Microwave Surface Plasmon Polariton-Like Sensor Based on Half-Mode Substrate Integrated Waveguide for Highly Sensitive Dielectric Constant Detection

Microwave sensors have attracted a considerable attention since they can provide non-invasive, label-free, and real-time detection; however, they often suffer from low sensitivity and resolution. In this paper, we present a novel highly sensitive microwave sensor based on half-mode substrate integrated waveguide (HM SIW) that supports surface plasmon polariton (SPP)-like propagation. Two comprising guiding parts of HM SIW, one of which contains the sensed analyte, exhibit the real parts of the effective permittivities of the opposite sign in a specific frequency range, which allows for SPP to propagate at their interface. Ultimately, such behavior causes a sharp transmission zero to occur in HM SIW response, whose spectral position is highly sensitive to the real part of the dielectric constant of the sensed analyte. To demonstrate the sensing potential, HM SIW sensor has been fabricated in low-cost PCB technology and its response is measured for different toluene/methanol mixtures whose real part of the dielectric constants range from 2.4 to 3.8. Measurement results together with a detailed theoretical and numerical analysis, confirm that the sensor is an excellent candidate for very sensitive dielectric constant measurements with low relative error, which can be applied in the engine and edible oil quality analysis.