Image scanner for the pocket

An image scanner that can be rolled up and carried in a pocket could be just around the corner, thanks to scientists in Japan.

A team led by Takao Someya and Takayasu Sakurai from the University of Tokyo has developed what it calls "the world's first bendable-sheet image-scanner".

The device consists of a polymer laminate sheet containing a two-dimensional array of light sensor cells, each featuring an organic transistor and an organic photodiode.

The result is an image scanner that is ultra-thin and lightweight and can flex to scan the image of a curved surface such as an open page in a book or a label on a wine bottle, for example.

Unlike conventional image scanners which mechanically scan a linear array of photodetectors over an object, the new Japanese design does not require any moving parts or internal optics to capture an image.

Instead, the sheet is placed over the target object in ambient light con-ditions and the transistors are probed to reveal to the light intensity of each photodetector.

Each sensor cell is also covered with an opaque light shield to prevent incident light from above distorting the signal generated by the object below.

Someya's current prototype has an effective sensing area of 2 x 2" and is just 0.4 mm thick and 1 g in weight.

It features an array of 72 x 72 (5184) sensor cells, each 700 µm in size, giving a scan resolution of 36 dpi.

However, experiments with a matrix of organic photodetectors without transistors suggests that it should be possible to scale this to at least 250 dpi or more and create sheets that are A4 in size.

The scanner is effectively made by bonding together two thin polymer sheets - one containing the array of organic photodiodes and the other the array of organic transistors.

The interface between the two sheets is then patterned with silver paste by a printing technique to create the necessary electrical connections between the light sensor cells.