Rapid terahertz imaging for non-destructive evaluation applications using Schottky receivers and spatial adaptive sampling
01 Mar 2019-Vol. 10917, pp 1091712
TL;DR: In this article, a CW THz system with incoherent detection scheme using Schottky receiver along with spatial adaptive sampling technique is employed to achieve rapid THz imaging of Glass Fibre Reinforced Polymer (GFRP) composite with artificial defects.
Abstract: Terahertz (THz) technology is a competent non-destructive evaluation (NDE) technique, particularly for advanced materials such as Fibre Reinforced Polymer (FRP) composites due to its ability to penetrate most non-metallic and nonpolar substances. Typically, THz NDE studies are carried out using expensive and broadband pulsed THz systems limiting their widespread use in practical applications. In contrast, Continuous wave (CW) THz systems can potentially be a narrowband, cost-effective and scalable solution for NDE applications. However, conventional CW THz systems employ a coherent detection scheme which results in large acquisition time per pixel thus limiting their real-time applicability. In this paper, a CW THz system with incoherent detection scheme using Schottky receiver along with spatial adaptive sampling technique is employed to achieve rapid THz imaging of Glass Fibre Reinforced Polymer (GFRP) composite with artificial defects. Here, an initial coarse scan of 2 mm step size has been done, and gradient based thresholding criterion is used for identifying the regions of interest to progressively scan the sample with finer resolution down to a step size of 0.5 mm. Results demonstrate a total reduction in the image acquisition time by a factor of 50 compared to the coherent CW THz imaging. Further, the THz image acquired through adaptive sampling shows excellent correlation with that of the traditional uniformly sampled THz image with 0.5 mm step size.
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02 Mar 2020
TL;DR: In this paper, a line scanner was used for defect detection in fiber reinforced polymers (GFRP) composites using a 100 GHz source and the total acquisition time for imaging the GFRP sample of dimensions 55× 35 mm2 is 10 s, which is >100 times faster compared to a conventional raster scanning technique.
Abstract: Terahertz (THz) imaging is an attractive alternate to ultrasonic based Non-destructive Evaluation (NDE) especially for Fiber Reinforced Polymers (FRPs) such as Glass FRP (GFRP) composites as the latter demands proximity and additional coupling medium for the best performance. Typically, THz imaging system uses a single emitter-detector configuration employing raster scan method for image acquisition. The image acquisition speed is greatly limited by the speed of the mechanical stages and hence its usage in real-time industrial NDT applications such as in-line quality control has been limited. Alternatively, having an array of detectors will significantly increase the system cost. As an optimal compromise for speed and cost, line scanners are highly desirable. In this work, rapid imaging performance of a THz line scanner has been studied by imaging closely spaced defects in GFRP composites using a 100 GHz source. The total acquisition time for imaging the GFRP sample of dimensions 55× 35 mm2 is 10 s, which is >100 times faster compared to a conventional raster scanning technique. In addition, image deconvolution techniques such as Lucy Richardson and Weiner deconvolution have been adopted to improve the quality of the acquired THz images. The results show that the THz line scanners can successfully be employed for rapid defect detection in GFRP composites.
1 citations
01 Jan 2022
TL;DR: In this article , the authors discuss how the sensors based on these frequency spectra can be used in various biomedical applications, classified into three major domains, i.e., diagnostics, imaging, and treatment.
Abstract: In recent years, terahertz radiationTerahertz radiation (THz = 1012 Hz) has attracted much attention due to its exceptional non-invasive and non-ionizing sensing capabilities. The sub-THz band (0.1–0.3 THz) and the THz band (0.3–10 THz) lie between millimeter waves (mm-waves) and light waves with the ability to harness their advantages. The capacity for these sub-THz and THz waves to penetrate deeply into dielectric materials combined with their high spatial resolution makes them well suited for biomedical applications, including in-vivo and ex-vivo experiments. The purpose of this chapter is to discuss how the sensors based on these frequency spectra can be used in various biomedical applications, classified into three major domains, i.e., diagnostics, imaging, and treatment, where they provide many advantages over the existing devices. Next, we will discuss the appropriateness of using photonics and electronics THz instruments in THz applications and the suitability of using electronics in the sub-THz regime. Finally, we'll look at artificial intelligence's function in enhancing the technology's versatility.
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TL;DR: In this article, the basics of pulsed thermal nondestructive testing (TNDT) including theoretical solutions, data processing algorithms and practical implementation are discussed along with 1D analytical and multi-dimensional numerical solutions.
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241 citations
TL;DR: This review article outlines the technological bottlenecks that have been overcome which have made biomedical terahertz research possible and the limitations that remain.
Abstract: Interest in biomedical terahertz research is growing rapidly and there are now several terahertz groups in Asia, Europe and the US investigating potential applications such as pharmaceutical quality control, protein characterization and cancer detection. This review article outlines the technological bottlenecks that have been overcome which have made biomedical terahertz research possible. Key research findings will be presented, and the limitations that remain and the research initiatives that strive to address them will also be discussed.
136 citations