Feasibility of pulse-echo thickness measurements in air with a laterally displaced receiver

Waag, Grunde; Hoff, Lars; Norli, Petter

doi:10.1109/ultsym.2014.0252

Cited by 1 publication

(1 citation statement)

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“…An alternative can be the use of two different transducers in pitch–catch mode, but the dead zone does not disappear completely, and the technique becomes more difficult to implement since two different transducers are involved [22]. If oblique incidence is considered, accuracy in the control of angle and location is critical in order to separate specular reflection from the front surface and back wall echoes originating from longitudinal and shear waves, which also requires accurate knowledge of the longitudinal and shear wave velocities in the material.…”

Section: Introductionmentioning

confidence: 99%

Air-Coupled and Resonant Pulse-Echo Ultrasonic Technique

Álvarez-Arenas

Camacho

2019

Sensors

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An ultrasonic, resonant, pulse-echo, and air-coupled nondestructive testing (NDT) technique is presented. It is intended for components, with regular geometries where it is possible to excite resonant modes, made of materials that have a high acoustic impedance (Z) and low attenuation coefficient (α). Under these conditions, these resonances will present a very large quality factor (Q) and decay time (τ). This feature is used to avoid the dead zone, produced by the echo coming from the first wall, by receiving the resonant echo from the whole specimen over a longer period of time. This echo is analyzed in the frequency domain to determine specimen resonant frequency, which can be further used to determine either velocity or thickness. Using wideband air-coupled transducers, we tested the technique on plates (steel, aluminum, and silicone rubber) by exciting the mode of the first thickness. As expected, the higher the Z and the lower the α, the better the technique performed. Sensitivity to deviations of the angle of incidence away from normal (±2°) and the possibility to generate shear waves were also studied. Then, it was tested on steel cylindrical pipes that had different wall thicknesses and diameters. Finally, the use of this technique to generate C-Scan images of steel plates with different thicknesses was demonstrated.

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Section: Introductionmentioning

confidence: 99%