The primary coil in the charger induces a current in the secondary coil in the device being charged.

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 portable equipment can be placed near a charging station or inductive pad without needing to be precisely aligned or make electrical contact with a dock or plug.

Inductive charging is named so because it transfers energy through inductive coupling. First, alternating current passes through an induction coil in the charging station or pad. The moving electric charge creates a magnetic field, which fluctuates in strength because the electric current's amplitude is fluctuating. This changing magnetic field creates an alternating electric current in the portable device's induction coil, which in turn passes through a rectifier to convert it to direct current. Finally, the direct current charges a battery or provides operating power.[1][2]

Greater distances between sender and receiver coils can be achieved when the inductive charging system uses resonant inductive coupling, where a capacitor is added to each induction coil to create two LC circuits with a specific resonance frequency. The frequency of the alternating current is matched with the resonance frequency, and the frequency is chosen depending on the distance desired for peak efficiency.[1] Recent improvements to this resonant system include using a movable transmission coil (i.e., mounted on an elevating platform or arm) and the use of other materials for the receiver coil such as silver-plated copper or sometimes aluminum to minimize weight and decrease resistance due to the skin effect.

History

Induction power transfer was first used in 1894 when M. Hutin and M. Le-Blanc proposed an apparatus and method to power an electric vehicle.[3] However, combustion engines proved more popular, and this technology was forgotten for a time.[2]

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.[2] In 1977, John E. Trombly was awarded a patent for an "Electromagnetically coupled battery charger." The patent describes an application to charge headlamp batteries for miners (US 4031449). The first application of inductive charging used in the United States was performed by J.G. Bolger, F.A. Kirsten, and S. Ng in 1978. They made an electric vehicle powered with a system at 180 Hz with 20 kW.[2] In California in the 1980s, a bus was produced, which was powered by inductive charging, and similar work was being done in France and Germany and Europe around this time.[2]

In 2006, MIT began using[clarification needed] resonant coupling. They were able to transmit a large amount of power without radiation over a few meters. This proved to be better for commercial needs, and it was a major step for inductive charging.[2][failed verification]

The Wireless Power Consortium (WPC) was established in 2008, and in 2010 they established the Qi standard. In 2012, the Alliance for Wireless Power (A4WP) and the Power Matter Alliance (PMA) were founded. Japan established Broadband Wireless Forum (BWF) in 2009, and they established the Wireless Power Consortium for Practical Applications (WiPoT) in 2013. The Energy Harvesting Consortium (EHC) was also founded in Japan in 2010. Korea established the Korean Wireless Power Forum (KWPF) in 2011.[2] The purpose of these organizations is to create standards for inductive charging. In 2018, the Qi Wireless Standard was adopted for use in military equipment in North Korea, Russia, and Germany.

Application areas

Applications of inductive charging can be divided into two broad categories: Low power and high power:

Advantages

Disadvantages

Charging with induction (left image) creates more waste heat than using a cable (right image).

The following disadvantages have been noted for low-power (i.e., less than 100 watts) inductive charging devices, and may not apply to high-power (i.e., greater than 5 kilowatts) electric vehicle inductive charging systems.[citation needed]

Inefficiency has other costs besides longer charge times. Inductive chargers produce more waste heat than wired chargers, which may negatively impact battery longevity.[14][better source needed] 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 brand 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.[15]

Newer approaches reduce transfer losses through the use of ultra thin coils, higher frequencies, and optimized drive electronics. This results in more efficient and compact chargers and receivers, facilitating their integration into mobile devices or batteries with minimal changes required.[16][17] These technologies provide charging times comparable to wired approaches, and they are rapidly finding their way into mobile devices.

Safety

An increase in high-power inductive charging devices has led to researchers looking into the safety factor of the electromagnetic fields (EMF) put off by larger inductor coils. With the recent interest in the expansion of high power inductive charging with electric cars, an increase in health and safety concerns has arisen. To provide a larger distance of coverage people would in return need a larger coil for the inductor. An electric car with this size conductor would need about 300 kW from a 400 V battery to emit enough charge in order to charge the vehicle. [clarification needed] This much exposure of electromagnetic waves to the skin of a human could prove harmful if not met within the right conditions. Exposure limits can be satisfied even when the transmitter coil is very close to the body.[18]

Testing has been done on how organs can be affected by these fields when put under low levels of frequency from these fields. When exposed to various levels of frequencies, dizziness, light flashes, or tingling through nerves can be experienced. At higher ranges, heating or even burning of the skin can be experienced as well. Most people experience low EMF in everyday life. The most common place to experience these frequencies is with a wireless charger, usually on a nightstand located near the head.[19][clarification needed]

Standards

Wireless charging station
Detail of the wireless inductive charging device

Standards refer to the different set operating systems with which devices are compatible. There are two main standards: Qi and PMA.[13] The two standards operate very similarly, but they use different transmission frequencies and connection protocols.[13] Because of this, devices compatible with one standard are not necessarily compatible with the other standard. However, there are devices compatible with both standards.

Electronic devices

Samsung Galaxy Z foldable smartphones have "Wireless PowerShare" technology.

Many manufacturers of smartphones have started adding this technology into their devices, the majority adopting the Qi wireless charging standard. Major manufacturers such as Apple and Samsung produce many models of their phones in high volume with Qi capabilities. The popularity of the Qi standard has driven other manufacturers to adopt this as their own standard.[23] Smartphones have become the driving force of this technology entering consumers’ homes, where many household technologies have been developed to utilize this technology.

Samsung and other companies have begun exploring the idea of "surface charging", building an inductive charging station into an entire surface such as a desk or table.[23] Contrarily, Apple and Anker are pushing a dock-based charging platform. This includes charging pads and disks that have a much smaller footprint. These are geared for consumers who wish to have smaller chargers that would be located in common areas and blend in with the current décor of their home.[23] Due to the adoption of the Qi standard of wireless charging, any of these chargers will work with any phone as long as it is Qi capable.[23]

Another development is reverse wireless charging, which allows a mobile phone to wirelessly discharge its own battery into another device.[24]

Examples

This section may contain excessive or irrelevant examples. Please help improve the article by adding descriptive text and removing less pertinent examples. (April 2022)
An iPhone X being charged by a wireless charger
Wireless power transfer from inductive charging pad to Deutsche Telekom T Phone Pro 5G

Qi devices

Wireless charging pad used to charge devices with the Qi standard

Furniture

Dual standard

Research and other

Transportation

A wirelessly powered model lorry at the Grand Maket Rossiya museum

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,[34]: 847  for example when a taxi slowly drives at a taxi rank.[35] 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.[36] The German Ministry of Economy, BMWK tested infrastructure by Electreon in 2023 with 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.[37]

Stationary charging

In one inductive charging system, one winding is attached to the underside of the car, and the other stays on the floor of the garage.[38] The major advantage of the inductive approach for vehicle charging is that there is no possibility of electric shock, as there are no exposed conductors, although interlocks, special connectors and RCDs (ground fault interruptors, or GFIs) can make conductive coupling nearly as safe. An inductive charging proponent from Toyota contended in 1998 that overall cost differences were minimal, while a conductive charging proponent from Ford contended that conductive charging was more cost efficient.[39]

From 2010 onwards car makers signaled interest in wireless charging as another piece of the digital cockpit. A group was launched in May 2010 by the Consumer Electronics Association to set a baseline for interoperability for chargers. In one sign of the road ahead a General Motors executive is chairing the standards, effort group. Toyota and Ford managers said they also are interested in the technology and the standards effort.[40]

Daimler's Head of Future Mobility, Professor Herbert Kohler, however, has expressed caution and said the inductive charging for EVs is at least 15 years away (from 2011) and the safety aspects of inductive charging for EVs have yet to be looked into in greater detail. For example, what would happen if someone with a pacemaker is inside the vehicle? Another downside is that the technology requires a precise alignment between the inductive pick-up and the charging facility.[41]

In November 2011, the Mayor of London, Boris Johnson, and Qualcomm announced a trial of 13 wireless charging points and 50 EVs in the Shoreditch area of London's Tech City, due to be rolled out in early 2012.[42][43] In October 2014, the University of Utah in Salt Lake City, Utah added an electric bus to its mass transit fleet that uses an induction plate at the end of its route to recharge.[44] UTA, the regional public transportation agency, planned to introduce similar buses in 2018.[45] In November 2012 wireless charging was introduced with 3 buses in Utrecht, The Netherlands. January 2015, eight electric buses were introduced to Milton Keynes, England, which uses inductive charging in the road with proov/ipt technology at either end of the journey to prolong overnight charges.,[46] Later bus routes in Bristol, London and Madrid followed.

Dynamic charging

The first working prototype of an electric vehicle that charges wirelessly while driving, which is known as "dynamic wireless charging" or "dynamic wireless power transfer", is generally regarded to have been developed at the University of California, Berkeley in the 1980s and 1990s. The first commercialized dynamic wireless charging system, Online Electric Vehicle (OLEV), was developed as early as 2009 by researchers at the Korea Advanced Institute of Science and Technology (KAIST).[34]: 848  Vehicles using the system draw power from a power source underneath the road surface, which is an array of inductive rails or coils.[47][48] Commercialization efforts of the technology have not been successful because of high costs,[49] and its main technical challenge is low efficiency.[50]: 57  Dynamic inductive charging infrastructure was found to increase the occurrence of reflective cracks in road surfaces.[50]: 64 [51] As of 2021, companies and organizations such as Vedecom,[52] Magment, Electreon, and IPT are developing dynamic inductive coil charging technologies.[53] IPT is additionally developing a system that uses inductive rails instead of coils, as the current standards which use coils are "extremely expensive" for dynamic charging, according to the CEO of IPT.[54]

Research and development

Work and experimentation is currently underway in designing this technology to be applied to electric vehicles. This could be implemented by using a predefined path or conductors that would transfer power across an air gap and charge the vehicle on a predefined path such as a wireless charging lane.[55] Vehicles that could take advantage of this type of wireless charging lane to extend the range of their onboard batteries are already on the road.[55] Some of the issues that are currently preventing these lanes from becoming widespread is the initial cost associated with installing this infrastructure that would benefit only a small percentage of vehicles currently on the road. Another complication is tracking how much power each vehicle was consuming/pulling from the lane. Without a commercial way to monetize this technology, many cities have already turned down plans to include these lanes in their public works spending packages.[55] However this doesn't mean that cars are unable to utilize large scale wireless charging. The first commercial steps are already being taken with wireless mats that allow electric vehicles to be charged without a corded connection while parked on a charging mat.[55] These large scale projects have come with some issues which include the production of large amounts of heat between the two charging surfaces and may cause a safety issue.[56] Currently companies are designing new heat dispersion methods by which they can combat this excess heat. These companies include most major electric vehicle manufacturers, such as Tesla, Toyota, and BMW.[57]

Examples

This section may contain excessive or irrelevant examples. Please help improve the article by adding descriptive text and removing less pertinent examples. (April 2022)
200kW Charging-Pad for Buses, 2020 Bombardier Transportation.

Medical implications

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.[56] 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.[56] 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.[56]

See also

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