Split Ring Resonator Inspired Implantable Platform for Wireless Brain Care
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Radio frequency identification (RFID) technology has seen a noticeable tendency in the implementation with biomedical applications. Implantable RFID microelectronic system has been considered as a promising strategy in continuous neural signal extraction to construct the interface between the human brain and computer. This brain-machine interface is believed to largely improve the patients’ potential to recovery from traumatic brain injury or spinal cord injury. The challenge of this approach is the establishment of a reliable wireless data and power link between the implant device and the off-body unit in the high lossy human tissue environment. Meanwhile, the limitation of the implant size also poses another strict requirement to system miniaturization. In this project, a novel split ring resonator (SRR) inspired antenna system comprising a small implantable split ring resonator carrying a UHF RFID microsystem and a wearable split ring is developed and analyzed. The implantable part is self-matched with the RFID IC without additional matching components in the simulated intra-cranial tissue environment. The wearable part concentrically affixed to the scalp is for directivity and radiation efficiency improvement. The physically separated parts of the system form a remotely detectable platform for the wireless brain care applications. In the wireless experiments, the prototyped antenna system is verified to have a backscattered detectable distance of 1.1 m within the entire UHF band from 840 to 960 MHz when the implantable part is submerged 10 mm deep in the human-tissue-like liquid. The detectable distance is also found to have a reverse relationship with the implant depth. With the 5 mm implant depth, the detectable distance reaches a maxi-mum of 1.5 mm at 950 MHz. In order to investigate the system reliability in practical implementation, the detectable distance of the system with lateral and rotational misalignments between the two parts was also measured. The system working distance re-mains higher than 90 cm under marked, up to 5 mm lateral or 45° rotational misalignments between the implantable and wearable parts.