Towards a smart experimental arena for long-term electrophysiology experiments

Wireless power and data transmission have created promising prospects in biomedical research by enabling perpetual data acquisition and stimulation systems. We present a work in progress towards such a system, called the EnerCage, equipped with scalable arrays of overlapping planar spiral coils (PSC) and 3-axis magnetic sensors for focused wireless power transmission to randomly moving targets, such as small freely behaving animal subjects. The EnerCage system includes a stationary unit for 3D non-line-of-sight localization and inductive power transmission through a geometrically optimized PSC array. The localization algorithm compares the magnetic sensor outputs with a threshold to activate a PSC. All PSCs are optimized based on the worst-case misalignment, considering parasitics from the overlapping and adjacent PSCs. EnerCage also has a mobile unit attached to or implanted in the subject's body, which includes a permanent magnetic tracer for localization and back telemetry circuit for efficient closed-loop inductive power regulation. The EnerCage system is designed to enable long-term electrophysiology experiments on freely behaving small animal subjects in large experimental arenas without requiring them to carry bulky batteries. A prototype of the EnerCage system with five PSCs and five magnetic sensors achieved power transfer efficiency (PTE) of 19.6% at the worst-case horizontal misalignment of 49.1 mm (1/3 of the PSC radius) and coupling distance of 78 mm with a mobile unit coil, 20 mm in radius. The closed-loop power management mechanism maintains the mobile unit received power at 20 mW despite misalignments, tilting, and distance variations up to a maximum operating height of 120 mm (PTE=5%).