The analysis and design of the modified PIFA on the wearable sensor nodes

Two printed planar inverted-F antennas (PIFA) are designed and implemented in a wearable inertial sensor (ISN) node and a pulsation measurement node (PMN). The ISN is implemented on a 4-layer FR4 PCB with 0.8mm thickness and the PMN on a 4-layer flexible PCB with 0.3mm thickness. The ISN is responsible for sensing the accelerations and angular velocities of the body segment attached and the PMN for returning the human pulse rate and waveform. These two sensor nodes are on-body devices and the performance of the integrated antenna suffers significant degrading due to the existence of the body segments. The body effects on the antenna performance are investigated and an electromagnetic band gap (EGB) surface is employed to construct the in-phase reflections from the surface. The radiation wave from the PIFA toward the human segment is then isolated from the nearby body segments by the EGB surface. Satisfactory results are obtained and reveal that integrating the antenna with the EGB surface onto the flexible PCB structure is feasible.