In this work, a multi-mode Hilbert-fork resonator consisting of two dual-mode resonators is presented. The behavior of the proposed configuration is analyzed in detail. To demonstrate the potential of the proposed resonator, tri-band bandpass and bandstop filters operating at 2.4/3.5/5.2 GHz have been designed, fabricated and measured. Both filters are characterized by good performances and very compact size of only 0.21λg × 0.11λg and 0.22λg × 0.1λg , respectively.

In this paper, we investigated the effect of humidity on paper substrates and propose a simple and low-cost method for their passivation using ZnO nanoparticles. To this end, we built paper-based microdevices based on an interdigitated electrode (IDE) configuration by means of a mask-less laser patterning method on simple commercial printing papers. Initial resistive measurements indicate that a paper substrate with a porous surface can be used as a cost-effective, sensitive and disposable humidity sensor in the 20% to 70% relative humidity (RH) range. Successive spin-coated layers of ZnO nanoparticles then, control the effect of humidity. Using this approach, the sensors become passive to relative humidity changes, paving the way to the development of ZnO-based gas sensors on paper substrates insensitive to humidity.

This paper describes the fabrication and the characterization of an original example of a miniaturized resistive-type humidity sensor, printed on flexible substrate in a large-scale manner. The fabrication process involves laser ablation for the design of interdigitated electrodes on PET (Poly-Ethylene Terephthalate) substrate and a screen-printing process for the deposition of the sensitive material, which is based on TiO₂ nanoparticles. The laser ablation process was carefully optimized to obtain micro-scale and well-resolved electrodes on PET substrate. A functional paste based on cellulose was prepared in order to allow the precise screen-printing of the TiO₂ nanoparticles as sensing material on the top of the electrodes. The current against voltage (I–V) characteristic of the sensor showed good linearity and potential for low-power operation. The results of a humidity-sensing investigation and mechanical testing showed that the fabricated miniaturized sensors have excellent mechanical stability, sensing characteristics, good repeatability, and relatively fast response/recovery times operating at room temperature.

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.

Conventional approaches to the control of acoustic waves propagating along boundaries between fluids and hard grooved surfaces are limited to the manipulation of surface geometry. Here we demonstrate for the first time, through theoretical analysis, numerical simulation as well as experimentally, that the velocity of acoustic surface waves, and consequently the direction of their propagation as well as the shape of their wave fronts, can be controlled by varying the temperature distribution over the surface. This significantly increases the versatility of applications such as sound trapping, acoustic spectral analysis and acoustic focusing, by providing a simple mechanism for modifying their behavior without any change in the geometry of the system. We further discuss that the dependence between the behavior of acoustic surface waves and the temperature of the fluid can be exploited conversely as well, which opens a way for potential application in the domain of temperature sensing.