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This paper presents a planar and compact microwave resonator sensor to characterize materials. The geometry of the resonator is based on the Sierpinski fractal curve and has four poles in the frequency range from 0.5 GHz to 5.5 GHz. Any of the four poles can be used to measure samples with low permittivity values, where the first pole is suitable for samples with high permittivity values. The sensitivity of the poles and return losses of the sensor are presented and obtained using a full-wave 3D simulator software. The device is manufactured and validated through a comparison between simulated and measured results. © 2020 P. H. B. Cavalcanti Filho et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This study presents a microwave planar sensor for characterisation of powdered foods. The sensor is based on four coupled resonators designed to have four poles in the frequency range of 1.0-3 GHz. The pole with more sensitivity is used to measure the samples. The frequency characteristics of the sensor are obtained measuring several well-known samples. It is used to estimate the permittivity of six types of grains. The grains are two types of oatmeal, three types of corn and wheat flour. The experimental results have shown a sensitivity of 36 MHz/Fm -1 . The estimated permittivity of materials can be used as the preliminary data for further investigation.

The authors present a reconfigurable frequency selective surfaces (RFSS) structure with two states based on the cross-dipole element. The structure is designed to behave as an array of cross-dipole elements in one state, and as an array of hash elements in the other state. The cross-dipole patch array has a stop-band filter response, and the hash array behaves as a pass band filter at the design frequency of 12.5 GHz. The frequency response of these filters is analysed using the equivalent circuit method. Computer simulation technology (CST) software simulations and experimental results are used to validate the RFSS design.

This paper proposes a new Frequency Selective Surface (FSS) with modifications on the Jerusalem Cross (JC) geometry to provide a multiband response. Fractal levels are created by introducing concentric self-similar JC copies in the original unit cell. This modification results in new dipoles at the structure which allows for the appearance of new bands proportional to these diploles’ lengths, while maintaining total unit cell size. Three fractal levels of the JC FSS are studied in this paper, and third level presents five resonant frequencies which are f1 = 1.78 GHz, f2 = 6.42 GHz, f3 = 8.69 GHz, f4 = 10.94 GHz and f5 = 12.98 GHz. Simulation results for the insertion loss (S21), surface current distribution and measurement results are presented.