Inductive charging, also known as wireless charging or cordless charging, is a type of wireless power transfer. It uses electromagnetic induction to provide electricity to portable devices. Inductive charging is also used in vehicles, power tools, electric toothbrushes, and medical devices. The equipment can be placed over an inductive pad free of any electrical contacts such as a dock or plug.
Inductive charging transfers energy through inductive coupling: alternating current passes through an induction coil, generating a fluctuating magnetic field, which creates an induced alternating electric current in a nearby secondary coil. The alternating current can be rectified to a direct current which charges a battery or provides operating power.
Greater distances between sender and receiver coils, such as those required for wirelessly charging electric vehicles, can be achieved with resonant inductive coupling. The alternating current of the system can use a resonance frequency tuned with capacitors to create a transmitter and receiver LC circuit with a specific resonance frequency. The frequency is chosen depending on the distance desired for optimal efficiency, and as of 2025 the frequency is commonly 85 kHz. Some systems use inductive loops made of Litz wire surrounding ferrite cores. Charging efficiency is sensitive to lateral, longitudinal, and vertical misalignment. Misalignment of more than can severely lower power transfer. Some systems align their coils by having the receiver coils mounted on a movable arm that can be lowered closer to the transmitter coils, for example it can be lowered from the underside of a truck closer to a transmitter coil on the ground.
Applications of inductive charging can be divided broadly into low power and high power. Low power applications generally target consumer electronic devices such as cell phones, handheld devices, computers, and similar devices which normally require power below 100 watts. The AC utility frequency of 50 or 60 hertz is often used,[1] or in the case of Qi-compliant devices, frequencies in the range of 87 to 205 kHz are typical.[2] Some methods, such as resonant inductive coupling, can be maintain charging at a distance of a few inches between the transmitter and receiver coil, though foreign objects pose a fire or burn risk if metals or organisms are between the active coils for high-power systems. High power inductive charging generally refers to power above 1 kilowatt. Such power is required for electric vehicles, and some implementations reach 300 kilowatts or higher. High-power inductive charging systems use resonant inductive coupling for higher efficiency. These systems are usually implemented in the long wave range of frequencies in the tens of kilohertz, commonly 85 kHz as the regulatory allowable noise levels are higher at this range than surrounding ranges. Short wave frequencies can enhance the system's efficiency and size but they're not used because they would create radio interference worldwide. High power at 85 kHz raise the concern of electromagnetic compatibility and radio frequency interference over background noise levels at ranges of up to .
Inductive charging offers protected connections free of need of corrosion protection. Induction circuits offer protection from faults such as short circuits due to insulation failure, especially where connections are made or broken frequently. Without the need to constantly plug and unplug the device, there is significantly less wear and tear on the socket of the device and the attaching cable. For embedded medical devices, the transmission of power via a magnetic field passing through the skin avoids the infection risks associated with wires penetrating the skin.[3] Automatic operation of inductive charging in roads can allows vehicles to operate without charging stops through opportunity charging over inductive coils embedded in the road.[4]
Due to the lower efficiency of inductive charging compared to conductive charging, devices took 15 percent longer to charge when supplied power is the same amount when tested in 2018.[5] An amateur 2020 analysis of energy use conducted with a Pixel 4 found that a wired charge from 0 to 100 percent consumed 14.26 Wh (watt-hours), while a wireless charging stand used 19.8 Wh, an increase of 39%. Using a generic wireless charging pad and mis-aligning the phone produced consumption up to 25.62 Wh, or an 80% increase. The analysis noted that while this is not likely to be noticeable to individuals, it has negative implications for greater adoption of smartphone wireless charging.[6]
Inductive chargers produce more waste heat than wired chargers, which may negatively impact battery longevity.[7] Waste heat is a concern for high-power implementations of inductive charging for transportation. Trials in France in 2023 found risk of thermal damage to the road under regular operating conditions due to the induction coils exceeding temperatures of 100C.
The most commercially-successful standard for compatibility between inductive chargers and small electronic devices is the Qi standard, which started development in 2008 and was first published in 2010. Qi quickly expanded in the mid 2010s, and after a period of having three competing standards Qi became ubiquitous by the mid 2020s. Other standards include: Power Matters Alliance (PMA), which was publicly announced in January 2012;[8] and Rezence, which was developed by the Alliance for Wireless Power (A4WP) and merged with PMA in 2015 under the AirFuel name.[9]
A group was launched in May 2010 by the Consumer Electronics Association to set a baseline for interoperability for chargers. General Motors, Toyota, and Ford expressed interest in the technology and the standards effort.[10] Daimler's Head of Future Mobility, Professor Herbert Kohler, expressed caution and said in 2011 that the inductive charging for EVs was at least 15 years away, and the safety aspects of inductive charging for EVs have yet to be looked into in greater detail.[11]
The first standard for vehicle wireless charging was the SAE J2954 standard. It allows inductive car charging over a pad, with power delivery up to 11 kW. The standard provides a methodology for activating the charger only when sufficient alignment is detected.[12] As of 2024, standards for higher-power wireless charging and for charging while driving are being developed. Magne Charge, a largely obsolete inductive charging system, also known as J1773, used to charge battery electric vehicles (BEV) formerly made by General Motors.
In the 2020s, organizations continued developing dynamic wireless power transfer (DWPT) electric vehicle (EV) charging technologies and standards. Among them: Vedecom, ENRX (formerly IPT), Magment, Electreon, Utah State University, Purdue University, and the University of Auckland. WiPowerOne (an offshoot of the KAIST OLEV project) and Electreon, two wireless electric road companies, have been working on new dynamic inductive charging standards in the early 2020s. IPT (which later became a subsidiary of ENRX) has been working on its PRIMOVE system that uses inductive cables instead of coils, as according to their CEO the existing standards which use coils are "extremely expensive" for dynamic charging. SAE International has started developing standards for dynamic wireless power transfer in 2023. The Michigan Department of Transportation (MDOT) has tested one wireless electric road technology from 2023 to 2025 on a quarter-mile stretch of public road. One of the project's goals is developing an interoperable system that will interact with the infrastructure regardless of manufacturer.
Manufacturers of smartphones have started adding inductive charging technology into their devices in the late 2010s, the majority adopting the Qi wireless charging standard.[13] Some battery-powered devices offer wireless bidirectional charging, allowing a charged device to charge the battery of another device.[14] [15] [16]
Electric vehicle wireless power transfer or wireless charging is generally divided into three categories: stationary charging when the vehicle is parked for an extended period of time; dynamic charging when the vehicle is driven on roads or highways; and quasi-dynamic or semi-dynamic charging, when the vehicle moves at low speeds between stops, for example when a taxi slowly drives at a taxi rank.
Inductive charging is not considered a mature dynamic charging technology as it delivers the least power of the three electric road technologies, its receivers lose 20%-25% of the supplied power when installed on trucks, and its health effects have yet to be documented, according to a French government working group on electric roads. Similarly, research in Germany by BASt in 2025 estimated 76%–81% overall efficiency for heavy goods transport. Trials in Norway in 2025 found that coil misalignment of more than can severely lower power transfer. SAE International notes that wireless charging systems do not have well-established foreign object detection technologies, and proposes establishing safety tests for these technologies. Foreign objects pose a fire or burn risk if metals or organisms are between the ground pad and the receiver when the system is active.
M. Hutin and M. Le-Blanc proposed in 1894 an apparatus and method to power an electric vehicle with inductive power transfer. At the time, combustion engines proved more popular, and this technology was not widely implemented. In 1972, Professor Don Otto of the University of Auckland proposed a vehicle powered by induction using transmitters in the road and a receiver on the vehicle. Bolger, Kirsten, and Ng implemented in 1978 an electric vehicle powered by inductive power transfer at a frequency of 180 Hz and power of 20 kW. An inductive-charging bus was operated in the 1980s in California, and similar developments in inductive power transfer were being explored in France, Germany, and other European countries.
Wireless charging of an electric vehicle while driving is known as "dynamic wireless charging" or "dynamic wireless power transfer", DWPT. The first working full-scale DWPT prototype is generally regarded to have been developed at the University of California, Berkeley in the 1980s and 1990s. The first commercialized DWPT system, Online Electric Vehicle (OLEV), was developed as early as 2009 by researchers at the Korea Advanced Institute of Science and Technology (KAIST). Vehicles using the system draw power from a power source underneath the road surface, which is an array of inductive rails or coils.[40] [41] Commercialization efforts of the technology have not been successful because of high costs.[42]
The main technical challenge of DWPT is low efficiency, and implementation has not been widespread as of 2025 due to high costs. The cost of a single wireless electric lane at 50% coverage at large-scale deployment was estimated in 2021 to be about 6.5 million dollars per mile.
The German Ministry of Economy, BMWK tested in-road wireless EV charging infrastructure implemented by Electreon in 2023. The tests included a bus equipped with inductive coils that receive power from a 200-meter strip of transmitters under the road surface. The receivers were able to collect 64.3% of the energy emitted from the transmitters. Installation proved complex and costly, and finding suitable locations for the coils' roadside power cabinets proved difficult.[43]
Inductive charging infrastructure was found in 2017 to increase the occurrence of reflective cracks in road surfaces.[44] Testing of various bonding materials between the inductive coils and the asphalt in 2023 at Nantes showed that standard installation techniques of inductive coils under the asphalt were not satisfactory and resulted in critical strains. Performance was satisfactory with the use of specific bonding resins, with non-critical degradation in performance compared to reference pavements with no inductive coils. Despite satisfactory results, even the best-performing methods showed risk of debonding of the casing of the coils from the top layer of the road. ÉTS and Université Laval studied the structural performance of in-pavement inductive coils in 2025, similarly finding evidence of debonding. The 2023 Nantes trials showed increased risk of thermal damage to the road under regular operating conditions due to the induction coils exceeding temperatures of 100C. INDOT has been testing in 2024 a DWPT installation with special polymer-concrete previously used for bridges.
Wireless charging is making an impact in the medical sector by means of being able to charge implants and sensors long-term that is located beneath the skin. Multiple companies offer rechargeable medical implant (e.g. implantable neurostimulators) which use inductive charging. Researchers have been able to print wireless power transmitting antenna on flexible materials that could be placed under the skin of patients. This could mean that under skin devices that could monitor the patient status could have a longer-term life and provide long observation or monitoring periods that could lead to better diagnosis from doctors. These devices may also make charging devices like pacemakers easier on the patient rather than having an exposed portion of the device pushing through the skin to allow corded charging. This technology would allow a completely implanted device making it safer for the patient. It is unclear if this technology will be approved for use – more research is needed on the safety of these devices. While these flexible polymers are safer than ridged sets of diodes they can be more susceptible to tearing during either placement or removal due to the fragile nature of the antenna that is printed on the plastic material. While these medical based applications seem very specific the high-speed power transfer that is achieved with these flexible antennas is being looked at for larger broader applications.[45]
