Editorial

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2 pages, 188 KiB

Open AccessEditorial

Terahertz Technologies and Its Applications

by Victor Pacheco-Peña

Electronics 2021, 10(3), 268; https://doi.org/10.3390/electronics10030268 - 23 Jan 2021

Cited by 8 | Viewed by 2090

Abstract

The terahertz frequency range (0 [...] Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

Research

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13 pages, 5152 KiB

Open AccessArticle

NDE Terahertz Wave Techniques for Measurement of Defect Detection on Composite Panels of Honeycomb Sandwiches

by Kwang-Hee Im, Sun-Kyu Kim, Jong-An Jung, Young-Tae Cho, Yong-Deuck Woo and Chien-Ping Chiou

Electronics 2020, 9(9), 1360; https://doi.org/10.3390/electronics9091360 - 21 Aug 2020

Cited by 6 | Viewed by 2044

Abstract

Terahertz wave (T-ray) technologies have become a popular topic in scientific research over the last two decades, and can be utilized in nondestructive evaluation (NDE) techniques. This study suggests an optimal scanning technique method for honeycomb sandwich composite panels, where skins were utilized [...] Read more.

Terahertz wave (T-ray) technologies have become a popular topic in scientific research over the last two decades, and can be utilized in nondestructive evaluation (NDE) techniques. This study suggests an optimal scanning technique method for honeycomb sandwich composite panels, where skins were utilized with two different skins, namely, carbon fiber-reinforced plastic (CFRP) skin and glass fiber-reinforced plastic (GFRP) skin, as layers of the panel surfaces. Foreign objects were artificially inserted between the skins and honeycomb cells in the honeycomb sandwich composite panels. For this experiment, optimal T-ray scanning methods were performed to examine defects based on the angle between the one-ply thin fiber skin axis and the angle of the electric field (E-field) according to the amount of conductivity of the honeycomb sandwich composite panels. In order to confirm the fundamental characteristics of the terahertz waves, the refractive index values of the GFRP composites were experimentally obtained and analyzed, with the data agreeing with known solutions. Terahertz waves (T-rays) were shown to have limited penetration in honeycomb sandwich composite panels when utilized with a skin of carbon fibers. Therefore, T-rays were found to interact with the electrical conductivity and electric field direction of honeycomb sandwich composite panels with glass fiber skins. The T-ray images were obtained regardless of the electric field direction and the fiber direction. In the honeycomb sandwich composite panels with carbon fiber skins, the T-ray images with higher signal-to-noise (S/N) ratios depended on the scanning angle between the angle of the carbon fiber and the angle of the electric field. Thus, the angle of optimum detection measurement was confirmed to be 90° between the E-field and the fiber direction, particularly when using a carbon fiber skin. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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8 pages, 2772 KiB

Open AccessArticle

A 350-GHz Coupled Stack Oscillator with −0.8 dBm Output Power in 65-nm Bulk CMOS Process

by Thanh Dat Nguyen and Jong-Phil Hong

Electronics 2020, 9(8), 1214; https://doi.org/10.3390/electronics9081214 - 28 Jul 2020

Cited by 2 | Viewed by 2067

Abstract

This paper presents a push-push coupled stack oscillator that achieves a high output power level at terahertz (THz) wave frequency. The proposed stack oscillator core adopts a frequency selective negative resistance topology to improve negative transconductance at the fundamental frequency and a transformer [...] Read more.

This paper presents a push-push coupled stack oscillator that achieves a high output power level at terahertz (THz) wave frequency. The proposed stack oscillator core adopts a frequency selective negative resistance topology to improve negative transconductance at the fundamental frequency and a transformer connected between gate and drain terminals of cross pair transistors to minimize the power loss at the second harmonic frequency. Next, the phases and the oscillation frequencies between the oscillator cores are locked by employing an inductor of frequency selective negative resistance topology. The proposed topology was implemented in a 65-nm bulk CMOS technology. The highest measured output power is −0.8 dBm at 353.2 GHz while dissipating 205 mW from a 2.8 V supply voltage. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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11 pages, 2648 KiB

Open AccessArticle

Terahertz Displacement Sensing Based on Interface States of Hetero-Structures

by Lan-Lan Xu, Ya-Xian Fan, Huan Liu, Tao Zhang and Zhi-Yong Tao

Electronics 2020, 9(8), 1213; https://doi.org/10.3390/electronics9081213 - 28 Jul 2020

Cited by 3 | Viewed by 1920

Abstract

Herein, we propose a nano displacement sensor based on the interface state of a terahertz hetero-structure waveguide. The waveguide consists of two periodically corrugated metallic tubes with different duty ratios, which can result in similar forbidden bands in their frequency spectra. It was [...] Read more.

Herein, we propose a nano displacement sensor based on the interface state of a terahertz hetero-structure waveguide. The waveguide consists of two periodically corrugated metallic tubes with different duty ratios, which can result in similar forbidden bands in their frequency spectra. It was found that the topological properties of these forbidden bands are different, and the hetero-structure can be formed by connecting these two waveguides. In the hetero-structure waveguide, the interface state of an extraordinary transmission can always arise within the former forbidden bands, the peak frequency of which is highly dependent on the cavity length at the interface of the two periodic waveguides. So, by carefully designing the structure’s topological property, the hetero-structure waveguide can be efficiently used to produce a displacement sensor in the THz frequency range. The simulations show that the resolution of the displacement can be as small as 90 nm and the sensitivity can reach over 1.2 GHz/μm. Such a sensitive interface state of the proposed hetero-structure waveguide will greatly benefit THz applications of functional devices, including not only displacement sensors but also switches with high extinction ratios, tunable narrow-band filters, and frequency division multiplexers. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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13 pages, 4737 KiB

Open AccessArticle

On-Chip Terahertz Detector Designed with Inset-Feed Rectangular Patch Antenna and Catadioptric Lens

by Fan Zhao, Luhong Mao, Weilian Guo, Sheng Xie and Clarence Augustine T. H. Tee

Electronics 2020, 9(6), 1049; https://doi.org/10.3390/electronics9061049 - 24 Jun 2020

Cited by 7 | Viewed by 3171

Abstract

This study proposes an on-chip terahertz (THz) detector designed with on-chip inset-feed rectangular patch antenna and catadioptric lens. The detector incorporates a dual antenna and dual NMOSFET structure. Radiation efficiency of the antenna reached 89.4% with 6.89 dB gain by optimizing the antenna [...] Read more.

This study proposes an on-chip terahertz (THz) detector designed with on-chip inset-feed rectangular patch antenna and catadioptric lens. The detector incorporates a dual antenna and dual NMOSFET structure. Radiation efficiency of the antenna reached 89.4% with 6.89 dB gain by optimizing the antenna inset-feed and micro-strip line sizes. Simulated impedance was 85.55 − j19.81 Ω, and the impedance of the antenna with the ZEONEX horn-like catadioptric lens was 117.03 − j20.28 Ω. Maximum analyzed gain of two on-chip antennas with catadioptric lens was 17.14 dB resonating at 267 GHz. Maximum experimental gain of two on-chip patch antennas was 4.5 dB at 260 GHz, increasing to 10.67 dB at 250 GHz with the catadioptric lens. The proposed on-chip rectangular inset-feed patch antenna has a simple structure, compatible with CMOS processing and easily implemented. The horn-like catadioptric lens was integrated into the front end of the detector chip and hence is easily molded and manufactured, and it effectively reduced terahertz power absorption by the chip substrate. This greatly improved the detector responsivity and provided very high gain. Corresponding detector voltage responsivity with and without the lens was 95.67 kV/W with NEP = 12.8 pW/Hz^0.5 at 250 GHz, and 19.2 kV/W with NEP = 67.2 pW/Hz^0.5 at 260 GHz, respectively. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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11 pages, 2980 KiB

Open AccessArticle

Terahertz Synthetic Aperture Imaging with a Light Field Imaging System

by Nanfang Lyu, Jian Zuo, Yuanmeng Zhao and Cunlin Zhang

Electronics 2020, 9(5), 830; https://doi.org/10.3390/electronics9050830 - 18 May 2020

Cited by 7 | Viewed by 2717

Abstract

In terahertz imaging systems based on Gaussian beam active illumination and focal plane array detectors, severe image distortion has been observed, which significantly reduces the resolving power of the imaging system. To solve this problem, a novel computational method, Light Field Imaging (LFI), [...] Read more.

In terahertz imaging systems based on Gaussian beam active illumination and focal plane array detectors, severe image distortion has been observed, which significantly reduces the resolving power of the imaging system. To solve this problem, a novel computational method, Light Field Imaging (LFI), has been introduced for terahertz imaging. A conventional transmission-type terahertz imaging system based on a gas-pumped terahertz source and terahertz Focal Plane Array Detectors (FPA) arrays is established to analyze the problem of image distortion. An experimental virtual camera array terahertz LFI system is also established. With the acquisition and reconstruction of synthetic aperture terahertz light fields, the improvement on resolving power and SNR performance have been validated. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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11 pages, 4169 KiB

Open AccessEditor’s ChoiceArticle

Application of Terahertz Spectroscopy to Rubber Products: Evaluation of Vulcanization and Silica Macro Dispersion

by Yasuyuki Hirakawa, Yuki Yasumoto, Toyohiko Gondo, Ryota Sone, Toshiaki Morichika, Takakazu Minato and Masahiro Hojo

Electronics 2020, 9(4), 669; https://doi.org/10.3390/electronics9040669 - 20 Apr 2020

Cited by 3 | Viewed by 2352

Abstract

Industrial applications of terahertz (THz) technology are becoming more widespread. In particular, novel evaluation methods for essential rubber products are being developed. THz absorbance spectra of various rubber polymers and reagents enable visualization of filler dispersions and vulcanization reactions. Here, improved visualization of [...] Read more.

Industrial applications of terahertz (THz) technology are becoming more widespread. In particular, novel evaluation methods for essential rubber products are being developed. THz absorbance spectra of various rubber polymers and reagents enable visualization of filler dispersions and vulcanization reactions. Here, improved visualization of the vulcanization reaction in thick rubber samples is discussed. Silica macro-dispersion is also analyzed because it is a general filler in automobile tires and has been difficult to evaluate with conventional techniques. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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10 pages, 2792 KiB

Open AccessArticle

Nondestructive Testing of Hollowing Deterioration of the Yungang Grottoes Based on THz-TDS

by Ju Feng, Tianhua Meng, Yuhe Lu, Jianguang Ren, Guozhong Zhao, Hongmei Liu, Jin Yang and Rong Huang

Electronics 2020, 9(4), 625; https://doi.org/10.3390/electronics9040625 - 09 Apr 2020

Cited by 6 | Viewed by 2369

Abstract

Terahertz (THz) spectroscopy is an important method in noninvasive detection and diagnosis for historic relics. A new nondestructive testing (NDT) method based on terahertz time-domain spectroscopy (THz-TDS) technology was developed to measure the hollowing deterioration of the Yungang Grottoes in this paper. Hollowing [...] Read more.

Terahertz (THz) spectroscopy is an important method in noninvasive detection and diagnosis for historic relics. A new nondestructive testing (NDT) method based on terahertz time-domain spectroscopy (THz-TDS) technology was developed to measure the hollowing deterioration of the Yungang Grottoes in this paper. Hollowing deterioration samples were strictly prepared, and a series of experiments were conducted to ensure the representativeness of the experimental results. A hollowing thickness model was established by the relationship between the thickness of the hollowing deterioration sample and the time difference of the front flaked stone surface and the stone wall surface of the hollowing deterioration samples. The results show that the R-squared value of the model equation reached 0.99795, which implies that this model is reliable. Therefore, the actual hollowing thickness of the Yungang Grottoes can be obtained by substituting the time difference in the proposed thickness hollowing model, where the time difference is obtained from measured THz spectra. The detection method of stone relic hollowing deterioration is easy to apply, which can not only realize qualitative NDT but also quantitative hollowing deterioration thickness determination. This method has crucial practical significance for the repair and strengthening of stone relics similar to the Yungang Grottoes. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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10 pages, 1943 KiB

Open AccessArticle

Improved InGaAs and InGaAs/InAlAs Photoconductive Antennas Based on (111)-Oriented Substrates

by Kirill Kuznetsov, Aleksey Klochkov, Andrey Leontyev, Evgeniy Klimov, Sergey Pushkarev, Galib Galiev and Galiya Kitaeva

Electronics 2020, 9(3), 495; https://doi.org/10.3390/electronics9030495 - 17 Mar 2020

Cited by 10 | Viewed by 4022

Abstract

The terahertz wave generation by spiral photoconductive antennas fabricated on low-temperature In_0.5Ga_0.5As films and In_0.5Ga_0.5As/In_0.5Al_0.5As superlattices is studied by the terahertz time-domain spectroscopy method. The structures were obtained by molecular beam [...] Read more.

The terahertz wave generation by spiral photoconductive antennas fabricated on low-temperature In_0.5Ga_0.5As films and In_0.5Ga_0.5As/In_0.5Al_0.5As superlattices is studied by the terahertz time-domain spectroscopy method. The structures were obtained by molecular beam epitaxy on GaAs and InP substrates with surface crystallographic orientations of (100) and (111)A. The pump-probe measurements in the transmission geometry and Hall effect measurements are used to characterize the properties of LT-InGaAs and LT-InGaAs/InAlAs structures. It is found that the terahertz radiation power is almost four times higher for LT-InGaAs samples with the (111)A substrate orientation as compared to (100). Adding of LT-InAlAs layers into the structure with (111)A substrate orientation results in two orders of magnitude increase of the structure resistivity. The possibility of creating LT-InGaAs/InAlAs-based photoconductive antennas with high dark resistance without compensating Be doping is demonstrated. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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11 pages, 4266 KiB

Open AccessArticle

Design and Measurement of a 0.67 THz Biased Sub-Harmonic Mixer

by Guangyu Ji, Dehai Zhang, Jin Meng, Siyu Liu and Changfei Yao

Electronics 2020, 9(1), 161; https://doi.org/10.3390/electronics9010161 - 15 Jan 2020

Cited by 4 | Viewed by 3584

Abstract

To effectively reduce the requirement of Local Oscillator (LO) power, this paper presents the design and measurement of a biased sub-harmonic mixer working at the center frequency of 0.67 THz in hybrid integration. Two discrete Schottky diodes were placed across the LO waveguide [...] Read more.

To effectively reduce the requirement of Local Oscillator (LO) power, this paper presents the design and measurement of a biased sub-harmonic mixer working at the center frequency of 0.67 THz in hybrid integration. Two discrete Schottky diodes were placed across the LO waveguide in anti-series configuration on a 50 μm thick quartz-glass substrate, and chip capacitors were not required. At the driven of 3 mW@335 GHz and 0.35 V, the mixer had a minimum measured Signal Side-Band (SSB) conversion loss of 15.3 dB at the frequency of 667 GHz. The typical conversion loss is 18.2 dB in the band of 650 GHz to 690 GHz. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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10 pages, 1881 KiB

Open AccessArticle

Correction of Optical Delay Line Errors in Terahertz Time-Domain Spectroscopy

by Alexander Mamrashev, Fedor Minakov, Lev Maximov, Nazar Nikolaev and Pavel Chapovsky

Electronics 2019, 8(12), 1408; https://doi.org/10.3390/electronics8121408 - 26 Nov 2019

Cited by 13 | Viewed by 3310

Abstract

One of the key elements of terahertz time-domain spectrometers is the optical delay line. Usually it consists of a motorized translation stage and a corner reflector mounted on its top. Errors in the positioning of the translation stage lead to various distortions of [...] Read more.

One of the key elements of terahertz time-domain spectrometers is the optical delay line. Usually it consists of a motorized translation stage and a corner reflector mounted on its top. Errors in the positioning of the translation stage lead to various distortions of the measured waveform of terahertz pulses and, therefore, terahertz spectra. In this paper, the accuracy of position measurements is improved by using an optical encoder. Three types of systematic errors are found: Increasing and periodic offsets of the translation stage position, as well as a drift of its initial position in a series of consecutive measurements. The influence of the detected errors on the measured terahertz spectra is studied and correction methods are proposed. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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11 pages, 3188 KiB

Open AccessArticle

Design of a 335 GHz Frequency Multiplier Source Based on Two Schemes

by Jin Meng, Dehai Zhang, Guangyu Ji, Changfei Yao, Changhong Jiang and Siyu Liu

Electronics 2019, 8(9), 948; https://doi.org/10.3390/electronics8090948 - 28 Aug 2019

Cited by 11 | Viewed by 3658

Abstract

Based on a W-band high-power source, two schemes are proposed to realize a 335 GHz frequency multiplier source. The first scheme involves producing a 335 GHz signal with a two-stage doubler. The first doubler adopts two-way power-combined technology and the second stage is [...] Read more.

Based on a W-band high-power source, two schemes are proposed to realize a 335 GHz frequency multiplier source. The first scheme involves producing a 335 GHz signal with a two-stage doubler. The first doubler adopts two-way power-combined technology and the second stage is a 335 GHz doubler using a balanced circuit to suppress the odd harmonics. The measured output power was about 17.9 and 1.5 dBm at 167.5 and 335 GHz, respectively. The other scheme involves producing a 335 GHz signal with a single-stage quadrupler built on 50 µm thick quartz circuit adopting an unbalanced structure. The advantage of the unbalanced structure is that it can provide bias to the diodes without an on-chip capacitor, which is hard to realize with discrete devices. The measured output power was about 5.8 dBm at 337 GHz when driven with 22.9 dBm. Such 335 GHz frequency multiplier sources are widely used in terahertz imaging, radiometers, and so on. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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11 pages, 2762 KiB

Open AccessArticle

Improvement in SNR by Adaptive Range Gates for RCS Measurements in the THz Region

by Shuang Pang, Yang Zeng, Qi Yang, Bin Deng, Hongqiang Wang and Yuliang Qin

Electronics 2019, 8(7), 805; https://doi.org/10.3390/electronics8070805 - 18 Jul 2019

Cited by 5 | Viewed by 3223

Abstract

One of the major concerns in radar cross-section (RCS) measurements is the isolation of the target echo from unwanted spurious signals. Generally, the method of software range gate is applied to extract useful data. However, this method may not work to expectations, especially [...] Read more.

One of the major concerns in radar cross-section (RCS) measurements is the isolation of the target echo from unwanted spurious signals. Generally, the method of software range gate is applied to extract useful data. However, this method may not work to expectations, especially for targets with a large length-width ratio. This is because the effective target zone is dependent on the aspect angle. The implementation of conventional fixed range gates will introduce an uneven clutter signal that leads to a decline in signal-to-noise ratio. The influence of this uneven clutter signal becomes increasingly severe in the terahertz band, where the wavelength is short and the illumination power is weak. In this work, the concept of adaptive range gates was adopted to extract a target echo of higher accuracy. The dimension of the range gate was determined by the angle-dependent radial projection of the target. In order to evaluate the performance of the proposed method, both experimental measurements and numerical simulations were conducted. Noticeable improvements in the signal-to-noise ratio at certain angles were observed. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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13 pages, 7507 KiB

Open AccessArticle

Accurately Modeling of Zero Biased Schottky-Diodes at Millimeter-Wave Frequencies

by Jéssica Gutiérrez, Kaoutar Zeljami, Tomás Fernández, Juan Pablo Pascual and Antonio Tazón

Electronics 2019, 8(6), 696; https://doi.org/10.3390/electronics8060696 - 20 Jun 2019

Cited by 7 | Viewed by 4977

Abstract

This paper presents and discusses the careful modeling of a Zero Biased Diode, including low-frequency noise sources, providing a global model compatible with both wire bonding and flip-chip attachment techniques. The model is intended to cover from DC up to W-band behavior, and [...] Read more.

This paper presents and discusses the careful modeling of a Zero Biased Diode, including low-frequency noise sources, providing a global model compatible with both wire bonding and flip-chip attachment techniques. The model is intended to cover from DC up to W-band behavior, and is based on DC, capacitance versus voltage, as well as scattering and power sweep harmonics measurements. Intensive use of 3D EM (ElectroMagnetic) simulation tools, such as HFSS^TM, was done to support Zero Biased Diode parasitics modeling and microstrip board modeling. Measurements are compared with simulations and discussed. The models will provide useful support for detector designs in the W-band. Full article

(This article belongs to the Special Issue Terahertz Technology and Its Applications)

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