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A Literal Sensor Web Comes into Its Own

It was only a matter of time before someone took the concept of a sensor web literally, and created a smart mesh web that could cover an object and detect when and where any breaches in the web occur.

Researchers from the Fraunhofer Institute for Reliability and Microintegration have ended the wait for such a literal approach, with a design they are billing as an anti-theft system. It is a woven fabric design that raises the alarm when it is penetrated, and is intelligent, with processing units inside it's own mesh so it can tell where the breech occurred.

Here we see the interconnected mesh of the smart textile - a fine web of insulated conductive threads, woven into a myriad of separate circuits, connected to actual circuit boards every few metres. These are microcontrollers which follow the path of each individual circuit to the next microcontroller.

By determining the precise pattern of circuits cut, it can determine exactly where the mesh was breached with pin-point accuracy.

The smart fabric was developed by researchers at the Fraunhofer Institute for Reliability and Microintegration IZM in Berlin in collaboration with the Technische Universität Berlin and ETTLIN Spinnerei und Weberei Produktions GmbH. The company in Ettlingen manufactures technical textiles, among other things, and has filed a patent for the innovative fabric.

. IZM project manager Erik Simon can envision a whole swathe of potential applications, particularly where there is a need to provide protection over a large surface area. “The fabric could be used to implement an entirely novel, invisible security system for buildings,” he says. For example, the textile could be laid on the rafters of a roof as an additional layer to the vapor barrier underlay, underneath the tiles. This might be a good solution for museums housing valuable collections, or jeweler’s shops, or banks. An alternative solution would be to integrate the fabric in concrete and blockwork walls, for instance those surrounding a bank vault. Another possibility is to use it as a backing material for floor coverings, in combination with pressure sensors that signal an alarm if an unauthorized person enters the room.

“The electric current flowing through the fabric is so weak that it presents no danger to humans or animals,” Simon has been very careful to stress. Indeed, because it is split up into so many separate threads, it is doubtful you would even feel a tingle when cutting through it with a conductive blade.

.One of the most important aspects of the web is that, although every path current follows is unique, the circuits are laid out in a tesselating mathematical pattern between microprocessors. This means the web can be churned out quite quickly and cheaply in long rolls of almost any length. The process makes exclusive use of standard materials and components such as silver-coated conductive threads and a simple but robust signal evaluation system. So, it can be cut to any necessary size like any other fabric. Once cut, the microprocessors learn where all the paths go now, and which ones are still valid. This also works in its favour when it comes to continuing to operate after a breech has occured. The microprocessors re-evaluate paths through the fabric, working aroundthe severed areas to minimise damage to the web. With larger breeches, again because the pattern repeats, a new piece of the material can be patched in over the hole, and the paths will go live again.

The conductive lattice and the data-processing module that triggers the alarm in the monitoring center are incorporated in a low-temperature process using joining techniques borrowed from the semiconductor industry such as adhesive pressure bonding and non-destructive welding. “This method has never been used before in this kind of application,” says Simon, who describes the process as “simple and reliable”. And this is precisely the selling point of the solution: the ability to create an entirely new product with immediately appreciable benefits using existing materials and joining techniques.

The all-important question was to determine the fabric’s reliability and durability, especially with respect to the electrical contacts. To verify this, the textile alarm system was put through a grueling series of tests in the IZM laboratories. It was beaten and tumbled in a washing machine at 40 degrees Celsius, and exposed to the elements for 1,000 hours at a relative humidity of 85 percent and a temperature of 85 degrees Celsius. It was then placed in a furnace in which it was subjected to 1,000 temperature cycles ranging from minus 40 to plus 85 degrees Celsius. It is highly unlikely that a building will face greater extremes of temperature, or that it will face stresses of quite the same magnitude.

It does however raise other interesting potential applications, such as a literal sensor web for your clothing. There you would likely be less interested in looking for breeches, but much more interested in a data connectivity network that forms unique paths to central microprocessors, no matter where you attach a network-ready device.


A smart fabric sets off the alarm

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