Dielectric Characterization of Ultrathin Softwear Flexible Substrates Intended for Wearable Biomedical Applications

In this paper, dielectric properties of low-cost and ultrathin flexible materials are accurately determined over frequency range from 1.0 GHz – 12.0 GHz. In particular, four substrate samples of cotton, jeans, Polydimethylsiloxane (PDMS), and silicone rubber (Ak-Sil T1310) owing to their flexibility and robustness are considered in this study. The dielectric constant ($\varepsilon_{\mathrm{r}}^{\prime}$) and loss factor ($\varepsilon_{\mathrm{r}}^{^{\prime\prime}}$) of these samples are extracted using microstrip resonator method and X-band rectangular waveguide method. The accuracy of the applied techniques for the dielectric characterization is confirmed by measuring the dielectric properties of a commercially available FR4 substrate using the same employed methods. The average dielectric constant values of 1.80, 168, 2.87, 2.70 for 0.4 mm thick cotton, 0.6 mm jeans, 1 mm PDMS, 1 mm Sk-Sil T1310 substrates, respectively are achieved in this study. The results demonstrated the use of such softwear materials in effective modeling of wearable biomedical antennas, frequency selective surfaces, and conformal reflectarray antennas.