Abstract
Available microwave techniques for crack detection have some challenges, such as design complexity and working at a high frequency. These challenges make the sensing apparatus design complex and relatively very expensive. This paper presents a simple method for surface and subsurface crack detection in metallic and non-metallic materials based on complementary split-ring resonators (CSRRs). A CSRR sensor can be patterned on the ground plane of a microstrip line and fabricated using printed circuit board technology. Compared to available microwave techniques for sub-millimeter crack detection, the methods presented here show distinct advantages, such as high spatial resolution, high sensitivity and design simplicity. The response of the CSRR as a sensor for crack detection is studied and analysed numerically. Experimental validations are also presented.
Highlights
The responses of materials to electrodynamic fields depend on their electrical properties, such as permittivity, permeability and conductivity
In [8], an open-ended waveguide operating at around 20 GHz was used as a microwave technique for crack detection in metallic materials, where a 840 μm wide surface crack was detected by direct correlation with the change in the reflection coefficient
We focus on the surface current distribution as the underlying physical mechanism behind the complementary split-ring resonators (CSRRs) sensor
Summary
The responses of materials to electrodynamic fields depend on their electrical properties, such as permittivity, permeability and conductivity. Sensors 2014, 14 changes in material is important in many areas, such as the food industry, bio-sensing applications and surface and subsurface crack detections, to name but a few [1,2,3,4,5,6,7] Material defects, such as sub-millimeter cracks in metallic and non-metallic materials, affect the near-field distribution of the electric and magnetic fields. Since the technique in [13] is based on the far field, which is based on reflection and refraction, the perturbation in the size of the defects or anomalies in the material under test needs to be proportional to the wavelength, requiring operation in the W band (75 GHz to 110 GHz) Such operation frequency makes the measurement setup expensive and complex. To overcome this problem, microwave near-field techniques were introduced to detect cracks in non-metallic materials. We show that the CSRR sensor is effective, for sensing cracks in metallic surfaces, and non-metallic material, such as fiberglass, plastics, carbon fibers, amongst other dielectric materials that are increasingly used in aircraft structures and high performance applications [15]
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