Reducing noise pollution was the goal of the recently-completed EU-funded InMar ('Intelligent Materials for Active Noise Reduction') project. It has successfully developed a series of smart materials and systems for use in automobiles and rail vehicles and infrastructures.

The four-year InMar project brought together 41 partners from 13 countries and was coordinated by the Fraunhofer Institute for Structural Durability in Darmstadt. It received close to €15 million under the EU's Sixth Framework Programme (FP6).

One team in the project investigated vibration transmission in the car body and how it can actively be reduced with the help of a special gearbox mounting. Meanwhile, another team developed a compressor for the air conditioning system on a tram, whose oscillations are actively reduced by a vibration absorber.

Yet another team worked on sound-proof windows for low frequency sounds from aircraft, for example. 'The window can reduce test signals in the frequency range between 50 and 1,000 hertz by an average six decibel, so that the noise is only half as loud,' says Dr Joachim Bös of the Technical University of Darmstadt. 'The volume of individual test signals can even be reduced by up to 15 decibel [dB].'

'With most of the active solutions developed for cars, trains and infrastructure elements, the noise pollution can be reduced by up to 10 decibel' adds Dr Thilo Bein of the Fraunhofer Institute for Structural Durability, the InMar project coordinator.

'Sound waves must be decreased exactly in the frequency ranges, which are perceived as very stressful,' Dr Bein explains. 'Noise consists of many overlapping sound waves in different frequency ranges. Due to the adaptability of active structure systems, the vibration behaviour can be changed in those areas where they are most effective.'

More than 100,000 people all over Europe are affected by the harmful impact of constant noise exposure, which can cause sleep disturbance, cardiovascular problems or other physical reactions to noise. Various studies have found that the effect of noise exposure on the human body should not be underestimated: For instance, a man's risk of suffering a heart attack increases by 30%, if he lives in an area where traffic noise regularly exceeds 65 dB for an extended period of time.

Following the European Environmental Noise Directive (2002/49/EC), cities and towns are required 'to avoid the harmful effects, including harassment by ambient noise, or prevent or decrease them.' In the long run, experts say that it should be the aim to reduce noise from road and train traffic to meet the limits suggested by the World Health Organization (WHO): 55 dB during the day and 45 dB at night.

The project results were recently presented at a conference in Darmstadt, Germany, to mark the International Noise Awareness Day on 16 April.

InMar project

Source: Community R&D Information Service (CORDIS)