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2 pages, 163 KiB

Open AccessEditorial

Special Issue on Development and Applications of Microwave/Millimeter Wave Diagnostics in Industry

by Atsushi Mase

Appl. Sci. 2023, 13(3), 1852; https://doi.org/10.3390/app13031852 - 31 Jan 2023

Viewed by 597

Abstract

Microwave/millimeter wave devices and systems have been developed as core technologies in the fields of communication and measurement [...] Full article

(This article belongs to the Special Issue Development and Applications of Microwave/Millimeter Wave Diagnostics in Industry)

Research

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13 pages, 4019 KiB

Open AccessArticle

Sub-Diffraction Focusing Using Metamaterial-Based Terahertz Super-Oscillatory Lens

by Ayato Iba, Makoto Ikeda, Valynn Katrine Mag-usara, Verdad C. Agulto and Makoto Nakajima

Appl. Sci. 2022, 12(24), 12770; https://doi.org/10.3390/app122412770 - 13 Dec 2022

Cited by 3 | Viewed by 1220

Abstract

This paper presents a metamaterial-based super-oscillatory lens (SOL) fabricated by photolithography on a glass substrate and designed to operate at sub-terahertz (sub-THz) frequencies. The lens consists of repeating crisscross patterns of five-ring slits with sub-wavelength diameter. The lens is capable of generating multiple [...] Read more.

This paper presents a metamaterial-based super-oscillatory lens (SOL) fabricated by photolithography on a glass substrate and designed to operate at sub-terahertz (sub-THz) frequencies. The lens consists of repeating crisscross patterns of five-ring slits with sub-wavelength diameter. The lens is capable of generating multiple focal points smaller than the diffraction limit, thereby allowing many points to be inspected simultaneously with sub-wavelength resolution. After elucidating the influence of the lens parameters on light collection through calculations by the finite element method, the fabricated lens was then evaluated through actual experiments and found to have a focal length of 7.5 mm (2.5λ) and a hot spot size of 2.01 mm (0.67λ) at 0.1 THz (λ = 3 mm), which is 0.27 times the diffraction limit of the lens. This demonstrated sub-diffraction focusing capability is highly effective for industrial inspection applications utilizing terahertz waves. Full article

(This article belongs to the Special Issue Development and Applications of Microwave/Millimeter Wave Diagnostics in Industry)

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10 pages, 3433 KiB

Open AccessCommunication

Visualizing Small Objects Using Amplitude-Modulated Laser Light at Microwave Frequencies

by Yuichiro Kogi, Narumi Kimura, Hiroyuki Ikezi, Masaaki Inutake and Atsushi Mase

Appl. Sci. 2022, 12(19), 9836; https://doi.org/10.3390/app12199836 - 29 Sep 2022

Cited by 1 | Viewed by 1413

Abstract

We reported on laboratory imaging experiments conducted using a system that utilizes amplitude-modulated infrared laser light at microwave frequencies. With modulations ranging from 11.1 to 15.1 GHz on a 1.55 μm near-infrared laser, the phase measurements of the modulation signals revealed a target [...] Read more.

We reported on laboratory imaging experiments conducted using a system that utilizes amplitude-modulated infrared laser light at microwave frequencies. With modulations ranging from 11.1 to 15.1 GHz on a 1.55 μm near-infrared laser, the phase measurements of the modulation signals revealed a target shape with sub-mm precision. We also tested whether our system is able to achieve cross-range resolution in the spot-light mode synthetic aperture scheme. With the aid of “position-compensated signal processing”, synthetic aperture images were formed successfully. According to predications based on the principle of normal synthetic aperture radar, the spatial resolutions of the images were shown to be inversely proportional to the width of the collected data placed in the wavenumber space. Full article

(This article belongs to the Special Issue Development and Applications of Microwave/Millimeter Wave Diagnostics in Industry)

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15 pages, 4254 KiB

Open AccessArticle

A Direction-Sensitive Microwave Sensor for Metal Crack Detection

by Boyang Qian, Liang Mou, Li Wu, Zelong Xiao, Taiyang Hu and Jinwei Jiang

Appl. Sci. 2022, 12(18), 9045; https://doi.org/10.3390/app12189045 - 08 Sep 2022

Cited by 4 | Viewed by 1378

Abstract

For metal crack nondestructive detection, most conventional crack sensors are unable to realize the crack direction detection. In this work, a direction-sensitive microwave sensor is proposed for metal crack detection. The proposed sensor consists of a rectangular patch resonator and two perpendicular coupled [...] Read more.

For metal crack nondestructive detection, most conventional crack sensors are unable to realize the crack direction detection. In this work, a direction-sensitive microwave sensor is proposed for metal crack detection. The proposed sensor consists of a rectangular patch resonator and two perpendicular coupled feeding ports, which improves the current distribution on patch surface and the sensitivity for crack direction detection. The performances of the proposed sensor are verified by simulation and measurement experiments. The results show that the width sensitivities of two feeding ports are 100 MHz/mm and 63.3 MHz/mm, respectively, and the sensitivity of the sensor for crack direction detection are 6.10 MHz/5 degrees and 1.93 MHz/5 degrees, respectively. Due to the advantages of a simple structure, low profile, large coverage area and high sensitivity, the proposed sensor has a great application potential in nondestructive detection fields. Full article

(This article belongs to the Special Issue Development and Applications of Microwave/Millimeter Wave Diagnostics in Industry)

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13 pages, 6261 KiB

Open AccessArticle

Application of Dual Frequency Comb Method as an Approach to Improve the Performance of Multi-Frequency Simultaneous Radiation Doppler Radar for High Temperature Plasma Diagnostics

by Tokihiko Tokuzawa, Shigeru Inagaki, Michiaki Inomoto, Akira Ejiri, Tatsuhiro Nasu, Toru Ii Tsujimura and Katsumi Ida

Appl. Sci. 2022, 12(9), 4744; https://doi.org/10.3390/app12094744 - 08 May 2022

Cited by 5 | Viewed by 1887

Abstract

A new Doppler radar using millimeter-waves in the Ka-band, named the “dual-comb Doppler reflectometer”, has been developed to measure the turbulence intensity and its velocity in high-temperature plasmas. For the realization of a fusion power generation, it is very important to know the [...] Read more.

A new Doppler radar using millimeter-waves in the Ka-band, named the “dual-comb Doppler reflectometer”, has been developed to measure the turbulence intensity and its velocity in high-temperature plasmas. For the realization of a fusion power generation, it is very important to know the spatial structure of turbulence, which is the cause of plasma confinement degradation. As a non-invasive and high spatial resolution measurement method for this purpose, we apply a multi-frequency Doppler radar especially with simultaneous multi-point measurement using a frequency comb. The newly developed method of synchronizing two frequency combs allows a lower intermediate frequency (IF) than the previously developed frequency comb radar, lowering the bandwidth of the data acquisition system and enabling low-cost, long-duration plasma measurements. In the current dual-comb radar system, IF bandwidth is less than 0.5 GHz; it used to be 8 GHz for the entire Ka-band probing. We applied this system to the high-temperature plasma experimental device, the Large Helical Device (LHD), and, to demonstrate this system, verified that it shows time variation similar to that of the existing Doppler radar measurements. Full article

(This article belongs to the Special Issue Development and Applications of Microwave/Millimeter Wave Diagnostics in Industry)

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9 pages, 4094 KiB

Open AccessArticle

Imaging Diagnostics of Inside of a Building Wall Using Millimeter-Wave Reflectometer

by Shota Osaki, Atsushi Mase, Yoshikazu Hirata and Munehiro Iwakura

Appl. Sci. 2022, 12(6), 2879; https://doi.org/10.3390/app12062879 - 11 Mar 2022

Cited by 1 | Viewed by 1483

Abstract

Progress in microwave and millimeter-wave technologies has enabled advanced diagnostics for industrial applications. The transmission, reflection, scattering and radiation processes of electromagnetic waves are utilized as diagnostic principles. Specifically, the reflectometric method has gained importance in various applications due to the possibility of [...] Read more.

Progress in microwave and millimeter-wave technologies has enabled advanced diagnostics for industrial applications. The transmission, reflection, scattering and radiation processes of electromagnetic waves are utilized as diagnostic principles. Specifically, the reflectometric method has gained importance in various applications due to the possibility of the high localization and accessibility of measurements, as well as the non-destructive nature of the systems. In this paper, radar reflectometers were applied to the measurement of the inside of a building wall, that is, the inspection of tile materials attached to a concrete wall. The measurement principle utilizes the phase interference effect of the reflected wave due to the multiple reflections between the two layers (Fabry–Perot effect). The results show the imaging inside the surface related to the peering condition between the tile and concrete wall, and the quantitative evaluation of the condition with non-destructive inspection. Full article

(This article belongs to the Special Issue Development and Applications of Microwave/Millimeter Wave Diagnostics in Industry)

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12 pages, 53359 KiB

Open AccessArticle

W-Band Modular Antenna/Detector Array for the Electron Cyclotron Emission Imaging System in KSTAR

by Gwan Hui Lee, Jung Seok Lee, Dong Hwi Kim, Syifa Haunan Nashuha, Mun Ju Kim, Byung Cheol Min, Jae Hyun Lee, Woo Chang Lee, Gun Su Yun, Tae Gyu Kim, Bong Tae Kim, Hyun Chul Choi, Hyeon Keo Park, Yong Kyoon In and Kang Wook Kim

Appl. Sci. 2022, 12(5), 2431; https://doi.org/10.3390/app12052431 - 25 Feb 2022

Cited by 3 | Viewed by 1559

Abstract

A design of a modular antenna/detector array for the electron cyclotron emission (ECE) imaging system at the Korea Superconducting Tokamak Advanced Research (KSTAR) is proposed. The modular antenna/detector array is based on a unit antenna/detector module, which consists of an elliptical mini-lens, a [...] Read more.

A design of a modular antenna/detector array for the electron cyclotron emission (ECE) imaging system at the Korea Superconducting Tokamak Advanced Research (KSTAR) is proposed. The modular antenna/detector array is based on a unit antenna/detector module, which consists of an elliptical mini-lens, a dual-dipole antenna, an antenna balun, a low-noise amplifier, and a metal frame. The proposed modular antenna/detector array resolves the problem in the conventional antenna/detector array where one faulty channel requires the entire array to be removed for the service. With the proposed modular array, each channel module can be easily and independently removed and replaced without interference to the rest of the array, thus minimizing the interrupted service time for maintenance. Moreover, the unit channel modules can be efficiently updated under a variety of the tokamak operation conditions. The antenna/detector modules are optimized to have improved performance, and are tested in a W-band test setup, and consistently provide the gain increase by 10~20 dB as compared with the conventional antenna/detector array. A set of the proposed modular antenna/detector array is currently installed and tested in the KSTAR ECE imaging system, and will consistently produce the improved ECE imaging to monitor MHD instability activities under various plasma operation conditions. Full article

(This article belongs to the Special Issue Development and Applications of Microwave/Millimeter Wave Diagnostics in Industry)

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14 pages, 38506 KiB

Open AccessArticle

A Novel Synthetization Approach for Multi Coupled Line Section Impedance Transformers in Wideband Applications

by Nan Zhang, Xiaolong Wang, Chunxi Bao, Bin Wu, Chun-Ping Chen, Zhewang Ma and Geyu Lu

Appl. Sci. 2022, 12(2), 875; https://doi.org/10.3390/app12020875 - 15 Jan 2022

Cited by 1 | Viewed by 1529

Abstract

In this paper, a novel synthetization approach is proposed for filter-integrated wideband impedance transformers (ITs). The original topology consists of N cascaded coupled line sections (CLSs) with 2N characteristic impedance parameters. By analyzing these characteristic impedances, a Chebyshev response can be derived [...] Read more.

In this paper, a novel synthetization approach is proposed for filter-integrated wideband impedance transformers (ITs). The original topology consists of N cascaded coupled line sections (CLSs) with 2N characteristic impedance parameters. By analyzing these characteristic impedances, a Chebyshev response can be derived to consume N + 2 design conditions. To optimize the left N − 2 variable parameters, CLSs were newly substituted by transmission lines (TLs) to consume the remaining variable parameters and simplify the circuit topology. Therefore, there are totally 2N − N − 2 substituting possibilities. To verify the proposed approach, 25 cases are listed under the condition of N = 5, and 7 selected cases are compared and discussed in detail. Finally, a 75–50 Ω IT with 100% fractional bandwidth and 20 dB bandpass return loss (RL) is designed and fabricated. The measured results meet the circuit simulation and the EM simulation accurately. Full article

(This article belongs to the Special Issue Development and Applications of Microwave/Millimeter Wave Diagnostics in Industry)

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17 pages, 3994 KiB

Open AccessArticle

Tree Internal Defected Imaging Using Model-Driven Deep Learning Network

by Hongju Zhou, Liping Sun, Hongwei Zhou, Man Zhao, Xinpei Yuan and Jicheng Li

Appl. Sci. 2021, 11(22), 10935; https://doi.org/10.3390/app112210935 - 19 Nov 2021

Cited by 1 | Viewed by 1385

Abstract

The health of trees has become an important issue in forestry. How to detect the health of trees quickly and accurately has become a key area of research for scholars in the world. In this paper, a living tree internal defect detection model [...] Read more.

The health of trees has become an important issue in forestry. How to detect the health of trees quickly and accurately has become a key area of research for scholars in the world. In this paper, a living tree internal defect detection model is established and analyzed using model-driven theory, where the theoretical fundamentals and implementations of the algorithm are clarified. The location information of the defects inside the trees is obtained by setting a relative permittivity matrix. The data-driven inversion algorithm is realized using a model-driven algorithm that is used to optimize the deep convolutional neural network, which combines the advantages of model-driven algorithms and data-driven algorithms. The results of the comparison inversion algorithms, the BP neural network inversion algorithm, and the model-driven deep learning network inversion algorithm, are analyzed through simulations. The results shown that the model-driven deep learning network inversion algorithm maintains a detection accuracy of more than 90% for single defects or homogeneous double defects, while it can still have a detection accuracy of 78.3% for heterogeneous multiple defects. In the simulations, the single defect detection time of the model-driven deep learning network inversion algorithm is kept within 0.1 s. Additionally, the proposed method overcomes the high nonlinearity and ill-posedness electromagnetic inverse scattering and reduces the time cost and computational complexity of detecting internal defects in trees. The results show that resolution and accuracy are improved in the inversion image for detecting the internal defects of trees. Full article

(This article belongs to the Special Issue Development and Applications of Microwave/Millimeter Wave Diagnostics in Industry)

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