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Acoustic Cloaking: Manipulating Sound with Artificial Materials

Acoustic Cloaking: Manipulating Sound with Artificial Materials. Bogdan Popa, Lucian Zigoneanu, Steven Cummer Electrical and Computer Engineering Department Duke University. Significant Demand for Acoustic Technology. Long range microphones

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Acoustic Cloaking: Manipulating Sound with Artificial Materials

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  1. Acoustic Cloaking: Manipulating Sound with Artificial Materials Bogdan Popa, Lucian Zigoneanu, Steven Cummer Electrical and Computer Engineering Department Duke University Bogdan Popa ECE Dept.

  2. Significant Demand for Acoustic Technology • Long range microphones • WW2 technology to achieve directivity ! Bad for low frequency sound Bogdan Popa ECE Dept.

  3. Significant Demand for Acoustic Technology • Long range communication systems / sonic weapons • Bulky phased array systems • Simple sonic lens would significantly reduce complexity but technology isn’t there yet Bogdan Popa ECE Dept.

  4. Electromagnetic Lenses Known 3000 Years Ago • Nimrud lens, 750 BC Bogdan Popa ECE Dept.

  5. Sound Isolation • Better sound shielding materials are needed Bogdan Popa ECE Dept.

  6. Hiding Ships • Ships invisible to sonar • Current solution: keep them out of the water as much as possible Bogdan Popa ECE Dept.

  7. Hiding Ships • Making ships undetectable may not be needed • Changing their acoustic signature may be much easier Bogdan Popa ECE Dept.

  8. Problem: Manipulating Sound is Difficult • Nature is not very generous with materials suitable for acoustic applications. • Example: Aerial acoustics - need easy to machine materials with properties close to those of air. • Need to build artificial materials (metamaterials) Bogdan Popa ECE Dept.

  9. Metamaterials • Metamaterials: artificial structures engineered to mimic the behavior of homogeneous fluids. Bogdan Popa ECE Dept.

  10. Focusing Lens in Air • Zigoneanu et al, Phys. Rev. B, 2011 Bogdan Popa ECE Dept.

  11. Fabrication

  12. Measurements BogdanPopa ECE Dept.

  13. Beam-Bending Lens • Popa et al, Phys. Rev. B, 2009 Bogdan Popa ECE Dept.

  14. Active (Smart) Materials • Acoustic properties can be electronically controlled by controlling unit cell geometry. • Endless possibilities: reconfigurable devices, feedback, etc. Bogdan Popa ECE Dept.

  15. Transformation Acoustics • New design technique that allows unprecedented control over sound propagation [Cummer & Schurig, New J. Phys., 2007] • Any geometric transformation of acoustic fields can be realized with complex materials. Bogdan Popa ECE Dept.

  16. Anisotropic Mass Density • Complex materials needed by transformation acoustics devices • Anisotropy: sound waves see different mass densities depending on the direction of propagation Bogdan Popa ECE Dept.

  17. Physically Realizable Anisotropic Effective Mass • Anisotropic mass is a strange sounding idea but not difficult to create. • Layers of fluids behave as one anisotropic fluid. • [Schoenberg & Sen, J. Acoust. Soc. Am., 1983] • Rotationally asymmetric solid inclusions produce acoustic anisotropy • [Popa & Cummer, Phys. Rev. B, 2009]. Bogdan Popa ECE Dept.

  18. Example: Cloak • Goal: bump placed in air on reflecting plane undetectable using sound. [Popa et al, Phys. Rev. Lett., 2011] • Material parameters given by transformation acoustics (relative to air): Bogdan Popa ECE Dept.

  19. Expected Behavior • Numerical simulation Object No object Cloaked object Bogdan Popa ECE Dept.

  20. Fabrication • Desired density and modulus  unit cell  bulk material Bogdan Popa ECE Dept.

  21. Measurements Uncloaked Object No object (reflecting surface only) Cloaked object Bogdan Popa ECE Dept.

  22. Acoustic Signature Numerical Simulations Measurements Bogdan Popa ECE Dept.

  23. Sound Shielding • Thick wall • Sound absorber Bogdan Popa ECE Dept.

  24. Sound Shielding = Easier Cloaking • Curve sound inside absorbing material. Bogdan Popa ECE Dept.

  25. Challenge: Thinner Devices 1:1 1:10 Volume ratio Cloak : Object ~5 ~150 Anisotropy factor (ratio of densities) Bogdan Popa ECE Dept.

  26. Extension to Other Types of Waves Electromagnetic waves [Pendry et al, Science, 2006] Acoustic waves [Cummer & Schurig, New J. Phys., 2007] Elastic waves ? Bogdan Popa ECE Dept.

  27. Controlling Elastic Waves Bogdan Popa ECE Dept.

  28. References • Schoenberg & Sen, Journal of Acoustical Society of America 73, 61 (1983) • Pendry et al, Science 312, 1780 (2006) • Cummer & Schurig, New Journal of Physics 9, 45 (2007) • Popa & Cummer, Physical Review B 80,174303 (2009) • Zigoneanu et al, Physical Review B 84, 024305 (2011) • Popa et al, Physical Review Letters 106, 253901 (2011) Bogdan Popa ECE Dept.

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