Acoustic Power Transfer Leveraging Piezoelectricity and Metamaterials

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Allam, Ahmed
Erturk, Alper
Sabra, Karim G.
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Acoustic power transfer, or ultrasonic power transfer (UPT) more specifically, has received growing attention as a viable approach for wireless power delivery to low-power electronic devices. It has found applications in powering biomedical implants, sensors in sealed metallic enclosures, and sensors deep in the ocean. The design of an efficient UPT system requires coupled multiphysics modeling to establish strategies toward maximizing the transferred power. This work, first, investigates different analytical and numerical models to analyze the performance of UPT systems to increase the transferred power. Various electromechanical models are developed to represent the transducer (transmitter or receiver) and overall system dynamics for a broad range of aspect ratios covering the diverse UPT applications. The main challenges that limit UPT system efficiency such as attenuation, power divergence, and reflection due to impedance mismatch issues are investigated using the developed models. These effects are investigated at the system level with an application to transfer power through metallic barriers using bonded piezoelectric disc transducers. A complete system for transferring power from the battery of a transmitter to the DC load of a receiver is designed and simulated, then experimentally tested. The experimental results of the system agree well with the modeling predictions, and the system can deliver 17.5 W to a DC load with a total DC-to-DC efficiency of 66 %. A second system with a portable and detachable dry-coupled transmitter is also experimentally tested. The dry-coupled system can deliver 3 W of DC power with 50 % efficiency from a 9V battery. Novel approaches using acoustic metamaterials/phononic crystals are introduced to enhance the efficiency of UPT through wave focusing. Specifically, two 3D phononic crystal structures based on air in a 3D-printed polymer matrix are introduced to manipulate acoustic waves both under water and in air. Two designs for gradient-index lenses are fabricated and experimentally characterized to focus acoustic waves on a piezoelectric receiver, thereby dramatically enhancing the power output. Finally, acoustic and electrical impedance matching are investigated for sending both power and data using ultrasonic waves. Several impedance matching techniques are proposed to maximize transducer bandwidth, power efficiency, as well as sensitivity for underwater data transfer. A novel approach is introduced for achieving simultaneous power and data transfer using frequency multiplexing with a single transducer. The introduced designs allow for configurable matching for maximizing power efficiency, maximizing data transfer, or simultaneously sending power to the transducer while receiving data with lower bandwidth.
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