• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.239-242
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• 2009

구조물의 표면에 부착된 압전소자(이하 PZT)의 전기역학적 어드미턴스(Electro-mechanical admittance)는 PZT와 구조물의 상호작용에 의해 발생하는 PZT의 압전효과와 유전성(dielectric)이 결합되어 발생되는 신호이다. 고주파수 대역에서 PZT의 전기역학적 어드미턴스는 구조물의 국부손상에 민감하게 반응하는 것으로 알려져 있다. 실험에서 측정된 PZT의 전기역학적 어드미턴스 분석에 널리 쓰이는 Liang 모델은 구조물을 단자유도계로 단순화하여 구조물의 동적특성이 전기역학적 어드미턴스에 미치는 영향을 정확하게 나타내기 어렵다. 유한요소법을 통해 PZT와 구조물의 상호작용을 해석하면 이러한 문제점을 해결할 수 있다. 그러나 고주파 대역에서 정확한 해석을 위해서는 유한요소망을 조밀하게 구성해야 하므로 많은 계산비용이 수반된다. 이 연구에서는 유한요소법과 비교하여 월등히 적은 계산비용으로 고주파 대역의 동적 응답을 매우 정확하게 모사할 수 있는 스펙트럼 요소법(Spectral Element Method ; 이하 SEM)을 통해 판구조물에 부착된 PZT의 전기-역학적 어드미턴스를 해석한다. 수치 예제 및 실험 예제를 통하여 내민보에 부착된 PZT에서 발생하는 전기-역학적 어드미턴스를 취득하고 이를 SEM해석 결과와 비교한다.

• Proceedings of the KIPE Conference
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• 2004.07a
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• pp.125-128
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• 2004

본 연구는 태양광 발전에서 MPPT제어시 동특성을 개선하기 위해 솔라셀 내부 어드미턴스와 부하 어드미턴스의 매칭을 할 수 있는 새로운 제어기법을 제안한다. 제안된 제어기법은 기존의 단순 적분 제어 개념에서 벗어나 솔라셀 내부 어드미턴스와 부하 어드미턴스 차에 의해 비례적분제어를 행함으로써 동특성을 개선하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.2A
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• pp.97-104
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• 2011

This study presents the aerodynamic admittance function of bridge girder under turbulent flow generated from wind velocity spectrum measured at bridge site. Three dimensional buffeting analysis of concrete cable-stayed bridge were performed considering aerodynamic admittance functions obtained from four different methods. It is revealed from the analysis that vertical buffeting responses considering proper aerodynamic admittance functions were just half of that neglecting aerodynamic admittance function. Grid turbulence was found to relatively lower the aerodynamic admittance function at low frequency range, and to underestimate the buffeting wind forces. It is recommended to use the aerodynamic admittance function evaluated from flutter derivatives or measured at active turbulence in order to properly predict the buffeting responses of bridges.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.11 s.116
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• pp.1140-1148
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• 2006

In this paper, transmission loss of smart panel was investigated using piezoelectric shunt damping. Admittance of piezoelectric system was introduced to represent electro-mechanical coupling of smart panel and to predict the performance of shunt damping. Finite element method was used to obtain numerical admittance. In order to illuminate the effect of noise reduction in the shunt system, transmission loss of the smart panel was investigated. Two models were considered to show the relation between admittance and transmission loss of smart panel. It was observed that admittance of piezoelectric system could be used as a design index of smart panel.

• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.6
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• pp.1-10
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• 2019

The wave motion inside the nozzle is known as one of the major damping elements of the rocket's combustion instability by it's aeroacoustic effects that result from the flow passage through the nozzle throat. These effects can be quantitatively evaluated by the nozzle admittance. In this study, one-dimensional linearized Euler equation was adopted to calculate the nozzle admittance, and trend analysis was performed depending on the nozzle's main design variables. As a result, when nozzle converging part shortens, it is verified that the frequency dependency of the nozzle admittance is decreased due to the widened frequency range with lowered longitudinal nozzle admittance. Also, admittance estimation using the short nozzle theory is not appropriate when the first tangential mode of the pressure perturbation arises.

• Journal of Biomedical Engineering Research
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• v.25 no.5
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• pp.335-342
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• 2004

This paper describes a trans-admittance scanner for breast cancer detection. A FPGA-based sinusoidal waveform generator produces a constant voltage. The voltage is applied between a hand-held electrode and a scan probe placed on the breast. The scan probe contains an 8x8 array of electrodes that are kept at the ground potential. Multi-channel precision digital ammeters using the phase-sensitive demodulation technique were developed to measure the exit current from each electrode in the array. Different regions of the breast are scanned by moving the probe on the breast. We could get trans-admittance images of resistor and saline phantoms with an anomaly inside. The images provided the information on the depth and location of the anomaly. In future studies, we need to improve the accuracy through a better calibration method. We plan to test the scanner's ability to detect a cancer lesion inside the human breast.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.724-729
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• 2017

The interaction between the flow of the nozzle and the acoustic motion in the combustion chamber acts as an important factor in suppressing combustion instability where nozzle damping effect can be evaluated by nozzle admittance. In this study, Modified Impedance Tube experiment is implemented to predict the acoustic nozzle damping effect. The experimental admittances are compared to numerical admittances values which are calculated from one-dimensional linearized Euler equation of Crocco's theory. As a result, it was possible to identify qualitatively the tendency between increasing and decreasing parts. Also, Efficient frequency bands of nozzle attenuation can be predicted.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.39 no.6
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• pp.9-19
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• 2002

An NAC(Natural Admittance Control) system design is presented for interaction controller that achieves high-performance and guarantees stability. The NAC can be classified as a particular flavor of impedance control similar to control schemes that have velocity compensator and force compensator. The NAC significantly improves the response characteristics when Coulomb friction is presented in One-link Robot System and guarantees stability when robot contacts with environment. Pragmatic rules for NAC synthesis are derived. It shows method to choose a target impedance for realizable force compensator. Important parameters are found experimentally. It is demonstrated, by the experimental result, that NAC algorithm is successful in rejecting Coulomb friction through velocity compensator and guarantees stability through force compensator. We implement an experimental set-up consisting of environment-generated one-link robot system and DSP system for controller development. We apply the natural admittance controller to the One-link robot system, and show the good performance on desired force control in case of contacting with arbitrary environment.

• Proceedings of the KIPE Conference
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• 2013.07a
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• pp.395-396
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• 2013

고주파 유도가열 시스템은 고효율 및 생산의 편의성으로 산업 전반에 걸쳐 다양하게 적용되고 있다. 이러한 고주파 유도 가열 시스템은 크게 정류부, 전압조절부, 공진형 인버터로 구분된다. 공진형 인버터는 공진 주파수로 스위칭 시, 순수 실수 어드미턴스만 남게 되어 최대 효율을 얻는다. 공진 주파수는 공진회로의 입력 어드미턴스에 의해 결정되는데, 용융과정에서 피가열체의 저항 값은 시간에 따라 변화한다. 이는 전체 입력 어드미턴스의 변화와 공진 주파수의 변화로 나타나고, 효율이 저하되는 단점이 있다. 본 논문에서는 공진 인버터의 공진 주파수를 스스로 추종하는 자기공진 추종 토폴로지를 제안한다. 제안된 토폴로지는 고주파 유도가열 시스템의 용융과정에서 피가열체의 저항 값이 시변하여 공진 주파수가 이동하더라도 반주기 내에 정확하게 추종 동작을 한다. 본 논문에서는 제안된 자동 공진 추종회로를 기존의 병렬 공진 유도가열 시스템에 적용하여 타당성을 검증하였다.

• Proceedings of the KIEE Conference
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• 2003.07c
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• pp.1973-1975
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• 2003

본 논문에선 보정된 차단영역 어드미턴스 인버터 등가회로를 이용하여 밀리미터파 대역의 NRD gap-coupled filter를 설계하였다. 설계된 filter는 3개의 반파장 공진기와 4개의 인버터 (gap)로 구성되어 있다. 인버터에 해당되는 gap (차단영역)의 S 파라미터를 EM 시뮬레이터로 추출해서 어드미턴스 인버터로 구현 하였다 위의 설계과정을 통하여 2% 대역폭, 0.1dB ripple, 38.3GHz를 중심주파수로 갖는 필터를 설계하였고, 보정된 인버터로 설계한 경우가 보정되지 않은 인버터로 설계한 경우보다 정확한 응답특성이 나옴을 확인하였다.