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Researchers are investigating the capabilities of linear elastic wave imaging and nonlinear ultrasonics, GHz acoustic microscope, nonlinear optics for sensing, electromagnetic and Superconducting Quantum Interference Device (SQUID) measurements for providing unique advancements in quantitative nondestructive evaluation of material microstructure. Imaging solutions using nonlinear optical approaches are under investigation as well as laser ultrasonic industrial process monitoring.

Much of the research featured on these pages has been funded by the Department of Energy’s Office of Science, Basic Energy Sciences program. Our BES program is titled Microstructure NDE using Imaging Laser Ultrasonics.

Individual web sites have been developed to describe each research thrust:

Linear Elastic Wave Imaging — Anisotropic properties of materials can be determined by measuring the propagation of elastic waves in different directions. A laser imaging approach has been developed at the INL that utilizes the adaptive property of photorefractive materials to produce a real-time measurement of the anti-symmetric Lamb or flexural traveling wave mode displacement and phase. Continuous excitation is employed and the data is recorded and displayed in all directions simultaneously at video camera frame rates. Fourier transform of the data produces an image of the wave slowness in all planar directions. The results demonstrate imaging of microstructural isotropy and anisotropy and stress induced ansiotropy in plates.

Nonlinear Ultrasonics — Researchers are investigating nonlinear acoustics as a tool for identifying material microstructure. Currently, their work involves reducing sensitivity to background nonlinearity by nonlinear mixing of surface acoustic waves.

GHz Acoustic Microscope — Acoustical Microscopy can be performed using laser ultrasonics by feeding both the generation and detection optical beams through the microscope objective. Sensitivities of 6x10-4 nm @ 880 MHz have been demonstrated with over 4 orders of magnitude dynamic range using 532 nm optical wavelength.

Nonlinear Optics for Sensing — Researchers are using photorefractivity for dynamic holography and dynamic interferometric detection of ultrasonic motion. We studied the two-wave mixing anisotropic diffraction process in GaAs for demodulation of static and dynamic phase encoded signals.

Electromagnetic and SQUID Measurements — Recent advances in the fabrication of SQUIDs from High Temperature Superconducting (HTS) materials has opened up the possibility of transforming this highly sensitive magnetic field detector into powerful, portable nondestructive evaluation (NDE) probe suitable for industrial applications. The high sensitivity of SQUIDs can be used to synchronously measure the magnetization signals generated by nonmagnetic excitation such as strain, heat, and electrical or optical fields.

Molten Metal Process Monitoring and Solidification Front Characterization — INL’s real-time method of locating and characterizing the shape of the solidification front permits an accurate assessment of the pool depth and the molten metal residence time. This is important in controlling the casting process, and thereby, material properties.

Laser Ultrasonic Industrial Process Monitoring — The INL Laser Ultrasonic Camera directly images (without the need for scanning) the surface distribution of subnanometer ultrasonic motion at frequencies from Hz to GHz. Ultrasonic waves form a useful nondestructive evaluation (NDE) probe for determining physical and mechanical properties of materials and parts.