Material Classification for Terahertz Images Based on Neural Networks

Kubiczek, Tobias; Balzer, Jan C.

doi:10.1109/access.2022.3200473

Cited by 11 publications

(9 citation statements)

References 25 publications

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“…Furthermore, the method can be combined with terahertz ellipsometry to determine reference-free material parameters from the images [27]. Additionally, the use of neural networks could enable a classification of the measured material [28].…”

Section: Discussionmentioning

confidence: 99%

3D THz-TDS SAR Imaging by an Inverse Synthetic Cylindrical Aperture

et al. 2023

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Terahertz time-domain spectroscopy (THz-TDS) is a promising tool for high-resolution 3D imaging of objects due to the high center frequency and bandwidth compared to microwave systems. In addition, terahertz waves have a higher penetration depth than visible or near-infrared radiation. Typically, optics are used to focus the terahertz radiation onto an object under test. This limits the imaging capability in the axial dimension to the depth of field and limits simple imaging of complex surfaces. In this work, we adapt a backpropagation algorithm from synthetic aperture radar (SAR) imaging to reconstruct highresolution 3D images from time-domain traces acquired with a lensless THz-TDS system. For this purpose, an inverse cylindrical aperture is used and an equation that describes the maximum achievable resolution as a function of the beam pattern, the bandwidth, and the length of the synthetic aperture is derived. The calculated resolution is 960 µm for the linear dimension of the aperture and 75 µm for the rotationally symmetric dimension of the cylindrical aperture for a bandwidth of 2 THz. The resolving power is verified by measurements on metallic and dielectric objects. In the future, this method can be used for non-destructive testing of objects with complex shaped surfaces and internal structures.INDEX TERMS Synthetic aperture radar, terahertz time-domain spectroscopy, lensless terahertz imaging, radar migration algorithms.

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Section: Discussionmentioning

confidence: 99%

3D THz-TDS SAR Imaging by an Inverse Synthetic Cylindrical Aperture

et al. 2023

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“…Examples of these databases are high-resolution transmission molecular absorption database (HITRAN) [57] and Cologne database for molecular spectroscopy (CDMS) [58]. In the future, these databases will play an important role in the development of new devices and can also be used for material identification by using machine learning [59]. Especially for strongly absorbing samples, systems with a high SNR are needed here.…”

Section: Comparision and Outlookmentioning

confidence: 99%

THz Systems Exploiting Photonics and Communications Technologies

et al. 2023

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Terahertz (THz) systems open up the possibility of new applications of electromagnetic waves. Enormous bandwidths up to several terahertz enable the development of powerful spectroscopy systems that can provide insights into the structure and material of objects with micrometer resolution. New high power and compact THz time-domain spectroscopy (TDS) systems will be presented. The wide bandwidth also enables high-resolution imaging under far-field conditions to analyze arbitrary objects from a distance. In addition, a near-field system-on-a-chip imaging system is presented that achieves a resolution of 10 μm. Additionally, the application of terahertz waves presents challenges due to the low transmit power of the sources, high attenuation in free space, and the high noise figures of the receivers. These challenges can be overcome by antennas with high gain. Since -depending on the application -spatial scanning or focusing in a time-varying direction is required, beam steering is an essential component of many THz systems. In terms of communications, terahertz carrier frequencies offer wide bandwidths, enabling correspondingly high data rates of 100 Gbit/s and more. As a result, the frequency bands between 250 GHz and 450 GHz have already been identified and/or allocated for communication services and are being discussed as a component of 6G mobile communications. Concepts and demonstrations for 6G terahertz mobile communications will be presented. The high bandwidth of terahertz waves can also be used for high-accuracy indoor localization.INDEX TERMS THz time-domain spectroscopy, high average power THz systems, THz far-field imaging, THz near-field imaging, THz communication, THz localization, MTT 70th Anniversary Special Issue.

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“…2. The visualization is for the material COC with the refractive index n = 1.52 (average of [20] and [21]) and the thicknesses d = 1 mm and d = 1.5 mm, respectively. The material losses are neglected.…”

Section: Single Fabry-pérot Resonatormentioning

confidence: 99%

“…Here, manufacturing is carried out by fused deposition modeling (FDM) 3D printing with the material COC. The low broadband absorption of COC, also known as TOPAS, in the terahertz region enables the manufacturing of high quality transmission devices like terahertz optics, waveguides, and filters [20][21][22][23]. Here, the 3D printer Ultimaker S5 is used with a 0.23 mm-diameter nozzle.…”

Section: Fabrication By 3d Printingmentioning

confidence: 99%

A highly frequency-selective 3D printed dielectric structure for the terahertz range

Tobias,

Kevin,

Thorsten

et al. 2023

Preprint

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In this paper, we present a terahertz transmission frequency-selective quasi surface (FSQS) showing strong absorption lines and a periodic band-pass characteristic. The structure is created by the lateral combination of Fabry-Pérot resonators with different thicknesses. The transfer function of the FSQS can be used as a broadband reference for testing the signal integrity of the transmission path for broadband terahertz systems. This is realized by the transfer function which shows a combination of band-pass characteristics and sharp resonances with a theoretical attenuation of more than 80 dB and with quality factors of more than 40,000 for a combination of 36 resonators. One FSQS consisting of a combination of four resonators is 3D printed by fused deposition modeling of a low-loss cyclic olefin copolymer (COC) filament. Finally, we perform a characterization of the 3D printed FSQS with a frequency-domain and a time-domain terahertz spectroscopy system showing an attenuation of more than 42 dB and a quality factor above 100.

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Material Classification for Terahertz Images Based on Neural Networks

Cited by 11 publications

References 25 publications

3D THz-TDS SAR Imaging by an Inverse Synthetic Cylindrical Aperture

3D THz-TDS SAR Imaging by an Inverse Synthetic Cylindrical Aperture

THz Systems Exploiting Photonics and Communications Technologies

A highly frequency-selective 3D printed dielectric structure for the terahertz range

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