A wireless phone charger works by the principle of inductive charging facilitated by special induction coils inside the charger and phone. Bringing the two close together creates a magnetic field between them, causing electrical power to be transmitted. It is a Near Field Communication technique involving radio frequency waves.
Below I’ve illustrated how inductive charging works, given a framework to show how a simple wireless phone charging system operates, wireless charging standards, and whether wireless charging is recommended.
Let’s get started!
How Wireless Charging Works
Inductive Charging and Wire Coils
Wireless Charging relies on the electromagnetic induction principle, which Michael Faraday discovered in 1831.
In the late 19th century, Nikola Tesla took the idea to transmit electricity wirelessly by creating a magnetic field between a transmitting and receiving circuit.
Inductive charging takes place between the two circuits. In a wireless mobile phone charging system, the electrical energy is transferred wirelessly between two special wire coils (see the illustration below), one in the charger and one in the mobile device.
The larger the coils inside the wireless charger, the farther away you can place the mobile device.
Near-Field Communication
Wireless phone charging operates using the NFC (Near Field Communication) technique for transferring power at close range proximity [Paglinawan et al., 2017].
Although inferior to Bluetooth, NFC can operate on minimal power to send an RF (Radio Frequency) signal to another device. So, a mobile phone can be charged wirelessly even if the battery is drained or the device is turned off.
Below is a simple conceptual framework of a wireless phone charging system.
The power transmitter starts functioning immediately upon sensing the receiver. This initial recognition is called a “handshake.” Once confirmed or initiated, “electromagnetic fields exert oscillating forces on the electrons in the receiving antenna, which causes current to be induced by it” (Paglinawan et al., 2017, p. 1747). In other words, the electric and magnetic fields cause the electrons in the antenna to vibrate, causing them to produce current.
The energy is then routed to a harvesting circuit connected to the NFC device’s battery.
Smart Wireless Charging
The RF power transmitter can search the nearby field for NFC-compatible devices in smarter wireless charging systems.
It will detect the NFC receiver (mobile phone antenna) when the device, i.e., the mobile phone, is brought near the transmitter’s inductive antenna. Bringing it near enough causes the RF power transmission to begin, the NFC receiving device, and the harvesting circuit to receive it for trickle charging the battery.
The system checks the battery to see how much it is charged. It disconnects the energy harvester from the battery when it is fully charged. The flowchart below illustrates how this smart wireless charging system works.
Charging Time
The time it takes to charge the battery wirelessly is computed as follows:
The numerator is the battery’s energy, and the denominator is the power flowing into the battery (voltage x current).
Wireless Charging Standards
Present-day wireless charging systems for mobile devices conform to one of two prominent standards: the Qi and the AirFuel Alliance Resonant standards.
Wireless Power Consortium’s Qi Standard
The Qi Standard, managed by the Wireless Power Consortium, is the most common smartphone use. It supports between 5 and 15 watts of wireless power transmission.
AirFuel Alliance Resonant Standard
The Resonant Standard managed by the AirFuel Alliance is a newer standard that allows charging from 50mm away. It dispenses with the need to align the mobile device with the charger’s base perfectly and allows for charging multiple devices simultaneously.
Quasistatic Cavity Resonance
Wireless mobile phone charging systems are still under heavy research because they are relatively new. The aim is to be able to transmit more power over a longer distance than is safely and conveniently possible at present.
One such attempt, Quasistatic Cavity Resonance, allows generating magnetic fields capable of delivering several kilowatts of power to receivers across a room.
Is Wireless Charging Recommended?
Wireless charging technology is becoming more advanced, but at the time of writing, it remains less efficient than wired charging.
Since it consumes more electrical energy, you can expect slightly higher electricity consumption and bills if you use this method heavily. It also generates more heat, and the battery experiences more wear and tear.
However, it offers the convenience of doing away with wires while charging and the extra convenience of simply putting your phone on the charger’s base to charge it.
References
Arnold C. Paglinawan, Leonardo C. Valiente Angelo A. Beltran et al. Wireless power transfer using near-field communication for mobile devices. IEEE 3rd International Future Energy Electronics Conference and ECCE Asia, held in Kaohsiung, Taiwan, 2017.
Belkin BoostCharge. https://www.belkin.com/10w-wireless-charging-pad-qc-3.0-wall-charger-cable/P-WIA001.html
Dual Wireless Charging Pad. https://www.amazon.com/Aluminum-Wireless-Charging-Certified-Supports/dp/B07RD1H2F8
