Nondestructive quality inspection with terahertz waves has become an emerging technology, especially in the automotive and aviation industries. Depending on the specific application, different terahertz systems—either fully electronic or based on optical laser pulses—cover the terahertz frequency region from 0.1 THz up to nearly 10 THz and provide high-speed volume inspections on the one hand and high-resolution thickness determination on the other hand. In this paper, we present different industrial applications, which we have addressed with our terahertz systems within the last couple of years. First, we show three-dimensional imaging of glass fiber–reinforced composites and foam structures, and demonstrate thickness determination of multilayer plastic tube walls. Then, we present the characterization of known and unknown multilayer systems down to some microns and the possibility of measuring the thickness of wet paints. The challenges of system reliability in industrial environments, e.g., under the impact of vibrations, and effective solutions are discussed. This paper gives an overview of state-of-the-art terahertz technology for industrial quality inspection. The presented principles are not limited to the automotive and aviation industries but can also be adapted to many other industrial fields.

中文翻译：

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太赫兹汽车和航空工业的质量检验

太赫兹波的无损质量检测已经成为一种新兴技术，尤其是在汽车和航空工业中。根据特定的应用，不同的太赫兹系统（全电子或基于光学激光脉冲）可覆盖从0.1 THz到接近10 THz的太赫兹频率区域，一方面可提供高速体积检查和高分辨率厚度确定另一方面。在本文中，我们介绍了不同的工业应用，在过去的几年中，我们已经使用太赫兹系统解决了这些应用。首先，我们展示了玻璃纤维增​​强复合材料和泡沫结构的三维成像，并展示了多层塑料管壁的厚度确定。然后，我们介绍了已知和未知的低至几微米的多层系统的表征，以及测量湿涂料厚度的可能性。讨论了工业环境中系统可靠性的挑战，例如在振动的影响下，以及有效的解决方案。本文概述了用于工业质量检查的最新太赫兹技术。提出的原理不仅限于汽车和航空工业，还可以适用于许多其他工业领域。本文概述了用于工业质量检查的最新太赫兹技术。提出的原理不仅限于汽车和航空工业，还可以适用于许多其他工业领域。本文概述了用于工业质量检查的最新太赫兹技术。提出的原理不仅限于汽车和航空工业，还可以适用于许多其他工业领域。