Nondestructive evaluation (NDE) of multilayered attenuative structures using ultrasonic Bessel beams

Abstract

In this article Nondestructive Evaluation (NDE) of structures with attenuative coating or a layer of thermal protection system is presented utilizing various designs of acoustic axicons. Generation of ultrasonic Bessel beam in single-layered and multi-layered structures to overcome the ultrasonic attenuation is discussed. The possible modulation and the effective increase of the acoustic energy inside the attenuative layer are investigated using axicons, which are proposed to be an ad-hoc element to the existing ultrasonic transducers. Upon confirming the existence and generation of the ultrasonic Bessel beam in an arbitrary host media the spatial intensity distribution of the zeroth-order Bessel beam is studied. Further, we show how the generated Bessels beams propagate and penetrate deep inside the multi-layered structures comprising of different material properties. It is shown that the intensity of the Bessel beams and their possible deep penetration capabilities are altered when the geometrical properties of the axicon and material properties of the media are changed. We also report the numerical characterization of the different degrees of Bessel beams with a unique multi-annular shaped axicon. Modulating the axicon angles and the geometry, the long-distance propagation of the Bessel beam is ensured. Such beam can correspond to the field of Nondestructive Evaluation (NDE) for investigating materials with attenuative layers.