What if a band's poster could actually transmit a sample of their music to your phone, or your t-shirt could monitor your vital signs while you exercise? Researchers at the University of Washington (UW) have pioneered a technique where everyday objects can be embedded with transmitters that piggyback ambient FM signals to send data to nearby smartphones and radios using almost no power.

The technique makes used of backscattering, which is the reflection of waves, particles, or signals back in the direction they came from. The system uses a low-power reflector to encode specific audio or data on top of reflected signals from an existing FM broadcast, with the data sent on an adjacent band so as not to interrupt any current radio transmissions. The key benefit of the technology is that it has an extraordinarily low level of power consumption, meaning that it can easily be incorporated into everyday objects at a low cost.

"The challenge is that radio technologies like Wi-Fi, Bluetooth and conventional FM radios would last less than half a day with a coin cell battery when transmitting," says study co-author and UW electrical engineering doctoral student Vikram Iyer. "So we developed a new way of communication where we send information by reflecting ambient FM radio signals that are already in the air, which consumes close to zero power."

The antennas are made of thin copper tape and can be simply embedded into objects like advertising posters or articles of clothing. Initial demonstrations of the technique showed the total power consumption of a transmitter embedded into a poster to be as little as 11 microwatts – an output that could run uninterrupted off a small coin-cell battery for two years.

The team at UW has previously showed how an ambient backscatter technique can convert existing TV and cellular signals into electricity, allowing for battery-free sensors to be embedded into objects. This latest innovation excitingly evolves that technique allowing objects to send more complex information on top of existing radio frequencies.

"What we want to do is enable smart cities and fabrics where everyday objects in outdoor environments – whether it's posters or street signs or even the shirt you're wearing – can 'talk' to you by sending information to your phone or car," explains Shyam Gollakota, one of the lead authors in the research.

Using materials such as conductive threads, these flexible FM antennas can be woven into fabrics, creating smart clothes that sense a wearer's vital signs and transmit information to a nearby smartphone. The low-power consumption of the system means that such clothing wouldn't require large batteries, allowing them to become much more functional as wearable items.

The UW team has produced two working proof-of-concept prototypes demonstrating the technology. The first was dubbed a "singing poster" that transmitted portions of a band's music to a smartphone up to 12 ft (3.6 m) away, or a car up to 60 ft (18 m) away.

The second demonstration involved sewing a conductive three-ply thread made of stainless steel fibers into a cotton t-shirt. The fibers were chosen specifically as they don't oxidize, enabling the garment to be easily washed with no damage to the transmitter. The smart t-shirt was found to be able to transmit data at rates up to 3.2 kilobits per second to a nearby smartphone.

The combination of such minimal power consumption with the piggy backing of FM signals that are so pervasively present in modern cities, make this an innovation that takes us one step closer to a world filled with smart objects that communicate information instantly as soon as they are approached.

Check out the FM Backscatter system in action in the video below.

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