• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.5
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• pp.445-451
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• 2022

Ultrasonic sensor is suitable as a next-generation autonomous driving assist device because its lower price compared to that of other sensors and its sensing stability in the external environment. Although Pb(Zr, Ti)O₃ (PZT)-relaxor ferroelectric system has excellent piezoelectric properties, the change in capacitance is large in the daily operating temperature range due to the low phase transition temperature. Recently, many studies have been conducted to improve the temperature stability of ferroelectric ceramics by controlling the grain size and crystal structure, so it is necessary to study the effect of the grain size on the piezoelectric properties and the temperature stability of PZT-relaxor ferroelectric system. In this study, the piezoelectric properties, phase transition temperature, and temperature coefficient of capacitance (TCC) of 0.9 Pb(Zr_1-xTi_x)O₃-0.1 Pb(Zn_1/3Nb_2/3)O₃ (PZT_x-PZN) ceramics with various grain sizes were investigated. PZT_x-PZN ceramics with larger grain size showed higher piezoelectric properties and temperature stability, and are expected to be suitable for ultrasonic devices in the future.

• Journal of Magnetics
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• v.16 no.2
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• pp.108-113
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• 2011

The electron spin resonance lineshape (ESRLS) function for the electron spin resonance linewidth (ESRLW) of $Cr^{3+}$ (S = 3/2) in ferroelectric lithium niobate single crystals doped with 0.05 wt% of Cr, is obtained by using the projection operator technique (POT), developed by Argyres and Sigel. The ESRLS function is calculated to be axially symmetric about the c - axis and analyzed by using the spin Hamiltonian $H_{SP}={\mu}_B(B{\cdot}{^\leftrightarrow_{g}}{\cdot}S)+S{\cdot}{^\leftrightarrow_{D}}{\cdot}S$ with the parameters g = 1.972 and D = $0.395\;cm^{-1}$. In the ca plane, the linewidths show a strong angular dependence, whereas in the ab plane, they are independent of the angle. This result implies that the resonance center has an axial symmetry along the c - axis. Further, from the temperature dependence of the linewidths that is shown, it can be seen that the linewidths increase as the temperature increases, at a frequency of v = 9.27GHz. This result implies that the scattering effect increases with increasing temperature. Thus, the POT is considered to be more convenient to explain the scattering mechanism as in the case of other optical resonant systems.

• Bulletin of the Korean Chemical Society
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• v.30 no.4
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• pp.817-820
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• 2009

To meet the high current load requirement from the high energy density realized by metal oxide and high power density graphite, we propose a novel hybrid supercapacitor consisting of Nb2O5 and KS6 graphite in 1.0 M LiPF6-EC:DEC (1:2). This new system exhibits a sloping voltage profile from 2.7 to 3.5 V during charging and presents a high operating voltage plateau between 1.5 and 3.5 V during discharging. The cell was tested at a current density of 100 mA/g with a cut-off voltage between 3.0 and 1.0 V. This novel energy storage system delivers the highest initial discharge capacity of 55 mAh/g and exhibits a good cycle performance.

• The Journal of the Acoustical Society of Korea
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• v.4 no.2
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• pp.48-55
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• 1985

포물선형 혼 도파관을 사용하여 입사파의 음향전력밀도를 증대시킴으로써 압전물질의 압전비선 형성을 이용한 평판형 구조의 탄성 음향파 콘벌버를 제작하고 스펙트럼 확산 통신방식에서 S/N 비가 S 높으며 프로그램이 가능한 자기상관정합 필터로 사용될 수있음을 실험적으로 제시하였다. 본 실험에서 는 포물선형 혼 도파관을 사용한 탄성 음향파 콘벌버를 압전 재료인 YZ-LiNbO\sub 3\ 위에 중심 주파 수 100MHz 압축비 11:1, 적분시간 6인 IDT, 포물선형 혼 도파관 및 출력단자를 설계한 후 이를 포토리 토그라피 바업으로 제작하여 100 MHz 로 펄스 변조된 신호를 탄성 음향파 콘벌버의 양 입력에 인가하 여 자기상관 출력을 얻음으로써 신호 처리 이득이 18dB인 정합필터를 구현하였다.

• Proceedings of the Acoustical Society of Korea Conference
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• 1985.10a
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• pp.43-46
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• 1985

In this paper, the SAW Comb filter which consists of 1 apodized IDT, 2 uniform IDTs, and the grating reflector is studied. The apodized IDT is designed by utilizing the Chebyshev window function, and the output IDTs are arrayed with 0.5$\mu$sec time delay to obtain the Comb characteristics. And also the frequency response below the first peak is sufficiently suppressed by the grating reflector which is constituted 180 electrodes. In experiment the SAW Comb filter is fablicated by depositing Al on the surface of YZ-LiNbO3 substrate. As the experimental result, the frequency characteristics of the SAW Comb filter are consistent with theoretical values in admitted errors.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.10
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• pp.1829-1834
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• 2008

An optical switch/modulator is designed and the light propagating characteristics is analyzed by the simplified BPM. The distinctive feature of the switch/modulator is that all the waveguide branches are designed to be single-mode. Principle of the device is based on the coupled mode theory in the Y-junction interconnecting waveguide. In spite of all the waveguides are designed to be single-mode, adjusting the interconnecting waveguide length of the device, the same characteristics as existing device up to date is obtainable. Numerical results show that the switching characteristics periodically depends on the interconnecting waveguide length with a spatial of about 150${\mu}m$ in the Ti:LiNbO3 step index waveguide. The concept of design would be utilized effectively in fabricating the monolithic high density of optical integrated circuit.

• Electrical & Electronic Materials
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• v.8 no.4
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• pp.443-450
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• 1995

A directional coupler which on the X-cut $LiNbO_3$ substrate is fabricated by using proton exchange method and self-aligned method. After proton exchange process, the waveguide is formed by annealing process. The relation ship between refractive index change of waveguide and maximum output was studied along with the annealing time. A self-aligned method was used to simplify the fabrication process of the waveguide and to maximize the efficiency of electric field. The on-off state of modulator has been observered with the switching of the directional coupler by the electric field effect and also the switching voltage of the directional coupler has been measured with 8.0 [V].

• Proceedings of the IEEK Conference
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• 2000.11b
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• pp.29-32
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• 2000

Meta1-ferroelectric-insulator-semiconductor(MFIS) devices using Pt/LiNbO$_{3}$/AIN/Si structure were successfully fabricated. AIN thin films were made into metal-insulator-semiconductor(MIS) devices by evaporating aluminum in a dot array on the film surface. The dielectric constant of the AIN film calculated from the capacitance in the accumulation region in the capacitance-voltage(C-V ) characteristic is 8. The gate leakage current density of MIS devices using a aluminum electrode showed the least value of 1$\times$10$^{-8A}$ $\textrm{cm}^2$ order at the electric field of 500㎸/cm. A typica] value of the dielectric constant of MFIS device was about 23 derived from 1MHz capacitance-voltage (C-V) measurement and the resistivity of the film at the field of 500㎸/cm was about 5.6$\times$ 10$^{13}$ $\Omega$.cmcm

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.10
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• pp.471-476
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• 2005

We proposed an optical modulator of reflective type to compose the electric field sensor, and theoretically analyzed the performance and characteristics. For the high sensitivity of the sensor, a method to improve the modulation index of the modulator was presented. The electric field sensor using Ti:LiNbO$_{3}$ waveguide was fabricated and qualitatively investigated the characteristics by measuring the low frequency electric field. Even though the sensor showed relatively low modulation index, the electric filed strength of 10$^{-2}$V/m was measured. The experimental results revealed the utilities of this type electric field sensor.

• Proceedings of the Optical Society of Korea Conference
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• 2003.02a
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• pp.224-225
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• 2003

Since group velocity (GV) mismatch significantly limits the efficiency of nonlinear interactions such as second harmonic generation (SHG), several techniques have been developed to compensate GV mismatch. The simplest way to avoid the GV mismatch problem is to reduce the device length. However, it results in a poor trade-off between the SHG spectral bandwidth and the conversion efficiency. (omitted)