Wireless power and communication system for medical implants
Item statusRestricted Access
Embargo end date30/11/2021
This thesis aims to examine the hypothesis that “Power of more than 1 mW can be received by the microsystem inside a human body through a wireless magnetic coupling link with a receiver of a diameter less than 2mm from a transfer distance as much as 20 cm” and “Data can be transmitted wirelessly from the microsystem to an external reader using the same magnetic coupling link as the wireless power system”. A 3-coil weakly coupled magnetic resonance wireless power transfer system has been built based on solenoid coils. The design of the transmitter of the system includes the designs of a single-turn coupling coil and a multi-turn primary coil. To maximise the magnetic field generated by the transmitter, the relative position of the two coils is optimised to match the impedances of the coils. Design flow is reported for the optimum dimensional parameters (coil diameter, gap interval, number of turns) of the primary coil after a detailed analysis of the co-dependencies of the parameters. The design of the receiver of the system includes the designs of the receiver coil and the rectifier. Two kinds of solenoid receiver coils have been analysed, the air-core coil and the ferrite-core coil. Due to the size limitation (2 mm-diameter) of the receiver, only the ferrite-core solenoid coil is able to meet the power demand. Design flow of the ferrite-core coil is reported. In terms of the rectifier, a novel static gate-control bootstrapping rectifier (static BSR) and a novel opto-coupled dynamic gate-control (OCDGC) bootstrapping rectifier are reported, which have low power consumption and high power conversion efficiency compared with junction-diode rectifiers and comparator-based rectifiers. The power delivered to load (PDL) of the whole WPT system is tested in air and human conductive tissue at transfer distances within 20 cm with consideration of rectifier power conversion efficiencies and different load conditions (500 Ω and 5 kΩ). Results show that, at 20 cm transfer distance, the system will be able to meet the 1 mW power demand for light load condition (5 kΩ) both in air and in human conductive tissue; But in heavy load condition (500 Ω), a high number of receiver coil turns will be needed to meet the power demand. The sensitivity of the data transfer of the whole WPT system is also analysed based on load shift keying (LSK) modulation. The S-parameter S11 ratio is the Figure of Merit (FOM) of the data transfer analysis. It can be concluded that the hypotheses of the thesis are feasible, which is an inspiration of multiple deep-tissue micro-implants for medical purposes.