playing with ultrasound in complex media...¾ acoustic waves & microwaves in complex media ¾...
TRANSCRIPT
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Playing with ultrasound in complex media
Arnaud Tourin
Mesoscopic Physics in Complex Media, 01002 (2010)
© Owned by the authors, published by EDP Sciences, 2010
This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial License 3.0, which permits unrestricted use, distribution, and reproduction in any noncommercial medium, provided the original work is properly cited.
Institut Lang in - ESPCI aris, Franceve P
DOI:10.1051/iesc/2010mpcm01002
Article published online by EDP Sciences and available at http://www.iesc-proceedings.org or http://dx.doi.org/10.1051/iesc/2010mpcm01002
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Playing with ultrasound in complex media
Arnaud Tourin
Cargèse – July, 13, 2010
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The Langevin Institute
Founded in january 2009 to gather people from
LOA (M. FINK) : ultrasound, sound, seismic waves, microwaves
LOP (C. BOCCARA) : optics, ultrasound
New devices for manipulating waves in various kinds of media
Time Reversal Mirror
Multiwave Imaging
IR SNOM, thermal radiation STM
Medical imaging & therapy,
non destructive testing,
underwater acoustics,
seismology,
telecommunications,
tactile objects,…
Fundamental physics/applications/companies
Echosens, Sensitive Object, SSI, TRCOM, LLTech (~200)
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92 people
34 permanent researchers
14 for the technical & administrative support
29 Phd students
15 Post-Doc
One Director (M. Fink) and two vice directors (R. Carminati and AT)
5 groups
Acoustic waves & microwaves in complex media
Nanophotonics & Optical waves in diffusive media
Wave Physics for medicine & Biology
Detection, Imaging, and characterization
Optical physics and wave theory
The Langevin Institute
Acoustic waves & microwaves in complex media
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Acoustic waves & microwaves in random media
Julien de Rosny
(Research scientist)
Geoffroy Lerosey
(Research scientist)
Arnaud Tourin
(Professor)
Mathias Fink
(Professor)
Agnès Maurel
(Research scientist)
Arnaud Derode
(Professor)
Alice Bretagne
(PhD student)
Marie Müller
(Associate professor)
Abdel Ourir
(Engineer)
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OUTLINE
Wave propagation in random media
The ballistic and coherent waves
The incoherent wave and the diffusion approximation
Beyond the DA : the backscattering cone
Using disorder for controlling wave propagation
Disorder for guiding ultrasound
Disorder for focusing ultrasound
A random (or ordered) bubbly medium for filtering US
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σ
<<
L
Mesoscopic physics with ultrasound
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Experimental approach : measuring the S matrix
i
j
++
Transducer arrays
f ~ 500 kHz à 5 MHz
λ ∼λ ∼λ ∼λ ∼ mm
=
−+++
−−+−
S ?
+ -
In optics, S. Popoff et al., Phys. Rev. Lett. 104, 100601 (2010)
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Experimental approach : measuring the S matrix
(average) time-resolved transmitted amplitude / intensity
(average) backscattered amplitude or intensity (BS Cone)
Perform a SVD and study the statistics of the singular values
Focusing using time reversal, wavefront shaping, inverse filter
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19 rods / cm²Density :
Diameter : 0.8 mm
5mm < L < 80mm
Experimental approach :
what can be measured with ultrasound ?
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128-transducer arrayPitch : 0.42 mm
Single transducerνννν=3.2 MHz, λλλλ=0.48 mm
2D random sample
Experimental approach
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0 10Time (µs)
Water
Time (µs)0 10
127
1
# t
ransducer
Am
plit
ude
Spatio-temporal distribution of the amplitude
Time (µs)0 10
127
1
0 10Time (µs)
L=7 mm
Am
plit
ude
# t
ransducer
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L=15 mm L=30 mm
0 10Time (µs)0 10Time (µs)
127
1
127
10 10Time (µs)0 10Time (µs)
Am
plit
ude
Am
plit
ude
Spatio-temporal distribution of the amplitude# t
ransducer
# t
ransducer
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0 225Time (µs)
0 225Time (µs)
L=70 mm
Am
plit
ude
127
1
Spatio-temporal distribution of the amplitude# t
ransducer
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ωωσ −=
Quantum waveClassical (acoustic) wave
ω
=
ωσωω Ψ=Ψ+∆Ψ
∂
∂
Ψ=∆Ψ
The wave equation in a heterogeneous medium
Ψ−+Ψ=Ψ σωωω
=σ
∂
∂ Ψ=Ψ
+∆−
ω =
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+
Ψσ−σ−ω+
Ψσ−ω+
Ψ=
Ψ
single scattered wave
unscattered wave
The Born expansion
double scattered wave
The wave equation in a heterogeneous medium
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−+=+∆ δωσωω
ωσωωω −+−=
The Dyson equation
−−Σ−+−=− ωωωωω
σ =
Beer-Lambert
−−
−
−∝=
πω
Scattering mean free path
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Source Receiving
array
How to build an estimator of the ensemble average ?
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average on 80
Configurations
L=30 mm
Time (µs)
127
1
Time (µs)
127
1
Time (µs)
Time (µs)
The coherent wave# t
ransducer
# t
ransducer
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L(mm)
=
Ln
[T
A(L
)]
Ballistic amplitude averaged over 80 random sample positions
Ballistic amplitude
Ballistic amplitude averaged over the 127 transducers
+=
The coherent wave
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127
1Time (µs)
Time (µs)
Am
plit
ude
FT
# t
ransducer
The coherent wave
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0
1
2
3
4
0 5 10 15 20 25 30 35
Thickness (mm)
2,7 MHz, l = 8,3mm
3,2 MHz, l = 4mm
Ln (
TA
(L))
Frequency (MHz)
Mean
free p
ath
( mm
)
The coherent wave
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Scattering from a single inclusion
θ
+→Ψ∞→
==π
θθθπσ
π
σ =
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Frequency (MHz)
σ (
mm
)
θ
( )θ θθσ =
θθσσπ
=
Scattering from a single inclusion
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+=
+σ+σ=σ→
MHz
Scattering from a single inclusion
σ (
mm
)
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The incoherent wave
0 225Time (µs)
0 225Time (µs)
L=70 mm
Am
plit
ude
127
1
# t
ransducer
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The Bethe Salpeter equation
+Ω+Ω−=Ω+Ω− ωωωω
=
Ω+Ω− ωω
Ω+Ω− ωω
• Boltzmann approximation Transfer radiative equation for the specific intensity
• Diffusion approximation Diffusion equation
∆=
∂
∂
=
The incoherent intensity
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=
=
=
=τ
Time-of-flight distribution
Total transmission varies as ~ /L (ohm’s law)
The incoherent wave
=
=
Time(µs)
0 100 200 300 400 500 600
=
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M.P. van Albada and A. Lagendijk, Phys. Rev. Lett. 55, 2692 (1985)
E. Wolf and G. Maret, Phys. Rev. Lett. 55, 2696 (1985)
A. Tourin, B. A. Van Tiggelen, A. Derode, P. Roux, M. Fink,, Phys. Rev. Lett 79, 3637 (1997)
θ
Beyond the diffusion approximation
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=∆=In
tensity
θ -10 -5 0 5 10
Speckle
One realisation
θ -10 -5 0 5 10
0
1
2
Averaging over
80 realisations
Inte
nsity
The backscattering cone
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Speckle Coherent contribution
==
Incoherent contribution
The backscattering cone
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φ °
∝
0
1
2
0
1
2
0
1
2
-10 -5 0 5 10
The backscattering cone
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D=3,2 mm²/µs
-2,5
-2
-1,5
-1
-0,5
0
0 1 2 3 4
ln(t)
∆θ
)
Dynamic CBE
Norm
alis
ed
inte
nsity
θ (degree)
=∆
0
1
2
-15 -10 -5 0 5 10 15
=
Stationary CBE
The backscattering cone
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L
cf. John Page’s lecture
Weak localisation
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Using disorder
for controlling wave propagation
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1. A random fiber
H. De Raedt, Ad Lagendijk, Pedro de Vries
« Transverse localization of light »
Phys. Rev. Lett. 62, 47 (1989)
ψ
ψ∂
=∂
( )
( )
∂ ∂≡ + +
∂ ∂
≡ −
π
ξ
=
ω−≡ ∝
Lee,P. A. et al., Rev. Mod. Phys. 57, 287-337 (1985)
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1. A random fiber
Schwartz et al., Nature 446, 52-55 (2007)
Intensity distribution after L=10 mm propagation
hexagonal lattice 15% positional disorder(average over 100
realizations)
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Steel rods (0.8 mm)
embedded in a PVA matrix
Transducer array
fc=7.5 MHz Point-like
receiving
transducer
1. A random fiber
Ordered sample
(triangular lattice, a=2.4mm)
Ordered (blue)
Disordered (red)Disordered sample
Energ
y(A
U)
Lateral distance
(cm)
Tim
e (
µs)
Tim
e (
µs)
Lateral distance
(cm)
Alice Bretagne, AT
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2. A random lens
<
Transducer arrays
f ~ 500 kHz à 5 MHz
λ ∼λ ∼λ ∼λ ∼ mm
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2. A random lens
Source
Time reversed waveforms
TRM
Multiple scatteringmedium
A.Derode, A. Tourin, P. Roux, M. Fink
>>
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2. A random lens
20 40 60 80 100 120 140 160
20 40 60 80 100 120 140 160
Time (µs)20 40 60 80 100 120 140 160
Waveform transmitted through the rods and received at transducer #64
Time reversed wave recorded at the source location
Waveform transmitted in water and received at transducer # 64
Time (µs)
Time (µs)
Am
plit
ud
eA
mp
litu
de
Am
plit
ud
e
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2. A random lens
Beamwidth at -12 dB : 1 mm (scattering medium) / 35 mm (free space)
Spatial resolution does not depend on the array aperture !
TRM
Time reversed waveforms
x
Spatial Focusing : the hyperfocusing effect
F
D
dB
λF/D
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One-channel time reversal mirror
Distance from the source (mm)
dB
Directivity patterns of the time-reversed waves
128 transducers
1 transducer
Time reversed signal
2. A random lens
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2. A random lens
• I.M. Vellekoop and A.P. Mosk
Optics Lett. 32, 2309 (2007)
• E. Herbert, M. Pernot, M. Tanter,G. Montaldo, M. Fink IEEE transactions on ultrasonics,
ferroelectrics, and frequencycontrol 56 (11), 2388 (2009)
α=∝∆
πϕ <<
a lot of iterations are neededTwo problematic issues
low sensitivity (one by one)
An alternative approach : wave front shaping
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2. A random lens
In the case of two transducers, the intensity at the intended focus is :
Φ−Φ++=
ρ
Φ+=
+Φ+=
When a phase x is added to the 2nd transducer, the intensity at focus is :
At least 3 measurements must be performed
i.e.,
Finally,Φ−
and are transmitted from the two transducers
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Extension to a N-transducer array using spatial coded excitations
Transmission ofV0(x,ωωωω) + ejx.Vi(x,ωωωω)
Recording of I = I(x,ωωωω)at focus
Repeat the transmissionfor four different values
(x=0, π, π, π, π, ππππ/2, -ππππ/2)
−−
−−
−−
=
Hadamard matrix
<<
2. A random lens
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=
Ψ
Ψ
Ψ
Ψ
Φ
Φ
Φ
Φ
=−=
−=−==Ψ
π
ππ
πππ −+−+=
2. A random lens
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10 20 30 40 50 60 70 80
20
40
60
80
100
120
140
160
10 20 30 40 50 60 70 80
20
40
60
80
100
120
140
160
10 20 30 40 50 60 70 80
50
60
70
80
90
100
110
120
130
140
150
V1(t) V31(t) V41(t)
10 20 30 40 50 60 70 80
10
20
30
40
50
60
70
80
Definition of spatio-temporal
vectors
2. A random lens
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Multiple scattering
medium
Transducer array
f=3.2 MHz
0 100 200 300 400 500 600 700 800 900-0.5
0
0.5
Time (ms)
Am
plit
ude (
AU
)
Typical waveform received at the focal point
after a Hadamard emission
A. Bretagne, J. Aulbach, M. Tanter, M. Fink, A. Tourin
2. A random lens
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-60 -40 -20 0 20 40 600
0.2
0.4
0.6
0.8
1
Distance from the focal point (l)
Monochromatic case
-0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.80.5
0.6
0.7
0.8
0.9
Norm
aliz
ed
am
plit
ud
e
TRWFS WFS (phase only)
2. A random lens
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Distance from focal point (λ)
Tim
e (
µs)
-60 -40 -20 0 20 40 60
880
885
890
895
900
905
910
915
920
-80
-70
-60
-50
-40
-30
-20
-10
0
Time Reversal Wavefront shaping
Broadband case
dB
-60 -40 -20 0 20 40 60
400
500
600
700
800
900
1000
1100
1200
Distance from focal point (λ)
2. A random lens
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-60 -40 -20 0 20 40 600
0.2
0.4
0.6
0.8
1
Distance from the focal point (λ)
Norm
aliz
ed
am
plit
ude
-1.5 -1 -0.5 0 0.5 1 1.5
0.5
0.6
0.7
0.8
0.9
TRWFS WFS (phase only)
Broadband case
2. A random lens
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3. A random (or periodic) bubbly medium
M. Kafesaki et al.
Air Bubbles in water : a strongly Multiple
Scattering Medium for Acoustic Waves
Phys. Rev. Lett. 84, 6050 (2000)
σ σ>>
ρω
βair
==
= =
Minnaert Resonance
10 % volume fraction
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V. Leroy, A. Bretagne, M. Fink, H. Willaime, P. Tabeling, A. Tourin
« Design and characterization of bubble phononic crystals »
App. Phys. Lett. 95, 171904 (2009)
h=78 µm, ax=200 µm, az=360 µm
3. A random (or periodic) bubbly medium
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Thank you for your attention !