Metamaterial - Acoustic material and properties.pptx

Meta material

1. Meta Material Periodic arrangement of subwavelength microstructure that is called unit cell. Unit cell have positive density and bulk modulus Shape, geometry and Arrangement make it to work like a meta material

2. Acoustical Meta Material Anti-resonant Resonant and dissipates energy Imaginary speed of sound Negative speed of sound

3. Bulk Acoustic Properties Effective mass density Bulk modulus these two properties collectively called bulk acoustic properties if any one or both of these are negative then a material can become acoustic meta material

4. It is an extended research of negative refractive index materials. Victor veselago first gave idea in 1967 It took 33 years for developing first AMM in 2000

5. First AMM (Sonic Crystal) In 2000 fist AMM was developed 1cm dia lead ball coated with 2.5mm silicone rubber Negative bulk modulus principle

6. In 2004 liu and chan proposed first double negative AMM Theoratical model only

7. Membrane type AMM

8. Applications of AMM Low frequency noise reduction As a filter in sensors and transducers to filter out negative density and bulk modulus sound

9. Acoustical cloaks

10. Membrane type AMM Membrane are not rigid and vibration varies with location These are distributed mass systems Stiff membranes are called penal First proposed by yang et al in 2008

11. Assumptions Uniformly stretched in all directions

12. Define net vertical force due to tension in the membrane due to small excitation Then equate it to mass × acceleration Dimension of unit cell should be less then wavelength

13. Membrane type AMM without centre mass Air + membrane + mass Membrane = spring System gets negative effective mass density in frequency range lower than critical frequency

14. Region of negative density depends Mass of membrane(density + thickness) Surface tension Young modulus Poisson ratio Mass attached to membrane