Hybrid Wireless Charger Tames Electric Fields and Shrugs Off Bad Parking

Wireless charging of electric vehicles has long promised a future in which drivers simply park over a pad and walk away, but the physics of moving kilowatts across an air gap without wires has always imposed awkward compromises. Inductive systems, which couple energy magnetically between coils, dominate today’s designs and can deliver tens of kilowatts at 90 to 95 percent efficiency across gaps of a few centimeters, yet their coupling collapses quickly when the car parks off-center. Capacitive systems, which push power across electric fields between metal plates, offer lighter and more compact couplers but demand megahertz frequencies and high plate voltages that concentrate dangerous fields at plate edges. A new simulation-based study published in Results in Engineering by Mahmoud A. Badwey and Umer Amir Khan of King Fahd University of Petroleum and Minerals argues that the way past this trade-off is to do both at once, inside a single, carefully sculpted coupler.

The proposed architecture is a hybrid wireless power transfer system rated at 22.68 kilowatts operating at 1 megahertz across a 100-millimeter air gap. On the inductive side, each coupler combines a planar spiral coil with three vertically oriented helical coils mounted on a common base with cross-shaped ferrite bars. The spiral provides a broad, stable magnetic field that tolerates changes in the air gap, while the helical windings extend the effective coupling region in three dimensions, so that magnetic flux continues to link transmitter and receiver even when their axes are offset. The ferrite structure guides the flux along a defined path, raising the magnetic coupling coefficient to roughly 0.1996 at the nominal gap while suppressing stray fields around the charger.

The capacitive side is where the geometry becomes genuinely inventive. Instead of the flat rectangular plates common in capacitive power transfer, the team chose hollow cylindrical electrodes, one embedded in the ground and one mounted beneath the vehicle chassis. The circular shape eliminates the sharp corners that concentrate electric field lines and trigger corona or arcing, and its symmetry means coupling degrades similarly no matter which direction the car drifts. Crucially, hollowing out the plates costs almost nothing in performance: because the fringing effect concentrates charge near the outer edges, a 100-millimeter-radius hollow retains about 97 percent of the mutual capacitance of a solid plate while saving weight and material.

Edge fields were attacked in stages. A finite-element model of a sharp-edged cylindrical plate showed a punishing peak field of 11,603 volts per centimeter. Simply rounding the edge cut that by about 10 percent. Adding nose-shaped profiles, conceptually cousins of the Rogowski electrodes used in high-voltage engineering, did far better: a 135-degree nose termination with a filleted stepped S-bend transition and an extended cylindrical section reduced the simulated peak to 4,102 volts per centimeter, a 65 percent reduction relative to the sharp-edged baseline. The extended metal section doubles as a field-grading element and as an electromagnetic shield for the helical coils nested inside the cylindrical assembly, so the same geometry that tames the electric field also confines the magnetic one.

On the circuit side, the designers selected a double-sided LC compensation network tuned to 1 megahertz on both transmitter and receiver. This choice is more than a matter of habit. Higher-order compensation schemes such as LCLC require large external capacitors in parallel with the coupling plates, which can drive enormous reactive power through the link and impose extreme voltage stress on the dielectric, inviting air breakdown at the 22-kilowatt level. The double-sided LC topology instead aligns the plate voltages at a 90-degree phase difference, transmitting essentially no reactive power across the gap while producing a load-independent, constant-current output that suits battery charging. The 1-megahertz frequency itself emerged from a constrained trade-off: the coupler’s resonance condition sets a minimum realizable frequency near 0.984 megahertz, and pushing higher sharply reduces achievable power while inflating ferrite, switching, dielectric, and conductor losses.

The simulated performance figures are striking. With only coil winding resistance included, the resonant AC link achieves 99.73 percent efficiency at the full 22.68-kilowatt output, splitting the load between roughly 54 percent carried magnetically and 46 percent carried capacitively. The authors then built a component-level loss budget that is unusually candid for a simulation study: 62 watts of Litz-wire winding loss extracted from a three-dimensional eddy-current solution, about 95 watts of ferrite core loss from a Steinmetz screening estimate, 65 watts of dielectric and plate loss, 839 watts of semiconductor loss from silicon carbide MOSFETs and Schottky rectifiers, 21 watts of eddy-current loss in the segmented plates, and roughly 43 watts in the compensation network. The projected end-to-end DC-to-DC efficiency settles at 95.27 percent, a figure the team explicitly labels a prediction rather than a measurement.

Even the parasitic eddy currents induced in the big capacitive plates by the neighboring coils were engineered away. Radial slits cut into the plates interrupt the circumferential current loops that would otherwise form hot rings of ohmic heating, reducing the peak volumetric loss density by roughly 90 percent and total eddy-current heating by about 80 percent. Meanwhile, the large 600-millimeter plate footprint doubles as a passive heat spreader, distributing the remaining dissipation over a wide area without active cooling. Sensitivity analyses also probed what happens when the vehicle-side and ground-side capacitances drift apart in a real installation; efficiency barely budges, but output power falls by up to about 19 percent and the input phase angle swings toward 44 degrees, signaling that practical systems will need adaptive retuning.

The misalignment results are the study’s headline act. At 125 millimeters of lateral displacement, the multi-helical structure retains 52.5 percent of its aligned magnetic coupling, compared with just 27.0 percent for a baseline geometry without the middle and outer helical extensions, a 2.73-fold improvement in the coupling coefficient. More importantly, the two transfer channels degrade at different rates, and the system exploits that asymmetry. As the magnetic path weakens, the capacitive path, less sensitive to horizontal offset, takes over an increasing share. At a 200-millimeter offset, the capacitive link carries 71.7 percent of the load, and the complete hybrid system still delivers 10.50 kilowatts at 95.82 percent AC-link efficiency, conditions under which a purely inductive charger would have largely decoupled. The authors are careful to note that this is complementary power redistribution, not preservation of full rated power.

Safety assessments round out the picture. Using the ICNIRP 2020 radiofrequency reference levels of 300 volts per meter and 2.76 microtesla at 1 megahertz, the team mapped fields above the coupler with and without ferrite and with an idealized four-plate chassis-and-ground environment. The chassis and ground plates act as natural electrostatic boundaries, confining the electric field between the conductive surfaces rather than letting it fringe into occupied space, a substantial improvement over the roughly 1.3-meter clearance implied by an unshielded two-plate model. The magnetic reference-level crossing sits near 0.75 to 0.78 meters in free space, but the authors stress that a real vehicle’s metallic floor pan, sitting well within that column, would attenuate the field further, and that no bystander-compliance claim is made beyond the evaluated monitor lines.

Everything in the study rests on three-dimensional finite-element analysis in ANSYS Maxwell coupled with circuit co-simulation in MATLAB, Simulink, and ANSYS Simplorer, and the authors are consistent in flagging the work as a numerical design benchmark rather than demonstrated hardware. Manufacturing tolerances, thermal aging of the ferrite, and environmental parasitics could all shift the resonance and the field picture in a physical prototype. Still, if the numbers survive experimental validation, the architecture offers a compelling template for the next generation of wireless EV chargers: one compact coupler that charges at kilowatt levels, forgives imperfect parking, and keeps its fields where they belong.

Subject of Research: Hybrid inductive-capacitive wireless power transfer for electric vehicle charging with field-safe capacitive plate design and enhanced misalignment tolerance

Article Title: Field-safe multi-helical hybrid wireless power transfer with edge-field mitigated hollow cylindrical plates and enhanced misalignment performance for electric vehicles

Article References: Badwey, M. A., & Khan, U. A. (2026). Field-safe multi-helical hybrid wireless power transfer with edge-field mitigated hollow cylindrical plates and enhanced misalignment performance for electric vehicles. Results in Engineering, 32, Article 113385. https://doi.org/10.1016/j.rineng.2026.113385

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113385

Keywords: wireless power transfer, electric vehicles, hybrid IPT-CPT, capacitive power transfer, inductive power transfer, misalignment tolerance, electric field mitigation, resonant compensation, SiC power electronics, electromagnetic safety, ICNIRP exposure limits, EV charging