Hybrid Bessel beam and metamaterial lenses for deep laparoscopic nondestructive evaluation

A unique non-diffracting hybrid order longitudinal Bessel beam with pronounced resilience to scattering using acoustic metamaterial, which we call hybrid Bessel beams (HYBEs), is currently unknown. Newly proposed hybrid Bessel beams are different than the conventional cross-sectional Bessel beams. In this article, we explain the physics of multifunctional ultrasonic capabilities of a bioinspired interlocking architecture of acoustic metamaterial. At first, for the newly proposed metastructure, understanding the physics and wave energy is predictively focused through attenuative surfaces at various ultrasonic frequencies (∼120 to ∼130 kHz). Finally, a zero-order first of its kind ultrasonic Bessel-like beam between frequencies of ∼265 and ∼272 kHz is shown propagating a long distance through the base material. The new propagation had minimal reduction in energy amplitude, while the displacement was nearly constant across the depth of the wave guide following a second-order Bessel function of the first kind. To explain the physics of the phenomena, mode shapes in the frequency-wavenumber domain are investigated. Furthermore, identification of the propagating wave vector using equi-frequency contours at multiple ranges confirmed the presence of the proposed acoustic features. These abilities of the proposed metamaterial have key advantages to propagate waves deeper into thick attenuative and aberrative structures such as brain tissue, soft skin and muscles, paint surface, and non-accessible composite materials. We envision potential applications of the proposed HYBE for the non-destructive evaluation (NDE) of attenuative materials that are not easily accessible for testing. To verify the wave focusing and long-distance wave propagation, an ad hoc metamaterial lens for the conventional NDE transducer is proposed, which demonstrated wave propagation through a 10 mm thick carbon fiber reinforced polymer composite structure.