Resonant Defects: A New Approach to Highly-Sensitive Ultrasound-Activated NDT Techniques

The presence of a defect leads to a local decrease in rigidity for a certain mass of the material and therefore manifests in a particular characteristic frequency of the defect. A frequency match between the driving ultrasonic wave and this characteristic frequency provides a Local Defect Resonance (LDR) and results in efficient energy delivery from the wave into the defect. In this paper, such a selective ultrasonic activation of resonant defects is suggested to enhance nonlinear ultrasonic, optical and thermal defect responses. Multiple case studies demonstrate that the resonant excitation of a defect results in a high local vibration and enhancement of sensitivity in ultrasonic NDT and imaging of defects via laser vibrometry, thermosonics, nonlinearity and shearography readily measurable even for a few mW of ultrasonic power. The LDR-based NDT methods require much lower ultrasonic power to activate the defects that makes it possible to avoid high-power ultrasonic instrumentatio