James Sabatier University of Mississippi

1
Multiple Beam Laser Doppler Vibrometry for
Landmine Detection

• James Sabatier - University of Mississippi
• Vyacheslav Aranchuk - MetroLaser, Inc.

This work has been supported by the U. S. Army
Research, Development, and Engineering Command,
Communications-Electronics Research, Development,
and Engineering Center, Night Vision and
Electronic Sensors Directorate, under Contract
DAAB15-02-C-0024.
2
Outline

• Acoustic method for landmine detection using LDV
• 16 beam Multi- Beam LDV and acoustic/seismic
  confirmation sensor
• Matrix laser Doppler vibrometer (MX LDV)

3
A/S coupling mine detection geophone sensing
A/S coupling setup
A/S FRP
A/S coupling setup
Velocity map
Scan time to produce images hours
4
Principle of LDV based acoustic landmine detection
5
LDV scan set-up, FRF and images
1m
1m
Scan time to produce images minutes Spatial
resolution 5 cm, Dwell time 0.2s
6
Plastic VS 1.6 antitank mine
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Modes in the VS 1.6 Landmine
Freq. (Hz), Admit. (mm/s/N)
n1
n0
m
320, 37
545, 56
0
-




-
219, 27
954, 162
1

-
-

• Red corresponds to maximum admittance.
• Light green corresponds to zero admittance.
• Note (0, 0) mode is shifted higher in frequency
  than (1, 0) mode.

-
420, 34
2


-
-


820, 71
3
-
-


-

-
1190, 43
4
-

-

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Multi-beam LDV optical layout
HWP1,2,3- half-wave plate, PBS1,2 polarizing
beam splitter, AOM 1, 2 acousto-optical
modulator, M1-M6 fold mirror, M 7 scanning
mirror, DOE1, 2 diffractive optical element,
QWP- quarter-wave plate, BE1,2 beam expander,
L1,2 lens, BC beam combiner, PD
fiber coupled 16 photodiodes array.
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Layout of the Scanning MB-LDV
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A/S confirmation sensor with MBV
Multiple-beam laser Doppler vibrometer
VS2.2 in 1 m tall grass
Custom shakers
2nd gen 1-D LDV
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Confirmation Sensor Test Results

• 20 seconds scans at 5cm/s
• 36 of 36 mines detected in dirt lane.
• 51 of 51 mines detected in gravel lane

Scan time to produce images 20s
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Matrix LDV Optical layout
Laser beams in the target plane
HWP half-wave plate PBS 1,2 polarizing
beamsplitter AOM1,2 acousto-optical modulator
M1 mirror L1,3 lens L2 objective lens L4
relay lens MBS 1,2 multiple beam splitter
NPBS non-polarizing beamsplitter
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Digital IQ Demodulation
Velocity
Displacement
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MX LDV breadboard prototype
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Membrane Vibrations Experimental Setup
Thin latex membrane stretched across a tube and
clamped on the outside Central 8 by 8 beams are
placed on the membrane Excite the membrane with
random noise Take one second of data for 1Hz
resolution
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Membrane Modes
mm/s
mm/s
0.3
0.2
-0.3
-0.2
Mode 0,1 at 176 Hz
Mode 0,2 at 408 Hz
mm/s
mm/s
0.15
0.25
-0.15
-0.25
Mode 1,1 at 290 Hz
Mode 1,2 at 515 Hz
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Traveling Wave Visualization Experimental Setup
Rubber sheet with fixed rim Central 8 by 8 beams
are placed on the sheet Rolling glass bead hits
the backside of sheet slightly off the
interrogated area Record one second of data
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Traveling Wave
mm/s
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Traveling Wave - animation
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Conclusions

• Acoustic/seismic sensor based on 16 beam
  Multiple-Beam LDV can detect a buried landmine in
  20 seconds
• A breadboard prototype of 16x16 beams Matrix LDV
  has been developed
• The system can measure the vibration at 2D array
  of points simultaneously, preserving the relative
  phase information between measurement points
• Transient phenomena can be investigated at
  multiple points simultaneously

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Future work

• Develop a fieldable prototype of Matrix LDV for
  landmine detection is a high priority task of the
  future work.