• 소음진동
• /
• 제6권5호
• /
• pp.635-644
• /
• 1996

In this paper, Allard's modelling method which employs the method of acoustic transfer matrix(ATM) is applied to yield more precise results in the analysis of porous sound absorbing material. The method of ATM, based on Biot's theory, is known to play an important role in the estimation of the sound absorption when a sound projects onto the material. In the case of a single layered porous sound absorbing material, the surface impedance and the absorption coefficient by using the method of ATM are estimated. With the variation of the material properties, sound absorption characteristics and analyzed. Transmission Loss in a combination of the porous sound absorbing material with a thin plate is predicted.

• 한국음향학회지
• /
• 제18권4호
• /
• pp.65-70
• /
• 1999

고유모드분포가 다른 정형(직방체), 부정형 잔향실을 해석대상으로 선정, 각각의 모델에 대한 음압의 공간편차에 대하여 유한요소법을 이용한 수치계산으로 검토하였다. 그 결과, 잔향실 내표면의 임피던스가 무한대인 경우는 주파수대역에 따른 편차가 부정형 잔향실이 작게 나타났다. 반면, 임피던스가 유한한 경우는 직방체 잔향실도 2변 혹은 3변의 치수가 같거나 정수배인 것을 제외하면 편차가 부정형 잔향실과 같은 정도라는 것이 확인되었다.

• 전기화학회지
• /
• 제17권3호
• /
• pp.179-186
• /
• 2014

Methanol electro oxidation on the surface of carbon paste modified by $NiCl_2/6H_2O$ was studied in 1M NaOH by potentiostatic and potentiodynamic methods. Ni/C catalyst by the concentration of 5% Ni showed about twice higher electro catalytic activity than Ni metal. The amount of monolayer's on the surface of electrode is almost one order higher for Ni/C than Ni electrode. The kinetic parameters and the diffusion coefficient of methanol were derived from chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) measurements.

• Corrosion Science and Technology
• /
• 제15권2호
• /
• pp.43-53
• /
• 2016

In this study, electrochemical impedance spectroscopy (EIS) was used to examine the changes in the electrochemical properties of biodegradable pure magnesium implanted into Sprague-Dawley rats for three days. The in vivo test results were compared with those of the in vitro tests carried out in Hank's, dilute saline and simulated body fluid (SBF) solutions. The in vitro corrosion rates were 20~1700 fold higher, as compared to the in vivo corrosion rates. This discrepancy is caused by biomolecule adsorption on the surface, which prevents the transport of water into the magnesium surface on in vivo testing. Among the in vitro experimental conditions, the corrosion rate in SBF solution had the least difference from the in vivo implanted specimen.

• Structural Engineering and Mechanics
• /
• 제54권4호
• /
• pp.623-648
• /
• 2015

A numerical approach is presented for the analysis of the forced vibration of a rigid surface foundation with arbitrary shape. In the analysis, the foundation is discretized into a number of sub squaree-lements. The dynamic response within each sub-element is described by the Green's function, which is obtained by the Fourier-Bessel transform and Precise Integration Method (PIM). Incorporating the displacement boundary condition and force equilibrium of the foundation, it obtains a system of linear algebraic equation in terms of the contact forces within each sub-element. Solving the equation leads to the desired dynamic impedance functions of the foundation. Numerical results are obtained for foundation not only with simple geometrical configurations, such as rectangular and circular foundation, but also the case of irregularly shaped foundation. Several comparisons between the proposed approach and other methods are made. Very good agreement is reached. Also, parametric studies are carried out on the dynamic response of foundation. Addressed in this study are the effects of Poisson's ratio, material damping and contact condition of soil-foundation interface. Several conclusions are drawn the significance of the factors.

• 한국표면공학회지
• /
• 제32권3호
• /
• pp.224-234
• /
• 1999

An attempt was made to characterize the relationship between pretreatment processes, electrolysis conditions and behaviors of the plated gold layer. In order to investigate the effect of pretreatment processes on plating, rest potential measurements of various pretreated stainless steels and a.c.-impedance spectroscopy tests were carried out in the strike plating solution. Characteristics of plated gold layers and adhesions between plated gold layers and stainless steel substrates were examined by scratching tests and micro-Vickers hardness tests. The result shows that the strike plating enhanced the adhesion of interface, the cathodic electro-activation pretreatment process improving both corrosion resistance and adhesion strength. The preferred orientations of plated gold layers were examined by the X-ray diffraction technique. As the current density increases, [111] preferred orientation of plated gold layers was found to become well developed.

• Smart Structures and Systems
• /
• 제5권6호
• /
• pp.633-644
• /
• 2009

A simple method has been developed to detect the bonding condition of active fiber composites (AFC) adhered to the surface of a host structure. Large deformation actuating capability is one of important features of AFC. Edge delamination in adhesive layer due to large interfacial shear stress at the free edge is typically resulted from axial strain mismatch between bonded materials. AFC patch possesses very good flexibility and toughness. When an AFC patch is partially delaminated from host structure, there remains sensing capability in the debonded part. The debonding size can be determined through axial resonance measured by the interdigitated electrodes symmetrically aligned on opposite surfaces of the patch. The electrical impedance and modal response of the AFC patch in part adhered to an aluminum plate were investigated in a broad frequency range. Debonding ratio of the AFC patch is in inverse proportion to the resonant frequency of the fundamental mode. Feasibility of in-situ detecting the progressive delamination between AFC patch and host plate is demonstrated.

• Transactions on Control, Automation and Systems Engineering
• /
• 제4권1호
• /
• pp.43-48
• /
• 2002

We show that humans execute the postural control ingeniously by regulating the impedance properties of the musculo-skeletal system as the motor command against the alteration of the environment. Adjusting muscle activity can control the impedance properties of the musculo-skeletal system. To quantify the changes in human arm viscoelasticity on the vertical plane during interaction with the environment, we asked our subject to hold an object. By utilizing surface electromyographic(EMG) studies, we determined a relationship between the perturbation and a time-varying muscle co-activation. Our study showed when the subject lifts the object by himself the muscle stiffness increases while the torque remains the same just before the lift-off. These results suggest that the central nervous system(CNS) simultaneously controls not only the equilibrium point(EP) and the torque, but also the muscle stiffness as themotor command in posture control during the contact task.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2004년도 하계학술대회 논문집 C
• /
• pp.1933-1935
• /
• 2004

본 연구에서는 변압기형 플라즈마 전류 모델을 기초로 한 평판형 유도 결합 플라즈마 장치에 대한 회로를 분석하여 임피던스 매칭 특성을 조사하였다. 장치 임피던스는 collisional surface impedance를 기반으로 계산된 플라즈마 임피던스와 안테나 임피던스로 결정된다. 매칭 network에 사용된 회로는 Altcmatc-typc의 회로이고, 매칭 소자인 $C_T$와 $C_L$은 임피던스 매칭 조건을 이용하여 계산하였다. 완전 매칭의 경우에는 $C_T$와 $C_L$을 플라즈마 변수들의 함수로 표현하여 의존성을 분석하고, 불완전 매칭의 경우에는 반사파에 대한 반사계수, 반사율을 계산하였다.

• 센서학회지
• /
• 제26권2호
• /
• pp.73-78
• /
• 2017

A tetrode is one of the neural electrodes, and it is widely used to record neural signals in the brain of a freely moving animal. The impedance of a neural electrode is an important parameter because it determines the signal-to-noise ratio of the recorded neural signals. Here, we developed a modification technique using carbon nanotube-polypyrrole composite nanostructures to decrease the impedances of tetrodes. The synthesis of the carbon nanotube and polypyrrole nanostructures was performed in two steps. In the first step, randomly dispersed carbon nanotubes and pyrrole monomers were gathered and aligned on the tetrode electrode. Next, they were electro-polymerized on the electrode surface. As the applied time (step-1 and step-2) and the offset voltage increased, the impedances of the tetrodes decreased. The modification technique is, therefore, an important and useful of lowering the impedances of tetrodes.