In this paper, we present a Fano metal-insulator-metal (MIM) structure based on an isosceles triangular cavity resonator for refractive index sensing applications. Due to the specific feeding scheme and asymmetry introduced in the triangular cavity, the resonator exhibits four sharp Fano-like resonances. The behavior of the structure is analyzed in detail and its sensing capabilities demonstrated through the responses for various refractive indices. The results show that the sensor has very good sensitivity and maximal figure of merit (FOM) value of 3.2 × 10⁵. In comparison to other similar sensors, the proposed one has comparable sensitivity and significantly higher FOM, which clearly demonstrates its high sensing potential.

In this paper, we present two novel dual-band bandpass filters based on surface plasmon polariton-like (SPP-like) propagation induced by structural dispersion of substrate integrated waveguide (SIW). Both filters are realized as a three-layer SIW where each layer represents asub-SIWstructure with intrinsic effective permittivity that depends on its width and filling dielectric material. The layers are designed to have effective permittivities of opposite signs in certain frequency ranges, which enables SPP-like propagation to occur at their interfaces. Since three layers can provide two distinct SPP-like propagations, the filters exhibit dual-band behaviour. A detailed theoretical and numerical analysis and numerical optimization have been used to design the filters, which were afterwards fabricated using standard printed circuit board technology. The independent choice of geometrical parameters ofsub-SIWsand/or the corresponding dielectric materials provide a great freedom to arbitrarily position the passbands in the spectrum, which is a significant advantage of the proposed filters. At the same time, they meet the requirements for low-cost low-profile configuration since they are realized as SIW structures, as well as for excellent in-band characteristics and selectivity which is confirmed by the measurement results.

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-like (SPP) 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 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 engine and edible oil quality analysis.

We explore the implementation of a spoof–fluid-spoof (SFS) acoustic waveguide, which is the acoustic analogue of a metal-insulator–metal waveguide in plasmonics. The proposed structure consists of two corrugated rigid surfaces separated by a fluid layer. The properties of the guided acoustic modes between corrugated rigid parallel plates are analytically and numerically studied by deriving their dispersion relation and through a careful analysis of symmetric and antisymmetric modes supported by this structure. Similar to plasmonic waveguides, it is shown that the dispersion relation of the proposed SFS acoustic waveguide, and the supported group and phase velocities, can be largely controlled by changes in the geometrical parameters of the waveguide, opening the possibility for application of this technology for acoustic delay lines, modulators, and sensors. The analytical and numerical results are validated through experiments in a controlled environment.

We present a plasmonic bandpass filter and refractive index sensor based on perturbed square cavity resonator with slits, which is fed by orthogonally oriented feeding waveguides. The slits provide size reduction in comparison to conventional square cavities and better coupling to the waveguides, while the perturbation and orthogonal feeding scheme provide a pair of transmission zeros in the response of the structure. In that manner, a bandpass filter with high transmission, narrow bandwidth, and excellent selectivity can be readily designed. Moreover, with a slight modification of the structure, a very sharp Fano-like response can be obtained and employed for refractive index sensing with high sensitivity and figure of merit.