Time-domain modeling, characterization, and measurements ofanechoic and semi-anechoic electromagnetic test chambers

We present time-domain techniques for modeling, characterizing, and measuring anechoic and semi-anechoic chambers used for emission and immunity testing of digital devices. The finite difference time-domain (FDTD) approach is used to model and characterize these chambers. In the FDTD model presented here, we discuss methods used to eliminate the need to spatially resolve the fine detail of the absorbing structures; present a differential-operator approach for incorporating both frequency-dependent permittivity and permeability into the time domain; and discuss the effects of gaps and holes in ferrite-tile absorbers on both absorber and chamber performance. Comparisons of the FDTD chamber model with measured data for different chamber sizes are presented. Finally, we discuss and illustrate how time-domain techniques can be used to characterize chambers, predict performance, and diagnose problems with both absorbers and chambers. With time-domain and frequency-domain techniques, we show how the performance of chambers can be significantly altered with only small changes in the type of absorbing structure used, and we illustrate how undesirable modal field distributions can occur inside a chamber when a nonoptimal absorber is used     

Electromagnetic wave absorbing characteristics of Ni-Zn ferritegrid absorber

The reflection loss of Ni-Zn ferrite grid absorber is studied in the low frequency limit which the period of the array is small compared with wavelength. The relative equivalent complex permeability and permittivity with air volume fraction is obtained using the Hashin-Shtrikman (1962) upper-bound formula. The impedance matching conditions for maximum electromagnetic wave absorption are obtained by the “contour map method.” Two impedance matching thicknesses and frequencies are compared with theoretical matching relationships derived under the limiting case of impedance matching formula. As the air volume fraction increases, the first matching frequency, f_m1 remains nearly constant, while the second one, f_m2 decreases and approaches f_m1. Therefore, the absorption band of a ferrite grid absorber is broader than that of the single layered ferrite plate absorber     

FDTD analysis of resistor-loaded bow-tie antennas covered withferrite-coated conducting cavity for subsurface radar

This paper presents a full-wave analysis of a ground penetrating radar (GPR) using the finite-difference time-domain (FDTD) method. The antenna treated here consists of a resistor-loaded bow-tie antenna, which is covered with a rectangular conducting cavity of which inner walls are coated partially or fully with ferrite absorber. Some techniques are introduced into the FDTD analysis to obtain the accurate results and to save the computer resources. The validity of the FDTD analysis is confirmed experimentally. Furthermore, the effects of the ferrite absorber on the GPR characteristics are theoretically investigated in detail. The FDTD results indicate that the remarkable improvement of the antenna characteristics for the GPR system cannot be attained by the ferrite absorber     

Fundamental investigation on a weakly magnetized ferrite absorber

Investigated are the matching characteristics of a magnetized ferrite absorber, which applies a weakly static magnetic field H_dc perpendicular to the sintered ferrite surface. Applying a static magnetic field to the ferrite enables the matching thickness of the absorber to be reduced from 8 mm in the absence of H_dc to 3 mm under 750 gauss. The matching frequency can also be changed broadly from 0.1 to 0.9 GHz by controlling ferrite thickness and H_dc, simultaneously. These are well explained in terns of an nonsaturated permeability rather than tensor permeability. A thin magnetized ferrite absorber is realized using a ferrite with a large value of imaginary part of permeability when real part takes the value near 1.0. Matching frequency characteristics, whether broad or narrow, correlates closely with the slant of the curve for real part of permeability taking the value near 1.0 in the present frequency     

Application of Ferrite to Electromagnetic Wave Absorber and its Characteristics

An electromagnetic wave absorber utilizing ferrite or rubber ferrite composed of ferrite powder and rubber is described. In our investigation, the existence of a matching frequency f/sub m/ and a matching thickness t/sub m/ has been found. The terms f/sub m/ and t/sub m/ mean that the ferrite which is backed with a conducting plate can be a perfect absorber only under the conditions that the frequency of the incident wave is f/sub m/ and that the thickness of the ferrite is t/sub m/.Each ferrite has two matching frequencies f/sub m1/, f/sub m2/, (f/sub m1相似文献   

On the Computation of Local-Demagnetization Tensor for Nonellipsoidal Ferrites

The distribution of the magnetization in ferrite devices is nonuniform due to their nonellipsoidal shapes. In this paper, the local-demagnetization tensor of magnetized nonellipsoidal ferrite is proposed and calculated. By analysing the distribution of the tensor elements, the distribution of the demagnetizing field can be obtained. The method is simple yet accurate. It can be used to calculate the nonuniform magnetizing distribution in ferrite devices as well as optimize the ferrite devices in the CAD of MMIC.     

Electromagnetic wave absorber with wide-band frequencycharacteristics using exponentially tapered ferrite

As a countermeasure of EMI or EMC, various types of electromagnetic wave absorbers are used. A wide-band design method of an electromagnetic wave absorber with using exponentially tapered ferrite, which has very wide-band frequency characteristics, is proposed and discussed. The wide-band electromagnetic wave absorber can be designed under some approximations by the theoretical model using the equivalent material constants (equivalent complex permittivity and permeability) method for the regions varying spatially in the shape of ferrite. Based on the model, wide-band electromagnetic wave absorbers with taper, which have not only excellent reflectivity frequency characteristics but also a bandwidth of 30 MHz to 2150 MHz or 2430 MHz under the tolerance limits of -20 dB reflectivity, were designed     

雷达波吸收剂的研究进展

叙述铁氧体、金属微粒、多晶铁纤维、纳米吸收剂和手征性吸收剂等吸收剂近年的研究发展状况 ,预测了吸收剂研究的未来发展趋势。     

Ultra-fast quantum-well saturable absorber devices and their application to all-optical regeneration of telecommunication optical signals

We review recent advances in the investigation of vertical cavity saturable absorber devices and their use for the all-optical regeneration of telecommunication signals in ultra-long-haul transmission systems. Such devices are polarization-insensitive and operate as fully passive nonlinear optical elements. Two approaches for obtaining fast recovery absorber materials are described, relying upon ion irradiation or upon iron doping. The vertical micro-cavity devices are designed so as to optimize the switching contrast and the operating power. Their functional behaviour as extinction ratio amplifiers has been characterized and their optimal operating conditions have been determined. The potential application of these devices to all-optical regeneration has been investigated through numerical simulations and fully demonstrated in several long-distance transmission loop experiments, with results obtained at 10, 20 and 40 Gbit/s, showing significant improvements in system haul or operational margins. A four-channel fibered module has also been fabricated, as a perspective towards the development of wavelength division multiplexing (WDM) saturable absorber modules.     

Ring-like testing of digital circuits

Here we propose a new approach to the testing of digital devices, which can potentially save diagnostic hardware. An example is given for testing combinational devices. Estimates are given for reliability and hardware complexity, and an algorithm for designing operability tests is described.     

Broadband electromagnetic absorber with ferrite/ferrite hybridstructure

A new broadband electromagnetic absorber has been constructed by using the NiZn/NiZn ferrite hybrid structure and analysed using the FEM (finite element method). The structure is only 55.5 mm high, and has a reflection loss of <-20 dB in the frequency range 30 MHz-3 GHz. These characteristics are superior to those of conventional absorbers which have been used in anechoic chambers     

铁氧体双模器件的广义理论

铁氧体双模器件包括双模移相器,圆极化移相器,旋转场移相器.双模变极化器等等.其种类繁多,每种器件由若干基本双模段级联而成.每个基本单元上,外加磁场形式各不相同,有四磁极磁化场,纵向磁化场,双磁极磁化场及其混合磁化场.本文拟用统一的理论对其进行处理及分析并引入具体实例使用CAD技术进行计算,从而进一步确认理论的正确性.     

Quasi-optical ferrite devices for millimeter and submillimeter wave bands

Main features of the development of quasi-optical ferrite devices, using Faraday effect, are considered. Properties of a polarizing divider and a ferrite rotator of a polarization plane are analysed with standpoint of minimum losses. A matching method, based on an utilization of the rotator element in a form of the multilayers ferrite structure, which can be adjusted independently for right-handed and left-handed cyrcularly polarized waves, is suggested. It is shown, that this method allows to obtain a total matching in a quasi-optical transmission line. Results of an investigation of quasi-optical ferrite devices for the oversized round waveguide withH ₁₁ mode are presented.     

Theory of Dielectric-Loaded and Tapered-Field Ferrite Devices

Loading a ferrite resonance isolator or differential phase shifter with a dielectric or biasing the ferrite with an inhomogeneous dc magnetic field are very useful ways of improving the performance of these ferrite devices. Whereas these methods are very commonly used in transverse-field ferrite devices, no extensive analytical treatment of the subject has appeared in the literature. It is the purpose of this paper to present a theoretical analysis of the problem, chiefly by means of combined boundary-value and perturbation-theory approach. It will be shown that dielectric-loading and tapered-field techniques increase the bandwidth of isolators and phase shifters, the isolation-to-insertion loss ratio of the former, and the phase shift of the latter.     

Scattering parameters measurement of a nonreciprocal couplingstructure

A novel ferrite image guide was designed and tested from 26.5 to 40 GHz. The nonreciprocal structure consisted of two dielectric image guides separated by a ferrite slab. M-type hexagonal ferrite was used with its C-axis oriented parallel and perpendicular to the direction of propagation. The S-parameters of the device were measured for a nonuniform external biasing magnetic field applied parallel to the C-axis of the ferrite slab. Nonreciprocal effects were observed for all cases considered above. The results imply applications for ferrite devices operating at millimeter wavelength frequencies, such as isolators, filters, modulators, switches, phase shifters, etc     

一种移相器快速化测试系统的设计

随着相控阵雷达技术的迅猛发展,在大型天馈线系统中铁氧体移相器得以大规模应用,相应地,提高铁氧体移相器测试生产效率以满足日益增长的需求已成为许多移相器生产厂家的努力方向。文中针对某一锁式铁氧体移相器组件,设计了一种快速化测试系统,通过与之前未使用测试系统对比,满足移相器的测试要求。该测试系统大大提升了移相器测试效率,同时,该测试系统设计思路同样可应用于其他种类铁氧体器件测试,从而提高了铁氧体器件批产能力。     

Stacked multijunction photodetectors of long-wavelength radiation

Uncooled, long-wavelength photovoltaic detectors suffer from poor quantum efficiency and low differential resistance. The problem can be solved by the use of stacked, multiple heterojunction-photovoltaic cells with thin absorber regions. We report here numerical simulation and optimization of the stacked, multiple Hg_1−xCd_xTe heterojunction cells used for detection of 10.6-μm infrared (IR) radiation, operating as zero-bias photovoltaic devices or Auger-suppressed photodiodes. It is shown that the devices can be used as high-performance and fast-response detectors of long-wavelength radiation operating at ambient temperature with detectivities larger by more than one order of magnitude than that of the present practical devices.     

C波段移相器用Li系铁氧体的研究

主要介绍研制C波段相器用Li系铁氧体过程中的一些体会,并给出所研制铁氧体材料的静磁参数及制成器件达到的技术指标。     

Application of Impedance Loading to Geometric Transition Radar Absorbent Material

This paper describes a novel, lightweight technique for significantly improving the low-frequency reflectivity performance of conventional geometric transition radar absorbent materials as used typically in anechoic chamber facilities for electromagnetic compatibility testing. The improvement is achieved by the inclusion of impedance-loading elements within the base region of the absorber, and these are implemented in the form of one or more frequency-selective surfaces (FSS). The discussion covers the design of the FSS using computer simulation technology microwave studio, its predicted effect on absorber performance at both normal and oblique incidence, the effect of manufacturing tolerances, and the fabrication and characterization of a prototype-loaded absorber panel.     

Assessment Methods for Demonstrating Compliance With Safety Limits of Wireless Devices Used in Home and Office Environments

Short-range wireless radio-frequency devices are rapidly pervading home and office environments. Nevertheless, their contribution to the electromagnetic field exposure of humans has not yet been systematically assessed, nor have the procedures for testing compliance been developed. In this paper, we have assessed the range of exposure in terms of the dosimetric and incident field quantities for devices of the most common technologies, i.e., digital enhanced cordless telecommunications, wireless local area networks and Bluetooth, as well as wireless communication devices based on proprietary standards in the frequency range from 30 MHz to 6 GHz. Well-defined procedures to obtain the worst case operational modes are presented. Since operation in the near-field of these devices cannot be excluded, dosimetric evaluation is the most straightforward technique for testing compliance when low-power exclusions are not applicable. The suitability of the suggested methods is demonstrated through the examination of five classes of short-range transmitters.