They may be facing extinction in the electric-transport revolution, but one benefit of cars with internal combustion engines is that they are easy and quick to refuel, so travelling a long way in one is rarely a problem. Not so for their successors. In the absence of universal standards, electric cars come with a variety of charging systems and different sorts of cables and sockets. Extended journeys therefore need careful planning to make sure that the battery is fully charged at the start and that compatible fast-charging stations are available en route.


It would be much more convenient if electric cars could be recharged wirelessly. Some electric toothbrushes and other small devices, such as mobile phones, can already be topped up in this way using a process called electromagnetic induction. This employs an alternating mains current flowing through a coil to create a varying magnetic field, which then generates another current in a second coil placed alongside it according to principles elucidated in the 19th century by Michael Faraday. The device containing the second coil then converts the transmitted power into direct current, which is used to recharge a battery.


As users of electric toothbrushes and phones will know, device and charger must be both close to each other and precisely aligned for this process to work. That is tricky to achieve with an electric car, which sits above the ground and requires higher levels of energy transfer.


WiTricity is working with a number of carmakers and sold its first commercial system in 2018 to bmw, which fits it to some of its 530e hybrid cars. Alex Gruzen, WiTricity’s boss, expects further developments soon. He says the arrangement can transmit power from the grid to the car’s battery with an efficiency of up to 93%, which is similar to that achieved by a plug-in system. Nor does a car’s receiving coil have to be positioned directly above the charging pad on the ground—a useful feature of resonating coils being that they do not have to be so closely aligned to transmit power.


Other companies are producing wireless-recharging systems which use various forms of magnetic-resonance induction. So far these are mostly for commercial vehicles, though such systems are bound to encourage the spread of the technology to cars as well. Momentum Dynamics, a Pennsylvanian firm, for instance, announced in March a deal to supply wireless rechargers to GreenPower Motor Company, a producer of electric shuttle buses.

其他企业正在生产无线充电装置,它们采用各种磁共振感应方式。目前大部分被用于商用车辆,但这种装置必将推动该技术在乘用车上的普及。例如:美国宾夕法尼亚州一家名为Momentum Dynamics的公司在3月份公布一笔交易,向电动区间车制造商GreenPower Motor Company供应无线充电装置。

Crucially, as did not happen for plug-in vehicles, standards are being developed that should, at least in theory, permit any suitably equipped electric vehicle to use any wireless charger. China recently ratified a set of national criteria similar to those being developed and promoted by industry groups in the West, including WiTricity. As China has been one of the countries most forcefully pushing the electrification of vehicles, its clout in the marketplace might ensure that most companies, foreign ones included, keep to the standards it has set.