Exploiting Self-Capacitances for Wireless Power Transfer.

Conventional approaches for wireless power transfer rely on the mutual coupling (near-field or far-field) between the transmitter and receiver transducers. As a result, the power-transfer efficiency of these approaches scales non-linearly with the cross-sectional area of the transducers and with the relative distance and respective alignment between the transducers. In this paper, we show that when the operational power-budget requirements are in the order of microwatts, a self-capacitance (SC)-based power delivery has significant advantages in terms of the power transfer-efficiency, receiver form-factor, and system scalability when compared to other modes of wireless power transfer (WPT) methods. We present a simple and a tractable equivalent circuit model that can be used to study the effect of different parameters on the SC-based WPT. In this paper, we have experimentally verified the validity of the circuit using a cadaver mouse model. We also demonstrate the feasibility of a hybrid telemetry system where the microwatts of power, which can be harvested from SC-based WPT approach, is used for back-scattering a radio-frequency (RF) signal and is used for remote sensing of in vivo physiological parameters such as temperature. The functionality of the hybrid system has also been verified using a cadaver mouse model housed in a cage that was retrofitted with 915 MHz RF back-scattering antennas. We believe that the proposed remote power-delivery and hybrid telemetry approach would be useful in remote activation of wearable devices and in the design of energy-efficient animal cages used for long-term monitoring applications.

Feasibility of Self-Powering and Energy Harvesting Using Cardiac Valvular Perturbations.

In this paper, we investigate the feasibility of harvesting energy from cardiac valvular perturbations to self-power a wireless sonomicrometry sensor. Compared to the previous studies involving piezoelectric patches or encasings attached to the cardiac or aortic surface, the proposed study explores the use of piezoelectric sutures that can be implanted in proximity to the valvular regions, where non-linear valvular perturbations could be exploited for self-powering. Using an ovine animal model, the magnitude of valvular perturbations are first measured using an array of sonomicrometry crystals implanted around the tricuspid valve. These measurements were then used to estimate the levels of electrical energy that could be harvested using a simplified piezoelectric suture model. These results were revalidated across seven different animals, before and after valvular regurgitation was induced. Our study shows that power harvested from different annular planes of the tricuspid valve (before and after regurgitation) could range from nano-watts to milli-watts, with the maximum power harvested from the leaflet plane. We believe that these results could be useful for determining optimal surgical placement of wireless and self-powered sonomicrometry sensor, which in turn could be used for investigating the pathophysiology of ischemic regurgitation.

Multiaccess In Vivo Biotelemetry Using Sonomicrometry and M-Scan Ultrasound Imaging.

Objective: In this paper, we investigate the use of commercial off-the-shelf diagnostic ultrasound readers to achieve multiaccess wireless in vivo telemetry with millimeter-sized sonomicrometry crystal transducers. METHODS: The sonomicrometry crystals generate ultrasonic pulses that supersede the echoes generated at the tissue interfaces in response to M-scan interrogation pulses. The traces of these synthetic pulses are captured on an M-scan image and the transmitted data are decoded using image deconvolution and deblurring algorithms. RESULTS: Using a chicken phantom and 1.3 MHz sonomicrometry crystals of diameter 1 mm, we first demonstrate that a standard ultrasound reader can achieve biotelemetry data rates up to 1 Mb/s for implantation depths greater than 10 cm. For this experiment the maximum power dissipation at the crystals was measured to be 20 and bit-error-rate of the telemetry link was shown to be . We also demonstrate the use of this method for multiaccess biotelemetry where several sonomicrometry crystals simultaneously transmit the data using different modulation and coding techniques. Using a live ovine model, we demonstrate a sonomicrometry crystal implanted in the sheep 's tricuspid valve can maintain a continuous, reliable telemetry link at data rates up tob 800 Kb/s in the presence of respiratory and cardiac motion artifacts. CONCLUSION: Compared to existing radio-frequency and ultrasound based biotelemetry devices, the reported data-rates are significantly higher considering the transducer's form-factor and its implantation depth. SIGNIFICANCE: The proposed technique thus validates the feasibility of establishing reliable communication link with multiple in vivo implants using M-scan-based ultrasound imaging.