Desenvolvimento de um absorvedor eletromagnético têxtil aplicado às bandas 4G E 5G

Abstract

Absorbing materials are developed to attenuate electromagnetic radiation and ensure the compatibility of electronic equipment in environments subject to interference. Although microwave frequency transmissions are essential for communication systems, absorber solutions are required to reduce the intensity of unwanted signals. This Thesis presents a flexible and low cost textile electromagnetic absorber designed for 4G and 5G technologies, operating at 2.5 GHz and 3.5 GHz. The developed material consists of a natural graphite and poly(vinyl alcohol) (PVA) composite applied onto a denim substrate. The electromagnetic losses of the device are based on the interaction of the incident wave with the conductivity and permittivity of the material, characterizing it as a resistive-type absorber. To verify the device efficiency, four samples were fabricated and tested, with thicknesses ranging from 0.96 mm to 1.05 mm, whose electromagnetic characterizations were performed using a Vector Network Analyzer (VNA) in the 2 GHz to 4 GHz frequency range. The electrical properties were analyzed to demonstrate its resistive behavior through conductivity and permittivity measurements, using the four-point probe and coaxial probe methods, respectively. To identify the structural and morphological properties of the composite, characterizations were performed by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and Fourier-transform infrared spectroscopy (FTIR). In the frequency band of interest, the results revealed significant attenuation between 2 GHz and 3.5 GHz, with values ranging from -11.89 dB (at 3.5 GHz) to -20.83 dB (at 2.14 GHz). The average attenuation was -16.96 dB in the 2 GHz to 2.5 GHz range; -16.93 dB between 2.5 GHz and 3 GHz; and -14.58 dB between 3 GHz and 3.5 GHz. The sample with the best absorption performance presented a direct current (DC) conductivity of 1.36 S/m, associated with an imaginary permittivity in the range of 1 < 𝜀′′ < 1.2 and a dielectric loss tangent between 0.1 < tan𝛿 < 0.15. These results demonstrated the efficiency of the absorber, which is characterized by electromagnetic losses predominantly driven by Joule heating.