1. 육방정 페라이트 복합상의 합성 및 GHz 대역 전자기파 흡수 특성

    Pyeong-Yeol Yu and Young-Min Kang

    Journal of the Korean Magneitcs Society, 30 Aug 2020, Vol.30 , No.4, pp.115-122

    육방정 페라이트 복합상의 합성 및 GHz 대역 전자기파 흡수 특성

    Multi-hexaferrites (Sr3-xCaxCo2Fe24O41, x = 0, 0.1, 0.2, 0.3, 0.4) with more than two types of hexaferrite phases were synthesized by solid-state reactions and substitution of Sr by Ca in the stoichiometric Z-type Sr3Co2 hexaferrite composition. Multi-hexaferrites consisting of Z + U +W, X + U +W, and X +W phases were formed for the samples with x = 0, x = 0.1, and x ≥ 0.2, respectively, upon first and second calcinations at 1160 and 1210 ℃. The saturation magnetization increased largely with Ca-doping (x ≥ 0.1). The complex permeability spectra were shifted to higher frequency and the imaginary permeability peak became broader by Ca doping. In the RL maps plotted as functions of sample thickness (d) and frequency (f), the strong EM absorbing area moved to higher f and lower d direction with increasing of x. For the Ca-doped samples (x ≥ 0.1), the minimum reflection loss (RL < -30 dB) corresponding to the maximum microwave absorption was obtained at f = 10 GHz vicinity and d = ~2 mm, while the undoped sample exhibited the minimum RL (-42 dB) at f = 4.6 GHz and d = 4.6 mm. The highest EM wave absorption performance of RL = -56.5 dB could be achieved at the sample of x = 0.3 with d = 2.2 m m and f = 11.4 GHz. For the x = 0.2 samples, RL < -10 dB (EM energy absorption above 90%) is satisfied in the full X-band frequency range (8~12 GHz) with d = 2.3 mm. The broad-band EM absorption properties could be achieved owing to the overlaps of the hard-soft magnetic properties of the multi-hexaferrites.

  2. 평면홀 저항 센서의 조화파 신호 분석

    Dong Young Kim and Seok Soo Yoon

    Journal of the Korean Magneitcs Society, 30 Aug 2020, Vol.30 , No.4, pp.123-128

    평면홀 저항 센서의 조화파 신호 분석

    We analyzed the magnetic field dependence of 0th, 1st and 2nd order harmonic signals (V0f0, V1f0 and V2f0) measured in planner Hall resistance (PHR) sensor. The magnetic field dependence of V1f0 showed the typical PHR signal properties with high sensitivity and linearity near H = 0. While, the magnetic field dependence of and V2f0 showed same as the derivative of the magnetic field dependence of V1f0, and were very sensitively response to the magnetic film on PHR sensor.

  3. 코일 센서와 평면홀 저항 센서로 측정한 와전류 신호 연구

    Dong Young Kim , Seok Soo Yoon and Cheong Worl Kim

    Journal of the Korean Magneitcs Society, 30 Aug 2020, Vol.30 , No.4, pp.129-133

    코일 센서와 평면홀 저항 센서로 측정한 와전류 신호 연구

    We used coil sensor and PHR sensor in order to measure the amplitude and phase of eddy current signals induced by flaws. The amplitude and phase of eddy current signals were propositional to depth of flaws in both sensor. The phase of eddy current signals measured by PHR sensor were more larger than that measured by coil sensor. The benefits of tiny PHR sensor compared with coil sensor were high spatial resolution as well as very high flaw detection capability at low frequency.

  4. 함정의 자화조건 변화에 대한 폐회로 소자 성능 분석

    Jaegyeong Mun , Yejin Kwak , HaeKyun Yoon , Dong-Hun Kim , Chang-Seob Yang and Hyun-Ju Chung

    Journal of the Korean Magneitcs Society, 30 Aug 2020, Vol.30 , No.4, pp.134-138

    함정의 자화조건 변화에 대한 폐회로 소자 성능 분석

    In this paper, the performance of the proposed closed-loop degaussing technique is analyzed through testing a mockup replicating a magnetic field condition of a ship due to the variation of on-board equipment’s or hull’s magnetization. In order to change a magnetic field condition of the mockup, a certain electric current is applied to triaxial coils installed in a nonmagnetic laboratory. Before and after the artificial field condition, degaussing current values are respectively derived from closed-loop degaussing algorithm and then applied to individual degaussing coils. The effectiveness of the proposed degaussing technique is verified by comparison of the magnitude of field signals generated on a certain depth of water.

  5. 펄스자기장이 적혈구의 응집성과 변형성에 미치는 영향

    Seunghwan Bang and Hyunsook Lee

    Journal of the Korean Magneitcs Society, 30 Aug 2020, Vol.30 , No.4, pp.139-144

    펄스자기장이 적혈구의 응집성과 변형성에 미치는 영향

    Imbalance of blood circulation caused by aggregation, rouleaux and morphological transform of red blood cell (RBC) influenced to cardiovascular diseases such as thrombosis, peripheral stenosis, and arteriosclerosis. This study intends to evaluate the effect of the pulsed magnetic field (PMF) on the aggregation and deformability of RBC. In hematocrit (HCT) 45% bloods diluted with phosphate buffered saline (PBS) and plasma, ESR rates were slowed by 1% and 6% after PMF stimulus of 2700 G, respectively. In addition, RBCs’ sedimentation rate after 12 hrs decreased to 25% at 2700 G, 28% at 1000 G, 32% at 400 G, compared to 34% at non-PMF group. After tBHP treatment in order to observe the RBC aggregation due to hemoglobin oxidation, the RBCs sedimentation proceeded rapidly, but progressed slowly after PMF stimulus. In RBC deformability experiment using filter having a size of 5 μm smaller than the volume of RBC, the number of filtered RBCs increased by 2% at 400 G, 16% at 1000 G and 29% at 2700 G, compare with non-PMF group. For oxidative RBCs group, it also increased by more than 34% after PMF stimulus. Improvement of RBCs’ aggregation after PMF stimulus could be interpreted as the instantaneous rapid flux change of PMF affecting the zeta potential of RBCs. Also it is believed that PMF also affects the Ca2+ ion pump which affects the hardening of RBCs’ membrane, thereby increasing the RBCs’ deformability. Therefore, the PMF stimulus could be used as a non-invasive treatment method for blood circulation disorder.