Theory, Design and Implementation of Energy-Efficient Biotelemetry using Ultrasound Imaging

This dissertation investigates the fundamental limits of energy dissipation in establishing a communication link with implantable medical devices using ultrasound imaging-based biotelemetry. Ultrasound imaging technology has undergone a revolution during the last decade due to two primary innovations: advances in ultrasonic transducers that can operate over a broad range of frequencies and progresses in high-speed, high-resolution analog-to-digital converters and signal processors. Existing clinical and FDA approved bench-top ultrasound systems cangenerate real-time high-resolution images at frame rates as high as 10000 frames per second. On the other end of the spectrum, portable and hand-held ultrasound systems can generate high-speed real-time scans, widely used for diagnostic imaging in non-clinical environments. This dissertation’s fundamental hypothesis is to leverage the massive data acquisition and computational bandwidth afforded on these devices to establish energy-efficient bio-telemetry links with multiple in-vivo implanted devices. In the first part of the dissertation, I investigate using a commercial off-the-shelf (COTS) diagnostic ultrasound reader to achieve reliable in-vivo wireless telemetry with millimeter-sized piezoelectric crystal transducers. I propose multi-access biotelemetry methods in which several of these crystals simultaneously transmit the data using conventional modulation and coding schemes. I validated the feasibility of in-vivo operation using two piezoelectric crystals tethered to the tricuspid valve and the skin’s surface in a live ovine model. I demonstrated data rates close to 800 Kbps while consuming microwatts of power even in the presence of respiratory and cardiac motion artifacts. In the second part of the dissertation, I investigate the feasibility of energy harvesting from cardiac valvular perturbations to self-power the wireless implantable device. In this study, I explored using piezoelectric sutures implanted in proximity to the valvular regions compared to the previous studies involving piezoelectric patches or encasings attached to the cardiac or aortic surface to exploit nonlinearity in the valvular dynamics and self-power the implanted device. My study shows that power harvested from different annular planes of the tricuspid valve could range from nano-watts to milli-watts. In the final part of this dissertation, I investigate beamforming in B-scan ultrasound imaging to further reduce the biotelemetry energy-budget. In this context, I will study variance-based informatics in which the signal representation takes a form of signal variance instead of the signal mean for encoding and decoding. Using a modeling study, I show that compared to the mean-based logic representation, the variance-based representation can theoretically achieve a superior performance trade-off (in terms of energy dissipation) when operating at fundamental limits imposed by thermal-noise. I will then discuss how to extend variance-based representation to higher signal dimensions. I show that when applying variance-based encoding/decoding to B-scan biotelemetry, the power-dissipation requirements can be reducedto 100 pW even while interrogating from depths greater than 10 cm in a water medium

Self Capacitance based Wireless Power Transfer for Wearable Electronics: Theory and Implementation

Wireless power transfer (WPT

Ultrasound data communication system for bioelectronic medicines

PhD ThesisThe coming years may see the advent of distributed implantable devices to support bioelectronic medicinal treatments. Such treatments could be complementary and, in some cases, may even prove superior to pharmaceutical treatments for certain chronic disease conditions. Therefore, a significant research effort is being undertaken in the bioelectronics domain. Target conditions include diabetes, inflammatory bowel disease, lupus, and arthritis. Modern active medical implantable devices require communications to transmit information to the outside world or other implantable sub-systems. This can include physiological data, diagnostics, and parameters to optimise the therapeutic protocol. However, the communication scheme can be very challenging especially for deeper devices. Challenges include absorption and scattering by tissue, and the need to ensure there are no undesirable heating effects. Wired connectivity is undesirable and tissue absorption of traditional radio frequency and optical methods mean that ultrasound communications have significant potential in this niche. In this thesis, a reliable and efficient ultrasonic communication telemetry is presented. An omnidirectional transducer has been employed to implement intra body communication inside a model of the human body. A prototype has been implemented to evaluate the system performance in saline and up to 30 distance between the transmitter and receiver. Short pulses sequences with guard intervals have been employed to minimise the multipath effect that leads to an increase in the bit and thus packet error rates with distance. Error detection and correction code have been employed to improve communication at a low signal to noise ratio. The data rate is limited to 0.6 due to the necessary guard intervals. Energy per bit and current consumption for the transmitter and receiver main parts are presented and discussed in terms of battery life. Transmission can be achieved at an energy cost of 642 per bit data packet using on/off power cycling in the electronics