[Culture in China · A Typical Case of Technology Empowerment]
A robotic arm turns nimbly as invisible terahertz waves quietly sweep across the mottled surface of a Sanxingdui bronze, revealing the secrets hidden beneath its rust layers. Recently, at the Sichuan Provincial Key Laboratory of Terahertz Science and Technology at UESTC (“the Lab”), a “dialogue” across time unfolded between modern scientists and ancient craftsmen. As “terahertz fingerprint spectra” rich in molecular-structure information appeared on the computer screen, the scientists obtained material information on corrosion products and surface deposits at different depths of the bronze artifact.
Accurately acquiring an artifact’s age and elemental composition while doing everything possible to avoid damage has long been the “spear and shield” of modern science and cultural-heritage conservation. With breakthroughs in conventional non-destructive testing such as X-rays and infrared, a new frontier has emerged: how to obtain pigment and coating information in situ, non-destructively, and holistically while “seeing through” an artifact.
The research team led by Prof. Min Hu, head of the Lab, is collaborating with Zhejiang University, the Sichuan Provincial Institute of Cultural Relics and Archaeology, the Sanxingdui Museum and other institutions. Using its self-developed, world-first vacuum-electronics-based terahertz near-field imaging system, the team performed tomographic analysis of Sanxingdui bronze artifacts — the first time worldwide that terahertz waves have been used for tomographic analysis of bronze relics.
“Terahertz waves, or THz for short, are electromagnetic waves with frequencies between 0.1 and 10 terahertz, corresponding to wavelengths of roughly 0.03 to 3 millimeters,” said Hu. Compared with ionizing techniques such as X-rays, terahertz photons carry extremely low energy and cause no harmful ionization, allowing researchers to probe internal structures and material compositions without damaging artifacts — and without risk to the researchers themselves. “It can penetrate most non-metallic materials. Through multi-layer reflections of the time-domain pulse inside an object, we obtain layered structural information without slicing the artifact.”
Dr. Xiaoqiuye Zhang, a postdoctoral researcher at the Lab, explained that for rust-layer identification on Sanxingdui bronzes, the team first uses structured-light technology to quickly build a 3D contour of the artifact — a “digital map”. Based on that map, intelligent algorithms plan the terahertz scanning path to ensure normal incidence for precise measurement of rust-layer thickness.
“During rust identification, the robotic arm steers the probe so the emitted terahertz waves penetrate the rust layer and collect the ‘secrets’ of its internal structure and material properties. The detection data are then combined with the bronze’s 3D contour to generate a 3D image of the rust layer, visually showing its distribution, morphology and thickness variation,” Zhang said. Combined with the “terahertz fingerprint spectrum”, conservators can clearly distinguish harmful from harmless rust and locate their distribution, making restoration more precise and efficient.
Terahertz scanning performs time-of-flight imaging with femtosecond pulses, delivering preliminary results on an artifact’s surface layers within as little as 10 minutes of excavation. It also achieves high-resolution imaging, with thickness accuracy down to 10 micrometers and lateral precision down to 50 nanometers. “Our laboratory will leverage its strengths in terahertz technology to provide non-destructive testing and pathology diagnosis for Sanxingdui artifacts. We have reached an agreement with the Sanxingdui Museum on deep cooperation in archaeological research, heritage conservation and cultural inheritance,” Zhang said.
“In the future, the Lab will also introduce artificial intelligence and machine learning, combining them with terahertz technology to improve the efficiency and accuracy of data processing and analysis, making inspection results more detailed and reliable,” Hu added. The team will also strengthen interdisciplinary collaboration with archaeology and materials science to drive innovative applications of terahertz technology in heritage conservation.
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Source: UESTC News (via Science and Technology Daily) Original article