• Journal of Biomedical Engineering Research
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• v.43 no.5
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• pp.319-330
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• 2022

In this study, the optimal driving frequency was derived through finite element analysis (FEA) to optimize the developed piezoelectric ultrasonic medical devices(PUMD) for bone surgery. The core of the PUMD is the piezoelectric ceramic (PZT), which is a vibrator that generates vibration energy. The piezoelectric ceramic shows the maximum current value with respect to the input voltage at the resonance frequency, which generates the maximum mechanical vibration. In the past, various studies have been conducted related to the analysis of PUMD, but most of the research so far has been limited to free vibration analysis. However, in order to derive the accurate resonant frequency, the initial stress generated by bolt tightening in the bolt-clamped Langevin type transducer (BLT) must be considered. In this study, after designing a PUMD, the driving performance according to the bolt tightening value was analyzed through FEA, and this was experimentally verified. First, the resonance mode and frequency response were confirmed through modal and harmonic analysis at 20-40 kHz, which is known as the optimal driving frequency band of PUMD for bone surgery. In addition, the design of the PUMD was confirmed by checking the mechanical behavior of the tip and the piezoelectric ceramic at the resonant frequency. Consequentially, the characteristic evaluation was performed, and it was confirmed that the resonant frequency result derived through the FEA was reasonable. Through this study, we presented a more rational FEA method than before for BLT transducers. We expect that this will shorten the time and cost of developing a PUMD, and will enable the development of more stable and high-quality products.

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.691-697
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• 2022

In this work, a straightforward component design of a direct current (DC) relay equipped in electric vehicles is discussed. The work aims to provide and evaluate effective measures for reducing high-frequency sound from the DC relay carrying electric power. From the operation experiments for the relay, it is observed that noise is caused by the resonance from the forced vibration by the electromagnetic repulsive force originating at the area of electric contacts with a resonance frequency of around 710 Hz ~ 730 Hz. A finite element model for the relay was established to conduct vibration mode analysis, consisting of stationary and movable contacts and a contact spring. Vibration mode analysis indicates that in the resonance frequency, the movable contact with two-point contacts experiences rotational vibration mode. For the proposed relay with a three-point contact, vibration mode analyses give reasonable results of reducing noise at that frequency. Furthermore, for the fabricated relays with the three-point contact, similar results have been obtained. In conclusion, one can see that the proposed measures provide one of the feasible solutions to the reduction of relay noise.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.9
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• pp.838-842
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• 2006

0.03Pb$(Sb_{0.5}Nb_{0.5})O_{3}-0.03Pb(Mn{1/3}Nb{2/3)O_{3}-(0.94-x)PbTiO_{3}-xPbZrO_{3}$ ceramics doped with $CeO_{2}$ were synthesized by conventional bulk ceramic processing technique. Phases analysis, microstructures and piezoelectric properties were investigated as a function of $CeO_{2}$ content (0.03, 0.05, 0.1 0.3, 0.5 and 0.7 wt%). Microstructures and phases information were characterized using a scanning electron microscope (SEM) and an X-ray diffractometer (XRD). Mechanical quality factor ($Q_{m}$) and coupling factor(kp) were obtained from the resonance measurement method. Both $Q_{m}$ and $k_{p}$ were shown to reach to the maximum at 0.1 wt% $CeO_{2}$. In order to evaluate the stability of resonance frequency and effective electromechanical coupling factor ($K_{eff}$) as a function of $CeO_{2}$, the variation of resonance and anti-resonance frequency were also measured using a high voltage frequency response analyzer under various alternating electric fields from 10 V/mm to 80 V/mm. It was shown that the stability of resonance frequency and effective electromechanical coupling factor were increased with increasing the $CeO_{2}$ contents.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2022.11a
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• pp.243-244
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• 2022

In this paper, experiments were conducted on signal amplification of polymer capsules for application to Ground Penetrating Radar so as to enable real-time monitoring of polymer capsules inside concrete using the Morphology Dependent Resonance phenomenon. A TEM CELL and a vector network analyzer were used to analyze the difference in resonance frequency depending on the material of the sphere and the presence or absence of fracture. In order to manufacture a capsule of a size that can be measured using millimeter waves used in GPR, we manufactured a capsule with a 3D printer and analyzed the effects of the presence or absence of coating and the size of the capsule on the resonance frequency. Resonant frequency or signal amplification is more affected by diameter than coating. The capsule showing the highest amplification is the resin-coated 50 mm diameter capsule with a 316-fold increase and the lowest capsule is the uncoated 10 mm diameter capsule with a signal amplification of 11.9 times. These results demonstrate the potential of GPR to measure the position and state of self-healing capsules, which are small-sized polymers, in real time using millimeter waves.

• Wind and Structures
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• v.38 no.1
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• pp.59-74
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• 2024

Large Eddy Simulation (LES) is used to explore the influence of vibration frequency and amplitude on the aerodynamic performance of a rectangular cylinder with an aspect ratio of B/D=5 (B: breadth; D: depth of cylinder) at a Reynolds number of 22,000 near resonance frequency. In smooth flow conditions, the research employs a sequence of three-dimensional simulations under forced vibration with diverse frequency ratios f_e / f_o = 0.8-1.2 (f_e : oscillation frequency; f_o : Strouhal frequency when the rectangular cylinder is stationary ) and oscillation amplitudes A_h/D = 0.05 - 0.3. The individual influences of f_e / f_o and A_h/D on the characteristics of integrated and distributed aerodynamic forces are the focal points of discussion. For the integrated aerodynamic force, particular emphasis is placed on the analysis of the dependence of velocity-proportional component C₁ and displacement-proportional component C₂ of unsteady aerodynamic force on amplitude and frequency ratio. Near the resonance frequency, the dependencies of C₁ and C₂ on amplitude are stronger than that of frequency ratio. For the distributed aerodynamic force, the increase in frequency and amplitude promotes the position of the main vortex core and reattachment to the leading edge in the streamwise direction. In the spanwise direction, vibration enhances the spanwise correlation of aerodynamic force to weaken the three-dimensional effect of the flow field, and a lower frequency ratio and larger amplitude amplify this effect.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.1
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• pp.27-38
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• 2016

The purpose of this study is to investigate the influence of moving mass on the vibration characteristics and the dynamic response of the simply supported beam. The three types of the moving mass(moving load, unsprung mass, and sprung mass) are applied to the vehicle-bridge interaction analysis. The numerical analyses are then conducted to evaluate the effect of the mass, spring and damper properties of the moving mass on natural frequencies and dynamic responses of the simply supported beam. Particularly, in the case of the sprung mass, variations of the natural frequency of simply supported beam are explored depending on the position of the moving mass and the frequency ratio of the moving mass and the beam. Finally the parametric studies on the resonance phenomena are performed with changing mass, spring and damper parameters through the dynamic interaction analyses.

• Nuclear Engineering and Technology
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• v.51 no.4
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• pp.1017-1023
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• 2019

The increase of the alternate current frequency results in increased rotational speed of the electrical motors and connected pumps. The consequence for the reactor coolant pumps is increased flow in primary coolant system. Increase of the current frequency can be initiated by the subsynchronous resonance phenomenon (SSR). This paper analyses the implications of the SSR and consequential increase of the frequency on the nuclear power plant safety. The Simulink $MATLAB^{(R)}$ model of the steam turbine and governor system and RELAP5 computer code of the pressurized water reactor are used in the analysis. The SSR results in fast increase of reactor coolant pumps speed and flow in the primary coolant system. The turbine trip value is reached in short time following SSR. The increase of flow of reactor coolant pumps results in increase of heat removal from reactor core. This results in positive reactivity insertion with reactor power increase of 0.5% before reactor trip is initiated by the turbine trip. The main parameters of the plant did not exceed the values of reactor trip set points. The pressure drop over reactor core is small discarding the possibility of core barrel lift.

• The Journal of the Acoustical Society of Korea
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• v.26 no.3
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• pp.115-122
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• 2007

In this study, the property and the structure of micro-speaker had been firstly shown to be treated as a ducted speaker-system, which was consisted of the unit and the ducted enclosure. With the decrease of total hole area. the resonance frequency of micro-speaker was decreased due to increasing the stiffness or reducing the compliance. The behavior of resonance frequency relative to the total hole area was exactly agreed with that of the square root of compliance. With decreasing the total hole area. the effective chamber volume was increased, but the reference sound pressure level was exponentially reduced in the low and middle frequency range.

• Journal of Biosystems Engineering
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• v.28 no.3
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• pp.253-260
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• 2003

In this study, the feasibility of magnetic resonance techniques for nondestructive internal quality evaluation of Korean red ginseng was examined. Relaxation time constants were measured using various grades of red ginsengs. Solid state magnetic resonance imaging technique was applied to image dried red ginsengs which have low moisture contents (about 13%). A 7 tesla magnetic resonance imaging system operating at a proton resonant frequency of 300 ㎒ was used for acquiring MR images of dried Korean red ginseng. The comparison test of cross cut digital images and magnetic resonance images of heaven grade, good grade with cavity inside, and good grade with white part inside red ginseng suggested the feasibility of the internal quality evaluation of Korean red ginsengs using MRI techniques. A good grade red ginseng included abnormal tissues such as cavities or white parts inside was observed by the signal intensity of MR image based on magnetic resonance properties of proton nucleus. Analysis on an one dimensional profile of acquired MR image of Korean red ginseng showed easy discrimination of normal and abnormal tissues. MR techniques suggested ways to detect internal defects of red ginsengs effectively.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.9
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• pp.122-132
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• 2000

A simplified modeling approach of forced vibration for occupied car seats was demonstrated by using a mathematical model presented in 'Free Vibration of Car seat and Mannequin System' nonlinear and linear equations of motions were rederived for forced vibration and the transfer function was used to calculate the frequency response function. The experimental apparatus were set up and hydraulic shaker was used to obtain the system responses. Through the tests mannequin's head had a lot of problems and the responses with a head and without a head were measured. To explore the effects of linear dampings and friction moments at the joints linear analyses were performed. New sets of linear spring and damping coefficients and torsional dampings at the joints were calculated through parameter study to match up with experimental results. Good agreement between experimental and simulation frequency response estimates were obtained both in terms of locations of resonances and system deflection shapes at resonance indicating that this is a feasible method of modeling seated occupants.