<title>Wide-area imaging of ultrasonic Lamb wave fields by electronic speckle pattern interferometry</title>

Abstract

Ultrasonic elastic waves have traditionally been examined using single point measurement techniques. in this paper, we present a technique capable of recording out-of-plane ultrasonic displacement data over wide areas. The method employs two-dimensional surface vibration data collected via electronic speckle pattern interferometry used in combination with laser modulation and optical phase stepping. Using this rapid, wide-area measurement method, images of ultrasonic Lamb waves on ideal and flawed plate structures are presented. For a single ultrasonic excitation frequency, multiple data records are collected as an externally excited traveling plate wave moves through the sample. When an optical phase shift is introduced between the data records, the data can be processed to yield quantitative displacement fields. The resulting processed images demonstrate evidence of Lamb wave reflection, transmission and scattering. Following the full field data collection, a novel inverse scattering algorithm was applied to reconstruct images of the scattering sources responsible for the measured displacement field data. The results of these investigations will be presented and discussed in the context of detecting hidden flaws in aging aircraft.

Fatigue crack detection in metallic structures with Lamb waves and 3D laser vibrometry

“…Laser-based Lamb wave sensing has found relatively less attention in practical applications than laser-induced Lamb wave generation due to perceptions of low sensitivity, high noise and high costs. Although area or multi-locational measurements are possible with electronic speckle interferometry, adaptive optical interferometry, shearography and laser vibrometers (e.g., [14][15][16][17]), the majority of recent applications involve single-point measurements.…”

Quantitative flaw reconstruction from ultrasonic surface wavefields measured by electronic speckle pattern interferometry

“…The modified ESPI system used to collect the digital phase-stepping holography data, described in detail in [47], is shown in Fig. 5(a).…”

Observation of Piezoelectrically Induced Lamb Wave Propagation in Thin Plates by Use of Speckle Interferometry

“…Gordon and Mast, cf. [6] and [9], set up a digital phase-stepping ESPI system with an improved accuracy. They implemented a series of optical phase shifts into the measurement procedure which are induced by a piezoelectrically adjustable mirror and a laser modulation.…”

“…However, the application of this measurement technique, especially the double pulsed Electronic Speckle Pattern Interferometry (ESPI), to Lamb wave observation is rare and only a few publications exist to the knowledge of the author, cf. Gordon and Mast [6] and Mast and Gordon [9].…”