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

Abstract

We present a design methodology for an overlapping hexagonal planar spiral coil (hex-PSC) array, optimized for creation of a homogenous magnetic field for wireless power transmission to randomly moving objects. The modular hex-PSC array has been implemented in the form of three parallel conductive layers, for which an iterative optimization procedure defines the PSC geometries. Since the overlapping hex-PSCs in different layers have different characteristics, the worst case coil-coupling condition should be designed to provide the maximum power transfer efficiency (PTE) in order to minimize the spatial received power fluctuations. In the worst case, the transmitter (Tx) hex-PSC is overlapped by six PSCs and surrounded by six other adjacent PSCs. Using a receiver (Rx) coil, 20 mm in radius, at the coupling distance of 78 mm and maximum lateral misalignment of 49.1 mm (1/√3 of the PSC radius) we can receive power at a PTE of 19.6% from the worst case PSC. Furthermore, we have studied the effects of Rx coil tilting and concluded that the PTE degrades significantly when θ > 60°. Solutions are: 1) activating two adjacent overlapping hex-PSCs simultaneously with out-of-phase excitations to create horizontal magnetic flux and 2) inclusion of a small energy storage element in the Rx module to maintain power in the worst case scenarios. In order to verify the proposed design methodology, we have developed the EnerCage system, which aims to power up biological instruments attached to or implanted in freely behaving small animal subjects’ bodies in long-term electrophysiology experiments within large experimental arenas.

Three-Phase Time-Multiplexed Planar Power Transmission to Distributed Implants

“…The origin of the proposed Tx architecture is a proven technology, called EnerCage [25]–[27], which was developed to continuously power and communicate with an electronic device attached to or implanted in a freely behaving animal in a smart cage. In the EnerCage system, three layers of overlapping hex-PSCs are used to provide homogeneous PTE over an extended area.…”

“…The solution offered in [27] for the angular misalignment was driving the adjacent coils closest to the Rx with a pair of out-of-phase carrier signals to reinforce the horizontal component of the magnetic field at the Rx location, as shown in Fig. 2(c).…”

“…To eliminate the aforementioned dead zones and create a homogeneous PTE over an extended volume around the Tx plane, we have combined three layers of hex-PSC arrays by offsetting the centers of every three adjacent hex-PSCs on three different layers to be on the corners of an equilateral triangle [27]. This is shown from the top and side views in Fig.…”

A smart cage for behavioral experiments on small freely behaving animal subjects

“…1 to any size or shape. The top three layers of these PCB modules consist of arrays of overlapping hexagonal PSCs (hex-PSCs) with optimized geometries at 13.56 MHz, and each layer is laterally offset from the other two layers so that a homogeneous field of overlapping PSCs is formed [8]. The 4 th layer of the PCB is reserved for driver interconnects.…”

Enhanced Wireless Power Transmission Using Strong Paramagnetic Response

“…Applications span over a broad range from submicrowatt radio-frequency identification transponders [1], milliwatt integrated circuit [2], and biomedical devices [3]–[5] to several watts for charging portable electronics [6]–[8] and a few kilowatts for charging batteries in electric vehicles [9]–[11]. …”