Terahertz non-destructive testing of power generator bars with a dielectric waveguide antenna

Abstract

Terahertz technologies for non-destructive testing (NDT) are continuing to find their way into the industrial sector in the context of very specific inspection tasks. Part of this development is the capability to adapt terahertz systems in such a way that they can meet the sometimes harsh challenges and requirements of real-world industrial scenarios. One such scenario is the inspection of components with limited available measurement space. In particular, we show here the terahertz NDT inspection of the mica insulation of generator bars of turbogenerators at power plants, where an early on-site detection of defects and cracks in the insulation can be crucial, but where only few centimeters of space between adjacent bars are available. To address this problem, we have developed a measurement system combining a 100 GHz all-electronic terahertz transceiver with a low-loss dielectric waveguide antenna with 90 degree tip. We achieve sub-wavelength image resolution by scanning the waveguide antenna's tip over the surface of the generator bars in a near-field measurement setup. Employing a frequency-modulated continuous wave technique, we obtain depth-resolved, volumetric terahertz images of the objects under test. We discuss here the implementation and performance of the implemented measurement system for terahertz NDT inspection. keywords: terahertz, non-destructive testing, dielectric waveguides, frequency-modulated continuous wave, millimeter waves, power generators

Extreme Ultra‐Wideband Optoelectronic Frequency‐Modulated Continuous‐Wave Terahertz Radar

“…It is shown that this prototype allows for state-of-the-art layer thickness determination and can provide full 3D terahertz images. The use of radar systems with comparable modulation rates for industrial imaging applications [23][24][25] demonstrates the great application potential of the new technology in this field. In addition to the unprecedented bandwidth of a terahertz FMCW radar to the best of our knowledge, the optoelectronic continuous wave concept offers a simple possibility to distribute terahertz modulated signals by means of optical fibers and thus to address several transmitter and receiver units simultaneously , e.g., as an imaging radar array.…”