The author received the Yahagi Memorial Award 2019 from the Technical Committee on Dielectrics and Electrical Insulation, thevInstitute of Electrical Engineering of Japan. In this paper, memories of the late Prof. Kichinosuke Yahagi and his teachings arevdescribed by a former student. The teachings of Prof. K. Yahagi can be summarized as “Seek the Truth.” The author pursued avnumber of truths according to said teachings in his research and development endeavors. The development of cross-linkedvpolyethylene insulated DC power cables rated for the world’s highest voltage was brought about as one of the results of thevteachings.

Optical fiber communication started to become practical use in 1970, when an optical fiber with a transmission loss of 20 dB/kmvand a laser diode continuously emitting at room temperature appeared. Sumitomo Electric Industries, Ltd. has enterprisinglyvdedicated the development and commercialization of optical fibers since the early days. Utilizing the vapor-phase axial depositionvmethod, which has spread worldwide as a preform manufacturing process, we have kept launching high-quality optical fibers andvcables such as ultra-low-loss silica core fibers and ultra-high-density optical cables. This way, we have continued to support thevexpansion of optical fiber networks as one of the indispensable social infrastructure. This paper looks at the evolution of opticalvfiber technology and our efforts in developing optical fibers and cables that would meet the need of the time.

Electric vehicles and hybrid electric vehicles are in widespread use and these vehicles are all equipped with DC/DC converters forvcharging lead-acid batteries from high-voltage storage batteries. To simplify the installation, DC/DC converters are required to bevsmall. This paper describes a DC/DC converter that has been downsized by 50% compared with conventional ones by increasingvthe switching frequency from 100 kHz to 500 kHz using GaN devices.

Magnetrons have long been used as transmitting devices for marine radar, however, gallium nitride high-electron-mobilityvtransistors (GaN HEMT) are increasingly adopted due to their long life, high performance, and compliance with radio laws andvregulations. This paper presents our internally-matched X-band GaN HEMT that feature the industry's highest output power of 300vW, targeting a variety of marine radars ranging from small-power radars for pleasure boats to high-power radar for largecommercialvvessels. We also report on a prototype compact solid-state amplifier that has been made to demonstrate thesevtransistors.

In recent years, gallium nitride high-electron-mobility transistor (GaN HEMT) amplifiers with high efficiency have been adopted due to the increasing demand for downsized and low-power-consumption base stations. In 5G networks, where further improvement in network capacity and data rates is required, the presence of GaN HEMTs is expected to grow further due to their advantages in broadening the bandwidth of amplifiers. This paper describes the characterization and analysis method for the current source of GaN HEMTs that we are working on to develop the GaN HEMT amplifiers for base stations. We newly adopted a large-signal lowfrequency measurement that enables evaluation under conditions close to the actual radio frequency operation, to explore design guidelines for GaN HEMTs. In addition, we analyzed the effect of gate voltage clipping in class-F and inverse class-F operation, which is known as a method for improving the efficiency of amplifiers by using a large-signal model to figure out the limiting factorvof efficiency.

A large capacity of the Internet is strongly demanded due to the increase of internet-connected devices and the diversification of internet-based services. To address these needs, we are in a new phase to upgrade the transmission speed of access optical networks from the current mainstream 10G class to 50G class. We have developed a new transimpedance amplifier (TIA) capable of receiving 25.78 Gbit/s burst signals to meet the demand for higher-speed transmission. Using the TIA and avalanche photodiode (APD), we have developed a 25.78 Gbit/s/λ burst-mode receiver, and confirmed its applicability to 50G-EPON optical transceivers for the first time in the world.

We have developed a wavelength division multiplexing transmission method to efficiently connect radio base stations and antennas with a small number of optical fibers. In the fifth generation (5G) radio access networks, there is demand for a technology that can economically transmit 25G Ethernet signals over up to 40 km by wavelength division multiplexing (WDM). This paper introduces the half-rate transmission method that enables 40 km WDM transmission by dividing 25.8 Gbit/s signals into two channels of 12.9 Gbit/s signals and transmitting them.

Silicon carbide (SiC) power devices are promising next-generation devices and their market is growing globally year by year. The quality of SiC epitaxial wafers is particularly important to secure the reliability of large-current power devices used for automotive applications. Basal plane dislocation (BPD) in the SiC epitaxial wafers causes stacking fault expansion, which leads to the fatal degradation of SiC bipolar devices. To suppress the stacking fault expansion, the introduction of highly nitrogen-doped layer called a “recombination-enhancing layer” has been proposed. In this study, we have established a method to evaluate BPD in the recombination-enhancing layer by investigating the receiving filter using photoluminescence imaging, and successfully obtained a 150 mm SiC epitaxial wafer with extremely low BPD density. We also confirmed that BPD and surface defects in the drift layer were simultaneously suppressed, demonstrating the new epitaxial wafer has stable characteristics for large chip devices.

To ensure the stable operation of utility-scale solar power plants over a long period, it is necessary to improve the inspection and maintenance levels, especially the inspection efficiency of the DC voltage parts, for which visual inspection has been conducted. Sumitomo Electric Industries, Ltd. has developed a system that detects abnormalities in solar panels by analyzing string data with AI. Data on detected abnormalities, including their types and urgency, are reported to the power plant manager via daily emails and used for efficient facility maintenance. Using the system, we also provide diagnostic services suggesting best inspection methods and countermeasures for the abnormalities.

With the expanding introduction of renewable energy sources and advances in semiconductor and energy storage technologies, direct current (DC) distribution systems that combine renewable energy sources and storage batteries have attracted attention as economical and environment-friendly next-generation power supply systems. These systems are also expected to help improve power system resilience and business continuity planning (BCP). This paper introduces the background of our study and the details of the DC distribution demonstration system built at the Nissin Academy Training Center.

We have developed a new diamond-like carbon film “HC-DLC," which is produced by vacuum arc deposition and contains hydrogen. With its appropriate hydrogen content, this film obtained extremely low attackability to soft metals without compensating its high wear resistance and seizure resistance in engine oil containing MoDTC. The film demonstrates excellent performance in protecting piston pins that repeatedly slide on soft metals. To meet market needs, the mass production of the film started in the fall of 2019, and now further application to the next-generation high-efficiency engines is under consideration.

Sumitomo Electric Industries, Ltd. has been engaged in the development of high-performance and long-length Bi2223 hightemperature superconducting wires. These wires and their applied products, such as current leads for magnetic resonance imaging, have been commercialized and well received by the market. This paper describes the recent development and commercialization of Bi2223 wires and typical products incorporating the wires, as well as wire joint technology and high-current conductor technology, which are indispensable for expanding the application of the wires.

For research and development in material science, it is important to understand the three-dimensional (3D) distributions of chemical species in samples. The effective utilization of 4D big data which contain a lot of information about the 3D distributions is a key factor. This paper demonstrates a new 4D data analysis technique called “two-step multivariate curve resolution (MCR)”. To obtain an intuitive expression of 4D data, we devised a process involving two iterations of MCR with digitization in between. The new technique was applied to the analysis of time-of-flight secondary ion mass spectrometry data derived from a thin-film sample to assist in the interpretation of complex three-dimensional local microstructures. Compared to conventional methods of data presentation, two-step MCR was found to greatly facilitate the clarification and understanding of the 4D analysis data.

In order to meet the demand for high dimensional accuracy in powder metallurgy products, we have been developing powder simulation techniques to support the design of the production process. Powder simulations provide a macroscopic interpretation of powder behavior by calculating the motion of individual particles that constitute the powder. In this paper, the powder simulation is applied to the milling process of raw powder and the powder feeding process of metal powder. Although the milling efficiency can be predicted from the collision energy of the balls in a ball mill, it is necessary to reproduce the motion of each ball with complicated collision process to predict the collision energy accurately. In this study, we have developed an analysis technique to predict the change of the collision energy when the milling conditions are changed, in order to improve the performance of the milling process. We have also developed an analytical technique to visualize the powder behavior in the powder feeding process to clarify the mechanism of the filling variation in the die.

"In recent years, there has been an increase in the demand for by-wire technologies for improved safety and convenience. Brake-by-wire and shift-by-wire technologies, which have been widely used, are essential for future selfdriving cars. The market is expected to expand for them in the future. However, as the by-wire-technology controls a device through electrical signals, a control failure occurs if the vehicle power source such as a lead-acid battery becomes out of order . Sumitomo Wiring Systems, Ltd. and AutoNetworks Technologies, Ltd. of the Sumitomo Electric Group have developed an x-by-wire backup battery designed for uninterrupted by-wire control even in the event of a vehicle power failure."