• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.2
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• pp.169-172
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• 2019

Frequency-modulated continuous wave(FMCW) radars with array antennas are widely used because of their light weight and relatively high resolution. A usual approach for the joint range and angle estimation of a target using an array FMCW radar is to create a range-angle matrix with the deramped received signal, and subsequently apply two-dimensional(2D) frequency estimation methods such as 2D fast Fourier transform on the range-angle matrix. However, such frequency estimation approaches cause bias errors since the frequencies in the range-angle matrix are not independent. Therefore, we propose a new maximum likelihood-based algorithm for joint range and angle estimation of targets using array FMCW radar, and demonstrate that the proposed algorithm achieves the Cram?r-Rao bounds, both for range as well as angle estimation.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.6
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• pp.1-10
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• 2018

An experimental study was performed for the behavior of the burner flame which results from burning of the liquid hydrocarbon fuel atomized by an ultrasonic transducer. Configurations of the flame and combustion-field were caught by both high-speed camera and thermo-graphic camera, and those images were analyzed in detail through a image post-processing. As a result, the combustion-field grew and reaction-temperature rose due to the strengthening of combustion reaction with the increasing flow-rate of carrier-gas. In addition, a phenomenon of flame flickering was discussed through the comparative analysis of the variational behavior between the visible flame and IR (Infrared) flame-field. Also, the flickering frequency of the flame was confirmed through FFT (Fast Fourier Transform) analysis employing the flame area.

• Journal of the Korea Convergence Society
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• v.10 no.8
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• pp.145-151
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• 2019

In this study, the effects were analyzed by applying the vibration absorption liner into the guide rail bracket as a part of method to reduce the vibration and noise on the high-rise apartment. As the result of vibration absorption liner performance, it was checked that the level of vibration and noise was reduced around 65.49% in the car side and around 90.05% in the counterweight side. Therefore, the vibration absorption effect by the vibration absorption liner of elevator guide rail bracket became fairly good. In case of the vibration absorption liner application, there was an effect on the reduction of 7.26 to 22.22% at hoistway section area, 3,840,000 to 9,780000 KRW at the cost of material and installation by comparing with the damping beam application. Also, in case of the vibration absorption liner application with light weight instead of damping beam with heavy weight, it was thought to become significant effect at preventing the safety from the accidents on installation site.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.1
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• pp.104-113
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• 2022

In this paper, we propose deep learning-based target distance and velocity estimation technique for OFDM radar systems. In the proposed technique, the 2D periodogram is obtained via 2D fast Fourier transform (FFT) from the reflected signal after removing the modulation effect. The periodogram is the input to the conventional and proposed estimators. The peak of the 2D periodogram represents the target, and the constant false alarm rate (CFAR) algorithm is the most popular conventional technique for the target's distance and speed estimation. In contrast, the proposed method is designed using the multiple output convolutional neural network (CNN). Unlike the conventional CFAR, the proposed estimator is easier to use because it does not require any additional information such as noise power. According to the simulation results, the proposed CNN improves the mean square error (MSE) by more than 5 times compared with the conventional CFAR, and the proposed estimator becomes more accurate as the number of transmitted OFDM symbols increases.

• The Journal of the Acoustical Society of Korea
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• v.27 no.7
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• pp.350-356
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• 2008

In this paper, we propose shading functions to the appropriate focused beamforming for near-field target estimation. This near field shading functions are based on Chebychev and Manning windows. In order to obtain the optimum sensor weighting values with the help of the proposed shading technique, we assume that the sensor positions associated to the non-uniformly distributed array are precisely known. We calculate a series of sensor weighting values from the FFT operation of given shading functions in time domain. By applying the shading weights on the sensor array, we can see that the level of sidelobe becomes diminished and the performance of estimating range and azimuth gets improved. In addition, we propose a non-uniform structure in terms of frequency bands, which may minimize the attenuation of incoming signals.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.4
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• pp.245-250
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• 2015

To verify the possibility of generating rattling noise from a motor on caliper brake system, a test was conducted using a caliper excited with vibrations similar to that in a vehicle running on actual roads; this test was conducted using a quiet shaker installed in an anechoic room. After several hours of external excitation, the test assembly was loosened, and the frequency of rattling noise generation increased. A microphone was used to record the generated noise. The measured signals were analyzed by conventional spectrum analysis. Since the noise is generated as an impact response, the advantages of employing Prony analysis was discussed, and the results were compared to those obtained using conventional fast Fourier transforms. The accuracy of Prony analysis was through endurance tests on different brake systems.

• Journal of Pharmacopuncture
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• v.19 no.3
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• pp.207-212
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• 2016

Objectives: Acupuncture treatments are safe and effective for a wide variety of diseases involving autonomic dysregulation. Heart rate variability (HRV) is a noninvasive method for assessing sympathovagal balance. The low frequency/high frequency (LF/HF) spectral power ratio is an index of sympathovagal influence on heart rate and of cardiovascular health. This study tests the hypothesis that from rest to 30% to 50% of peak oxygen consumption, the nonlinear Conte-Zbilut-Federici (CZF) method of computing the LF/HF ratio is a more reliable index of changes in the HRV than linear methods are. Methods: The subjects of this study were 10 healthy young adults. Electrocardiogram RR intervals were measured during 6-minute periods of rest and aerobic exercise on a cycle ergometer at 30% and 50% of peak oxygen consumption ($VO_{2peak}$). Results: The frequency domain CZF computations of the LF/HF ratio and the time domain computations of the standard deviation of normal-to-normal intervals (SDNN) decreased sequentially from rest to 30% $VO_{2peak}$ (P < 0.001) to 50% $VO_{2peak}$ (P < 0.05). The SDNN and the CZF computations of the LF/HF ratio were positively correlated (Pearson's r = 0.75, P < 0.001). fast Fourier transform (FFT), autoregressive (AR) and Lomb periodogram computations of the LF/HF ratio increased only from rest to 50% $VO_{2peak}$. Conclusion: Computations of the LF/HF ratio by using the nonlinear CZF method appear to be more sensitive to changes in physical activity than computations of the LF/HF ratio by using linear methods. Future studies should determine whether the CZF computation of the LF/HF ratio improves evaluations of pharmacopuncture and other treatment modalities.

• Composites Research
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• v.34 no.3
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• pp.155-160
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• 2021

Metamaterials are complexes of elements that can create properties not found in naturally occurring materials, such as changing the direction of forces, creating negative stiffness, or altering vibration and impact properties. In the case of wood pile metamaterials that are easy to manufacture and have excellent performance in reducing vibration and shock in the vertical direction, basic research on variables affecting shock transmission is needed to reduce shock. Although research on impact reduction according to geometrical factors is being conducted recently, studies on the effect of material variables on impact reduction are insufficient. In this paper, finite element analysis was carried out by variablizing the geometrical properties (lamination angle, diameter, length) and material properties (modulus of elasticity, specific gravity, Poisson's ratio) of wood pile cylinders. Through finite element analysis, the shape of the wooden pile cylinder delivering impact was confirmed, and the effect of each variable on the reduction of impact force and energy was considered through main effect diagram analysis, and frequency band analysis was performed through fast Fourier transform. proceeded In order to reduce the impact force and vibration, it was found that the variables affecting the contact area of t he cylinder have a significant effect.

• Journal of the Korean Geotechnical Society
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• v.38 no.12
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• pp.91-101
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• 2022

The 1995 Kobe earthquake caused a massive damage to the Port of Kobe. Therefore, it was pointed out that it was impossible to design port structures for Level II (Mw 6.5) earthquakes with quasi-static analysis and Allowable Stress Design methods. In Japan and the United States, where earthquakes are frequent, the most advanced design standards for port facilities are introduced and applied, and the existing seismic design standards have been converted to performance-based design. Since 1999, the Korean Port Seismic Design Act has established a definition of necessary facilities and seismic grades through research on facilities that require seismic design and their seismic grades. It has also established a performance-based seismic design method based on experimental verification. In the performance-based seismic design method of the breakwater proposed in this study, the acceleration time history on the surface of the original ground was subjected to a fast Fourier transform, followed by a filter processing that corrected the frequency characteristics corresponding to the maximum allowable displacement with respect to performance level of the breakwater and the filtered spectrum. The horizontal seismic coefficient for the equivalent static analysis considering the displacement was calculated by inversely transforming (i.e., subjected to an inverse fast Fourier transform) into the acceleration time history and obtaining the maximum acceleration value. In addition, experiments and numerical analysis were performed to verify the performance-based seismic design method of breakwaters suitable for domestic earthquake levels.

• Journal of the Korea Computer Industry Society
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• v.6 no.5
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• pp.675-686
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• 2005

This paper proposes a new method of mathematically modeling and computer simulating television ghosts wherein television signals that have undergone multipath fading are generated without using approximations by considering the attenuation, time delay, phase, and timing jitter between consecutive frames. Conventional methods used polynomial interpolation or complex arithmetic to take into account the ghost phase, but our method uses only real arithmetic by employing the Hilbert transform and also reduces the computation time using the FFT (fast Fourier transform) algorithm. Furthermore, it is also possible to observe the transmit waveforms in both RF and IF ranges. Various ghost patterns generated in software provide for essential data required for the development of ghost canceling algorithms, and are deemed to be very useful in analyzing the constituent blocks of the transmitter and receiver chain in television broadcasting. The development of ghost cancelers needs to be preceded by the task of mathematically modeling ghosts and their extensive computer simulations.