• 대한의용생체공학회:의공학회지
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• 제9권2호
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• pp.165-170
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• 1988

The purpose of this study was to prove the accuracy of impedance cardiography by measuring cardiac outputs of patients simultaneously by thermodilution method, and impedance cardiography developed in our department. The subjects were eight patients with mitral stenosis admitted to the cathete rization laboratory in Severance Hospital. The correlation coefficient was 0.895, which is thought quite high considering the fact that accuracy of cardiac outputs of patients with valvular diseases measured by both methods was known to be low.

• 소음진동
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• 제6권2호
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• pp.225-231
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• 1996

A free field method using two microphones is used for measuring surface impedance and absorption coefficient of the absorbent materials. It is shown that this method can be performed in a large non-anechoic room. Precise values of the surface impedance can be obtained by changing the spaces between the two microphones. Comparison between experimental values of the surface impedance of the glass wool and the mineral wool and Miki's empirical model shows agreement.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 춘계학술대회논문집
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• pp.791-796
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• 2003

Some basic guidelines for changing non-uniform boundary condition in an acoustically small cavity are presented. In this paper, modal summation technique is used to represent inside sound field. From this formulation, corner effect is defined and proposed. The corner in a cavity is good position for changing boundary condition effectively. Impedance circle with same absorption coefficient is defined to find appropriate impedance of absorptive material for better noise control performance.

• 한국환경과학회지
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• 제10권1호
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• pp.9-12
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• 2001

In this study, development of new sound absorbent which is safety, economical and efficient with using recycled materials is tried for substitution of commercial sound absorbent. The sound absorbents, used in this investigation, were made of used paper or filters of cigarette butts. With the variation of the material densities, sound absorptions of materials were measured. The impedance tube method is used for measuring sound absorption coefficient of the new sound absorbent materials. The measured frequency range was 250Hz to 4000Hz in 1/3 octave band. The sound absorption coefficient of the commercial materials and that of the materials synthesized in the our laboratory show almost same value.

• Journal of Biosystems Engineering
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• 제34권6호
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• pp.434-438
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• 2009

This study was conducted to design an cone penetrometer type impedance sensor that can measure soil water content in realtime. The best width between electrical probe was determined by 5 mm. For optimization about realtime application device, linear regression analysis was applied between soil water content and impedance signal. It was concluded that proper combination of excitation frequency, impedance parameter, and model would provide acceptible performance of a soil waler content sensoe. Best model was obatained at a 36.5 MHz with |Z| as a predictor variable, with a coefficient of determination of 0.96 (RMSE=1.35, RPD=4.98).

• 분석과학
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• 제8권4호
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• pp.663-668
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• 1995

Ion transport of a polypyrrole/chloride (PPy/Cl) film and a polypyrrole/poly(styenesulfonate) (PPy/PSS) film as a function of applied dc potential was investigated by employing electrogravimetric impedance technique and electrochemical impedance technique. The cation and anion contribution to the whole charge capacitance and the diffusion coefficients of cation and anion in a PPy/PSS film were calculated by fitting the electrogravimetric impedance data with proposed model circuit. The diffusion coefficients of $Na^+$ in a 1 M $NaClO_4$ solution are over 1 order of magnitude larger than those of $ClO{_4}^-$, and $ClO{_4}^-$ contribution to charge compensation decreases as dc potential lowers. The charge compensation of a PPy/Cl film ir a 1 M CsCl solution is carried out largely by $Cl^-$ at 0.2 V vs. Ag/AgCl and by $Cs^+$ as well as $Cl^-$ at -0.4 V.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 추계학술대회논문집
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• pp.409-414
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• 2000

A new impedance tube method is presented for the measurement of transmission loss of sound isolation sheets. The two-microphone method based on the sound decomposition theory proposed by Seybert and Ross is reviewed in this impedance tube method, which has been used for the determination of absorption coefficient of absorptive materials as well as transmission loss of automotive mufflers. Sound transmission losses for rubber, polyvinyl and asphalt sheets are measured in an impedance tube and reverberation room facility, respectively. By comparing two measurement methods, the reliability of impedance tube method used in this study is validated. From the experimental results, it is shown that the accuracy of sound isolation capability obtained by the impedance tube method depends upon the microphone spacing and the distance of the first microphone from the test sample surface.

• Journal of Korean Vacuum Science & Technology
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• 제7권1호
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• pp.13-17
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• 2003

The influence of structural transition on the resistance and impedance behavior of Ni$_2$MnGa alloy was investigated. The temperature-dependent resistance and impedance were measured in a temperature range of 4 - 350 K and 185 - 300 K, respectively. The dependence of temperature coefficient of resistivity on temperature shows a kink at 220 K, which is related to the structural transition. The change in dominant scattering mechanism results in the observed kink. Significant increases were also observed around the transition temperature for both real and imaginary parts of impedance. It is thought that this phenomenon originates from disappearance of the martensite twin boundaries during the structural transformation.

• 한국음향학회지
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• 제37권4호
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• pp.181-187
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• 2018

본 논문은 원형 단면 임피던스 튜브내에 고정된 미세천공 탄성판의 흡음을 해석적으로 구하는 방법을 다루었다. 판의 진동과 덕트 내부 음장을 모드 함수의 무한 급수의 합으로 전개하였는데 반경방향으로는 Bessel 함수를 포함한다. 평면파 가정하에서 저주파수 대역의 근사식을 판의 처음 몇 개의 모드만 고려하여 흡음율을 유도하였으며 등가 임피던스를 갖는 단일 표면의 형태로 제시하였다. 본 논문에서 제안한 공식과 FEM(Finite Element Method)을 이용한 결과는 잘 일치 하였는데 탄성의 효과는 판의 고유진동수에 해당하는 골 또는 피크의 형태로 나타난다. 천공율이 매우 작으면 진동의 영향이 지배적이나 천공율이 어느 한계이상 되면 박판의 탄성거동은 매우 작게 나타나고 강체 MPP(Micro-Perforated Plate)의 흡음 특성이 지배적이 된다.

• ETRI Journal
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• 제38권5호
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• pp.962-971
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• 2016

A wireless power transfer (WPT) system is generally designed with the optimum source and load impedance in order to achieve the maximum power transfer efficiency (PTE) at a specific coupling coefficient. Empirically or intuitively, however, it is well known that a high PTE can be attained by adjusting either the source or load impedance. In this paper, we estimate the maximum achievable PTE of WPT systems with the given load impedance, and propose the condition of source impedance for the maximum PTE. This condition can be reciprocally applied to the load impedance of a WPT system with the given source impedance. First, we review the transducer power gain of a two-port network as the PTE of the WPT system. Next, we derive two candidate conditions, the critical coupling and the optimum conditions, from the transducer power gain. Finally, we compare the two conditions carefully, and the results therefore indicate that the optimum condition is more suitable for a highly efficient WPT system with a given load impedance.