• 전기학회논문지
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• 제57권7호
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• pp.1213-1217
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• 2008

Poling is an important process in fabricating PZT ceramic devices such as filters and resonators and activates piezoelectricity to sintered PZT ceramics. Tolerance of the operating frequency of these devices is tightly required in applications. And a factor to attribute the tolerance is the temperature dependence of the resonance frequency of PZT ceramics. In this paper the relationship of poling strength and temperature dependence of resonance frequency of PZT specimens was studied. The $Pb(Zr_{0.53}Ti_{0.47})O_3$ ceramics were fabricated and the poling strengths were chosen to be 0.5, 1.5, 2.5 and 3.5 [kV/mm]. The dielectric constant of the specimen poled in poling strength 0.5 [kV/mm] was less than that of unpoled specimen and the specimen poled in higher electric field had the higher dielectric constant. (002) peak in X-ray diffraction patterns of the specimens increased as poling strength increased. And the change of resonance frequency of the specimens according to the variation of temperature was measured. Resonance frequency of all specimens increased as the temperature increased. The specimen poled in higher electric field had the smaller positive temperature coefficient of resonance frequency. The effect that temperature coefficient of resonance frequency becomes smaller is obtained when Zr mole in PZT composition equation increase. Controlling the poling strength is believed to be a method to adjust the temperature stability of resonance frequency of the PZT ceramic devices.

• Archives of Plastic Surgery
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• 제41권4호
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• pp.344-349
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• 2014

Background An abnormally obtuse cranial base angle, also known as platybasia, is a common finding in patients with 22q11.2 deletion syndrome (22q11DS). Platybasia increases the depth of the velopharynx and is therefore postulated to contribute to velopharyngeal dysfunction. Our objective was to determine the clinical significance of platybasia in 22q11DS by exploring the relationship between cranial base angles and speech resonance. Methods In this retrospective chart review at a tertiary hospital, 24 children (age, 4.0-13.1 years) with 22q11.2DS underwent speech assessments and lateral cephalograms, which allowed for the measurement of the cranial base angles. Results One patient (4%) had hyponasal resonance, 8 (33%) had normal resonance, 10 (42%) had hypernasal resonance on vowels only, and 5 (21%) had hypernasal resonance on both vowels and consonants. The mean cranial base angle was $136.5^{\circ}$ (standard deviation, $5.3^{\circ}$; range, $122.3-144.8^{\circ}$). The Kruskal-Wallis test showed no significant relationship between the resonance ratings and cranial base angles (P=0.242). Cranial base angles and speech ratings were not correlated (Spearman correlation=0.321, P=0.126). The group with hypernasal resonance had a significantly more obtuse mean cranial base angle ($138^{\circ}$ vs. $134^{\circ}$, P=0.049) but did not have a greater prevalence of platybasia (73% vs. 56%, P=0.412). Conclusions In this retrospective chart review of patients with 22q11DS, cranial base angles were not correlated with speech resonance. The clinical significance of platybasia remains unknown.

• Journal of Electrical Engineering and Technology
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• 제13권6호
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• pp.2335-2343
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• 2018

This paper proposes an optimal damping control algorithm of the DTI (Direct Two-level Inverter) to miniaturize and reduce the weight of auxiliary power supply for railway vehicles. The conventional auxiliary power supply for railway vehicles uses a DC-DC converter to maintain the inverter input power from the line voltage smoothly. The proposed topology does not use a DC-DC converter for reducing of manufacturing and maintenance costs. It also proposes a DTI topology removed damping resistors that generate ground signal noise in a certain period. At this time, a resonance phenomenon of DC-link voltage occurs due to variation of the inductive load, and a method of controlling the resonance phenomenon of DC-link voltage is required. In order to suppress the resonance phenomenon of the DC-link voltage, at a point before resonance occurs, this paper introduces an algorithm to suppress the resonance phenomenon of DC-link voltage by compensating the resonance component of the q axis voltage of the synchronous reference frame. The proposed algorithm verifies the effect through simulation and experiment.

• 한국음향학회지
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• 제16권1호
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• pp.76-80
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• 1997

Hofler 타입의 열음향 냉장시스템에 있어서 음향학적 공진특성을 해석하고, 공진특성이 냉장성능에 미치는 영향을 시스템의 제작 및 냉장 실험을 통하여 확인하였다. 열음향 냉장시스템의 공진특성을 결정하는 주요 인자는 공명구(cavity)와 가는 관, 그리고 굵은 관으로 구성되는 공명기의 특성과, 구동 스피커의 특성, 그리고 스피커 후면부의 음향학적 특성이며, 다시 스피커의 전기적 특성과 결합되어 전기적 공진특성이 정해진다. 또한 공명기에서 발생하는 벽-효과(wall effect)를 통한 감쇠로 인하여 공진특성이 둔해진다. 제작된 열음향 냉장시스템에 대한 해석 및 실험결과 전체 공진특성은 공명기에 의하여 결정되지만 후면부의 강성과 감쇠로 인하여 공진특성이 상당히 둔화되고, 냉장실험 결과 정확한 공진특성의 유지가 냉장성능에 큰 영향을 마침을 확인하였다.

• Transactions on Electrical and Electronic Materials
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• 제6권4호
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• pp.159-163
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• 2005

We analyzed the fault current limiting characteristics of a flux-lock type $high-T_c$ super­conducting fault current limiter (HTSC-FCL) using series resonance between capacitor for series resonance and magnetic field coil which was installed in coil 3. The capacitor for the series resonance in the flux-lock type HTSC-FCL was inserted in series with the magnetic field coil to apply enough magnetic field into HTSC element, which resulted in higher resistance of HTSC element. However, the impedance of the flux lock type HTSC-FCL has started to decrease since the current of coil 3 exceeded one of coil 2 after a fault accident. The decrease in the impedance of the FCL causes the line current to increase and, if continues, the capacitor for the series resonance to be destructed. To avoid this operation, the flux-lock type HTSC-FCL requires an additional device such as fault current interrupter or control circuit for magnetic field. From the experimental results, we investigated the parameter range where the operation as mentioned above for the designed flux-lock type HTSC-FCL using series resonance occurred.

• International Journal of Fluid Machinery and Systems
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• 제6권2호
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• pp.75-86
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• 2013

The effects of acoustic resonance and volute geometry on phase resonance are studied theoretically and experimentally using a centrifugal fan. One dimensional theoretical model is developed taking account of the reflection from the discharge pipe end. It was found that the phase resonance occurs, even with the effects of acoustic resonance, when the rotational speed of rotor-stator interaction pattern agrees with the sound velocity. This was confirmed by experiments with and without a silencer at the discharge pipe exit. The pressure wave measurements showed that there are certain effects of the cross-sectional area change of the volute which is neglected in the one dimensional model. To clarify the effects of area change, experiments were carried out by using a ring volute with a constant area. It was demonstrated that the phase resonance occurs for both interaction modes travelling towards/away from the volute. The amplitude of travelling wave grows towards the volute exit for the modes rotating towards the volute exit, in the same direction as the impeller. However, a standing wave is developed in the volute for the modes rotating away from the volute exit in the opposite direction as the impeller, as a result of the interaction of a growing wave while travelling towards the tongue and a reflected wave away from the tongue.

• 센서학회지
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• 제15권5호
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• pp.347-351
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• 2006

A novel surface plasmon resonance sensor, which can measure 2-dimensional array of immobilized ligands without using imaging devices such as CCD, has been proposed. Regular surface plasmon resonance can be directly used due to the insertion of additional layers with different thickness, on which each ligands are immobilized. Surface plasmon resonance signals are separated depending on the thickness of additional layers. The possibility of multi-sensing capability of the proposed surface plasmon resonance sensor has been verified by the modeling that is based on Fresnel reflection model.

• 한국전자파학회논문지
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• 제8권3호
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• pp.264-272
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• 1997

본 논문에서는 리액턴스 소자률 갖는 전기적 소형다이폴 안테나의 강제 공진특성을 해석하고 있다. 이론 해석 에는 다이폴 안테나에 흐르는 전류분포에 관한 적분방정식을 풀기 위해 모멘트 법을 적용했으며, 강제 공진특성 을 검토하기 위하여 급전점 및 장하점에 착목한 2단자 동가 회로망으로부터 안테나가 강제적으로 공진하도록 하는 리액턴스의 값을 결정하는 결정방정식을 도출하고 있다. 공진특성의 해석결과 리액턴스 소자를 적절히 조절 하면 안테나가 강제적으로 공진하며, 강제 공진에는 직렬공진 및 병렬공진의 두 가지 종류가존재한다는 것을 밝 히고 있다. 또한, 이들 강제 공진특성을 미지 주파수의 측정에 이용할 수 있다는 것을 원리적인 변을 중심으로 이 론적으로 검토하고 있다.

• Journal of Biosystems Engineering
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• 제28권3호
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• pp.253-260
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• 2003

In this study, the feasibility of magnetic resonance techniques for nondestructive internal quality evaluation of Korean red ginseng was examined. Relaxation time constants were measured using various grades of red ginsengs. Solid state magnetic resonance imaging technique was applied to image dried red ginsengs which have low moisture contents (about 13%). A 7 tesla magnetic resonance imaging system operating at a proton resonant frequency of 300 ㎒ was used for acquiring MR images of dried Korean red ginseng. The comparison test of cross cut digital images and magnetic resonance images of heaven grade, good grade with cavity inside, and good grade with white part inside red ginseng suggested the feasibility of the internal quality evaluation of Korean red ginsengs using MRI techniques. A good grade red ginseng included abnormal tissues such as cavities or white parts inside was observed by the signal intensity of MR image based on magnetic resonance properties of proton nucleus. Analysis on an one dimensional profile of acquired MR image of Korean red ginseng showed easy discrimination of normal and abnormal tissues. MR techniques suggested ways to detect internal defects of red ginsengs effectively.

• The Journal of the Acoustical Society of Korea
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• 제15권4E호
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• pp.65-71
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• 1996

In shallow water with a thermocline, the characteristics of sound propagation strongly depend on the signal frequency. When only one of the source and the receiver is above the themocline, it is known that the intensity of the received signal changes largely and almost periodically as the signal frequency varies. This is the so-called channel resonance. By using the ray-mode approach, the formula relating the resonance frequency and the sound speed profile is obtained, and the resonance phenomenon is analyzed. Also this analysis is verified by numerical calculation.