Imager Detects Bruised Fruit

Ever bought what you thought was a unblemished apple or peach, only to have it develop a nasty-looking bruise the next day? Well, researchers at the Fraunhofer Institute for Photonic Microsystems (IPMS) in Dresden feel your pain, and have developed an affordable way to do something about it.

Hyperspectral imaging can tip grocers off to which apriots or other fruits on display have been manhandled enough to develop blemishes that quicken their spoilage, but the equipment is very expensive. So scientists at Fraunhofer IPMS developed a cheaper version of the technique that can also be used to sort plastic bottles for recycling.

The prototype spectral imager developed at the Fraunhofer Institute for Photonic Microsystems analyzes the type of polymer in plastic bottles so that they can be sorted for recycling. The same instrument can also be used to detect bruising in fruit – before it is visible to the naked eye. (Photo: Copyright ©Fraunhofer IPMS)

With their system, the Fraunhofer researchers shine broadband infrared light, i.e. light comprised of different wavelengths -- onto a sample. The light reflected by the sample is captured by a microscanner mirror with a superimposed diffraction grating that splits the light into its constituent wavelengths, like a prism. The detector onto which the light subsequently falls is usually 2-D: It is divided up like a checkerboard, with the different wavelengths represented along one axis and the points on the surface of the inspected fruit shown along the other.

“Instead of being fixed in place, our microscanner mirror is movable and can deflect light of different wavelengths in different directions. This enables us to make do with a linear detector, which costs only about one-tenth of the conventional type. Since the detector is the most expensive component of the imager, this makes a big difference to the price of the instrument,” said IPMS business unit manager Dr. Michael Scholles.

Damaged fruit detected by the imager could be immediately sent to manufacturers of fruit juice or yogurts for processing instead of having them spoil on supermarket shelves.

Another application for the spectral imager, the researchers said, is automatically sorting plastic bottles for recycling by identifying what type of polymer they contain.

A prototype of the spectral imager has been built, and Fraunhofer IPMS researchers will be giving a live demonstration of the way it analyzes plastic bottles at the Electronica 2008 trade fair in Munich, Nov. 11-14 (Hall A2, Stand 420).

For more information, visit: www.ipms.fraunhofer.de/en