Environmental electromagnetic characterization framework for wearable antenna materials

In wearable antenna design, the prevailing atmospheric conditions can have a significant effect on the electromagnetic properties of the fabric substrate and hence the resulting antenna performances. Therefore, an accurate characterization of this effect is an important issue in textile antenna design. This paper presents a dedicated constitutive parameter extraction method as a function of relative humidity of all materials used. The method relies on a comparison between measured and simulated antenna figure´s of merit in order to extract complex permittivity of the substrate and effective bulk conductivity of the e-textile. A two-step approach is used for separating conductor losses from substrate losses. The problem of finding the best fit between simulated and measured data is solved by relying on a surrogate based optimization technique. Here, two fabric materials are characterized for relative humidity levels ranging from 10% to 90%.