An approach to the measurement of dielectric constant and loss tangent of fabric substrate materials, used for the development of wearable antennas, is presented in this paper. This technique is based on the parallel plate method of measuring capacitance, and focuses on the use of RF impedance/material analyzer. The permittivity of the material under study is obtained by its relationship with the capacitance. The insertion loss is measured by the material analyzer, and therefrom, the loss tangent is determined. The validity of the method is demonstrated for a well-characterized substrate material such as Teflon. The technique is then applied to the insulating fabric substrates.

Communication technologies are heading towards a future in which user-specified information would be available on demand. In order to ensure the smooth transition of information from surrounding networks and from shared devices, computing and communication equipment need to be body centric. A wearable antenna is an essential part of wireless body-centric networks (Zhi Ning Chen, 2007). To design an antenna for wearable devices deployed for commercial applications, an accurate knowledge of dielectric properties of fabric materials is needed. Taeyoung Yang et al. (2005) characterized the camouflage cloth for use in wearable ultra-wide band half disk antenna, employing the two microstrip line method (Lee and Nam, 1996). In 2004 (Pekka Salomen et al., 2004), the cavity perturbation technique was reported for the characterization of different synthetic fabric materials.

The technique of measuring the dielectric properties of the fabric samples, as presented in this paper, is based on capacitance measurement, in which the given insulating fabric material is sandwiched between two electrodes, forming a capacitor. Measurements are carried out for the frequency range of 0.3-3.0 GHz, which covers many hot applications such as W-CDMA, Bluetooth and wireless LAN. In this experiment, RF impedance/material analyzer (model-E4991A) from Agilent Technologies, and a dielectric fixture from Novocontrol Technologies, have been used.

The paper describes the theoretical background on which this technique is based. Then, the measurement setup and the procedures are detailed, followed by a demonstration of the validity of this technique. It then discusses the measurement results, before offering some concluding remarks.

Electrical and Electronics Engineering Journal, Fabric Substrate Materials, Communication Technologies, Novocontrol Technologies, Device Under Test, DUT, Intermediate Frequency , IF, Gold Plated Electrodes, Measurement Techniques, Agilent Technologies, Dielectric Fixture.