• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 추계학술대회 논문집 학회본부 C
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• pp.413-415
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• 2000

Piezoelectric ceramics of PZT have been developed to apply for transformers in notebook. Use of piezoelectric ceramics in applications like piezoelectric transformers was made possible by the development of new materials with high electromechanical coupling coefficients and high mechanical quality factor. "Hard" ferroelectiric ceramics of complex composition based on lead zirconate titanate with Mn additive have been prepared. The perovskitic phase reaction of the oxides. The crucial role played by the intermediate mixing and grinding procedures in the assessment of the final properties of the material was investigated. Densification up to approximately the theoretical density value was achieved. The polarization was obtained by subjecting the samples at $30kVcm^{-1}$ poling electric field, in a silicon oil bath heated at $110^{\circ}C$. Their microstructural and morphological properties were checked by X-ray diffraction analysis and scanning electron microscopy. The optimized samples presented very high qualify and electromechanical coupling factors, together with small dielectric loss.

• 한국음향학회지
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• 제15권1호
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• pp.17-22
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• 1996

소나 시스템에 주로 사용이 되는 평면 배열형 음향 트랜스듀서는 수중에서 음을 방사하여 빔(beam)을 형성하게 된다. 이러한 빔은 트랜스듀서 진동체에서 발생하는 음향 출력이 공간상에 분포되어 일어난다. 따라서 방사 출력의 산출은 트랜스듀서의 성능 및 효율을 예측하는데 필요하다. 본 논문에서는 무한 배플에 고정된 9개의 음향 진동체를 모델로 선정하였다. 개별 진동체에서의 음향 방사량은 자기방사 및 상호방사의 조합으로 표현이 되며 전기적 등가회로 기법을 이용하여 진동체 상호간의 음향 간섭 영향을 고려하여 평면 배열형 음향 트랜스듀서 진동체의 방사 출력 예측 기법을 제안 하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.53-53
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• 2008

Piezoelectric transformers have been widely used such as DC-DC convertor, invertor, Ballast, etc. Because, the y have some merits compared with electro-magnetic transformers such as step-up ratio, high efficiency, small size and lg hit weight, etc. Piezoelectric transformer require high electromechanical coupling factor kp in order to induce a large out put power in proportional to applied electric field. And also, high mechanical quality factor Qm is required to prevent mechanical loss and heat generation. In general, PZT system ceramics should be sintered at high temperatures between 1200 and $1300^{\circ}C$ in order to obtain complete densification. Accordingly, environmental pollution due to its PbO evaporation. Hence, to reduce its sintering temperature, various kinds of material processing methods such as hot pressing, high energy mill, liquid phase sintering, and using ultra fine powder have been performed. Among these methods, liquid phase sintering is basically an effective method for aiding densification at low temperature. In this study, In order to comparis on low temperature sintering and solid state sintering piezoelectric transformers, rosen type transformers were fabricated u sing two PZT ceramics compositions and their electrical properties were investigated.

• 전기학회논문지
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• 제62권6호
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• pp.762-766
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• 2013

Interest in Wireless Power Transmission (WPT) technology has been increasing worldwide recently. This trend is proved by commercialized products such as electric toothbrush, wireless razor, and wireless charger for mobile phone battery. Studies for enhancing the applicability of the technology have been continuously conducted. Currently the WPT technology is based on the technologies using microwave, inductively coupling, and magnetic resonance. In the meantime, development of the microwave-based WPT faces difficulty due to health hazards involved in the technology, and application of the WPT technology using inductively coupling is restricted by area due to the problem of transmission length. In comparison, the WPT technology using magnetic resonance draws attention in terms of efficiency and transmission length. In this study, the sending coil based on the WPT technology using magnetic resonance system was replaced with an HTS coil to enhance transmission efficiency. Since the HTS coil has a zero resistance, power transmission loss can be minimized. At the same time, size of the current density could be increased to 100 times or more than typical coils. In addition, through impedance matching of LC device, maximal resonance properties were induced and consequently, frequency selection quality characteristics or Q was enhanced. As a result, the WPT type using the HTS coil showed a longer transmission length and better transmission efficiency compared with the WPT type using typical coils.

• 전자공학회논문지A
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• 제31A권8호
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• pp.7-15
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• 1994

In this paper, the directional coupler for Ku-band, which is designed is of the crossguide type with a coupling value of about 3-dB. The apertures chosen for this design are crosses. We used polynomial approximations of rounded end slot to obtain the electric and magnetic polarizability of crossed-slot and compared the results with Cohn's experimental results. The optimized dimensions and positions of the cross aperture are obtained by a trial-and-error reiteration of the program. This paper presents the measurement results for the designed coupler. The very flat coupling shows a total variation of only 29.80$\pm$0.04dB for the design frequency ranges of 12.25GHz-12.75GHz. The measured minimum directivity is 25dB. The aperture attenuation for the finite diaphragm thickness is about 2dB pr 0.5mm, which is in agreement with the theoretical value. The transmission loss and input return loss at center frequency are 0.0564dB and 48.16dB respectively. We obtained the measured minimum directivity of the coupler. Whose apertures are both circles is better than that containing holes in the performance of directivity.

• 한국전기전자재료학회논문지
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• 제14권11호
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• pp.892-897
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• 2001

Variations of dielectric and piezoelectric properties and associated phase transformation of <001> -oriented rhombohedral 0.92Pb (Zn$\sub$1/3/Nb$\sub$2/3/)O$_3$-0.08PbTiO$_3$ single crystals were investigated. The longitudinal strain level was found to abruptly increase at 15 kV/cm, corresponding to that where an induced phase appears within a multidomain matrix. Drastic decreases in the dielectric constant, transverse coupling, and transverse piezoelectric coefficient associated with the E-field induced phase were the result of increased crystal anisotropy in PZN-PT crystals. By contrast, the thickness coupling increased from 53 % at 0 kV/cm to 64 % at 45 kV/cm, also associated with this phase transition under the E-field. The measured dielectric and piezflelectric properties found for the induced phase state were nearly identical to those of <001> poled tetragonal (1-x)PZN-xPT (x>0.1) crystals. Based on these results, it is evident that the symmetry of induced phase is tetragonal.

• Structural Engineering and Mechanics
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• 제85권2호
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• pp.247-263
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• 2023

The paper deals with the study of the mechanical time-harmonic forced vibration of the hydro-piezoelectric system consisting of the piezoelectric plate and compressible viscous fluid with finite depth. The exact equations of motion of the theory of linear electro-elasticity for piezoelectric materials are employed for describing the plate motion, however, the fluid flow is described by employing the linearized Navier-Stokes equations for a compressible (barotropic) viscous fluid. The plane-strain state in the plate and the plane flow of the fluid are considered and the corresponding mathematical problems are solved by employing the Fourier transform with respect to the space coordinate which is on the coordinate axis directed along the platelying direction. The expressions of the corresponding Fourier transform are determined analytically, however, the inverse transforms are found numerically. Numerical results on the interface pressure and the electrical potential are obtained for various PZT materials and these results are discussed. According to these results, in particular, it is established that the electromechanical coupling effect can significantly decrease the interface pressure.

• 대한전자공학회논문지TC
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• 제37권2호
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• pp.68-74
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• 2000

유전체 슬랩으로 덮힌 평행평판 도파관의 좁은 슬릿을 통한 슬랩 위의 도체 스트립과의 전자기적인 결합문제를 평행평판 도파관에 TEM파가 입사되는 경우에 대하여 고려하였다. 슬릿의 접선성분 전계와 도체 스트립에 유기된 전류에 관한 결합 적분방정식을 유도하고 모멘트방법으로 풀었다. 도체 스트립이 결합에 미치는 영향을 보이기 위하여 도파관내에서의 반사 및 투과 전력, 슬릿을 통해 결합된 전력, 슬릿의 등가 어드미턴스, 그리고 복사패턴 등에 대한 수치해석결과를 제시하였다 그 결과 슬릿을 통해 평행평판 도파관 외부로 결합된 전력의 최대치가 도파관 내부 입사전력의 약 50%가 됨을 관찰하였다.

• 대한전자공학회논문지TC
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• 제41권8호
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• pp.93-97
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• 2004

전력선 통신의 매체인 전력선은 60Hz 전력 공급을 위해 설계되었기 때문에 고속 전력선 통신을 위한 1MHz∼30MHz 대역에서는 전력선은 전기적으로 많은 다른 특징을 갖는다. 따라서 고속 전력선 통신을 위해서는 전력선의 고주파 특성-감쇄 지연, 임피던스-등이 자세하게 분석되고 연구되어야 한다. 본 논문에서는 고속 전력선 통신용 1MHz∼30MHz 주파수 대역 옥내저압 전력선 (220V) 임피던스를 측정하였다. 벡터 회로망 분석기와 저압 전력선 결합 장치(coupling unit)를 이용하여 임피던스를 측정하였다. 결합 장치를 T형 등가회로로 바꾸어, 전체 회로에서 얻은 산란계수를 이용하여 저압 전력선 임피던스를 구했다. 제안된 방법으로 표준 한국형 저층 연립 아파트에 대한 임피던스를 측정하고, 그 특성을 분석하였다. 또한 임피던스 정합을 위하여 평균 임피던스를 구하였고, 측정결과 평균 임피던스는 약 100Ω이었다.

• 한국전기전자재료학회논문지
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• 제33권2호
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• pp.130-134
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• 2020

Metal oxide varistors (MOVs) protect circuits and devices from transient overvoltages in electric power systems. However, a MOV continuously deteriorates owing to manufacturing defects or repetitive protective operations from transient overvoltages. A deteriorated MOV may result in a short circuit or a line-ground accident. Previous studies focused on the analysis of deterioration mechanisms and condition diagnosis techniques for MOVs owing to their recent growth of use. An accelerated deterioration experiment under the same conditions in which a MOV operates is essential. In this study, we designed and fabricated a surge generator that can apply a surge current to a MOV connected to AC mains. The coupling network operates at a low impedance against the surge current from the surge generator and transfers the surge current to the MOV under test. It also acts as a high impedance against AC mains for the AC voltage not to be applied to the surge generator. The decoupling network operates at a high impedance against the surge current and blocks the surge current from AC mains. It also acts as a low impedance against AC mains for the AC voltage to be applied to the MOV under test. The prototype surge generator can apply the 8/20 us up to 15 kA on AC voltages in the approximate range of 110~450 V, and it fully operates on a LabVIEW-based program.