• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.6
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• pp.628-633
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• 2009

The helmholtz resonator with the perforated neck has demerits that the absorption performance is not so outstanding in an anti-resonance frequency and high frequency bandwidth. In order to overcome these problems, in the paper, a resonator combined with porous material is proposed. The absorption performances of resonators are measured by two-microphone method and estimated by transfer matrix method. The experimentally measured values of normal absorption coefficients agree well with the corresponding values from the transfer matrix method. Because of the porous material, it is shown that the absorption performance have been significantly improved in the anti-resonance frequency and high frequency bandwidth.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.467-472
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• 2007

A modern MEMS resonator is a micro-scale structure operated over a high frequency range. In order to predict its resonant behavior in a design process, High-frequency response analysis (Hi-FRA) is demanded. Algebraic substructuring (AS) is known as a fast numerical technique to construct an eigenspace for FR and frequency sweep (FS) algorithm efficiently solves the frequency response system projected on the eigenspace. However, the existing FS algorithm using AS is developed for low-FRA, say over the range 1Hz-2KHz. In this work, we extend the FS algorithm using AS for FRA over an arbitrary frequency range. Therefore, it can be efficiently applied to systems operated at a high frequency, say over the range 230MHz-250MHz. The success of the proposed method is demonstrated by Hi-FRA of a checkerboard resonator.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.7
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• pp.1225-1232
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• 2000

In this paper, a new coupled resonator which expands free spectral ranges (FSR) of the W. G. mode resonators is presented. The proposed coupled resonator consists of two dielectric disks. The resonance frequency of the coupled resonator is equivalent to the frequency, which satisfies the individual resonance conditions of each disk at the same time. As the results, the FSR is expanded. The coupled resonator proposed in this paper at K-Band is fabricated by using dielectric disks and the dielectric straight waveguides. The validity of proposed coupled resonator was verified through experiments.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.2
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• pp.280-283
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• 2015

This paper demonstrates a new radio frequency (RF) resonator at 3 T magnetic resonance imaging (MRI) system. An approach based on a split ring resonator (SRR) having effective metamaterial properties is investigated. Electromagnetic simulation results are compared for RF resonators and discussed in detail at 3 T. A new RF resonator has approximately 10% higher magnetic fields at the center of the human phantom than the previous RF resonator.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.75-80
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• 2012

Helmholtz resonator is widely used acoustic instrument which has high absorption characteristics at its resonance frequency. Particularly it maintains good performance even in the low frequency region that is difficult to control by general porous absorptive materials. However, under severely high sound pressure level, the absorption characteristics are changed by increase of resistance due to nonlinear behavior of neck impedance. Because of this nonlinear behavior, it is difficult to obtain the expected absorption performance under high sound pressure environment. Thus, in order to prevent excessive rise of resistance, the resonator with neck having cross section dimension decrease away from the entry of the resonator cavity could be suggested. This paper introduces the experiment method and results about nonlinear characteristics of Helmholtz resonator with tapered neck and proposes the approximate nonlinear impedance model.

• Journal of Institute of Control, Robotics and Systems
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• v.15 no.3
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• pp.258-264
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• 2009

This paper presents two control algorithms for the frequency and amplitude of the resonator of a micro sensor. One algorithm excites the resonator at its a priori unknown resonant frequency, and the other algorithm alters the resonator dynamics to place the resonant frequency at a fixed frequency, chosen by the designer. Both algorithms maintain a specified amplitude of oscillations. The control system behavior is analyzed using an averaging method, and a quantitative criterion is provided for the selecting the control gain to achieve stability. Tracking and estimation accuracy of the natural frequency under the presence of measurement noise is also analyzed. The proposed control algorithms are applied to the MEMS dual-mass gyroscope without mechanical connecting beam between two proof-masses. Simulation results show the effectiveness of the proposed control algorithms which guarantee the proof-masses of the gyroscope to move in opposite directions with the same resonant frequency and oscillation amplitude.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.8
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• pp.756-762
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• 2012

A method of the low-frequency noise reduction in an enclosure by using an array of Helmholtz resonator is presented. An integral form of equation, which represents the acoustical coupling between the internal sound field and the resonator array, is formulated so that the boundary element method can be applied to solve the coupling problem. It is shown that the resonator array on the surface of the enclosure can be regarded as impedance patches on the boundary element. Experiments on a simple enclosure acoustically coupled with an array of resonators are conducted to verify the method. The predicted noise reduction by the boundary element method shows good agreement with the measured one. The effects of the resistance of resonators as well as the number of resonators on the noise reduction are demonstrated. As a practical example, the presented method is applied to the payload fairing of a space launcher with resonator arrays. It is demonstrated that the resistance of resonators affects significantly the required number of resonators to achieve a desired noise reduction.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.4
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• pp.357-364
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• 2011

In this study, ring-shaped acoustic resonators were proposed to be installed in a silencer to increase the acoustic performance of silencer in the low-frequency range. Evaluation of noise reduction performance of acoustic resonator arrays was carried out by measuring the random-incidence absorption coefficient. It was found that the absorption coefficient of resonator array was measured up to 1 at 125 Hz of 1/3-octave band center frequency. Insertion losses of silencers with ring-shaped acoustic resonator arrays were measured based on ISO 7235. The results were shown that the ring-shaped resonator could increase the insertion loss up to 13 dB without flow, whereas 7 dB when flow speed reached 15 m/s. As increasing the flow speed above 15 m/s, the effect of acoustic resonator decreased due to the effect of nonlinear air damping of the resonator. It was also found that the increment of pressure drop by the presence of resonator arrays was about 9 % at flow speed of 25 m/s.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.1
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• pp.169-174
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• 2011

For a double-walled carbon nanotube resonator with a short outer nanotube, the free edge of the short outer wall plays an important role in the vibration of the long inner nanotube. For a double-walled carbon nanotube resonator with a short inner nanotube, the short inner nanotube can be considered as a flexible core, thus, the fundamental frequency is influenced by its length. In this paper, we analysis frequency variation in ultrahigh frequency nanomechanical resonators based on double-walled carbon nanotubes with different wall length. This results will widely apply to the realization of frequency devices controlling the length of the inner or outer nanotube.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.51-56
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• 2002

High pressure hose having tuning cables, called 'Resonator hose' is frequently used to attenuate pressure ripple generated by the pump for reducing the vehicle interior noise. A number of studies have been conducted on the resonator hose and its analytical models. However, there are few studies which deal with the influence of resonator hose on vehicle interior noise because the most of studies focused on transmission loss of the resonator hose. This paper presents NVH test results of power steering system and frequency analysis results. In the frequency analysis, both the relations between vibration, pressure ripple and vehicle interior noise and also the design parameters of high pressure hose influencing on vehicle interior noise were discussed. The test was done for various high pressure hose specimens in full turn condition.