• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.24 no.1
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• pp.21-27
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• 2014

In this paper, an approximate formula for radiation efficiency of the plate surround by an infinite rigid baffle is studied. The plate is simply supported and one side is in contact with air, while other side with water. By assuming an infinite plate, the fluid loading effect is derived in terms of an effective mass. Based on the observation that the fluid loading effect decreases as frequency increases, the radiation efficiency formula at high frequency, which was originally derived for a plate vibrating in the air, is modified as the approximate formula for a submerged plate. The fluid loading effect is taken into account in the wavenumber of the plate. Comparisons of the approximate formula with the numerical results shows that they match well except the mid-frequency range in which numerical results show many oscillations. In numerically solving the fully coupled equations of motion, fourfold integrals of the impedance coefficients are reduced to single nonsingular integrals, which results in substantial reduction in computing time.

• Journal of the Korean Institute of Telematics and Electronics
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• v.4 no.4
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• pp.22-27
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• 1967

The general mutual impedance expression for two staggered parallel, centerfed, linear antennas of unequal length and confirmed that the general expression being applied to a special case, reduced to the equation presented by other. Furthermore, calculation is done for a special cast, and it is confirmed that the general mutual impedance expression is applicable to the calculation of radiative curreut distribution on antenna system given above.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.395-400
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• 2002

Epoxy coating and sealing used in nuclear plants for the protection of radiation degrades with aging and hazardous atmosphere. In order to evaluate the degradation of the epoxy, dependence of the acoustic impedance on the change of mechanical properties has been used. Unlike metals, the surface of the epoxy coating on a concrete liner is so wavy that the acoustic impedance is difficult to measure by using the reflectivity of the ultrasound on the interface surface because of the irregular reflection and propagation from the epoxy surface. SA(simulated annealing) algorithm is applied to calculate the acoustic impedance using a reflection wave from the rough epoxy surface. The surface waviness and acoustic impedance are taken into account and determined by SA method to evaluate the state of degradation quantitatively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2004.11a
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• pp.155-159
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• 2004

In this paper, it was analyzed the characteristics of electrical and acoustical variations for loudspeaker due to fabrication processes. First, mass of each components of loudspeaker was measured by electric precision scale and performed statistical analysis. Second. Thiele-Small parameters of sample loudspeakers produced by unskilled students were identified by known mass parameter identification method using electrical impedance method and investigated on the variations of each parameter. Electrical impedance tests and acoustic frequency responses were measured on sample loudspeakers and variations were examined to grasp relationship between components variation and fabrication processes. Main factors to effect the changes of electrical impedance were concluded by fabrication processes errors not by components of loudspeaker.

• Journal of the Korean Institute of Telematics and Electronics
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• v.19 no.6
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• pp.80-83
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• 1982

A quarter-wavelength open circuited microstripline slot array is realized at X-band froquency. The optimal feeding point is experimentally determined. The input impedance of the slot array for various frequencies and its radiation pattern are measured. The bandwidth of the slot array is increased by using the 4$\times$4 elements which are slightly different in length and feeding network which is suggested in this papers.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.9
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• pp.204-209
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• 2001

The finite element model for automotive muffler analysis is improved by modifying the boundary condition of outlet and the mesh of finite element model. The model minimizes the difference between transmission loss from analysis and that from experiment. Four different boundary conditions and the four types of finite element model are tested to find out the best one of those. From the case study it is verified that the bevel of transmission loss can be changed by the variation of radiation impedance value. Also the resonance or anti-resonance frequencies of transmission loss can be shifted by the variation of finite element mesh. An improved finite element model of muffler is proposed in consideration with the accuracy and the computing time of analysis.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.4
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• pp.636-644
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• 1999

Experimental and simulation results are presented on the Aperture-Coupled microstrip patch antennal with U-shaped slot. Experiment and simulation results include impedance bandwidth, copolar and crosspolar-pattern characteristics and gain measurements. Simulation results show the advantages of U-slotted patch antenna comparing with the normal patch antenna. More than 35% impedance bandwidth is obtained with reasonably restricted cross-polar radiation pattern. The U-slotted radiation element fed by aperture-coupling method can be more easily extended to array structure, compared with that fed by coaxial cable.

• Journal of electromagnetic engineering and science
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• v.7 no.3
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• pp.116-121
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• 2007

Novel design of a wideband monopole antenna for DVB-H service is presented. The proposed antenna is designed based on a monopole antenna. It consists of folded monopole and parallel parasitic element. The folded segment of the folded monopole makes the antenna shorter. The length of the parasitic element obtains additional resonance frequencies. The gap distance between the folded monopole and the parasitic element is a key parameter to control impedance matching for wideband operation. The antenna has wide band performance, good impedance and radiation characteristics from 470 MHz to 870 MHz. The measured return loss for operating frequencies over DVB-H band is better than 10 dB. Good radiation patterns are also obtained. The measured results are compared with calculated results using Ansoft HFSS(High Frequency Structure Simulator).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11b
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• pp.97-100
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• 2005

Precise prediction of resonance frequency has been the subject of numerous papers related to Helmholtz resonator design because of its high performance at the frequency. The resonance frequency is dependent upon not only the internal dimensions of resonator but also the external boundary conditions such as the existence of other resonators in Helmholtz resonator array panel. However, the latter effect, which changes the external end correction of resonator, has not been well studied. We propose a formula to calculate the radiation impedance (or external end correction) of Helmhoitz resonator array panel. Any distance between adjacent resonators and any angle of Incidence can be allowed in the method. Numerical examples show how and how much the distance affects the resonance frequency of the panel. It is also found that the maximum absorption of the panel varies with the resonator arrangement.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.6
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• pp.1587-1595
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• 1996

We obtained the predicted and measured results for the reflection coefficient and radiation pattern of Ka-band (20- GHz) corrugated horn, which is usually used for feeder of reflector antenna for satellite communication, using suface impedance condition. In order to predict the reture losses of corrugated horn, we analyzed propagation constant of hybrid mode in the corrugated waveguide and then obtained the total reflection coefficient using the circuti theory of multi-step transformer. We also got the radiation pattern of corrugated horn with small flare angle, considering the phase deviation and integrate transverse field on aperture. A test model of corrugated horn antenna for Ka-band designed using theory and program displayed performance and the results agree with the theoretical prediction.