In this blog post, we’ll examine the principles and characteristics of magnetic resonance wireless charging and explore how wireless charging technology is evolving today.
In the past, cell phones could last 2–3 days on a single charge, but as smartphone features have diversified and performance has improved, it has often become difficult to even get a full day’s use out of the battery. This issue can be attributed to the fact that advancements in battery technology have not kept pace with the rapid evolution of smartphone performance and features. To address this issue, various solutions—such as power-saving modes, power banks, and portable chargers—have emerged; however, most of these were merely stopgap measures designed to reduce the inconvenience of charging rather than directly extending battery life.
When Samsung Electronics’ “Galaxy S3” was released in 2012, rumors that the device would support magnetic resonance wireless charging became a hot topic. At the time, magnetic resonance technology garnered attention as a method capable of transferring power even when the charger and smartphone were not in direct contact, and it was anticipated to enable a more flexible charging environment than conventional contact-based charging. However, the method of charging a smartphone from a distance of 1 to 2 meters away from the charger—as initially envisioned—was not immediately commercialized. Currently, the mainstream method for wireless smartphone charging involves transmitting power using electromagnetic fields between a charging pad and the device’s coil, and magnetic resonance is also being researched as one of the key methods for advancing this wireless power transfer technology.
Magnetic resonance is a method of wireless power transfer that utilizes the phenomenon of resonance. Resonance is a phenomenon in which the vibration of an object with a specific frequency is greatly amplified when energy of the same frequency is continuously applied to it. For example, when swinging on a playground swing, applying force in sync with the swing’s natural oscillation period allows you to lift the swing higher even with minimal effort. Similarly, in magnetic resonance, the transmitter and receiver coils are designed to resonate at a specific frequency, enabling energy to be transferred to the receiver coil via the changing magnetic field generated by the transmitter coil. Unlike simple inductive wireless charging, which requires the transmitter and receiver coils to be placed close together, the use of resonance conditions offers the advantage of being able to transfer power even if the coils are slightly separated or not perfectly aligned. For example, consider a wine glass that shakes violently or shatters when a person sings a specific note loudly—the frequency of that note resonates with the glass. This occurs because the frequency of the sound wave matches the wine glass’s resonant frequency, allowing energy to be transferred effectively. Just as the resonant frequency varies depending on the size and shape of the wine glass, in magnetic resonance-based wireless charging, energy can be transferred more effectively by properly aligning the resonant conditions of the transmitter and receiver.
Charging a battery using the magnetic resonance method is not simply a matter of transmitting high-frequency electromagnetic waves over a distance through the air; rather, it is a process of transferring power by utilizing the resonant coupling between the changing magnetic field generated by the transmitter coil and the receiver coil. When an alternating current flows through the transmitter coil of the charger, a changing magnetic field is created, and this magnetic field induces a voltage in the receiver coil. In the magnetic resonance method, this energy transfer can be made more efficient by matching the resonance conditions of the transmitter and receiver. However, as the distance between the coils increases or their alignment becomes misaligned, the coupling weakens, which can reduce power transfer efficiency; in actual systems, factors such as coil design, alignment, and power conversion circuits must all be considered together. Therefore, it is difficult to provide a universal figure—such as “charging efficiency drops below 50% at distances exceeding 2 meters”—that applies equally to all systems. Furthermore, it cannot be concluded outright that the electromagnetic fields used in wireless charging are harmful to the human body. Wireless power transmission systems must be designed and evaluated to meet human exposure standards, taking into account factors such as the operating frequency, output power, and the intensity of magnetic and electric fields. In fact, international standards have been established to evaluate human exposure to wireless power transmission systems, and safety regarding magnetic and electric fields is assessed separately based on the technology used, frequency, and power conditions.
While the magnetic resonance method must address issues such as charging distance, efficiency, positional alignment, and human exposure, wireless power transmission technology continues to advance steadily. In particular, as standardization efforts to enhance the convenience and efficiency of wireless charging in smartphones have progressed, new specifications such as Qi2—which features magnetic alignment—have emerged. Qi2 began to be widely adopted in 2023, and in 2025, Qi2 25W, which supports 25W-class charging, was announced. Development of the Qi2 50W standard is also underway for 2026, aiming for higher power output and greater compatibility. Therefore, while it is difficult to say that the technology—where a smartphone charges simply by being placed far away from the charging pad, as once envisioned—has become mainstream, it is clear that wireless charging technology is evolving toward providing power more conveniently without the need to directly connect a charging cable. If the efficiency, safety, charging range, and interoperability of wireless power transmission continue to improve in the future, the inconvenience of having to directly connect a smartphone charger or carry a separate power bank will likely diminish over time.
