The complex frequency-dependent electromagnetic physics on rough samples is prohibitive for analytical and even numerical minimization based material extraction methods for THz time-domain spectrometers. To deal with such nonlinear complexity, we resort to machine learning (ML) Gated Recurrent Unit (GRU) alongside 3-D printing and automatic THz time-domain imaging to demonstrate the ability to extract the complex refractive index of materials from transmission measurements without prior knowledge of the sample’s thickness or the surface roughness properties, even in regimes where perturbation theory is not valid. The ML methodology is first validated with smooth samples of varying thicknesses from five types of indoor materials (wood, engineered wood, plastic, stone, and glass); mean squared error (MSE) for these smooth samples is in the range of 10$^{-5}$–10$^{-6}$, which is at least one order of magnitude lower than that of convolutional neural network (CNN) and linear models trained with the same number of epochs. Then, three different 3-D printable materials are used to construct 12 rough samples with spatial correlation length of 0.2 mm (drawn from Gaussian or exponential distribution) and root mean square surface roughness varying from 0.2 to 0.4 mm. While a numerical minimization based extraction algorithm fails to provide good results, the GRU successfully retrieves the material properties of the sample with MSEs for these rough samples still in the range of 10$^{-5}$–10$^{-6}$, again outperforming CNN and linear models proposed in the literature.
{"title":"Deep Learning for Scattering Robust TeraHertz Time Domain Spectroscopy","authors":"Yeganeh Farahi;Nikolas Hadjiantoni;Nicholas Klokkou;Vasilis Apostolopoulos;Miguel Navarro-Cía","doi":"10.1109/TTHZ.2025.3620486","DOIUrl":"https://doi.org/10.1109/TTHZ.2025.3620486","url":null,"abstract":"The complex frequency-dependent electromagnetic physics on rough samples is prohibitive for analytical and even numerical minimization based material extraction methods for THz time-domain spectrometers. To deal with such nonlinear complexity, we resort to machine learning (ML) Gated Recurrent Unit (GRU) alongside 3-D printing and automatic THz time-domain imaging to demonstrate the ability to extract the complex refractive index of materials from transmission measurements without prior knowledge of the sample’s thickness or the surface roughness properties, even in regimes where perturbation theory is not valid. The ML methodology is first validated with smooth samples of varying thicknesses from five types of indoor materials (wood, engineered wood, plastic, stone, and glass); mean squared error (MSE) for these smooth samples is in the range of 10<inline-formula><tex-math>$^{-5}$</tex-math></inline-formula>–10<inline-formula><tex-math>$^{-6}$</tex-math></inline-formula>, which is at least one order of magnitude lower than that of convolutional neural network (CNN) and linear models trained with the same number of epochs. Then, three different 3-D printable materials are used to construct 12 rough samples with spatial correlation length of 0.2 mm (drawn from Gaussian or exponential distribution) and root mean square surface roughness varying from 0.2 to 0.4 mm. While a numerical minimization based extraction algorithm fails to provide good results, the GRU successfully retrieves the material properties of the sample with MSEs for these rough samples still in the range of 10<inline-formula><tex-math>$^{-5}$</tex-math></inline-formula>–10<inline-formula><tex-math>$^{-6}$</tex-math></inline-formula>, again outperforming CNN and linear models proposed in the literature.","PeriodicalId":13258,"journal":{"name":"IEEE Transactions on Terahertz Science and Technology","volume":"16 3","pages":"247-257"},"PeriodicalIF":3.9,"publicationDate":"2025-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146216620","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-10-07DOI: 10.1109/TTHZ.2025.3618946
Zhaoxin Guo;Juntai Xu;Dongwei Zhai;Bing Teng
In this work, we used a silicon-based waveguide technique that can be easily employed with common THz time-domain spectroscopy setups and enable the characterization of the indium tin oxide (ITO) nanostructured samples with great precision. We were measuring the so-called M-line spectrum of the device when guide modes are excited in the silicon waveguide, thanks to a grating coupler engraved at its top surface. When a 418.8-nm-thick ITO sample is deposited on the waveguide, we observed a 9-GHz-frequency shift of the 5 GHz-full width at the half maxima M-lines and a 27-times transmission ratio at 0.644 THz. Over 0.1–1 THz, we carefully extracted the complex refractive index and permittivity by fitting the recorded curves with differential methods. By defining a 2-D error function, we gave the frequency-dependent experimental error bar with great precision. The conductivity is then calculated and fitted with the Drude–Smith model. The so-determined conductivity shows a nice dielectric property, which is due to the large carrier concentration ($N=text{1.21}times {text{10}}^{text{19}}$ cm$^{-3}$) in such ITO nanostructured material. The carrier lifetime (41 fs) is linked to the morphology of the structure, which offers an ultrafast dielectric response. Our work indicates that waveguide-coupled terahertz spectroscopy at guided frequencies provides a more precise characterization of the optoelectronic parameters of ITO nanostructured materials, which will serve as a crucial supplement in the development of ITO nanostructures for advanced functional devices.
{"title":"Superprecision Characterization of ITO Nanostructured Material by Waveguide Coupled Terahertz Time-Domain Spectroscopy","authors":"Zhaoxin Guo;Juntai Xu;Dongwei Zhai;Bing Teng","doi":"10.1109/TTHZ.2025.3618946","DOIUrl":"https://doi.org/10.1109/TTHZ.2025.3618946","url":null,"abstract":"In this work, we used a silicon-based waveguide technique that can be easily employed with common THz time-domain spectroscopy setups and enable the characterization of the indium tin oxide (ITO) nanostructured samples with great precision. We were measuring the so-called M-line spectrum of the device when guide modes are excited in the silicon waveguide, thanks to a grating coupler engraved at its top surface. When a 418.8-nm-thick ITO sample is deposited on the waveguide, we observed a 9-GHz-frequency shift of the 5 GHz-full width at the half maxima M-lines and a 27-times transmission ratio at 0.644 THz. Over 0.1–1 THz, we carefully extracted the complex refractive index and permittivity by fitting the recorded curves with differential methods. By defining a 2-D error function, we gave the frequency-dependent experimental error bar with great precision. The conductivity is then calculated and fitted with the Drude–Smith model. The so-determined conductivity shows a nice dielectric property, which is due to the large carrier concentration (<inline-formula><tex-math>$N=text{1.21}times {text{10}}^{text{19}}$</tex-math></inline-formula> cm<inline-formula><tex-math>$^{-3}$</tex-math></inline-formula>) in such ITO nanostructured material. The carrier lifetime (41 fs) is linked to the morphology of the structure, which offers an ultrafast dielectric response. Our work indicates that waveguide-coupled terahertz spectroscopy at guided frequencies provides a more precise characterization of the optoelectronic parameters of ITO nanostructured materials, which will serve as a crucial supplement in the development of ITO nanostructures for advanced functional devices.","PeriodicalId":13258,"journal":{"name":"IEEE Transactions on Terahertz Science and Technology","volume":"16 1","pages":"68-75"},"PeriodicalIF":3.9,"publicationDate":"2025-10-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145778308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-10-03DOI: 10.1109/TTHZ.2025.3617783
Lucy A. Downes;Charles Stuart Adams;Kevin J. Weatherill
We present a temporally multiplexed dual-color terahertz (THz) imaging technique using THz-to-optical conversion in atomic vapor. By rapidly alternating the pump laser frequency, we sequentially excite two atomic states, each absorbing a different THz frequency: 0.5 and 1.1 THz. Each THz field induces optical fluorescence at a distinct wavelength, enabling the creation of a sequence of alternating, interleaved images for each frequency. Synchronizing the laser switching with camera acquisition allows video capture at 1000 frames per second for both frequencies. The system’s speed is limited only by laser power and fibre switching hardware. The presented method can be scaled to image more THz frequencies through the addition of further laser frequencies, paving the way for THz hyperspectral imaging in many real-world settings.
{"title":"Temporally Multiplexed Dual-Frequency Terahertz Imaging at Kilohertz Frame Rates","authors":"Lucy A. Downes;Charles Stuart Adams;Kevin J. Weatherill","doi":"10.1109/TTHZ.2025.3617783","DOIUrl":"https://doi.org/10.1109/TTHZ.2025.3617783","url":null,"abstract":"We present a temporally multiplexed dual-color terahertz (THz) imaging technique using THz-to-optical conversion in atomic vapor. By rapidly alternating the pump laser frequency, we sequentially excite two atomic states, each absorbing a different THz frequency: 0.5 and 1.1 THz. Each THz field induces optical fluorescence at a distinct wavelength, enabling the creation of a sequence of alternating, interleaved images for each frequency. Synchronizing the laser switching with camera acquisition allows video capture at 1000 frames per second for both frequencies. The system’s speed is limited only by laser power and fibre switching hardware. The presented method can be scaled to image more THz frequencies through the addition of further laser frequencies, paving the way for THz hyperspectral imaging in many real-world settings.","PeriodicalId":13258,"journal":{"name":"IEEE Transactions on Terahertz Science and Technology","volume":"16 2","pages":"151-155"},"PeriodicalIF":3.9,"publicationDate":"2025-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=11192672","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146102958","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-10-02DOI: 10.1109/TTHZ.2025.3617144
Jiameng Wang;Kangmin Zhou;Bowen Fan;Zhi Li;Jie Hu;Qiang Zhi;Siyuan Zhao;Jing Li;Shengcai Shi
With moderate cooling requirements, YBCO-based superconducting detectors are promising for space applications from microwave to the terahertz regime. Their sensitivities, however, are still rather limited. The dielectric loss of the substrate on which YBCO films are deposited might play an important role in the detector performance. This study systematically characterizes the dielectric properties of three common commercially available substrates for YBCO film, i.e., Sapphire (Al2O3), Lanthanum aluminate (LaAlO3), and Magnesium oxide (MgO), from 0.22 to 3 THz at 300, 77, and 20 K. It has been found that both Al2O3 and MgO substrates exhibit significantly reduced loss tangents (tanδ < 1×10-5) at cryogenic temperatures (77 and 20 K), whereas LaAlO3 maintains high dielectric loss tangents (tanδ > 3×10-3) across all measured temperatures and frequencies.
{"title":"Dielectric Properties of MgO, Al2O3, and LaAlO3 From 0.22 to 3 THz at Different Temperatures","authors":"Jiameng Wang;Kangmin Zhou;Bowen Fan;Zhi Li;Jie Hu;Qiang Zhi;Siyuan Zhao;Jing Li;Shengcai Shi","doi":"10.1109/TTHZ.2025.3617144","DOIUrl":"https://doi.org/10.1109/TTHZ.2025.3617144","url":null,"abstract":"With moderate cooling requirements, YBCO-based superconducting detectors are promising for space applications from microwave to the terahertz regime. Their sensitivities, however, are still rather limited. The dielectric loss of the substrate on which YBCO films are deposited might play an important role in the detector performance. This study systematically characterizes the dielectric properties of three common commercially available substrates for YBCO film, i.e., Sapphire (Al<sub>2</sub>O<sub>3</sub>), Lanthanum aluminate (LaAlO<sub>3</sub>), and Magnesium oxide (MgO), from 0.22 to 3 THz at 300, 77, and 20 K. It has been found that both Al<sub>2</sub>O<sub>3</sub> and MgO substrates exhibit significantly reduced loss tangents (tanδ < 1×10<sup>-5</sup>) at cryogenic temperatures (77 and 20 K), whereas LaAlO<sub>3</sub> maintains high dielectric loss tangents (tanδ > 3×10<sup>-3</sup>) across all measured temperatures and frequencies.","PeriodicalId":13258,"journal":{"name":"IEEE Transactions on Terahertz Science and Technology","volume":"16 3","pages":"213-222"},"PeriodicalIF":3.9,"publicationDate":"2025-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146216627","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-10-02DOI: 10.1109/TTHZ.2025.3617172
Valeri A. Mikhnev;Dmytro B. But;Tommaso Zugno;Mate Boban;Josef Eichinger;Wojciech Knap
Thanks to large available bandwidths and unique propagation characteristics, terahertz (THz) communication systems offer the potential for high-throughput, low-latency communications, while also enabling precise sensing capabilities. The accurate modeling of THz channels in indoor environments—such as offices, meeting rooms, hallways, and living rooms—requires precise knowledge of the dielectric properties of common building materials. In this article, we present the characterization of the most common building materials between 100 and 400 GHz, including window glass, ceiling board, floorboard, wood, plywood, plasterboard, brick, marble, concrete, and chipboard samples. Our measurements have been carried out using a custom setup based on a state-of-the-art frequency-domain spectroscopy system. To ensure an accurate material characterization, we developed a custom beam-guide fixture and an ad hoc signal processing pipeline. Using our measurements, we extend the ITU-R P.2040 model by deriving custom parameters to describe the dielectric properties of these materials. The results of this study contribute to the improved modeling of wireless channels at sub-THz frequencies.
{"title":"THz-FDS Characterization of Building Materials and Extension of the ITU-R P.2040 Model for Sub-THz Frequencies","authors":"Valeri A. Mikhnev;Dmytro B. But;Tommaso Zugno;Mate Boban;Josef Eichinger;Wojciech Knap","doi":"10.1109/TTHZ.2025.3617172","DOIUrl":"https://doi.org/10.1109/TTHZ.2025.3617172","url":null,"abstract":"Thanks to large available bandwidths and unique propagation characteristics, terahertz (THz) communication systems offer the potential for high-throughput, low-latency communications, while also enabling precise sensing capabilities. The accurate modeling of THz channels in indoor environments—such as offices, meeting rooms, hallways, and living rooms—requires precise knowledge of the dielectric properties of common building materials. In this article, we present the characterization of the most common building materials between 100 and 400 GHz, including window glass, ceiling board, floorboard, wood, plywood, plasterboard, brick, marble, concrete, and chipboard samples. Our measurements have been carried out using a custom setup based on a state-of-the-art frequency-domain spectroscopy system. To ensure an accurate material characterization, we developed a custom beam-guide fixture and an ad hoc signal processing pipeline. Using our measurements, we extend the ITU-R P.2040 model by deriving custom parameters to describe the dielectric properties of these materials. The results of this study contribute to the improved modeling of wireless channels at sub-THz frequencies.","PeriodicalId":13258,"journal":{"name":"IEEE Transactions on Terahertz Science and Technology","volume":"15 6","pages":"985-995"},"PeriodicalIF":3.9,"publicationDate":"2025-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145435691","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-10-01DOI: 10.1109/TTHZ.2025.3616808
Umair Rafique;Mourad Elkailech;Kimmo Rasilainen;Jiangcheng Chen;Asad Husein;Dániel Sebök;Imre Szenti;Sami Myllymäki;Marko E. Leinonen;Aarno Pärssinen;Ákos Kukovecz;Krisztian Kordas;Ping Jack Soh
This article describes the design, fabrication process, and operation of an extended hemispherical low-permittivity lens antenna for subterahertz (sub-THz) frequency bands to alleviate some of the performance limitations seen with high-permittivity (e.g., silicon) lenses. The proposed lens concept is intended to enhance the radiation characteristics of an on-chip antenna designed on a high-permittivity substrate: customized matching layers are placed between the low-permittivity lens and the source that provide a smooth permittivity transition (from high to low) toward the air interface to improve radiation characteristics and impedance matching. The permittivity of each matching layer and the lens is obtained using the theory of reflections at multiple interfaces. For proof of concept, the lens is illuminated with a WR-3.4 rectangular waveguide (RWG) that is placed at an optimized distance to obtain optimal impedance matching at 220–330 GHz and a high directivity ($>$22 dBi). By customizing the material and layer properties, the proposed lens concept can be made compatible with different semiconductor technologies. To verify the performed simulations, a prototype of the lens antenna was fabricated and measured, with a good agreement observed between both results. Additionally, a study was conducted to observe the beamsteering characteristics of the designed lens in the $E$- and $H$-planes. Results indicate beamsteering capability in the range of $pm 19^circ$–21$^circ$ with a maximum scan loss of 5.5 and 4.5 dB in the $E$- and $H$-planes, respectively.
{"title":"Design and Characterization of a Sub-THz Lens Antenna Based on Customized Composite Materials","authors":"Umair Rafique;Mourad Elkailech;Kimmo Rasilainen;Jiangcheng Chen;Asad Husein;Dániel Sebök;Imre Szenti;Sami Myllymäki;Marko E. Leinonen;Aarno Pärssinen;Ákos Kukovecz;Krisztian Kordas;Ping Jack Soh","doi":"10.1109/TTHZ.2025.3616808","DOIUrl":"https://doi.org/10.1109/TTHZ.2025.3616808","url":null,"abstract":"This article describes the design, fabrication process, and operation of an extended hemispherical low-permittivity lens antenna for subterahertz (sub-THz) frequency bands to alleviate some of the performance limitations seen with high-permittivity (e.g., silicon) lenses. The proposed lens concept is intended to enhance the radiation characteristics of an on-chip antenna designed on a high-permittivity substrate: customized matching layers are placed between the low-permittivity lens and the source that provide a smooth permittivity transition (from high to low) toward the air interface to improve radiation characteristics and impedance matching. The permittivity of each matching layer and the lens is obtained using the theory of reflections at multiple interfaces. For proof of concept, the lens is illuminated with a WR-3.4 rectangular waveguide (RWG) that is placed at an optimized distance to obtain optimal impedance matching at 220–330 GHz and a high directivity (<inline-formula><tex-math>$>$</tex-math></inline-formula>22 dBi). By customizing the material and layer properties, the proposed lens concept can be made compatible with different semiconductor technologies. To verify the performed simulations, a prototype of the lens antenna was fabricated and measured, with a good agreement observed between both results. Additionally, a study was conducted to observe the beamsteering characteristics of the designed lens in the <inline-formula><tex-math>$E$</tex-math></inline-formula>- and <inline-formula><tex-math>$H$</tex-math></inline-formula>-planes. Results indicate beamsteering capability in the range of <inline-formula><tex-math>$pm 19^circ$</tex-math></inline-formula>–21<inline-formula><tex-math>$^circ$</tex-math></inline-formula> with a maximum scan loss of 5.5 and 4.5 dB in the <inline-formula><tex-math>$E$</tex-math></inline-formula>- and <inline-formula><tex-math>$H$</tex-math></inline-formula>-planes, respectively.","PeriodicalId":13258,"journal":{"name":"IEEE Transactions on Terahertz Science and Technology","volume":"15 6","pages":"963-975"},"PeriodicalIF":3.9,"publicationDate":"2025-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=11186145","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145435674","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This article presents an efficient continuous-wave THz computed tomography, which can be achieved based on the utilization of deep learning approach together with object shape information. A modified U-Net architecture that can incorporate object shape information was proposed to mitigate effects due to several wave phenomena arising during measurements, such as reflection, refraction, diffraction, or large beam geometry. This is beneficial for most conventional tomographic reconstruction techniques, which, while computationally efficient, struggle to achieve high image quality due to their assumption of straight and narrow ray wave propagation that overlooks such effects and results in strong artifacts in the reconstructed images. The proposed method was evaluated on various sample geometries and materials, and its performance was also compared with other similar deep learning architectures. Results show significant improvements both in terms of image appearance and structural similarity index measure (SSIM). The SSIM values range from 0.681 to 0.953, and from 0.599 to 0.890, for image reconstructions in simple and complex cases, respectively. The proposed method effectively mitigates boundary artifacts and enhances overall image appearance compared with cases where measurements are transformed by other similar deep learning architectures. This suggests its potential as an efficient THz computed tomography technique for nondestructive testing applications.
{"title":"Deep Learning Network With Object Shape Information for Efficient Continuous-Wave THz Computed Tomography","authors":"Rungroj Jintamethasawat;Sirawit Inpuak;Kan Kaewhanam;Manassanan Nilruang;Praewa Choobanna;Kanit Bunyinkgool;Chaiwoot Boonyasiriwat","doi":"10.1109/TTHZ.2025.3615105","DOIUrl":"https://doi.org/10.1109/TTHZ.2025.3615105","url":null,"abstract":"This article presents an efficient continuous-wave THz computed tomography, which can be achieved based on the utilization of deep learning approach together with object shape information. A modified U-Net architecture that can incorporate object shape information was proposed to mitigate effects due to several wave phenomena arising during measurements, such as reflection, refraction, diffraction, or large beam geometry. This is beneficial for most conventional tomographic reconstruction techniques, which, while computationally efficient, struggle to achieve high image quality due to their assumption of straight and narrow ray wave propagation that overlooks such effects and results in strong artifacts in the reconstructed images. The proposed method was evaluated on various sample geometries and materials, and its performance was also compared with other similar deep learning architectures. Results show significant improvements both in terms of image appearance and structural similarity index measure (SSIM). The SSIM values range from 0.681 to 0.953, and from 0.599 to 0.890, for image reconstructions in simple and complex cases, respectively. The proposed method effectively mitigates boundary artifacts and enhances overall image appearance compared with cases where measurements are transformed by other similar deep learning architectures. This suggests its potential as an efficient THz computed tomography technique for nondestructive testing applications.","PeriodicalId":13258,"journal":{"name":"IEEE Transactions on Terahertz Science and Technology","volume":"16 3","pages":"223-233"},"PeriodicalIF":3.9,"publicationDate":"2025-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146216641","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In this article, we report the development of an optical system for a 600-GHz gyrotron, which was developed as a light source for electromagnetic field exposure experiments to conduct exposure assessment and investigate the biological effects of the terahertz wave. In this study, we employed triaxial elliptical mirrors to shape the elliptical beam emitted from the gyrotron. The radiation from the optical system was measured and compared with the design value. Furthermore, stable irradiation power control was demonstrated without any change in the gyrotron operating conditions by integrating an irradiation power control module consisting of three wire grids into the beamline.
{"title":"Development of a 600-GHz Optical System for Electromagnetic Field Exposure Assessment Using a Gyrotron","authors":"Masafumi Fukunari;Maya Mizuno;Yoshinori Tatematsu;Yuusuke Yamaguchi;Shota Yamazaki;Tomoaki Nagaoka","doi":"10.1109/TTHZ.2025.3608314","DOIUrl":"https://doi.org/10.1109/TTHZ.2025.3608314","url":null,"abstract":"In this article, we report the development of an optical system for a 600-GHz gyrotron, which was developed as a light source for electromagnetic field exposure experiments to conduct exposure assessment and investigate the biological effects of the terahertz wave. In this study, we employed triaxial elliptical mirrors to shape the elliptical beam emitted from the gyrotron. The radiation from the optical system was measured and compared with the design value. Furthermore, stable irradiation power control was demonstrated without any change in the gyrotron operating conditions by integrating an irradiation power control module consisting of three wire grids into the beamline.","PeriodicalId":13258,"journal":{"name":"IEEE Transactions on Terahertz Science and Technology","volume":"16 1","pages":"27-34"},"PeriodicalIF":3.9,"publicationDate":"2025-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=11176984","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145778368","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-23DOI: 10.1109/TTHZ.2025.3610193
Jessica F. Smith;Martynas Beresna;Irshaad Fatadin;Wanvisa Talataisong;Natthawat Phanchat;Robert Ferguson;Mira Naftaly;Gilberto Brambilla
Terahertz (THz) frequencies have become a promising candidate for sixth-generation communications technology due to the large continuous bandwidths available allowing for a large increase in a peak data rate, compared to frequencies currently utilized in fifth generation. As THz over-the-air (OTA) signals are blocked by environmental obstacles such as building walls, short lengths (<5>−2, which is below the soft-decision forward error correction threshold of 2.7 × 10−2. This was achieved by transmitting the signal first through the THz fiber and then OTA over a ∼1.7-m non-line-of-sight beam path. To the best of our knowledge, this is the first published demonstration of a hybrid fiber-to-OTA beam path at 250 GHz.
{"title":"60-Gbit/s THz Communication Hybrid Propagation Through Hollow-Core Fiber and Over the Air","authors":"Jessica F. Smith;Martynas Beresna;Irshaad Fatadin;Wanvisa Talataisong;Natthawat Phanchat;Robert Ferguson;Mira Naftaly;Gilberto Brambilla","doi":"10.1109/TTHZ.2025.3610193","DOIUrl":"https://doi.org/10.1109/TTHZ.2025.3610193","url":null,"abstract":"Terahertz (THz) frequencies have become a promising candidate for sixth-generation communications technology due to the large continuous bandwidths available allowing for a large increase in a peak data rate, compared to frequencies currently utilized in fifth generation. As THz over-the-air (OTA) signals are blocked by environmental obstacles such as building walls, short lengths (<5>−2</sup>, which is below the soft-decision forward error correction threshold of 2.7 × 10<sup>−2</sup>. This was achieved by transmitting the signal first through the THz fiber and then OTA over a ∼1.7-m non-line-of-sight beam path. To the best of our knowledge, this is the first published demonstration of a hybrid fiber-to-OTA beam path at 250 GHz.","PeriodicalId":13258,"journal":{"name":"IEEE Transactions on Terahertz Science and Technology","volume":"15 6","pages":"1033-1040"},"PeriodicalIF":3.9,"publicationDate":"2025-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145435687","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2025-09-16DOI: 10.1109/TTHZ.2025.3609821
Arash Karimi;Zachery B. Harris;Erica Heller;Paul Vahey;M. Hassan Arbab
Coating thickness measurement and inspection of defects beneath optically opaque surfaces are among the most promising commercial applications of the terahertz (THz) imaging technology. However, there are two main sources of complexity in THz spectral measurements that have resulted in reduced accuracy and high uncertainty in the determination of coating thicknesses. These factors include: The need for a priori knowledge of the complex index of refraction of each coating layer, and the complex and polarization-sensitive reflectivity of samples with carbon-fiber-reinforced polymer substrates. In this article, we propose a combined hardware and software solution to address these two limitations. We employ the polarimetric version of our portable handheld spectral reflection scanner and use a novel training model on time-of-flight measurements obtained by sparse deconvolution of the THz time-domain pulses. Our method does not depend on separate measurements of the index of refraction of the coating layers; rather, it relies on a physics-based linear model, trained using a small subset of the sample data. We show that thickness measurements with mean square error of about 10 $mu$m and accuracy of more than 90% can be achieved when the useful bandwidth of the scanner is limited to about 1.5 THz using photoconductive antenna emitters and detectors. Finally, we simulated the spectral response of samples with slight variations in the refractive index of the coating sublayers to evaluate the validity of the linear model in extracting the optical properties of individual layers. We show that the anisotropic response of the carbon fiber bundles and the weave pattern structure of the substrate can significantly influence the accuracy of the coating measurement, and therefore, a polarimetric imaging approach should be used for inspection of similar samples.
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