Electricity is usually known to flow through wires, but in reality, there exists a technology called 'Wireless Power Transfer (WPT)' that can send power through the air.

Basic Principle of Wireless Power Transfer

• Wireless power transfer transmits energy through electromagnetic fields.

• The main methods are Magnetic Induction and Magnetic Resonance.

  • Both methods involve a structure where the transmitting coil creates an alternating magnetic field that the receiving coil converts back into current.

  • In simple terms, it bridges the gap of invisible electromagnetic energy.

Short-range Applications — 'Wireless Charging'

• Smartphone 'Qi' pads, smartwatches, wireless earphone chargers, and electric vehicle parking charging pads fall into this category.

• The shorter the distance between coils, typically a few centimeters, the higher the efficiency, and the latest Qi 2 standard supports outputs of over 15 W and automatic alignment features.

• The ability to charge 'sealed and waterproof' devices like medical implant batteries and electric toothbrushes without cables is also a strong point.

Medium to Long-range Experiments — 'Aerial Power Transmission'

• Microwave (MW) Beams: Tests have been conducted in the US and Japan to supply power to drones located several dozen meters away by focusing GHz band waves with parabolic antennas.

• Laser Power Beams: Research is underway on methods to shoot semiconductor lasers over several kilometers to convert them into solar cells. This is possible at night, but atmospheric absorption and safety regulations pose challenges.

• RF Energy Harvesting: Experiments are also ongoing to enable low-power IoT sensors to operate without batteries by collecting minimal power from surrounding broadcast and Wi-Fi signals.

Historical Background and Standardization Movements

• In the early 1900s, Nikola Tesla attempted to transmit 200 kW of high frequency via the Wardenclyffe Tower to resonate with the Earth, but it was halted due to lack of funding.

• Currently, IEEE and AirFuel Alliance are establishing standards for 6.78 MHz resonant and 13.56 MHz short-range methods to enhance interoperability.

• Standards for charging electric vehicles while driving, such as ISO 15118 (including both plug and wireless), are also being gradually refined.

Limitations and Challenges

1. Efficiency Loss: As the transmission distance increases, electromagnetic radiation losses become greater.

2. Safety: To meet human exposure standards (e.g., ICNIRP guidelines), output density must be limited, making high-power long-distance transmission difficult.

3. Interference Issues: Overlapping frequencies with medical devices and communication signals can cause electromagnetic interference (EMI).

4. Equipment Costs: High-performance coils, shielding, and precision power electronics circuits are needed, resulting in high initial investment costs.

Commercialization and Research Trends

• Microwave and laser charging tests are underway in the defense sectors of Japan and the US to extend drone flight times.

• Some startups are demonstrating solutions that embed transmitting antennas in office ceilings and furniture, allowing for "automatic charging no matter where the phone is placed."

• In Germany and Israel, pilot projects are underway to charge electric vehicles while driving by embedding coils under highways and bus routes.

• The European Space Agency (ESA) is promoting the concept demonstration of 'solar power satellites' that transmit power beams to the ground in the 2030s.

In the near future, it is highly likely that a 'fully wireless charging environment' will first settle in everyday devices such as smartphones, wearables, and home appliances. Long-distance and high-power transmission must meet efficiency and safety standards, so gradual development alongside energy storage technology is expected. Ultimately, to usher in the "wireless era," it is important to remember that high-efficiency power electronics, antenna engineering, and electromagnetic safety regulations must align.