On Body Characterization of Flexible Electrodes for Human-Body Communication

Human Body Communication (HBC) has recently emerged as a new technology that is applicable to everyday life as well as in the medical domain. HBC systems refer to ultralow-power devices attached to the human body (wearable devices) and in the human body (implantable devices) that are used to monitor vital markers of health and wellbeing that can be used for a myriad of applications, including fitness, preventative medicine, and chronic disease monitoring. By communicating directly through the body, HBC transceivers can achieve a significant reduction in area and power compared to radio frequency (RF)-based solutions. A key component of HBC systems is the HBC electrode, which is used for both sensing and communication and has to be integrated with ultrasmall wearable devices. This paper investigates the design and characterization of flexible electrodes that can be used for capacitive and galvanic HBC systems. We study and characterize the effect of the shape (e.g., circular and square), size, the separation between electrodes, and the feeding point location on the overall input impedance, return loss, and path loss. Finally, electrodes are fabricated and tested using a wearable HBC system, where the bit error rate (BER) and signal to noise (SNR) versus distance variation are tested and the results are presented and compared to those obtained with commercial electrodes at 21 MHz carrier-frequency (compliant with IEEE 802.15.6 standard carrier frequency).