Dynamic measurement of temperature dependent permittivity of liquid material using microwaves

Microwave heating is one of the key technology in medicine such as sterilization, synthesis of pharmacy and treatment. In application, it is necessary to obtain temperature dependent complex permittivity of material. For accurate measurement, one way is to apply a cylindrical cavity resonator. To apply microwave heating using the cavity resonator, it becomes possible to measure the temperature dependent permittivity of liquid material. In this study, TM₀₁₀ mode cylindrical cavity resonator is designed in 2.45GHz band and developed the system to measure complex permittivity of liquid material in various temperatures. The cylindrical cavity resonator allows high microwaves power excitation and it can heat the sample dynamically with the measurement. The characteristics of the complex permittivity of material as the temperature are measured by measuring transmission coefficient of the cylindrical cavity resonator with high power transmission. The result of changing permittivity of water and ethyl alcohol are obtained in various temperatures. In the case of water, the permittivity decreases as increasing the temperature. In the case of ethyl alcohol, the permittivity is increased and becomes the maximum at a point and then gradually decreased as increasing the temperature. In that temperature range, dielectric loss of ethyl alcohol gradually decreased. It is obtained that high accuracy measurement has been realized to evaluate temperature characteristic. It is useful for the measurement of complex permittivity in various liquid materials applied in medical field.