An 8-Shaped Antenna-Based Battery-Free Neural-Recording System Featuring 3 cm Reading Range and 140 pJ/bit Energy Efficiency

Wireless neural recording is envisaged to be an effective way of monitoring neural behaviors in long term, which requires a miniature device deeply implanted in the brain tissue. Wireless power transfer (WPT) enables neural-recording devices to be battery-free, while it's challenging to realize a centimeter-level telemetry range through a millimeter-scale implantable antenna. In conventional battery-free wireless techniques, backscatter radios show limited communication range, whereas dual-antenna active radios enlarge the system size. In this work, we proposed a battery-free wireless neural-recording system based on 8-shaped overlapped antennas and a beat impulse radio, taking an overall dimension of 4.7 \times 4.7 mm. The system is implemented in a 65-nm CMOS process, and an animal experiment validates the system performance on a male Sprague-Dawley rat. The proposed system achieves a communication range of 3 cm in a battery-free fully wireless way, where the proposed beat impulse radio shows 140 pJ/bit energy efficiency.