Nondestructive monitoring of aircraft composites using terahertz radiation Nikolay S. Balbekin a , Evgenii V. Novoselov b , Pavel V. Pavlov c , Victor G. Bespalov a , Nikolay V. Petrov a a Department of photonics and optical informatics, ITMO University, Kadetskaya Linia 3, St. Petersburg, Russia, 199004. b Chalmers Univ. of Technology, Chalmersplatsen 4, Gothenburg, Sweden, 41296. c Military Aviation Engineering University, Starih Bolshevikov st. 54-a, Voronezh, Russia, 394064. ABSTRACT In this paper we consider using the terahertz (THz) time domain spectroscopy (TDS) for non destructive testing and determining the chemical composition of the vanes and rotor-blade spars. A versatile terahertz spectrometer for reflection and transmission has been used for experiments. We consider the features of measured terahertz signal in temporal and spectral domains during propagation through and reflecting from various defects in investigated objects, such as voids and foliation. We discuss requirements are applicable to the setup and are necessary to produce an image of these defects, such as signal-to-noise ratio and a method for registration THz radiation. Obtained results indicated the prospects of the THz TDS method for the inspection of defects and determination of the particularities of chemical composition of aircraft parts. Keywords: Terahertz radiation, terahertz spectroscopy, terahertz imaging, nondestructive testing, aircraft. 1. INTRODUCTION The qualitatively new technologies are implemented in a global aircraft industry to ensure not only flight safety but also maximum efficiency of aircraft operation. Substantially it is achieved by increasing use of composite materials for aircraft. The composition and therefore the properties of these materials may varied depending on desired values of strength, heat resistance, modulus, abrasion resistance, and moreover differ in their magnetic, dielectric, radio and other properties. Glass fiber, epoxy resin and carbon fiber composite materials are increas- ingly used as structural airframe elements, due to their high strength to weight ratio, improved aerodynamic performance, reliability, and reduced corrosiveness compare to other construction materials. However, composite structure modifications during the exploitation are possible due to the strong thermal influence (e.g., from tur- bines) or various material strains due to external influences (such as unsuccessful plane landing or bullet hits). Also material deterioration is possible caused by a prolonged operation period. The widespread use of compos- ites requires a new approaches both for aircraft design and manufacture, and maintenance and repair services including the high-quality diagnostics. The most common methods for non-destructive testing are ultrasonic techniques, 1, 2 thermography 3, 4, 5 and shearography, 4, 6 but all of them have some disadvantages as expensive- ness, insufficient sensitivity, a problem with the detection of subsurface defects and suitability not for all kinds of defects. 7 During the past few years THz spectroscopy has been applied as a technic for non-contact composite material diagnostics. THz radiation is located between infrared and microwave bands of electromagnetic spectrum. High transparency of smoke, clothing , paper, wood, plastic, ceramic surfaces and other materials for THz radiation provides a great potential for intravision with high signal to noise ratio. THz radiation is non-ionizing unlike X- rays and has less scattering and greater penetration depth in comparison with optical and infrared radiation. By use of the electro-optical detection in THz TDS it is possible to register real part of THz field complex amplitude, that can provide us information both on amplitude and phase radiation and yield to fuller measurement of optical E-mail: NBalbekin@niuitmo.ru Saratov Fall Meeting 2014: Optical Technologies in Biophysics and Medicine XVI; Laser Physics and Photonics XVI; and Computational Biophysics, E. A. Genina, V. L. Derbov, K. V. Larin, D. E. Postnov, V. V. Tuchin, Eds., Proc. of SPIE Vol. 9448, 94482D · © 2015 SPIE · CCC code: 1605-7422/15/$18 · doi: 10.1117/12.2180021 Proc. of SPIE Vol. 9448 94482D-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/25/2015 Terms of Use: http://spiedl.org/terms