This work describes a novel measurement technique for determining the complex permittivity of powdered materials, based on resonant-perturbation of a Substrate Integrated Waveguide (SIW) resonator operating at ~2.5 GHz and calculations from General Dielectric Mixture Model equations. The proposed method is validated with standard powder samples measurement and comparison with the measured data by 3D electromagnetic simulation. The influence of the powder density is also discussed. The technique is then used to investigate the effect of hydrogen gas adsorption and humidity on the dielectric properties of tin oxide and zinc oxide powders, respectively. The SIW-resonator is a low cost and simple structure with good sensitivity. It is adapted for dielectric characterizations of both semi-solid and non-solid materials.
In this work, a novel microwave sensor fully based on Substrate Integrated Waveguide (SIW) technology filled with nanofibrillated cellulose for humidity detection is presented for the very first time. The proposed structure consists of a circular SIW cavity resonator perturbed by the inclusion of nano-fibrillated cellulose inside the cavity. Due to the presence of humidity, the relative permittivity of the eco-friendly dielectric, which is known as a humidity sensitive material, changes, leading to a shift of the resonance frequency of the Substrate Integrate Cavity Circular Resonator (SICCR). The proposed humidity sensor structure operates between 4.28 to 4.32 GHz and exhibits a frequency shift of around 20 MHz for relative humidity in the range of 11.7% to 91% RH. The proposed sensing device operates with very low-cost sustainable and renewable material, is simple to manufacture, co-integrates with existing microwave planar circuits and has the advantage of demonstrating high sensitivity performance.
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