SAR reduction of wearable SWB antenna using FSS for wireless body area network applications

A flexible Super Wide Band (SWB) antenna with a frequency selective surface (FSS) reflector is presented to reduce the specific absorption rate (SAR) and to improve the gain of the proposed antenna for Wireless Body Area Network (WBAN) Applications. A tapered feed circular monopole antenna with arrowhead-shaped slot structure is designed on Jeans substrate with a compact physical dimension of 22 x 28 x 0.3 mm3. The use of a Jeans substrate makes the proposed antenna thin and highly flexible. The impedance bandwidth of the proposed antenna is 28 GHz (3.2-31.2 GHz) with a peak gain of 5.61 dBi. Since the antenna is intended for body wearable applications, its performance has been observed by placing the antenna near a human body phantom. This placement increased the SAR and reduced the gain. Further to reduce the SAR and to enhance the gain of the proposed SWB antenna a novel FSS reflector, which consists of a 2 x 2 array of elements, is located at a distance of 1.138 lambda (13 mm) below the proposed antenna. In order to reduce the SAR, the FSS array structure is placed between the antenna and the human's forearm. This placement reduced the specific absorption rate (SAR) by more than 95%. To make the proposed antenna with FSS structure user agreeable, the gap between the antenna and FSS is filled by polyethylene foam, with a dielectric constant of 2.26, a loss tangent of 0.00031, and a density of 2.2 lb. Further, there is also a 3-4 dBi improvement in antenna gain after the application of the FSS. The proposed antenna has great potential to be applied in human microwave imaging due to its immense wide bandwidth, high gain and compact size, and low SAR value.