12 April 2002 Wideband system for measuring dielectric properties of concrete
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Proceedings Volume 4758, Ninth International Conference on Ground Penetrating Radar; (2002) https://doi.org/10.1117/12.462198
Event: Ninth International Conference on Ground Penetrating Radar (GPR2002), 2002, Santa Barbara, CA, United States
Abstract
The use of bow-tie antennas with time domain GPR systems has become quite common in civil engineering for investigation of structural integrity and location of defects in concrete structures. The depth of a sub-surface feature is evaluated by measuring the time taken for a signal pulse to reflect back from the feature and return to the surface antenna. Optimum interpretation using this approach thus depends upon an accurate knowledge of the speed of propagation of the radar signal, which is very sensitive to the moisture condition of the concrete. The amount of moisture in concrete is usually unknown, variable and very difficult to assess rapidly & non-destructively for in-situ concrete. The paper discusses the development of a wide-band system at Liverpool University, which will be used to make measurements of the complex permittivity and conductivity of concrete structures at radar frequencies, thus enabling a detailed knowledge of the variation of moisture content with depth to be acquired. Instead of using a conventional bow-tie antenna, a much wider-band TEM horn antenna has been developed and can be used in conjunction with a battery-powered portable network analyser suitable for use in the field. Results are presented showing the performance of the new antenna over a wide frequency range. Laboratory tests are discussed in which a variable moisture profile in concrete can be reliably simulated using discrete layers of dielectric material to obtain a closely stepped profile, that closely approximates to the desired linearly varying dielectric model.
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Steven G. Millard, Steven G. Millard, J. Davis, J. Davis, Yi Huang, Yi Huang, J. H. Bungey, J. H. Bungey, } "Wideband system for measuring dielectric properties of concrete", Proc. SPIE 4758, Ninth International Conference on Ground Penetrating Radar, (12 April 2002); doi: 10.1117/12.462198; https://doi.org/10.1117/12.462198
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