Scientists at Eindhoven University of Technology have developed what they say is the final piece in the puzzle of developing a smart sensor that could be integrated within food packaging to provide a readout of that food’s freshness: A plastic analog-to-digital converter. The invention was presented in late February at the ISSCC in San Francisco, an important conference on solid-state circuits.
Costing less than one euro cent each, the ADC could be combined with three other components that already exist: An electronic sensor circuit that, for example, undergoes an irreversible change when food goes above a freezing temperature; an amplifier for that signal; and an RFID radio that can send ADC’s digital signal to a base station. From there, the “fresh” or “toss” verdict could be read by a scanner or mobile phone.
“Each element would be printed at low-temperature on the food wrapping,” explains Eugenio Cantatore, PhD, of Eindhoven University’s Department of Electrical Engineering. “Although printed sensors, amplifiers and RFID radios are already known as the state of the art, no printed ADC had previously been demonstrated. The next step is integrating all the elements.”
The sensors could be used to monitor freshness for virtually any food product, Dr. Cantatore says. The simplest example would be a sensor that detects if a deep-frozen item was ever defrosted. “For more complex applications like predicting expiration dates, several parameters must be checked—for instance PH, temperature, and composition of the conservation atmosphere—and this will need more complex sensors that are able to measure all these quantities,” Dr. Cantatore says. “Based on this information and knowing which kind of product is monitored, software in the reader can compute the quality of the preserved item. In this way, just one kind of integrated sensor able to measure several parameters could monitor a large variety of products, as the customization to the specific product to compute the expiration date is made in the software.”
The fully-integrated electronic sensor is probably still a few years away, Dr. Cantatore cautions. “We cannot now see major technological roadblocks for scaling up the ADCs, but sensors for different parameters need to be better developed and integrated with the printed electronics. This is a big challenge and needs some research.”