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Acoustical Properties of Meta-Materials


   Faculty of Engineering and Informatics


About the Project

Porous materials such as foams and felts are often used to reduce noise levels. However, these materials are often ineffective at low frequencies. Acoustic meta-materials, which consist of regular arrays of resonant elements, have been proposed as an alternative which would allow absorption at lower frequency relative to the size of the absorber. When applying these silencers in practical situations the performance of these materials is measured in terms of far field radiated sound power. Therefore it is desirable to account for the effects of the geometry surrounding the silencer, the characteristics of the noise sources, the presence of mean flow and the far field radiation pattern in addition to the underlying behaviour of the material. The goal of this project is to predict the performance of silencers which use porous materials or acoustic meta-materials within the context of consumer goods. This should allow improved silencer design and reduced noise levels.

Meta-materials are usually defined as engineered materials which exhibit properties not usually found in nature such as negative refractive index, acoustic filters and even cloaking. In other words they can control, direct, and manipulate sound waves in ways that were not possible before. Meta-materials are usually modelled through the periodic arrangement of some unit cells in a 3-D (meta-materials) or a 2-D fashion (meta-surfaces). Many different unit cells can be created and they can be arranged in different manner in order to suit the particular application. It is a major challenge to pick the optimum configuration. Analytic mathematical methods are particularly suited to this challenge being an inexpensive way of rapidly exploring different possibilities of design. They also offer insights into the underlining physical mechanism and hence the key to tailored adaptations.

Noise pollution at home and in workplaces is becoming a large problem. It can result in annoyance, loss of concentration, disturbed sleep and reduced productivity due to population densification, increased traffic flows and high power home entertainment systems. We are also realising that a loss of acoustic privacy in dwellings is sensed as a loss as important as a loss of visual or spatial privacy.

Mechanical, that is acoustic and elastic, meta-materials are able to achieve extraordinary properties that go beyond (”meta”) those of their constituent materials. This is an opportunity to create systems with previously impossible vibro-acoustic performance.

Research topics within this programme include the development of new, more compact acoustic meta-materials based on Helmholtz resonators for very low frequencies; of new mechanical meta-materials that suppress bending waves in the coincidence frequency region; of computational intelligence techniques and generative design of meta-materials; innovation in acoustic meta-materials for integration into double-glazed window systems; and translation to industrial scale. Novel acoustic insulation systems materials are an expected outcome of this research, with considerable potential for commercialisation.

This PhD project aims to develop novel meta-materials using 3D printing technology tailored for various applications e.g. acoustic, thermal, and vibrational.

Your part will be to develop the material geometry, test and model the new materials. You will have the opportunity to advance science in one or more of the following related topics:

  1. Optimisation of the meta-material performance
  2. Composites of metamaterials with fibrous materials
  3. Simulation/modelling the performance of the meta-materials and comparing with experimental data.

Funding Notes

This is a self-funded PhD project; applicants will be expected to pay their own fees or have a suitable source of third-party funding. A bench fee may also apply to this project, in addition to the tuition fees. UK students may be able to apply for a Doctoral Loan from Student Finance for financial support.

References

• A. Khan, M. Mohamed, N. Al Halo, H. Benkreira, “Acoustical properties of novel sound absorbers made from recycled granulates”, Applied Acoustics, vol. 127, pp. 80-88.
• F. Pompoli, K. V. Horoshenkov, A. Khan, et al. “How reproducible is the acoustical characterisation of porous media”, Journal of the Acoustical Society of America”, vol. 141(2), pp. 945-955.
• G. Watts, R. Pheasant, A. Khan, “Noise and disturbance caused by vehicles crossing cattle grids: Comparison of installations”, Applied Acoustics, vol. 116, pp. 87-93.

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