• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.24 no.4
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• pp.466-473
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• 2013

In this paper, a compact planar multi-loop self-resonant coil of high quality factor with a coaxial cross section is proposed for effective wireless charging. The proposed coil has high Q-factor and a resonant frequency of a coil can be easily controlled by adjusting distributed capacitance. For designing the coil, a self-inductance and a distributed capacitance are calculated theoretically. The self-inductance is calculated from the sum of the mutual energies between small circular loops that are made by dividing the cross section of the coil. To verify its properties and calculation results, the self-resonant coils are fabricated by using a coaxial cable with characteristic impedance of $50{\Omega}$. The measured frequencies are very consistent with the calculated ones. In addition, the resonant frequency can be adjusted slightly by the tuning parameter ${\gamma}$. The resonant coils are applied to a tablet PC, the Q-factors of the Tx and Rx resonant coils are 282 and 135, respectively. As a result of measurement when height between the two resonant coils is 4.4 cm, the power transfer efficiency is more than 80 % within a radius of 5 cm.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.7
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• pp.692-700
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• 2012

Vibration intensity has been used to localize vibration source of a vibrating system. Not only that, vibration intensity has also been used for structural diagnostic in identifying crack and mounted stiffeners. To clearly identify the location of vibration source and understand the changes of energy transmission path, clear flow visualization is required. Most of previous works used vectors to indicate the magnitude and direction of emerging vibration energy and transmission paths. However, due to the large surface area of a plate like-structure, clear transmission paths cannot be achieved using vector visualization. This becomes an issue when detail vector flow at all locations of the whole plate surface is required. In this study, streamlines visualization is used to clearly indicate the power flow transmission path at all plate surface. By using streamlines representation, not only clear transmission paths are obtained, but also improves the vector visualization which helps us to understand the changes of the energy flow especially for stiffened plates. In this study, vibration intensity computation is firstly compared to previous work to validate the vibration intensity computation. To clearly show the power flow transmission paths, streamlines representation is shown. This representation overcomes the unclear vector direction especially for stiffened plates. Different pattern of energy transmission path can be observed using streamlines representation for stiffened and unstiffened plate. The complex streamlines pattern can also be observed at high resonance frequencies which is unclear by using vector representation.

• The Journal of the Acoustical Society of Korea
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• v.37 no.5
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• pp.378-386
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• 2018

The present paper suggests the original form of the bell pavilion for the King Song-Dok bell which is one of the precious national treasure of Korea. In order to this, many literatures were reviewed including both historical and acoustical references. As the results, the model of the bell pavilion for the King Song-Dok bell is suggested as follows considering acoustical characteristics of the King Song-Dok bell and the traditional Korean bells ; 1) The bell pavilion has the rumbling puddle beneath the bell on the ground floor for resonance of sound 2) Many lumbers are used for columns and beams rather than boards since natural frequencies of the bell are 64 Hz and 168 Hz so that the sound absorption of the low frequency sound may not be occurred. 3) Only some boards may be used for the area between upper and middle molding of lintel in order to prevent of direct sunlight and sea breeze since this type of structure were used for bell pavilion of the same age. 4) Square form with the odd number of 3 or 5 Kans is adopted for bell pavilion considering the weight and the size of the bell which had been used traditionally 5) Finally, half-hipped structure is used for the roof of the bell pavilion which was the predominant form of the age.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.6977-6984
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• 2015

It is faced with the necessity of multi roll forming process of the ball slide rail which is made by adding the separate manufacturing processes, piercing, bending, trimming, to the roll forming process of a continuous plastic deformation, to improve the quality. However, the vibration and noise of the press machine in this process leads to the quality degradation of slide rail manufactured in this process. In this study, the roll was designed considering the optimal strain rates by the roll forming program with finite element method. And to estimate the static stability of the multi process the Von-Mises stress and deformation on the press was calculated with a structural analysis program. Also, to avoid driving systems in the resonance region their natural frequencies in the 1st and 2nd mode were calculated through the modal analysis. To verify its dynamic stability improvement the magnitudes of noise and vibration in the existing and studied system were compared using a microphone and accelerometers. And the widths and surface roughnesses of the rails which had been produced in the existing and studied process were measured. Therefore, it is known that multi roll forming process is stable in the analytical and experimental study.

• Journal of the Korean Ceramic Society
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• v.45 no.11
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• pp.701-706
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• 2008

High frequency dielectric ceramics have potential for applications in mobile and satellite communications systems at frequencies higher than 10GHz. The Ba$(Zn_{1/3}Ta_{2/3})O_3$ ceramics are known to have a high quality factor, a small temperature coefficient of the resonance frequency and a high dielectric constant. On the other hands, sintering at high temperature for extended time is required to obtain the ordered structure for high quality factor. In this study, the microwave dielectric properties of $ZrO_2$ and NiO-added Ba$(Zn_{1/3}Ta_{2/3})O_3$ ceramics prepared by solid-state reaction have been investigated. Adding $ZrO_2$ and NiO could effectively promote the densification even the case of decreasing the sintering time. At the surface of samples, secondary phase of Ba-Ta compounds was formed possibly due to the evaporation of ZnO, however, the interior of the samples remained as pure Ba$(Zn_{1/3}Ta_{2/3})O_3$. The samples sintered at $1600^{\circ}C$ for 2h exhibited 1:2 ordering of Zn and Ta cations. Excellent microwave dielectric properties of $Q{\cdot}f$(>96,000 GHz) and ${\varepsilon}_r$=30 has been obtained.

• Journal of the Korean Society for Railway
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• v.15 no.5
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• pp.485-497
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• 2012

Recently, with increasing social interests on noise and vibration induced by railway traffic, the application of floating slab track that can efficiently reduce the railway vibration is increasing. In this study, to more accurately understand the dynamic behavior of the floating slab track, a laboratory mock-up test has been performed, and the static and dynamic behaviors at frequency range near the system resonance frequency were explored. Based on the test results, the design of the floating slab track and the structural analysis model used in the design have been verified. The analytic and test results demonstrate that the dominant frequency of the floating slab track occurs at the frequencies between vertical rigid body mode natural frequency and bending mode natural frequency, and the dominant deformation mode is close to the bending mode. This suggests that in the design of the floating slab track, the bending rigidity of the slab and the boundary conditions at slab joints and slab ends should be taken into consideration. Also, the analytic results by the two-dimensional finite element analysis model using Kelvin-Voigt model, such as static and dynamic deflections and force transmissibility, are found in good agreement with the test results, and thus the model used in this study has shown the reliability suitable to be utilized in the design of the floating slab track.

• The Journal of the Acoustical Society of Korea
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• v.39 no.4
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• pp.270-278
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• 2020

In this paper, sound transmission of Micro-Perforated Plates (MPPs) installed in an impedance tube with a circular cross-section is described using an analytic method. Vibration of the plates is expressed in terms of an infinite series of modal functions, where modal function in the radial direction is given by the Bessel function. Under the plane wave assumption, a low frequency approximation is derived, and a formula for the sound transmission coefficient of multi-layered MPPs is presented using the transfer matrix method. The Sound Transmission Losses (STLs) of single and double MPPs are computed using the proposed method and compared with those done by the Finite Element Method (FEM), which shows an excellent agreement. As the perforation increases, the STL is degraded, since the STL becomes dominated by the perforation ratio rather than by vibration of the plate. The STL shows dips at natural frequencies as well as at the mass-spring-mass resonance frequency. The proposed model for the STL prediction in this study can be applied to an arbitrary number of MPPs, where each MPP may or may not have a perforation.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.12
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• pp.1327-1336
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• 2012

In this paper, the dual-faced monopole antenna, which is arranged by numerous rectangular ring patches in sequence for the multi-bands is proposed. The ring type structure of the patch can be increased the bandwidth. Therefore the bandwidth and beam width are improved by using multiple arrayed patches. When the ring type patches are inserted serially, the resonance frequencies are occurred by the current flow from the first ring patch. It is possible because the gap between the patches is very narrow. In addition, if the patches are composed on the same plane as the feed-line, fabrication could be very difficult because the gap between the patches is extremely narrow. The thickness and permittivity of the antenna, moreover, are very important parameters because both sides of the substrate are used. We finally found the optimal thickness and permittivity to generate the coupling effect by simulation. All patches are consisted of 4-steps which the patch size was decreased 85 % by each step. In conclusion, the resonant frequency bands are 1.75~2.6 GHz(850 MHz), 3.24~3.46 GHz(220 MHz), 3.8~4.0 GHz(200 MHz), and 4.4~4.9 GHz(500 MHz).

• International journal of advanced smart convergence
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• v.10 no.4
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• pp.241-255
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• 2021

The human auricle is the first part to receive sound from the outside. In this part, the frequency range of human recognizable form is divided and organized. In this study, we propose modeling by applying a single sound source to the surface of the human auricle. This means that when the sound pressure of a low frequency (low frequency) sound enters the pinna, the impedance felt at the tip of a part of the non-linear surface of the pinna is mainly due to the tensile force at the end of the part of the non-linear surface of the pinna. By expressing the situation of moving at a very small speed, the characteristic impedance of the pinna was confirmed to be negative infinity, and it was also confirmed that the speed at the tip of a part of the non-linear surface of the pinna was 0 in the anti-resonance state. It was found that the wave propagation phenomenon that determines the characteristics of the filter is determined by how large the wavelength, kL, is compared to the length of the tip of a part of the non-straight surface of the pinna. Humans first receive sounds from outside through their ears. The auricle is non-linear and has a curved shape, and it is known that it analyzes frequencies while receiving external sounds. The human ear has an audible frequency range of 20Hz - 20,000Hz. Through the study, we applied the characteristics of the notch filter to hypothesize that the human audible frequency range is separated from the auricle, and applied filter theory to analyze it, and as a result, meaningful results were obtained. The curved part and the inner part of the auricle function as a trumpet, collecting sounds, and at the same time amplifying the weak sound of a specific band. The point was found and the shape of the envelope detected in the auricle was found. Selectivity for selecting sounds coming from the outside is the formula of the pinna that implements the function of Q. The function of distinguishing human-recognizable sound from the pinna from low to high through frequency analysis is performed in the pinna, and the 2-3kHz area, where human hearing threshold is the most sensitive, is also the acoustic impedance of the most recessed area of the pinna. It can be seen that starting from.

• Journal of the Korean Geotechnical Society
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• v.25 no.5
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• pp.75-86
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• 2009

Salt, one of the most common soluble materials in engineering soil, may have an effect on mechanical behaviors of soils under its cementation process. In order to investigate this natural phenomenon, non-soluble material by using glass beads is mixed with salt electrolyte and cemented by using oven to evaporate water. Three different sizes of glass bead particles, 0.26, 0.5, and 1.29 mm, with different salt concentration, 0, 0.1, 0.2, 0.5, 1.0, and 2.0M, are explored by using P- and S-waves, excited by bender elements and piezo disk elemets, respectively. The velocities of the P-wave and S-wave of the particulate medium cemented by salt show three stages with the degree of saturation: 1) S-wave velocities increase while P-wave velocities reduce with degree of saturation changing from 100% to 90%; 2) Both velocities are stable with degree of saturation varying from 90% to 10%; 3) The velocities change enormously when the specimens are nearly dry with degree of saturation from 10% to 0%. Besides, the resonance frequencies of S-wave show similar stages to the S-wave velocities. This study demonstrates meaningful trends of elastic wave characteristics of geo-materials according to the cementation of dissolved salt.