Impedance of a finite insulated antenna in a cold plasma with a perpendicular magnetic field

A variational formulation is developed for the impedance of a finite strip antenna embedded in a planar dielectric slab which is surrounded by a magnetoionic medium (cold electron plasma) with a static magnetic field impressed in a direction perpendicular to the antenna surface. Closed form expressions are obtained in the limit of low frequencies, and for a short antenna in a uniaxial medium. The impedance becomes large at the plasma frequency, near the upper hybrid resonance frequency, and further resonances are observed near the gyro-frequency if the gyro-frequency exceeds the plasma frequency. The reactance of a short antenna is inductive at low frequencies, but becomes capacitive as the thickness of the insulation around the antenna is increased. For very thin insulating layers the wave number of the variationally approximated current distribution exceedssqrt{sqrt{epsilon_{1}} sqrt{epsilon_{3}}} k_{0}(epsilon_{1}andepsilon_{3}are the two diagonal elements of the permittivity matrix), whereepsilon_{1}andepsilon_{3}may have positive or negative real parts. However, this approximation does not apply to current distributions along an insulated antenna. The present calculations are also compared with earlier work on antenna impedances.     

Impedance of a finite insulated cylindrical antenna in a cold plasma with a longitudinal magnetic field

A variational formulation is developed for the impedance of a finite cylindrical antenna embedded in a dielectric cylinder, which is surrounded by a magnetoionic medium (cold electron plasma) with the static magnetic field impressed in a direction parallel to the antenna axis. Closed form expressions are obtained in the limit of low frequencies, and for short antennas in a uniaxial medium. The impedance of a short antenna is nearly the same as for an assumed triangular current distribution, except that further resonances are observed in the vicinity of the gyro frequency, where the antenna becomes electrically long. These resonances may be shifted to frequencies exceeding the gyro frequency in the presence of an insulating layer around the antenna. For very thin insulating layers the wave number of the variationally approximated current distribution is to the first order equal tosqrt{epsilon_{1}} k_{0}(epsilon_{1}is the leading diagonal element of the permittivity matrix), where the gyro frequency may be both smaller or larger than the plasma frequency. However, this approximation does not apply to current distributions along the insulated antenna. The present calculations are also compared with earlier work on antenna impedances.     

Aperture-coupled microstrip antenna with a perpendicular feed

A new technique is described for feeding printed antennas. A microstrip antenna on one substrate is coupled through an electrically small aperture to a microstrip feed line on a perpendicularly oriented substrate. No direct connection is made to the patch. Such a geometry allows two separate substrates to be used for the antenna and feed functions. Measurements of a prototype design are presented.     

Impedance of a short dipole antenna in a cold plasma

This paper presents the analysis of the impedance of a short dipole antenna in a cold plasma using a quasi-static approach. Two radically different current distributions on the antenna are considered and their influences on the antenna impedance are studied. These distributions include a one-dimensional (1-D) triangular distribution and a three-dimensional (3-D) exponential current distribution. Balmain (1964) analytically solved the first problem. Staras (1964) proposed the second one. In this paper, we offer an analytical solution for the second one as proposed by Staras. We compare both distributions and find that impedances resulting from them are remarkably close. We conclude that the impedance of a short antenna, as derived using the quasi-static approximation, is insensitive to the choice of current distribution. Therefore, any of these two theories can be used when analyzing data from an impedance probe immersed in a space plasma     

Superconducting cylinder in a static transverse magnetic field

A piecewise continuous distribution of the critical currents is proposed to make compatible the Maxwell equations and constitutive equations of superconducting media. A magnetic moment of the infinite superconducting cylinder is calculated on the base of the proposed shell model. Some generalizations of the calculation method are given for superconductors of more complicated shapes     

Fields of an electric dipole perpendicular to a magnetostatic field in a hot plasma

The radiation fields of an electric dipole oriented perpendicular to the magnetostatic field in a hot uniaxial plasma are considered. The behavior of the fields near the resonance cone for the perpendicular and parallel orientations are found to be similar. A procedure is shown for estimating the electron temperature and density by measurements on the characteristic angular distribution of the fields near the resonance cone.     

On VLF radiation fields along the static magnetic field from sources immersed in a magnetoplasma

The focusing of waves from radiating VLF sources immersed in a cold magnetoplasma is investigated for the case in which the focusing takes place along the static magnetic field direction. The explicit form of tensor Green's function valid along the field line is derived for the far field, and the frequency ranges where focusing may be expected are specified. The theory is applied to calculate the power flux along the field line for an electric dipole and a magnetic loop with two orientations with respect to the static magnetic field.     

Optical magnetic field probe with a loop antenna element doubly loaded with electrooptic crystals

We propose a new type of optical probe designed to detect magnetic near-fields with high accuracy up to the gigahertz range. Its probe head consists of a loop antenna element doubly loaded with electrooptic crystals. Using optical technology, it realizes hybrid operation of a conventional double-loaded loop probe and requires no metallic cables or electrical hybrid junction. We examined probe characteristics for magnetic field detection up to 10 GHz. We confirmed that the probe can measure magnetic fields near a microstrip line with high accuracy in the gigahertz range and can suppress influence of electric fields.     

An aperture coupled microstrip antenna with a proximity feed on a perpendicular substrate

A new feeding configuration for microstrip antennas is described, where separate substrates are used for the radiating patch element and the microstrip feedline. The substrates are joined perpendicular to each other, and the patch is excited through an aperture in the antenna substrate ground plane by proximity coupling to the microstrip feedline, This design thus has a number of advantages over other feeding configurations, particularly when used in an integrated phased array application. These features, as well as the measured results from two experimental models, are described.     

On the near-wavefront behavior of the magnetic field of an infinitely long antenna

A simple formula is given for the magnetic field around an infinitely long dipole antenna which is valid over the entire spherical wavefront which is moving out from the slice generator.     

On the aperture field of a solid cylindrical antenna

The situation of a solid cylindrical antenna excited by a narrow circumferential gap is considered, and an approximation which is realistic, simple, and very accurate is obtained for the aperture electric field.     

On the crossed field antenna performance

Lately, short antennas and Crossed Field Antennas (CFA) have attracted broadcast and amateur community attention. The CFA antenna has been developed in the last decade of the 20th century, trying to obtain a compact transmitting antenna for low and medium frequency AM bands. The CFA is intended to be used in order to get a low profile antenna and a supposed performance similar or better compared to a quarter-wave monopole. The CFA has a short monopole and a metallic disk close to the monopole base, both mechanical structures being fed by means of two separated generators. Thus, the CFA has two ports and can be analyzed from the Network Theory point of view. In this paper, the CFA has been studied exhaustively using the Transmission Line Method (TLM) in order to obtain an equivalent network and the antenna performance. Due to the lack of theoretical data to explain the CFA antenna behavior, the TLM has been validated by means of Moment Method simulations and some available experimental data.     

Slot-coupled dielectric resonator antenna using a proximity feed ona perpendicular substrate

The slot-coupled dielectric resonator antenna with a proximity feed on a perpendicular substrate is investigated experimentally. The return loss, radiation pattern, and antenna gain of the new configuration are measured and discussed     

Radiation resistance of small electric and magnetic antennas in a cold uniaxial plasma

A study is made to evaluate the radiation resistance of dipole and loop antennas embedded in a cold, uniaxial plasma. Analytical closed-form expressions for the radiation resistance are derived.     

Complex antenna factor of a V-dipole antenna with two coaxialfeeders for field measurements

In transient field measurements, an antenna with wide band performance both in amplitude and in phase is desired. The complex antenna factor (CAF) is an appropriate characteristic of such an antenna. It is convenient that the CAP of the wide-band antenna is able to be calculated easily. For this purpose, a V-dipole antenna with a balun consisting of two coaxial feeders is investigated. The calculated complex antenna factors are compared with the measured values. The results show that the V dipole has the wide-band performance and the CAF is calculable     

红外光谱法研究静磁场对大鼠脑组织的影响

电气工业的发展使得人们生存的环境中充满了各类频率的电磁污染,为了探讨静磁场可能产生的生物学效应及其发生机制,从实验上研究了0.17 T静磁场曝露作用30天后对于大鼠脑组织红外光谱特征的影响,实验结果显示实验组1549 cm-1附近的酰胺Ⅱ带吸收峰有较为明显的红移现象,在1635 cm-1处为蛋白质酰胺Ⅰ带峰位置有较大的差异,另外,利用二阶导数谱分析了实验组与对照组在分子结构上存在的差异。这些变化可以反映脑组织在静磁场曝露作用前后组成成分的变化,说明傅里叶变换红外光谱方法是研究电磁场不同生物效应的发生机制的一种有效手段。     

用光镊研究稳恒磁场对血红细胞的活性影响

为了研究稳恒磁场对离体血红细胞的活性衰变产生的影响,采用非接触、无损伤的光镊技术进行了实验与分析。光镊中的高斯激光光束作用使红细胞发生形变,待细胞稳定后切断光路,得到形变血红细胞的相对形变量值,该量值大小与红细胞活性相关;对比了正常离体血液与静置于稳恒磁场中的红细胞活性衰变规律。结果表明,0.20T稳恒磁场可以提高红细胞的变形能力,增强红细胞的活性;同时加速了细胞体内能量的消耗,因离体环境没有能量的补充,能量的消耗加速了红细胞的衰老。这一结果为磁场对细胞的活性影响和动力学分析提供了一些参考。     

A loop antenna in a compressible plasma

An analysis is made of the radiation of an electron plasma wave from a circular-loop antenna with an arbitrary dimension immersed in a compressible plasma. The radiation resistance due to plasma-wave radiation is calculated and is compared with that due to electromagnetic-wave radiation.     

On input impedance of an arbitrarily oriented small loop antenna in a cold collisionless magnetoplasma

Closed-form expressions are derived for the input impedanceZof a small loop antenna with arbitrary orientation in a cold collisionless uniform multicomponent magnetoplasma. The closed-forms results ofZare compared with numerical results from a full-wave formal solution. It is found that for small loops these approximate formulas adequately represent the loop input impedance.     

Integrated instrumental chain for magnetic pulse measurement in strong static field environment

This paper describes an integrated analogue instrumental chain dedicated to measuring magnetic pulses with an amplitude of a few tens or hundreds of microteslas, superimposed to a strong static magnetic field, i.e. 1.5 T. The system features a silicon Hall sensor with nested-chopping-like biasing circuitry, DC Hall voltage compensation, amplifying and multistage filtering. Low-noise performances are achieved by applying 100 kHz spinning current to the Hall device and chopping at 200 kHz to the signal conditioning blocs downstream. The microsystem achieves 20 μT resolution over a 1.6 kHz bandwidth extending from 5 Hz to 1.6 kHz under 1.5 T static field.