Moisture hunters in Norrköping

Isak Engquist and Xiaodong Wang, members of an organic electronics research group in Norrköping, are hunting moisture in buildings – in close collaboration with the construction giant PEAB. The results will be achieved via inexpensive printed moisture sensors, papered onto walls and placed under bathroom floors. The first prototype is being tested in a building in Norrköping.

According to the Swedish National Housing Board (Boverket), at least 750,000 Swedish buildings suffer from moisture damage, which, in turn, affects their indoor environment. It’s obvious that there is great benefit in detecting moisture early before it causes greater problems. Of course there are other moisture sensors on the market, but until now they have been both complicated and expensive. A better solution is on the way.

Isak Engquist and Xiaodong Wang, a researcher and a doctoral student in organic electronics at LiU respectively, are waiting for just that. They fastened small organic electronic moisture sensors made of plastic and aluminium onto the walls of a house under construction in Kneippen Syd, on the fringes of Norrköping. In a week or two it will be time to go back and see if they can find the sensors. Several layers of drywall and tile cover them. They should be able to be read wirelessly with the help of a specially developed reader.

“We’ll certainly find the sensor labels, but I don’t think we’ll find much moisture,” says Wang with a laugh.

The sensor labels are 0.5 mm thick and 6.5 x 8 cm in area, and from tests in the lab he knows that the signal can be read wirelessly through wood and several layers of drywall, but he’s still a little nervous now that the sensors are in an actual wall of a real house.

At the lab in Norrköping, Wang shows how the frequency alters when he blows moist air over the sensor; it should work the same way if moisture leaks in under a window or under a bathroom mat.

The moisture sensors and technology have patents pending and are being developed in collaboration between:

• Linköping University
• ACREO
• The construction company PEAB
• Mid-Sweden University and its spin-off companies Webshape and Sensible Solutions Sweden. Isak Engquist, a researcher at LiU is the project leader.

“We’re right in the middle of the project; we have a prototype but not a finished product,” he says.

Researchers need to work more on making the sensor more sensitive and making the signal narrower – that is, high intensity at a certain frequency so that it can be clearly read from at least 20 cm away. A simple, hand-held reader also remains to be constructed.

But the goal is still in sight – namely producing the sensors in a printer in large enough amounts that they cost no more that SEK 0.25 per unit, so cheap that they can be papered in where a risk for moisture occurs.

“Construction materials manufacturers can put them directly into the drywall,” Engquist says.

Lars Gutwasser, head of logistics at PEAB Sweden, is pleased with the collaboration, which he thinks has increased understanding between the university and the business world.

“At PEAB, we want to be on the cutting edge. We understand that research takes time, since this is basic research, but despite that we’ve worked out scheduled operations plans as part of Brains & Bricks”, he says. (see box at right)

Text and photo Monica Westman Svenselius, picture at top: Norrköping Science Park

Oscar Larsson’s thesis Polyelectrolyte-Based Capacitors and Transistors, Oscar Larsson, Department of Science and Technology, Linköping University, Norrköping Campus. 2011.

Read more about his thesis: Printed electronics gains momentum