A novel microwave cancellation circuit for measuring nonlinear dielectric changes of polar solution under microwave fields

In this paper, an experimental set-up based on a novel microstrip cancellation circuit is presented for investigating the effects of external microwave fields on the dielectric properties of polar solution. The circuit consists of a 3 dB Wilkinson power combiner, a conventional 20 dB backward coupler, and a specially designed 20 dB single-sectioned forward coupler. Besides, in order to realize a uniform electric field in the tested solution, a nicked microstrip ring is designed in the circuit. An improvement of measurement sensitivity in the proposed circuit was obtained when compared to the conventional transmission lines method. We exploit interference cancellation processes to suppress the probing signal at the output port under the principle that two identical amplitude signals with 180° phase difference will completely cancel each other. The measurements are carried out at the frequency of 2.45 GHz, and the temperature effects caused by microwave heating are excluded by the flowing fluid. Experimental results show that the dielectric properties of DMSO–methanol/ethanol mixtures change at the electric field intensity of 10⁵ V m  −  1 and present a distinctly nonlinear dielectric change with the electric fields. The study of the microwave-material interaction has expanded our insights into the high-power microwave's industry application. (paper)