• Journal of electromagnetic engineering and science
• /
• v.8 no.3
• /
• pp.110-113
• /
• 2008

In this paper, we designed and fabricated an electromagnetic(EM) wave absorber for automotive radar in cars using $TiO_2$ as a dielectric material and chlorinated polyethylene(CPE) as a binder. First of all, we confirmed that the optimum composition ratio of $TiO_2$ was about 70 wt.%. The complex relative permittivity of a sample containing $TiO_2$: CPE=70:30 wt.% was calculated from S-parameter. The EM wave absorption abilities were simulated for the EM wave absorbers of different thickness using the calculated relative permittivity, and the EM wave absorber was manufactured based on the simulated design. A comparison of simulated and measured results is in good agreement. Measurement shows that a 1.85 mm thick absorber has absorption ability higher than 20 dB in the frequency range of $76{\sim}77$ GHz for automotive radars.

• Journal of electromagnetic engineering and science
• /
• v.15 no.3
• /
• pp.167-172
• /
• 2015

Research results on possible effects caused by radiofrequency fields in children are limited because most of the studies published so far have focused on adults, rather than children. Mobile phone use is now widespread, even among younger children. If a biological risk due to mobile phone exposure is found, it might be greater in children because their bodies might be more sensitive to radiofrequency energy. The issue of a possible difference in sensitivity between adults and children begins with whether any difference exists physically in terms of electromagnetic absorption. This paper presents a review of recent publications on dosimetric comparisons between children and adults with respect to radiation from mobile phones. The issue of the health effects of mobile phone use is beyond the scope of the present review. Most of the dosimetry research on possible differences in power absorption between children and adults has been based on numerical modeling and analysis. The understanding of the results so far is presented and needed studies are described.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.14 no.7
• /
• pp.756-761
• /
• 2003

The microwave absorption properties of silicone, chloride polyethylene(CPE), and natural lacquer which is newly suggested in this study as a binder for composite microwave absorber were investigated to develop a superior microwave absorber. MnZn ferrite composite microwave absorbers mixed with them were prepared and their absorption property was investigated. A MnZn ferrite microwave absorber mixed with natural lacquer showed an excellent microwave absorption property in expanded frequency band.

• Journal of electromagnetic engineering and science
• /
• v.19 no.2
• /
• pp.71-81
• /
• 2019

This paper presents a design methodology for wideband single-layered microwave absorbers with arbitrary absorption at the design center frequency using reactive Salisbury screens. The bandwidth of the absorber increases when the flatness of the reflection response at the design center frequency is maximized. Based on this observation, closed-form design formulas for wideband absorbers are derived. As they are scalable to any design frequency, wideband reactive screens can be systematically realized using two-dimensional periodic crossed-dipole structures patterned on a resistive sheet. Based on this method, a single-layered absorber with a 90% bandwidth improved to 124% of the design center frequency is presented. For the purpose of physical demonstration, an absorber with a design center frequency of 10 GHz is designed and fabricated using a silver nanowire resistive film with a surface resistance of 30 Ω/square. The measured absorption shows a good agreement with both the calculation and the electromagnetic simulation.

• Journal of electromagnetic engineering and science
• /
• v.15 no.2
• /
• pp.97-103
• /
• 2015

This paper investigates the effect of absorption loss by a human body to the received signal strength with respect to on-body transmitting antenna positions in on-to-off wireless body area networks. This investigation is based on measurement results obtained from experiments performed on human bodies (male and female) using planar inverted-F antennas in an anechoic chamber. The total absorption loss by the human body is also presented through the SEMCAD-X simulations. Our investigation showed that the received signal strength becomes lower when the transmitting antenna is mounted at a specific position where more absorption loss is experienced. The statistical analyses of on-to-off body channel characteristics based on the measurement results are presented.

• Journal of the Korean Magnetics Society
• /
• v.23 no.3
• /
• pp.83-88
• /
• 2013

The soft magnetic Fe-Si-Cr flakes with the thickness of about 1 ${\mu}m$ were annealed at 500 and $700^{\circ}C$ for 1 h, and the composite sheets for electromagnetic wave noise absorber available for quasi-microwave band were fabricated by using these annealed flakes and polymer. Further the power loss characteristics of the composite sheets was investigated to clarify the annealing effect on electromagnetic wave absorption properties. The power loss decreased in the frequency range of several GHz when the annealed flakes were used as compared to the sheet using the as-milled FeSiCr alloy flakes. Moreover the sheets using annealed flakes exhibited lower value of real and imaginary part of complex permeability. These inferior electromagnetic wave absorption properties of the composite sheets using annealed alloy flakes were considered to be obtained by the enhanced eddy current effect upon annealing-induced recovery of microstructure and resulted low complex permeability.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.14 no.4
• /
• pp.421-430
• /
• 2003

In this paper, we propose a method to consider SAR(Specific Absorption Rate) at beginning stage of handsets development. First, simulation was carried out with changing folding angle from 150$^{\circ}$to 142$^{\circ}$. Simulation results show that SAR value is decreased with decreasing the folding angle. When folding angle is 142$^{\circ}$, error between simulation and measurement results is about 3.95 %. Second, we made some experiments with EMI (Electromagnetic Interference) paint, and its results show that different pattern of EMI paint have different SAR values. After removing EMI paint at the lower part of antenna feeding point, we got the decrease efficiency of 15.46 % for SAR value. When we applied zigzag painting pattern, we got the highest SAR decrease efficiency.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.27 no.4
• /
• pp.399-402
• /
• 2016

We propose a thin electromagnetic wave absorber using varactor diodes combined with intentionally introduced multiple slits, which enables continuous sweep of an absorption frequency band throughout relatively wide frequencies. The absorption frequency range of conventional electrically tunable absorbers has been restricted by high capacitance of varactor diodes. In order to overcome the problem, we introduce parasitic capacitance and connect them with varactors in series, which reduces the total capacitance dramatically. As a result, we can raise the operating absorption frequency up to the X-band region. Moreover, we can also control the operating frequencies by modifying the number of slits with little change in an entire frequency sweep range. Good agreement between simulated and measured results show the validity of our proposal.

• Journal of Powder Materials
• /
• v.16 no.6
• /
• pp.424-430
• /
• 2009

Electromagnetic wave energies are consumed in the form of thermal energy, which is mainly caused by magnetic loss, dielectric loss and conductive loss. In this study, CNT was added to the nanocrystalline soft magnetic materials inducing a high magnetic loss, in order to improve the dielectric loss of the EM wave absorption sheet. Generally, the aspect ratio and the dispersion state of CNT can be changed by the pre-ball milling process, which affects the absorbing properties. After the various ball-milling processes, 1wt% of CNTs were mixed with the nanocrystalline $Fe_{73}Si_{16}B_7Nb_{3}Cu_1$ base powder, and then further processed to make EM absorption sheets. As a result, the addition of CNT to Fe-based nanocrystalline materials improved the absorption properties. However, the increase of ball-milling time for more than 1h was not desirable for the powder mixture, because the ballmilling caused the shortening of CNT length and the agglomeration of the CNT flakes.

• Electrical & Electronic Materials
• /
• v.8 no.6
• /
• pp.744-751
• /
• 1995

This paper describes a study on absorption properties of electromagnetic wave by the composition ratio of Ni-Zn ferrite. Ni-Zn ferrite was composed of 48-52mol% Fe$\_$2/O$\_$3/, 18-22mol% NiO and 26-34mol% ZnO. The sintering of the composition was carried out at 1200.deg. C for 2 hours. Through the experiments, it was found that the resonance phenomenon occured at low frequency range for high permeability and vice versa. In the case of the composition of 49mol% Fe$\_$2/O$\_$3/, 20mol% NiO and 31mol% ZnO, the bandwidth ranged from 0.35GHz to 0.95GHz with the absorption thickness of 10mm. Also, in the case of the composition 51mol% Fe$\_$2/O$\_$3/, 22mol% NiO and 27mol% ZnO, the bandwidth ranged from 0.48GHz to 1.2GHz with the absorption thickness of 6mm.