Low dielectric loss and low-cost recycled borosilicate (BRS) glass-reinforced polytetrafluoroethylene (PTFE) composites were fabricated for microwave substrate applications. The composites were prepared through a dry powder processing technique by dispersing different micron sizes (25 µm, 45 µm, 63 µm, 90 µm, and 106 µm) of the recycled BRS filler in the PTFE matrix. The effect of the filler sizes on the composites’ thermal, mechanical, and dielectric properties was studied. The dielectric properties of the composites were characterised in the frequency range of 1–12 GHz using an open-ended coaxial probe (OCP) connected to a vector network analyser (VNA). XRD patterns confirmed the phase formation of PTFE and recycled BRS glass. The scanning electron microscope also showed good filler dispersion at larger filler particle sizes. In addition, the composites’ coefficient of thermal expansion and tensile strength decreased from 12.93 MPa and 64.86 ppm/°C to 7.12 MPa and 55.77 ppm/°C when the filler size is reduced from 106 μm to 25 μm. However, moisture absorption and density of the composites increased from 0.01% and 2.17 g/cm³ to 0.04% and 2.21 g/cm³. The decrement in filler size from 106 $\mathsf{\mu }$m to 25 $\mathsf{\mu }$m also increased the mean dielectric constant and loss tangent of the composites from 2.07 and 0.0010 to 2.18 and 0.0011, respectively, while it reduced the mean signal transmission speed from 2.088 × 10⁸ m/s to 2.031 × 10⁸ m/s. The presented results showed that PTFE/recycled BRS composite exhibited comparable characteristics with commercial high-frequency laminates.

This study was aimed at fabricating composites of polylactic acid (PLA) matrix-reinforced oil palm empty fruit bunch (OPEFB) fiber filled with chemically reduced graphene oxide (rGO). A total of 2–8 wt.% rGO/OPEFB/PLA composites were characterized for their complex permittivity using an open-ended coaxial probe (OEC) technique. The shielding efficiency properties were calculated using the measured transmission (S₂₁) and the reflection (S₁₁) coefficient results. All the measurements and calculations were performed in the 8–12 GHz frequency range. The morphological and microstructural study included X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Fourier transform infrared spectroscopy (FTIR). The results indicated that the incorporation of rGO as filler into the composites enhanced their complex permittivity properties. The composites showed a total shielding efficiency (SE_T) of about 31.2 dB at a frequency range of 8–12 GHz, which suggests their usefulness for microwave absorption.

The purpose of this study was to improve the dielectric, magnetic, and thermal properties of polytetrafluoroethylene (PTFE) composites using recycled Fe₂O₃ (rFe₂O₃) nanofiller. Hematite (Fe₂O₃) was recycled from mill scale waste and the particle size was reduced to 11.3 nm after 6 h of high-energy ball milling. Different compositions (5–25 wt %) of rFe₂O₃ nanoparticles were incorporated as a filler in the PTFE matrix through a hydraulic pressing and sintering method in order to fabricate rFe₂O₃–PTFE nanocomposites. The microstructure properties of rFe₂O₃ nanoparticles and the nanocomposites were characterized through X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). The thermal expansion coefficients (CTEs) of the PTFE matrix and nanocomposites were determined using a dilatometer apparatus. The complex permittivity and permeability were measured using rectangular waveguide connected to vector network analyzer (VNA) in the frequency range 8.2–12.4 GHz. The CTE of PTFE matrix decreased from $65.28\times {10}^{-6}/°\mathrm{C}$ to $39.84\times {10}^{-6}/°\mathrm{C}$ when the filler loading increased to 25 wt %. The real (ε′) and imaginary (ε″) parts of permittivity increased with the rFe₂O₃ loading and reached maximum values of 3.1 and 0.23 at 8 GHz when the filler loading was increased from 5 to 25 wt %. A maximum complex permeability of $\left(1.1-j0.07\right)$ was also achieved by 25 wt % nanocomposite at 10 GHz.

Polytetrafluoroethylene (PTFE)-based substrates are in high demand for high-frequency (microwave) applications because of their low relative permittivity, enabling efficient signal transfer. In this work, PTFE composites have been prepared with different content (5 wt.% - 25 wt.%) of soda lime silica glass (SLSG) for substrate application. The composites were characterized by their complex permittivity and S-parameters through the rectangular waveguide (RWG) measurement method over x-band frequency (8.2 GHz – 12.4 GHz). The RWG set-up was connected to a vector network analyser for the characterization. Power loss of the composites due to material absorption was calculated using the measured S-parameters. As the content of the SLSG increased from 5 - 25 wt.%, complex permittivity rose from 2.18-j0.0035 to 2.56-j0.0047 in the frequency range considered. In addition, |S11| reduced from 0.623 and 0.700 to 0.418 and 0.441, whereas |S21| varied from 0.780 and 0.713 to 0.906 and 0.895 for 5 wt.% and 25 wt.% SLSG contents at 8.2 GHz and 12.4 GHz, respectively. The calculated power loss increased from 2.94 dB to 3.29 dB and 4.01 dB to 4.88 dB for the same filler contents and frequency. Furthermore, the S-parameters were simulated using the finite element method (FEM) via COMSOL software and compared with the measured values. The comparison revealed a mean relative error of < 0.1, denoting the accuracy of the RWG method. Also, the electric field distribution across the waveguide length was visualized. Thus, the optimal performance of the composite was found at 5 wt.% SLSG filler content for microwave substrate application.