A new technology is enabling everyday objects, such as posters and clothing, to be transformed into FM radio stations, according to research from the University of Washington.

The team has introduced a technique called ‘backscattering’ which uses ambient low-power radio signals to broadcast messages from random objects to smartphones in the local vicinity. The researchers hope that the development could help support various smart city applications, and picture a future where anything from a poster at a bus stop to a road sign can transmit audio updates and information to passers-by.

During testing, the researchers were able to use the backscattering technique to create a ‘singing poster’ which could send out the music of an advertised band to smartphone users at a distance of up to 4 metres and to cars in an 18-metre radius.

‘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,’ explained lead faculty and UW assistant professor of computer science and engineering Shyam Gollakota.

‘The challenge is that radio technologies like WiFi, Bluetooth and conventional FM radios would last less than half a day with a coin cell battery when transmitting,’ added study co-author and 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,’ he added.

The backscattering system transmits the messages by reflecting and encoding audio and data found in outdoor radio signals, without interfering with the original transmissions.

The researchers propose three methods for transmitting audio signals through the backscatter techniques. These involve either overlaying new data on top of existing signals, using unoccupied frequency in the FM radio band, or using cooperation between two smartphones to decode the message.

smart-t-shirt‘Because of the unique structure of FM radio signals, multiplying the original signal with the backscattered signal actually produces an additive frequency change. These frequency changes can be decoded as audio on the normal FM receivers built into cars and smartphones,’ detailed co-author and postdoctoral computer science and engineering researcher Vamsi Talla.

The researchers further suggested that low-power connectivity could also allow smart fabrics integrated with sensors to monitor a runner’s vital signs and transmit that data directly to a user’s phone.

A test of this application found that conductive thread in a cotton t-shirt could use ambient radio signals to transmit information to a smartphone at rates of up to 3.2 kilobits/second.

In both demonstrations, the total power consumption of the backscatter system was 11 microwatts, which could easily be delivered by small coin cell batteries or solar cells.

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