We report on our recent industrial development projects on millimeter-wave and terahertz imaging solutions for non-destructive testing. This involves system realizations as well as their integration in industrial environments.
Multiple-input multiple-output (MIMO) imaging systems in the terahertz frequency range have a high potential in the field of non-destructive testing (NDT). With such systems it is possible to detect defects in composite materials, for example cracks or delaminations in fiber composites. To investigate mass-produced products it is necessary to study the objects in close to real-time on a conveyor without affecting the production cycle time. In this work we present the conception and realization of a 3D MIMO imaging system for in-line investigation of composite materials and structures. To achieve a lateral resolution of 1 mm, in order to detect such small defects in composite materials with a moderate number of elements, precise sensor design is crucial. In our approach we use the effective aperture concept. The designed sparse array consists of 32 transmitters and 30 receivers based on planar semiconductor components. High range resolution is achieved by an operating frequency between 220 GHz and 260 GHz in a stepped frequency continuous wave (SFCW) setup. A matched filter approach is used to simulate the reconstructed 3D image through the array. This allows the evaluation of the designed array geometry in regard of resolution and side lobe level. In contrast to earlier demonstrations, in which synthetic reconstruction is only performed in a 2D plane, an optics-free full 3D recon- struction has been implemented in our concept. Based on this simulation we designed an array geometry that enables to resolve objects with a resolution smaller than 1mm and moderate side lobe level.
The sub-terahertz (THz) frequency band has proved to be a noteworthy option for nondestructive testing (NDT) of nonmetal aeronautics materials. Composite structures or laminates can be inspected for foreign objects (water or debris), delaminations, debonds, etc., using sub-THz sensors during the manufacturing process or maintenance. Given the harmless radiation to the human body of this frequency band, no special security measures are needed for operation. Moreover, the frequency-modulated continuous-wave sensor used in this study offers a very light, compact, inexpensive, and high-performing solution. An automated two-dimensional scanner carrying three sensors partially covering the 70- to 320-GHz band is operated, using two complementary measurement approaches: conventional focused imaging, where focusing lenses are used; and synthetic aperture (SA) or unfocused wide-beam imaging, for which lenses are no longer needed. Conventional focused imagery offers finer spatial resolutions but imagery is depth-limited due to the beam waist effect, whereas SA measurements allow imaging of thicker samples with depth-independent but coarser spatial resolutions. The present work is a compendium of a much larger study and describes the key technical aspects of the proposed imaging techniques and reports on results obtained from human-made samples (A-sandwich, C-sandwich, solid laminates) which include diverse defects and damages typically encountered in aeronautics multilayered structures. We conclude with a grading of the achieved results in comparison with measurements performed by other NDT techniques on the same samples.
The high demand for beam shaping technology by the display industry has lead to higher resolutions, smaller pixel pitch
and reduced costs. Nowadays high quality, nematic Liquid Crystal on Silicon microdisplays (LCoS) with resolutions of
1920 × 1080 pixels and 8 μm pixel pitch are available. The optical properties of these microdisplays allow for their
application as an adaptive optical element where instantaneous change between arbitrary beam profiles is necessary.
Laser material processing which often requires high beam qualities with various beam profiles is one industry where this
technology could be applied. In this paper, a compact beam shaping setup and simple characterization methods for
practical use of the LCoS at micromachining stations are presented.
Conference Committee Involvement (4)
Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications XIV
6 March 2021 | San Francisco, California, United States
Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications XIII
3 February 2020 | San Francisco, California, United States
Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications XII
4 February 2019 | San Francisco, California, United States
Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications XI
29 January 2018 | San Francisco, California, United States