Identifying Scatter Targets in 2D Space using In Situ Phased Arrays for Guided Wave Structural Health Monitoring Eric Flynn Metis Design Corporation / Los Alamos National Laboratory LA-UR 11-04921 Seth Kessler Metis Design Corporation Michael Todd University of California, San Diego
Guided Wave SHM Mechanical Excitation 100 µs 6 ms 2 ))) Measured Scatter Imaging
Outline Sensor Hardware Review of Time Domain Processing Review of Spatial Domain Processing The problem of multi-damage Target Identification Proof on Concept Conclusions 3
Sensor Hardware (MD7) All-Digital Communications Line (No Analog) 6 Sensors 1 Actuator 4
Time Domain Processing Filter Complex Envelope Downsample Whiten W CE Transform to Spatial Domain (Time Propagation Distance) Center Excitation Frequency exp 2 y t y t j f t CE A C Mean H 1 y y μ C Analytic Signal Covariance 5
Spatial Domain Processing Incoherent Beamforming M I I m m m m 1 I x a x w d x Coherent Beamforming M C C m m m m 1 I x a x w d x Hybrid Beamforming N 6 H I C 1 1 I x a x a x w d x n m nm nm n m 6
The Multi Damage Problem Incoherent Hybrid 7
Target ID: Matching Pursuit Decompose ultrasonic scan into sum of wave reflection packets Target Amplitude Target Range Target Bearing r (,, ) I AK r R, i i i i 2 r 2,, exp, K r B i 2 i Pulse Width Beamshape Parameters determined through Greedy Algorithm 8
Reconstruction Example Targets 9
Why Identify Targets? Easier to identify individual sources of scatter Impossible targets can be surgically removed Secondary echoes can be reduced/eliminated through matched filtering Greatly reduced communications and storage requirements 10
Simple Experiments 3mm Aluminum Plate 3 MD7 Nodes 50 KHz Excitation Damage 10mm Disc Magnets 91 cm 91 cm MD7 Nodes 11
Structural Identifying Health Scatter Monitoring Targets and in Bayesian 2D Space Experimental using In Situ Design Phased Arrays Metis Design / UC San Diego / Los Alamos National Laboratory University of California, San Diego 12 Matching Pursuit Beamformed Incoherent
Structural Identifying Health Scatter Monitoring Targets and in Bayesian 2D Space Experimental using In Situ Design Phased Arrays Metis Design / UC San Diego / Los Alamos National Laboratory University of California, San Diego 13 Matching Pursuit Beamformed Incoherent
Advanced Experimental Setup 6 mm Aluminum Plate 4 MD7 Nodes Test conducted at Metis Design, Cambridge, MA 60 khz Excitation Bolted Doubler Structural Through-Holes MD7 Nodes 3mm Notch Loose Bolt 183 cm 14
Results Original Scan Composite Reconstructed Alternative Shape Function Matched Filtering 15
Comments Just a proof on concept Verification through statistical analysis is necessary Operating in the spatial domain seems more robust So far only applies to phased arrays Images using single transducer pairs have ambiguous target locations Room for more advanced algorithms: Clustering 16
Acknowledgements This work was primary supported through a Small Business and Technology Transfer (STTR) grant sponsored by the Office of Naval Research (ONR) and under the direction of Dr. Ignacio Perez. 17
Summary All Digital Communications Line (No Analog) Sensors Actuator Original Scan Composite Reconstructed Alternative Shape Function Matched Filtering 18