Textile Antennas for Biomedical Telemetry: How Safe Are They?

This investigation aims at determining the safety level of textile antennas for on-body biomedical telemetry applications. The dual-band antennas are designed to operate at 2.4 GHz and 5.2 GHz with unidirectional radiations and broad bandwidths. They are fabricated using two different materials to assess factors influencing their Specific Absorption Rates (SAR). Simulations and measurements indicated a maximum SAR of 0.6 W/kg, which is well below the European limit of 2 W/kg, with a maximum measurement uncertainty of 10.5%. The emergence of Body Area Networks (BAN) for applications in healthcare and medical monitoring have triggered an extensive research effort into utilizing conformal materials for wireless communications. This option is promising as the applicability of such materials has been successfully demonstrated recently [1-4]. The user’s mobility and comfortableness can be hindered by the use of wires, besides the increased risk of system failure. Despite the existence of contactless monitoring systems, the use of such conformal antennas to relay measurements collected from clothing-integrated sensors is certainly a more favourable approach, as certain biological signals are more accurately collected with body worn sensors. Due to the need for Extra-BAN (EBAN) communication which requires seamless data transfer across various wireless standards, these antennas are also preferred to be operable across a multitude of wireless applications. Antenna performance parameters, i.e., reflection and radiation characteristics are expected to be affected by coupling and absorption by the human body. Moreover, placement of such radiating structures in close-proximity to the human user poses operational safety hazard to the user. This article highlights the safety evaluation of these antennas, defined as the Specific Absorption Rate (SAR). This parameter is a measure of power (heat) distribution in a body medium, and characterizes the absorption of the electromagnetic energy by the human tissues operating in the vicinity of an antenna/electronic device. A set of dual band antennas fabricated fully using textiles is evaluated at 2.45 GHz and 5.2 GHz, where they are operational with at least -10 dB of reflection coefficient. They are designed based on the planar inverted-F antenna (PIFA) topology, which consists of a ground plane, shorting wall and radiator, as shown in Fig. 1. The prototyping materials felt as the substrate, ShieldIt Super and copper foil as the conducting elements are commercially available, which gives an idea of the resulting SAR from these common materials. Details of the topology, materials, and dimensions are provided in [5], while their fabrication procedure is provided in [4]. Figure 1: The dual-band PIFA (DBPIFA): (a) schematic, (b) SH FPIFA (fabricated) with D = 24 mm, GL = 44 mm, GW = 34 mm, SW = 4mm, h = 6 mm, fL = fW = 9 mm, WF = 1 mm.