Wireless power, when coupled with miniaturized implantable electronics, has the potential to provide a solution to several challenges facing neuroscientists during basic and preclinical studies with freely behaving animals. The EnerCage system is one such solution as it allows for uninterrupted electrophysiology experiments over extended periods of time and vast experimental arenas, while eliminating the need for bulky battery payloads or tethering. It has a scalable array of overlapping planar spiral coils (PSCs) and three-axis magnetic sensors for focused wireless power transmission to devices on freely moving subjects. In this paper, we present the first fully functional EnerCage system, in which the number of PSC drivers and magnetic sensors was reduced to one-third of the number used in our previous design via multicoil coupling. The power transfer efficiency (PTE) has been improved to 5.6% at a 120 mm coupling distance and a 48.5 mm lateral misalignment (worst case) between the transmitter (Tx) array and receiver (Rx) coils. The new EnerCage system is equipped with an Ethernet backbone, further supporting its modular/scalable architecture, which, in turn, allows experimental arenas with arbitrary shapes and dimensions. A set of experiments on a freely behaving rat were conducted by continuously delivering 20 mW to the electronics in the animal headstage for more than one hour in a powered 3538 cm2 experimental area.
This paper presents recent progress towards the development of the EnerCage system for efficient wireless power and data transmission with a focus on its real time control and tracking algorithms. The EnerCage is meant to be used in long-term uninterrupted electrophysiology experiments on small, freely behaving animal subjects in large experimental arenas. It includes a stationary unit for closed-loop inductive power transmission, an array of 3-D magnetic sensors for non-line-of-sight positioning of the animal subject, and a mobile unit to efficiently power the target device and establish wireless data communication. The stationary unit, which includes a scalable array of overlapping hexagonal coils, takes advantage of 3-and 4-coil links to further increase the power transmission efficiency (PTE) and decrease the required number of drivers. A magnetic tracking algorithm is presented that reduces the number of magnetic sensors needed for localization. The algorithm achieves a worst-case localization error of 3 cm at the nominal height of 12 cm above the surface of the coil array. Measurement results show the functionality of the closed-loop power transmission and subject tracking over 70 cm.
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