A planar, via-less zeroth-order antenna for wearable electrocardiography

Abstract

Summary form only given. Wireless medical telemetry service is one of the fastest emerging technologies in healthcare industries worldwide. In addition, the proliferation of smartphones is currently serving as a catalyst to the increasing growth in this sector. Based on a secure, close-range wireless body area network (WBAN) which relays the patient's physiological information to a nearby cellular device, a real-time monitoring system for those who require a relatively close medical attention can be realized. Among the physiological parameters, the pulse and the respiration rates are important indicators for wide range of healthcare applications ranging from recreational sports to wireless medical monitoring. Despite the significant advantages, the technical challenges of devising a wearable, sturdy health monitoring device with a reliable radio must be fully resolved. When operating at the industrial, medical and scientific (ISM) radio band, the antenna is expected to be one of the largest components within the device. It is imperative for the antenna to remain low-profile and yet be capable of exhibiting efficient radiation characteristics albeit the detrimental effects of the user's body on the antenna matching and radiation. In this paper, a planar, zeroth-order resonance (ZOR) antenna is proposed for a wearable and detachable electrocardiography (ECG) sensor device. The profile of the proposed antenna topology is minimized using two distinctive techniques: 1.The elimination of vias unlike the conventional mushroom-shaped ZOR topologies. 2. Modeling of the radiator, series capacitance, shunt inductance and the ground on a single printed circuit board (PCB) layer. An air-bridge employed co-planar waveguide (CPW) structure is designed as the antenna feed network between the antenna element and the in-house low power 2.4 GHz RFIC. The overall dimension of the planar ZOR antenna is 15 mm × 9.6 mm × 3 mm when fabricated using a flexible PCB (İr = 2.2, tan = 0.02). The antenna is placed above the main board PCB of the ECG device and subsequently covered with flexible polycarbonate chassis. The radiation properties of the ZOR antenna within the assembled ECG device is studied by placing the device on the surface of the human body model with electrical properties as follows: Skin (ı=1.46 S/m, h=0.5mm), Body fat (ı=0.27 S/m, h=10.5mm), Muscle (ı=1.74 S/m, h=20mm) where h is denoted as the thickness. Simulation and measurements confirm a -10 dB S11 bandwidth of more than 80 MHz and a radiation efficiency of more than 30% in the presence of the human body. Overall, the ZOR antenna is confirmed to feature more than 3.5 m enhanced communication coverage and more than 20% higher antenna radiation efficiency in comparison to that using conventional chip antennas and monopoles under identical measurement conditions.