Enhanced-Sensitivity Noncontact Measurement of Liquid Concentration Based on Passive GPT-Symmetry

This paper presents a new sensing method based on passive generalized Parity-Time (GPT)-symmetry with enhanced sensitivity compared with the traditional method in the microwave frequency range. GPT-symmetry circuit that is the basis of the sensing method is derived, facilitating the establishment of a sensor. The perturbation of equivalent lumped elements including R, L and C to reflection coefficients of the circuit is investigated, showing better sensitivity of the resonant frequency shift, and in particular, reflection magnitude change to the perturbation than the conventional method. In addition, the operating frequency in this method can be tuned by the coupling coefficient. An experiment of noncontact measuring concentrations of glucose water is implemented to verify the method, showing the sensitivity in terms of the resonant frequency and reflection magnitude change is 12 MHz/[g/dl] and 20 dB/[g/dl] respectively which have a good consistency with the simulation. Noteworthily, weak coupling needed in this sensor indicates that we can easily carry out long-distance noncontact measurement with the high sensitivity.