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Wireless charging of mobile phones
title Wireless charging of mobile phones

Symbol of empty battery

Smartphone, Tablet and Smartwatch are our daily companion today. All these devices have in common that they are pretty useless without wireless network connections by LTE, WLAN or Bluetooth. While mobiles had power for a couple of days the might be empty in the afternoon today. Besides the network connections also the high resolution display and GPS quite some power.

Photo of a wired charger

Every mobile has to be recharged sooner or later to get new energy. And they are not alone as a lot of electronic devices need a charger, too. While these are kind of hidden at home or at work behind the desk one discovery on journeys what ballast has to be carried. On the other hand with network connections by LTE, WLAN or Bluetooth the cable of the charger is often the only thing hanging on the perfectly designed notebook or smartphone like a foreign object.

Photo of a Qi charger

The solution is actually simple. What works for the electric toothbrush should also work for the mobile phone – inductive charging. As early as 1891 >Nikola Tesla experienced with wireless energy transfer. Besides the mentioned toothbrush the technique did not succeed for a long time. The first system being used in mass production was the Touchstone named system in 2009 within the >Palm Pre. Disadvantage of this and similar solutions from third party accessory manufacturers was that they only worked with a few devices from the same company. As every company built these chargers differently they consisted of many ICs, an individually designed coil, many different additional parts and an own technique to transfer the power. Except for the integrated Palm solution the third party accessories were all thick batteries with new back cover which did not look good on the smartphones which aimed to get thinner with each new device. Because of the missing mass production these solutions could not be offered affordable and failed at the consumer with prices around $100. The solution could only be an interoperable standard which would be fully integrated and produced affordable in masses.

Qi Logo

The Wireless Power Consortium (WPC) was established on 17. December 2008 and consists of over 100 members in diverse industries, including cellular technology, consumer electronics, batteries, integrated circuits, wireless technologies, network providers and manufacturers of furniture and car equipment. The WPC standardized a specification called Qi and develops different wireless charging techniques. The Standard was named after the Chinese language word Qi respectively Chee (air or spiritual energy flow). Devices of different companies equipped with the Qi logo may now be charged with standardized Qi chargers. When the standard becomes utilized in many devices and one can use one's colleagues Qi charging pad in the bureau also in public places (airports, hotels, cafes, restaurants, etc.) offers will arise and the charger can stay at home. Like Wi-Fi is offered in many places today, in the future wireless charging may be offered. For the shops this would be a competitive advantage.

Qi uses a magnetic induction between sender and receiver. Both exchange data with 2 kilobits per second to maintain an optimal energy transfer. The sender modulates the sending field. RFID like technology is used by the receiver to send data to the sender. The transmitted power is 5 Watt (Low Power) or 120 Watt (Medium Power) at a transmission frequency from 110 to 205 kHz (Long Wave). Multi-Layer Foreign Object Detection (FOD) ensures metallic objects may be placed on the charging pad without becoming hot due to the magnetic field. Known Qi compatible mobile phones are e.g. >Nokia Lumia 920 and >Google Nexus 4.

Qi Versions

The standard was developed as follows:


Wireless Charging Pad

An example for a mobile charging pad with Qi 1.2.2 standard and up to 15 W charging power in the Extended Power Profile is the >Belkin BOOST↑UP P-F7U014.

Wireless Charger integrated in furniture

An example for a charger which is integrated in furniture with Qi 1.2 standard and up to 10 W charging power is the >Qinside Qi1001v4. Due to a lack of interest the 15 W version has been currently postponed.

iPhone X

Since the >iPhone 8, >iPhone 8 Plus and >iPhone X Apple also supports the wireless charging standard Qi. Up to iOS, only Qi version 1.0 is supported and thus charging with up to 5 watts. As of iOS 11.2, Qi 1.1 is supported and thus charging with up to 7.5 watts.

AirFuel Logo

Besides Qi there is another standard from the AirFuel Alliance which resulted from a merger of Duracell founded Power Matters Alliance (PMA) with its standard PowerMat and the Alliance for Wireless Power (A4WP) in mid 2015. The first two smartphones with built in PowerMat were the >Samsung Galaxy S6 and >Samsung Galaxy S6 Edge which both feature Qi in addition. PowerMat has the benefits of being able to charge multiple devices and this with higher power. However, Qi is found in more smartphones today than PowerMat and even Ikea already sells furniture with built in Qi chargers. The AirFuel Alliance also realized this early in 2018 and joined the WPC.

Market overview

>All Cellular phones with inductive charging technology

Recommended Links

>Homepage of Wireless Power Consortium


>Homepage of AirFuel Alliance


>Qi Specs


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