Study On New Methods To Measure Permittivity Of Biological Tissue By Using Open-ended Coaxial-line

Permittivity measurement is one of important bio-electromagnetic researches. In this paper, an improved open-ended coaxial-line probe is designed, which is suitable for measuring permittivity of erosion solutions. Moreover, a new method to get Debye parameters of biological tissue is presented.The traditional coaxial-line probe is difficult to resist the erosion and it's not sensitive, so several improved protective probes are designed. Finite difference time-domain method is used to calculate the reflection for these probes and absorbing boundary condition is used to deal with the singularity in the axis of the coaxial-line in the simulation. By comparing the reflection of different probes, the best probe has been selected according to sensitive requirement. The influence of parameters: such as thickness of protective film, length of protruding inner conductor of the coaxial-line probe to the measurement has been studied. And the optimal parameters for measurement are decided. When using the best probe to measure the solution whose permittivity has been known, measurement results agree with calculation results well.When coaxial-line probe is used to measure the permittivity of biological tissues, the pulse is used as an excitation in order to get more information in frequency domain. So frequency-dependent finite difference time-domain method is used to calculate the forward problem. It need not change the pulse into frequency-domain, and can calculate the problem in time-domain, which saves the memory space and makes calculation fastGenetic Algorithm (GA) is used to solve the inverse problem. It is a global optimal algorithm with many advantages, such as simple feasibility, easy common use, strong robustness, and so on. Calculation results prove that using GA can well efficaciously reconstruct the information of biological tissues, such as thickness and Debye parameters. In order to simulate the practical measurement, disturbance is added to the forward calculation results to find the effects of measure errors.Moreover, it proves that building right calculation model and finding good fitness function are key ways of improving calculation efficiency.