A Theoretical Evaluation of Impulse Radar Wave Propagation Through Concrete

Abstract

Abstract It has been shown that one of the most important factors affecting a radar survey of a concrete structure is the operational frequency of the antenna. The operational choice of frequency is difficult as there is always a compromise between signal penetration and resolution. Whilst case histories have proved valuable sources of information, they have not yielded the systematic data needed by structural engineers specifying investigative studies. In the work reported herein, a systematic parametric analysis was undertaken of electromagnetic wave propagation through concrete structures. From this, the use of the simplified expression for wave velocity in relation to concrete structures is seen to be erroneous at lower frequencies - especially at higher conductivities. For a given frequency the skin depth )a measure of penetration( drops as conductivity increases. Also, the frequency of the electromagnetic pulse through concrete is shown to be the order of 75% of the centre frequency of the antenna as measured in air.Clutter, the effect of the dominant particle size, influences the skin depth. Thus a 900MHz antenna may give a cleaner signal than a I Ghz antenna on concrete. Parametric analyses have yielded guidance on choice of antenna frequency in relation to both horizontal and vertical resolution. Overall, it has been shown that a careful assessment has to be made of the different objectives of a radar survey before the range of antennae can be chosen. Three-dimensional graphs are given illustrating the above relationships. keywords: Radar; concreteattenuationwave velocityclutterskin depth