pMUT and a COTS transducer with the same lateral dimensions as the pMUT. It is iv demonstrated that the pMUT has a more robust performance in the presence of location and orientation uncertainties compared to COTS bulk-mode piezoelectric transducers. Finally, this project compares the efficiency of acoustic power transfer systems to RF systems. The highest efficiency of the systems evaluated is an APT system with 12.8 mm diameter receiver, which achieves 46.5% efficiency at 30 mm separation distance. However, an APT with a smaller (2 mm ´ 2 mm) pMUT receiver results in 0.14% efficiency (4.5% area normalized efficiency) with at the same depth. This system can be slightly improved with a larger transmitter. |
