• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.6
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• pp.41-49
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• 2017

Theoretical modelling and computational results for frequency coordination are presented over mobile base station and fixed wireless systems in urban or sub-urban area. Computational results with key parameters needed for interference analysis are performed and discussed in terms of system characteristics, propagation model, protection ratio, frequency dependent rejection, and discrimination angle with signal-interference plane. Based upon minimum coupling loss methodology, calculated interference powers of victim receiver for assumed system parameters are compared with maximum allowable interference power derived from protection ratio as functions of discrimination angle and distance including height-gain model in urban or sub-urban area. The proposed method is applicable for technical analysis on co-existence or interoperability for the various wireless systems, mandatory for frequency coordination or reallocation process.

• Journal of Korean Tunnelling and Underground Space Association
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• v.15 no.3
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• pp.345-356
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• 2013

Numerical simulation on rock cutting by a TBM disc cutter was carried out using SPH (Smoothed Particle Hydrodynamics) code. AUTODYN3D, a commercial software program based on finite element method, was used in this study. The three-dimensional geometry of a disc cutter and a rock specimen were modeled by Lagrange and SPH code respectively. The numerical simulation was carried out for Hwangdeung granite for 10 different cutting conditions. The results of the numerical simulation, i.e. the relation between cutter force and failure behavior, had a good agreement with those from LCM test. The cutter forces measured in the numerical simulation had 10% deviation from the LCM test results. Moreover, the optimum cutter spacing was almost identical with the experimental results. These results indicate that SPH code can be successfully used had applicability for simulation on rock cutting by a TBM disc cutter. However, further study on Lagrange-SPH coupled modelling would be necessary to reduce the computation time.

• Journal of Advanced Navigation Technology
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• v.22 no.1
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• pp.27-30
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• 2018

In this study, a 40 GHz band pass filter(BPF) employing a hair-pin structure has been designed, fabricated, and characterized for millimeter-wave wireless communication applications. Using the 3 dimensional(3-D) electromagnetic(EM) tool and design equations of the hairpin BPF, the BPF was desgned on the 5 mil-thick Duroid substrate(RT5880) with a relative dielectric constant (${\varepsilon}_r$) of 2.2. The tapping point (t) of the U-shape resonator in the input and output port has been determined using extracted an external Q-factor ($Q_e$). The coupling coefficients between the other resonators are calculated by adjusting the physical dimensions for the desired response of the BPF. The fabricated BPF was characterized using probing method on a probe station. Its measured center frequency(fc) and fractional BW are 41.6 GHz and 7.43 %, respectively. The measured return loss is below -10 dB at the pass band and the insertion loss is 3.87 dB. The fabricated BPF is as small as $9.1{\times}2.8mm^2$.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.89-95
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• 2013

This study investigates a parallel manipulator that can move over two parallel sliders and in which the end-effector of the manipulator can be adjusted arbitrarily. Through the direct and inverse kinematics of the manipulator, position equations are derived. These equations represent the relationship between the positions of the sliders and the position of the end-effector. The Jacobian matrices of the direct and inverse kinematics are obtained by these equations. By using the condition number defined from these matrices, the local performance index of the manipulator is proposed. By using the simulation results of the performance index, we find that the manipulator can smoothen movements in only one quadrant and that the distribution of the maximal performance index is affected by the ratio of the length of links and the orientation of the end-effector.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.23 no.5
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• pp.145-150
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• 2023

Non-uniform optical taper waveguides have been widely used as devices for high-efficiency mode coupling, as they are integrated with single-mode optical fibers or photonic crystal waveguides. In this paper, we present a new platform for chemical sensing and bio-sensing using optical taper waveguides with these characteristics. The principle of operation is based on the coupling efficiency and interference properties of optical directional coupler (DC) and multi-mode interference coupler (MMIC). First, the curvature characteristics of taper sections of DC and MMIC is explained, and the design specifications of optimized taper waveguide to increase waveguide sensitivity is selected. Next, the sensor response to the change in refractive index of sensing analyte is numerically analyzed. Numerical results show that as the length of couplers increases, the effective index per change in refractive index unit (RIU) of analyte increases, and that sensitivity can be tuned using taper DC and MMIC design techniques.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.1
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• pp.1-10
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• 2013

In this paper, a broadband planar monopole antenna for multi-band services is proposed. The physical size of the proposed antenna is miniaturized by folding a rectangular loop. And a resonance point in the 3.9 GHz band is reduced by a coupling phenomenon with the central part of the T-shaped patch and the folded rectangular loop. In addition, the T-shaped patch is inserted to the rectangular shaped monopole antenna due to deriving the broadband frequency characteristics. The frequency characteristic is optimized by adjusting the gap and length of the folded rectangular loops and a transverse diameter of the T-shaped patch. The antenna dimensions including the ground plane are $40{\times}60{\times}1.6mm^3$. It is fabricated on the FR-4 substrate(${\epsilon}_r$=4.4) using a microstrip line of $50{\Omega}$ for impedance matching. In the measured result, the bandwidth corresponding to the VSWR of 2:1 is 162 MHz(815~977 MHz) and 2,530 MHz(1.43~3.96 GHz). For analyzing the human effect by the proposed antenna, 1 g and 10 g averaged SARs are simulated and measured. As the simulated results, 1 g-averaged SAR is 1.044 W/kg, and 10 g-averaged SAR is 0.718 W/kg. This result are satisfied by the SAR guidelines which are 1.6 W/kg(1 g-averaged) and 2.0 W/kg(10 g-averaged).

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2004.05b
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• pp.506-510
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• 2004

A torque transmission system composed of several gears and couplings is flexible. In order to get an exact response of motor, the torsional vibration due to an unexpected change of motor speed must be suppressed. Therefore, it is very important that motor control suppress vibration. Various methods to control it including dual inertia system are proposed. Specially, the method of vibration suppression is that vibration can be suppressed to fee㏈ack the estimated torsion torque via the disturbance observer filter being of normal filter. The suitable Proportional controller and coefficient parameter can be designed using CDM and the torsional vibration also be suppressed, but it has a low degree of adaptability to disturbance. The PID controller can be designed easily, but makes the excessive overshoot and oscillation for system response in the early period. To resolve these problems, simple and practical PID controller with two degree of freedom is proposed recently that it ran improve performance of obeying the reference unconcerned in any disturbance by changing the proportional gain by two degree of freedom parameter. But it has also the defect that parameter a must be changed to obtain the ideal Proportional parameter. On this paper, we design the controller which automatically adjusts parameter u using fuzzy Algorithm to overcome such defects. Also, we compare the proposed method with established one and evaluate them to confirm performance of the designed controller.

• Geophysics and Geophysical Exploration
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• v.24 no.4
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• pp.180-193
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• 2021

The complex resistivity method is an exploration technique that can obtain various characteristic information of underground media by measuring resistivity and phase in the frequency domain, and its utilization has recently increased. In this paper, a three-dimensional inversion algorithm for the CR data was developed to increase the utilization of this method. The Poisson equation, which can be applied when the electromagnetic coupling effect is ignored, was applied to the modeling, and the inversion algorithm was developed by modifying the existing algorithm by adopting comlex variables. In order to increase the stability of the inversion, a technique was introduced to automatically adjust the Lagrangian multiplier according to the ratio of the error vector and the model update vector. Furthermore, to compensate for the loss of data due to noisy phase data, a two-step inversion method that conducts inversion iterations using only resistivity data in the beginning and both of resistivity and phase data in the second half was developed. As a result of the experiment for the synthetic data, stable inversion results were obtained, and the validity to real data was also confirmed by applying the developed 3D inversion algorithm to the analysis of field data acquired near a hydrothermal mine.