Waveguide Probes for Complex Permittivity Measurement

Paper deals with the complex permittivity measurement of biological tissues. Application of a waveguide probe for this measurement is shown. A non-destructive and non-invasive method based on reflection coefficient measurement attaching the material under test is used. New types of the probes are under investigation - the section of waveguide with H cross-section, the section of waveguide with the rectangular cross-section and with shorted walls, the section of waveguide with inserted dielectric wedge and finally the section of waveguide filled by the liquid dielectric. Properties of these prototypes are studied in the frequency range from 300 kHz to 3 GHz. The method of finite difference in time domain is utilized for the numerical modeling and simulation of the reflection coefficient. The condition for the input reflection coefficient of the waveguide probe is the range from (0.7 - 0.3) in the broad frequency band. Although the waveguide is a narrowband microwave component, its modifications could have broadband frequency behavior of the reflection coefficient. Results indicate that the most interesting and suitable is the solution with removable dielectric. This liquid dielectric with the low value of permittivity has significant influence on the cut-off frequency of waveguide with dominant mode propagation.