• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.3
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• pp.15-19
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• 2003

In This paper, we developed 1.96 GHz air gap type FBAR BPF using ZnO as piezoelectric sputtered by RF magnetron at room temperature. FBAR BPF was fabricated by sputtering bottom electrode (Al), ZnO as piezoelectric and top electrode (Mo) on Si wafer one by one with RF magnetron sputter, then Si was dry etched to make an air hole. XRD test result of fabricated FBAR BPF showed that ZnO crystal was well pre-oriented as (002) and sigma value of XRC was 1.018. IL(Insertion loss) showed excellent result as 1 dB.

• The Journal of the Acoustical Society of Korea
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• v.28 no.4
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• pp.363-369
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• 2009

In this paper, an estimation method is presented to determine the equivalent circuit model of an underwater acoustic piezoelectric transducer with multiple resonant modes. A fitness function that includes the coupled resonant effects is proposed to minimize an error between the measured impedance of the transducer and the calculated impedance of the equivalent model. Unknown parameters of the equivalent circuit are estimated by using PSO algorithm. The proposed method is applied to an example transducer of the sandwich type with 3 resonances in the frequency band of interest. The analytical impedance of the estimated equivalent circuit model is compared with the measured impedance of the transducer and the validity of proposed method is verified.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.5
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• pp.553-567
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• 2011

During the last three years, the possibility of the time reversal Lamb waves has been paid attention to for structural health monitoring of a plate. This study proposes a numerical scheme which can simulate the spatial focusing of time reversal Lamb waves on a rectangular plate. In this scheme, a time reversal process is formulated in the frequency domain using active virtual sensors being equivalent to the mirror effects of an actual sensor due to wave reflection on the plate boundary. Forward and backward Lamb wave propagations are represented by scalar functions for simulating the spatial focusing of time reversal Lamb waves. The validity of the proposed scheme is demonstrated through the comparison to the results of finite element analysis in which the spatial focusing of time reversal Lamb waves is realized by wafer-type piezoelectric(PZT) transducers collocated on a rectangular plate.

• Journal of Advanced Navigation Technology
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• v.17 no.3
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• pp.332-345
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• 2013

In this paper, recently, it is described to the piezoelectric transformer technology develops, because it was have to favorable characteristics such as electromagnetic-noise free, compact size, higher efficiency, and superior power density, flux linkage, noiseless, etc. its resonance frequency was used to output waveform of a sine wave. A rotor speed identification method of induction motor based on the theory of flux model reference adaptive system(FMRAS). The estimator execute the rotor speed identification so that the vector control of the induction motor may be achieved. The improved auxiliary variable of the model are introduced to perform accurate rotor speed estimation. The control system is composed of the PI controller for speed control and the current controller using space voltage vector PWM techniuqe and DC-DC converter. High speed calculation and processing for vector control is carried out by digital signal one chip microprocessor. Validity of the proposed control method is verified through simulation and experimental results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.2
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• pp.75-82
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• 2022

Nondestructive method to predict buckling load for the propellant tank of launch vehicle should be evaluated. Vibration correlation technique can predict the global buckling load of unstiffened cylindrical structure with geometric initial imperfection using correlation of natural frequency and compressive load from compressive test below the buckling load. In this study, vibration and buckling tests of a thin metal unstiffened propellant tank model subjected to internal pressure and compressive loads were performed and the test results were used for VCT to predict global buckling load. For the vibration test of thin structure, non-contact excitation method using a speaker was used. The response was measured with piezoelectric polymer(PVDF) sensor. Prediction results of VCT were compared with the measured buckling load in the test and the nondestructive global buckling load prediction method was verified.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.40 no.3
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• pp.10-17
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• 2003

In this paper, genetic algorithm (GA)-based Thin Film Bulk Acoustic Resonator (FBAR) RF filter design technique is proposed. Since the BVD(Butterworth-Van Dyke) lumped element model is valid only around the resonance, FBAR filter design technique based on BVD circuit has an approximate error. Instead of using BVD model, optimizing filter design method utilizes an analytical electrical impedance equation of FBAR. The geometry of FBAR such as thickness of the piezoelectric layer and area which significantly affect the filter response is optimized by GA. US-PCS Rx Bandpass filter obtained by the proposed technique shows a better response comparing with the typical and BVD-based filter.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.4
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• pp.398-413
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• 2011

For railway safety, it is very important to detect damages of rails at their early stage because any undetected damage in a rail can break the rail and cause a serious railway accident. In this paper, several NDT applicable to rail inspections are described. Major damage types in rails are discussed first and the rail inspection technology using conventional piezoelectric ultrasonic transducers, which is widely adopted for damage detection of rails, is explained. Other NDT being researched or tested for rail inspection are also discussed as complementary technologies to the concurrent contact type ultrasonic inspection. Characteristics of each rail inspection technologies are evaluated in order to provide requirements for future development of a new rail inspection method.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.94-94
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• 2011

배관 구조물에서는 내부 미세 균열에서부터 국부 좌굴, 볼트 풀림, 피로 균열 등과 같이 다양한 형태의 손상이 복합적으로 발생 가능하다. 이러한 복합 손상은 배관 구조물의 누수, 누유 등의 사고를 야기할 수 있다. 하지만 기존의 단일 스케일 계측 시스템으로부터 복합 손상에 의한 실시간 누수를 진단하기는 매우 어렵다. 본 연구 단계에서는 누수를 야기하는 복합 손상을 효율적으로 진단하기 위하여 선행 연구에서 제안된 압전센서를 이용한 자가 계측 회로 기반의 다중 스케일 계측 시스템을 구조물의 복합 손상 진단에 적용하였다. 자가 계측 회로 기반 다중 스케일 계측 시스템은 크게 두 가지 형태의 신호를 계측한다. 첫 번째 스케일은 임피던스 계측으로부터 특정 주파수 대역폭에 대한 구조 응답을 계측하며, 두 번째 스케일은 유도 초음파 계측으로부터 단일 중심 주파수에 해당하는 구조물의 응답을 계측한다. 복합 손상을 손상 유형별로 분류하기 위하여 E/M 임피던스(Electro-mechanical impedance)및 유도 초음파(Guided wave) 계측으로부터 추출한 특성을 이용하여 2차원 손상지수를 계산하고 이를 지도학습 기반 패턴인식 기법(Supervised learning based pattern recognition) 중 확률론적 신경망 기법(Probabilistic Neural Network, PNN)에 적용한다. 제안된 기법의 적용성 검토를 위하여 파이프 구조물에 인위적으로 다중 손상을 생성시켜 시험을 수행하였다. 본 연구에서 제안된 기법이 실제 배관 구조물에 성공적으로 적용된다면 손상 부재의 거동 및 구조물 성능의 손상에 대한 영향을 효율적으로 진단하고 평가함으로써 배관 구조물의 효과적인 유지관리가 가능할 것으로 예상된다.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.4
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• pp.323-329
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• 2003

In this paper, the method of material constants extraction in a thin-film bulk acoustic resonator(FBAR) using a genetic algorithm(GA) is proposed. The material constants are extracted from the input impedance of a FBAR by a GA optimizer. The characteristics of the FBAR input impedance affected by the material constants were studied to decide the fitness function for GA. As a result, the fitness was estimated by the series- and parallel -resonance frequencies and the FBAR bandwidth, as determined from the input impedance of the FBAR. A flowchart for the GA and a procedure fur the proposed extraction method are explained in detail, and the results of the material constants extraction are presented.

• Journal of Aerospace System Engineering
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• v.11 no.3
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• pp.8-15
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• 2017

In this paper, an equivalent brake hydraulic circuit with a piezoelectric hydraulic pump was constructed, and load pressure control for better pressurization/depressurization characteristics was conducted. To understand pressurization/depressurization characteristics of the equivalent hydraulic circuit, the relation between the load pressure and the input voltage was revealed experimentally. Experiments were also conducted to observe effect of the solenoid valve on depressurization characteristics. In the pressurization experiment, it was validated that transient response time required to achieve desired load pressure may be reduced through voltage control to change pressurization gradient. By applying the valve on/off time control and voltage control, it was also possible to reduce response time in the depressurization process. Therefore, transient response time may be improved within 10ms for pressurization and within 30 ms for depressurization using the control technique suggested in this study. The load pressure control method proposed in this study is useful for controlling load pressure of a hydraulic brake system with the piezoelectric hydraulic pump.