Hilbert fractal acoustic metamaterials

Noise insulation is an important feature required for health, safety and protection of human occupants in aerospace and automotive structures. It is a difficult problem to tackle with light and thin layers at low frequencies. This can be solved using traditional strategies like heavy materials, but it requires space and weight to be effective. In order to achieve the same results with less weight and consequently wasting less energy a new approach is needed, and metamaterials for acoustic applications seem to be the likely solution. Studying the effect of cavities shaped as fractals or other geometries in traditional materials show unexpected physical behaviour of acoustic waves that can be exploited.

To develop this study several steps are needed.
- Measuring the effectiveness of the metamaterials manufactured, recording the Transmission Loss, Absorption and Reflection Coefficients, using different test rigs like impedance tube and waveguide.
- Use a statistical approach like the full factorial design, to validate results.
- Experiment with different infill materials with macro-meso-micro porosity.
- Investigate additive manufacturing methods to produce composite metamaterials.
- Exploring space infilling curves like Peano and Lebesque and other geometries, to understand their effect.
- Perform Finite Element simulations in order to increase the efficiency during testing and predict which geometries will be more effective, hereby reducing waste.
- Test the vibrational transmissibility of the designed geometries with and without infilling materials, to understand their damping characteristics.

The potential impact of this research could apply composite metamaterials in real-world applications for passive devices in technology used for sound insulation.

The chief impacts are twofold:

1. Supply of doctoral level engineers trained to the very highest standards in advanced composites. They will take up positions in industry as well as academia.
2. Development of next generation advanced composite materials and applications for wealth creation in the UK.

Other important impacts are:

3. Enhanced UK reputation as a world leading centre in advanced composites that attracts inward investment and export opportunity.
4. Attracting elite overseas students, enhancing the UK's global reputation for excellence in Advanced Composite materials and their applications and widening the pool of highly skilled labour for UK industry.
5. Engaging with local schools and media, to disseminate, enthuse and raise the profile of Engineering to school children and to the wider public.