In this paper, we propose a novel gradient index metamaterial lens to focus elastic wave energy in polymer pipes. We investigate multi-mode focusing of guided ultrasonic waves in a poly-vinyl chloride (PVC) pipe by designing and integrating an embedded gradient index (GRIN) lens within the pipe wall. The metamaterial lens is composed of equally spaced cylindrical brass inserts embedded into the pipe wall. All the inserts are of same height which is equal to the half-thickness of the pipe. Insert diameters are varied in circumferential direction to realize hyperbolic secant distribution of refractive index around the circumference of pipe. We explore focusing of three pipe wave modes commonly used for guided wave inspection of pipelines namely, L(0,2), L(0,1) and T(0,1), using a single lens design. We further verify the lens performance through numerical simulations estimating the amplification of wave energy in focal regions of the GRIN lens for these three modes. We also estimate attenuation of guided waves propagating in PVC pipe through experimental measurements.

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