Posters and shirts turned into FM radio transmitters thanks to new technique

A team of engineers at the University of Washington has demonstrated new technology that can turn everyday objects into tiny FM radio stations.

Technology could be used for advertising and smart clothing

Concert posters equipped with FM antennas could transmit a link to your smartphone where you can buy tickets. (University of Washington)

You may have listened to CBC Radio, which covers a huge part of our country. But the future may be filled with lots and lots of very small radio transmitters.

A team of engineers at the University of Washington has demonstrated new technology that can turn everyday objects into tiny FM radio stations.

CBC tech Dan Misener columnist explains. 

How did the engineers make everyday objects into tiny FM radio stations? 

The engineers found a way to, for the first time, use a technique called backscattering on FM radio signals. Essentially, they take existing FM signals, change them by adding new audio (such as music) then reflect them back out, without affecting the original radio transmissions. 

"You've got these big FM transmitters that are transmitting kilowatts of power, and we're just reflecting those signals and encoding our own information on top of it," said Vikram Iyer, one of the engineers who worked on the project.

In short, they're piggybacking on top of other radio signals, such as the CBC. 

Of course, FM radio signals are all around us, floating through the airwaves. And many FM signals are very powerful.

Using this technology, my voice and your voice could be used to power a bunch of tiny little mini radio stations, built into all kinds of everyday objects. But we're talking about a radio stations with a very small broadcast radius of 20 metres or less.

What did the engineers make into a tiny FM radio stations?

The engineers equipped a concert poster with an antenna made of copper tape and turned it into a radio transmitter. 

Researchers embedded posters with FM antennas so they could broadcast music and data. (University of Washington)

They also made a T-shirt into a radio transmitter, which we will get to later.

These tiny radio stations can not only transmit audio, like a traditional broadcast tower, but they can also transmit data, so you could pick up their signal with your car stereo or your smartphone. 

From a technical standpoint, the real innovation here is how little energy these tiny radio stations use. They consume almost zero power. In fact, they use so little energy that a single radio station could run continuously for three years on a single coin cell, like a watch battery.

Why would anyone want to build a radio station into a poster?

One obvious use is advertising.

The engineers who developed this technology built a small radio station into a concert poster and put it up at a bus stop.

So if you were nearby, not only would you be able to see the poster, if your radio was tuned to the right frequency, you would also hear it playing a sample of the band that was being advertised.

The poster can also send digital information over FM frequencies. For instance, it could transmit a link to your smartphone where you could buy tickets.

Again, these are very close-range transmitters, and you'd have to be within a few metres for it to work properly.

How else could this technology be used?

It could also be used for wearable technology.

Off the top, I mentioned that the team at the University of Washington built a radio station into a T-shirt.

Researchers sewed an antenna into this T-shirt using conductive thread so it could use FM radio signals to transmit data to a smartphone. (University of Washington)

The idea is that you could create smart fabrics and smart clothing that could communicate with your phone through radio frequencies.

One of the big challenges with wearable technology is the question of power. Where do you put the batteries? What's the trade-off between battery life and size and weight?

With this approach, because the shirt is using ambient radio waves that are already in the air, you can dramatically reduce the amount of power required.

So you can imagine a smart T-shirt that monitors your vital signs and only requires a tiny watch battery to operate.

What's the broader trend here?

I think this story is less about buying concert tickets and much more about some of the bigger infrastructure challenges of so-called smart cities.

There's a lot of hype about embedding communications technology in the world around us and what becomes possible when the environment around us is online.

Of course, there are some real challenges that need be overcome first, and among them is cost and power.

What I find so compelling about this work is that it tries to address those challenges using technology that already exists and is already ubiquitous.

I also really like the idea of having my very own mini radio station inside my house.


Dan Misener

CBC Radio technology columnist

Dan Misener is a technology journalist for CBC radio and Find him on Twitter @misener.