Design and Experimental Validation of a Switchable Frequency Selective Surface with Incorporated Control Network.

Tunable/switchable devices are more and more required in modern communication systems. However, the realization of the tuning requires the presence of active devices, which in turn must be biased. The current paper comes up with a solution for designing and experimentally validating such a switchable Frequency Selective Surface. Two different metallic structures are simulated and measured, having incorporated the same topology control network (CN). In this scenario, the main innovation of this paper is the presence of the feeding part, namely the control network. In this work, the main FSS structure is flanked by three parallel CN microstrip lines and several via holes that allow biasing the active elements, namely PIN diodes. The switchability of the proposed structure is achieved through PIN diodes, whose bias determines the values of the elements in the equivalent circuit. At different biases, the response of the FSS changes accordingly. From all possible values of the bias, the extreme cases when the diodes act as (almost) short- and open-circuits are considered in the submitted manuscript for the sake of brevity. These cases are modeled by the main and cut-slot structures, respectively. The proposed structures have been evaluated using electromagnetic simulation and implemented on an FR4 substrate having a thickness of 1.58 mm. With the periodicity of the square-shaped unit cell of 18 mm edge length, different filtering bands are obtained below 12 GHz. Another novelty that has received very little consideration in the existing literature is the use of a finite array of unit cells instead of an infinite one. And finally, tests in an anechoic chamber have proved that there is a good agreement between practical and simulation results and also demonstrated the proper performance of the devices for wide angular incidence for both TE and TM polarizations.

Frequency Selective Surface for Ultra-Wide Band Filtering and Shielding.

A frequency selective surface for spatial filtering in the standardized Ultra-Wide Band (UWB) frequency range is proposed. A very large stop-band of 1.75-15.44 GHz has been obtained, with good polarization insensitivity and an angular stability of more than 60∘ and more than 50∘ in TE and TM incidence, respectively. Circuit models have been devised. The structure has been assessed by electromagnetic simulation and implemented on an FR4 substrate of 1.6 mm thickness, with an edge of the square-shaped unit cell of 15 mm. Tests in an anechoic chamber demonstrated good matching between simulation and experimental results and proper operation of the device.

Calprotectin in viral systemic infections-COVID-19 versus hepatitis C virus.

This study aims to evaluate differences in serum and fecal calprotectin in patients with HCV chronic hepatitis and COVID-19 infection and compare them to a control group. This observational study was performed between April 2020 and October 2020 in a single Internal Medicine center. We determined serum and fecal calprotectin, as well as levels of transaminases, C-reactive protein, ferritin, in 25 patients with COVID-19 infection, 30 patients with active HCV chronic infection and 38 patients with cured HCV infection. Serum levels of ALT, AST, C-reactive protein and ferritin were significantly higher in patients with COVID-19 infection (mean values of 127 IU/mL, 135 IU/mL, 123 mg/L and 1034 ng/mL, respectively) than in patients with active HCV infection (mean values of 68 IU/mL, 51 IU/mL, 17 mg/L and 528 ng/mL, respectively) or in patients with cured HCV infection (37 IU/mL, 29 IU/mL, 3.4 mg/L and 274 ng/mL, respectively). Also, serum and fecal calprotectin had increased concentrations in patients with COVID-19 (7.3 µg/mL and 394 µg/mg) versus patients with active hepatitis (2.4 µg/mL and 217 µg/mg) and patients with cured hepatitis (1.2 µg/mL and 38 µg/mg). Values were significantly higher in patients with digestive symptoms related to COVID-19. Serum and fecal calprotectin can be used as inflammatory markers in patients with active viral infections. In COVID-19, calprotectin concentrations can be correlated to the severity of disease, particularly in patients with digestive symptoms.