• The Journal of Korean Institute of Information Technology
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• v.17 no.3
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• pp.43-50
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• 2019

In this paper, we propose a S-band oscillator with a reduced electrical size by applying a vertical split ring resonator(VSRR). The VSRR is a type of split ring resonator that operates as a resonator by the capacitance and inductance generated between the microstrip lines arranged on the top and bottom of the dielectric substrate and it has an advantage that the electrical size of the resonance circuit can be reduced as compared with the conventional ring resonator. In this paper, we design a VSRR operating over S-band and an oscillator using the VSRR as the resonant circuit. The proposed oscillator showed the output of 5.9dBm at 2.4HGz and showed the phase noise characteristics of -112.58dBc at 100KHz offset frequency and -117.85dBc at 1MHz offset.

• The Journal of the Acoustical Society of Korea
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• v.41 no.1
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• pp.9-15
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• 2022

In order to overcome the limitation of conventional nanoparticle dispersion methods such as sonicator or homogenizer, a filtration method using an ultrasonic atomization effect and cyclones was proposed in this study. A 0.5 wt% suspension was made with Al₂O₃ powder with an average diameter of 250 nm. The suspension was filtered by the proposed method after pre-dispersing using a sonicator and a homogenizer, respectively. As the result, in the case of the suspension after pre-dispersing with a sonicator, the particle size distribution of the filtered suspension started showing up a single normal distribution indicating the mode of the average diameter only after the 3rd cyclone process. On the other hand, in the case of the suspension with the homogenizer pre-dispersion, similar results appeared from the 2nd cyclone process. Filtration of various types of nanoparticles is expected to be possible by adjusting ultrasonic atomization frequency and manipulating the design of the cyclone.

• The Journal of the Acoustical Society of Korea
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• v.40 no.3
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• pp.192-200
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• 2021

Korean bell is a macroscopically axi-symmetrical structure, but has a slight asymmetry due to complex patterns and casting irregularity. Small asymmetry separates one vibration mode into a mode pair with slight frequency difference. The mode pair interferes and creates a beat. The vivid beat with an appropriate period makes the bell sound magnificent and lively feeling. In this study, we propose a method to make the vivid beat using artificial dumshoi. This method creates the vivid beat by designing artificial dumshoi that overwhelms the bell asymmetry. To this end, the asymmetry of Korean bell is quantified by analyzing the beat period data of a number of Korean bells cast in modern times. Based on the measured beat period data, the magnitude of asymmetry is quantified using an equivalent bell model and artificial dumshoi is applied. The movement of mode pair by dumshoi is predicted through finite element analysis. Finally, a design example of the artificial dumshoi for clear beat is introduced.

• Journal of the Korean Geotechnical Society
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• v.23 no.12
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• pp.117-124
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• 2007

This study investigates the effect of spatial averaging and compliance taken account of in the analysis of earthquake-induced permanent deformation of slopes. At present, the rigid block analysis originally proposed by Newmark is widely used in the deformation analysis, mainly because of its computational efficiency. This type of approach, however, adopts the so-called decoupled approach, in which seismic response and deformation analyses are carried out separately. Original Newmark block analysis assumes the potential sliding mass to be noncompliant, and has been criticized to be potentially unconservative. This paper reviews the impact of the noncompliance assumption of the potential sliding mass in the Newmark-type analysis. The gross effects of earthquake shaking on the potential sliding mass are estimated by spatial averaging method and analyzed in frequency domain. The results indicate that there is a simple criterion that can be used to determine the level of compliance of the potential sliding mass.

• The Journal of the Acoustical Society of Korea
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• v.42 no.3
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• pp.203-213
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• 2023

In medical ultrasound imaging systems, Side lobes may appear if signals outside the imaging point are not completely removed during receive focusing. If the time signal of the side lobe overlaps with the time signal (main lobe) from the image point, it is difficult to completely remove it using filter processing in the time domain. However, In the receive focusing process, when time-channel signals are Fourier-transformed, the main lobe and side lobe signals are spatially separated in the spectral domain. Therefore, the side lobes can be suppressed by multiplying the image with magnitude weights, which are determined by the magnitudes of the main and side lobes calculated in the spectral domain. In addition, when the main lobe and the side lobe spectrum are adjacent, the distance weight was applied based on the distance between them. In a 5 MHz ultrasound imaging system using a 64-channel linear transducer, point reflector and speckle images with cysts of various brightness were synthesized and weights were applied to the ultrasound image. Using computer simulations, we confirmed that the side lobes were greatly reduced without affecting the spatial resolution in the point reflector image, and the contrast was significantly improved in the cyst image with computer simulations.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.131-142
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• 2022

In order to examine the possibility of horizontal simulations of acoustic waves on the environments of big water depth variations, this study introduces a 3-dimensional model based on the pababolic equation. The model gives approximated solutions by separating the cross- and non cross-terms in the equation. Assuming artificial bathymetry (25 km × 4 km) with a source frequency 75 Hz, the simulations give clear horizontal refractions on the transmission loss distributions. The degree of refractions shows non-linear increase along the propagating range and proportional increase with water depth along the cross range. Another simulations with the real bathymetry (25 km × 8 km) also give clear horizontal refractions. The horizontal distributions present little difference with the depth resolution variations of the same data source because the model gives interpolations over the depth data before simulations. Meanwhile, the horizontal distributions show big difference with those of different data sources.

• The Journal of the Acoustical Society of Korea
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• v.29 no.1
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• pp.69-75
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• 2010

In this paper, the pitch is detected after the elimination of formant ingredients by flattening the spectrum in frequency domain. In order to remove impact of formant and transition frequency in the signal spectrum, formant envelop is made by linear interpolation with any points each sub-band and the spectrum of speech signal is compensated by the reverse of the envelop interpolated linearly after we divide frequency band into several segment based on LSP and detect the points. The experimental result showed the proposed method appeared an outstanding performance in compared with LPC, Cepstrum, Lifter methods. The method reduced the gross error rate 1.30% than the LPC method which appeared a good performance except the proposed method. Also, the proposed method showed low error rate in noise environment.

• Investigative Magnetic Resonance Imaging
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• v.8 no.1
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• pp.42-49
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• 2004

Purpose : The quantization noise in magnetic resonance imaging (MRI) systems is analyzed. The signal-to-quantization noise ratio (SQNR) in the reconstructed image is derived from the level of quantization in the signal in spatial frequency domain. Based on the derived formula, the SQNRs in various main magnetic fields with different receiver systems are evaluated. From the evaluation, the quantization noise could be a major noise source determining overall system signal-to-noise ratio (SNR) in high field MRI system. A few methods to reduce the quantization noise are suggested. Materials and methods : In Fourier imaging methods, spin density distribution is encoded by phase and frequency encoding gradients in such a way that it becomes a distribution in the spatial frequency domain. Thus the quantization noise in the spatial frequency domain is expressed in terms of the SQNR in the reconstructed image. The validity of the derived formula is confirmed by experiments and computer simulation. Results : Using the derived formula, the SQNRs in various main magnetic fields with various receiver systems are evaluated. Since the quantization noise is proportional to the signal amplitude, yet it cannot be reduced by simple signal averaging, it could be a serious problem in high field imaging. In many receiver systems employing analog-to-digital converters (ADC) of 16 bits/sample, the quantization noise could be a major noise source limiting overall system SNR, especially in a high field imaging. Conclusion : The field strength of MRI system keeps going higher for functional imaging and spectroscopy. In high field MRI system, signal amplitude becomes larger with more susceptibility effect and wider spectral separation. Since the quantization noise is proportional to the signal amplitude, if the conversion bits of the ADCs in the receiver system are not large enough, the increase of signal amplitude may not be fully utilized for the SNR enhancement due to the increase of the quantization noise. Evaluation of the SQNR for various systems using the formula shows that the quantization noise could be a major noise source limiting overall system SNR, especially in three dimensional imaging in a high field imaging. Oversampling and off-center sampling would be an alternative solution to reduce the quantization noise without replacement of the receiver system.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.3
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• pp.75-85
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• 2009

This work proposes a 13b 100MS/s 0.13um CMOS ADC for 3G communication systems such as two-carrier W-CDMA applications simultaneously requiring high resolution, low power, and small size at high speed. The proposed ADC employs a four-step pipeline architecture to optimize power consumption and chip area at the target resolution and sampling rate. Area-efficient high-speed high-resolution gate-bootstrapping circuits are implemented at the sampling switches of the input SHA to maintain signal linearity over the Nyquist rate even at a 1.0V supply operation. The cascode compensation technique on a low-impedance path implemented in the two-stage amplifiers of the SHA and MDAC simultaneously achieves the required operation speed and phase margin with more reduced power consumption than the Miller compensation technique. Low-glitch dynamic latches in sub-ranging flash ADCs reduce kickback-noise referred to the differential input stage of the comparator by isolating the input stage from output nodes to improve system accuracy. The proposed low-noise current and voltage references based on triple negative T.C. circuits are employed on chip with optional off-chip reference voltages. The prototype ADC in a 0.13um 1P8M CMOS technology demonstrates the measured DNL and INL within 0.70LSB and 1.79LSB, respectively. The ADC shows a maximum SNDR of 64.5dB and a maximum SFDR of 78.0dB at 100MS/s, respectively. The ABC with an active die area of $1.22mm^2$ consumes 42.0mW at 100MS/s and a 1.2V supply, corresponding to a FOM of 0.31pJ/conv-step.

• Korean Journal of Food Science and Technology
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• v.26 no.5
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• pp.596-602
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• 1994

To separate and concentrate mucilage from yam(Dioscorea batatas DECNE), yam was dried, microparticulated using impact mill and air-classified at different air classifying wheel speed(ACWS) in classifier. As ACWS increased from 5,000 rpm to 22,500 rpm, the contents of dietary fiber, protein and lipid of air classified microparticles(ACM) increased remarkably. Especially the ACM with ACWS over 15,000 rpm showed 36.41% dietary fiber and 16.66% protein. The dietary fiber and protein components were concentrated to $2.5{\sim}9.0$ times as compared with whole yam powder. Concomitantly the non-fibrous carbohydrate decreased from 88.31% to 16.84. The damaged starch(%), WSI and WAI of ACM of ACWS over 15,000 rpm were $1.5{\sim}3.0$ times higher than those of ACM under ACWS 15,000 rpm. The apparent viscosity of ACM was 0.0800 Pa s over ACWS 15,000 rpm and 0.0080 Pa s under ACWS 15,000 rpm. Judging from viscosity of ACM, the mucilage component of yam was concentrated to 10 times. In conclusion, the optimum process to separate and concentrate the mucilage from yam consisted of the microparticulation to $5{\sim}30{\mu}m$ and the air-classification at ACWS over 15,000 rpm.