The detection and identification of conducting objects using electromagnetic pulses to excite circulating eddy currents within the object is demonstrated by numerical simulation using a finite element time domain electromagnetic solver. The ability to discriminate between objects is based on the decay rate of the induced currents in the object, typically ~ 100 μS. The decay rates are different for a wide variety of everyday objects, allowing threat objects such as handguns, grenades and knives to be discriminated from benign objects such as mobile phones handsets, watches, keys, etc. Crucially, the time constant characterising an object depends only upon the electrical properties of the object (conductivity) and the shape and size of the object; the orientation of the object is irrelevant. This aspect independence of temporal current decay rate forms the basis of a potential object detection and identification system. By application of an algorithm based on the generalized pencil of function method, the authors demonstrate the ability to effectively count and indentify multiple objects carried in close proximity providing that the objects do not have very similar time constants and that signal to noise ratio is high.
Stuart William Harmer,
Nicholas John Bowring,
"Resolution of Multiple Concealed Threat Objects Using Electromagnetic Pulse Induction," Progress In Electromagnetics Research M,
Vol. 26, 55-68, 2012. doi:10.2528/PIERM12061113
1. Nelson, C. V., C. B. Cooperman, W. Schneider, D. S. Wenstrand, and D. G. Smith, "Wide bandwidth time-domain electromagnetic sensor for metal target classification," IEEE Trans. on Geosci. Remote Sens., Vol. 39, No. 6, 1129-1138, Jun. 2001. doi:10.1109/36.927425
2. Nelson, C. V., "Wide-area metal detection system for crowd screening," Proc. SPIE AeroSense 2003 Conf., Sensors and Command, Control, Communication, and Intelligence (C3T) Technologies for Homeland Defense and Law Enforcemnt II, Orlando, FL, Apr. 22-25, 2003.
3. Nelson, C. V., "Metal detection and classification technologies," Johns Hopkins APL technical Digest, Vol. 24, No. 1, 62-66, 2004.
4. Paulter, N. G., "Guide to the technologies of concealed weapon and contraband imaging and detection NIJ Guide 60200,", Electricity Division, National Institute of Standards and Technology Gaithersburg, MD 20899, Prepared for: National Institute of Justice O±ce of Science and Technology Washington, DC 20531, Feb. 2001.
5. Agurto, A., Y. Li, G. Y. Tian, N. Bowring, and S. Lockwood, "A review of concealed weapon detection and research in perspective," Proceedings of the 2007 IEEE International Conference on Networking, Sensing and Control, London, UK, Apr. 15-17, 2007.
6. Agurto, G. A., "New proposal for the detection of concealed weapons: Electromagnetic weapon detection for open areas,", Ph.D. Thesis, Hudders¯eld, UK, 2009.
7. Hunt, A. R., R. D. Hogg, and W. Foreman, "Concealed weapons detection using electromagnetic resonances," Proc. of the SPIE The International Society for Optical Engineering Conference of Enforcement and Security Technologies, Vol. 3575, 62-67, Boston, MA, Nov. 1998.
8. Van Bladel, J. G., Electromagnetic Fields, 2nd Ed., 1170, Wiley --- IEEE Press, 2007. doi:10.1002/047012458X
9. Kriezis, E. E., T. D. Tsiboukis, S. M. Panas, and J. A. Tegopoulos, "Eddy currents: Theory and applications ," Proc. of the IEEE, Vol. 80, No. 10, 1559-1589, Oct. 1992. doi:10.1109/5.168666
10. Theodoulidis, T. P., N. V. Kantartzis, T. D. Tsiboukis, and E. E. Kriezis, "Analytical and numerical solution of the eddy-current problem in spherical coordinates based on the second-order vector potential formulation," IEEE Trans. on Mag., Vol. 33, No. 4, 2461, Jul. 1997. doi:10.1109/20.595899
11. Davey, K. R., "Working nonlinear transient eddy current problems with time harmonic solutions," IEEE Trans. on Mag., Vol. 40, No. 2, Mar. 2004. doi:10.1109/TMAG.2004.824709
12. Baum, C. E., N. Geng, and L. Carin, "Integral equations and polarizability for magnetic singularity identification,", Interaction Note 524, Phillips Lab, Mar. 1997.
13. Kaufman, A. A. and G. V. Kellier, Inductive Mining Prospecting Part 1: Theory, 620, Elsevier, Amsterdam, 1985.
14. Sower, G. D., "Eddy current resonances of canonical metallic targets --- Theory and measurements,", EG & G MSI, Interaction Note, Feb. 1997.
15. Detection and Identification of Visually Obscured Targets, Editor, C. E. Baum, 434, Taylor and Francis, 1999.
16. Wait, J. R. and K. P. Spies, "Quasi-static transient response of a conducting permeable sphere," Geophysics, Vol. 34, No. 5, 789-792, 1969.
17. Kaufman, A. A. and P. A. Eaton, The Theory of Inductive Prospecting, Amsterdam, Netherland , 2001.
18. Sower, G. D. , S. P. Cave, and , "Detection and identification of mines from natural magnetic and electromagnetic resonances," Proc. SPIE, Vol. 2496, 1015-1024, Orlando, FL, 1995.
19. Geng, N. and C. E. Baum, "On the low-frequency natural response of conducting and permeable targets," IEEE Trans. on Geosci. Remote Sens., Vol. 37, No. 1, Jan. 1999.
20. Baum, C. E., "Low-frequency near-field magnetic scattering from highly, but not perfectly, conducting bodies,", Interaction Note 499, Phillips Laboratory, Nov. 1993.
21. Baum, C. E., "On the singularity expansion method for the solution of electromagnetic interaction problems,", Interaction Notes, Note 88, Air Force Weapons Laboratory, 1971.
22. Baum, C. E., E. J. Rothwell, K. M. Chen, et al., "The singularity expansion method and its application to target identification," Proc. of the IEEE, Vol. 79, No. 10, 1481-1492, 1991. doi:10.1109/5.104223
23. Wang, Y. and N. Shuley, "Complex resonant frequencies for the identifcation of simple objects in free space and lossy environments," Progress In Electromagnetics Research, Vol. 27, 1-18, 2000. doi:10.2528/PIER99040501
24. Harmer, S. W., S. E. Cole, N. J. Bowring, N. D. Rezgui, and D. Andrews, "On body concealed weapon detection using a phased antenna array," Progress In Electromagnetics Research, Vol. 124, 187-210, 2012. doi:10.2528/PIER11112105
25. Harmer, S. W., D. A. Andrews, N. D. Rezgui, and N. J. Bowring, "Detection of handguns by their complex natural resonant frequencies ," IET Microw. Antennas Propag., Vol. 4, No. 9, 1182-1190, Sep. 2010. doi:10.1049/iet-map.2009.0382
26. Harmer, S., D. Andrews, N. Bowring, N. Rezgui, and M. Southgate, "Ultra wide band detection of on body concealed weapons using the out of plane polarized late time response," Proc. SPIE, Vol. 7485, 748505, 2009. doi:10.1117/12.830520
27. Zhang, L. , Y. Hao, and C. G. Parini, "Natural resonant frequency extraction for concealed weapon detection at millimetre wave frequencies," 2nd European Conference on Antennas and Propagation (EuCAP), 2007/11961, Edinburgh, UK, Nov. 11-16, 2007.
28. Alabaster, C. M., "The microwave properties of tissue and other lossy dielectrics,", Ph.D. Thesis, Cranfield, UK, Mar. 2004.
29. Secman, M. and G. Turhan-Sayan, "Radar target classification method with reduced aspect dependency and improved noise performance using multiple signal classification algorithm," IET Radar, Sonar and Navigation, Vol. 3, No. 6, 583-595, 2009. doi:10.1049/iet-rsn.2008.0112
30. Harfield, N. and J. R. Bowler, "Theory of thin-skin eddy-current interaction with surface cracks," J. Appl. Phys., Vol. 82, 4590, 1997. doi:10.1063/1.366196
31. Cao, B.-H., M.-B. Fan, and X.-F. Yang, "Analytical time-domain model of transient eddy current field in pulsed eddy current testing," Acta Phys. Sin., Vol. 59, No. 11, 7570-7574, 2010.
32. Tian, G. Y., A. Sophian, D. Taylor, and J. Rudlin, "Multiple sensors on pulsed eddy-current detection for 3-D subsurface crack assessment," IEEE Sensors Journal, Vol. 5, No. 1, 90-96, 2005. doi:10.1109/JSEN.2004.839129
33. Hua, Y. and T. K. Sarkar, "Generalized pencil-of-function method for extracting poles of an EM system from its transient response," IEEE Trans. on Antennas and Propag., Vol. 37, No. 2, 229-234, 1989. doi:10.1109/8.18710
34. Hua, Y. and T. K. Sarkar, "Matrix pencil method for estimating parameters in noise," IEEE Trans. on Acoust. Speech, Signal Processing, Vol. 38, 814-824, May 1990. doi:10.1109/29.56027