In this blog post, we’ll explore the principles of wireless power transfer technology—which could solve the inconvenience of smartphone batteries—as well as its current level of development and future potential.
How much do you use your smartphone? With their endless features and portability, smartphones have become an essential part of modern life. If that sounds like you, you’ve likely faced many situations where a rapidly draining battery has caused trouble. To alleviate this frustration, some people charge a spare battery the night before, while others carry a charger in their bag and end up wandering around looking for an outlet. Recently, more people have started carrying portable battery chargers. However, this method comes with several drawbacks. First, it takes a considerable amount of time to fully charge the battery, and it’s not easy to charge it outside the home unless you can find an outlet. Additionally, portable battery chargers must be charged at home beforehand, and carrying them around while connected to your smartphone isn’t very convenient.
Why is charging a battery this inconvenient? The fundamental reason lies in the “method of power transmission.” To charge a battery, we always need a charger with a “cord” and an “outlet.” So, simply put, wouldn’t it be better to transmit power “wirelessly” rather than via a “wired” connection? “Wireless power transmission” technology has been researched and developed with this very idea in mind. If power can be transmitted wirelessly, we can charge devices without having to connect them directly to cumbersome wires. In fact, wireless power transmission has long been recognized as one of the key technologies of the future, and it is now widely implemented in actual products, particularly smartphones and wearable devices. In particular, wireless charging has gradually become mainstream since the introduction of the Qi standard. In 2023, Qi 2—which features magnetic alignment—was introduced, and by 2025, Qi 2 25W, supporting power transmission of up to 25W, had emerged.
So why hasn’t this technology—which promises to make our lives so much easier—been easily commercialized in all situations until now? In fact, Samsung Electronics has previously introduced smartphones and related accessories that support wireless charging. However, early wireless charging methods were limited by their very short charging range. Since the smartphone had to be placed close to the power source to charge, users ultimately had to align the charging pad with the smartphone. This did not offer a significant improvement in convenience compared to wired charging, where the charging port is connected directly. The issue of power transmission efficiency decreasing as the distance increased was one of the major limitations of wireless power transmission technology. However, technology has steadily advanced, and convenience and efficiency are now improving with the emergence of standards such as Qi2, which uses magnetic alignment to position the smartphone and charger correctly. Apple also adopted a magnetic charging method for the Apple Watch, released in 2015, and since then, the use of magnets to align the charger has become an important technology in wireless charging for smartphones and wearable devices.
Wireless power transfer technology can be broadly categorized into magnetic induction, magnetic resonance, and radiative methods that utilize electromagnetic waves. First, the magnetic induction method utilizes the phenomenon of electromagnetic induction, in which a current flows through a coil due to changes in a magnetic field. You may have conducted an “electromagnetic induction” experiment in high school, where you repeatedly moved a magnet in and out of a coil to induce a current. When a magnet moves, the magnetic field passing through the coil changes. In this system, the component that creates this changing magnetic field is placed in the power source, while a coil is installed on the battery side to receive power based on these changes in the magnetic field. The method widely used in wireless charging pads for smartphones today also fundamentally relies on this principle of electromagnetic induction.
Second, the magnetic resonance method utilizes “resonance,” which occurs between two objects with the same natural frequency. The 1940 collapse of the Narrows Bridge in Tacoma, Washington, is a case often cited to illustrate the phenomenon of resonance. The cause of this bridge’s collapse cannot be explained simply by strong winds. The combination of aerodynamic instability caused by the wind and the structure’s vibrations significantly amplified the vibrations, ultimately leading to the bridge’s collapse. Every object has its own unique “natural frequency.” However, when a periodic force from an external source matches the object’s vibrational characteristics, the amplitude of its vibrations can increase significantly. This can be likened to a swinging swing: if an external force is applied in sync with the swing’s natural period, the swing will rise even higher. This phenomenon, in which vibrations are greatly amplified under specific conditions, is known as resonance. However, it would be inaccurate to attribute the collapse of the Tacoma Narrows Bridge solely to resonance; complex phenomena such as aerodynamic flutter played a significant role.
The core of the magnetic resonance method lies in applying this principle to power supply. By adjusting the frequency of the alternating current generated by the power source to match the resonant characteristics of the coil inside the cell phone, energy can be transferred more efficiently between the two coils. While this method has the advantage of potentially transmitting power over relatively longer distances than magnetic induction, it also has the limitation that power transmission efficiency may decrease as the distance increases or if the positions of the transmitter and receiver become misaligned. Therefore, to apply this method in real-life scenarios, improvements are needed in efficiency, safety, and the ability to adapt to positional changes.
Finally, the radiative method, which utilizes electromagnetic waves, is—as the name suggests—a method of transmitting power via electromagnetic waves. Although it employs electromagnetic principles similar to those used in cell phones and wireless communications, wireless power transmission differs from these technologies in terms of purpose and design. This method has the advantage of being able to transmit power over relatively long distances; however, as the distance increases, the power density received decreases, and significant losses can occur during transmission. Furthermore, to safely transmit large amounts of power using electromagnetic waves, various issues must be considered simultaneously, including human exposure, electromagnetic interference, energy efficiency, and the size and cost of receiving devices. Consequently, magnetic induction—which achieves high efficiency over short distances—is primarily used in current smartphone wireless charging, while long-range wireless power transmission remains an area requiring further research.
Wireless power transmission technology, which is being researched and developed through various approaches, presents a truly groundbreaking paradigm: “the ability to transmit electricity without wires.” While wireless power transmission was once considered a technology of the distant future, it is now actually in use in everyday devices such as smartphones and smartwatches. However, the ability to charge wirelessly is distinct from the ability to freely supply large amounts of power over long distances without wires. Most current wireless charging systems require the charger and device to be placed in close proximity, and as the transmission distance increases, issues such as efficiency and safety become more significant. Therefore, it can be said that wireless power transmission technology currently consists of both commercially available applications and areas still under active research. Nevertheless, many researchers and companies are striving to develop more convenient and efficient wireless power transmission technologies, and related standards are continuously evolving.
In a future where wireless power transmission technology is even more deeply integrated into our daily lives, we will be able to use smartphones without worrying about running out of battery, charge electric vehicles more conveniently, and supply power to various electronic devices without connecting them directly to power cords. Perhaps the messy tangles of cables scattered across the floor will also decrease noticeably. Furthermore, if wireless power transmission technology is applied to fields such as satellites or space-based solar power generation as we venture into space, there is potential to realize a new energy system that converts solar energy into electrical energy and transmits it wirelessly to where it is needed. Of course, while this technology still faces many challenges, it is recognized as an important field of research because it offers a new method for continuously delivering energy. With the potential to transform the very paradigm of our lives, aren’t you looking forward to this future era of wireless power transmission?
