Highly-Sensitive and Frequency-Selective Imaging of Defects via Local Defect Resonance

Abstract

In this paper, a consistent way to enhance acoustic, optical and thermal defect responses is suggested by using selective ultrasonic activation of defects based on the concept of local defect resonance (LDR). For simulated and realistic defects, the LDR-induced local resonance “amplification” of the vibration amplitude averages up to 20–40 dB. A strong increase in vibration amplitude at LDR enables to reliably detect and visualize the defect as soon as the driving ultrasonic frequency is matched to its LDR frequency. This also provides a high frequency selectivity of the LDR-based imaging, i.e. an opportunity of detecting a certain defect among a multitude of other defects in material. Multiple case studies demonstrate a strong increase in sensitivity for both optical (laser vibrometry and shearography) and thermosonic frequency-selective imaging of defects (flat-bottomed holes, delaminations, cracks, impacts, etc.) in a variety of materials and components.