A slide presentation of the area of phononics, with a twist tpwords phononic crystals

1. Phononics,
phononic crystals,
and beyond
Vincent Laude
Institut FEMTO-ST
Université de Franche-Comté, CNRS
Besançon, France
vincent.laude@femto-st.fr

2. What is phononics?
 Phononics is the art of engineering artificial acoustic
materials with tailored dispersion properties
 Phononic crystals are periodically arranged materials;
strong contrast in the constituents can mean:
 Strong energy confinement
 Band gaps = evanescent waves
 Strong diffraction
 Positive and negative refraction
 Strong dispersion
 Tunneling (evanescent waves)
 Slow / fast waves (propagating waves)
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3. Phononics: playing tricks on waves
Sound
Phonons Negative
insulation
refraction
Sound
Solid state Acoustics
Nanoscale physics
thermal
control Periodicity
Metamaterials
Elastic waves
SAW & BAW Band gaps Vibrations
Electrical Applied Nonlinear waves
engineering mechanics
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http://www.topopt.dtu.dk/

4. Tutorial: band structures
 Bloch-Floquet theorem: periodic media have modes of the form
u (r , t ) = U (r ) exp( j (ωt − kr )) with U (r ) periodic
a Band structure shows propagating waves
Negative group
3 bands at low freq.: velocity
2 shear and 1 long. Full band ω / ∂konly evanescent waves
v g = ∂ gap =
Y
π M
0
Γ π
X
Brillouin zone
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5. Recent achievements in
phononics
Which concepts have been
demonstrated?

6. Ultrasonic band gaps
Experimen
t gap Emitting ΓX Receiving ΓM
Theory transducer
transducer
ΓX
2D water/steel PC
ΓM
Khelif et al., Phys. Rev. B 68, 214301 (2003)
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7. Tunneling
3D steel/water crystal
 The evanescent character of
transmission inside a band gap
is analogous to the tunnel effect
Yang et al., Phys. Rev. Lett. 88, 104301 (2002)
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8. Locally resonant materials
 Sound shield
 Centimeter-size arrangement
 stops audible sound!
A “soft” silicone coating over a rigid
lead sphere creates localized modes
(Fano resonances).
Wavelength = 85 cm @ 400 MHz
Silicone
Longitudinal velocity = 23 m/s
Shear velocity = 5.5 m/s
Liu et al., Science 289, 1735 (2000)
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9. Confinement inside defects
 The existence of complete band gaps with very high
impedance contrasts enables highly confined acoustic
waveguides Band gap
Khelif et al., Appl. Phys. Lett. 84, 4400 (2004)
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10. SAW and Lamb wave devices
10 µm
10 µm
Benchabane et al., Phys. Rev. E 73, 065601(R) (2006)
Wu et al., J. Appl. Phys. 97, 094916 (2005) Mohammadi et al., Appl. Phys. Lett. 92, 221905 (2008)
Wu et al., Appl. Phys. Lett. 94, 101913 (2009) Mohammadi et al., Appl. Phys. Lett. 94, 051906 (2009)
Papers 6H-1 and 6H-4
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11. Positive refraction
 Phononic lens for sound (1700 Hz)
Refraction is here positive:
the dispersion is that
of a homogenized medium
(small wave vectors limit)
Cervera et al., Phys. Rev. Lett. 88, 023902 (2002)
 Gradient-index phononic crystals
Lin et al., Phys. Rev. B 79, 094302 (2009)
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12. Negative refraction
 Demonstration of negative refraction
 (using a phononic band with a negative curvature)
Ref.
Exp.
Th.
Yang et al., Phys. Rev. Lett. 93, 024301 (2004)
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13. Acoustic metamaterials
Ultrasonic metamaterial with negative modulus
Cloaking via acoustic metamaterials
Fang et al., Nat. Mater. 5, 452 (2006) Torrent et al., New J. Phys. 10, 083015 (2008)
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14. Nanophononics
 Confinement of phonons inside a planar 1D
GaAs/AlAs cavity
Trigo et al., Phys. Rev. Lett. 89, 227402 (2002)
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15. Watching waves on phononic crystals
f = 206 MHz
Profunser et al., Phys. Rev. Lett.. 97, 055502 (2005)
Profunser et al., Phys. Rev. B 80, 014301 (2009)
Kokkonen et al., Appl. Phys. Lett. 91, 083517 (2007) Papers 6B-1 & 6B-2
Invited paper 6B-3
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16. Phonons in photonic crystal fibers
 Photonic crystal fibers are excellent guides for phonons
Dainese et al., Nature Phys. 2, 388 (2006)
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17. Perspectives
What is the state of the art in phononic
crystals?
What can YOU do?

18. Phononic crystal for bulk waves
 A lot has been done in 2D
 Centimeter-size structures in air
 Millimeter-size structures in water
Steel beads
in epoxy (3D)
 Almost nothing has been achieved in 3D!
 fcc (face centered cubic) crystals of metal beads in air or water
 What is the next frontier?
 Demonstrate 3D band gaps at the micro- and nanoscale
 (Only indirect characterization by Brillouin light scattering has
been performed)
 Self-organized crystals
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19. Phononic crystals for SAW
 We clearly need to move to the GHz range
 Incorporate phononic crystals in SAW devices
 500 MHz to 5 GHz range for present applications
 This means holes around or smaller than one micron
 This is difficult for deep vertical holes!
 Alternative: why not use pillars instead of holes?
 Pillars on a surface are resonators
storing mechanical energy
 Same lithography requirements as holes
 Deposition or epitaxy techniques
to be developed 1D high-aspect-ratio
electrode array
Laude et al., Appl. Phys. Lett. 89, 083515 (2006)
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20. Phononic crystals for Lamb waves
 Plates provide vertical confinement; 2D periodic
structuration is enough for 3D confinement
 Holes only need to be as deep as the plate
 Piezoelectric thin films (AlN, ZnO) on silicon membranes
 Self-standing piezoelectric thin films
 But beware: obtaining complete band gaps can be more
difficult in the plate geometry than in the bulk or SAW
geometries
 More modes are involved
 Transduction of Lamb waves can be an issue
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21. Phononic crystal layer on a substrate
 Use a “slow velocity” phononic crystal layer
on a “high velocity” substrate
 Vertical confinement can be achieved in a 2D structure
 Holes need only be as deep as the layer
 Can be combined with a Bragg mirror for vertical confinement
Bonello et al., Appl. Phys. Lett. 90, 021909 (2007)
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22. Other applications of phononic crystals
 Sound insulation
 Slow / fast sound: processing of acoustic pulses?
 Store and retrieve information in phonon packets
 Design really slow delay lines
 Enhance nonlinearities
 Create phononic circuits
 Thermal management through phonon transport control
 Protect microelectronic devices (processors)?
 PhoXonic crystals
 Achieve a nanostructure that is both a phononic crystal and a
photonic crystal
 Enhance acousto-optical interactions
 See Sarah Benchabane, paper 6F-4 (Tuesday)
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23. Outlook on phononics
Who’s active in phononics?
Ressources

24. Who’s active in phononics?
 Geopolitics of phononics
 Europe (Spain, France, Greece, Denmark, Russia)
 Asia (China, Taiwan, Singapore, Japan)
 USA, Canada
 No specific phononics conference so far!
 Special sessions in recent years:
 IEEE Ultrasonics Symposium 2007-2009: 3 sessions this year!
 Phonons 2008
 Acoustics 2008
 USNCCM 2005, IUTAM RAAWS 2009
 First International Workshop on Phononic Crystals, in Nice, France
(June 2009)
 Journals?
 Physical Review (APS), Appl. Phys. Lett./J. Appl. Phys. (AIP), Nature
Publishing, Ultrasonics (Elsevier), JASA, J. Phys. D (IOP), IEEE
Trans. on UFFC, and more.
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25. Ressources
 Phononic crystal database
 http://www.phys.uoa.gr/phononics/PhononicDatabase.html
 The field is growing! Don’t join too late…
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