Electromagnetic induction, or the production of electric current in conductive elements as they move through a magnetic field, has been used to generate electricity for a range of consumer products, so-called "shake-to-charge" or "battery-free" products.
Technology based on this phenomenon has been used for many years to power small, energy efficient devices such as flashlights and radios. To obtain sufficient electrical charge, these systems typically use thick coils, sized to fit the copper wire as the conductor.
Apple's invention proposes the use of printed inductors with one or more moving magnets, altering the traditional configuration in which heavy copper coils are moved across a stationary magnet. The magnets in Apple's system move next to a printed circuit board that holds the coils to create "electromotive force," or voltage, along the length of the coil, which can be used to generate electricity.
The key to the system's functionality is the creation of printed spools that can be created using any technique for printing modern circuit boards. By way of example, printed coils can be created by "depositing copper onto a substrate to form coil traces" or "selectively etching copper" to achieve the effect described above.
In order to achieve the required power level, the board can contain several layers on which the printed coil is formed. To create a coil, multiple layers are then connected together using interlayer holes or electrical connectors. Apple notes that in one variation, the coil can be formed from printed circuit boards.
A magnet or set of magnets can move freely along the boards to create electromotive force through the coils. One embodiment of the invention provides a housing for holding magnets in which lubricant is introduced to facilitate free movement.
Electric current is generated by the movement of magnets along the printed coil, or by shaking the device by the user, or simply by moving it under normal operating conditions. After passing through the power support circuit, the generated electrical current is stored in large capacitors or batteries connected to the control circuit.
The entire unit can be installed directly inside a portable device, specifically an iPod or iPhone from Apple, as two possible candidates. Currently, the requirements of these two devices are probably too high to use an electromagnetic induction system, meaning they will continue to be powered from a wall outlet or computer. The electronic components inside Apple's iOS devices are becoming more efficient and will one day reach the point where such a system can provide enough power for everyday use.
It is not yet clear if Apple will use such technology to power its future devices. The invention serves as an indicator that the company is actively looking for ways to make its electronic devices truly wireless.