Torsional wave focusing in cylindrical structures with the conformal gradient-index phononic crystal lens

We present torsional wave focusing in cylindrical structures integrated with conformal gradient-index phononic crystal (GRIN-PC) lenses. The mechanical lens modifies the refractive characteristics of propagating waves along axial direction such that energy focuses at a desired point an increased amplitude. In this paper, our main goal is to exploit GRIN-PC concept for amplification fundamental mode, namely, T(0,1), which especially favorable guided ultrasonic testing pipelines and can extend important structural information over long-range pipelines. To end, we first study d35 piezoelectric transducer arrays through multiphysics simulations coupling solid mechanics models determine optimal number transducers achieve excitation plane wave. Two-dimensional Fourier transform as well tangential displacement histories around pipe circumference various positions verify pure T(0,1) excitation, validated experiments. Next, design, fabricate, numerically experimentally mode range frequencies, from 30 50 kHz. Measurements show amplitude amplified by 39% focal presence lens.