• 한국정보기술응용학회:학술대회논문집
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• 한국정보기술응용학회 2005년도 6th 2005 International Conference on Computers, Communications and System
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• pp.215-218
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• 2005

We have investigated on the development of 2-2 piezocomposites that have better piezoelectric activity and lower acoustic impedance than those of conventional piezoceramics. In this study, we have investigated the piezoelectric and acoustic properties of 2-2 piezocomposites sensor which were fabricated using dice-and-fill technique for the different volume fraction of PZT. The resonance characteristics measured by an impedance analyzer were similar to the analysis of finite element method. The resonance characteristics and the electromechanical coupling factor were the best when the volume fraction PZT was 0.6. It also showed the highest result from the standpoint of sensitivity, bandwidth and ring-down property and so on at the same condition. The specific characteristics shows that the 2-2 piezocomposites turned out to be superior to the ultrasonic sensor composed by single phase PZT.

• 한국세라믹학회지
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• 제31권10호
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• pp.1133-1140
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• 1994

Nonlinear resonance characteristics of transverse type-PZT ceramic resonator were investigated, and their nonlinear coefficients were calculated using the nonlinear theory proposed by Duffing. Resonance characteristics of sample showed nonlinearity by the thermal effects due to driving current. Nonlinear coefficients greatly affected by sample dimension, however comparing with respect to current density, it was almost constant. Nonlinear coefficients were not changed as driving current increased upto 40 mA/$\textrm{cm}^2$, when $\alpha$ and $\beta$ was 920 and -10.6, respectively, while nonlinear coefficients exponentially increased beyond the current density of 40 mA/$\textrm{cm}^2$. Nonlinear coefficients were slightly increased as temperature increased.

• Journal of information and communication convergence engineering
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• 제5권4호
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• pp.320-323
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• 2007

This paper presents the resonance characteristics of the ZnO-based FBAR devices with multilayered Bragg reflectors with Cr adhesion layer inserted between $SiO_2$ and W layers. Due to the post- annealing, the return loss ($S_{11}$) and series/parallel quality factor are significantly improved when compared with the non-post annealing. This post-annealing method seems to be a very efficient way to improve the resonance characteristics of FBAR devices.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 춘계학술대회논문집
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• pp.496-503
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• 2001

The suspension of the optical pickup actuator is damped by the presence of silicone rubber damper bond at its termination. In spite of the presence of it, the actuator still exhibits a strong mechanical resonance which affects its settling time and vibrational characteristics. This resonance can cause errors in reading information from the disk, particularly in high speed CD-ROM and DVD-ROM drives. Ferrofluids are stable colloidal suspensions of sub-micron sized magnetic particles in a carrier liquid. In the actuator design, ferrofluid is applied to the surface of the magnets until the quantity is sufficient to maintain intimate contact with the bobbin/carrier assembly. The fluid is retained in the magnetic field and its viscosity provides the desired mechanical damping to the moving assembly, improving the actuators settling time and vibrational characteristics. Access time is also improved, particularly on warped or eccentric discs.

• 한국소음진동공학회논문집
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• 제19권9호
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• pp.863-869
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• 2009

Acoustic noises generated during motor operation in mechanical system are from electromagnetic, mechanical, aerodynamic and electrical sources. For identification of mechanical noise origins, misalignment, unbalance, fan shape, resonance, and vibration modes have been extensively considered to describe noise behavior. An experiment-based approach as well as a mathematical approach needs to be adopted for a realistic study into noise and vibration of the motor, because motor noise characteristics differ from type to type due to various noise sources. This paper analyzes noise characteristics of a brushless DC motor for air-conditioner fan, and proves that the test motor noise originates from acoustic modes of airspace in the motor. The motor noise sensitivity analysis by design of experiments reveals that the noise characteristics are closely related to switching frequency and frame thickness.

• Journal of electromagnetic engineering and science
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• 제1권2호
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• pp.176-181
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• 2001

This paper presents the farced resonant characteristics of an electrically small cavity partially filled with dielectric material. The method of moments with Galerkins procedure is used to determine the farced resonant characteristics of the small cavity. In order to obtain the equations of the external reactance gives rise to the farced resonance at a given frequency, the cavity with external reactance can be treated as two-port network which has the admittance parameters. Numerical results show that the forced resonance, series or parallel resonance, can be obtained by the controlling the external reactance. To verify the availability of the theoretical analysis, experiments are carried out for the bakelite as the material by measuring the length of external reactance at operating frequencies.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1921-1926
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• 2004

The tone generation mechanism and aeroacoustic characteristics have been investigated for flow over open cavities using direct acoustic numerical simulations. Physically the tone generation mechanism of open cavity is more complicated when flow instabilities are excited by the correlation effects of flow parameters. From non-dimensional parameter studies in very low Mach number range, it is shown that characteristics of cavity resonance inherently involve typical acoustic pattern at each discrete tone frequency, and especially in laminar flow the fundamental tone frequency is determined within flow instability criterion of laminar shear layer as well as cavity geometry, length to depth ratio.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 추계학술대회 논문집 전력기술부문
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• pp.249-251
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• 2004

Harmonic resonant overvoltage during restoration of primary restorative transmission system originates in switching operations and nonlinear characteristics of equipments. Actually it is difficult to predict the occurrence of harmonic overvoltage, since they result from nonlinear characteristics of transformers and other equipments. This paper describes the analysis of domestic primary restorative transmission system using PSCAD/EMTDC. The harmonic resonance is verified and showed the relation with equipments which have nonlinear characteristics such as generator and transformer in this paper. And the solution to prevent harmonic resonance is proposed too. As a result, the PSCAD/EMTDC simulation showed slightly conflictive results that had been presented by IEEE Power System Restoration Working Group report.

• 동력기계공학회지
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• 제6권4호
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• pp.36-42
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• 2002

In the structures of automobiles and ships which have engines for works, the vibration energies generated by the engines are transferred to dissipation parts through the structures which is welded and bolted with beams and plates. The vibration energies generated by resonance frequencies are the reasons of the resonance phenomena. To solve these problems, up to the present, we have studied to avoid the resonance, and add the higher damping characteristics. However, we need to understand the structural energy flows, to design the structures clearly which have the characteristic of welding. The object of this study is to make differences clear in the characteristics of structures which have some welded part on an homogenous flat plate. In this investigation, we study the flows of structural vibration energy experimently, and then, some knowledge for dynamic structural design is obtained.

• 한국전자파학회논문지
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• 제23권4호
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• pp.515-523
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• 2012

본 논문에서는 구형 유전체 위에 있는 구형 패치의 전파 특성으로서 공진 특성과 방사 특성을 분석하였다. 공진 주파수와 Q를 계산하여 특정 모드의 공진 특성을 해석하였으며, 원거리에서의 전기장을 계산하여 방사 특성을 해석하였다. 구형 유전체의 해석을 위해 스펙트럴 영역 해석법(spectral domain analysis method)를 적용하였으며, Vector Legendre transform pair와 Galerkin's method를 이용하여 스펙트럴 영역으로 변환한 후 대수식으로 정리하여 효율적인 계산을 할 수 있었으며, 이를 통해 구형 패치의 반지름이나 곡률, 유전체의 특성이 구형 패치의 특성에 미치는 영향을 해석하였다.