Inductive charging
How it works
An alternating current flows in the transmitter (primary) coil, producing a time-varying magnetic field. This field induces a voltage in a nearby receiver (secondary) coil according to the law of electromagnetic induction. The induced alternating current is then rectified and conditioned by power electronics into a DC voltage that charges the battery. In resonant systems, both coils are tuned with capacitors to a shared resonant frequency, improving efficiency and range under loose coupling. Control and communication circuits handle alignment, power regulation, and safety (e.g. foreign-object detection).
Problem solved
Removes the need for physical plugs and connectors, which wear out, corrode, and require manual connection. It enables hands-free, automatic charging of autonomous vehicles and robots, and safe powering of devices in wet or sealed environments.
Components
Coil in the charging pad/mat driven by high-frequency alternating current.
Coil in the device/vehicle in which the field induces an alternating current.
Converts DC to high-frequency AC and back from AC to DC to charge the battery.
Optional element in resonant charging that increases efficiency and range under loose coupling.
Official
Handles power regulation and safety functions such as foreign-object detection.
Evolution
The physical basis of inductive charging — a changing magnetic field induces a voltage in a conductor.
An MIT team led by Marin Soljacic demonstrates power transfer via magnetic resonance; the WiTricity spin-off is founded.
On 17 December 2008 the consortium is formed and soon publishes the open Qi standard.
In August 2009 the WPC publishes the Qi low-power specification — the first widely adopted open inductive-charging standard; version 1.0 follows in 2010.
At the 10 October 2024 reveal Tesla states the Cybercab will charge wirelessly (inductively), with no plug — an example of contactless, automatic robotaxi-fleet charging.
Hyperparameters (configurable axes)
Frequency of the alternating current in the transmitter coil; affects efficiency, range, and standards compliance.
Separation between the transmitter and receiver coil; larger distance lowers coupling and efficiency.
Near-field inductive vs. resonant inductive coupling (greater range and misalignment tolerance).
Transferred power — from watts (electronics) to kilowatts (vehicles, robots).