MIT researchers have developed a small, affordable, and secure cryptographic ID tag that improves upon traditional radio frequency identification (RFID) tags by using terahertz waves, which are smaller and have higher frequencies than radio waves. Traditional RFIDs are often attacked by counterfeiters who take them off genuine items and reattach to a fake one; the authentication system does not detect the swap. The team has now improved the security by integrating microscopic metal particles into the glue that attaches the tag to an object. Using terahertz waves, they detect the unique pattern formed by these particles on the item’s surface. This creates a distinct pattern similar to a fingerprint for the item’s authentication.
Ruonan Han, an associate professor in Electrical Engineering and Computer Science (EECS) who leads the Terahertz Integrated Electronics Group in the Research Laboratory of Electronics, likens the security process to reflecting light off scattered mirror pieces. The oriented, sized, and placed metal particles create a distinct reflected pattern that gets destroyed when the tag is removed and reattached.
The researchers have developed a light-powered antitampering tag that’s about 4 square millimeters in size. They also applied a machine-learning model that recognizes tampering by identifying similar glue pattern fingerprints with over 99% accuracy. This makes the terahertz tag not just small and cheap, but also highly secure, and it’s suitable for use in large supply chains and on smaller items that traditional RFIDs can’t attach to, like certain medical devices.
The researchers specifically targeted the glue at the interface between the tag and the item’s surface to secure the tag. The tag contains minuscule slots that allow terahertz waves to pass through and strike the microscopic metal particles mixed into the glue. As terahertz waves are small enough to detect these particles, they can gather detailed information from the object’s surface. Larger radio waves wouldn’t have enough sensitivity to accomplish this. The use of terahertz waves with a 1-millimeter wavelength also allowed the researchers to create a chip that doesn’t need a separate, larger antenna.
After passing through the tag and hitting the object’s surface, the terahertz waves are reflected to a receiver for authentication. The manner of backscattering depends on how the metal particles are arranged. The application of multiple slots in the chip helps to gather information from different points on the object’s surface, providing information about the random distribution of particles for authentication.
The researchers secured the data in a cloud for a vendor to take an initial reading once the antitampering tag is stuck on an item, which can later be used for verification.
However, the researchers found it challenging to take precise enough measurements to determine whether two glue patterns match. This problem was overcome by training a machine-learning model to compare the patterns and calculate their similarity with more than 99% accuracy.
There are limitations in the system, such as high levels of loss experienced by terahertz waves during transmission, necessitating a close 4-centimeter distance from the tag for accurate reading. Any angle more than 10 degrees between sensor and tag may degrade the signal too much. Despite these challenges, the researchers are optimistic about the potential applications of terahertz waves and are working on improvements for future implementations.
