The teams at Eindhoven University of Technology, Universitá di Catania, CEA-Liten and STMicroelectronics invented the plastic analog–digital converter which brings cheap costing plastic sensor circuits within reach in a bid to cut down on unnecessary food waste.
Food wasteage often occurs due to the difficulty in estimating how long it will stay usable with ‘best before’ dates being “cautious estimates”, found the inventors.
The researchers have succeeded in making two different plastic ADCs, with each one converting analog signals, such as the output value measured by a sensor, into digital form.
"This paves the way toward large area sensors on plastic films in a cost-effective way through printing manufacturing approaches", said Isabelle Chartier, printed electronics business developer at CEA-Liten.
Four components
A sensor circuit consists of four components: the sensor, an amplifier, an ADC to digitize the signal and a radio transmitter that sends the signal to a base station.
Producers could include an electronic sensor circuit in their packaging to monitor the acidity level of the food, said the researchers.
The sensor circuit could be read with a scanner or mobile phone to show the freshness of the steak, or whether the frozen food was defrosted.
Plastic ADC breakthrough
The plastic ADC has been the missing link; the other three components already exist, said researcher Eugenio Cantatore of Eindhoven University of Technology (TU/e).
However, he predicted that it will still take at least five years before the devices should expect to be seen on supermarket shelves.
The development falls under the EU project: Complementary Organic Semiconductor and Metal Integrated Circuits (COSMIC).
Silicon costly
Cantatore said the problem with using currently available standard silicon ICs, was the cost.
“They easily cost ten cents. And that cost is too much for a one euro bag of crisps. We’re now developing electronic devices that are made from plastic rather than silicon. The advantage is you can easily include these plastic sensors in plastic packaging.”
The plastic semiconductor can be printed on flexible surfaces, which makes it cheaper to use and the printed ADC circuit offers a resolution of four bits, and has a speed of two hertz.
The circuits include more than 100 n- and p-type transistors and a resistance level on transparent plastic substrates.
The electrical characteristics of ordinary transistors are predictable, while those of plastic transistors vary greatly, added Cantatore.
“All plastic transistors behave differently in the low-cost production processes at low temperatures.
“That makes it much more difficult to use them in devices. You need complex mathematical models to be able to predict their behavior accurately.”