Ryuji Koga

Ground‐based network observation of Asian dust events of April 1998 in east Asia

We coordinated a ground-based network that has been in use since 1997 to observe Asian dust during springtime. Huge Asian dust events that occurred in the middle of April 1998 were captured by this network. In this paper we present the organization of the network; a description of the instruments, including the lidar, sky radiometer, and optical particle counter; and the results of the observation, and offer discussions regarding the transport mechanism of Asian dust in east Asia using an on-line tracer model. We discussed the time series of the surface concentration and the height distribution of the dust. A cutoff cyclone generated during the dust episode was responsible for trapping and sedimentation during the transportation of the Asian dust, particularly in the southern parts of China and Japan. Horizontal dust images derived from NOAA/AVHRR clearly revealed the structure of the vortex. The lidar network observation confirmed the general pattern of dust height distribution in this event; the height of the major dust layer was about 3 km over Japan but was higher (4 to 5 km) in Seoul and Hefei. A thin dust layer in the upper troposphere was also commonly observed in Hefei and Japan. Evidence of the coexistence of dust and cirrus was shown by the polarization lidar. The lidar network observation of Asian dust and satellite remote sensing provide key information for the study of the transport mechanism of Asian dust. Further extension of the lidar network toward the interior of the continent and the Pacific Rim would reveal the greater global mechanism of the transportation.

Convergence acceleration and accuracy improvement in power bus impedance calculation with a fast algorithm using cavity modes

Based on the cavity-mode model, we have developed a fast algorithm for calculating power bus impedance in multilayer printed circuit boards. The fast algorithm is based on a closed-form expression for the impedance Z matrix of a rectangular power bus structure; this expression was obtained by reducing the original double infinite series into a single infinite series under an approximation. The convergence of the single series is further accelerated analytically. The accelerated single summation enables much faster computation, since use of only a few terms is enough to obtain good accuracy. In addition, we propose two ways to compensate for the error due to the approximation involved in the process of reducing the double series to the single series, and have demonstrated that these two techniques are almost equivalent.

Modeling of gapped power bus structures for isolation using cavity modes and segmentation

Resonance characteristics of gapped power bus structures with a slit or a gap were studied, using a fast algorithm based on a full cavity-mode resonator model and the segmentation method. Inductance and capacitance models were used to account for a field coupling along the slit and across the gap, respectively. The effectiveness of the segmentation method and the inductance model for the slit has been demonstrated by good agreement between the calculated and measured results, while the capacitance model for the gap is shown to be useful when the coupling between the segments is relatively weak.

8” Uniform Electron Cyclotron Resonance Plasma Source Using a Circular TE01 Mode Microwave

A new type of electron cyclotron resonance (ECR) plasma source has been developed using a circular TE 01 mode microwave converted from the principal TE 01 rectangular mode. The ion saturation current density of 36 mA/cm 2 is achieved for the input microwave power of 3 kW at the nitrogen gas pressure of 5×10 -4 Torr. The uniformity of the ion saturation current density is within ±3% over 8 inches in diameter, which is better than that produced by a conventional TE 11 mode microwave. The mean ion energy at the substrate position in this ECR plasma source is in the range of 20-30 eV, depending on the shape of magnetic fields

High-speed simulation of PCB emission and immunity with frequency-domain IC/LSI source models

Some recent results from research conducted in the EMC group at Okayama University are reviewed. A scheme for power-bus modeling with an analytical method is introduced. A linear macro-model for ICs/LSIs, called the LECCS model, has been developed for EMI and EMS simulation. This model has a very simple structure and is sufficiently accurate. Combining the LECCS model with analytical simulation techniques for power-bus resonance simulation provides a method for high-speed EMI simulation and decoupling evaluation related to PCB and LSI design. A useful explanation of the common-mode excitation mechanism, which utilizes the imbalance factor of a transmission line, is also presented. Some of the results were investigated by implementing prototypes of a high-speed EMI simulator, HISES.

Lidar network observation of Asian dust (Kosa) in Japan

We have organized a network campaign for the observation of Asian dust in the spring of 1997 and 1998 in Japan. Through the communication with electric mail, we have successfully observed Kosa events by lidar, sunphotometer, and particle counter, etc. These data must be useful to analyze the transport mechanism of Asian dust and validate the satellite observations.

Power current model of LSI and parameter identification for EMI simulation of digital PCBs

A power current model of LSIs for EMI simulation of digital printed circuit boards, and a parameter identification method based on the model are presented. The model consists of equivalent internal impedance and an equivalent internal current source. The equivalent internal impedance is obtained by measuring the impedance between the power and ground terminal of an LSI by means of an impedance analyzer, and an equivalent internal source is obtained from the measured current through the power terminal under the conditions of known external impedance. Furthermore, it is shown that simulation results generated using this model have good agreement with the results of measurements made under a range of external impedances.

Miniaturization of Electromagnetic Bandgap (EBG) Structures with High-Permeability Magnetic Metal Sheet

Electromagnetic bandgap (EBG) structures in a pair of parallel planes are quite effective for suppressing simultaneous switching noise, but they are too large to be applied to compact electronic devices. To miniaturize the EBG structures, we investigated an approach to interpose a high-permeability magnetic metal sheet between the parallel planes. The experimental results show that high permeability of the sheet shifts the stopband towards lower frequencies. This suggests that such sheets contribute to the miniaturization of the EBG structures. In addition, it is demonstrated that the imaginary part of the permeability can expand the stopband.

High-Resolution Measurement of Size Distributions of Asian Dust Using a Coulter Multisizer

Abstract A Coulter Multisizer, which is based on the electrical sensing zone (ESZ) or the Coulter principle, was used to measure the size distribution of Asian dust. Coulter Multisizer analysis provides high-resolution size measurements of water-insoluble aerosol particles (WIPs) and the number concentration at each size bin. Aerosol filter sampling was conducted at four sites in Japan during spring 2003. The measured volume size distributions fit fairly well with a lognormal distribution. The results show that the WIP size distributions of the same Asian dust air mass varied at each sampling site and the volume mode diameter at the sites reduced from west to east. The derived volume mode diameter ranged from 1.4 to 2.2 μm and was comparatively smaller than those in previous studies on Asian dust. This can be explained by the possible internal mixing of Asian dust with other components and by the breaking of particles and dispersion of aggregations by ultrasonification during extraction. The analysis meth...

Analysis of resonance characteristics of a power bus with rectangle and triangle elements in multilayer PCBs

One of the major sources of radiated EMI is attributed to power bus resonance in a printed circuit board (PCB). A fast algorithm, combined with the segmentation method, is applied for calculating resonance characteristics of a power bus whose pattern consists of several segments of rectangles and/or right-angled triangles. Good agreement between the calculated and measured results demonstrates the usefulness and accuracy of the fast algorithm and the segmentation method.