A low-profile and flexible wideband antenna for on-body vital sign monitoring applications

Abstract The key characteristics of wearable antennas include ultra-wideband (UWB) capabilities, miniaturization, and flexibility. In this paper, a novel wideband wearable antenna sensor has proposed for biomedical sensing applications, which utilizes stepped slots loaded with a coplanar waveguide feed. This antenna features a rectangular patch with stepped slot-type curves located along the left, right, and top edges of a standard microstrip patch, along with a symmetrical coplanar ground that incorporates reversed L-type arms. The radiator of the proposed antenna, along with the coplanar waveguide (CPW) ground plane, is constructed on a flexible denim fabric substrate (dielectric constant of 1.6 and a loss tangent of 0.08). It has a compact size of 40 × 40 × 2.035 mm 3 , corresponding to an electrical dimension of 0.33 λ c × 0.33 λ c × 0.017 λ c, where λ c characterizes the wavelength of electromagnetic waves in free space at a frequency of 2.45 GHz. The main merit of this prototype antenna is that it has lightweight, compact, and sufficiently flexible for integration into the human body. The proposed antenna shows a wideband characteristic that spans from 2.13 GHz to 8.3 GHz, resulting in a total bandwidth of 5.85 GHz. It achieves the highest gains of 7.5 dBi and 8.9 dBi, respectively, under off-body and on-body conditions. Furthermore, it has been evaluated for its effects on specific absorption rates (SAR) resulting from human-body interaction. The results indicate SAR values of 0.417 W kg −1 and 0.222 W kg −1 for 1 g of human tissue, and 0.652 W kg −1 and 0.155 W kg −1 for 10 g of human tissue in the chest area, at frequencies of 5.8 GHz and 7.3 GHz, respectively. Finally, the performance of the antenna sensor has been validated for practical applications in real-world scenarios by successfully detecting vital signs, including the human heartbeat and breathing rate.