A lick of paint can improve the look of anything but at Dublin City University's National Centre for Sensor Research, paint is expected to do more. The Centre's Optical Sensor Laboratory is using a pressure-sensitive paint to study the effects of air on fast-moving objects.
The special coating changes colour in response to air pressure and these colour changes can be monitored to discover flaws in the design of new aircraft, cars or anything exposed to rapid air movement, explained the Centre's director, Prof Brian MacCraith.
"The basic information you want to know using a scale model is will the design cause problems with pressure distribution," he said. There could be hidden design flaws causing instability or unexpected oscillation. Severe pressure points might also require special reinforcement or even a contour change to improve an aircraft or car's aerodynamics.
The university has just begun a new project to study the paint's use in aerodynamic analysis, funded under Enterprise Ireland's Strategic Research Programme. The principal scientists at DCU are Dr Colette McDonagh and Prof MacCraith.
The two-year project involves close collaboration with University of Limerick researchers, led by Dr Tara Dalton, where wind tunnel facilities will be available. The US Air Force is also involved and will provide technical consultancy.
The project got underway after Prof MacCraith was approached by the US Air Force, which knew of his involvement in pressure responsive coatings. It operates a scheme which facilitates interaction between researchers and he met US scientists working with similar coatings.
DCU researchers were already using these coatings in sensor devices designed for oxygen measurement in environmental monitoring and water quality testing. Its devices measured oxygen levels down to parts per billion. "We have a lot of expertise on oxygen sensitive coatings," he said.
The coating at the heart of the technology is based on a special dye that is chemically synthesised at the Centre by Prof Han Vos. In fact the dye, which is incorporated into a paint-like coating, responds to the presence of oxygen and not pressure as such.
The coating dries to a glassy surface that contains microscopic pores, allowing the dye to interact with oxygen. When the coating is exposed to blue light the dye molecules undergo excitation, giving off an orange-red light, Prof MacCraith explained.
"The strength of this orange light is dependent on the number of oxygen molecules that are around. The oxygen collides with the dye and de-excites it," he said, in a form of "collisional quenching". The more oxygen present, the weaker the orange light and the reaction was "fully reversible and extremely fast".
This combination is ideal for detecting the presence of oxygen in a point sampler, but the technology must take a significant leap forward to be applied to aerodynamics. The dye only responds to oxygen, but more oxygen is available if there is a moving stream of air and this stream produces air pressure.
According to Prof MacCraith, a number of companies including NASA, Ford, Boeing and Lockheed Martin are attempting to develop this technological application. The idea would be to apply the coating to a scale model aircraft or automobile and then place it in a wind tunnel. A camera would be used to record changes in the light emissions being given off as the air pressure - and hence the amount of oxygen present - changed.
The accompanying image shows how the coating gives a colour gradient which is dependent on air pressure. In this way, a design can be tested for points of unexpected stresses and can be changed before an actual plane or car is built, saving hundreds of thousands of pounds, Prof MacCraith said.
"We will be developing advanced camera detecting technology to develop our point sensing into two dimensional sensing," he said. This would involve software-based image processing that would be able to interpret the colours and deliver information about pressure gradients on the model.
This technology has other possible applications, Prof MacCraith added. "The spoiling of food is often related to oxygen getting into packaging," he said. Strips carrying the coating could be positioned inside sealed food packaging and then exposed to blue light. A purpose-built detector could measure whether oxygen was getting through the packaging and putting the food at risk of spoilage.