Transmission Line Measurement for Characterization of New Textile Sample

Accurate simulation and modelling is a very important aspect in designing a wearable antenna. In some cases, due to the complexity and non-homogenous properties of an electro-thread structure, the radiating element of the antenna is sometimes modelled as a perfect metallic surface, which is not the exact representative of the actual electro-thread and may cause deviation between simulation and measurement results. However, it is known that the exact fabric pattern and thread structure are very difficult to be physically modelled and designed. In order to reduce the uncertainties and the inaccuracy factors, the modelling of electro-textile in electromagnetic solver is reduced to bulk conductivity parameter of the radiating element. Therefore, an accurate method to measure the exact conductivity of a new or self-developed textile material, specifically for radio frequency application shall be determined. In this paper, a new technique is adopted to characterize the material's electrical properties. This method is based on the measurement of scattering parameters, S21 of a two-port transmission line to determine the conductivity of any conductive textiles that are normally used in wearable antenna design. Here, the experiments were performed for two test samples; printed copper as the control sample and off-the-shelf conductive textile known as ShieldIt Super. Both samples were fabricated on a low-loss substrate, Rogers RO5880 having a very low dielectric loss of 0.0009 and dielectric constant of 2.2. The behavior and performance of these two samples operating at 2.45 GHz were investigated and studied in this paper through measurement and detailed simulation. As a result, the calculated conductivity derived from the theoretical transmission line equation based on the scattering parameter data and the substrate's low-dielectric-loss-approximation was found to be very close to the expected conductivity values. Therefore, this method seems to be more reliable than the I-V curve measurement that was normally used for typical electronic application. However, specifically for radio frequency application, the reliability of the proposed technique shall be verified further especially in terms of its frequency range.