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No. 2853:
Radio Frequency Identification

Today, we ease on down the road. The University of Houston's College of Engineering presents this series about the machines that make our civilization run, and the people whose ingenuity created them.

Driving comfortably down the road, you look up ahead and see a sign. It reads: "Toll: two axles, $1.40." You glide smoothly forward at seventy miles an hour without so much as tapping on the brakes. Moments later your credit card is charged the designated amount. It's a far cry from the days of fumbling through your pockets to find money for the toll keeper. What makes it all work?

TX highway picture

The most common technology for collecting tolls is radio frequency identification, or simply RFID. RFID tags are typically flat and cover an area of a few square inches. They send out a unique radio signal that identifies the tag, and they're popping up not just on toll roads, but everywhere.

Years ago price tags were replaced by bar codes. Now major retailers are replacing bar codes with RFID tags. Bar codes and RFID tags carry similar information, but there's one big difference. To get the information from a bar code, it must pass in front of a scanner. That's not true of RFID tags. The scanner is replaced by a receiver that just has to be in the vicinity of the RFID tag. So, for example, a clerk can take inventory of everything on the shelf by simply walking down the aisle holding a radio receiver. No need to scan each individual item. That's a tremendous time saver.

So why haven't RFID tags replaced bar codes? Well for one thing, RFID tags are more expensive. They come in two flavors: tags that send signals and tags that reflect signals. Tags that send out their own radio signal work over long distances but cost a few dollars each. Tags that simply reflect a signal sent out by the receiving device cost around five to ten cents. That's not much if you're buying a hundred dollar pair of designer jeans, but it's pretty expensive to slap on a two dollar bag of pretzels. Still, if prices come down, it's fun to think about the possibilities. Imagine checking out of a grocery store by simply walking through a device that looks like a metal detector.

That's essentially what your car is doing on a toll road. For many years cars were required to carry tags that sent out their own signals. That's changed in recent years as the technology's improved. Tags that reflect signals can now be read up to thirty feet away with proper sensing devices. The tags are encased in paper thin window stickers, and use the car's windshield to amplify the reflected signal. If a tag's not properly attached to the windshield it won't work — and you'll get a ticket.

TX toll tag

So hat's off to RFID technology. It's another way that engineering is making life's journey just a little bit easier.

[audio: Ease on Down the Road

I'm Andy Boyd at the University of Houston, where we're interested in the way inventive minds work.

(Theme music) 

Notes and references:

EZ Tag. From the Wikipedia website: Accessed January 1, 2013.

Radio Frequency Identification. From the Wikipedia website: Accessed January 1, 2013.

The picture of the 31 millimeter RFID tag is from Wikimedia Commons. All other pictures are from websites of the Texas Department of Transportation.

This episode was first aired on January 3, 2013.