THz-TDS Techniques of Thickness Measurements in Thin Shim Stock Films and Composite Materials

• Published in: Applied sciences Vol. 11; no. 19; p. 8889
• Main Authors: Im, Kwang-Hee, Kim, Sun-Kyu, Cho, Young-Tae, Woo, Yong-Deuck, Chiou, Chien-Ping
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.10.2021
• Subjects: Aviation; Carbon fibers; Composite materials; Electromagnetic properties; Experiments; Fiber composites; Glass fiber reinforced plastics; Measurement techniques; Nondestructive testing; Plastics; Polymer matrix composites; reflection mode; refractive index; Refractivity; Scanning; Shim stock films; Spectrum analysis; Terahertz frequencies; terahertz waves; Thickness measurement; Thin films; Velocity
• ISSN: 2076-3417; 2076-3417
• DOI: 10.3390/app11198889

Terahertz wave (T-ray) scanning applications are one of the most promising tools for nondestructive evaluation. T-ray scanning applications use a T-ray technique to measure the thickness of both thin Shim stock films and GFRP (glass fiber-reinforced plastics) composites, of which the samples were selected because the T-ray method could penetrate the non-conducting samples. Notably, this method is nondestructive, making it useful for analyzing the characteristics of the materials. Thus, the T-ray thickness measurement can be found for both non-conducting Shim stock films and GFRP composites. In this work, a characterization procedure was conducted to analyze electromagnetic properties, such as the refractive index. The obtained estimates of the properties are in good agreement with the known data for poly methyl methacrylate (PMMA) for acquiring the refractive index. The T-ray technique was developed to measure the thickness of the thin Shim stock films and the GFRP composites. Our tests obtained good results on the thickness of the standard film samples, with the different thicknesses ranging from around 120 μm to 500 μm. In this study, the T-ray method was based on the reflection mode measurement, and the time-of-flight (TOF) and resonance frequencies were utilized to acquire the thickness measurements of the films and GFRP composites. The results showed that the thickness of the samples of frequency matched those obtained directly by time-of-flight (TOF) methods.