Spherical Wave Diffraction by a Slit in an Impedance Screen

An exact solution is developed for the problem of diffraction of an E-polarized and an H-polarized spherical waves by a slit in an impedance screen. This consideration is important in the sense that point sources are regarded as better substitutes for real sources than line sources/plane waves. The two independent problems are solved using the Fourier transform, the Wiener-Hopf technique and asymptotic approximations.     

Impedance of a sphere oscillating in an elastic medium with and without slip

The dynamic impedance of a sphere oscillating in an elastic medium is considered. Oestreicher's [J. Acoust. Soc. Am. 23, 707-714 (1951)] formula for the impedance of a sphere bonded to the surrounding medium can be expressed in a relatively simple form in terms of three lumped impedances associated with the displaced mass and the longitudinal and transverse waves. If the surface of the sphere slips while the normal velocity remains continuous, the impedance formula is modified by adjusting the definition of the transverse impedance to include the interfacial impedance.     

Impedance of an electric dipole located in a cylindrical cavity in a dissipative medium

The electromagnetic fields of an electric dipole located inside a cylindrical cavity or empty tunnel are formulated. The results are used to deduce an expression for the change of self-impedance due to the presence of the cavity or tunnel walls. A numerical evaluation of the resultant convergent integral and a summation of the angular harmonic series were performed. An important finding is that the input resistance of the dipole is approximately a constant for frequencies less than about 25 MHz for a typical tunnel radius of 2 m. Such results are shown to be in qualitative agreement with an earlier analysis of an electric dipole over a dissipative half-space.     

Effective Impedance of a Slightly Rough Surface of an Arbitrarily Anisotropic Medium

We consider a boundary-value problem for the electromagnetic field in an arbitrarily anisotropic half-space with a rough surface. In the case of a small roughness height, we derive the impedance boundary condition with a nonlocal impedance in the fourth order of the perturbation theory. In addition to the general case, we analyze the case of a perfectly conductive surface with a Gaussian roughness.     

Impedance Spectroscopy Study of a Polymer Composite with Carbon Nanotubes in Contact with an Electrolyte

Technical Physics - The measured frequency dependence of the electric impedance of a composite based on ultra-high molecular weight polyethylene reinforced with carbon nanotubes in contact with an...     

对北京正负电子对撞机阻抗的研究

比较全面地研究了北京正负电子对撞机(BEPC)的耦合阻抗并试图从降低耦合阻抗的角度来探讨压缩BEPC束长的可能性.     

Study of BEPC Impedance

The impedance of Beijing Electron positron Collider (BEPC) is studied in detail, and the possibility of suppressing bunch lengthening in BEPC is discussed in the view of decreasing the coupling impedance.     

Impedance spectra of polymer electrolytes

The authors present a phenomenological view on dielectric relaxation in polymer electrolytes. Polymer electrolytes are seen as molecular mixtures of an organic polymer and an inorganic salt. The following is based on systems with high molar mass poly(ethylene oxide) (PEO) and epoxidized natural rubber with 25 mol% of epoxide content (ENR-25) filled with lithium perchlorate (LiClO₄). Dielectric properties of these systems have been studied as a function of salt content at room temperature. Additionally, properties of neat low molar mass PEO were studied as function of temperature. Relaxation-coined dielectric behavior rules the system with PEO in the frequency that ranged up to 10⁶ Hz. Imaginary parts of impedance, tangent loss, and electric modulus spectra show distribution of relaxation times. Comparison of tangent loss (tan δ) spectra and imaginary part of electric modulus (M″) spectra reveals that localized motion dominates long-range motion of dipoles in the low-frequency range. However, discrepancy between them decreases with growing salt content. Scaling of tan δ spectra demonstrates that distribution of relaxation times does not depend on salt content in the range of low frequencies. The ENR-25 system exhibits solely relaxation like a macroscopic dipole. In conclusion, the system with PEO is characterized by individual relaxation of well-interacting dipoles, whereas the system based on ENR-25 is coined by immobilized dipoles that lead in the state of high-salt content to the relaxation behavior of a macroscopic dipole.     

Minimization of Impedance of the NICA Collider Ring

Physics of Atomic Nuclei - Impedances of the NICA collider ring elements have been simulated to minimize them to the values ensuring beam stability. To this end, the structure of the elements is...     

Diffraction by an Elongated Body of Revolution with Impedance Boundaries: the Boundary Integral Parabolic Equation Method

Acoustical Physics - The problem of diffraction by an elongated body of revolution with impedance boundary conditions is studied. The case of axial incidence of a high-frequency wave is considered....     

Impedance study of BIMGVOX ceramics

The polycrystalline samples of Bi₂V_0.9Mg_0.1O_5.35 were synthesised. The conductivity of the samples with Pt electrodes was determined by non-linear least-squares analysis of the impedance spectra. The total conductivity of the samples exhibits Arrhenius-type dependence on temperature with two straight line sections. In the transition from one linear section to the other a time dependence of conductivity was observed. The conductivity decreases both on heating and cooling during several hours at constant temperature (between 665 and 680K and between 710 and 695K on heating and cooling respectively). During heating at temperatures between 685 and 790K the Arrhenius plot are not linear. It may be expected that a process of slow ordering/disordering of oxygen vacancies is responsible for this phenomenon. The values of conductivity at low temperatures were dependent upon the length of time the sample was allowed to reach equilibrium - the structure of the material seems to be frozen in a metastable state, probably β type. At high temperature region the conductivity do not depend on the thermal history of sample. Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996     

电沉积复合丝及其巨磁阻抗效应的研究

采用脉冲电沉积工艺在Cu丝上沉积Fe Ni合金镀层 ,成功地制备出巨磁阻抗效应 (GMI)复合丝材料 ,研究了复合丝的磁性能和巨磁阻抗效应 .复合丝外壳磁性镀层软磁性越好 ,巨磁阻抗效应越明显 ,制备的复合丝最高巨磁阻抗效应为 2 7.19% .研究了复合丝阻抗与巨磁阻抗比值GMI随外加磁场的变化 ,其变化曲线的形状受复合丝磁各向异性场的影响 .此外 ,还研究了复合丝巨磁阻抗效应与驱动交变电流频率的关系 ,复合丝Fe17Ni83 样品巨磁阻抗效应的临界频率为 30kHz(GMI为 9.95 % ) ,特征频率为 30 0kHz(GMI为 2 7.19% ) ,截止频率为 10MHz (GMI为 10 .36 % ) .如此低的临界频率和特征频率及较宽的频率段对于实际应用非常有利 .     

Impedance characteristics of crystal-like structures

Simulation of crystal-like structures (CSs) based on the impedance model is considered. It is shown that CSs peculiarly transform the wave impedance, inducing unusual properties of the medium. The impedance characteristics for various CSs are considered.     

光电导天线辐射阻抗特性模拟分析(英文)

针对连续太赫兹光电导天线辐射功率较低的缺点,利用有限积分方法对三种常用的光电导天线,包括偶极天线、蝶形天线和螺旋天线,进行数值模拟并分析比较其辐射阻抗特性.仿真结果表明,偶极天线的辐射阻抗与偶极长度、宽度、电极间隙以及传输线宽度有关,且在其谐振频率存在峰值阻抗,适用于特定频率的太赫兹波辐射.蝶形天线和螺旋天线在所研究的太赫兹波段具有近似稳定的辐射阻抗,广泛应用于宽带领域.对带有交叉电极的电极间隙进行计算,结果表明由交叉电极引入的附加电容降低了天线的高频阻抗.     

BEPC静电分离器分路阻抗和功率损耗研究

通过测量BEPC静电分离器各主要模式的分路阻抗,分析了BEPC运行过程中静电分离器的高压电缆隔离层不时烧化的原因,同时对BEPC流强进一步提高时静电分离器中的功耗进行了计算.     

Impedance response of polycrystalline tungsten oxide

Polycrystalline tungsten oxide (WO₃) pellets were prepared by conventional ceramic processing technology. The ac small-signal electrical data acquired in the frequency (f) range 100 Hz≤f≤1 MHz at temperature (T) ranging the 31-100 °C revealed distinct semicircular relaxation in the impedance plane. This relaxation indicates device behavior originating from the grain boundaries. The lumped grain impedance associated with the device action remained too small to detect when the large resistance scale is realized. The semicircular relaxation is thermally activated indicating 0.58 eV as the activation energy for the relaxation time.