Showing papers in "International Journal of Infrared and Millimeter Waves in 1998"
TL;DR: In this paper, the development status of high-power millimeter-wave windows with emphasis on CVD diamond windows is summarized, and water-edge-cooled single-disk CVD-diamond windows and distributed windows are investigated in order to solve the window problem.
Abstract: Electron cyclotron heating (ECH) is one of the main candidates for heating and current drive on ITER (170 GHz) and W7-X (140 GHz). High unit power (1 MW or greater) and high efficiency single-mode continuous-wave (CW) gyrotrons are under development in order to reduce significantly the systems costs. Face-cooled double-disk sapphire and silicon nitride windows (FC-75 liquid cooling), cryogenically edge-cooled single-disk sapphire (liquid nitrogen, liquid neon or liquid helium cooling) and silicon (230 K refrigerator cooling) windows, water-edge-cooled single-disk CVD-diamond windows and water-cooled distributed windows are being investigated in order to solve the window problem. A water-cooled window has two very important advantages; it employs a cheap and effective coolant and it is compact and probably more reliable than other solutions and thus can also be easily used as a torus window. The present paper summarizes the development status of high-power millimeter-wave windows with emphasis on CVD diamond.
89 citations
TL;DR: In this paper, a millimeter and submillimeter wave ESR system was developed in Kobe University, which can measure in the field range up to 30 T in the temperature range from 1.8 K to 4.2 K and from 18 K to room temperature.
Abstract: New systems for millimeter and submillimeter wave ESR have been developed in Kobe University. In the previous system the pulsed magnetic field was limited up to 17 T in the temperature range from 1.8 to 86 K. Using the new systems, we can measure in the field range up to 30 T in the temperature range from 1.8 K to 4.2 K and from 18 K to room temperature. The resolution of the magnetic field has been also improved in the new ESR system. The details of our new ESR systems are presented. In addition, the measurements of Yb2Cu2O5 using these new systems are presented.
58 citations
TL;DR: In this article, the phase velocity of waves in folded waveguide is slowed down to the velocity of electron beam in a linear fashion, and the linear theory predicts a gain of 2 dB/cm and a bandwidth of 37% at the center frequency of 14 GHz.
Abstract: A wideband folded waveguide traveling-wave tube (TWT) amplifier has advantages of simpler coupling structures and robust structure over the conventional helix TWT. The phase velocity of waves in folded waveguide is slowed down to the velocity of electron beam. Slow-wave interaction with the electron beam in folded waveguide is studied in a linear fashion. For a cold beam, the linear theory predicts a gain of 2 dB/cm and a bandwidth of 37% at the center frequency of 14 GHz. A closed algebraic dispersion relation for the frequency and the axial phase shift per period is obtained using an equivalent circuit model. Numerical solution calculated from the dispersion relation and three-dimensional electromagnetic code, HFSS simulations predict a mode coalescing in the folded waveguide. And a theoretical phase velocity prediction of the electromagnetic wave in this circuit is verified by HFSS simulations.
48 citations
TL;DR: In this article, the RF loss in NbTiN films, a 15K Tc compound superconductor, was investigated by incorporating them into quasi-optical slot antenna SIS devices.
Abstract: Recent results at 1 THz using normal-metal tuning circuits have shown that SIS mixers can work well up to twice the gap frequency of the junction material (niobium). However, the performance at 1 THz is limited by the substantial loss in the normal metal films. For better performance superconducting films with a higher gap frequency than niobium and with low RF loss are needed. Niobium nitride has long been considered a good candidate material, but typical NbN films suffer from high RF loss. To circumvent this problem we are currently investigating the RF loss in NbTiN films, a 15K Tc compound superconductor, by incorporating them into quasi-optical slot antenna SIS devices.
43 citations
TL;DR: In this paper, the influence of reflections on oscillatory processes in gyrotrons has been studied, and the conditions for oscillation stability in the presence of a reflected signal are given.
Abstract: Influence of some types of reflections on oscillatory processes in gyrotrons has been studied. Estimations of the conditions for oscillation stability in the presence of a reflected signal are given. The processes in a gyrotron with a fixed structure of the RF field have been modeled numerically, and enhancement of the spectrum signal in the presence of reflections has been studied.
36 citations
TL;DR: In this article, complete harmonic gyrotron oscillators in axial arrangement including cavity, uptapers, collector waveguide and output window have been numerically simulated using a scattering matrix resonator code.
Abstract: Complete harmonic gyrotron oscillators in axial arrangement including cavity, uptapers, collector waveguide and output window have been numerically simulated using a scattering matrix resonator code. The output mode purity and the influence of window reflections on the performance of a step-tunable, very high frequency gyrotron, Gyrotron FU IV A, at Fukui University was analyzed.
32 citations
TL;DR: In this article, a mildly relativistic electron beam (500keV, 200A, 10ns) injected into an X-band rectangular waveguide immersed in a uniform axial magnetic field (4-10kG) produced magnetically tunable microwave radiation in the 9-13 GHz frequency range with an estimated output power of 1MW.
Abstract: A mildly relativistic electron beam (500keV, 200A, 10ns) injected into an X-band rectangular waveguide immersed in a uniform axial magnetic field (4-10kG) produced magnetically tunable microwave radiation in the 9-13 GHz frequency range with an estimated output power of 1MW. The frequency range and tunability of the radiated microwave agreed with a theoretical model for a gyrotron backward wave oscillator taking into account the low energy component of the beam electron.
32 citations
TL;DR: In this paper, the experimental results are compared with simulations for the complete gyrotron oscillator, which has an additional advantage to cover the wide frequency range in submillimeter wave region.
Abstract: The cavity of the newest gyrotron, Gyrotron FU IVA in the high frequency series of Fukui University gyrotrons (the Gyrotron FU series) is designed to minimize the mode conversion from the main cavity mode to the higher modes. In this paper, the experimental results are compared with simulations for the complete gyrotron oscillator. The gyrotron has an additional advantage to cover the wide frequency range in submillimeter wave region.
27 citations
TL;DR: In this article, the authors compare the predictions for the noise power of a bolometer observing through an emissive atmosphere, considering the effect of atmospheric absorption, telescope optical efficiency, and detector optical efficiency.
Abstract: With the advent of large submillimeter telescopes at high, dry sites, the atmospheric background noise in a moderate bandwidth can be low enough to challenge the ability of instrument designers to produce sufficiently low noise bolometers to be background limited. We compare the predictions for the noise power of a bolometer observing through an emissive atmosphere, considering the effect of atmospheric absorption, telescope optical efficiency, and detector optical efficiency, with measurements through the atmosphere over Mauna Kea.
27 citations
TL;DR: In this paper, it was shown that in order to be an effective attenuator of microwave radiation, a plasma layer has to have a number density in the 1013 cm−3 range, and a thickness equal or larger than the wavelength of the incident wave.
Abstract: Plasma layers at atmospheric pressure, are good broad band absorbers of electromagnetic radiation However, to get substantial attenuations, two parameters have to be optimized These are the plasma number density, and the thickness of the plasma layer It is found that in order to be an effective attenuator of microwave radiation, a plasma layer has to have a number density in the 1013 cm−3 range, and a thickness equal or larger than the wavelength of the incident wave However, as the frequency increases, the amount of attenuation tends to reach a limiting value directly proportional to the number density
27 citations
TL;DR: In this paper, the authors studied the effect of misalignment in a submillimeter-wave gyrotron and its effect on its total efficiency as well as the excitation of rotating and counterrotating modes.
Abstract: Electron beam misalignment in a submillimeter-wave gyrotron strongly affects its total efficiency as well as excitation of rotating and counterrotating modes. Some of misalignment phenomena were studied theoretically and experimentally.
TL;DR: In this article, a new quasi-optical concept of electrically proof delay line distribution system (DLDS) for high-energy electron/positron accelerators is proposed.
Abstract: A new quasi-optical concept of electrically proof Delay Line Distribution System (DLDS) for high-energy electron/positron accelerators is proposed. In order to increase microwave power, used for particle acceleration, the concept assumes summing up of a few wavebeams in multimode rectangular waveguide. Operating by mutual phases of the wavebeams, to be produced by coherent sources, the system allows also a distribution of long multiplied RF pulses on a set of acceleration sections. Calculations of key components are fulfilled at 34 GHz frequency.
TL;DR: In this paper, the equivalent circuit modelling technique is used to study the resonant frequency and Q factor of plane parallel Fabry-Perot cavities with square aperture metal mesh mirrors.
Abstract: The equivalent circuit modelling technique is used to study the resonant frequency and Q factor of plane parallel Fabry-Perot cavities with square aperture metal mesh mirrors. Comparison of different models found in literature with experimental data in the 60 GHz band is given for thin and thick cavities. Chen's model is shown to give a good agreement with measurements, as long as the cavity is not too selective and for large enough cavity.
TL;DR: A suite of polarization-sensitive automatic target detection and recognition algorithms on sets of simulated and real polarimetric IR imagery are presented and show that a noticeable improvement over the non-polarimetric ATR can be achieved.
Abstract: Automatic detection and recognition of targets by means of passive IR sensors suffer from limitations due to lack of sufficient contrast between the targets and their background, and among the facets of a target. In this paper the results of a suite of polarization-sensitive automatic target detection and recognition algorithms on sets of simulated and real polarimetric IR imagery are presented. A custom designed Polarimetric IR (PIR) imaging sensor is used for collecting real polarimetric target data-three of the four Stokes parameters under a variety of conditions. Then a set of novel algorithms are designed and tested that uses the target and background Stokes parameters for detection, segmentation and classification of targets. The empirical performance results are obtained in terms of the probabilities of detection, false alarm rate, segmentation accuracy, and recognition probabilities as functions of number of pixels on target, aspect and depression angles and under several background conditions (clutter densities) on the polarimetric and non-polarimetrirc data. These results show that a noticeable improvement over the non-polarimetric ATR can be achieved.
TL;DR: The first cw operation of a submillimeter wave gyrotron (Gyrotron FU IV) using a 12 T superconducting magnet has been successfully carried out as discussed by the authors.
Abstract: The first cw operation of our submillimeter wave gyrotron (Gyrotron FU IV) using a 12 T superconducting magnet has been successfully carried out. Output power is more than 20 W at a frequency of 301 GHz in the TE031 resonant cavity mode. Time-resolved frequency measurement s shows that the frequency fluctuation of the gyrotron output is smaller than 2 MHz. This frequency fluctuation is mainly due to the fluctuation in the output voltage of the power supply.
TL;DR: In this paper, an efficient numerical method was devised for the study of wave circulating by a magnetized ferrite body of an arbitrary shape, including spheres, circular cylinders and cylinders.
Abstract: An efficient numerical method has been devised for the study of wave circulating by a magnetised ferrite body of an arbitrary shape. It is a finite-difference time-domain formulation that incorporates Mur's absorbing boundary conditions and a perfectly matched layer. Several shapes of interest have been studied, including spheres, circular cylinders. The electromagnetic fields inside ferrite and the power-density distribution on the ferrite's surface normal to the bias external magnetic field are obtained. It is observed that an incident plane wave would circulate around the magnetised ferrite body in an open space as if the ferrite were placed inside a waveguide junction circulator.
TL;DR: In this article, two low-noise cooled receivers based on planar Schottky diode mixers were designed and built for the Lebedev Physics Institute (LPI) spectrometer for ground-based measurements of the atmospheric ozone spectral line of 142.5 GHz.
Abstract: Two new low-noise cooled receivers based on planar Schottky diode mixers were designed and built for the Lebedev Physics Institute (LPI) spectrometer for ground-based measurements of the atmospheric ozone spectral line of 142.175 GHz central frequency. The receivers differ in the intermediate frequency (IF) bands, of around 3.7 and 1.5 GHz. Review description of the spectrometer equipped with the 3.7–GHz IF receiver is given, and its performance is compared with other millimeter-wave ground-based ozone spectrometers. Special attention was paid to design of the input Gaussian optics and the mixers. Techniques of laboratory tests of the receivers and results of the tests through all 2–mm wavelength range are considered and discussed. SSB mixer noise temperature of 460±60 K was obtained at 151 GHz for room temperature mixer, and the value of 180±30 K was measured at 134 GHz under cooling to 85 K in liquid nitrogen cryostat. SSB mixer conversion losses were less than 5.5 dB in both the cases. SSB noise temperature of the spectrometer is less than 1500 K without cooling and less than 700 K at cryogenic operation at 142 GHz. This provides sensitivity of about 0.2 and 0.1 K for the narrowest spectral channel width of 0.1 MHz and signal integration time of 1 hour. Using the optimized spectrum analyzers delivers data on high-accuracy retrieval of the ozone vertical profile in the atmosphere at altitudes about from 15 to 75 km. Examples of the ozone observation data are given.
TL;DR: In this paper, a tomographic method of image reconstruction of two-dimensional cross-sections of volumetric objects in the millimeter wavelengths band is proposed and considered. But this method is not suitable for the reconstruction of 2D objects.
Abstract: Tomographic methods of image reconstruction of two-dimensional cross-sections of volumetric objects in millimeter wavelengths band are suggested and considered.
TL;DR: In this paper, a heat equilibrium equation of the object surface is established, and the heat transfer inside the object and on the boundary surface of an object is computed using Gouraud shading.
Abstract: Most of current image synthesis models are based on optics of visible-spectrum. While simulating the illumination effect of visible light, they cannot show the infrared signature of the objects. This paper presents a synthesis model for generating realistic infrared images. We first establish a heat equilibrium equation of the object surface. Then according to it and the heat transfer inside the object and on the boundary surface of the object, we compute the temperature and radiometries of each surface patch of the object. Finally on the basis of the radiometries, each patch is drawn by Gouraud Shading. Experimental examples of the generated infrared images are presented, which illustrate the potential of our method.
TL;DR: Two-frequency operation of an 850 nm semiconductor optical amplifier was achieved by simultaneously injection seeding it with two diode lasers, which is suitable for the difference-frequency generation of coherent terahertz radiation in ultra-fast photoconductors or nonlinear optical media.
Abstract: Two-frequency operation of an 850 nm semiconductor optical amplifier was achieved by simultaneously injection seeding it with two diode lasers. The two frequencies could be independently amplified without strong interference when they were separated by more than 10 GHz, and the spectral purity was preserved by the amplification process. At frequency differences below 10 GHz, unbalanced two-frequency output was observed, which can be explained by a two-mode interaction driven by the refractive index modulation at the beat frequency. The laser system is suitable for the difference-frequency generation of coherent terahertz radiation in ultra-fast photoconductors or nonlinear optical media.
TL;DR: In this article, the reflection characteristics and refractive indices of some interior construction materials (glass, brick, plasterboard, silencing board, etc.) at the Ka-band were measured using free-space reflection method.
Abstract: Millimeter waves is expected to be used for indoor broadband wireless access for its rich frequency spectrum resources. To implement the indoor MMW wireless system, it is important to know its propagation characteristics in building, which are governed by the transmission properties of construction materials. This paper focuses on the measurements of reflection characteristics and refractive indices of some interior construction materials (such as glass, brick, plasterboard, silencing board, etc.) at Ka–band. The free–space reflection method was used to measure the reflection and transmission coefficients. Then the complex refractive indices of various materials could be calculated by using the Fresnel's formula.
TL;DR: In this paper, the ESR of Cr3+ in dark ruby was measured using a high frequency ESR spectrometer with a wide frequency range which uses a gyrotron as the radiation source.
Abstract: The ESR of Cr3+ in dark ruby is measured using a high frequency ESR spectrometer with a wide frequency range which uses a gyrotron as the radiation source. For this purpose, GYROTRON FU- IV A developed at Fukui University was optimized for use in an ESR apparatus operating in the millimeter-wave range.
TL;DR: In this paper, the propagation characteristics of a planar waveguide with chiral media filled in the cladding were studied and the effect of chirality on cutoff, dispersion and field distribution of the waveguide was analyzed.
Abstract: The propagation characteristics of a planar waveguide with chiral media filled in the cladding are presented. The effect of chirality on cutoff, dispersion and field distribution of the waveguide are studied. The results show that the cladding chirality may lead to a single-mode operation in the planar waveguide.
TL;DR: In this article, the authors derived expressions for the source-region electromagnetic field in an affinely transformable Axially Uniaxial Bianisotropic Medium (AUBM) by employing a technique originally developed by Fikioris for free space (i.e., vacuum).
Abstract: We derive expressions for the source–region electromagnetic field in an affinely transformable Axially Uniaxial Bianisotropic Medium (AUBM) by employing a technique originally developed by Fikioris for free space (i.e., vacuum). The obtained results may be used to determine the scattering response of an electrically small bianisotropic particle embedded in an affinely transformable AUBM. They can therefore be further used to homogenize a wide class of particulate composites.
TL;DR: In this paper, the dispersion characteristics, cut-off wavelength, guide wavelength and field distribution for the main mode of trapezoidal-groove guide are analyzed by using the finite element method.
Abstract: In this paper, the propagation properties such as the dispersion characteristics, cut-off wavelength, guide wavelength and field distribution for the main mode of trapezoidal-groove guide are analysed by using the finite element method. The dispersion is very low, and the field distribution in a trapezoidal-groove guide is similar to that of rectangular one. The results have important values in design, manufacture, and application of groove guides.
TL;DR: In this paper, the conditions under which gyrotrons operate at the third and even fourth harmonics of the electron cyclotron frequency were described in detail and the output lies in the millimeter to submillimeter wavelength range.
Abstract: Higher harmonic operation of gyrotrons is necessary to obtain high frequencies. Some gyrotrons included in the Gyrotron FU series developed at Fukui University have achieved operation at the third and even fourth harmonics of the electron cyclotron frequency. The output lies in the millimeter to submillimeter wavelength range and the output powers are several watts to several tens of watts. In this paper, the gyrotrons and the conditions under which they operate are described in detail.
TL;DR: The Kuhn algorithm is introduced firstly and the numerical methods for resolving the complex transcendental equations in the electromagnetic theory are researched in this article, where the numerical examples are given to confirm the validity and efficiency of numerical methods.
Abstract: The Kuhn algorithm is introduced firstly and the numerical methods for resolving the complex transcendental equations in the electromagnetic theory are researched. The numerical examples are given to confirm the validity and efficiency of the numerical methods.
TL;DR: An autodyne phenomenon in the O-type Weak-Resonant Backward Wave Oscillator of Ka-band working in chaotic oscillatory regime is investigated in this paper, where the main attention is paid to the studying of the decorrelated reflected signals on the modulation of the power spectral density of the chaotic oscillations.
Abstract: An autodyne phenomenon in the O-type Weak-Resonant Backward Wave Oscillator of Ka-band working in chaotic oscillatory regime is under investigation. The main attention is paid to the studying of the action of decorrelated reflected signals on the modulation of the power spectral density of the chaotic oscillations. Physical mechanisms are revealed and phenomenological model is suggested to explain the strong PSD modulation observed under the affect of the small refelected signal. The PSD modulation index has been introduced and its anomalous increase with the enlargement of the distance to the load is revealed experimentally, as well as the physical explanation for that effect is presented. All physical results obtained are valid for the autodyne effect in any chaotic oscillator. The results obtained can be used for the design of different autodyne based devices for the remote sensing, microwave telemetry and control systems.
TL;DR: Using Meissner Boundary Condition (MBC), the properties of a high-temperature superconductive (HTS) rectangular waveguide are studied in this paper, and the results show that the modes properties in a HTS's waveguide is much different from those in a normal conductive waveguide.
Abstract: Using Meissner Boundary Condition (MBC), the properties of a high-temperature superconductive (HTS) rectangular waveguide are studied. The results show that the modes properties in a HTS's waveguide is much different from those in a normal conductive waveguide. The investigation indicates that all design formulations for normal mettalic waveguides can not be applied to design HTS's waveguides and related circuits. New design formulations should be developed in future.
TL;DR: In this article, the general eigenequations and the field expressions for circular waveguides containing chiral material in both the core and the cladding are given in a simple formulation.
Abstract: The general eigenequations and the field expressions for circular waveguides containing chiral material in both the core and the cladding are given in a simple formulation. The results indicate that there are two types of field distribution which is related to the operating wavelength and chiral admittance. When the chiral admittance is larger than a critical value, the fields of one kind of circularly polarized wave in the core become exponentially-like damping in the transverse direction. Based on the eigenequations, the characteristics of a circular waveguide with chiral medium filled in the core are investigated. The relation between the cutoff frequency and the chiral admittance, the dispersion curves for some modes with different angular mode number and the transverse distribution of fields are presented. Some features different from the ordinary circular waveguide are resulted.