Bluetooth Antenna Stretchability Analysis And Optimization Design

In recent years,the rise of Io T has led to the rapid development of wearable area,and the emergence of body area networks has brought new demands to wearable devices: In biomedical applications,the wearable devices are required to fit on the skin surface closely,which requires the antenna of the wearable device also has stretchable and bendable flexibility.Traditional onboard antennas usually use PCBs as a substrate,which means they do not have flexibility and are hardly to apply in flexible wearable area directly.Therefore,designing antennas with stretchable flexibility has become a new research hotspot.For the demand of flexible antennas in the wearable field,this paper starting from the basic structure of the traditional Bluetooth antenna,by replacing the traditional rigid substrate with a flexible PDMS substrate,the performance of five common Bluetooth antenna structures when the antenna is stretched by external force is simulated and analyzed.Simulation results show that when stretched by external force,the performance of the antenna with linear arm is greatly influenced by the deformation,while antennas with a meandering structure,whether in the form of a right-angle or circular-arc,exhibit a stable working bandwidth under stretching conditions,and the antenna with a right-angle arm also reflects the oscillation characteristics of the center frequency during the stretching process.The results also show that the traditional antenna's bandwidth moves out of the Bluetooth band when stretched by less than 10%,therefore they cannot be directly applied to the flexible wearable devices by simply replacing rigid substrate with the flexible material,and stretchable antenna structure needs to be re-designed.Based on the stretching results,two stretchable antenna structures are proposed: a stretchable Inverted-F antenna and a stretchable dual-arm Inverted-F antenna.The in-plane stretchability and bending properties of the two antennas are analyzed.Under the condition that the working bandwidth fully covering the Bluetooth band,the stretchable Inverted-F antenna can be stretched by 20% in the X-axis and 60% by the Y-axis and a minimum radius of curvature of 8 mm(limit value)is achieved;the stretchable dual-arm Inverted-F antenna can be stretched by 30% in the X-axis and 20% by the Y-axis and a minimum radius of curvature of 10 mm(limit value)is achieved.For the us of PDMS as substrate,the designed two antennas have better biocompatibility,so that they could well adapt to the surface skin's tensile and bending deformation and maintain stable performance.