Microwave NDE is the method of using microwaves to detect embedded defects in low loss dielectric structures. Microwaves can travel large distances in free space and penetrate deep into non conducting materials. This makes them suitable for rapid inspection of dielectrics and composites as the probe stand off distances can be large in far field mode. However, the resolution of such far-field microwave systems are diffraction limited, which means that defects or anomalies, that are smaller than the operating wavelength go undetected under such a rapid scan.Metamaterials (MM) are artificially engineered materials with properties not found in naturally occurring materials. It has been shown that such specially designed periodic structures can be manipulated to offer materials with negative refractive index that can overcome natural limitations, such as diffraction limited resolution. Therefore, enhancement of microwave imaging using negative refractive index metamaterials will offer sub wavelength detection capabilities from far field. Likelihood of missing small and intricate defects will be lowered resulting in a more robust and reliable microwave NDE system.Negative refractive index of a metamaterial occurs due to the EM response of the periodic building blocks, known as unit cells. The building blocks/unit cells of metamaterials are passive, and hence, once they are fabricated, the frequency response of these MMs are fixed. Moreover, metamaterials work in a relatively narrow frequency regime which makes its application limited in terms of operating wavelength, λ and imaging resolution become restricted due to the narrowband nature of the MM lens. A tunable or reconfigurable MM lens are composed of passive as well as active components. These tunable MMs allow greater degree of freedom in choosing its operating wavelength by controlling the active components. The lens can be configured to work in a specific frequency regime depending on the composite structures under investigation. Higher frequency will allow for greater resolution of defects within the structures while lower frequency allows for greater penetration. This work will look into the design of passive and active metamaterial lens for subwavelength defect detection.

Design of Passive and Active Metamaterial Lens for Subwavelength Microwave Detection

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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