Novel Variable Coupling Technique for Microwave Liquid Heating and Sensing

A simple new variable coupling technique is presented in this paper. The aim of the design is to optimize the coupling between the source and the microwave resonator in which the resonator can be used either as a microwave applicator or sensor. This technique suggests terminating the loop coupling between the coaxial transmission line and the cylindrical cavity with a variable capacitor. To prove the validity, the proposed approach was applied to a 2.45 GHz $\mathbf{TM}_{\pmb{010}}$ cylindrical cavity for heating and sensing of several types of solvents. The experimental results show the capability to reach any coupling value when the resonator is loaded with various liquid samples by adjusting the value of the terminating capacitor.