Configuration-based coaxial cable sensors have recently been developed to detect cracks in reinforced concrete (RC) structures. These sensors have shown a high sensitivity when applied to several short RC flexural members. However, the signal losses resulting from a long cable sensor may distort the initial waveform of the electromagnetic wave propagating along the cable, thereby compromising the spatial resolution and sensitivity of this sensor. The signal losses consist of the contributions from the skin effect of conductors, energy absorption in the dielectric material, and impedance mismatch loss due to multiple signal reflections resulting from discontinuities caused by the separation between the adjacent spirals, which acts as the outer conductor of a cable sensor. This paper summarizes the basic physics of signal losses in cable sensors, and investigates the impact of the signal losses on the spatial resolution and sensitivity of a cable sensor over distance. Several methods are proposed to simulate and quantify various factors affecting the signal losses.
This study was aimed at developing and validating a new type of coaxial cable sensors that can be used to detect cracks or measure strains in reinforced concrete (RC) structures. The new sensors were designed based on the change in outer conductor configuration under strain effects in contrast to the geometry-based design in conventional coaxial cable sensors. Both numerical simulations and calibration tests with strain gauges of a specific design of the proposed cables were conducted to study the cables' sensitivity. Four designs of the proposed type of sensors were then respectively mounted near the surface of six 3-foot-long RC beams. They were tested in bending to further validate the cables' sensitivity in concrete members. The calibration test results generally agree with the numerical simulations. They showed that the proposed sensors are over 10~50 times more sensitive than conventional cable sensors. The test results of the beams not only validate the sensitivity of the new sensors but also indicate a good correlation with the measured crack width.
Electromagnetic emissions from electronics associated with explosives is a potential detection modality, both passive listening, and stimulated RF emissions. However, the parasitic paths by which energy is coupled off a printed circuit board from an active device, and by which external energy can be coupled onto the board and to a device, must be identified and characterized. One such noise-coupling path is identified in this work, and a modeling approach demonstrated. In particular, coupling of noise from the DC power bus of a multilayer printed circuit board that uses entire metal layers for power and ground, and an I/O line that transitions through the DC power planes is investigated.
Electromagnetic emissions from electronics associated with explosives - mines, timers, and fuses - have been experimentally observed. The emissions fall into two categories, those resulting from the natural functioning of the electronics themselves - an electromagnetic interference (EMI) signature, and stimulated emissions resulting from RF irradiation of the electronics and re-radiation by the circuit. In order to develop suitable detection modalities for these processes, an understanding of the basic physics of the radiation process is essential. The basic physics of radiation and stimulation of electronic circuits are being studied, and electromagnetic interference characterization and measurement procedures are being developed. Finite- difference time-domain modeling is being applied to gain insight into radiation processes and levels so that the feasibility of detection of these signatures can be evaluated, and detection systems developed.
O. Robert Mitchell, Thomas Herrick, David Summers, Richard Rechtien, James Drewniak, Srinivasa Somu, Sriram Srinivasan, Vittal Rao, Randy Moss, Richard DuBroff
The complexity of the detection and discrimination problem for land mines requires that multiple sensors and algorithms be employed. We have been attempting to develop a range of new sensors and sensor combinations that will contribute to the solution to this problem. The sensors discussed in this paper include heated waterjets combined with infrared images, non- contact acoustic focusing, and the detection of electromagnetic emissions from smart land mines.
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