December 7, 2011 Acoustic Cloaking: Manipulating Sound with Artificial Materials Bogdan Popa, Lucian...
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December 7, 2011 Acoustic Cloaking: Manipulating Sound with Artificial Materials Bogdan Popa, Lucian Zigoneanu, Steven Cummer Electrical and Computer Engineering Department Duke University Bogdan Popa ECE Dept.
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Transcript of December 7, 2011 Acoustic Cloaking: Manipulating Sound with Artificial Materials Bogdan Popa, Lucian...
December 7, 2011
Acoustic Cloaking: Manipulating Sound with Artificial Materials
Bogdan Popa, Lucian Zigoneanu, Steven CummerElectrical and Computer Engineering Department
Duke University
Bogdan PopaECE Dept.
TTI/Vanguard
December 7, 2011
Significant Demand for Acoustic Technology
• Long range microphones
• WW2 technology to achieve directivity ! Bad for low frequency sound
Bogdan PopaECE Dept.
TTI/Vanguard
December 7, 2011
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 PopaECE Dept.
TTI/Vanguard
December 7, 2011
Electromagnetic Lenses Known 3000 Years Ago
Bogdan PopaECE Dept.
•Nimrud lens, 750 BC
TTI/Vanguard
December 7, 2011
Sound Isolation
• Better sound shielding materials are needed
Bogdan PopaECE Dept.
TTI/Vanguard
December 7, 2011
Hiding Ships
• Ships invisible to sonar
• Current solution: keep them out of the water as much as possible
Bogdan PopaECE Dept.
TTI/Vanguard
December 7, 2011
Hiding Ships
Bogdan PopaECE Dept.
• Making ships undetectable may not be needed
• Changing their acoustic signature may be much easier
TTI/Vanguard
December 7, 2011
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 PopaECE Dept.
TTI/Vanguard
December 7, 2011
Metamaterials
• Metamaterials: artificial structures engineered to mimic the behavior of homogeneous fluids.
Bogdan PopaECE Dept.
TTI/Vanguard
December 7, 2011
Focusing Lens in Air
Bogdan PopaECE Dept.
• Zigoneanu et al, Phys. Rev. B, 2011
TTI/Vanguard
December 7, 2011
Fabrication
TTI/Vanguard
December 7, 2011
Measurements
Bogdan PopaECE Dept.
TTI/Vanguard
December 7, 2011
Beam-Bending Lens
Bogdan PopaECE Dept.
• Popa et al, Phys. Rev. B, 2009
TTI/Vanguard
December 7, 2011
Active (Smart) Materials
• Acoustic properties can be electronically controlled by controlling unit cell geometry.
• Endless possibilities: reconfigurable devices, feedback, etc.
Bogdan PopaECE Dept.
TTI/Vanguard
December 7, 2011
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 PopaECE Dept.
TTI/Vanguard
December 7, 2011
Anisotropic Mass Density
• Complex materials needed by transformation acoustics devices
• Anisotropy: sound waves see different mass densities depending on the direction of propagation
Bogdan PopaECE Dept.
TTI/Vanguard
December 7, 2011
Physically Realizable Anisotropic Effective Mass
• Anisotropic mass is a strange sounding idea but not difficult to create.
Bogdan PopaECE Dept.
• 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].
TTI/Vanguard
December 7, 2011
Example: Cloak
• Goal: bump placed in air on reflecting plane undetectable using sound. [Popa et al, Phys. Rev. Lett., 2011]
Bogdan PopaECE Dept.
• Material parameters given by transformation acoustics (relative to air):
25.1;1.1 ;7.5 21 B
TTI/Vanguard
December 7, 2011
Expected Behavior
• Numerical simulation
Bogdan PopaECE Dept.
No object Object
Cloaked object
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December 7, 2011
Fabrication
• Desired density and modulus unit cell bulk material
Bogdan PopaECE Dept.
25.1;1.1 ;7.5 21 B
TTI/Vanguard
December 7, 2011
Measurements
Bogdan PopaECE Dept.
No object (reflecting surface only) Uncloaked Object
Cloaked object
TTI/Vanguard
December 7, 2011
Acoustic Signature
Bogdan PopaECE Dept.
Numerical Simulations Measurements
TTI/Vanguard
December 7, 2011
Sound Shielding
• Thick wall• Sound absorber
Bogdan PopaECE Dept.
TTI/Vanguard
December 7, 2011
Sound Shielding = Easier Cloaking
• Curve sound inside absorbing material.
Bogdan PopaECE Dept.
TTI/Vanguard
December 7, 2011
Challenge: Thinner Devices
Bogdan PopaECE Dept.
Volume ratioCloak : Object 1:1 1:10
Anisotropy factor(ratio of densities) ~5 ~150
TTI/Vanguard
December 7, 2011
Extension to Other Types of Waves
Bogdan PopaECE Dept.
Electromagnetic waves[Pendry et al, Science, 2006]
Acoustic waves[Cummer & Schurig, New J. Phys., 2007]
Elastic waves ?
TTI/Vanguard
December 7, 2011
Controlling Elastic Waves
Bogdan PopaECE Dept.
TTI/Vanguard
December 7, 2011
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 PopaECE Dept.
