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Research Papers

On the Use of Ultrasound-Based Technology for Cargo Inspection

[+] Author and Article Information
Yuri Álvarez-López

Área de Teoría de la Señal y Comunicaciones,
Universidad de Oviedo,
Edificio Polivalente,
Mod. 8, 8.1.02. Campus Universitario de Gijón,
Gijón 33203, Spain
e-mail: yalopez.tsc@gmail.com

José A. Martínez-Lorenzo

Department of Mechanical and
Industrial Engineering,
Northeastern University,
211 Snell Engineering Center,
360 Huntington Avenue,
Boston, MA 02115
e-mail: j.martinez-lorenzo@neu.edu

1Corresponding author.

Contributed by the Noise Control and Acoustics Division of ASME for publication in the JOURNAL OF VIBRATION AND ACOUSTICS. Manuscript received July 3, 2015; final manuscript received January 18, 2016; published online April 7, 2016. Assoc. Editor: Nicole Kessissoglou.

J. Vib. Acoust 138(3), 031009 (Apr 07, 2016) (13 pages) Paper No: VIB-15-1247; doi: 10.1115/1.4032724 History: Received July 03, 2015; Revised January 18, 2016

A new guided wave imaging application for fast, low-cost ultrasound-based cargo scanning system is proposed. The ultimate goal is the detection of high-atomic-number, shielding containers used to diminish the radiological signature of nuclear threats. This ultrasonic technology has the potential to complement currently deployed X-ray-based radiographic systems, thus enhancing the probability of detecting nuclear threats. An array of ultrasonic transceivers can be attached to the metallic structure of the cargo to create a guided Lamb wave. Guided medium thickness and composition variation creates reflections whose placement can be revealed by means of an imaging algorithm. The knowledge of the reflection position provides information about the shielding metallic container location inside the cargo. Moreover, due to the low coupling between metallic and nonmetallic surfaces, only the footprint of metallic containers shows up in the imaging results, thus avoiding false positives from plastic or wooden assets. As imaging capabilities are degraded if working with dispersive Lamb wave modes, the operating frequency is tuned to provide a tradeoff between low dispersion and real-time image resolution. Reflected waves in the guided domain bounds may limit the performance of imaging methods for guided media. This contribution proposes a solution based on real-time Fourier domain analysis, where plane wave components can be filtered out, thus removing nondesired contributions from bounds. Several realistic examples, scaled due to limited calculation capabilities of the available computational resources, are presented in this work, showing the feasibility of the proposed method.

Copyright © 2016 by ASME
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References

Figures

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Fig. 1

Two examples of cargo containers with a metallic base plate, the second having a shielded camouflaged compartment that can be used for concealing goods or radioactive threats. Cargo schemes extracted from Ref. [4].

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Fig. 2

General layout for ultrasound imaging applied to cargo inspection. Ultrasonic units are placed at inspected cargo sides, each formed by one transmitter and an array of receivers. Ultrasound images are created as the cargo moves across the scanning point. The whole ultrasonic image of the base plate is created by combining images retrieved at every cargo position.

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Fig. 3

Ultrasound imaging setup for detecting the footprint of objects place on a metallic plate. A point sourcelike transmitter is placed at (xTx, yTx). Receiving sensors are located at (x, yobs). (x′, y′) is the point where the reflectivity is evaluated.

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Fig. 4

Observed displacement representation in the Fourier domain. (a) Before filtering: dashed lines represent the limits of the filtered domain, defined by angle α = ±5 deg. (b) After filtering. Both kx, ky space (upper row of plots) and kx-frequency (lower row) representations are depicted.

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Fig. 5

Setup for the first simulation example. Several transmitting and receiving layouts (numbered from I–III) are considered. Units in cm.

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Fig. 6

Time-range ((a1)–(d1)) and frequency–wavenumber responses ((a2)–(d2)) recorded at x = 40 cm. Excitation tone burst: (a) 50 kHz, (b) 100 kHz, (c) 200 kHz, and (d) 400 kHz.

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Fig. 7

Time-range ((a1)–(d1)) and frequency–wavenumber responses ((a1)–(d1)) recorded at x = 22 cm. Excitation tone burst: (a) 50 kHz, (b) 100 kHz, (c) 200 kHz, and (d) 400 kHz.

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Fig. 8

Layout I, (a) recorded displacement along yobs = 0 m line: time-cross range response. (b) Displacement in the k-space domain. (c) Backpropagated displacement in the imaging domain.

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Fig. 9

Layout I, recovered displacement as a function of the separation between receiving array elements, Δx. (a) Δx = 1 cm, (b) Δx = 2 cm, (c) Δx = 5 cm, and (d) Δx = 10 cm.

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Fig. 10

Layout II, single transmitter placed at xTx = 25 cm. (a) Recorded displacement along yobs = 0 m line: time-cross range response. (b) Displacement in the k-space domain. (c) Backpropagated displacement in the imaging domain. (d) Displacement in the k-space domain after filtering with α = 5 deg. (e) Backpropagated displacement in the imaging domain after filtering with α = 5 deg. (f) Comparison of the nonfiltered and filtered displacements for x = 25 cm.

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Fig. 11

Layout II, single transmitter placed at xTx = 30 cm. Comparison for different filtering angles α: ((a) and (b)) no filtering. ((c) and (d)) Filtering angle α = 40 deg. ((e) and (f)) Filtering angle α = 5 deg. Left column plots represent the displacement in the k-space after filtering. Right column plots represent the backpropagated displacement in the imaging domain.

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Fig. 12

Layout II, multiple transmitters evenly spaced every 5 cm in the y = 0 axis. Imaging results for every transmitter are masked with L = 5 cm width mask centered on the corresponding transmitter.

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Fig. 13

Imaging results for layout III, receiving array of length LRx, with a point transmitter placed in the center. The transmitter and the receiving array are displaced in 5 cm-steps. (a) LRx = 10 cm, (b) LRx = 20 cm, and (c) LRx = 40 cm.

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Fig. 14

Phased array analysis of layouts I, II, and III. Comatrix and coarray representation [35]. Co array is an indicator of the effective aperture of the system.

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Fig. 15

Imaging results for: (a) no box on top of the steel plate, (b) wooden box, (c) aluminum box, and (d) lead box. Transmitting and receiving layout I is considered.

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Fig. 16

Setup for the second simulation example. Transmitting and receiving layout I is considered (units in cm).

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Fig. 17

Imaging results for the second simulation example (setup depicted in Fig. 16) consisting of a closed metallic container with a metallic box in it

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Fig. 18

Setup for the third simulation example. Transmitting and receiving layout I is considered. Colors indicate the composition of each asset.

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Fig. 19

Imaging results for the third simulation example (setup depicted in Fig. 18) consisting of a closed metallic container with several assets in it. Solid lines indicate the true footprint and the material of each asset.

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