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Shopping Sensors to Determine Produce Quality

Whilst supermarkets -and to a lesser extent small shops – try their hardest to ensure the produce they stock is fresh, and free from rot, it doesn't always work. Particularly, as produce sit on the shelves for a few days, what was once fresh and firm, may become less so. The only real way to be (relatively) sure has been to throw the whole lot out every couple of days.

But what if you could test each fruit, vegetable, cheese, slice of meat or fish to see how fresh it is? Better, what if you could give an inexpensive device to every shopper so that they could do the testing, and be able to only select the freshest, rot-free produce to purchase?

That is the goal of a group of researchers at the relevant business unit at the Fraunhofer Institute for Photonic Microsystems IPMS in Dresden, Germany. They already have a tiny spectrometer smaller than a sugar cube, far, far smaller than any other spectrometer on the market.

The plan is to perfect the device, then integrate it into future smartphones – near future smartphones. For the user, what is hoped is that all the user will need to do is hold their smartphone near the product in question, activate the corresponding app, choose the food type from the menu – e.g. “pear” – and straight away the device will make a recommendation: the fructose content of the pear is high, so buy it!

The application is based on a near infra-red spectrometer which measures the amount of water, sugar, starch, fat and protein present in the products. The system “looks” several centimetres below the outer surface of the foodstuffs – which means it can detect, for instance, whether the core of an apple is already rotting. Thin packaging film is no problem for the device as it takes measurements straight through it.

Of course, this also means it has medical applications way beyond looking at foodstuffs. Are you diabetic? Hold the spectrometer near your skin, and select an app to study glucose levels. The system looks through your skin, several centimetres into your body and analyses the glucose levels found within. No needles, no puncture wounds, no damage. All that's needed is an app to go with the sensor, and that won't take long to emerge.

One of the prototype sensors

The truly novel things about this spectrometer are its tiny size, and it's truly inexpensive cost. It is also very suitable even in its current state, for mass production. With a volume of only 2.1 cc, it is 30 percent smaller than a sugar cube, and thus substantially more compact than its commercially available counterparts, which are around 350 times larger.

“We expect spectrometers to develop in the same way that digital cameras did,” says Dr. Heinrich Grüger, who manages the relevant business unit at IPMS. “A camera that cost 500 euros ten years ago is far less capable than the ones you get virtually for free today in your cell phone.”
Spectrometers are usually manufactured by assembling individual components: The mirrors, optical gaps, grating and detector each have to be put in place individually and properly aligned. The IMPS researchers instead manufacture the individual gratings and optical gaps directly on silicon wafers.

The thin silicon wafers are large enough to hold the components of several hundred spectrometers, which means that hundreds of near infrared systems can be produced in one go. The scientists stack the wafers containing the integrated components on top of the ones bearing the optical components. They then align and bind the wafers, and isolate them to form individual spectrometers. This means the researchers do not need to position each component, but only the respective composite substrates.

At the Sensor+Test trade show being held in Nuremberg from May 22 to 24 2012, the researchers will be exhibiting a prototype of the spectrometer (in Hall 12, Booth 202). They are hoping to have it on the market within a couple of years, but need commercial partnerships now.

The researchers are also working on creating a corresponding infrastructure. “We are developing intelligent algorithms that analyse the recorded spectrum immediately, compare them with the requirements and then advise the consumer whether or not to buy the item. 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 device can also detect forgeries, and can verify whether a product is made of high-quality original materials or whether it is a cheap fake. It can also reveal whether parts of a vehicle’s body have been repainted, as well as test the contents of drugs and cosmetic creams.


Rapid testing of food quality

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