• Journal of the Korean Society for Nondestructive Testing
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• v.37 no.1
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• pp.7-12
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• 2017

A nonlinear ultrasonic parameter is defined by the ratio of displacement amplitude of the fundamental frequency component to that of the second-order harmonic frequency component. In this study, the ultrasonic displacement amplitude of an SUS316 specimen was measured via a piezo-electric-based method to identify the validity of piezo-electric detection method. For comparison, the ultrasonic displacement was also determined via a laser-based Fabry-Pérot interferometer. The experimental results for both measurements were in good agreement. Additionally, the stability of the repeated test results from the piezo-electric method exceeded that of the laser-interferometric method. This result indicated that the piezo-electric detection method can be utilized to measure a nonlinear ultrasonic parameter due to its excellent stability although it involves a complicated process.

• Journal of the Korean Society for Nondestructive Testing
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• v.33 no.1
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• pp.40-45
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• 2013

The purpose of this study was to detect the pin hole defect of dental composite restoration using lock-in thermography method. Amplitude and phase images of the composite resin specimens were analyzed according to the lock-in frequency and the diameter of defect area. Through the amplitude image analysis, at lock-in frequency of 0.05 Hz, defect diameters 2-5 mm exhibited the highest amplitude contrast value between defective area and sound area. The lock-in frequency range of 0.3-0.5 Hz provided good phase angle contrast for the defect area. At lock-in frequency range of 0.5 Hz, defect diameter of 5 mm exhibited the highest phase contrast value. It is concluded that the infrared lock-in thermography method verified the effectiveness for detecting the pin hole defect of dental composite restoration.

• Journal of Electrical Engineering and Technology
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• v.13 no.5
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• pp.1945-1955
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• 2018

High frequency signal injection (HFI) is an alternative method for estimating rotor position of interior permanent magnet synchronous motor (IPMSM). The general method of frequency and amplitude selection is based on error tolerance and experiments, and is usually set with only one group of HF parameters, which is not efficient for different working modes. This paper proposes a novel rotor position estimation scheme by HFI with optimized frequency and amplitude, based on the mathematic model of IPMSM. The requirements for standstill and low-speed operational modes are met by applying this novel scheme. Additionally, the effects of the frequency and amplitude of the injected HF signal on the position estimation results under different operating conditions are analyzed. Furthermore, an optimization method for HF parameter selection is proposed to make the estimation process more efficient under different working conditions according to error tolerance. The effectiveness of the propose scheme is verified by the experiments on an IPMSM motor prototype.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.21 no.5
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• pp.162-170
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• 2022

In this paper, the phased-array transceiver (TRX) channel amplitude and phase calibration method for a radar wind profiler (RWP) based on the 256 active phased array is discussed. Without the additional module, the TX and RX calibration paths were secured using couplers and switches in the TRX front ends and the TRX switching duplexers, and the amplitude and phase of the 256 TRX were calibrated using a gain and phase detector. The beam widths and side lobes of five beams (vertical, east, west, south, and north) of the calibrated 256 active phased array antenna were confirmed by a near-field which agreed well with the simulation results. The proposed calibration method can be easily applied to a system based on an active phased array operated in an outdoor environment.

• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.2082-2086
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• 2003

This paper presents the analysis of satellite received signal by focus on the new prediction method for amplitude scintillation expression. A predict method based in the relationship of standard deviation values and the peak to peak values of amplitude scintillation in various of time period and various of sampling rate of signal variation. The principal techniques finding, the proper sampling rate and time interval, for the best expression method. The experiment has been performed in Bangkok of Thailand, at King Mongkut's Institute of Technology, Ladkrabang, data collected in C-Band and Ku-Band on high elevation angles. The result of analysis shows the relationship between two methods is given by ${\sigma}_x={\alpha}(P-P)+{\beta}$. The value of ${\alpha}$ depends on sampling rate by closely with three-minute maximum time interval.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.11 s.242
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• pp.1455-1462
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• 2005

In this paper, we intend to introduce a nonlinear finite element method based on the fully nonlinear potential flow theory in order to simulate the large amplitude sloshing flow in two-dimensional baffled tank subject to horizontally forced excitation. The free surface is tracked by a direct time differentiation scheme with the four-step predictor-corrector time integration method. The flow velocity is accurately recovered from the velocity potential by second-order least square method. In order to maintain the finite element mesh regularity and total mass, the semi-Lagrangian surface tracking method with area conservation is applied. According to the numerical formulae, we perform the parametric experiments by varying the installation height and the opening width of baffles, in order to examine the effects of baffle on the nonlinear liquid sloshing. From the numerical results, the hydrodynamic characteristics of the large amplitude sloshing are investigated.

• IEIE Transactions on Smart Processing and Computing
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• v.6 no.4
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• pp.246-252
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• 2017

Non-invasive and non-restrictive methods for measuring the physiological functions of the human body are useful for health care, security, and surveillance. In this paper, a new method that extracts human heartbeat information by utilizing ultra-wideband (UWB) impulse radar is proposed. The amplitude spectra of received radar pulses reflected from the human body are accumulated at specific time intervals, and chirp z-transform (CZT) is used to extract the heartbeat frequency from the amplitude spectra. The heartbeat frequency can be extracted with high-frequency resolution in the frequency band of the heartbeat of interest using CZT. Experimental results to verify the performance of the proposed method show that a highly accurate extraction of the heartbeat frequency is possible using this method.

• Proceedings of the Korea Water Resources Association Conference
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• 1985.07a
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• pp.275-281
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• 1985

The analytical procedure of the boundary element method on potential poblems is introduced and the method is used to analyze the wabe poblem which has the boundary condition based on the small amplitude wave theory. The accuracy of the computational scheme is investigated by comparing the results of progressive wave and standing wave on two dimensional (x-z plane) constant depth and the possibility about analyzing more complicated water wave theories using this method is discussed.

• Journal of the Korean Institute of Telematics and Electronics B
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• v.30B no.4
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• pp.44-55
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• 1993

In this paper, we proposed a new optical method for the efficient recognition of Korean characters. There are six filters in the proposed method which employed the concepts of amplitude-modulated phase-only filter(AMPOF) and spatial frequency modulation(SFM). Here, amplitude modulation is used to achieve improved correlation discrimination and SFM is to reduce the number of filters. We also used a simplified synthetic discriminant function(SDF) for distortion invariance of input image. In order to recognize the partial rotation invariant Korean characters, the proposed distortion invariant minimum average correlation energy (MACE) filter is synthesized SFM, partial rotation invariant filter (PRIF), AMPOF and MACE for partial rotation invariance in the frequency domain. The advantage of the proposed filters is to supress the sidelobes of cross correlation peak away from the autocorrelation peak and to produce sharp correlation peaks. We performed simulation and optical experiment for some of Korea characters using the proposed method. The results show that the proposed method has more improved discriminant ability and reduced processing time than the conventional methods.

• 제어로봇시스템학회:학술대회논문집
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• 1998.10a
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• pp.271-274
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• 1998

This paper describes a new method for separation of the Volterra kernels which are identified by use of M-sequence. One of the authors has proposed a method for identification of Volterra kernels of nonlinear systems using M-sequence and correlation technique. When M-sequence are applied to a nonlinear systems, the cross-correlation function between the input and the output of the nonlinear systems includes cross-sections of high-order Volterra kernels. However, if various order Volterra kernels exixt on the obtained cross-correlation function, it is difficult to separate the Volterra kernels. In this paper, the authors show that the magnitude of Volterra kernels is maginified by the amplitude of M-sequence according to the order of Volterra kernels. By use of this property, each order Volterra kernels is obtained by solving linear equations. Simulations are carried out for some nonlinear systems. The results show that Volterra kernels can be separated in each order successfully by the proposed method.