A smart fabric incorporating conductive threads and a processor module provides protection against intrusion and theft. Image: Fraunhofer Institute

Researchers
have developed a new kind of anti-theft system, based on a woven fabric
that triggers an alarm when penetrated by intruders. The smart fabric
enables the exact location of the break-in to be identified, and is
significantly cheaper than other burglary detection systems. It is also
suitable as an invisible means of protecting entire buildings.

Thieves
are unlikely to appreciate this fabric, which looks innocuous but in
fact incorporates a fine web of conductive threads connected to a
microcontroller that detects warning signals emitted when the fabric is
cut and triggers an alarm. This system can be used to protect buildings,
bank vaults, and trucks against even the most wily of intruders.
Vehicles parked overnight at truck stops are particularly vulnerable to
attacks by thieves who slit open the canvas tarp covering the trailer
while the driver is asleep and make off with the cargo. If the tarp were
made from the smart fabric, the driver in the bunk would be immediately
alerted.

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,” says Simon reassuringly.

Precise identification of the point of entry

What
makes this solution unique is the fact that it not only signals the
presence of intruders but also indicates the precise point of forced
entry. The fine lattice of conductive threads woven into the fabric
enables the place where it was cut to be identified to the nearest
centimeter. Other solutions currently on the market require a complex
system of optical fibers, which naturally makes them more expensive.

There
are also other reasons why this fabric is cheap to produce. The process
makes exclusive use of standard materials and components such as
silver-coated conductive threads and a simple but robust signal
evaluation system. A further advantage is that “the conductive thread
can be incorporated in the polyester substrate using an
industry-standard textile-weaving process,” explains Simon. The result
is reams of fabric that can be trimmed to any length and customized to
provide the desired functionality for surfaces of any size, from one
square meter upward.

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.

Tested from every angle

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 C, and exposed to the elements for 1,000 hours at a
relative humidity of 85% and a temperature of 85 C. It was then placed
in a furnace in which it was subjected to 1,000 temperature cycles
ranging from -40 to 85 C. The smart textile stood up to this torture
without flinching. Simon: “It didn’t fail once.”

Source: Fraunhofer Institute