A team of European researchers is studying the use of piezoelectric ceramics in windshields to reduce noise inside a vehicle.
Vibrations created when a vehicle is driven shudder through the body and reach the windshield, where they are reflected as sound waves in the car’s interior.
Since its launch in 2004, the European Union-funded Intelligent Materials for Active Noise
Reduction (InMar) project has made significant strides in making vehicle gearboxes and air- conditioning systems quieter.
For instance, researchers installed loud speakers close to a vehicle’s transmission that emitted low- frequency sounds at exactly the same frequency of noise created by a car’s gears.
The InMar team also studied using soft mounts for gearboxes, limiting the vibrations they pass onto the chassis, as well as rubber mountings for air-conditioner compressors.
“The pressure (in the vehicle) goes down,” says Project Manager Arthur Berkhoff. “The principle really works.”
InMar now is experimenting with developing a thin transparent film made of piezoelectric ceramics that could cover a windshield, making it less susceptible to vibration and noise generation, Berkhoff says.
“If the transparency could be improved, you could integrate the ceramics into the windshield and this would make a much more powerful (noise dampener),” he says. “We have started research, and we have already made improvements.”
The more transparent InMAR scientists can make the ceramics, the thicker a windshield film could be, making it better able to cancel out vibrations from the rest of the car.
“If we can cancel the sound from the windshield, the noise in the interior can be reduced,” Berkhoff says.
The principle is similar to that of noise-cancelling headphones given to air travelers. They emit noise at the same frequency as ambient sounds outside and cancel those noises out.
Funded by the EU’s sixth framework program for research, InMAR involves 41 partner organizations from 13 countries and is coordinated by the Fraunhofer LBF institute in Darmstadt, Germany, with a €27 million ($35 million) budget.