Although battery technology has improved many times over, mobile devices remain always hungry for power, thanks to the demands from always-on wireless, GPS, hi-performance audio and video along with the ever-increasing applications and nearly constant use of the mobile devices. People are looking for more convenient and accessible ways of charging their mobile gadgets. That has led to the availability of wireless charging systems, where one needs only to place the mobile device on the charging pad for an effective charging. The demand can be estimated from the fact that more than five million wireless charging devices were shipped in 2012, with a forecast of more than 100 million more to ship by 2015. Apart from smartphones, these numbers include MP3 players, digital cameras and other mobile devices.
Foremost among wireless charging technologies is the technique offered by Qi (pronounced as “Chee”). Using a wireless charging pad and a properly equipped mobile device, the intention is to create an international standard for interoperability. A conglomerate of nearly 200 organizations including phone manufacturers, semiconductor suppliers and wireless service providers came together to form the Wireless Power Consortium. They released the Qi open standard in 2009. Since then the market has over 350 types of Qi-compliant devices. Among them are the Samsung Galaxy S3 and S4, which can be equipped with after-market receiver sleeves suitable for Qi wireless charging. The Qi wireless charging pads are available off the shelf at eBay and Amazon. Other manufacturers who are directly integrating Qi into their devices include Google Nexus 4, Nokia Lumia 920, LG Optimus LTE2 and phones from Panasonic Eluga.
A Qi wireless charging system is available as a single-position, guided placement or a single-position, free placement. For those who want to charge more than one device at a time, there is the Qi three-position charging pad. The single-position guided placement is the cheapest type where the user can charge only a single mobile that he has to set in a specific position. The single-position, free placement is a little more expensive, as the user does not have to lock the mobile to the charger in any particular position. The Qi charging sleeve is very inexpensive and can be fitted to several models of mobiles.
The wireless charging standard makes it simpler for the consumer because of the ease of interoperability. Only a single wireless charger is enough for all devices in the household. Imagine that you are visiting the local coffee shop that has a Qi wireless charger. While enjoying your coffee, not only can you sample their free Wi-Fi, but make use of their wireless charging, without any concern about the compatibility of your device.
Qi works on the principles of magnetic induction between two coils. The charging pad holds one of the coils, which acts as the transmitter. The other coil is positioned inside the mobile device, usually just under the battery cover. Maximum power transfer requires one transmitter for each receiver, less than 4 cms of separation between the coils and a specific positioning of the mobile in relation to the transmitter. Qi chargers overcome the last limitation by providing more number of transmitter coils.