Electronics-free passive ultrasonic communication link for deep-tissue sensor implants

Wireless communication technologies are critical for the non-invasive in-situ monitoring of vital signs in deep tissues. Wireless ultrasonic links demonstrated so far solved the shortcomings of electromagnetic wave-based communication methods. However, they either require highly customized and complex designs for the implant electronics or rely on physical changes in implanted metamaterials. This thesis proposes a novel wireless ultrasonic communication method for implantable applications. The method utilizes a small piezoelectric material used as an antenna, connected to a capacitive sensor in parallel. The capacitive changes occurring in the integrated sensor cause the resonance characteristics of the antenna to change. These changes can be captured by ultrasound pulse-echo measurements conducted by a broadband interrogator ultrasonic transducer. Thus, a wireless and electronics-free ultrasonic communication link can be realized for deeply implanted capacitive sensors. The ultrasonic antenna is designed based on the equivalent circuit modeling results. The bulk piezoceramic material selection is done considering the piezoelectric properties and availability. The fabricated antenna and the proposed communication method are characterized. Additionally, the antenna is integrated with a commercial capacitive pressure sensor and the proposed method is demonstrated in vitro at a depth of 5 cm in order to evaluate the systems's applicability using medically relevant pressures. The method demonstrates decent performance, with a maximum sensitivity of -236.2 Hz/pF. The proposed communication method enables simple implant design and fabrication, eliminates the need for integrated circuits and power harvesting circuitry, and offers flexibility in terms of sensor integration since any capacitive sensor can be integrated into the system.