Terahertz Wave Approach and Application on FRP Composites

Kwang-Hee Im,Jong-An Jung,David K Hsu,Daniel J Barnard,Chien-Ping Chiou,In-Young Yang

doi:10.1155/2013/563962

Abstract

Terahertz (THz) applications have emerged as one of the most new powerful nondestructive evaluation (NDE) techniques. A new T-ray time-domain spectroscopy system was utilized for detecting and evaluating orientation influence in carbon fiber-reinforced plastics (CFRPs) composite laminates. Investigation of terahertz time-domain spectroscopy (THz-TDS) was made, and reflection and transmission configurations were studied as a nondestructive evaluation technique. Here, the CFRP composites derived their excellent mechanical strength, stiffness, and electrical conductivity from carbon fibers. Especially, the electrical conductivity of the CFRP composites depends on the direction of unidirectional fibers since carbon fibers are electrically conducting while the epoxy matrix is not. In order to solve various material properties, the index of refraction (n) and the absorption coefficient (α) are derived in reflective and transmission configurations using the terahertz time-domain spectroscopy. Also, for a 48-ply thermoplastic polyphenylene-sulfide-(PPS-) based CFRP solid laminate and nonconducting materials, the terahertz scanning images were made at the angles ranged from0°to180°with respect to the nominal fiber axis. So, the images were mapped out based on the electrical field (E-field) direction in the CFRP solid laminates. It is found that the conductivity (σ) depends on the angles of the nominal axis in the unidirectional fiber.

Highlights

The terahertz radiation has been recognized for their importance in technological applications
The terahertz time-domain spectroscopy (THz-timedomain spectroscopy (TDS)) is leading noncontact accurate detection of flaws and impact damages in composites, in which the THz-TDS is based on photoconductive switches, which rely on the production of few-cycle terahertz pulses using a femtosecond laser to excite a photoconductive antenna [2]
We report our initial investigations of the index of refraction (n) and the absorption coefficient (α), the electrical conductivity of epoxy matrix composites containing carbon fibers, and the THz scan images of carbon fiber-reinforced plastics (CFRPs) solid laminates

Summary

Introduction

The terahertz radiation has been recognized for their importance in technological applications. The terahertz time-domain spectroscopy (THz-TDS) is leading noncontact accurate detection of flaws and impact damages in composites, in which the THz-TDS is based on photoconductive switches, which rely on the production of few-cycle terahertz pulses using a femtosecond laser to excite a photoconductive antenna [2] This can generate subpicosecond bursts of THz radiation and subsequently detect them with high signal-to-noise ratio. We report our initial investigations of the index of refraction (n) and the absorption coefficient (α), the electrical conductivity of epoxy matrix composites containing carbon fibers, and the THz scan images of CFRP solid laminates. The THz effective scan images can be made according to the angels at the orientation of carbon fibers It follows that the higher contrast images are being governed by the E-field direction. It was found that the best scanning angles were optimized based on the Efield direction to the function of fiber angles

Theory and Experiment

Results and Discussion

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