A Fermi-level managed barrier (FMB) diode was used for the heterodyne detection of terahertz waves for the first time. A quasi-optical module integrating an FMB diode and a broadband trans-impedance ...amplifier exhibited an intermediate frequency bandwidth of 11 GHz. A very low noise-equivalent-power of 1.1 × 10−18 W/Hz was achieved at ∼300 GHz with a very low local oscillator power of 6 × 10−6 W.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The fluid‐flow properties of fractures have received increasing attention regarding the role of geofluids in the genesis of slow and fast earthquakes and recent advances in geoengineering ...developments. Geophysical observations are promising tools to remotely estimate crustal permeability changes; however, quantitative interpretations are limited by the rock‐physical models' paucity for fractures. This study investigated changes in permeability, resistivity, and their respective relationships at elevated stress by performing numerical simulations of different fracture models with varying fracture size, roughness, and shear displacement. Numerical results and microscopic flow analysis demonstrate that permeability–resistivity relationships are controlled by percolation and are less dependent on fracture geometric characteristics. Our finding suggests that the permeability evolution of fractures can be formulated with resistivity changes independent of both fracture size and microstructure, the trends of which can be predicted using Archie's exponent. The extension to the electro‐mechanical relationship further derives the potential applications of estimating stress changes.
Plain Language Summary
Monitoring the flow of fluids through underground fractures is important for developing earth resources and understanding the generation of both slow and fast earthquakes. This can be realized by observing physical properties underground such as electrical resistivity; however, the relationships between electrical and hydraulic properties are poorly understood because we have limited data on rock fractures. Thus, in this study, we explored changes in the hydraulic and electrical properties of synthetic rock fractures by subjecting them to increasing normal stress and shear displacement while varying the properties of the fracture surface topographies and length scales referring to natural data. We formulated the relationship between electrical resistivity and permeability invariant of fracture size, roughness, shear displacement, and normal stress based on both the theoretical model and empirical Archie's equation. We found that the rigorous relationship is controlled by the local connection of the fluid‐flow paths based on the microscopic flow analysis. The proposed formula can estimate the permeability evolution of fractures using resistivity data and is a better approach compared to porosity estimation because resistivity–porosity relationship can change depending on the tortuosity or connectivity. The extension to the electro‐mechanical relationship also derives the potential applications of estimating changes in pore pressure.
Key Points
Numerical results clarify the dependencies of fracture size, roughness, shear displacement, and stress on permeability and resistivity
Flow path percolation can be correlated with tortuosity, which controls the rigorous resistivity–porosity and –permeability relationships
Archie's exponent is constant for a percolated single fracture and can be used for monitoring permeability and pore pressure change
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
An anti-parallel (AP) diode pair based on a Fermi-level managed barrier (FMB) diode was developed for the sub-harmonic mixing of terahertz waves. A quasi-optical module integrating an AP–FMB diode ...pair and a trans-impedance amplifier exhibited a very low noise-equivalent-power of 9 × 10−19 W/Hz at an input signal frequency of 304 GHz with a very low local oscillator power of 30 μW.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A zero-biased Fermi-level managed barrier diode that was packaged with a WR-3 rectangular-waveguide-input port was developed. For direct (square-law) detection operations, the fabricated module ...exhibited a 3 dB bandwidth covering the whole WR-3 band. The intermediate frequency bandwidth in heterodyne detection was, therefore, dominated by the bandwidth of the integrated preamplifier, and it was measured to be about 40 GHz. The minimum noise-equivalent power obtained was as low as 7 × 10−18 W/Hz at around 300 GHz even with a very low local oscillator power of 30 μW.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
We carried out an experimental comparison study of the two most established optoelectronic emitters for continuous-wave (cw) terahertz generation: a uni-traveling-carrier photodiode (UTC-PD) and a ...pin-photodiode (PIN-PD). Both diodes are commercially available and feature a similar package (fiber-pigtailed housings with a hyper-hemispherical silicon lens). We measured the terahertz output as a function of optical illumination power and bias voltage from 50 GHz up to 1 THz, using a precisely calibrated terahertz power detector. We found that both emitters were comparable in their spectral power under the operating conditions specified by the manufacturers. While the PIN-PD turned out to be more robust against varying operating parameters, the UTC-PD showed no saturation of the emitted terahertz power even for 50 mW optical input power. In addition, we compared the terahertz transmission and infrared (IR) blocking ratio of four different filter materials. These filters are a prerequisite for correct measurements of the absolute terahertz power with thermal detectors.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A novel Fermi-level managed barrier diode has been developed for achieving broadband and low-noise terahertz-wave detection. The fabricated quasi-optical module detected signals at frequencies from ...200 GHz to 1 THz. The typical voltage sensitivity was 1020 V/W, and the current sensitivity for a 50 Ω load was 4.5 A/W at 300 GHz for a zero-biased condition. Square-law detection with good linearity was demonstrated at 300 GHz with an output current density exceeding 103 A/cm2.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Magneto-optical (MO) imaging using an MO material is one of the most important imaging techniques for measuring magnetic field distributions. The technique is attracting attention because of its ...ability to visualize magnetic fields and current distributions at a wide range of temperatures from cryogenic to room temperature or higher, a wide range of length scales from micrometers to several tens of centimeters, and a wide range of frequencies from DC to GHz. Nevertheless, further development of films with good MO properties is required in order to extend the range of applications of MO imaging. In this paper, developments related to bismuth-substituted iron garnet films, R3−xBixFe5−yGayO12 (R = Y, Nd; 1 ≤ x ≤ 3), prepared by metal–organic decomposition for MO imaging plates are reviewed. In addition, an MO imaging plate with an electroluminescent backlight, which enables wide-area MO imaging, and the MO color imaging technique, which indicates the strength of a magnetic field using colors, are reviewed.
A hollow-waveguide-output uni-travelling-carrier photodiode (UTC-PD) module operating at frequencies from 400 to 900 GHz has been developed. The module consists of a UTC-PD, a photodiode-to-waveguide ...coupler, and a metallic package with a waveguide rectangular (WR)-1.5 rectangular waveguide. The coupler is monolithically integrated with the UTC-PD chip. The fabricated module exhibits the output power as high as −19 dBm at 500 GHz and the 3 dB bandwidth of 340 GHz, which is the widest among ever-reported photodiode modules.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
There has been an increasing interest in photonic generation of RF signals in the millimeter‐wave (30 GHz∼300 GHz) and/or terahertz‐wave (0.1 THz∼10 THz) regions, and photodiodes play a key role in ...it. This paper reviews recent progress in the high‐power RF photodiodes such as Uni‐Traveling‐Carrier‐Photodiodes (UTC‐PDs), which operate at these frequencies. Several approaches to increasing both the bandwidth and output power of photodiodes are discussed, and promising applications to broadband wireless communications and spectroscopic sensing are described.
There has been an increasing interest in photonic generation of RF signals in the millimeter‐wave (30 Ghz∼300 Ghz and/or terahertz‐wave (0.1 Thz∼10 THz) regions, and photodiodes play a key role in it. This paper reviews recent progress in the high‐power RF photodiodes such as Uni‐Traveling‐Carrier‐Photodiodes (UTC‐PDs), which operate at these frequencies. Several approaches to increasing both the bandwidth and output power of photodiodes are discussed, and promising applications to broadband wireless communications and spectroscopic sensing are described.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The unitraveling-carrier photodiode (UTC-PD) is a novel photodiode that utilizes only electrons as the active carriers. This unique feature is the key for its ability to achieve excellent high-speed ...and high-output characteristics simultaneously. To date, a record 3-dB bandwidth of 310 GHz and a millimeter-wave output power of over 20 mW at 100 GHz have been achieved. The superior capability of the UTC-PD for generating very large high-bit-rate electrical signals as well as a very high RF output power in millimeter/submillimeter ranges can lead to innovations in various systems, such as broadband optical communications systems, wireless communications systems, and high-frequency measurement systems. Accomplishments include photoreceivers of up to 160 Gb/s, error-free DEMUX operations using an integrated UTC-PD driven optical gate of up to 320 Gb/s, a 10-Gb/s millimeter-wave wireless link at 120 GHz, submillimeter-wave generation at frequencies of up to 1.5 THz, and photonic frequency conversion with an efficiency of -8 dB at 60 GHz. For the practical use, various types of modules, such as a 1-mm coaxial connector module, a rectangular-waveguide output module, and a quasi-optic module, have been developed. The superior reliability and stability are also confirmed demonstrating usefulness of the UTC-PD for the system applications.
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