A team from the University of Tokyo are developing inductive power transfer methods that will allow charging of mobile devices without the hassle of wires.

Although such systems are already close to commercial roll-out, for example from UK-based Splashpower, the Japanese technology would seem to promise very thin and flexible charging mats that could be integrated into everyday materials.

Dr Takao Someya and Dr Takayasu Sakurai have used printed organic transistors and printed MEMS switches to create their 1mmm thick power sheet.

The sheet (pictured left embedded in a table) contains an 8x8 cell array combining position-sensing and power transmission circuits. An object's position is sensed by electromagnetic coupling, using an organic active transistor matrix.

Power is fed to the object, such as a mobile phone or laptop, inductively from an array of copper coils driven by the MEMS-switching matrix.

The benefit of sensing the position of the object and selectively feeding power to that area in increased efficiency, explained Someya. "Net power-coupling efficiency is 62.3 per cent. Power levels as high as 29.3W have been transferred in this fashion."

Other inductive power developments
Splashpower seems to be closest to commercial sales of an inductive charging pad for mobile electronics. The firm is promising products from partners next year from its system, which uses a standalone pad, looking much like a fat mouse mat.

"We have seen a few announcements for wireless power systems recently and I think this validates the strong demand for such a system," James Hay, co-founder of Splashpower, told Electronics Weekly.

However, Dr Someya told EW: "There is little disclosure on the details of their [Splashpower's] technology while we publish the technical details in international conferences. There are no products of this kind available in the marketplace at this moment."

Someya points to the size difference in the technologies: "It is easy to place the wireless power transmission sheet on walls, ceilings or in imaginative locations, opening up new ways to interact with electronic products."

Fundamental details of the Japanese technology will be presented at IEDM this week, while details of the organic integrated circuit will be shown at ISSCC 2007.

The picture on the right shows a how LEDs can be powered through a 5mm piece of perspex.