CMM-2011 – Computer Methods in Mechanics 9–12 May 2011, Warsaw, Poland The initial results of THz spectroscopy non-destructive investigations of epoxy-glass composite structure Robert Panowicz 1 , Danuta Miedzińska 2 , Norbert Pałka 3 and Tadeusz Niezgoda 4 1 Department of Mechanics and Applied Computer Science, Military University of Technology, Faculty of Mechanical Engineering Kaliskiego Street 2, 00-908 Warsaw, Poland e-mail: rpanowicz@wat.edu.pl 2 Department of Mechanics and Applied Computer Science, Military University of Technology, Faculty of Mechanical Engineering Kaliskiego Street 2, 00-908 Warsaw, Poland e-mail: dmiedzinska@wat.edu.pl Institute of Optoelectronics, Military University of Technology, Department of Optoelectronic Technology Kaliskiego Street 2, 00-908 Warsaw, Poland e-mail: npalka@wat.edu.pl 4 Department of Mechanics and Applied Computer Science, Military University of Technology, Faculty of Mechanical Engineering Kaliskiego Street 2, 00-908 Warsaw, Poland e-mail: tniezgoda@wat.edu.pl Abstract The paper presents the initial results of the epoxy-glass composite samples analyses carried out with the use of terahertz spectroscopy. Firstly, the standard specimens made of epoxy resin and glass fibers were researched. The first sample consisted of one layer of glass fiber, the second one had two such layers. To compare the results the results of the composite material sample shut with the 7.62 mm caliber bullet THz analyses were shown. The terahertz spectroscopy uses the well known spectroscopy research methodology however with the use of the new radiation scope. Terahertz bandwidth is mostly defined as (0.1 ÷ 10) THz. Terahertz waves penetrate many materials apart from metals or polar mediums (like water). Therefore, terahertz radiation allows to research many materials such as composite. Keywords: composites, damage, experimental mechanics, laminates 1. Introduction Recent advances in generation and detection of terahertz radiation with conjunction with spectroscopy methodology have enabled the undertaking of new non-destructive investigations of composite materials. The range of terahertz radiation has many definitions in literature. Terahertz bandwidth is defined as (0.1 ÷ 10) THz, what corresponds to wavelength (3000 ÷ 30 μm) 2 . Development and implementation of terahertz technology is connected with unique features of terahertz radiation. Frequency of terahertz radiation corresponds well to frequency of a normal mode (vibrational and rotational) of oscillating molecules of chemical compounds in room temperature and acoustic vibrations of molecules. Accordingly, chemical compounds of organic materials are characterised by specific absorption and emission spectra in the terahertz range. Terahertz waves penetrate many materials apart from metals or polar mediums (like water). Therefore, terahertz radiation can ―see‖ through many materials such as composite. Transmissivity varies significantly dependently on different types of composite. It is greater in glass composite than carbon composite. The next major factor contributing to this interest is that THz radiation poses minimal health risk to a suspected person or the system’s operation due to the fact that photon energy is very small (4,4 meV @ 1THz) 2 . 2. THz radiation The electromagnetic spectrum runs from long-wavelength radio at one end to high-energy, short-wavelength X-rays and gamma rays on the other. Between microwaves and X-rays, in the least explored region of the spectrum, lie T-rays, or terahertz radiation, the most common form of radiation in the universe. In physics, terahertz radiation refers to electromagnetic waves propagating at frequencies in the terahertz range. It is synonymously termed submillimeter radiation, terahertz waves, terahertz light, T-rays, T-light, T-lux, THz. The term typically applies to electromagnetic radiation with frequencies between high-frequency edge of the microwave band, 300 gigahertz (3×10 11 Hz), and the long-wavelength edge of far-infrared light, 3000 GHz (3×10 12 Hz or 3 THz). In wavelengths, this range corresponds to 0.1 mm (or 100 μm) infrared to 1.0 mm microwave. The THz band straddles the region where electromagnetic physics can best be described by its wave-like characteristics (microwave) and its particle-like characteristics (infrared). According to some authors the THz band is also designated as Tremendously high frequency or THF. Terahertz radiation is emitted as part of the black body radiation from anything with temperatures greater than about 10 kelvin. Much of the recent interest in terahertz radiation stems from its ability to penetrate deep into many organic matrials without the damage associated with ionizing radiation such as X-rays (albeit without the spatial resolution). Also, be- cause terahertz radiation is readily absorbed by water, it can be used to distinguish between materials with varying water