Terahertz time-gated spectral imaging for content extraction through layered structures (original) (raw)
Related papers
Inspection of panel paintings beneath gilded finishes using terahertz time-domain imaging
Scientific analysis of panel paintings could provide key information to art historians and conservators about the composition and condition of the constituent layers. Knowledge of the structure, stratigraphy, and condition of the subsurface layers of these objects is highly relevant to conservation measures, when stability problems such as delamination or internal cracking are considered. Terahertz time-domain imaging (THz-TDI) in reflection geometry is capable of highlighting interfaces between layers in a stratigraphic buildup, and thus makes structural information available in the form of subsurface 3D images and stratigraphic images (B-scans). The technique is contactless and non-invasive, and has been successfully applied to investigation of panel paintings. Regarding gilded panel paintings, the extremely high reflectivity of metals at submillimeter wavelengths generally precludes the transmission of electromagnetic waves through metallic films. Therefore, imaging of subsurface features below gilded finishes may be regarded as Very challenging. A small but non-negligible direct transmission through metal films occurs if the film thickness is of the order of the skin depth of the metal in the terahertz range, due to the skin effect. The thickness of gold leaf, a fraction of a micrometer, matches the skin depth of gold in the terahertz frequency range covered by THz-TDI devices. We therefore investigated and imaged subsurface features of panel paintings through gilded finishes with THz-TDI. Subsurface layers of three gilded panel paintings (two contemporary tempera panel replicas and one fourteenth-century icon) have been successfully imaged behind gold finishes with THz-TDI.
Terahertz time domain spectroscopy and imaging applied to cultural heritage
2013
The spectroscopy and imaging techniques using the terahertz (THz) range have progressed rapidly, and are expected to become useful examination tools in heritage science. Its nondestructive cross-section images are especially useful to understand the techniques of artworks, especially panel paintings.
Time-domain imaging system in the terahertz range for immovable cultural heritage materials
Strain
In the field of Cultural Heritage science, the use of non-destructive and contact-free techniques has increased sharply over the past 10 years. Compared to conventional spectroscopic and imaging techniques such as X-ray, Ultraviolet (UV), Infrared (IR) and laser spectroscopy, terahertz time-domain imaging (THz-TDI) is an innovative, non-invasive and safe technique, which provides good penetration depth (~1 cm) and broad spectral bandwidth (0.1-10 THz). This paper sets out the protocol and methodology for the application of THz-TDI to immovable Cultural Heritage, illustrated by a series of case studies. The case studies demonstrate the efficacy of the technique in providing structural and material information for conservators.
Terahertz Time-Domain Imaging to Guide a Conservation Intervention on a Stratified Easel Painting
Journal of Infrared, Millimeter, and Terahertz Waves, 2018
Very few real easel paintings have been scanned by means of terahertz time-domain imaging (THz-TDI) up to now. In this study, four different areas of an eighteenth century easel painting have been scanned by THz-TDI with the aim of proving useful information to the conservators for its imminent restoration treatment, owing to the complexity of its structure. Despite the unevenness of the layers composing the painting (lining canvas, original canvas, patching materials, and paint layers), the recorded THz dataset has been processed so that the THz images of the single layers composing the multilayered object have been clearly obtained. Relevant information about the painting structure, the presence of structural defects, overpainting, and the existence and extension of the original remains could have been determined. Infrared photography and X-ray radiography have been used for integrating the collected THz data and comparing the different outputs.
Terahertz imaging for analysis of historic paintings and manuscripts
2008 33rd International Conference on Infrared, Millimeter and Terahertz Waves, 2008
Through the application of terahertz spectroscopy and imaging to the analysis of art, we have developed a spectral database of art materials containing more than 200 spectra of various pigments and binders. With this database, a red ink used in a thirteenth-century manuscript was identified; the results were verified by X-ray fluorescence elements mapping. Terahertz transmission spectral component analysis successfully distinguished stains on the red ink. Reflection imaging also can be used to distinguish materials. Similar techniques can be applied to construct images of specific materials on objects not only in art conservation science but also in various other industries.
Mail Inspection Based on Terahertz Time-Domain Spectroscopy
Applied Sciences
One of the most prominent applications of terahertz time-domain spectroscopy is the spectral investigation of materials covered by visibly opaque objects. Therefore, terahertz waves are well suited to inspect the content of mail. We report on our work on mail inspection in this spectral range including machine design, optical layouts, data analysis, and implementations.
Terahertz imaging for non-destructive evaluation of mural paintings
Optics Communications, 2008
The feasibility of applying time-domain, terahertz spectroscopic imaging to the evaluation of underdrawings and paint layers embedded within wall paintings is demonstrated. Metallic and dielectric paint patterns and a graphite drawing are resolved through both paint and plaster overlayers using a pulsed-terahertz reflectometer and imaging system. We calculated the bulk refractive indices of four common pigments and used them to
Terahertz spectroscopy and imaging for material analysis in conservation science
2010 10th IEEE International Conference on Solid Dielectrics, 2010
Terahertz (THz) waves can penetrate opaque materials and fingerprint spectra appear as those in infrared bands. The technique is expected to be used as a new non-invasive analysis method for various materials. Time domain reflection imaging, in particular, uses THz pulses that propagate in specimens, and in this technique, pulses reflected from the internal boundaries of the specimen indicate the internal structure. We have developed a spectral database of painting materials, and applied THz time domain imaging for analysis of artworks. Experimental results, including first ever non-invasive cross section image of a tempera masterpiece, proved that THz wave can observe layer structure of the artwork from the wood support, gesso preparation layers, and the painting layer. This technique should also be useful to detect internal defect of various types of opaque dielectric materials such as multi layer insulations.
Journal of Cultural Heritage, 2014
Over the past two decades, terahertz (THz) technology has gained in importance and visibility as an emerging technique to be applied in a variety of fields. Since 2006, noninvasive THz time domain spectroscopy (TDS) imaging technology has been proposed for the study of artworks. When applied to panel paintings, THz-TDS imaging makes it possible to fill in the information gap on these artworks between two diagnostic imaging techniques, namely IR reflectography and X-ray radiography, because it provides useful data on the internal physical structure of non-metallic objects without touching the artworks investigated. The resulting noninvasive cross-section image of the object is acquired by extracting the reflected pulse from a particular interface of two media that have different refractive indexes. In this paper, we used a portable THz-TDS imaging system to acquire THz images on a laboratory panel painting and on two artworks, namely the Badia Polyptych (c. 1300-1) by Giotto di Bondone in the Uffizi Gallery in Florence and the San Giovenale Triptych (1422) by Masaccio in the Masaccio Museum at the Pieve (Parish Church) of San Pietro at Cascia di Reggello, near Florence. This was the first application of THz-TDS on masterpieces that is part of conservation-restoration projects focussed on acquiring data on the materials and techniques used by the artists and the state of conservation of the paintings, as well as on testing the potentials of an application of the new emerging THz-TDS imaging technique for the art conservation field. In particular, the data acquired noninvasively on the panel paintings provided useful information on the internal structure of the paintings and on their conditions, as well as a tentative chemical composition of the works or some of their parts. Lastly, this paper offers some basic information on the application of the THz-TDS imaging technique to panel paintings.