• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11a
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• pp.497-502
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• 2005

In mobile phones of multimedia era, microspeakers of high quality sound are essential parts to generate human voice in speaker phone and MP3 song player. In this paper, two types of microspeakers, outer permanent magnet (PM) and combined PM type, are analyzed using electromagnetic, mechanical, acoustical and their coupling analysis. For performance comparison, voice coil diameter is chosen as a design parameter to change excitation position and magnet volume for both types. For combined PM type, sound pressure level (SPL) is improved due to increased PM volume compared to outer PM type. Also, with the decreased voice coil diameter for combined PM type, the 1st resonant mode of the diaphragm is more efficiently excited due to concentrative excitation, resulting in lower and broader frequency range. Therefore, it can be said that the combined PM type microspeakers are more advantageous for high performance microspeaker which are essential for multimedia era.

• Journal of Korea Society of Industrial Information Systems
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• v.14 no.1
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• pp.9-16
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• 2009

In this paper, a method is proposed for the analysis of radiowave receiving characteristics of an ammunition with electric detonator. In this method, an ammunition with electric detonator is modelled as a receiving antenna with its gain obtained by computer simulation or measurement. The induced radiowave power is obtained by inserting the gain of the electric detonator in the antenna coupling formula. Radiowave receiving characteristics at very close distances are obtained by Treasuring the transmission coefficient between a half-wave dipole and the electric detonator model. Radiowave receiving characteristics of the electric detonator in a 105mm tank ammunition are obtained using the proposed method and the safety of the 900 MHz RFID reader on the detonator is assessed.

• Geomechanics and Engineering
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• v.32 no.2
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• pp.233-244
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• 2023

With the increasing amount of resources required by the society development, mining operations go deeper, which raises the requirements of studying the effects of temperature on the physical and mechanical properties of coal and adjacent rock. For now, these effects are yet to be fully revealed. In this paper, a mechanical-electromagnetic radiation (EMR) test system was established to understand the mechanical deterioration characteristics of coal by the effect of thermal treatment and its deformation and fracture characteristics under thermo-mechanical coupling conditions. The mechanical properties of high-temperature-treated coal were analyzed and recorded, based on which, reasons of coal mechanical deterioration as well as the damage parameters were obtained. Changes of the EMR time series under unconstrained conditions were further analyzed before characteristics of EMR signals under different damage conditions were obtained. The evolution process of thermal damage and deformation of coal was then analyzed through the frequency spectrum of EMR. In the end, based on the time-frequency variation characteristics of EMR, a method of determining combustion zones within the underground gasification area and combustion zones' stability level was proposed.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.5
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• pp.492-501
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• 2013

In this paper, a multi polarization reconfigurable microstrip antenna that can be used selectively for four polarizations(vertical polarization, horizontal polarization, right hand circular polarization, left hand circular polarization) at the S-band is presented. The proposed antenna consists of four PIN diodes and a microstrip patch with a cross slot and a circular slot and is fed by utiliting electromagnetic coupling between the microstrip patch and the feed line. The proposed antenna has a DC bias network to supply DC voltage to each PIN diode and the polarization can be determined by controlling the ON /OFF states of four PIN diodes. The fabricated antenna has a VSWR below 2 in the vertical polarization(3.17~3.21 GHz), the horizontal polarization(3.16~3.20 GHz), the left hand circular polarization (3.08~3.19 GHz), and the right hand circular polarization(3.10~3.2 GHz) frequency bands. The designed antenna has the cross polarization level higher than 20 dB, a gain over 5 dBi for the linear polarization states, and 3 dB axial ratio bandwidth wider than 50 MHz in the circular polarization states.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.5
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• pp.366-372
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• 2017

In this paper, the analysis of baluns that are inevitably required to design a differential low noise amplifier, The balun converts a single signal input from the antenna into a differential signal, which serves as an input to the differential amplifier. In addition, it protects the circuit from ESD(Electrostatic Discharge) coming through the antenna and helps with input matching. However, in the case of a passive balun used in general, since the AC signal is transmitted through electromagnetic coupling formed between two metal lines, it not only has loss without gain but also has the greatest influence on the total noise figure of the receiving end. Therefore, the design of a balun in a low-noise amplifier is very important, and it is important to design a balun in consideration of line width, line spacing, winding, radius, and layout symmetry that are necessary. In this paper, the factors to be considered for improving the quality factor of balun are summarized, and the tendency of variation of resistance, inductance, and capacitance of the balun according to design element change is analyzed. Based on the analysis results, it is proved that the design of input balun allows the design of low noise, high gain differential amplifier with gain of 24 dB and noise figure of 2.51 dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.12
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• pp.907-914
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• 2018

Wireless charging has been actively researched and popularized owing to the potential convenience of being able to charge electronic devices without wires for users. However, the receiver on the wireless charging pad is not charged when the center of the receiver is misaligned; thus, the center of the receiver must be adjusted well. This misalignment may greatly reduce the convenience of wireless charging. To overcome this limitation of wireless charging, a coil is designed to improve the positional freedom of the receiver. The positional freedom of the Rx coil is improved when the outer diameter of Tx coil is larger than when Rx and Tx coils are almost the same size. When the Tx coil has a larger outer diameter than that of the Rx coil, the efficiency at the center is somewhat lowered, but the efficiency is improved compared to when the center is out of order. In this paper, a double coil structure having an outer and an inner coil is proposed. The double coil structure further improves the efficiency, compared with one coil with the same outer size. The simulation and measurement results demonstrated that the tendency was consistent, and it was verified that the degree of freedom of the Rx coil is improved by adding the inner coil, while the size of the outer coil was the same. The measurement shows that the transmission efficiency of the conventional Tx coil is 37 %, the larger outer diameter coil is 45 %, and double coil is 47 % when the distance of the Tx/Rx coil is 3 mm, the misalignment is 15 mm and current flowing in the Rx coil is 1 A at an operating frequency of 105 to 210 kHz.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.19 no.4
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• pp.477-483
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• 2008

The paper introduces mobile handset multi-band chip antenna to be used on meander line PIFA structure and parasite patch. The proposed antenna uses an FR-4 substrate. The top layer is consist of meander lines PIFA structure to implement GSM900 and is connected with each rad and meander line on the via-hole for maximize space efficiency. The middle layer is designed with the signal line and gap to implement a DCS and PCS bands, the bottom layer which is added to a parasite patch on the ground can be show an adjust of frequency and impedance character by the connection of the radiators of middle layer and coupling. The fabricated antenna with the dimension of $28{\times}6{\times}4\;mm^3$. The ground plane a dimension of $45{\times}90\;mm$, designed by a commercial software CST simulator. The experimental results show that the bandwidth for(VSWR<3) is 90($875{\sim}965$) MHz in GSM900 band operation and 380($1,670{\sim}2,050$) MHz in DCS, PCS band operation. The maximum gains of antenna are 0.25 dBi, 3.65 dBi and 3.3 dBi at resonance frequencies and it has omni-directional pattern practically.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.10
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• pp.1101-1107
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• 2014

A heavy ion accelerator is a device that accelerates heavy ions in the radio frequency (RF) range. The electric field that flows into the RF cavity continuously accelerates heavy ions in accordance with the phase of the input electromagnetic wave. For the purpose, it is necessary to design a coupler shape that can stably transfer the RF wave into the cavity. The RF coupler in a heavy ion accelerator has a large temperature difference between the input port and output port, which radiates the RF waves. It is necessary to consider the heat deflection on the RF coupler that occurs as a result of the rapid temperature gradient from an ultra-low temperature about 0 K to a room temperature about 300 K. The purpose of this study was to improve the system performance through an analysis of the intensity of the output electric field and temperature distribution considering various shapes of the RF coupler, along with an analysis of the durability considering the heat deflection and heat loss.

• Journal of Magnetics
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• v.11 no.4
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• pp.195-207
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• 2006

The recently published and new results on design and fabrication of magnetophotonic crystals of different dimensionality are surveyed. Coupling of polarized light to 3D photonic crystals based on synthetic opals was studied in the case of low dielectric contrast. Transmissivity of opals was demonstrated to strongly depend on the propagation direction of light and its polarization. It was shown that in a vicinity of the frequency of a single Bragg resonance in a 3D photonic crystal the incident linearly polarized light excites inside the crystal the TE- and TM-eigen modes which passing through the crystal is influenced by Brags diffraction of electromagnetic field from different (hkl) sets of crystallographic planes. We also measured the faraday effect of opals immersed in a magneto-optically active liquid. It was shown that the behavior of the faraday rotation spectrum of the system of the opal sample and magneto-optically active liquid directly interrelates with transmittance anisotropy of the opal sample. The photonic band structure, transmittance and Faraday rotation of the light in three-dimensional magnetophotonic crystals of simple cubic and face centered cubic lattices formed from magneto-optically active spheres where studied by the layer Korringa-Kohn-Rostoker method. We found that a photonic band structure is most significantly altered by the magneto-optical activity of spheres for the high-symmetry directions where the degeneracies between TE and TM polarized modes for the corresponding non-magnetic photonic crystals exist. The significant enhancement of the Faraday rotation appears for these directions in the proximity of the band edges, because of the slowing down of the light. New approaches for one-dimensional magnetophotonic crystals fabrication optimized for the magneto-optical Faraday effect enhancement are proposed and realized. One-dimensional magnetophotonic crystals utilizing the second and the third photonic band gaps optimized for the Faraday effect enhancement have been successfully fabricated. Additionally, magnetophotonic crystals consist of a stack of ferrimagnetic Bi-substituted yttrium-iron garnet layers alternated with dielectric silicon oxide layers of the same optical thickness. High refractive index difference provides the strong spatial localization of the electromagnetic field with the wavelength corresponding to the long-wavelength edge of the photonic band gap.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.12
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• pp.933-940
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• 2017

A wireless power transfer system with a negative impedance converter(NIC) was designed and tested. The system was investigated to identify the effects of ferrites and conductors. To improve the power transfer efficiency(PTE), the Q-factor of the transmitter was enhanced by the negative resistance generated by the NIC. The NIC was composed of an Op-Amp and resistors. The negative resistance was obtained with respect to a resistor connected in a feedback loop. The dimension of the Tx coil was $250mm{\times}250mm{\times}0.8mm$. The impedance and Q-factor were $31+j1874{\Omega}$ and 60, respectively. The negative resistance was selected to be $30{\Omega}$, and the Q-factor was increased to 900 by reduction of the transmitter resistance, which was about 15 times higher than that of a conventional transmitter. The measured PTE was greatly improved in comparison to that of a conventional system. These results demonstrate that the PTE is enhanced by using the NIC.