Space foil helping to build safer cars
A special foil sensor developed to measure the pressure on a spaceplane鈥檚 wings during reentry into Earth鈥檚 atmosphere is now helping to build safer cars.
This 鈥榮pace鈥� foil has been transformed into a new super-thin and accurate sensor used by VW to measure every deformation suffered by cars during crash tests.
Space research leads to new technology
It all started in the early 1990s, when German engineer Paul Mirow was working on Europe鈥檚 Hermes spaceplane at Technical University Berlin. Hermes was planned as a reusable manned vehicle launched on Ariane 5.
To map the pressure distribution on the wings as Hermes returned through the atmosphere, a new sensor was needed because regular instruments were too bulky and added unrealistic drag. So Paul鈥檚 team turned to a special 鈥榩iezoelectric鈥� foil to do the job.
Piezoelectric materials have a special property that converts physical effects like vibration and pressure into minute electric pulses. 鈥淚t takes movement, forces or vibration, and turns it into an electrical signal,鈥� Paul notes.
Super-thin sensor
In foil form, piezoelectric materials can serve as extremely lightweight sensors, able to cover an entire surface without distorting the results by adding drag.
鈥淭he piezoelectric foil is very thin, about 30 microns 鈥� a third of the thickness of a human hair,鈥� explains Paul.
While other types of sensors create obstacles, with these piezoelectric foils, 鈥淵ou can just glue it to the surface, without creating any disturbances in the structure.鈥�
The tests of Hermes鈥� wing in a hypersonic wind tunnel went well, and in 1995 Paul and his partners decided to adapt their piezoelectric foil for terrestrial applications.
One was even created for a dental company: 鈥淲e painted a tooth with piezoelectric paint so they could measure the forces created by the toothbrush on the molar.鈥�
Making cars safer
One of the most exciting applications was developed for VW to use in their crash tests.
At the yearly Hannover Fair, the German car company saw Paul鈥檚 products at the stand organised by ESA鈥檚 Technology Transfer Programme Office and its German partner, technology broker MST Aerospace.
VW hoped that the space sensors would solve a problem encountered in crash tests: sensors on cars are often destroyed at impact, making it difficult to collect highly accurate data throughout the crash process.
Contained in a highly flexible polymer film, the piezoelectric sensor is simply applied to the car鈥檚 surfaces. It moves with the metal as the car crashes, rather than being destroyed by the impact.
鈥淭he VW people asked, 鈥榠s it possible to use this in crash tests?鈥欌�� recalls Paul. 鈥淲e said, 鈥榣et鈥檚 try.鈥欌��
鈥淲e wanted to know at which moment which parts of the car are deformed,鈥� explained Jens Weinrich, an engineer at VW.
鈥淚n a crash situation, it鈥檚 always a problem that you never know exactly what will happen.鈥�
Paul鈥檚 firm developed a sensor in which each strip of foil contains 50 piezoelectric sensors, each about a square centimetre.
This makes it possible to measure exactly what is happening, and when, in exactly which places on the car. How fast is the metal bending? Is it bending 20潞 in one direction, or 60潞 in the other? And where precisely did it bend?
At the end of each strip, an equally thin, flexible printed circuit board with a 50-channel amplifier records the electrical impulses created by the mechanical deformations.
鈥淲e wanted not just qualitative, but also quantitative results,鈥� said Mr Weinrich. 鈥淲e wanted to know where it folded, and how much it folded.鈥�
Following the development of the piezoelectric foil sensors, VW has now used them in a number of crash tests. The latest wrapped up last year after two years of intensive testing, helping VW to improve car safety.
Provided by European Space Agency
