• 한국컴퓨터정보학회논문지
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• 제22권1호
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• pp.71-76
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• 2017

Recently, there are various researches using inaudible high frequencies like as wireless communication based smart devices, data transmission algorithm, indoor positioning trace technologies. However, when they use high frequencies of inaudible range, they have a problem that the accuracy of data transmission with high frequencies was low because of interference from ambient noise in our real life. To solve this problem, in this paper, we proposed an application based on smart phone and server system for collection of ambient noise and detection of robust high frequency range. The server system could detect the robust high frequency range from statistical analysis of collected noise and the robust high frequency could avoid interference from ambient noise. We tested the proposed application's ability to gather noise and high frequencies for a certain period of time to evaluate performance. According to the testing results, we confirmed that the proposed application and server system could detect a robust high-frequency range via noise analysis in real life. Therefore, the proposed application and server could be a useful technology for future research on inaudible high frequencies.

• Smart Structures and Systems
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• 제13권3호
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• pp.473-500
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• 2014

Tuned mass dampers (TMDs) have been installed in many high-rise buildings, to improve their resiliency under dynamic loads. However, high-rise buildings may experience natural frequency changes under ambient temperature fluctuations, extreme wind loads and relative humidity variations. This makes the design of a TMD challenging and may lead to a detuned scenario, which can reduce significantly the performance. To alleviate this problem, the current paper presents a proposed approach for the design of a robust and efficient TMD. The approach accounts for the uncertain natural frequency, the optimization objective and the input excitation. The study shows that robust design parameters can be different from the optimal parameters. Nevertheless, predetermined optimal parameters are useful to attain design robustness. A case study of a high-rise building is executed. The TMD designed with the proposed approach showed its robustness and effectiveness in reducing the responses of high-rise buildings under multidirectional wind. The case study represents an engineered design that is instructive. The results show that shear buildings may be controlled with less effort than cantilever buildings. Structural control performance in high-rise buildings may depend on the shape of the building, hence the flow patterns, as well as the wind direction angle. To further increase the performance of the robust TMD in one lateral direction, active control using LQG and fuzzy logic controllers was carried out. The performance of the controllers is remarkable in enhancing the response reduction. In addition, the fuzzy logic controller may be more robust than the LQG controller.

• 융합신호처리학회논문지
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• 제9권2호
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• pp.98-103
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• 2008

기존의 대표적인 디지털 통신방식으로 주파수 편이 변조(FSK: frequency shift keying), 위상 편이 변조(PSK: phase shift keying), 진폭 편이 변조(ASK: amplitude shift keying) 방식들이 있다. 본 논문에서는 디지털 통신에서 스케일링 함수(scaling function)와 웨이브릿(wavelet)을 이용한 새로운 웨이브릿 편이 변조(wavelet shift keying) 시스템을 제안한다. 웨이브릿 변환은 저주파 계수와 고주파 계수로 구성된다. 입력이 1인 신호에 대하여 임펄스 응답을 구하면, 스케일링 함수와 웨이브릿 함수로 나누어진다. 스케일링 함수를 1로, 웨이브릿 함수를 0으로 할당하여 2진 데이터를 변조한다. 모의실험 결과 제안한 알고리즘이 잡음에 강인함을 확인하였다.

• Smart Structures and Systems
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• 제25권2호
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• pp.155-167
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• 2020

This paper demonstrates a real-time hybrid substructuring (RTHS) shake table test to evaluate the seismic performance of a base isolated building. Since RTHS involves a feedback loop in the test implementation, the frequency dependent magnitude and inherent time delay of the actuator dynamics can introduce inaccuracy and instability. The paper presents a robust stability and performance analysis method for the RTHS test. The robust stability method involves casting the actuator dynamics as a multiplicative uncertainty and applying the small gain theorem to derive the sufficient conditions for robust stability and performance. The attractive feature of this robust stability and performance analysis method is that it accommodates linearized modeled or measured frequency response functions for both the physical substructure and actuator dynamics. Significant experimental research has been conducted on base isolators and dampers toward developing high fidelity numerical models. Shake table testing, where the building superstructure is tested while the isolation layer is numerically modeled, can allow for a range of isolation strategies to be examined for a single shake table experiment. Further, recent concerns in base isolation for long period, long duration earthquakes necessitate adding damping at the isolation layer, which can allow higher frequency energy to be transmitted into the superstructure and can result in damage to structural and nonstructural components that can be difficult to numerically model and accurately predict. As such, physical testing of the superstructure while numerically modeling the isolation layer may be desired. The RTHS approach has been previously proposed for base isolated buildings, however, to date it has not been conducted on a base isolated structure isolated at the ground level and where the isolation layer itself is numerically simulated. This configuration provides multiple challenges in the RTHS stability associated with higher physical substructure frequencies and a low numerical to physical mass ratio. This paper demonstrates a base isolated RTHS test and the robust stability and performance analysis necessary to ensure the stability and accuracy. The tests consist of a scaled idealized 4-story superstructure building model placed directly onto a shake table and the isolation layer simulated in MATLAB/Simulink using a dSpace real-time controller.

• Journal of Power Electronics
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• 제13권5호
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• pp.814-828
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• 2013

The LCL resonant inductive power transfer (IPT) system is increasingly used because of its harmonic filtering capabilities, high efficiency at light load, and unity power factor feature. However, the modeling and controller design of this system become extremely difficult because of parameter uncertainty, high-order property, and switching nonlinear property. This paper proposes a frequency and load uncertainty modeling method for the LCL resonant IPT system. By using the linear fractional transformation method, we detach the uncertain part from the system model. A robust control structure with weighting functions is introduced, and a control method using structured singular values is used to enhance the system performance of perturbation rejection and reference tracking. Analysis of the controller performance is provided. The simulation and experimental results verify the robust control method and analysis results. The control method not only guarantees system stability but also improves performance under perturbation.

• ETRI Journal
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• 제28권4호
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• pp.509-512
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• 2006

In a real environment, sound recordings are commonly distorted by channel and background noise, and the performance of audio identification is mainly degraded by them. Recently, Philips introduced a robust and efficient audio fingerprinting scheme applying a differential (high-pass filtering) to the frequency-time sequence of the perceptual filter-bank energies. In practice, however, the robustness of the audio fingerprinting scheme is still important in a real environment. In this letter, we introduce alternatives to the frequency-temporal filtering combination for an extension method of Philips' audio fingerprinting scheme to achieve robustness to channel and background noise under the conditions of a real situation. Our experimental results show that the proposed filtering combination improves noise robustness in audio identification.

• JSTS:Journal of Semiconductor Technology and Science
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• 제15권2호
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• pp.202-207
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• 2015

A CMOS relaxation oscillator, with high robustness over process, voltage and temperature (PVT) variations, is designed in $0.18{\mu}m$ CMOS. The proposed oscillator, consisting of full-differential charge-discharge timing circuit and switched-capacitor based voltage-to-current conversion, could be expanded to a simple open-loop frequency synthesizer (FS) with output frequency digitally tuned. Experimental results show that the proposed oscillator conducts subcarrier generation for frequency-modulated ultra-wideband (FM-UWB) transmitters with triangular amplitude distortion less than 1%, and achieves frequency deviation less than 8% under PVT and phase noise of -112 dBc/Hz at 1 MHz offset frequency. Under oscillation frequency of 10.5 MHz, the presented design has the relative FS error less than 2% for subcarrier generation and the power dissipation of 0.6 mW from a 1.8 V supply.

• 한국통신학회논문지
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• 제37권1A호
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• pp.73-81
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• 2012

본 논문에서는 DRM(Digital Radio Mondiale) 수신기를 위한 고속 동기화 방식을 제안한다. 제안하는 방식에서는 DRM 수신기에서 요구하는 고속 수신 성능을 만족시키기 위해 기존 동기화 방식에서 수행하는 초기 샘플링 주파수 동기과정을 생략하고 정수배 주파수(Integer Frequency) 동기 및 프레임(Frame) 검출을 수행한 후, 추적(Tracking) 과정에서 샘플링 주파수 동기를 수행한다. 샘플링 주파수 옵셋(Sampling Frequency Offset)이 포함된 OFDM(Orthogonal Frequency Division Multiplexing) 복조 심볼로부터 프레임 옵셋을 추정하기 위해 참조셀(Reference cell)에 상관 기반 추정 알고리즘을 적용하고 그 성능을 분석하여 샘플링 주파수 옵셋에 강한 알고리즘을 선정한다. 제안된 구조는 DRM 수신 신호에 샘플링 주파수 옵셋이 존재하는 경우에도 초기 샘플링 주파수 동기화 과정에 소요되는 시간을 단축할 수 있으며, 참조셀간 차동 상관(Inter-cell Differential Correlation) 기법을 사용할 경우 초기 샘플링 주파수 옵셋의 영향에 강인함을 프레임 검출 모의실험을 통해 확인한다.

• 대한기계학회논문집A
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• 제20권10호
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• pp.3079-3094
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• 1996

Recently, the high-precision vibration attenuation technology becomes the essence fo the seccessful development of high-integrated and ultra-precision industries, and is expected to continue playing a key role in the enhancement of manufacturing technology. Vibration isolation system using an air-spring is widely employed owing to its excellent isolation characteristics in a wide frequency range. It has, however, some drawbacks such as low-stiffness and low-damping features and can be easily excited by exogenous disturbances, and then vibration of table is remained for a long time. Consequently, the need for active vibration control for an air-spring vibration isolation system becomes inevitable. Furthermore, for an air-spring isolation table to be successfully employed in a variety of manufacturing sites, it should have a guaranteed robust performance not only to exogenous disturbances but also to uncertainties due to various equipments which might be put on the table. In this study, an active vibration suppression control system using H.inf. theory is designed and experiments are performed to verify its robust performance. An air-spring vibration isolation table with voice-coil-motors as its actuators is designed and built. The table is modeled as 3 degree-of-freedom system. An active control system is designed based on $H_\infty$control theory using frequency-shaped weighting functions. Analysis on its performance and frequency responce properties are done through numerical simulations. Robust characteristics of$H_\infty$ control on disturbances and model uncertainties are experimentally verified through (i) the transient response to the impact excitation of the table, (ii) the steady-state response to the harmonic excitation, and (iii) the response to the mass change of the table itself. An LQG controller is also designed and its performance is compared with the $H_\infty$ controller.

• Journal of Advanced Marine Engineering and Technology
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• 제29권1호
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• pp.132-139
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• 2005

This paper describes the application of sliding mode control based on the variable structure control(VSC) concept for high-performance position control of an induction servo motor A design method based on external load parameters has been developed for the robust control of AC induction servo drive. Also, a slip frequency vector control with software current control technique has been adopted to achieve fast response of an induction motor drive The position control scheme is comprised of a variable structure controller and slip frequency vector control for inverter fed induction servo motor. Simulated results are given to verify the proposed design method by adoption of sliding mode and show robust control for a change of shaft inertia, viscous friction and torque disturbance.