Wireless Charging
The Nokia Lumia 1520 can use Qi wireless charging pads like the DT-900 shown.
PHOTO COURTESY OF: http://thenextweb.com/ Benefits
Phones Without Wireless-Charging Capabilities
Although the iPhone (4 in this photo) cannot wirelessly charge on its own, accessories like the Duracell Powermat and case allow it to do so.
PHOTO COURTESY OF: www.amazon.com Although many top smartphones now have wireless capabilities, some, notably the iPhone and Samsung Galaxy S5, do not.
For these phones, however, there are accessories like the Duracell Powermat 24-Hour Charge, shown above, which typically use a case of some sort, which is connected to the phone. Since the case has the receiving coil built in, when the coil in the pad is charged the coil in the case still has energy induced despite not being part of the phone. To transfer the charge, the case simply uses the microUSB/Lightning/30-pin adapter spot to recharge the phone with. However, the case has to have the special charging coils in order to induce electricity and have a positive value of EMF. If the case does not have the coils built in, then it cannot induce electricity and charge the phone. |
How Does it Work?Wireless charging uses magnetic induction to charge devices The bottom coil, also known as the transmitting coil, is charged by an external source (this is usually plugged into the wall socket, which supplies the power source).
These pads are called Qi pads, which is the Chinese word for "air," and do not have more than 5 W of power (however, not much is required to charge a phone - please see "Wired Charging" - iPhones, for instance, have 5 W/1 A/5 V power/current/voltage in their chargers. When the pad is connected to the external source, the chrage moves through the coil, which will create a current. This also creates a magnetic (B) field. As shown in the diagram below, the magnetic field will cause the coil on top (if the device on top has a receiving coil which allows it to charge - this is often known as Qi-enabled) to also have a current. This is done by electromagnetic induction, which explains why wireless is also often called inductive charging. From then on, it is quite simple: the current induced in the receiving coil will charges the internal battery of the device. This will continue until the device is fully charged, at which point the receiving/secondary coil will not have any more current induced in it. 
A brief diagram of how wireless/inductive charging works.
PHOTO COURTESY OF: web1.handymanclub.com
AvailabilityLike any new technology, wireless charging is growing, but still is not even close to being as commonly used as wired chargers. Despite that it is more convenient to charge with, wireless chargers have not yet been shown to sync data, so in many cases wired chargers may still be more convenient. However, they are becoming more prominent, as Starbucks is one of the first companies to have wireless chargers on their counters and tables and phones or phones + cases with a receiving coil can charge them by induction.
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Constructing the Wireless Charger - What We Would Have Done
We did not construct a wireless charger, as we would not have anything to test its functionality with. However, if we did, we would have created a pad for the phone to be placed on (this would likely be a cardboard box of some sort, but the material would not make a difference since it would not affect the induction. Then, we would put a coil in the box on the bottom, which we would connect to an external power source. We could wrap copper wire around some sort of metal object (nail, magnet, etc.), creating an electromagnet when we added current to it from the external source. On top of the box, we would put the device with the receiving coil (one that is wireless-charging enabled) or a device with a case that has a receiving coil (see above left). Then, theoretically, once we turned on the external power source, we would be able to induce current in the receiving coil and charge that device.
