Painted on micro sensors

Tiny radios embedded in paint could be used to pick up sound, detect whether wine or ice cream has been stored properly or even be painted on the heart to prevent arrhythmias.

BAE Systems researchers developed the miniature wireless sensors, which are powered by scavenging ambient radiation from the atmosphere.

Dr Karl Brommer, an engineering fellow at BAE Systems, started exploring this technology based on radio frequency identification (RFID) tags in 2002, and filed patents in 2005. 'People complain that most of the cost in manufacturing RFID tags is not in making the circuit, it's in placing the circuit on the seed of the antenna, the tag,' he said.

Brommer proposed a solution that would work like inkjet printing, squirting an ensemble of identical radios near the seed point to create sensor technology with a range of more sophisticated applications than conventional RFID technology.

Though other companies have investigated similar ideas, BAE Systems' technology has a unique solution to battery-free operation that gives them an almost indefinite shelf life.

'They could use ambient radiation from mobile phone and television signals, or an interrogator that you point at the micro-radios,' said Brommer.

The paint is used to package the radios in a similar way to other tiny electronic components and can be included in flexible plastics, electronic ink or organic electronics that can be synthesised chemically.

'There is no minimum quantity you need to work together to function,' said Brommer. 'If you have more of them you can start to create ensembles of radios that radiate coherently, or you can start to create a communication system where each sensor sends a packet of information.'

To pick up and interpret the radio signals emitted by the nanopaint, scientists would use a highly asymmetric communications link such as a parabolic dish and a powerful amplifier to pick up the weak signals from the radios embedded in paint.

One application could be replacing RFIDs as inexpensive, long-life sensors. A sticker using the technology could be applied to each box of ice cream in a lorry load. When the shipment arrives at its destination, the storage temperature recorded every three minutes over months could be downloaded. In a similar vein, someone buying vintage wine could be sure it had been stored properly over decades.

Recording sounds would require a lot more data. 'When you or I talk, we each talk for about one third of the conversation, and we need regular sampling to get anything meaningful out of that — so you'd record and transmit about 600 bits a second,' said Brommer. 'That might be a lot for one little radio, so we would need to develop some kind of time-slicing scheme where all the information gets recorded and re-radiated out.

'That sounds far-fetched until you realise there are cheap computers you can buy now that are a millimetre square and give you 128K of memory. If you were to incorporate a computer like that in one of these devices, someone could get that to work, but it would be very ambitious.'

Brommer became interested in potential medical applications for the nanopaint through Prof Ted Sargent at Toronto University, who has been working with a surgeon at Harvard Medical School to use quantum nanodots inside the body to monitor functions and potentially to administer cancer treatments.

'You have to coat the quantum dots in such a way that the material inside them, though toxic, is isolated from the human body until they are passed out of the body, and we'd use a similar idea with the radios,' said Brommer.

'The disadvantage to the quantum dots is you have to use a laser to interrogate them and they're hard to control.

'We're looking at building little computers that would offer radio control for the medical applications we contemplate.'

These applications include remote dispersal of drugs, or using the paint to place the radios on the surface of the heart to control arrhythmias as an alternative to radio frequency ablation, a non-surgical procedure used to treat some types of rapid heart beating.

Brommer emphasised that radio paint is nascent technology and practical applications could be years off. 'It's like when microprocessors first came out no one could imagine they'd control your car or be in your wristwatch,' he said.

The researchers are looking for partners to invest in taking the technology further.

In the meantime, BAE Systems has several patents regarding the technology in the pipeline, which could see more innovations and applications for the radio paint coming to light over the next few years.

Berenice Baker