Passive RFID Tracks Changes in Structural Micro-Cracks

By Claire Swedberg

Dai Nippon Printing has developed a passive adhesive sheet with a built-in Identiv UHF RFID tag, to detect when a crack to which a sheet is affixed widens, and to transmit that event when interrogated.

Japanese construction companies have been testing a new RFID-enabled product that automates the inspection of infrastructure cracks, with a goal of preventing catastrophic failures to bridges, tunnels or other structures. Dai Nippon Printing Co. (DNP) developed a new tag that employs passive ultrahigh-frequency (UHF) RFID technology to monitor the conditions of structures as they age. The tag has a built-in Identiv UHF RFID inlay that transmits a unique ID number when interrogated, but that ceases working properly when damaged by the expansion of a small crack on a structure to which it is attached.

The tag has been tested by multiple companies in Japan, according to a DNP spokesperson who has asked to remain unnamed. DNP's full solution consists of the company's Passive IC Tag Sheet with the built-in RFID tag, as well as handheld readers to interrogate those tags and dedicated management software that captures read data, interprets that information and makes the results available to users. It can also display alerts if a tag has not been read properly.

The solution is intended to make inspections faster, easier and more accurate for companies that are responsible for railway tunnels or infrastructure, as well as for road works companies, general contractors for construction sites and local governments.

Much of Japan's infrastructure was built during the country's economic growth period from 1954 to 1973. As a result, many of these structures are still in use but require inspection and maintenance. Owners and operators of infrastructure, such as bridges or tunnels, must monitor the conditions of their structures on a regular basis, for their own purposes as well as to meet regulations by governing bodies. That typically requires inspectors to regularly visit each site, visually inspect existing micro-cracks, and use a tool similar to a ruler that measures the length and width of each crack. Inspectors then manually record the results on paper, and the information must be entered into a management system to compare against earlier results. If the crack has become larger, it may require remedial action.

With RFID, DNP's solution is aimed at making this process more automatic. The Passive IC Tag Sheet is a rubberized tag measuring 60 millimeters by 108 millimeters, with an adhesive back that is affixed directly over a micro-crack that needs to be watched. The sheet has a built-in tamper-evident Identiv inlay. The rubber on the Passive IC Tag Sheet allows the tag the flexibility to adjust with any widening of a crack over which it is placed. Identiv tuned the antenna on its inlay to accommodate the material to which the tag would typically be applied, in order to ensure a proper read from a handheld reader, says Manfred Mueller, Identiv's chief operating officer.

If a crack were to widen, the rubber tag would stretch with that movement, but the tamper-resistant Identiv inlay would be damaged—the antenna's contact with the chip would be broken. Such a break can occur if a crack widens even by a few millimeters.

With the crack-detection system in use, inspectors will still arrive onsite as they always have, but in this case, they would bring a UHF RFID handheld reader with them. An inspector waves the reader within about 1 meter of a tag. If the tag has been damaged by a change in the crack, it will not respond in the expected way to interrogation by the reader. Mueller likens it to sending an X with the ID number if it is operating properly, and an O if the antenna has been compromised.

The make and model of RFID reader that will be used with the tag has not yet been determined, according to DNP. Thus far, testing has found that the tag can be read at a distance of about 1 meter, though in the future Identiv expects the technology could accomplish up to a three- or ten-foot range. To date, the material in the construction environment makes longer read ranges impossible. Therefore, an inspector must still come close to the tag, but need not use the measuring tools, or record data manually, as he or she would have done in the past.

The product is expected to be commercially launched in early 2018. "We envisage to introduce this solution in Japan first," the DNP spokesperson says. "And then we intend to consider developing the overseas market after studying their regulations, inspection standards, etc."

Identiv conducted some modification to its tamper-resistant inlay to ensure it could detect the widening of a crack by as little as a millimeter, Mueller reports. "We've been happy to leverage the relationship we have developed with DNP," he says, "to be able to contribute to this technology."