Wearable BLE Wireless Sensor Based on U-Shaped EBG Monopole Antenna

Abstract

In this paper, a compact wearable U-shaped monopole antenna operating at 2.4 GHz frequency band is proposed for Medical Body Area Network applications. The antenna has a compact size of $0.37\lambda \times 0.31\lambda$ , covering a band from 2.14 GHz to 3.03 GHz with a gain of 2.3 dBi at 2.45 GHz, and an efficiency of 93% in free space. In addition, an Electromagnetic Band Gap (EBG) metamaterial is utilized to isolate the integrated antenna on the circuit and the body, reducing the Specific Absorption Rate (SAR). In consequence, an integrated circuit employing the EBG ground plane provides a safe value of SAR (0.68 W/kg) when it is attached to a human arm followed by a 74% reduction of SAR value compared to the circuit without EBG (2.57 W/kg). Furthermore, the on-body efficiency of the EBG-based antenna is improved from 54% to 73.68%. Finally, experimental results of a wearable heart rate and blood oxygen level BLE sensor based on the proposed U-shaped EBG monopole antenna exhibit an average power consumption of 108 mW, a sensitivity of -74 dBm, and a maximum Bluetooth Low Energy (BLE) transmission distance with a mobile phone of 16 m in the complex environment.