Trial by Tire

By Pat King

April 3, 2006—In simplest terms, singulation theory states that an RFID practitioner needs to understand the deployment of an isolated tag (hence, the term 'singulation') before attempting to manage a group of tags (see Six Sigma and the Single Tag). Using RFID labels on tires as an example, this column demonstrates the risks associated with not applying this theory, as well as some techniques to apply it successfully.

The majority of Michelin's publications regarding tire RFID have focused on embedded RFID tags. Michelin has developed a permanent RFID tag capable of being cured directly into the tire. In order to provide a practical example of singulation theory, however, this article will focus instead on the deployment of a temporary RFID label applied to the tire's surface.


RFID Label for Tires
A completely successful label capable of being applied to a tire's surface may never exist. The history of tire labels shows that they easily fall off or become damaged. The particular label used in this test completed a battery of tests including application (hot and cold), shipping (hot and cold) and wheel-mounting.

The key to success is to employ a label stock able to breathe and remain flexible. Since tires exude oils over time, they tend to reject most labels and adhesives. Labels made more like cloth or duct tape make better candidates, whereas traditional thin film plastic or vinyl labels tend to fail quickly. The label design employed in this test was a cloth-type label.

Two different styles of UHF RFID transponders were used, each utilizing an SOP chip soldered to an antenna.

RFID Transponders
Two different styles of UHF RFID transponders were used in this test. Each type utilized an SOP (small outline package) chip soldered to an antenna. An SOP is a traditional electronic package employed to protect the chip from its environment, including the ability to cure the device into rubber.

Other tag-antenna attachment techniques—such as flip-chip or direct bonding—have been proven non-robust in tire-tagging applications. One SOP tag for this test was manufactured on a flexible substrate, while the other was the tag developed by Michelin that could be cured directly into the tire. This Michelin transponder has a spring wire antenna soldered directly to the SOP on a miniature thin circuit board