Non-destructive crack detection technique by means of microwave imaging
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Date
2015-01-01
Authors
iya Adama Enoch
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Abstract
Building and civil structures are often overburdened with load above their threshold
value that led to deterioration and weakening of the supporting members, and
resulted in cracks. Cracks in concrete or cement based materials present a significant
threat to any civil structures; they are very dangerous and have caused much
destruction and damages. Even small cracks, which look insignificant grow and
eventually lead to severe structural failure. Besides manual inspection that is
ineffective and time-consuming, several non-destructive evaluation techniques have
been used for crack detection. For instance, ultrasonic, vibration and strain-based
techniques, however some of the sensors used are either too big or limited in
resolution. The main objective is to study the possibility of crack detection in
concrete or cement based materials using microwave imaging with Delay-and-Sum,
(DAS) algorithm. First, models of various crack types in bricks were simulated using
finite difference time domain method (FDTD) method. The simulation results were
used to determine the design parameters for the experimental setup. Single brick and
a constructed concrete structure with cracks were used as phantoms. From the
experimental results, signal with frequency of 1 to 7 GHz gave an optimum
resolution and signal penetration. Cracks of at least 5 mm in size were detected with
a resolution of λ/4 that enabled crack detection at the early stage of development. In
conclusion, microwave imaging technique showed the potential to detect cracks in
concrete or cement-based materials with high-resolution image.