Microwave wireless power transmission techniques with microstrip antennas in human tissue for biomedical applications

Abstract

The main aim of this thesis is the investigation and optimisation of microstrip antennas and microwave techniques for wireless power transmission in human tissue at 2.45 GHz (i.e., in the Industrial, Scientific, and Medical band). For this purpose, microstrip antennas of different geometries and sizes and a microwave two-antenna setup that includes an implantable encased antenna and an external antenna, are designed and investigated computationally and experimentally. An implantable antenna module was designed by enclosing a microstrip rectangular patch antenna inside a protective dielectric housing. The simulation results showed that, by optimising the dimensions and the dielectric properties of the protective housing, the influence of the surrounding material on the performance of the implanted antenna can be reduced and the efficiency of wireless power transmission can be increased. The performance of wireless power transmission in different materials including tissue mimicking gel and fresh minced meat was experimentally investigated using a measurement system with the two-antenna setup. A parametric study was performed using the measured and simulated transmission coefficients to determine the unknown electrical properties of the materials. The measurement and simulation results are in good agreement. An implantable miniature encased microstrip ring disk antenna was designed and optimised for wireless power transmission in human tissue, and a computational model of a measurement system was proposed and used to characterise microwave two-antenna setup techniques. It was found that, by matching the resonant frequencies, aligning the directions of propagation of the electromagnetic waves and electric field polarisation vectors of the external and implanted antennas, maximum wireless power transmission in human tissue can be achieved even if the external and implanted antennas have different geometries and sizes. It was also found that reflections of the electromagnetic waves at the air-tissue interface can be reduced and the efficiency of microwave wireless power transmission techniques can be significantly enhanced by adding a matching dielectric layer between the external antenna and human tissue. A novel implantable open cylindrical-rectangular microstrip patch antenna was proposed and investigated. This antenna has a geometry and size that facilitates its direct implantation on nerves for the purpose of nerve stimulation. The simulation results showed that the two-antenna setup with the proposed antenna and a rectifier is capable of delivering a DC stimulus that can be used for nerve regeneration with a specific absorption rate that conforms to the IEEE safety standards. The results in this thesis showed that wireless power transmission in human tissue using microwave techniques with implantable microstrip antennas can provide sufficient power levels to be used for biomedical applications such as nerve stimulation. The use of microwave wireless power transmission with miniature implanted antennas can result in significant miniaturisation of implantable medical devices by eliminating the need for the implanted battery.

Date of Award	2015
Original language	English