THz-TDS Reflection Measurement of Coating Thicknesses at Non-Perpendicular Incidence: Experiment and Simulation

Area of Science:

• Materials Science
• Nondestructive Testing
• Spectroscopy

Background:

• Terahertz time-domain spectroscopy (THz-TDS) is crucial for nondestructive testing of dielectric materials.
• Accurate layer thickness measurement requires knowledge of the material's refractive index.
• Existing methods for refractive index extraction are limited to perpendicular incidence.

Purpose of the Study:

• To extend refractive index extraction methods for non-perpendicular incidence in THz-TDS.
• To incorporate the effects of surface roughness into thickness measurement models.
• To validate new methods using experimental and simulation data.

Main Methods:

• Developed novel THz-TDS analysis techniques for non-perpendicular incidence, considering polarization.
• Integrated surface roughness effects into the measurement and analysis framework.
• Verified methods using COMSOL simulations and experimental data from Inconel steel coated with YSZ.

Main Results:

• Achieved high accuracy in layer thickness measurements, with average errors of 1% for simulations and under 4% for experimental data.
• Demonstrated the effectiveness of the extended methods for non-perpendicular incidence and rough surfaces.
• Validated results against scanning electron microscopy (SEM) for layer structure confirmation.

Conclusions:

• The developed THz-TDS methods provide accurate dielectric coating thickness measurements.
• The techniques are robust for non-perpendicular incidence and account for surface topography.
• This advancement enhances nondestructive testing capabilities for coated materials.