Electromagnetic characterisation of textile materials for the design of wearable antennas and systems

Abstract

The accurate characterisation of textile materials to be used as a dielectric substrate in wearable systems is fundamental. However, little information can be found on the electromagnetic properties of regular textiles. Woven, knits and non-wovens are inhomogeneous, highly porous, compressible and easily influenced by the environmental hygrometric conditions, making their electromagnetic characterisation difficult. For these reasons, there is no standard method to measure the dielectric properties of textiles. This chapter presents a survey on the evolution of flexible antennas and the textile materials used to manufacture them. Besides, it gives an overview of several methods used to characterise the permittivity of textile materials. Furthermore, it presents and applies a resonator-based experimental technique to characterise textile materials. This experimental technique is based on the theory of resonant methods and consists in calculating the electromagnetic parameters of the material under test (MUT), at a single frequency, by measuring the shift in frequency and the value of Q-factor of one resonator board with a microstrip patch antenna. To validate the experimental characterisation method, four textile antennas have been designed to resonate in the 2.45 GHz ISM band. This bandwidth (BW) also supports the Wireless Local Area Network (WLAN), Bluetooth and Short Range Communication Systems (SRCS) applications. All antennas operated in the targeted frequency band and showed excellent agreement between simulated and measured parameters, supporting the validation of this method. The resonator-based experimental technique proved to be an efficient, simple, easy and fast technique for the characterisation of electromagnetic propertiesof textile materials for the development of wearable antennas and body-centric communication.