• Title/Summary/Keyword: High Impedance Surface

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Analysis of High Efficiency Small Antenna with Matching Circuit (정합회로 장착 고효율 소형안테나의 해석)

  • Hwang, Jae-Ho
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.16 no.7
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    • pp.1358-1363
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    • 2012
  • This paper deals with the analysis of high efficiency small antenna like superconductor antenna. The superconductor antenna is useful to low frequency range because surface resistance of superconductor increased with the rate of square of frequency. Thus, the used antenna increases in size. For such a reason, the role of the matching circuit is very important in small antenna. In this paper, low loss antenna included the optimal structure of matching circuit is analyzed by using quasi-static approximation. To verify the results of this paper, input impedance and radiation characteristics of this antenna have been evaluated.

A Study on the Acoustic Characteristics and Absorption Performance Improvement Method of Double Layered Sound Absorption System Using High Density Polyester Absorbing Materials (고밀도 폴리에스터 흡음재를 이용한 이중층 흡음시스템의 음향특성 및 흡음성능 향상 방안에 관한 연구)

  • Yoon, Je-Won;Jang, Kang-Seok;Cho, Yong-Thung
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.26 no.3
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    • pp.331-339
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    • 2016
  • To improve the acoustic performance of sound absorbing materials, the thickness of the material should be increased or the sound absorbing material having an irregular surface shape should be used. In this study, the acoustic characteristics and methods to improve the acoustic performance of a sound absorbing system equipped with double layered polyester sound absorbing materials were investigated. The numerical model was set up and the results obtained from the model were compared with the actual measurement data. And, strategies to improve the acoustic performance of sound absorbing systems with double layered sound absorbing materials made of polyester with different configuration were shown. So, this study is expected to be usefully used at sites that require high acoustic absorption performance with minimal installation thickness to reduce sounds reflection in narrow spaces such as interior of subway tunnels or in noise barriers installed adjacent to rails.

A study on the Frequency Analysis Function of the Auricle Using A Notch Filter

  • Park, Dong-Cheol
    • International journal of advanced smart convergence
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    • v.10 no.4
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    • pp.241-255
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    • 2021
  • The human auricle is the first part to receive sound from the outside. In this part, the frequency range of human recognizable form is divided and organized. In this study, we propose modeling by applying a single sound source to the surface of the human auricle. This means that when the sound pressure of a low frequency (low frequency) sound enters the pinna, the impedance felt at the tip of a part of the non-linear surface of the pinna is mainly due to the tensile force at the end of the part of the non-linear surface of the pinna. By expressing the situation of moving at a very small speed, the characteristic impedance of the pinna was confirmed to be negative infinity, and it was also confirmed that the speed at the tip of a part of the non-linear surface of the pinna was 0 in the anti-resonance state. It was found that the wave propagation phenomenon that determines the characteristics of the filter is determined by how large the wavelength, kL, is compared to the length of the tip of a part of the non-straight surface of the pinna. Humans first receive sounds from outside through their ears. The auricle is non-linear and has a curved shape, and it is known that it analyzes frequencies while receiving external sounds. The human ear has an audible frequency range of 20Hz - 20,000Hz. Through the study, we applied the characteristics of the notch filter to hypothesize that the human audible frequency range is separated from the auricle, and applied filter theory to analyze it, and as a result, meaningful results were obtained. The curved part and the inner part of the auricle function as a trumpet, collecting sounds, and at the same time amplifying the weak sound of a specific band. The point was found and the shape of the envelope detected in the auricle was found. Selectivity for selecting sounds coming from the outside is the formula of the pinna that implements the function of Q. The function of distinguishing human-recognizable sound from the pinna from low to high through frequency analysis is performed in the pinna, and the 2-3kHz area, where human hearing threshold is the most sensitive, is also the acoustic impedance of the most recessed area of the pinna. It can be seen that starting from.

Fabrication of 1-3 Piezo-composites with a "Dice & Fill" Method and Characterization of Their Piezoelectric Properties as a Function of Lateral Spatial Scale ("Dice와 fill" 방식을 이용한 1-3 압전복합재의 제조와 횡방향 단위 크기에 따른 압전특성 평가)

  • Kim, Young-Deog;Kim, Kwang-Il;Jeong, Woo-Cheol;Kim, Heung-Rak;Kim, Dong-Su
    • Journal of the Korean Society for Nondestructive Testing
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    • v.22 no.4
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    • pp.354-360
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    • 2002
  • The piezoelectric composites had many advantages in comparison with conventional piezoelectric ceramics and piezopolymers for ultrasonic transducers used in NDT and in medical ultrasionic imaging. The electromechanical coupling coefficient should be high and the acoustic impedance should be low in these applications. However, the cross-coupling with spurious oscillations caused by laterally running plate waves exhibited complex motions in the surface of piezoelectric composites with coarse lateral spatial scale. The thickness mode electromechanical coupling coefficient of 1-3type of piezoelectric compoistes were 0.36 to 0.64, and the acoustic impedance of them were 9.8 to 22.7 MRayl. The lateral resonance frequency of 1-3 type piezoelectric composites shifted to high frequency region with decreasing lateral spatial scale.

Corrosion Behavior of High Pressure Die Cast Al-Ni and Al-Ni-Ca Alloys in 3.5% NaCl Solution

  • Arthanari, Srinivasan;Jang, Jae Cheol;Shin, Kwang Seon
    • Corrosion Science and Technology
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    • v.16 no.3
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    • pp.100-108
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    • 2017
  • In this investigation corrosion behavior of newly developed high-pressure die cast Al-Ni (N15) and Al-Ni-Ca (NX1503) alloys was studied in 3.5% NaCl solution. The electrochemical corrosion behavior was evaluated using open circuit potential (OCP) measurement, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. Potentiodynamic polarization results validated that NX1503 alloy exhibited lower corrosion current density ($i_{corr}$) value ($5.969{\mu}A/cm^2$) compared to N15 ($7.387{\mu}A/cm^2$). EIS-Bode plots revealed a higher impedance (${\mid}Z{\mid}$) value and maximum phase angle value for NX1503 than N15 alloy. Equivalent circuit curve fitting analysis revealed that surface layer ($R_1$) and charge transfer resistance ($R_{ct}$) values of NX1503 alloy was higher compared to N15 alloy. Immersion corrosion studies were also conducted for alloys using fishing line specimen arrangement to simultaneously measure corrosion rates from weight loss ($P_W$) and hydrogen volume ($P_H$) after 72 hours and NX1503 alloy had lower corrosion rate compared to N15 alloy. The addition of Ca to N15 alloy significantly reduced the Al3Ni intermetallic phase and further grain refinement may be attributed for reduction in the corrosion rate.

Magnetic Saliency Estimation of SMPM Motor for Precise Torque Control using State-Filter in Flux-Weakening Operation (정밀 토크 제어를 위한 SMPM 전동기의 약자속 영역에서 자기 돌극성 추정)

  • Jang, Ju-Young;Choi, Chan-Hee;Seok, Jul-Ki
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.23 no.8
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    • pp.67-73
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    • 2009
  • The magnetic saliency effect in surface-mounted permanent-magnet (SMPM) motors on the torque control at high speeds is first presented and analyzed in this paper. The d- and q- axes impedance are measured by proposed State-Filter. Measurement of the d- and q- axes impedance difference is performed to prove the existence of the magnetic saliency. Then, the saliency effects on the torque control performance in the flux weakening region are discussed. Based on the developed motor modeling with the reluctance torque, the proposed control adjusts the d- and q-axis current toward the operating point to track the commanded torque. The feasibility of the presented idea is verified by experimental results on a commercial 600[W] SMPM motor.

Microwave Absorbing Properties of Fiber Reinforced Composites with Sandwitch Structure (샌드위치 구조형 섬유강화 복합재료의 전파흡수특성)

  • Kim, Sang-Yeong;Kim, Sang-Su
    • Korean Journal of Materials Research
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    • v.12 no.6
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    • pp.442-446
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    • 2002
  • Design of microwave absorbers using high frequency properties of fiber reinforced composites are investigated. Two kinds of composite materials (glass and carbon) are used and their complex permittivity and permeability are measured by transmission/reflection technique using network analyzer. Low dielectric constant and nearly zero dielectric loss are determined in glass fiber composite. However, carbon fiber composites show the high dielectric constant and large conduction loss which is increased with anisotropy of fiber arrangement. It is, therefore, proposed that the glass and carbon fiber composites can be used as the impedance transformer (surface layer) and microwave reflector, respectively. By inserting the foam core or honeycomb core (which can be treated as an air layer) between glass and carbon fiber composites, microwave absorption above 10 dB (90% absorbance) in 4-12 GHz can be obtained. The proposed fiber composites laminates with sandwitch structure have high potential as lightweight and high strength microwave absorbers.

High-Frequency Bistatic Scattering from a Corrugated Sediment Surface

  • Cho, Hong-Sang;La, Hyoung-Sul;Yoon, Kwan-Seob;Na, Jung-Yul;Kim, Bong-Chae
    • The Journal of the Acoustical Society of Korea
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    • v.25 no.2E
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    • pp.60-68
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    • 2006
  • High-frequency bistatic scattering measurements from a corrugated surface were made in an acoustic water tank. First the azimuthal scattering pattern was measured from an artificially corrugated surface which has varying impedance. The corrugated surface was installed both transverse to the direction of incident wave and longitudinal to the direction of incident wave. The angle between the corrugated surface and the direction of the incident wave was about $45^{\circ}$. Second, the scattering strengths were measured from the flat sediment and the corrugated sediment. A critical angle of about $37^{\circ}$ was calculated in the acoustic water tank. The measurements were made at three fixed grazing angles: $33^{\circ}$ (lower than critical angle), $37^{\circ}$ (critical angle), and $41^{\circ}$ (higher than critical angle). The scattering angle and the grazing angle are equal in each measurement. Frequencies were from 50 kHz to 100 kHz with an increment of 1 kHz. The corrugated sediment was made transverse to the direction of the incident wave. The first measurement indicates that the scattering patterns depend on the relations between the corrugated surface and the direction of the incident wave. In the second measurement, the data measured from the flat sediment were compared to the APL-UW model and to the NRL model. The NRL model's output shows more favorable comparisons than the APL-UW model. In case of the corrugated sediment, the model and the measured data are different because the models used an isotropic wave spectrum of sediment roughness in the scattering calculations. The isotropic wave spectrum consists of $w_2$ and ${\gamma}_2$. These constants derived from sediment names or bulk size. The model which used the constants didn't consider the effect of a corrugated surface. In order to consider a corrugated surface, the constants were varied in the APL-UW model.

Effect of RF Superimposed DC Magnetron Sputtering on Electrical and Bending Resistances of ITO Films Deposited on PET at Low Temperature (DC마그네트론 스퍼터링법으로 PET 기판위에 저온 증착한 ITO박막의 비저항과 굽힘 저항성에 대한 RF인가의 영향)

  • Park, Mi-Rang;Lee, Sung-Hun;Kim, Do-Geun;Lee, Gun-Hwan;Song, Pung-Keun
    • Journal of the Korean institute of surface engineering
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    • v.41 no.5
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    • pp.214-219
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    • 2008
  • Indium tin oxide (ITO) films were deposited on PET substrate by RF superimposed DC magnetron sputtering using ITO (doped with 10 wt% $SnO_2$) target. Substrate temperature was maintained below $750^{\circ}C$ without intentionally substrate heating during the deposition. The discharge voltage of DC power supply was decreased from 280 V to 100 V when superimposed RF power was increased from 0 W to 150 W. The electrical properties of the ITO films were improved with increasing of superimposed RF power. In the result of cyclic bending test, relatively high mechanical property was obtained for the ITO film deposited with RF power of 75 W under DC current of 0.75 A which could be attributed to the decrease of internal stress caused by decrease in both deposition rate and plasma impedance.

An Analysis of the Ground Surface Potential Rise and Hazardous Voltages Caused by Impulse Currents (임펄스전류에 의한 대지표면전위상승 및 위험전압의 분석)

  • Lee, Bok-Hee;Lee, Kyu-Sun;Choi, Jong-Hyuk;Seong, Chang-Hoon
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.25 no.4
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    • pp.117-123
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    • 2011
  • Lightning and switching surges propagating through the grounding conductors lead to transient overvoltages, and electronic circuits in information technology systems are very susceptible to damage or malfunction from the electrical surges. Surge damages or malfunctions of electrical and electronic equipment may be caused by potential rises. To solve these problems, it is very important to evaluate the ground surface potential rises and hazardous voltages such as touch and step voltages at or near the grounding systems energized by electrical surges. In this paper, the performance of grounding systems against the surge current containing high frequency components on the basis of the actual-sized tests is presented. The ground surface potential rises and hazardous voltages depending on impulse currents for vertical or horizontal grounding electrodes are measured and analyzed. Also the touch and step voltages caused by the impulse currents are investigated. As a result, the ground surface potential rises, the touch and step voltages near the grounding electrodes are raised and the conventional grounding impedances are increased as the front time of the injected impulse currents is getting faster.