• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1347-1352
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• 2001

In this study, the acoustic properties of polyester sound absorbing materials with three different bulk densities were investigated by calculating and measuring the acoustic parameters in terms of characteristic impedance, propagation constant, and absorption coefficient. For the calculations, Delany and Bazley's empirical equation was used together with the experimentally obtained specific flow resistivities under steady flow conditions. For the experimental measurements, the well-known two-thickness method was accessed. The experimentally measured values of characteristic impedance and propagation constant were generally agreed well with the corresponding calculated values. Based on the comparisons between the calculations and measurements, it was found that the magnitude of the absorption coefficient was closely related to the characteristic impedance and the real part of the propagation constant. Especially, the maximum magnitude of the absorption coefficient was depended upon the imaginary part of the propagation constant indicating the phase change of the propagation constant.

• 한국음향학회지
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• 제26권2호
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• pp.80-86
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• 2007

본 연구에서는 압전세라믹과 고분자재료를 사용하여 다이스와 필 방법으로 2-2형 압전복합재료를 제작하고 이것을 이용하며 초음파 센서를 설계하고 제작하여 전기적 및 음향 특성을 조사하였다. 제작된 시편의 공진특성은 유한요소 해석 결과와 임피던스 분석기(HP4194A)를 이용하여 실제로 측정한 결과와 유사하게 나타났다. 2-2형 압전복합재료의 고유음향 임피던스는 PZT의 부피분율이 감소함에 따라 선형적으로 감소하였다. 이것을 이용하여 제작된 초음파 센서의 공진특성 및 전기기계결합계수는 PZT의 부피분율이 0.6일 때 가장 우수하였다. 또한, 이것의 음향특성을 측정한 결과 PZT 부피분율이 0.6일때 진폭, 주파수 대역폭, 울림감쇠 특성 등이 가장 우수하게 나타났으며, 단일 압전세라믹으로 제작된 센서에 비하여 상당히 우수한 감도 특성을 나타내었다.

• 한국정보기술응용학회:학술대회논문집
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• 한국정보기술응용학회 2005년도 6th 2005 International Conference on Computers, Communications and System
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• pp.215-218
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• 2005

We have investigated on the development of 2-2 piezocomposites that have better piezoelectric activity and lower acoustic impedance than those of conventional piezoceramics. In this study, we have investigated the piezoelectric and acoustic properties of 2-2 piezocomposites sensor which were fabricated using dice-and-fill technique for the different volume fraction of PZT. The resonance characteristics measured by an impedance analyzer were similar to the analysis of finite element method. The resonance characteristics and the electromechanical coupling factor were the best when the volume fraction PZT was 0.6. It also showed the highest result from the standpoint of sensitivity, bandwidth and ring-down property and so on at the same condition. The specific characteristics shows that the 2-2 piezocomposites turned out to be superior to the ultrasonic sensor composed by single phase PZT.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.1317-1322
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• 2001

What changes in the eigen values and eigen functions are produced if the boundary surface S is no longer rigid but has a specific acoustic admittance which may vary from point to point on S. In this paper, changes in eigen values and eigen functions are derived by using Kirchhoff-Helmholtz integral equation. And acoustic potential energy, which is representative measure describing the physical quantity in cavity, is defined. Acoustic potential energy can be divided into primary one and secondary one. Primary one is the acoustic potential energy through unchanged eigen functions, and secondary one is through changed eigen functions. Using these two term, we can find the eigenvalue problem, which gives the control performance when the boundary condition is changed.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 추계학술대회 논문집
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• pp.245-248
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• 1997

The distilled water is used for the ultrasonic wave propagating material in the measurements of broadband ultrasonic attenuation (BUA) that is applied in industrial and medical applications, The acoustic impedance of water is significantly changed with its temperature. Therefore, the quantitative evaluation of BUA with temperature and the ultrasonic wave propagating distance is highly needed. In this study, we evaluated the variation of attenuation with change in temperature. To measure the variation of BUA in the low frequency region at the temperatures, 27$^{\circ}C$, 29$^{\circ}C$, and 31$^{\circ}C$, we tested the Plyethylene, Teflon, MC-Nylon, Urethane specimens and analyzed the center frequency, frequency bandwidth, spectral peak amplitude. The results showed that BUA value appeared to be lower with increasing temperature. This may be due to the fact that the frequency feature of ultrasonic wave is affected by not only the specific gravity, acoustic impedence, but material crystalline, porosity, the distance of ultrasonic wave propagation in water.

• 대한조선학회논문집
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• 제60권1호
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• pp.20-30
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• 2023

In this paper, the Energy Flow Finite Element Analysis (EFFEA) was performed to predict the acoustic and vibrational responses of complicated plate structures considering improved Fluid-Structure Interaction (FSI). For this, a new power transfer relationship was derived at the area junction where two different fluids are in contact on both sides of the plate. In order to increase the reliability of EFFEA of complicated plate structures immersed in a high-density fluid, the corrected flexural wavenumber and group velocity considering fluid-loading effect were derived. As the specific acoustic impedance of the fluid in contact with the plate increases, the flexural wavenumber of the plate increases. As a result, the flexural group velocity is reduced, and the spatial damping effect of the flexural energy density is increased. Additionally, for the EFFEA of arbitary-shaped built-up structures, the energy flow finite element formulation for the acoustic tetrahedral element was newly performed. Finally, for validation of the derived theory and developed software, numerical applications of complicated plate structures submerged in seawater or air were successfully performed.

• 한국소음진동공학회논문집
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• 제12권9호
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• pp.709-716
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• 2002

A practical method of predicting the sound absorption coefficient for multiple perforated-plate sound absorbing system was developed using transfer matrix method. The proposed method was validated by comparing the calculated absorption coefficients of a single layer perforated plate with the values measured by the two-microphone impedance tube method for various porosity and spacing of the perforated plate. The developed transfer matrix method was further applied to estimate the multiple layer perforated plates and it is shown that the estimated absorption coefficients agree well with the measured values.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.1244-1249
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• 2002

In this study, the physical characteristics of steel-wire sound absorbing materials with different thickness and bulk density is experimentally obtained in terms of the porosity and specific flow resistivity. Based on the experimental results, the following conclusions can be made. The porosities of steel-wire sound absorbing materials are smaller than those of general absorbing materials, which are inversely proportional to the volume densities. For the porosity measurement with a good accuracy, the dynamic correction based on the system compliance should be involved in porosity measurement. In addition, the flow condition for the precise measurement of the specific flow resistivity of steel-wire sound absorbing materials should be limited in the laminar flow region.

• 전자공학회논문지SC
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• 제38권3호
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• pp.47-54
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• 2001

본 논문에서는 경락의 실체를 객관화하기 위한 방법으로서, 경락과 비경락을 음향 자극하고 인체의 임피던스 변화를 분석하였으며, 인체 에너지에 대한 고전 동양의학 이론인 경락순행통로 학설의 타당성을 입증하기 위하여 경락지하수 학설을 제안하였다. 현대의학의 주장과 같이 경락은 그 존재를 증명할 만한 채널이나 파이프 형태의 해부학적 실체를 가지고 있지 않다. 그러나 생체에너지는 인체 안에서 관상구조없이 지하를 흐르는 지하수 흐름과 유사하게 경락을 따라 흐른다. 이러한 모델의 반응특성을 확인하기 위하여, 인체의 경락을 지하수가 흐르는 관로로 보고 지하수를 탐지하는 산업용 음향탐사기법을 적용하기 위하여, 피부와 청각을 구분하여 음향자극하고 경혈과 대조적인 비경혈에서의 인체 임피던스 반응을 분석하였다. 특히 자극 음향과 12경락과의 주파수 상관성을 추출하기 위하여, 5개의 특정 음으로 자극하고 측정전류의 평균치와 변화율을 처리하였다. 분석결과 전류 변화율은 족궐음간경(宮), 수소음심경(商) 30.6%, 족소음신경(角) 33.1%, 족태음비경(徵) 33.9%, 수태음폐경(羽) 30.7%로 대조점과 구별되는 특성을 가지고 있어서, 경락은 비경락과 구별되는 채널 특성을 나타내고 있으며 5개 경락은 5개의 특정 음과 상관성이 있음을 확인하였다.

• Journal of electromagnetic engineering and science
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• 제12권4호
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• pp.227-233
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• 2012

This paper describes a novel and compact biosensing platform using an RF active system. The proposed sensing system is based on the oscillation frequency deviation due to the biomolecular binding mechanism on a resonator. The impedance variation of the resonator, which is caused by a specific biomolecular interaction results in a corresponding change in the oscillation frequency of the oscillator so that this change is used for the discrimination of the biomolecular binding, along with concentration variation. Also, a Surface Acoustic Wave (SAW) filter is utilized in order to enhance the biosensing performance of our system. Because the oscillator operates at the skirt frequency range of the SAW filter, a small amount of oscillation frequency deviation is transformed into a large variation in the output amplitude. Next, a power detector is used to detect the amplitude variation and convert it to DC voltage. It was also found that the frequency response of the biosensing system changes linearly with three streptavidin concentrations. Therefore, we expect that the proposed RF biosensing system can be applied to bio/medical applications capable of detecting a nano-sized biomolecular interaction.