采用無線充電給可穿戴設備帶來便利

The wearable device is fast emerging as an important market sector for electronics. A key requirement of these devices is convenience， not just in the ability to access data on the move but to ensure that it has enough battery life to last an entire day， and do so every day.

If a user has to plug a device in to recharge it overnight， there is a high probability they will forget on some occasions and wake up to find the product is unable to remain active for the rest of the day. Wireless charging offers a more convenient way of charging electronic devices. Instead of having to plug a mini-USB or similar cable into the device， it can be placed on a charging mat that the user can keep in an easily accessible location. If the wireless-charging system is designed appropriately， multiple devices can be charged on the same mat， reducing duplication and making it easier for users to take the device and charger when they travel.

Wearables are not the only types of electronic device that can benefit from wireless charging. The technology is already widely used for electric toothbrushes and is even being scaled up to recharge the batteries in electric vehicles.

Inductive charging works on the same basis as a power transformer. An induction coil in the mat creates an alternating electromagnetic field that is picked up by a secondary coil in the device to be charged where it is converted back to a usable electrical current. Like a conventional transformer， basic inductive charging requires close proximity between the coils to provide high efficiency. Otherwise， substantial losses can build up through resistance in the primary coil.

The efficiency of energy transfer over longer distances can be improved through the use of resonant inductive coupling using two coils that are tuned through the combination of inductance and capacitance loading to resonate at the same frequency. This resonance allows significant power to be transmitted from one coil to the other over distances of up to a few times the diameter of the coil.