1. Field of the Invention
The present invention relates to wireless power transfer.
2. Description of the Related Art
Wireless power transfer between fixed and portable devices eliminates power connectors and concomitant issues of contact cleanliness, dirty and wet environments and shock hazard. Often connectors are the least reliable component in electronic systems.
Wireless power transfer has been adopted for charging portable battery-powered devices such as cell phones and motorized toothbrushes. The portable device may be a wireless integrated circuit card and the fixed device may be a card coupling device. Alternatively, the portable device may be a mobile telephone, smart phone or computer tablet and the fixed device may be a battery charger. In the present disclosure, chargers are representative of a wider class of fixed devices.
For example, the Qi standard developed by the Wireless Power Consortium has been adopted by many companies for inductive wireless power transfer. One disadvantage of inductive power transfer is the need to contain a relatively strong magnetic field by means of shielding in both the charger and portable device, increasing costs. With people in close proximity to the charger, such shielding is required to limit the magnetic field strength to a permissible level.