This paper presents the results on the utilization of a wavelet transform to study the dispersion of laser-generated surface waves in an epoxy-bonded copper-aluminum layered specimen with and without unbond areas. Laser ultrasonic experiments based on the point-source/point-receiver (PS/PR) technique were undertaken to measure surface wave signals in a layered specimen. The wavelet transform with a Morlet wavelet function was adopted to analyze the group velocity dispersion of the surface wave signals. A novel hybrid formula for group velocity dispersion is proposed for measurements across unbond regions. Results and data obtained are in good agreement with calculated and experimental dispersion curves. The general behavior of the group velocity dispersion for different measurement, configurations can be utilized to differentiate the unbond regions in a layered structure.

1.
Braga
MB
1990
Wave Propagation in Anisotropic Layered Composites
Ph.D. dissertation
Stanford University
Stanford, CA
2.
Castagnede
B
Kim
KY
Sachse
W
Thompson
MO
1991
Determination of the Elastic Constants of Anisotropic Materials Using Laser-Generated Ultrasonic Signals
J. Appl. Phys
, vol. 
66
 
2
(pg. 
150
-
157
)
3.
Chai
J-F
Wu
TT
1994
Determinations of Anisotropic Elastic Constants Using Laser Generated Surface Waves
J. Acoustic Soc. Am
, vol. 
66
 
2
(pg. 
3232
-
3241
)
4.
Chen
Y-C
1994
Dispersion of Surface Waves in an Anisotropic Layered Medium
M.S. thesis
National Taiwan University
5.
Cho
H
Ogawa
S
Takarnoto
M
1996
Noncontact Laser Ultrasonics for Detecting Subsurface Lateral Defects
NDT&E International
, vol. 
66
 
2
(pg. 
301
-
306
)
6.
Dewhurst
R. J
Edwards
C
McKie
A. D. W
Palmer
S. B
1987
Estimation of the Thickness of Thin Metal Sheet Using Laser Generated Ultrasound
Appl. Phys. Lett
, vol. 
66
 
2
(pg. 
1066
-
1068
)
7.
Doyle
P. A
Scala
C. M
1991
Ultrasonic Measurement of Elastic Constants for Composite Overlays
Rev. Prog. in QNDE
, vol. 
66
 
2
(pg. 
1453
-
1459
)
8.
Ewing
WM
Jardetzky
WS
Press
F
1957
Elastic Waves in Layered Media
McGraw-Hill
New York
9.
Hlawatsch
F
Boudreaus-Bartels
GF
1992
Linear and Quadratic Time-Frequency Signal Representations
IEEE Signal Process Mag.
, vol. 
66
 
2
(pg. 
21
-
67
)
10.
Hurley
DA
Spicer
JB
Conant
RJ
Telschow
KL
1997
Determination of the Optical Absorption Coefficient via Analysis of Laser Generated Plate Waves
IEEE Ultrasonics, Ferro. Freq. Control
, vol. 
66
 
2
(pg. 
902
-
908
)
11.
Hutchins
DA
Lundgren
K
Palmer
SB
1989
A Laser Study of the Transient Lamb Waves in Thin Materials
J. Acoust. Soc. Am
, vol. 
66
 
2
(pg. 
1441
-
1448
)
12.
Johnson
MA
Berthelot
YH
Brodeur
PH
Jacobs
LA
1996
Investigation of Laser Generation of Lamb Waves in Copy Paper
Ultrasonics
, vol. 
66
 
2
(pg. 
703
-
710
)
13.
Kishimoto
K
Inoue
H
Hamada
M
Shibuya
T
1995
Time-Frequency Analysis of a Dispersive Waves by Means of Wavelet Transform
ASME JOURNAL OF APPLIED MECHANICS
, vol. 
66
 
2
(pg. 
841
-
846
)
14.
Nakano
H
Nagai
S
1991
Laser Generation of Anti-symmetric Lamb Waves in Thin Plates
Ultrasonics
, vol. 
66
 
2
(pg. 
230
-
234
)
15.
Onsay
T
Haddow
AG
1994
Wavelet Transform Analysis of Transient Wave Propagation in a Dispersive Medium
J. Acoustic Soc. Am.
, vol. 
66
 
2
2
(pg. 
1441
-
1449
)
16.
Proctor
TM
Jr
1982
An Improved Piezoelectric Acoustic Emission Transducer
J. Acoustic Soc. Am
, vol. 
66
 
2
(pg. 
1163
-
1168
)
17.
Rioul
O
Vetterli
M
1991
Wavelet and Signal Processing
IEEE Sp. Magazine
Oct
(pg. 
14
-
38
)
18.
Ruskai
MB
Belykin
G
Daubechies
I
Meyer
Y
Coifman
R
Mallat
S
Ralphel
L
1992
Wavelets and Their Applications
Jones and Bartlett
Boston
19.
Scruby
CB
Drain
LE
1990
Laser Ultrasonics: Techniques and Applications
IOP Publishing Ltd
Bristol, UK
20.
Scudder
LP
Hutchin
DA
Guo
N
1996
Laser-Generated Ultrasonic Guided Waves in Fiber-Reinforced Plates: Theory and Experiment
IEEE Trans. Ultra. Ferro. and Freq. Control
, vol. 
66
 
2
(pg. 
870
-
880
)
21.
Spicer
JB
McKie
ADW
Wagner
JW
1990
Quantitative Theory for Laser Ultrasonic Waves in a Thin Plate
Appl. Phys. Lett
, vol. 
66
 
2
(pg. 
1882
-
1884
)
22.
Stroh
AN
1962
Steady-State Problems in Anisotropic Elasticity
J. Math. and Phys
, vol. 
66
 
2
(pg. 
77
-
103
)
23.
Veidt
M
Sachse
W
1994
Ultrasonic Point-Source/Point-Receiver Measurements in Thin Specimens
J. Acoust, Soc. Am
, vol. 
66
 
2
(pg. 
2318
-
2326
)
24.
Wu
TT
Chai
J-F
1994
Propagation of Surface Waves in Anisotropic Solids: Theoretical Calculation and Experiment
Ultrasonics
, vol. 
66
 
2
(pg. 
21
-
29
)
25.
Wu
T-T
Chen
YC
1996
Dispersion of Laser Generated Surface Waves in an Epoxy-Bonded Layered Medium
Ultrasonics
, vol. 
66
 
2
(pg. 
793
-
799
)
26.
Wu
T-T
Liu
Y-H
1999
Inverse Determinations of Thickness and Elastic Properties of a Bonding Layer Using Laser-Generated Surface Waves
Ultrasonics
, vol. 
66
 
2
(pg. 
23
-
30
)
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