Hand-Guided Mobile Terahertz 3D Imaging Platform with Aspherical Telecentric f-θ Optics

High resolution imaging technique will play an essential role in the future smart imaging applications to provide potential solutions for accurate detection, monitoring and classification of the target. The potential of synthetic aperture radar (SAR) systems to acquire high resolution images has opened new frontiers and led to its exploration in new applications. The conventional microwave radar imaging suffers limited range resolution in the sub-millimeter wave range and optical imaging methods are constrained by the diffraction limit. In the terahertz (THz) regime of the spectrum, the SAR systems could be operated in all the weather, all the time and are capable of penetrating through clouds, smoke, dust etc. to achieve high resolution images beyond the diffraction limit. The curved SAR presents a SAR system created by circularly encircling the target scene. The Circular SAR and Spiral SAR which are based on a circular and cylindrical spiral scanning trajectory, respectively are the scanning methods used for curved SAR. In this paper, we have explored a new toolbox that enables the rapid development of near-field THz-SAR imaging systems and generation of large near-field THz imaging scenarios with the goal to support and facilitate data driven research such as deep learning in the THz community through synthetically generated SAR images as well as its potential for THz based high resolution and 2D/3D near-field imaging application. Initially, the potential advantages of THz-SAR over Microwave SAR and optical imaging methods are presented. Further, a frequency modulated continuous wave (FMCW) radar testbed is simulated in multi-input multi-output (MIMO) configuration for the target frequency band. Moreover, the circular and cylindrical SAR scanning methods are explored for near-field imaging of point targets to obtain 2D and 3D THz-SAR images, respectively. Also, the radar images are reconstructed using the Back Propagation and Polar Formatting Algorithms, focusing on short range applications like indoor environments. Finally, the SAR performance evaluation metrics are reported and a roadmap for future work is presented.

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“… 3D live superimposed AR view. [43] FMCW  Integration of FMCW, line scanning optics and position encoder.  Hand guided THz scanner for NDT.…”

Section: B Related Workmentioning

confidence: 99%

Curved Synthetic Aperture Radar for Near-Field Terahertz Imaging

Gezimati

Singh

2023

IEEE Photonics J.

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“…Contactless measurements and, in contrast to X-Ray inspection, the absence of radiation protection requirements make terahertz scanning techniques an important addition to current inspection practices [5]. Typical applications in an industrial context are nondestructive layer thickness determination and defect detection using volumetric imaging [6], [7], [8], [9], [10]. Materials of interest range from ceramics, glass-fiber reinforced composites [2] and plastics [6] over paints and coatings [9] to paper [11] and wood [12].…”

Section: Introductionmentioning

confidence: 99%

A Priori Information and Off-Axis Measurements in Terahertz Tomography

et al. 2023

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Terahertz tomography is a non-contact inspection technique to image objects from multiple angles and reconstruct their 3D volume from intensity and time-of-flight transmission data, without the need for radiation protection measures. Unlike X-rays, terahertz radiation is subject to strong diffraction and refraction when propagating through dielectric materials, which often deteriorate the image reconstruction quality. Our solution to this problem applies ray tracing, considering the beam shape and an a priori model of the sample under investigation to predict the beam paths of the terahertz radiation. We present two reconstruction methods based on the resulting beam path predictions yielding higher image quality. Method 1 filters out beams deviating strongly, thus removing induced artifacts and errors from the reconstruction image. Method 2 employs off-axis measurements that acquire data along the full detection plane and in this way detect even strongly deflected beams. Considering these beams and the information they carry in the reconstruction enhances the image quality. Applying these methods to terahertz tomography, even complicated structures can be imaged. We display the significant enhancements achieved with the two methods by comparing the reconstruction results of different polymeric samples.INDEX TERMS Terahertz radiation, computed tomography, non-destructive testing, a priori information, off-axis measurement, reconstruction algorithms, imaging, time-of-flight, conjugate gradient least square (CGLS).

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“…In our previous work that was presented at the EuMW2021 Conference [12], a highly compact 80 GHz MMIC radar module [13], shown in Fig. 1(b), was used instead of the waveguide integrated components.…”

Section: Introductionmentioning

confidence: 99%

“…We presented the first implementation and evaluation of such a hand-guided volumetric terahertz imaging platform in [12]. In this contribution, we discuss the new improvements on the system.…”

Section: Introductionmentioning

confidence: 99%

Compact hand-guided 3D scanning terahertz sensor platforms with 3D-printed aspherical telecentric f-θ lens

Mohammadzadeh

Hussung

Keil

et al. 2023

Int. J. Microw. Wireless Technol.

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We report on the development of a handheld three-dimensional (3D) terahertz scanning system with an aspherical telecentric 3D-printed f-θ lens using selective laser sintering. The lens covers a broader scan line of 50 mm with its larger aperture, compared to the 20 mm range in our initial work, which was presented at the European Microwave Week 2021. In order to evaluate the adaptability of the optomechanical components with different sensor units, two different integrated frequency-modulated continuous wave radar modules based on monolithic microwave integrated circuit technology, operating in W- and D-bands are tested within the measurement scheme. The optomechanical part consists of a galvanometer scanner mirror and the f-θ lens. The optical system enables B-scans perpendicular to the manual translational movement of the sensor unit by its user. An integrated guiding wheel system with rotary encoder makes it possible to correlate the measurement points to their respective locations, enabling complete 3D volumetric inspection of the corresponding structures, which is particularly useful for the inspection along cracks and welds.

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Hand-Guided Mobile Terahertz 3D Imaging Platform with Aspherical Telecentric f-θ Optics

Cited by 11 publications

References 12 publications

Curved Synthetic Aperture Radar for Near-Field Terahertz Imaging

Curved Synthetic Aperture Radar for Near-Field Terahertz Imaging

A Priori Information and Off-Axis Measurements in Terahertz Tomography

Compact hand-guided 3D scanning terahertz sensor platforms with 3D-printed aspherical telecentric f-θ lens

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