Geometrical Design of a Scalable Overlapping Planar Spiral Coil Array to Generate a Homogeneous Magnetic Field

Area of Science:

• Electrical Engineering
• Electromagnetics
• Wireless Power Transfer

Background:

• Wireless power transfer requires efficient magnetic field generation.
• Random movement of objects necessitates robust power delivery systems.
• Optimizing coil geometry is crucial for maximizing power transfer efficiency (PTE).

Purpose of the Study:

• To present a design methodology for an overlapping hexagonal planar spiral coil (hex-PSC) array.
• To optimize the array for homogenous magnetic field generation for wireless power transmission to randomly moving objects.
• To ensure maximum PTE under worst-case coil-coupling conditions to minimize power fluctuations.

Main Methods:

• Iterative optimization procedure to define hexagonal planar spiral coil (hex-PSC) geometries in three parallel conductive layers.
• Design considering worst-case coil-coupling scenarios where a transmitter (Tx) hex-PSC is overlapped by six and surrounded by six adjacent PSCs.
• Analysis of receiver (Rx) coil tilting effects on PTE.

Main Results:

• Achieved 19.6% PTE from a worst-case PSC with a 20 mm radius Rx coil at 78 mm coupling distance and 49.1 mm lateral misalignment.
• Identified significant PTE degradation when Rx coil tilt angle θ > 60°.
• Proposed solutions include simultaneous out-of-phase excitation of adjacent hex-PSCs and incorporating an Rx energy storage element.

Conclusions:

• The proposed design methodology enables efficient wireless power transfer to randomly moving objects.
• The EnerCage system, developed to verify the methodology, can power biological instruments in freely behaving small animals.
• The study provides a robust solution for maintaining stable power delivery in challenging wireless scenarios.