• International Journal of Computer Science & Network Security
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• 제22권12호
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• pp.245-251
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• 2022

In this paper, a high gain, broadband planar vivaldi antenna (PVA) by utilizing a broadband stripline feed is developed for wireless communication for IoT systems. The suggested antenna is designed by attaching a tapered-slot construction to a typical vivaldi antenna, which improves the antenna's radiation properties. The PVA is constructed on a low-cost FR4 substrate. The dimensions of the patch are 1.886λ₀×1.42λ₀×0.026λ₀, dielectric constant Ɛ_r=4.4, and loss tangent δ=0.02. The width of the feed line is reduced to improve the impedance bandwidth of the antenna. The computed reflection coefficient findings show that the suggested antenna has a 46.2% wider relative bandwidth calculated at a 10 dB return loss. At the resonance frequencies of 6.5 GHz, the studied results show an optimal gain of 5.82 dBi and 85% optimal radiation efficiency at the operable band. The optometric analysis of the proposed structure shows that the proposed antenna can achieve wide enough bandwidth at the desired frequency and hence make the designed antenna appropriate to work in satellite communication and medical internet of things (M-IoT) healthcare applications.

• 한국전기전자재료학회논문지
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• 제37권4호
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• pp.457-463
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• 2024

(Bi_1/2Na_1/2)TiO₃(BNT) piezoelectric ceramics are one of the promising materials that can replace Pb(Zr, Ti)O₃(PZT) piezoelectric ceramics due to the high electromechanical strain properties. However, it is still difficult to use practical applications because the required electric field for inducing electromechanical strain is relatively higher than that of PZT ceramics. To overcome this problem, it has been intensively studied on doping impurity or modifying other ABO₃ for BNT-based piezoelectric ceramics. Therefore, this study investigated the effects of La₂O₃ doping on the phase transition behavior and electromechanical strain properties in BNT-SrTiO₃ (BNT-ST) lead-free piezoelectric ceramics. In the case of the temperature-dependent dielectric properties, it was confirmed that a phase transition from ferroelectrics to relaxors is induced with increasing La₂O₃ content. As a result, the electromechanical strain properties of BNT-ST ceramics were improved. The highest S_max/E_max value corresponding to 300 pm/V was obtained at 2 mol% La₂O₃-dopped BNT-ST ceramics. Accordingly, this study successfully demonstrated that La₂O₃ doping is effective on the inducing phase transition from ferroelectrics to relaxors and the improving electromechanical strain properties of BNT-ST lead-free piezoelectric ceramics.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 C
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• pp.1552-1554
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• 2004

The modeled resonant frequency and electrical properties of Pb(Zr, Ti)$O_3$ (PZT) film with various thicknesses have been investigated in film bulk acoustic wave resonators (FBARs). PZT films and Pt electrodes were fabricated by rf-magnetron sputtering. Fabrication process of electrodes and PZT were patterned by simple lift-off process and then back side of silicon was etched by 45wt% KOH. The crystal structure of PZT films with 0.5, 1 and 2 ${\mu}m$ thickness was investigated by x-ray deflection (XRD) and scanning electron microscopy (SEM). The dielectric constant and performance characteristics of PZT FBAR strongly depended on the film thickness. The resonant frequency of PZT films decreased with increasing film thickness. These sputtered PZT FBAR with simple lift-off process enable us to fabricate high Q values with resonant frequencies. (0.71 - 1.48 GHz).

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.235.1-235.1
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• 2015

Artificially-engineered materials, whose electromagnetic properties are not available in nature, such as negative reflective index, are called metamaterials (MMs). Although many scientists have investigated MMs for negative-reflective-index properties at the beginning, their interests have been extended to many other fields comprising perfect lenses. Among various kinds of MMs, metamaterial absorbers (MM-As) mimic the blackbody through minimizing transmission and reflection. In order to maximize absorption, the real and the imaginary parts of the permittivity and permeability of MM-As should be adjusted to possess the same impedance as that of free space. We propose a dual-wide-band and polarization-independent MM-A. It is basically a triple-layer structure made of metal/dielectric multilayered truncated cones. The multilayered truncated cones are periodically arranged and play a role of meta-atoms. We realize not only a wide-band absorption, which utilizes the fundamental magnetic resonances, but also another wide-band absorption in the high-frequency range based on the third-harmonic resonances, in both simulation and experiment. In simulation, the absorption bands with absorption higher than 90% are 3.93 - 6.05 GHz and 11.64 - 14.55 GHz, while the experimental absorption bands are in 3.88 - 6.08 GHz and 9.95 - 13.84 GHz. The physical origins of these absorption bands are elucidated. Additionally, it is also polarization-independent because of its circularly symmetric structures. Our design is scalable to smaller size for the infrared and the visible ranges.

• 한국세라믹학회지
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• 제48권4호
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• pp.307-311
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• 2011

Solid solutions of the (1-x)$BiFeO_3-xSrTiO_3$ ceramic system (x = 0~0.4) are explored here in attempts to obtain multiferroic properties in these systems. The polarization-electric field hysteresis, magnetization-magnetic field curves, and dielectric properties are also characterized. This solid-solution system shows a crystal structural transition from a noncentrosymmetric (R3c) structure to a centrosymmetric (Pm-3m) structure at 0.3 < x < 0.4. The solid solution ceramic shows unsaturated M-H behavior and low remanent magnetization over the composition region of 0.1 ${\leq}$ x ${\leq}$ 0.3. The $0.7BiFeO_3-0.3SrTiO_3$ system shows the largest value of $M_s$ at 0.17 emu/g and the smallest value of $H_c$ at 1.06 kOe. The P-E hysteresis curves were not saturated under an electric field as high as E = 70 kV/cm. This system is considered to have multiferroic characteristics in the composition range of 0.1 ${\leq}$ x ${\leq}$ 0.3.

• 대한화학회지
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• 제39권10호
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• pp.806-811
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• 1995

정온도저항계수(PTCR) 특성을 지닌 $(Ba,Sr)_{1-x}Y_xTiO_3$(x = 0.001-0.009, BSYT)를 옥살산공침범으로 합성하여 이트륨 혼입량 변화에 따른 전기적 특성을 관찰하였다. 온도변화에 따른 저항을 측정한 결과 이트륨의 농도가 0.3mol%로 증가할때까지는 큰 PTCR 효과를 나타낸 반면 농도가 0.5mol% 이상에서는 적은 PTCR 효과를 나타내었다. 상전이 온도($T_c$) 이상에서 온도와 $1{\varepsilon}$m(T)의 관계를 나타낸 도시에 의하면 유전상수의 변화가 Curie-Wiess 법칙에 잘 따름을 알 수 있었다. 측정한 비저항과 유전상수로부터 계산한 전위장벽위 높이를 온도에 따라 도시한 결과 PTCR 효과와 마찬가지로 이트륨의 혼입량이 0.3mol%로 증가할때까지는 높은 전위장벽이 유지되나 0.5mol% 이상에서는 비교적 낮은 전위장벽을 나타내었다.

• 한국안광학회지
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• 제1권2호
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• pp.37-42
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• 1996

$Bi_{12}(Si,Ge)O_{20}$ 단결정의 전기 및 광학적 특성을 규명하기 위하여 Czochralski법으로 단결정을 성장시켜, 직류전기전도도와 교류전기전도도 그리고 광투과도를 측정하였다. 직류전기전도도에 대한 활성화 에너지 $E_g$는 1.12 eV 이고, 광학적 갭 $E_{opt}$는 2.3 eV였다. $Bi_{12}(Si,Ge)O_{20}$ 단결정의 교류전기전도도는 측정온도 범위는 290 K에서 570 K까지 였으며 측정주파수는 50 kHz에서 30 MHz 까지 였다. 교류전기전도도는 ${\omega}^s$에 비례하는 hopping 전도 가구를 나타내었으며, 고주파수영역에서 지수값은 s=2로 구해졌다. 유전상수는 $Bi_{12}(Si,Ge)O_{20}$ 단결정의 경우 54이고 $Bi_{12}(Si,Ge)O_{20}$ 단결정의 경우 41정도의 크기를 보였다.

• 한국산학기술학회논문지
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• 제17권2호
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• pp.259-264
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• 2016

본 논문에서는 코프래너 그라운드 도파관(CPWG)에 의해 급전되는 패치 안테나의 설계 방법 및 안테나 특성을 연구하였다. 안테나의 패치 길이, 폭, 위치를 조절하여 안테나와 CPWG 급전선이 임피던스 정합 되도록 하였다. 또한 안테나의 특성을 향상시키기 위해 CPWG 안테나의 설계 변수인 패치 길이. 패치 넓이, 패치 위치 및 그라운드 포지션에 따른 안테나 특성 변화를 HFSS 프로그램을 사용하여 안테나의 주파수 특성을 시뮬레이션 하였다. 이 결과를 바탕으로 1.8GHz LTE 대역에서 사용 가능한 CPWG 안테나를 설계하고, 설계 된 안테나를 유전율 4.4, 두께 0.8mm인 FR4-epoxy 기판을 사용 하여 포토리소그래피 방법으로 안테나를 제작하였다. 제작된 안테나는 최종적으로 회로망 분석기(Network Analyzer)를 통해 안테나 특성을 분석하였다. 측정된 안테나의 주파수 특성은 시뮬레이션 결과와 잘 일치하여 본 연구의 타당성을 확인 할 수 있었다. 제작된 CPWG 안테나는 중심주파수 1.80 GHz, 입력반사손실 -32.1 dB, 대역폭 22 MHz, 임피던스 $50.2{\Omega}$의 결과 값을 보였다. 본 연구에서 제안된 안테나는 LTE 대역에 응용이 가능할 것으로 기대된다.

• 한국전기전자재료학회논문지
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• 제19권9호
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• pp.838-842
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• 2006

0.03Pb$(Sb_{0.5}Nb_{0.5})O_{3}-0.03Pb(Mn{1/3}Nb{2/3)O_{3}-(0.94-x)PbTiO_{3}-xPbZrO_{3}$ ceramics doped with $CeO_{2}$ were synthesized by conventional bulk ceramic processing technique. Phases analysis, microstructures and piezoelectric properties were investigated as a function of $CeO_{2}$ content (0.03, 0.05, 0.1 0.3, 0.5 and 0.7 wt%). Microstructures and phases information were characterized using a scanning electron microscope (SEM) and an X-ray diffractometer (XRD). Mechanical quality factor ($Q_{m}$) and coupling factor(kp) were obtained from the resonance measurement method. Both $Q_{m}$ and $k_{p}$ were shown to reach to the maximum at 0.1 wt% $CeO_{2}$. In order to evaluate the stability of resonance frequency and effective electromechanical coupling factor ($K_{eff}$) as a function of $CeO_{2}$, the variation of resonance and anti-resonance frequency were also measured using a high voltage frequency response analyzer under various alternating electric fields from 10 V/mm to 80 V/mm. It was shown that the stability of resonance frequency and effective electromechanical coupling factor were increased with increasing the $CeO_{2}$ contents.

• 한국재료학회지
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• 제19권5호
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• pp.253-258
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• 2009

Mn-substituted $BiFeO_3$(BFO) thin films were prepared by r.f. magnetron sputtering under an Ar/$O_2$ mixture of various deposition pressures at room temperature. The effects of the deposition pressure and annealing temperature on the crystallization and electrical properties of BFO films were investigated. X-ray diffraction patterns revealed that BFO films were crystallized for films annealed above $500^{\circ}C$. BFO films annealed at $550^{\circ}C$ for 5 min in $N_2$ atmosphere exhibited the crystallized perovskite phase. The (Fe+Mn)/Bi ratio decreased with an increase in the deposition pressure due to the difference of sputtering yield. The grain size and surface roughness of films increased with an increase in the deposition pressure. The dielectric constant of BFO films prepared at various conditions shows $127{\sim}187$ at 1 kHz. The leakage current density of BFO films annealed at $500^{\circ}C$ was approximately two orders of magnitude lower than that of $550^{\circ}C$. The leakage current density of the BFO films deposited at $10{\sim}30\;m$ Torr was about $5{\times}10^{-6}{\sim}3{\times}10^{-2}A/cm^2$ at 100 kV/cm. Due to the high leakage current, saturated P-E curves were not obtained in BFO films. BFO film annealed at $500^{\circ}C$ exhibited remnant polarization(2Pr) of $26.4{\mu}C/cm^2$ at 470 kV/cm.