Development of a microwave ablation system for medical applications

Abstract

Microwave ablation is a type of cancer treatment that can be performed percutaneously. This ablation technique can be used as an alternative to standard surgical therapies, with potential benefits of reduced morbidity. The treatment is performed by inserting a needle-like applicator, incorporating a microwave antenna. The microwaves propagates in the surrounding tissue, generate heat through a process known as dielectric hysteresis. The frequency of operation of such treatment is 2.45GHz and 915MHz. This thesis investigated the design of a coaxial based monopole antenna. The design involved a simulation model on Computer Simulation Technology (CST) Studio. The validity of the model was proven methodological by design of experiments. The series of tests were performed using a Vector Network Analyser (VNA). In the primary phase of this project a coaxial cable was characterised to serve as the base on which the coaxial based monopole antenna will be designed. The characterisation of the coaxial cable also assisted to get acquainted with the CST studio software and equipment. The process involved using transmission line theory of a matched terminated transmission and measure and compare Scattering Parameters (S-Parameters) from the simulation model and the experimental setup by means of Smith Charts. The second phase of this thesis involved the validation of biological model, included in the CST studio library. This was followed with the design of a coaxial based monopole antenna. Series of tests were conducted using tissue mimicking solutions. Using impedance transformation techniques as a tool the characteristic impedances were compared using different variants of lengths of antennae and solutions. Finally proceeding to the validation of the model, the design of the antenna was optimised on the simulation model. The result was constructed and tested using the experimental setup. In this thesis, base models of two different coaxial cables were verified where one was used as the base to design the coaxial base monopole antenna. The models of biological tissue in CST studio of muscle, blood and liver also showed consistency with the mimicking solutions used in the lab. A base model of a monopole antenna was designed and verified were results revealed to be compatible with theory.