Although wireless ID tags are becoming increasingly popular for authenticating assets as they change hands, these tags come with various size, cost, energy, and security trade-offs that limit their potential. Popular radio-frequency identification (RFID) tags are too large to fit on tiny objects such as medical and industrial components, automotive parts, or silicon chips. Some tags are built with encryption schemes to protect against cloning and ward off hackers, but they’re large and power hungry. Shrinking the tags means giving up both the antenna package (required for radio-frequency communication) and the ability to run strong encryption, the researchers note, offering to circumvent all these trade-offs with a millimetre-sized ID chip.
Presented at the IEEE International Solid-State Circuits Conference (ISSCC), the tiny chip runs on relatively low levels of power supplied by integrated photovoltaic diodes. It also transmits data at far ranges, using a power-free “backscatter” technique that operates at a frequency hundreds of times higher than RFIDs. Algorithm optimization techniques also enable the chip to run a popular cryptography scheme that guarantees secure communications using extremely low energy.
“We call it the ‘tag of everything.’ And everything should mean everything,” says co-author Ruonan Han, an associate professor in the Department of Electrical Engineering and Computer Science and head of the Terahertz Integrated Electronics Group in the Microsystems Technology Laboratories (MTL).
“If I want to track the logistics of, say, a single bolt or tooth implant or silicon chip, current RFID tags don’t enable that. We built a low-cost, tiny chip without packaging, batteries, or other external components, that stores and transmits sensitive data.”
One innovation the researchers came up with is an array of small antennas that transmit data back and forth via backscattering between the tag and reader in the terahertz range. Backscatter, used commonly in RFID technologies, happens when a tag reflects an input signal back to a reader with slight modulations that correspond to data transmitted. In the researchers’ system, the antennas use some signal splitting and mixing techniques to backscatter signals at THz frequencies. Those signals first connect with the reader and then send data for encryption. Implemented into the antenna array is a “beam steering” function, where the antennas focus signals toward a reader, making them more efficient, increasing signal strength and range, and reducing interference. This is the first demonstration of beam steering by a backscattering tag, according to the researchers.
Tiny holes in the antennas allow light from the reader to pass through to photodiodes underneath that deliver about 1V of output and power up the chip’s processor, which runs the chip’s “elliptic-curve-cryptography” (ECC) scheme. In the researchers’ system, the tag uses a private key and a reader’s public key to identify itself only to valid readers. That means any eavesdropper who doesn’t possess the reader’s private key should not be able to identify which tag is part of the protocol by monitoring just the wireless link. The researchers reported a signal range of about 5 centimetres, which is just convenient enough to use a portable tag scanner, but increasing the reading distance to within meters would allow tags to be read out from a single reader hub at a supply chain checkpoint.
The researchers also hope to fully power the chip through the terahertz signals themselves, eliminating any need for photodiodes. Measuring about 1.6 square millimetres, the chips would cost only a few cents and would be small enough to be embedded into larger silicon computer chips too, preventing counterfeiting.
MIT – www.mit.edu