Wireless charging, also known as inductive charging, is a technique which uses an electromagnetic field to transfer energy between two objects, usually a stationary charging station and the portable device being charged.
Energy is sent through an inductive coupling from the station to the device, which makes use of that energy to charge the device’s battery. Each device is fitted with an induction coil, and an alternating electromagnetic field is generated in the station’s coil in order to induce power into the coil in the device, which takes power from the field, and uses it to charge the battery.
The two coils in combination essentially act in the same fashion as an electrical transformer, but lack the transformer’s combination in one complete unit.
Most wireless chargers rely on the close proximity between the coils, but certain advanced designs, using resonant inductive coupling, can function with some distance between them.
Wireless charging has a number of advantages and disadvantages when compared with a conventional wired connection. On the positive side, there is no physical electrical connection, and all the active componentry can be completely enclosed, rendering it immune to adverse and isolated from corrosive elements in the atmosphere.
However, the technique brings no benefits in energy saving solutions, with one of chief disadvantages being that it is less efficient than a conventional wired connection, and generates more heat due to the resistive nature of the coils used.
Whilst the construction of a wireless charging setup is more complex and more expensive than a wired connection, it has advantages in terms of safety and convenience. When used in medical implants, recharging can be accomplished without penetrating the skin of the patient, reducing any risk of infection.
In normal use, the device can simply be placed upon the charging station, and this makes it safer and more convenient for handicapped users.
Wireless charging does, however, take longer than conventional charging for the same power supplied, largely due to the lower efficiency of the power transfer. Moreover, wired connections sometimes offer greater flexibility, in that the connected device can be moved around and actively operated whilst connected, without moving the charging station as well; this can’t be yet achieved with wireless charging.
Newer developments are achieving greater efficiency in both charging stations and devices by the user of higher frequencies, thinner coils, and other optimisations of the electronics, and charging times for wireless recharging are now getting closer to the times that can be achieved with conventional wired connections.
Of course, whilst the most obvious applications of this technology appear in the home, used in devices such as electric toothbrushes, mobile phones, and other electronics, larger-scale applications have been under development for some time.
With an increased focus on hybrid and electric cars as a result of various energy crises over the years, vehicle manufacturers have looked to inductive charging as a standardised method for vehicle charging.
The principle is now being taken even further, with developments intended to supply driving power to vehicles through induction coils laid in the streets, and into the vehicles themselves.
In 2009 a Korean research group managed to provide 60 per cent of the power required to drive a bus, over a charging gap of 12cm.