A Dual-Band Wireless Power Transmission System for Evaluating mm-Sized Implants.

Distributed neural interfaces made of many mm-sized implantable medical devices (IMDs) are poised to play a key role in future brain-computer interfaces (BCI) because of less damage to the surrounding tissue. Evaluating them wirelessly at preclinical stage (e.g. in a rodent model), however, is a major challenge due to weak coupling and significant losses, resulting in limited power delivery to the IMD within a nominal experimental arena, like a homecage, without surpassing the specific absorption rate (SAR) limit. To address this problem, we present a dual-band EnerCage system with two multi-coil inductive links, which first deliver power at 13.56 MHz from the EnerCage (46×24×20 cm3 ) to a headstage (18×18×15 mm3 , 4.8 g) that is carried by the animal via a 4-coil link. Then a 60 MHz 3-coil link from the headstage powers up the small IMD (2.5×2.5×1.5 mm3 , 15 mg), which in this case is a free-floating, wirelessly-powered, implantable optical stimulator (FF-WIOS). The power transfer efficiency (PTE) and power delivered to the load (PDL) from EnerCage to the headstage at 7 cm height were 14.9%-22.7% and 122 mW; and from headstage to FF-WIOS at 5 mm depth were 18% and 2.7 mW, respectively. Bidirectional data connectivity between EnerCage-headstage was established via Bluetooth Low Energy (BLE). Between headstage and FF-WIOS, on-off-keying (OOK) and load-shift-keying (LSK) were used for downlink and uplink data, respectively. Moreover, a closed-loop power controller (CLPC) stabilized PDL to both the headstage and the FF-WIOS against misalignments.