Better detection with self-healing wireless sensor network

node talks to its neighbors and one unit has a gateway capability that sends the information to a PC. Britton said: “Every device is the same and there’s no tree structure like Zigbee, just a blob of devices that send the information. Like a biological network, it’s a robust system with little structure. But if something goes wrong, as long as each device is not too far away from others, the information will find its way round, even if half the network is destroyed.”

Senceive overcame early battery-life problems by building tight synchronization schedules into the wireless network. Each sensor wakes up for a few milliseconds every 10 seconds or so, collaborates with its neighbors then goes back to sleep if nothing untoward is reported. They also report back on battery status and give plenty of advance notice when they need to be replaced. Senceive has carried out a number of monitoring projects for Network Rail to detect such events as bridge strikes, changes in track geometry, or embankment landslides. Britton said: “For the prototype embankment-monitoring project, we installed 30 nodes fitted with sensitive tilt-monitoring devices fitted on poles stuck deep in the ground. Installation needed to be quick as it costs a lot of money to get track possession. We deployed it in one day either side of a track. We simulated a landslide by tilting nodes over manually. If two neighboring devices measured a tilt, we called that a landslip. If it was just one, it could be that someone just knocked it over. If one disappeared from the network, neighboring devices reported that as a catastrophic failure as the device could have been buried.”

The water industry has expressed interest in using Flatmesh to monitor pressure at pumping stations, across bound aries managed by different authorities and coming into people’s homes. Britton said: “If just one node sees a drop in pressure, there may be a leak, but if several see it, there may not be a problem, just standard flow deviance.”

There are also potential military and security applications, such as a perimeter network that can detect intrusion through breaking a light beam, or triggering a tripwire, or proximity sensor.

The Technology Strategy Board has sponsored an 18-month, £500,000 Flatmesh project with a number of partners. These include the British Museum, which is concerned about volatile chemicals from some objects damaging others, and Historic Royal Palaces, which wants to monitor damp over hundreds of locations in the Tower of London. The National Trust wants to keep track of the light budget in rooms and around objects — there is only a certain amount of light exposure allowed over time, after which they need to be stored in the dark.

The next step for Senceive is to release a GPRS version of Flatmesh that will work over the mobile phone network. In the longer term, the company aims to develop Flatmesh into its proposed Intellimesh product, where more intelligence is embedded into the network, interpreting the results as it operates so that less human interaction is required.