Design and optimization of mm-size implantable and wearable on-body antennas for biomedical systems

Battery-free cortical implants enable data telemetry in wireless brain-machine interface systems (BMI). In this paper, we analyze the power transfer in a wireless link from a wearable on-body transmit antenna to a miniature 2×2×2-mm³ implant antenna. For the first time, we assess the feasibility of using electro-textiles in the realization of the wearable on-body BMI reader antenna. Simulations using a 4-layered spherical head model predicted -20 dB and -23 dB link power efficiencies in a wireless link from a wearable copper fabric and an embroidered reader loops, respectively, to a 2×2×2-mm³ implant loop. This performance is comparable to that achieved with a bulk copper transmit antenna. Measurements of the fabricated prototypes using Human-Head Equivalent Liquid matched with the expected results thus confirming the applicability of the transmitting antennas made of electro-textiles.