How Does a Wireless Charging Function?

How Does a Wireless Charging Function?

Enterprise Networking Mag | Wednesday, October 20, 2021

Wireless power transmission (WPT) delivers electrical power without cables or other physical means.

FREMONT, CA: Wireless, or inductive, charging provides electricity to portable electronics such as smartphones and tablets by electromagnetic induction. The most prevalent type nowadays is the so-called Qi wireless charging standard for smart gadgets.

However, the technology is also found in some automobiles, power tools, and other consumer gadgets such as toothbrushes and a few medical equipments. To utilize it, compatible electronic devices are put near a charging station and charge without the need for precise alignment or electrical contact with the station.

There are three primary forms of wireless charging. These include the following:

Charging pads: These operate through the use of tightly connected electromagnetic inductive or non-radiative charging.

Charging bowls or through-surface chargers: These chargers distribute charge across a few centimeters by loosely coupled or radiative electromagnetic resonant charging.

Wireless charging through uncoupled radio frequency (RF): This type of system enables "trickle" charging across distances of several meters.

These devices operate on the same principle: they generate a time-varying magnetic field to induce a current in a closed wire loop.

The majority of wireless charging is accomplished through a mechanism called inductive coupling. This is accomplished by applying an alternating current to the charging station or pad using an induction coil.

When every moving electrical charge generates a magnetic field, the transmission coil generates one that fluctuates in intensity regularly as the amplitude of the alternating current is varied.

As a result of this change in magnetic field strength, an electromotive field is generated, as stated by Faraday's law of induction. This equation states that the induced voltage in a circuit is proportional to the rate at which the magnetic flux in the circuit changes over time. In simple terms, the faster a magnetic field changes, the higher the circuit's voltage. Any change in the direction of the magnetic field likewise defines the direction of an induced current.

Thus, the voltage of a circuit can be increased by adding additional loops. Thus, a coil with two loops produces twice the voltage of a coil with only one loop. This is the fundamental law governing the construction and operation of electrical motors and generators, explaining why these devices typically contain many coils.

This is why smartphone wireless charging pads have a limited range, as the copper coils inside are only a few centimeters in diameter.

Additionally, wireless charging distance and efficacy can be significantly improved by increasing the coil(s) size. The larger the coils are, or the more of them, the larger the action area.

Wireless charging works by inducing another AC current in another induction coil within the portable device via the magnetic field generated by the transmission coil. Often referred to as a receiving or secondary coil, the induced alternating current is subsequently converted to direct current via a rectifier, which charges the gadget's battery or supplies direct power to the device.

One or more receiving coils are possible (or antennae).

This is all well and good, but this type of setup often has a limited range. Resonant inductive coupling (or magnetic resonance) can be used to increase the range. This is accomplished by adding a capacitor to each induction coil, creating two LC circuits with a distinct resonance frequency.

Increase the amount of induced current in the receiving current by using a capacitor that ensures the loops resonate at the same frequency. This also significantly increases the range of wireless charging.

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