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Tiny spectrometer evaluates food quality

BioPhotonics
Jul 2012
Ashley N. Paddock, ashley.paddock@photonics.com

DRESDEN, Germany – An inexpensive spectrometer about 30 percent smaller than a sugar cube could soon help shoppers determine whether groceries on the shelves are of high enough quality to purchase.

Fraunhofer Institute for Photonic Microsystems (IPMS) researchers developed the device, which can be mass-produced for volume applications such as smartphones, to determine the ripeness of pieces of fruit and the tenderness of meat. The application is based on a near-infrared spectrometer that measures the amount of water, sugar, starch, fat and protein present in products by “looking” several centimeters below the outer surface of the foodstuffs. For instance, it can detect whether the core of an apple is already rotting.

To use the device, a shopper would need only to hold a smartphone near the product in question, activate the app, and select the food type from a menu. The device determines whether that piece of fruit the shopper is eyeing has a high enough fructose content to be deemed worthy of buying.

The Fraunhofer spectrometer is substantially more compact than its commercially available counterparts, which are about 350 times larger. The new devices are inexpensive to make and suitable for mass production.


Complete with integrated diffraction grating, grating drive, position detector and optical gaps, the Fraunhofer spectrometer is much more compact than those currently on the market. Courtesy of ©Fraunhofer IPMS.


“We expect spectrometers to develop in the same way that digital cameras did,” said Dr. Heinrich Grüger, who manages the business unit of Fraunhofer IPMS, where the system is being developed. “A camera that cost €500 (about $629) 10 years ago is far less capable than the ones you get virtually for free today in your cell phone.”

Conventional spectrometers are manufactured by assembling individual components: The mirrors, optical gaps, grating and detector each have to be put into place individually and properly aligned.

The Fraunhofer researchers instead manufacture the individual optical gaps and gratings directly onto silicon wafers, which are large enough to hold the components of several hundred spectrometers, enabling hundreds of near-infrared systems to be created at one time. The wafers containing the integrated components are stacked atop the ones bearing the optical components, then aligned and bound together, isolating them to form individual spectrometers. The resulting devices are more robust than their handmade counterparts.

The scientists are now working to develop a corresponding infrastructure, which could be ready for market within the next three to five years.

“We are developing intelligent algorithms that analyze the recorded spectrums immediately, compare them with the requirements and then advise the consumer whether or not to buy the item,” Grüger said. “This advice is based solely on quality features such as ripeness and water content. The system cannot carry out a microbiological or toxicological analysis.”

The spectrometer also could be used, for example, to verify whether a product is made of high-quality original materials or is just a cheap knockoff. It could even determine whether parts of a vehicle’s body have been repainted, or test the contents of cosmetic creams and drugs.


GLOSSARY
spectrometer
A kind of spectrograph in which some form of detector, other than a photographic film, is used to measure the distribution of radiation in a particular wavelength region.  
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