• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.1711-1714
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• 2006

Anchoring energy of liquid crystals on solid substrates is a key parameter in liquid crystal technology. A nonperturbative method of its measurement by dynamic light scattering on thermal orientational fluctuations is presented, The ratio of the zenithal and azimuthal anchoring coefficients is shown to be equal to the ratio of the orientational elastic constants.

• Journal of Power Electronics
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• v.14 no.4
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• pp.806-813
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• 2014

Planar electromagnetic interference (EMI) filters are widely used to restrain the conducted EMI of switching power supplies. Such filters are characterized by small size, low parasitic parameters, and better high-frequency performance than the passive discrete EMI filter. However, EMI filter performance cannot be exactly predicted by using existing methods. Therefore, this paper proposes a method to use scattering parameters (S-parameters) for the measurement of EMI filter performance. A planar EMI filter sample is established. From this sample, the relationship between S-parameters and insertion gain (IG) of EMI filter is derived. To determine the IG under different impedances, the EMI filter is theoretically calculated and practically measured. The differential structure of the near-field coupling model is also deduced, and the IG is calculated under standard impedance conditions. The calculated results and actual measurements are compared to verify the feasibility of the theory.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.5
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• pp.541-548
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• 2013

This paper presents a vector network analysis system for 2-port scattering parameters of microwave devices using some basic microwave instruments/devices such as signal generators, vector voltmeter, directional couplers and frequency mixers. The analytical model and implementation method for scattering parameter measurements - which can replace the vector network analyzers - are presented. The performance of the implemented system is evaluated through 1- and 2-port scattering parameter measurements, respectively. The vector volt signals which determine the scattering parameters are detected in two distinct methods depending on the frequency band of interests; a direct-detection method with a single signal generator and vector voltmeter for relatively low band and a heterodyne method to frequency down-mix associated with an additional signal source as well as frequency mixers for high band are used, respectively. Using these two methods, scattering parameters of UHF and X bands are evaluated and their performances are verified through a comercial vector network analyzer.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.6
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• pp.168-178
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• 1994

This paper presents an optical surface roughness sensor developed for intermediate- process measurement on the machine. The light scattering method is adopted for the sensor, which is designed conpact and flexible enough to apply to 'on the machine' measurement of surface roughness. The developed sensor has special features such that it makes use, as the measurement parameter, of the ratio between fluxes of the incident light, and the specularly and partly diffusely reflected light, and that it can adjust the incident light angle. The experimental investigation reveals not only the sensor has good performance as a surface roughness sensor but the sensor is very robust so as to be useful in in-process measurement.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.1
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• pp.9-15
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• 2011

This paper suggested the fast and easy method of the dielectric constant measurement for planar dielectrics using a microstrip line. The complex permittivity and permeability were presented by the first reflection and transmission coefficient which were derived from the scattering parameters. This method was verified by the measurement of a known planar dielectric using a microstrip line. This method can be applied to the dielectric constant measurement of unknown planar dielectric.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.28 no.3
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• pp.96-107
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• 2024

We consider the bifocusing method (BFM) for a fast identification of small objects in microwave imaging. In many researches, it was very hard to measure the scattering parameter data if the location of the transmitter and the receiver is the same. Due to this reason, the imaging function of BFM has mainly been designed by converting unknown measurement data into the zero constant; this approach has yielded reliable imaging results, but the theoretical reason for this conversion has not been investigated yet. In this study, we converted unknown measurement data to a fixed constant and applied the BFM to retrieve small objects. To demonstrate the effect of the converted constant, we show that the imaging function of the BFM can be represented in terms of an infinite series of the Bessel functions of an integer order, antenna setting, material properties, and applied constant. Based on the theoretical result, we concluded that converting unknown measurement data to constant zero guarantees good imaging results, including the unique determination of the objects. Simulation results obtained with synthetic and real data support the theoretical result.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.40-48
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• 2019

New concept of fine dust measurement method is suggested based on ultrasonic scattering. These days, fine dust has been social problem in Korea, and many researches has been conducted including the area structural maintenance. Conventional measurement system such as optical scattering and semiconductor has a limit from environmental factors like relative humidity. However, ultrasound is based on mechanical waves, which perturb mechanical properties of medium such as density and elastic constants. Using the advantage, the algorithm for fine dust measurement is derived and evaluated using 2-D finite difference method. The numerical analysis simulates ultrasonic wave propagation inside multiple scattering medium like fine dust in air. Signal processing scheme is also suggested and the results show that the error of the algorithm is around minimum of 0.7 and maximum of 24.9 in the number density unit. It is shown that cross-section of fine dust is a key parameter to improve the accuracy of algorithm.

• JSTS:Journal of Semiconductor Technology and Science
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• v.13 no.6
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• pp.589-593
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• 2013

An efficient measurement methodology is proposed to construct the scattering parameters of a multi-port device using a four-port vector network analyzer (VNA) without the external un-terminated ports. By using the four-port VNA, the reflected waves from the un-terminated ports could be minimized. The proposed method significantly enhances the accuracy of the S-parameters with less number of measurements compared to the results of classical renormalization technique which uses two-port VNA. The proposed method is validated from the measured data with the coupled 8-port micro-strip lines.

• The Journal of the Acoustical Society of Korea
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• v.18 no.2E
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• pp.18-23
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• 1999

This paper proposes a method of separately determining three intrinsic mechanical parameters of an unknown object in the framework of ultrasound inverse scattering tomography. Those parameters are the speed of sound, density, and absorption whose values are given as the solution of an inhomogeneous Helmholtz wave equation. The separate reconstruction method is mathematically formulated, the integral equations are discretized using the sinc basis functions, and the Newton-Raphson method is adopted as a numerical solver in a measurement configuration where the object is insonified by an incident plane wave over 360˚ and the scattered field is measured by detectors arranged in a rectangular fashion around it. Two distinct frequencies are used to separate each parameter of three Gaussian objects that are either located at the same position or separately from each other. Computer simulation results show that the separate reconstruction method is able to separately reconstruct the three mechanical parameters. The absorption parameter turns out to be a little difficult to reconstruct as compared with the other two parameters.

• 한국초전도학회:학술대회논문집
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• v.14
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• pp.50-50
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• 2004