Mid Infrared Tomography of Polymer Pipes
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Mid Infrared Tomography of Polymer Pipes D. A. Hutchins1
· P. Huthwaite2 · L. A. J. Davis1 · D. R. Billson1 · L. Senni3 · S. Laureti4 · M. Ricci4
Received: 25 September 2019 / Accepted: 28 August 2020 © The Author(s) 2020
Abstract Mid-infrared signals in the 2–5 μm wavelength range have been transmitted through samples of polymer pipes, as commonly used in the water supply industry. It is shown that simple through-transmission images can be obtained using a broad spectrum source and a suitable camera. This leads to the possibility of tomography, where images are obtained as the measurement system is rotated with respect to the axis of the pipe. The unusual 3D geometry created by a source of finite size and the imaging plane of a camera, plus the fact that refraction at the pipe wall would cause significant ray bending, meant that the reconstruction of tomographic images had to be considered with some care. A result is shown for a thinning defect on the inner wall of a polymer water pipe, demonstrating that such changes can be reconstructed successfully. Keywords Tomography · Mid infrared
1 Introduction Infrared signals have been used for some time for industrial measurements. One example is infrared spectroscopy [1], which can be used for the characterisation of materials, especially food [2]. Typically, the technique relies on the absorption of signals in the 0.78–2 μm wavelength range. In general, the resultant spectra are complex, being due to vibrational modes and overtones of the main absorption bands. However, it is still possible to identify the presence of constituents and their concentration, often via the use of chemometrics [3]. In this near infrared (NIR) wavelength range, signals will penetrate into many non-conducting mateElectronic supplementary material The online version of this article (https://doi.org/10.1007/s10921-020-00714-0) contains supplementary material, which is available to authorized users.
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D. A. Hutchins [email protected]
1
School of Engineering, University of Warwick, Coventry CV4 7AL, UK
2
Department of Mechanical Engineering, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
3
Dipartimento di Ingegneria, Polo Scientifico Didattico di Terni, Università di Perugia, Strada di Pentima 4, 05100 Terni, Italy
4
Dipartimento di Ingegneria Informatica, Modellistica, Elettronica e Sistemistica, Università della Calabria, Via Pietro Bucci, Arcavacata, 87036 Rende, CS, Italy
rials, often to a limited extent due to absorption and scattering mechanisms. This is made use of in certain medical procedures, where there is reasonable transmission of NIR signals through human tissue. This allows techniques such as blood oxygen measurement by differential absorption at two wavelengths [4] and breast imaging for cancer diagnosis [5] to be developed. Other applications include intraocular imaging where there is greater penetration into the eye than in the visible region [6, 7]. NIR signals generated over a range of discrete wavelengths (e.g. using laser diodes)
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