Planar Fractal Metamaterial Resonator and Energy-Focusing Device for Wireless Power Transfer

Compact, High-Efficiency Wireless Power Transfer Resonator Based on Capacitor-Coupled Fractal Split-Ring Resonators

This technology is a planar metamaterial resonator for wireless power transfer, featuring a fractal split-ring resonator formed on a substrate with an inner conductor surrounded by an outer conductor, each with a lumped-element capacitor inserted into its split gap. Arranging multiple such resonators on a substrate creates an energy-focusing device that concentrates magnetic fields between the transmitter and receiver.

Resonant wireless charging for devices like smartphones typically uses frequencies at or below 6 MHz. To accommodate these long wavelengths, bulky helical coils with many turns or large spiral structures are required, leading to device size constraints. Furthermore, transmission efficiency drops sharply as the distance between the transmitter and receiver increases.

This technology extends the electrical length by repeating rectangular pulse-wave fractal elements for both inner and outer conductors and lowers the resonant frequency using split-gap capacitors. This allows for resonance in the 6 MHz, 6.78 MHz, and 13.56 MHz bands within a planar structure under 9 cm in width and length. An energy-focusing device using an array of these resonators concentrates magnetic fields toward the receiver, mitigating efficiency loss over distance. This enables application in smartphone and wearable wireless charging pads and small IoT power modules, achieving high power transfer efficiency even with thin, compact chargers.

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Key Features:

• A fractal metamaterial resonator comprising a substrate and a fractal split-ring resonator formed on the substrate, including an inner conductor and an outer conductor surrounding the inner conductor.
• A first lumped-element capacitor formed in the split gap of the inner conductor and a second lumped-element capacitor formed in the split gap of the outer conductor.
• A resonator where the inner and outer conductors are each extended into a fractal structure with repeating rectangular pulse-wave fractal elements, with a length and width of 9 cm or less.
• An energy-focusing device for wireless power transfer, featuring an array of multiple fractal metamaterial resonators on a substrate that resonate at or below 6 MHz, as well as at frequencies near 6 MHz, 6.78 MHz, and 13.56 MHz.

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This invention was developed with support from the Ministry of Science, ICT and Future Planning for the development of antennas for future radio services using hybrid radio media.

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