Dongjin Kim

We propose a slot array antenna for dual-polarization operation in the 60 GHz band. To realize the dual-polarization, cross-shaped radiating slots and a multilayer feeding structure are employed. A 16 × 16-element array is fabricated by diffusion bonding of laminated thin copper plates, which has the advantages of high precision and low loss characteristics. To suppress the grating lobes, we employ several design techniques, such as a thick cavity structure and dense element spacing. The high an

Despite the rapid progression of silicon carbide (SiC) power devices, the thermal characteristic evaluation during power cycling at high temperature (>200 °C) is an issue. In this article, a fast and miniaturized evaluation system with online thermal characteristic measurement function was introduced by an n-doped 4H SiC thermal engineering group (TEG) chip. Online thermal resistance measurement of a power module structure by Ag sinter joining with micron/submicron Ag particles paste in low temp

This study focuses on the realization of rapid Ag sintering in 10 min under various temperature conditions without pressure in the air. In each temperature range from 175 °C to 250 °C, the factors of microstructure that can retard joint failure were thoroughly investigated. The maximum bonding strength in the bonding temperature range exceeded 50 MPa. In particular, an increase in bonding temperature from 175 °C to 250 °C increased the grain size of the Ag sintered structure by up to about 90%,

We propose a 4 × 4-element corporate-feed waveguide slot array antenna with outer cavities for the 120 GHz band. To adjust the mutual coupling effects in a small sized array antenna, an outer cavity structure is employed for each radiating slot. The outer cavity in this antenna structure provides adequate mutual coupling effects for each radiating element. As a result, high antenna efficiency is achieved over a broad bandwidth. A 4 × 4-element array with the outer cavities was fabricated by diff

The present study investigates a fatigue property and its microstructural and interface geometrical effect on the resistance element welded (REWed) aluminum (Al)/high-strength steel (Fe) lap joint. The assembled Al/Fe joints were subjected under the fatigue strength up to 80% of tensile-shear loads with 0.1 of the load ratio. As a result, an exceptional fatigue strength has been secured inducing the base material fracture because there are no noticeable interfacial defects at the 10.5 kA welding

This study introduced the SiC micro-heater chip as a novel thermal evaluation device for next-generation power modules and to evaluate the heat resistant performance of direct bonded copper (DBC) substrate with aluminum nitride (AlN-DBC), aluminum oxide (DBC-Al₂O₃) and silicon nitride (Si₃N₄-DBC) ceramics middle layer. The SiC micro-heater chips were structurally sound bonded on the two types of DBC substrates by Ag sinter paste and Au wire was used to

In this paper, a composite right-left-handed (CRLH) rectangular waveguide satisfying a balanced condition above the cutoff frequency and a beam scanning leaky-wave slot antenna are presented. The proposed metamaterial waveguide consists of one shorted stub and two H-plane irises, which produce a negative permittivity and negative permeability, respectively. To design a balanced CRLH transmission line, the H -plane irises are materialized by twisted shapes that present a minimized coupling with t

The refill-friction stir spot welding (RFSSW) process on the Al5052–H32 alloy joined with high-purity Cu film resulted in notable changes in the work-hardened Al alloy. The stirring action caused dynamic recrystallization in the weld zone, leading to the loss of work-hardening. Surprisingly, the plot of grain size-hardness in Al alloy after RFSSW did not follow the Hall-Petch relationship. Obtained through combined analysis with a transmission electron microscope, X-ray diffraction, and thermody

Abstract This study was carried out to evaluate the reliability of GaN die-attached on a direct bonded aluminum (DBA) substrate with Ag sinter joining in up to 1000 harsh thermal shock cycles over a temperature range from −50 °C to 250 °C. For joining the die-attached structure, metallized Ti/Ag was prepared first on the substrates of DBA and GaN chips. A GaN die and DBA substrate were bonded by a micron/submicron Ag sinter paste in air at 250 °C without pressure. The initial die shear strength

This study proposes an effective repair technology using arc additive manufacturing for pressurized water reactors (PWRs) in nuclear power plants (NPP) aimed at avoiding complete replacements and post-weld-heat treatments (PWHTs) of component parts while ensuring safety and reliability. Effective repair technology is defined as economic and process efficiency, because of maintenance costs and radiation exposure, and it is critical in related industries. The technology is designed to relieve the