Embedded-ultrasonics Structural Radar for In Situ Structural Health Monitoring of Thin-wall Structures

Abstract

Embedded-ultrasonics structural radar (EUSR) is a new concept and methodology for in situ nondestructive evaluation (NDE) and structural health monitoring (SHM) of thin-wall structures. EUSR consists of: (a) an array of piezoelectric wafer active sensors (PWAS) embedded into the structure; and (b) electronic modules for signal transmission/reception, processing, and interpretation. EUSR utilizes guided elastic waves (Lamb waves) generated omnidirectionally into the thin-wall structure by surface-mounted permanently attached PWAS. The paper starts with the general concepts of the EUSR algorithm: transmission beamforming, reception beamforming, and time-of-fight (TOF) determination. Next, details of the Lamb wave generation with PWAS, verification of group-velocity dispersion curves, identification of optimal excitation frequency, and confirmation of wave front omnidirectionality are discussed. In the third part of the paper, the actual implementation of the EUSR method in a proof-of-concept demonstration is presented. The construction of the PWAS-phased array is described, and detection of cracks located broadside and offside of the PWAS array is illustrated. The method is shown to be easy to use through a visually interactive LabView TM interface. Very good detection accuracy is observed. The proof-of-concept experiments presented in this paper were illustrated on metallic structures; however, the EUSR concept may also work on composite and hybrid structures, although the range of detection may be reduced by the medium attenuation.

Analytical and finite element prediction of Lamb wave scattering at delaminations in quasi-isotropic composite laminates

“…As shown in Fig 11, wave based imaging algorithms [13,42], especially for Lamb wave diffraction tomography [31][32], if the delamination is located far away from the mid-thickness of the composite laminates.…”

Structural Health Monitoring for Composite Materials

“…Every array element, commonly PZT wafer, is individually used as actuator and sensor in a round-robin fashion such that a group of sensor signals are collected. Based on the synthetic-beam principles [33], all the signals, supplied with different phase delays, can be combined into one synthetic beamforming signal at one given steering angle, which can be implemented in either time or wavenumber domain [34]. Through the similar processes for all angles, the virtual scanning can be achieved without any physical manipulation of the array.…”

“…Usually, the existence of flaw exhibits as the resonance frequency or amplitude modification in the spectrum. Since the imaginary part of ( ) Z  is temperature-sensitive due to 33 T  in equation (3), the real part is more reactive to defects and can be considered for damage assessment. For instance, a damage index is computed as the Euclidean norm of the real portion of the spectrum [39], i.e., …”

Detection and localization of closely distributed damages via lamb wave sparse reconstruction

“…Based on the assumption that reflection occurs when Lamb wave encounters damage, the DAS image is generated by shifting and adding the reflected waves according to an appropriate time shifting rule [2]. In practical application, DAS is generally applied to residual signals, i.e.…”