Jong Hwa Kwon

Novel Electromagnetic Bandgap Array Structure on Power Distribution Network for Suppressing Simultaneous Switching Noise and Minimizing Effects on High-Speed Signals

To supply high-speed digital circuits with stable power, power/ground noise, such as simultaneous switching noise (SSN) and ground bounce noise caused in multilayer printed circuit boards (PCBs) and packages need to be sufficiently suppressed. The electromagnetic bandgap (EBG) is widely recognized as a good solution for suppressing the propagation of SSN in the gigahertz range. However, a typical coplanar EBG structure etched onto the power and ground planes may degrade the quality of high-speed signals passing over the perforated reference plane. In this paper, a novel method of arranging EBG unit cells on both the power/ground planes in multilayer PCBs and packages is proposed, not only as a means of sufficiently suppressing the propagation of power noise, but also as a means of minimizing the effect of EBG-patterned reference planes on a high-speed signal. On the assumption that noise sources and noise-sensitive devices exist only in specific areas, the proposed method partially positions EBG unit cells only near these critical areas. The SSN suppression performance of the proposed structure is verified by conducting simulations and measurements in the time and frequency domains. Furthermore, signal quality is investigated to verify whether the proposed EBG-patterned reference planes are superior to conventional EBG-patterned planes in terms of signal integrity.

Design of Optimized Multilayer PIFA With the EBG Structure for SAR Reduction in Mobile Applications

This paper proposes an optimized multilayer planar inverted-F antenna (PIFA) with an electromagnetic bandgap (EBG) at personal communication services band for specific absorption rate (SAR) reduction. The EBG structure, which has bandgap capability and acts as a perfect magnetic conductor surface, can suppress surface waves and reduce undesired radiation from an antenna. Thus, the EBG structure is capable of preventing electromagnetic (EM) fields being emitted in the direction of the human head. To optimize the multilayer PIFA structure for SAR reduction, the EBG structure between the printed circuit board and antenna layer is designed first. Second, a parameter study about the EBG cell numbers, height, and location of the PIFA with the EBG structure is performed. Finally, the optimized multilayer PIFA with the EBG is investigated and the S-parameters, radiation patterns, total radiated power values, and SAR values are presented. The results demonstrate the reduction of SAR values while maintaining the antenna performance. Thus, the human head can be protected from hazardous EM fields using the EBG structure.

Hybridization of oxidized MWNT and silver powder in polyurethane matrix for electromagnetic interference shielding application

Multiwalled carbon nanotubes (MWNTs) are chemically modified with respect to various different oxidative conditions, including the acid concentration, treatment time, and temperature. The conductivity of polyurethane (PU) composites filled with the MWNTs oxidized under optimal condition is measured as a function of frequency with the content of MWNTs and analyzed using percolation theory. Because the PU composites filled only with the MWNTs cannot satisfy the requirements for materials providing shielding against electromagnetic waves, conductive polymer composites are fabricated by the hybridization of MWNTs with Ag flakes. It is observed that a small amount of the MWNTs remarkably enhances the conductivity and shielding effectiveness of the MWNT/Ag flake/PU composites, by bridging the gap between the flaky Ag clusters. The electromagnetic interference shielding effectiveness of the composites can be controlled from about 60 dB to more than 80 dB at an extremely low loading level of both the MWNTs and the Ag flakes in the frequency range from 10 to 1000 MHz.

1950 MHz Electromagnetic Fields Ameliorate Aβ Pathology in Alzheimer's Disease Mice.

The involvement of radiofrequency electromagnetic fields (RF-EMF) in the neurodegenerative disease, especially Alzheimer’s disease (AD), has received wide consideration, however, outcomes from several researches have not shown consistency. In this study, we determined whether RF-EMF influenced AD pathology in vivo using Tg-5xFAD mice as a model of AD-like amyloid β (Aβ) pathology. The transgenic (Tg)-5xFAD and wild type (WT) mice were chronically exposed to RF-EMF for 8 months (1950 MHz, SAR 5W/kg, 2 hrs/day, 5 days/week). Notably, chronic RF-EMF exposure significantly reduced not only Aβ plaques, APP, and APP carboxyl-terminal fragments (CTFs) in whole brain including hippocampus and entorhinal cortex but also the ratio of Aβ42 and Aβ40 peptide in the hippocampus of Tg-5xFAD mice. We also found that parenchymal expression of β-amyloid precursor protein cleaving enzyme 1(BACE1) and neuroinflammation were inhibited by RF-EMF exposure in Tg-5xFAD. In addition, RF-EMF was shown to rescue memory impairment in Tg-5xFAD. Moreover, gene profiling from microarray data using hippocampus of WT and Tg-5xFAD following RF-EMF exposure revealed that 5 genes (Tshz2, Gm12695, St3gal1, Isx and Tll1), which are involved in Aβ, are significantly altered inTg-5xFAD mice, exhibiting different responses to RF-EMF in WT or Tg-5xFAD mice; RF-EMF exposure in WT mice showed similar patterns to control Tg-5xFAD mice, however, RF-EMF exposure in Tg-5xFAD mice showed opposite expression patterns. These findings indicate that chronic RF-EMF exposure directly affects Aβ pathology in AD but not in normal brain. Therefore, RF-EMF has preventive effects against AD-like pathology in advanced AD mice with a high expression of Aβ, which suggests that RF-EMF can have a beneficial influence on AD.

SAR reduction on a mobile phone antenna using the EBG structures

In this paper, specific absorption rate (SAR) reduction at the PIFA type for a mobile phone using various types of EBG structure are tested. Two EBG structures, that is a via or a via-less, are designed. The EBG structures can reduce the surface wave and prevent the undesired radiation from the ground plane. Thus, the EBG structure which is designed for mobile terminal enables to comply with the exposure guideline. From the simulation and measured results demonstrated the reduction of the radiation pattern towards the direction of human head and the SAR value.

Design of PIFA With Metamaterials for Body-SAR Reduction in Wearable Applications

This letter proposes a planar inverted-F antenna (PIFA) with an artificial magnetic conductor (AMC) structure for body specific absorption rate (SAR) reduction in a wideband-code-division-multiple-access band. As wireless devices such as wearable phones and smart watches become more common, health risks originating from electromagnetic waves generated by devices worn on the body have become an important issue. AMC structures are a type of metamaterial that can act as a perfect magnetic conductor and control the radiation pattern of an antenna. Thus, an antenna with an AMC structure is capable of preventing hazardous electromagnetic fields being emitted in the direction of the body. The S-parameters, radiation patterns, total radiated power values, and SAR values of such a designed structure are presented. The results demonstrate a 43.3% reduction in the SAR value at the center frequency. Thus, the human body can be protected from electromagnetic waves using metamaterials.

Magnetic Shielding Analysis of a Slit on a Conducting Plate Coated With a Ferrite Sheet: Transverse Incidence

In this paper, an analytical solution is presented for magnetic shielding analysis of a slit on a conducting plate coated with a ferrite sheet. The Fourier transform and the mode matching technique are employed to obtain the analytical solution for magnetic vector potential. Magnetic shielding effectiveness is investigated in terms of the geometrical parameters of a slit on a conducting plate and a ferrite sheet. The proposed method is numerically validated by a commercial finite element solver with good agreement. In addition, the proposed analytical solution is in a rapidly converging series so that it is more efficient than other numerical techniques.

Design of multilayer PIFA based on an EBG structure for SAR reduction in mobile applications

This paper propose a optimized multilayer PIFA in PCS bands based on the electromagnetic bandgap (EBG) for SAR reduction. The EBG structure which has bandgap capability and acts as PMC surfaces can reduce the surface waves and prevent the undesired radiation from the antenna. Thus, the EBG structure can reduce the electromagnetic fields toward the human head direction. First, to optimize of multilayer PIFA structure for SAR reduction, the EBG structure with the PCB and antenna layer is designed. And second, a parameter study of location and height of a PIFA with the EBG structure is performed. Finally, the optimized multilayer PIFA with EBG is investigated, both on the S-parameters, radiation patterns and on the SAR value. The results demonstrated the reduction of SAR value with maintaining the antenna performance and the human body can be protected from hazard electromagnetic fields.

Comparison of the SAR in the human head using the EBG structures applied to a mobile handset

In this paper, the SAR measurement values are compared with a conventional mobile handset and with EBG structures. In order to protect a human head from the exposure of electromagnetic field and to comply with the exposure guideline, the designed EBG components are inserted in a commercial US-PCS handset. The total width and length of the EBG structures are 31 mm and 8 mm, respectively. The measured results in this paper demonstrated the movement of a hot spot, the reduction of total radiated power toward the head direction and the reduction of the SAR in the human head.

Autonomous Coil Alignment System Using Fuzzy Steering Control for Electric Vehicles with Dynamic Wireless Charging

An autonomous coil alignment system (ACAS) using fuzzy steering control is proposed for vehicles with dynamic wireless charging. The misalignment between the power receiver coil and power transmitter coil is determined based on the voltage difference between two coils installed on the front-left/front-right of the power receiver coil and is corrected through autonomous steering using fuzzy control. The fuzzy control is chosen over other control methods for implementation in ACAS due to the nonlinear characteristic between voltage difference and lateral misalignment distance, as well as the imprecise and constantly varying voltage readings from sensors. The operational validity and feasibility of the ACAS are verified through simulation, where the vehicle equipped with ACAS is able to align with the power transmitter in the road majority of the time during operation, which also implies achieving better wireless power delivery.