Passive RFID (radio frequency identification) tags are small, inexpensive, battery-less labels that are already used to track and identify a wide variety of items. If MIT's experimental RFIQ system enters general use, they may also soon allow consumers to check if food products are contaminated.
Upon being temporarily powered up by radio waves emitted from a handheld reader device, passive RFID tags use a tiny integrated antenna to transmit a radio signal back to that device. That signal contains information on the item to which the tag is adhered, such as its stock number, batch number or production date.
When one of those tags is stuck to the outside of a container, the radio waves emitted by the tag travel back through the wall of that container, and are subtly distorted by the molecules and ions of its contents. As an example, the signals from identical RFID tags placed on identical containers filled with either water or air will be distorted in different ways, upon being received by a reader device.
RFIQ takes advantage of this phenomenon, which is known as "weak coupling." Linked to a reader, a computer is trained by humans to identify the unique signal distortions associated with specific contaminants within specific foods or beverages. Machine-learning algorithms help the system to subsequently build upon that training.
When lab-tested, RFIQ was 97-percent accurate at detecting varying concentrations of methanol that had been added to distilled ethanol ("drinking" alcohol), and 96-percent accurate at detecting different concentrations of melamine within baby formula. The researchers are now working on building up its database, and on compensating for differences in the shape and size of containers, along with various environmental variables. Once perfected, the technology could conceivably be integrated into smartphones.
"In recent years, there have been so many hazards related to food and drinks we could have avoided if we all had tools to sense food quality and safety ourselves," says Asst. Prof. Fadel Adib, co-author of a paper on the research. "We want to democratize food quality and safety, and bring it to the hands of everyone."