In this paper, we present a gradient-index (GRIN) metamaterial lens design toward enhanced sensing by amplifying ultrasonic guided wave signal carrying defect information in pipelines. The curved GRIN lens conforms over the steel pipe and consists of cylindrical steel stubs with varying height according to the hyperbolic secant profile of the refractive index around the circumference of the pipe. We design the lens to perform above the audible frequency range as utilized in ultrasonic inspection of pipelines. By tailoring the dispersion curves of the longitudinal and torsional pipe modes that are commonly used in guided wave testing elastic wave focusing is successfully achieved at focal spots of the lens. Amplification of the multi-mode guided wave signals is validated through experiments performed on a lab scale steel pipe.
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