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Millimeter Wave and Terahertz Source, Sensing and Imaging

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Optical Sensors".

Deadline for manuscript submissions: closed (15 July 2024) | Viewed by 16714

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Prof. Dr. Yubin Gong

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Guest Editor

School of Electronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, China
Interests: MMW/THz devices
Special Issues, Collections and Topics in MDPI journals

Dr. Min Hu

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Guest Editor

School of Electronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu 610054, China
Interests: terahertz; vacuum electron devices; near field optics
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Xuyuan Chen

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Guest Editor

Department of Microsystems, University of South-Eastern Norway, 3603 Tønsberg, Norway
Interests: laser displays; MEMS/NEMS; energy storage; supercapacitors; 1/f noise; THz
Special Issues, Collections and Topics in MDPI journals

Dr. Xuequan Chen

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Guest Editor

Great Bay Area Branch of Aerospace Information Research Institute, Chinese Academy of Sciences, Guangzhou 510530, China
Interests: devices; systems and methods for THz applications

Special Issue Information

Dear Colleagues,

Recently, we have seen a number of technical breakthroughs made in millimeter- and terahertz-wave applications, components, sources, and instruments. These have brought terahertz (THz)-wave technologies from laboratory demonstrations to industrial applications such as non-destructive inspection and testing, security scanning, electromagnetic biology effect, medical imaging, disease diagnostics, recognition of protein structural states, measurement techniques for materials science and characterization, monitoring of ultrafast dynamics, short-range communications, etc. To support more emerging applications, worldwide efforts are piling up for continuous technological development which focuses on sources, detectors, imaging arrays, spectrometers, and system integrations.

This Special Issue therefore aims to collect original research and review articles on recent advances and new challenges in the field of Millimeter Wave and Terahertz Sensing and Imaging. We encourage authors to submit original manuscripts with a focus on the topics outlined in the keywords below.

Prof. Dr. Yubin Gong
Dr. Min Hu
Prof. Dr. Xuyuan Chen
Dr. Xuequan Chen
Guest Editors

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Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

new technologies using millimeter and terahertz wave for sensing and imaging
millimeter and terahertz non-destructive testing (NDT)
terahertz- and millimeter-wave technology for materials research
terahertz- and millimeter-wave measurement systems
terahertz sources, detectors, and sensors

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Published Papers (10 papers)

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Research

11 pages, 3441 KiB

Open AccessArticle

THz Polarimetric Imaging of Carbon Fiber-Reinforced Composites Using the Portable Handled Spectral Reflection (PHASR) Scanner

by Kuangyi Xu, Zachery B. Harris, Paul Vahey and M. Hassan Arbab

Sensors 2024, 24(23), 7467; https://doi.org/10.3390/s24237467 - 22 Nov 2024

Cited by 1 | Viewed by 768

Abstract

Recent advancements in novel fiber-coupled and portable terahertz (THz) spectroscopic imaging technology have accelerated applications in nondestructive testing (NDT). Although the polarization information of THz waves can play a critical role in material characterization, there are few demonstrations of polarization-resolved THz imaging as an NDT modality due to the deficiency of such polarimetric imaging devices. In this paper, we have inspected industrial carbon fiber composites using a portable and handheld imaging scanner in which the THz polarizations of two orthogonal channels are simultaneously captured by two photoconductive antennas. We observed significant polarimetric differences between the two-channel images of the same sample and the resulting THz Stokes vectors, which are attributed to the anisotropic conductivity of carbon fiber composites. Using both polarimetric channels, we can visualize the superficial and underlying interfaces of the first laminate. These results pave the way for the future applications of THz polarimetry to the assessment of coatings or surface quality on carbon fiber-reinforced substrates. Full article

(This article belongs to the Special Issue Millimeter Wave and Terahertz Source, Sensing and Imaging)

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9 pages, 5085 KiB

Open AccessCommunication

Research of a 0.14 THz Dual-Cavity Parallel Structure Extended Interaction Oscillator

by Chuanhong Xiao, Ruizhe Ren, Zhenhua Wu, Yijun Li, Qing You, Zongjun Shi, Kaichun Zhang, Xiaoxing Chen, Mingzhou Zhan, Diwei Liu, Renbin Zhong and Shenggang Liu

Sensors 2024, 24(18), 5891; https://doi.org/10.3390/s24185891 - 11 Sep 2024

Viewed by 867

Abstract

This paper presents a method to enhance extended interaction oscillator (EIO) output power based on a dual-cavity parallel structure (DCPS). This stucture consists of two conventional ladder-line structures in parallel through a connecting structure, which improves the coupling efficiency between the cavities. The dual output power fusion structure employs an H-T type combiner as the output coupler, which can effectively combine the two input waves in phase to further increase the output power. The dispersion characteristics, coupling impedance, and field distribution of the DCPS are investigated through numerical and simulation calculations, and the optimal operating parameters and output structure are obtained by PIC simulation. At an operating voltage of 12.6 kV, current density of 200 A/

{cm}^{2}

, and longitudinal magnetic field of 0.5 T, the DCPS EIO exhibits an output power exceeding 600 W at a frequency of 140.6 GHz. This represents a nearly three-fold enhancement compared with the 195 W output of the conventional ladder-line EIO structure. These findings demonstrate the significant improvement in output power and interaction efficiency achieved by the DCPS for the EIO device. Full article

(This article belongs to the Special Issue Millimeter Wave and Terahertz Source, Sensing and Imaging)

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13 pages, 1022 KiB

Open AccessArticle

Unveiling the Terahertz Nano-Fingerprint Spectrum of Single Artificial Metallic Resonator

by Xingxing Xu, Fu Tang, Xiaoqiuyan Zhang and Shenggang Liu

Sensors 2024, 24(18), 5866; https://doi.org/10.3390/s24185866 - 10 Sep 2024

Cited by 1 | Viewed by 1111

Abstract

As artificially engineered subwavelength periodic structures, terahertz (THz) metasurface devices exhibit an equivalent dielectric constant and dispersion relation akin to those of natural materials with specific THz absorption peaks, describable using the Lorentz model. Traditional verification methods typically involve testing structural arrays using reflected and transmitted optical paths. However, directly detecting the dielectric constant of individual units has remained a significant challenge. In this study, we employed a THz time-domain spectrometer-based scattering-type scanning near-field optical microscope (THz-TDS s-SNOM) to investigate the near-field nanoscale spectrum and resonant mode distribution of a single-metal double-gap split-ring resonator (DSRR) and rectangular antenna. The findings reveal that they exhibit a dispersion relation similar to that of natural materials in specific polarization directions, indicating that units of THz metasurface can be analogous to those of molecular structures in materials. This microscopic analysis of the dispersion relation of artificial structures offers new insights into the working mechanisms of THz metasurfaces. Full article

(This article belongs to the Special Issue Millimeter Wave and Terahertz Source, Sensing and Imaging)

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12 pages, 5787 KiB

Open AccessArticle

A Symmetrical Quasi-Synchronous Step-Transition Folded Waveguide Slow Wave Structure for 650 GHz Traveling Wave Tubes

by Duo Xu, Tenglong He, Yuan Zheng, Zhigang Lu, Huarong Gong, Zhanliang Wang, Zhaoyun Duan and Shaomeng Wang

Sensors 2024, 24(16), 5289; https://doi.org/10.3390/s24165289 - 15 Aug 2024

Cited by 1 | Viewed by 957

Abstract

For the purpose of improving performance and reducing the fabrication difficulty of terahertz traveling wave tubes (TWTs), this paper proposes a novel single-section high-gain slow wave structure (SWS), which is named the symmetrical quasi-synchronous step-transition (SQSST) folded waveguide (FW). The SQSST-FW SWS has an artificially designed quasi-synchronous region (QSR) to suppress self-oscillations for sustaining a high gain in an untruncated circuit. Simultaneously, a symmetrical design can improve the efficiency performance to some extent. A prototype of the SQSST-FW SWS for 650 GHz TWTs is designed based on small-signal analysis and numerical simulation. The simulation results indicate that the maximum saturation gain of the designed 650 GHz SQSST-FW TWT is 39.1 dB in a 34.3 mm slow wave circuit, occurring at the 645 GHz point when a 25.4 kV 15 mA electron beam and a 0.43 mW sinusoidal input signal are applied. In addition, a maximum output power exceeding 4 W is observed at the 648 GHz point using the same beam with an increased input power of around 2.8 mW. Full article

(This article belongs to the Special Issue Millimeter Wave and Terahertz Source, Sensing and Imaging)

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9 pages, 4745 KiB

Open AccessCommunication

A Staggered Vane-Shaped Slot-Line Slow-Wave Structure for W-Band Dual-Sheet Electron-Beam-Traveling Wave Tubes

by Yuxin Wang, Jingyu Guo, Yang Dong, Duo Xu, Yuan Zheng, Zhigang Lu, Zhanliang Wang and Shaomeng Wang

Sensors 2024, 24(12), 3709; https://doi.org/10.3390/s24123709 - 7 Jun 2024

Viewed by 1084

Abstract

A staggered vane-shaped slot-line slow-wave structure (SV-SL SWS) for application in W-band traveling wave tubes (TWTs) is proposed in this article. In contrast to the conventional slot-line SWSs with dielectric substrates, the proposed SWS consists only of a thin metal sheet inscribed with periodic grooves and two half-metal enclosures, which means it can be easily manufactured and assembled and has the potential for mass production. This SWS not only solves the problem of the dielectric loading effect but also improves the heat dissipation capability of such structures. Meanwhile, the SWS design presented here covers a −15 dB S₁₁ frequency range from 87.5 to 95 GHz. The 3-D simulation for a TWT based on the suggested SWS is also investigated. Under dual-electron injection conditions with a total voltage of 17.2 kV and a total current of 0.3 A, the maximum output power at 90 GHz is 200 W, with a 3 dB bandwidth up to 4 GHz. With a good potential for fabrication using microfabrication techniques, this structure can be a good candidate for millimeter-wave TWT applications. Full article

(This article belongs to the Special Issue Millimeter Wave and Terahertz Source, Sensing and Imaging)

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10 pages, 3783 KiB

Open AccessCommunication

Resonant Gas Sensing in the Terahertz Spectral Range Using Two-Wire Phase-Shifted Waveguide Bragg Gratings

by Yang Cao, Kathirvel Nallappan, Guofu Xu and Maksim Skorobogatiy

Sensors 2023, 23(20), 8527; https://doi.org/10.3390/s23208527 - 17 Oct 2023

Cited by 3 | Viewed by 1635

Abstract

The development of low-cost sensing devices with high compactness, flexibility, and robustness is of significance for practical applications of optical gas sensing. In this work, we propose a waveguide-based resonant gas sensor operating in the terahertz frequency band. It features micro-encapsulated two-wire plasmonic waveguides and a phase-shifted waveguide Bragg grating (WBG). The modular semi-sealed structure ensures the controllable and efficient interaction between terahertz radiation and gaseous analytes of small quantities. WBG built by superimposing periodical features on one wire shows high reflection and a low transmission coefficient within the grating stopband. Phase-shifted grating is developed by inserting a Fabry–Perot cavity in the form of a straight waveguide section inside the uniform gratings. Its spectral response is optimized for sensing by tailoring the cavity length and the number of grating periods. Gas sensor operating around 140 GHz, featuring a sensitivity of 144 GHz/RIU to the variation in the gas refractive index, with resolution of 7 × 10⁻⁵ RIU, is developed. In proof-of-concept experiments, gas sensing was demonstrated by monitoring the real-time spectral response of the phase-shifted grating to glycerol vapor flowing through its sealed cavity. We believe that the phase-shifted grating-based terahertz resonant gas sensor can open new opportunities in the monitoring of gaseous analytes. Full article

(This article belongs to the Special Issue Millimeter Wave and Terahertz Source, Sensing and Imaging)

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12 pages, 11463 KiB

Open AccessCommunication

A Novel Staggered Double-Segmented Grating Slow-Wave Structure for 340 GHz Traveling-Wave Tube

by Zechuan Wang, Junwan Zhu, Zhigang Lu, Jingrui Duan, Haifeng Chen, Shaomeng Wang, Zhanliang Wang, Huarong Gong and Yubin Gong

Sensors 2023, 23(10), 4762; https://doi.org/10.3390/s23104762 - 15 May 2023

Cited by 1 | Viewed by 1832

Abstract

In this paper, a novel staggered double-segmented grating slow-wave structure (SDSG-SWS) is developed for wide-band high-power submillimeter wave traveling-wave tubes (TWTs). The SDSG-SWS can be considered as a combination of the sine waveguide (SW) SWS and the staggered double-grating (SDG) SWS; that is, it is obtained by introducing the rectangular geometric ridges of the SDG-SWS into the SW-SWS. Thus, the SDSG-SWS has the advantages of the wide operating band, high interaction impedance, low ohmic loss, low reflection, and ease of fabrication. The analysis for high-frequency characteristics shows that, compared with the SW-SWS, the SDSG-SWS has higher interaction impedance when their dispersions are at the same level, while the ohmic loss for the two SWSs remains basically unchanged. Furthermore, the calculation results of beam–wave interaction show that the output power is above 16.4 W for the TWT using the SDSG-SWS in the range of 316 GHz–405 GHz with a maximum power of 32.8 W occurring at 340 GHz, whose corresponding maximum electron efficiency is 2.84%, when the operating voltage is 19.2 kV and the current is 60 mA. Full article

(This article belongs to the Special Issue Millimeter Wave and Terahertz Source, Sensing and Imaging)

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12 pages, 7092 KiB

Open AccessCommunication

An Angular Radial Extended Interaction Amplifier at the W Band

by Yang Dong, Shaomeng Wang, Jingyu Guo, Zhanliang Wang, Huarong Gong, Zhigang Lu, Zhaoyun Duan and Yubin Gong

Sensors 2023, 23(7), 3517; https://doi.org/10.3390/s23073517 - 28 Mar 2023

Viewed by 1538

Abstract

In this paper, an angular radial extended interaction amplifier (AREIA) that consists of a pair of angular extended interaction cavities is proposed. Both the convergence angle cavity and the divergence angle cavity, which are designed for the converging beam and diverging beam, respectively, are investigated to present the potential of the proposed AREIA. They are proposed and explored to improve the beam–wave interaction capability of W-band extended interaction klystrons (EIKs). Compared to conventional radial cavities, the angular cavities have greatly decreased the ohmic loss area and increased the characteristic impedance. Compared to the sheet beam (0°) cavity, it has been found that the convergence angle cavity has a higher effective impedance and the diverging beam has a weaker space-charge effect under the same ideal electron beam area; the advantages become more obvious as the propagation distance increases. Particle-in-cell (PIC) results have shown that the diverging beam (8°) EIA performs better at an output power of 94 GHz under the condition of lossless, while the converging beam (−2°) EIA has a higher output power of 6.24 kW under the conditions of ohmic loss, an input power of 0.5 W, and an ideal electron beam of 20.5 kV and 1.5 A. When the loss increases and the beam current decreases, the output power of the −2° EIA can be improved by nearly 30% compared to the 0° EIA, and the −2° EIA has a greatly improved beam–wave interaction capacity than conventional EIAs under those conditions. In addition, an angular radial electron gun is designed. Full article

(This article belongs to the Special Issue Millimeter Wave and Terahertz Source, Sensing and Imaging)

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10 pages, 2859 KiB

Open AccessCommunication

Ultrafast Modulation of THz Waves Based on MoTe₂-Covered Metasurface

by Xing Xu, Jing Lou, Mingxin Gao, Shiyou Wu, Guangyou Fang and Yindong Huang

Sensors 2023, 23(3), 1174; https://doi.org/10.3390/s23031174 - 19 Jan 2023

Cited by 5 | Viewed by 2706

Abstract

The sixth generation (6G) communication will use the terahertz (THz) frequency band, which requires flexible regulation of THz waves. For the conventional metallic metasurface, its electromagnetic properties are hard to be changed once after being fabricated. To enrich the modulation of THz waves, we report an all-optically controlled reconfigurable electromagnetically induced transparency (EIT) effect in the hybrid metasurface integrated with a 10-nm thick MoTe₂ film. The experimental results demonstrate that under the excitation of the 800 nm femtosecond laser pulse with pump fluence of 3200 μJ/cm², the modulation depth of THz transmission amplitude at the EIT window can reach 77%. Moreover, a group delay variation up to 4.6 ps is observed to indicate an actively tunable slow light behavior. The suppression and recovery of the EIT resonance can be accomplished within sub-nanoseconds, enabling an ultrafast THz photo-switching and providing a promising candidate for the on-chip devices of the upcoming 6G communication. Full article

(This article belongs to the Special Issue Millimeter Wave and Terahertz Source, Sensing and Imaging)

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12 pages, 6282 KiB

Open AccessArticle

High-Speed THz Time-of-Flight Imaging with Reflective Optics

by Hoseong Yoo, Jangsun Kim and Yeong Hwan Ahn

Sensors 2023, 23(2), 873; https://doi.org/10.3390/s23020873 - 12 Jan 2023

Cited by 6 | Viewed by 3064

Abstract

In this study, we develop a 3D THz time-of-flight (TOF) imaging technique by using reflective optics to preserve the high-frequency components from a THz antenna. We use an Fe:InGaAs/InAlAs emitter containing relatively high-frequency components. THz-TOF imaging with asynchronous optical sampling (ASOPS) enables the rapid scanning of 100 Hz/scan with a time delay span of 100 ps. We characterize the transverse resolution using knife edge tests for a focal length of 5; the Rayleigh resolution has been measured at 1.0 mm at the focal plane. Conversely, the longitudinal resolution is determined by the temporal pulse width, confirmed with various gap structures enclosed by a quartz substrate. The phase analysis reveals that reflected waves from the top interface exhibit a phase shift when the gap is filled by high-indexed materials such as water but shows in-phase behavior when it is filled with air and low-indexed material. Our imaging tool was effective for inspecting the packaged chip with high lateral and longitudinal resolution. Importantly, the phase information in 2D and 3D images is shown to be a powerful tool in identifying the defect—in particular, delamination in the chip—which tends to be detrimental to the packaged chip’s stability. Full article

(This article belongs to the Special Issue Millimeter Wave and Terahertz Source, Sensing and Imaging)

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