Microwave Properties of Lithium Ferrites (Short Papers)

Low-power loss and high-power threshold properties have been measured between 3.0 and 17.2 GHz on three Li-Ti ferrite compositions of magnetizations 1250, 2250, and 3600 G. In each composition the use of cobalt resulted in a linear increase in mu/sub 0/ and h/sub crit/. Temperature measurements were performed at 9.2 GHz on the 2250-G material. An illustration of how the data might be applied is given.     

Microwave Characterization of Partially Magnetized Ferrites

In order to assist the microwave engineer in predicting the performance of partially magnetized devices, we have characterized the microwave permeability of partially magnetized materials. The real part of the tensor permeability elements, /spl mu/, /spl kappa/, and /spl mu//sub z/, depends primarily on the parameters /spl gamma/4/spl pi/M//spl omega/ and /spl gamma/4/spl pi/M/sub s/ / /spl omega/. Empirical formulas have been developed which show the dependence. At frequencies sufficiently below /spl omega/ = /spl pi/4/spl pi/M/sub s/, the loss can be characterized by the value of /spl mu/' at 4/spl pi/M = 0./spl mu/, /spl kappa/, and /spl mu//sub z/ depend weakly on composition, whereas /spl mu/' (4/spl pi/M = 0) does depend upon the chemical composition.     

Compact Microwave Single-Sideband Modulator Using Ferrites

This paper describes a single-sideband modulator for shifting the frequency of an x-band signal by means of a rotating magnetic field transverse to a ferrite differential half-wave section. The device is one of the first practical applications of the double-refraction properties of ferrites. Improvements over an earlier model include reduction in size and continuous operation without drift. An efficient and compact magnetic structure has been designed for producing the rotating magnetic field. Excessive heating of the ferrite and voltage breakdown of the coils is eliminated by a forced-air cooling system. The modulator shifts the microwave-carrier frequency of 9375 mc by plus or minus 20 kc. With a rotating field of approximately 200 oersteds the microwave insertion loss is 1.0 db. The undesired sideband suppression is above 40 db while the carrier suppression is 23 db. For a frequency bandwidth of 500 mc, the insertion loss remains below 5 db.     

Improved Microwave Noise Measurements Using Ferrites

The ferrite isolator and the ferrite circulator have been applied separately to improve the accuracy of measuring small microwave noise powers or small power differences. Either the isolator or the circulator effectively isolated the input circuit of a microwave receiver from the impedance of the source. As a result, the measurement errors introduced by mismatched source impedances were reduced by as much as 98 per cent. The added input circuit losses of the ferrite components reduced the receiver sensitivity by only about 10 per cent. Since the accuracy of measuring small noise power differences was limited principally by impedance errors, the addition of ferrite isolation to the receiver input circuit increased the sensitivity of measurement to near the theoretical limit. The ferrite isolator was used as a passive transmission element in these experiments. The ferrite circulator, however, was used as an electrically-operated, microwave switch. This switch was used to replace the mechanical chopper in a Dicke-type radiometer. In addition to impedance isolation, the ferrite switch makes possible rapid comparison measurements of the microwave noise powers from any two sources, or of the noise powers from the same source in two different polarizations.     

Ferrites with Planar Anisotropy at Microwave Frequencies

Materials with an easy plane of magnetization (planar anisotropy) have recently been discovered. The large anisotropy field that tends to keep the magnetization in the easy plane reduces the field required to cause ferromagnetic resonance, which makes the material promising for microwave applications. Equations are derived for the susceptibility, taking into account losses and a finite medium. Propagation in a longitudinal and transverse static field is considered. The location of a slab in a rectangular waveguide for minimum loss in the forward direction, and the use of the material as a phase shifter, are discussed. Experimental microwave data on some materials are given, and also data on an isolator and phase shifter incorporating these materials.     

Zn 、Ti 、Sn 取代的锂铁氧体饱和磁化强度研究

采用普通陶瓷工艺,并加入微量杂质：Bi2O3,NiO,Co2O3和MnCO3,且利用氧气氛烧结制备了目前尚未见报道的锂铁氧体Li0.625Zn0.1Ti0.25Sn0.1Fe1.925O4。该材料具有较高的居里温度和较低的介电损耗。利用Pierre weiss分子场理论,自发磁化理论对Li0.625Zn0.1Ti0.25Sn0.1Fe1.925O4锂铁氧体的比饱和磁化强度随温度的变化进行了理论计算,结果表明,铁,钛离子取代了B位的铁离子,而锌取代了A位的铁离子。     

The Status of Microwave Applications of Ferrites and Semiconductors

The recent developments in the field of ferrite devices are reviewed. Emphasis is placed on the extension of nonreciprocal devices to lower microwave frequencies. and high powers. The design considerations and achievements of broad banding also are covered. Fundamental principles leading to the applications of non-linear properties of ferrites are described briefly. Preliminary experimental accomplishments in the construction of frequency doublers, mixers, and ferromagnetic resonance amplifiers are summarized. The possible role of the new ferromagnetic garnet material is indicated. Although no significant new semiconductor devices have been developed at microwave frequencies, possibilities are considered for doing this with use of cyclotron resonance and spin resonance phenomena and their related properties in semiconductors.     

Dielectric Constant Ferrites and Loss Tangent of Microwave at Elevated Temperatures

Experimental data are given on the effect of elevated temperature on the dielectric properties of ferrites intended for microwave applications. Measurements were made at X band. The real part of the dielectric constant generally increases slowly with temperature, the maximum temperature coefficient observed being 300 parts per million per degree C. The dielectric loss tangent also generally increases with temperature. Measurements were made in a rectangular waveguide cavity, using a modified perturbation technique. It is shown that the simple perturbation technique may cause an appreciable error in the measurement of the real part of the dielectric constant. The effect of the finite resistivity of the cavity walls and the effect of the cavity irises on the measurement of the dielectric loss tangent, are also considered.     

锂离子电池安全技术综述

综述了锂离子电池的危险性,分析了产生锂离子电池产品安全问题的原因。从材料、设计和工艺3个角度,简要地介绍了一些常用的安全技术,并提出了一些安全性设计的实例。     

Magnetocardiography: An Overview

Since 1963 when recording of the human magnetocardiogram (MCG) was first reported, the number of clinical studies has been limited. High-quality tracings can now be easily obtained in special shielded chambers, but problems remain if records are to be made in hospitals without such chambers. Measurement techniques, theory of the MCG, and model studies are discussed. Configuration of the MCG waveform is much the same as that of the electrocardiogram (ECG). Measurements of dc currents of injury in dogs by means of the MCG have been reported, and are potentially of great clinical interest. Effects of magnetic susceptibility changes in the torso associated with blood movement may contribute to variations in the external field. The questions of what new diagnostic information is available in the MCG and what lead systems are most appropriate remain to be answered.     

Dielectric Waveguide Microwave Integrated Circuits---An Overview

An integrated circuit technique for microwave and millimeter wavelengths which uses refractive-type waveguides and signal processing coupled with planar integration techniques characteristic of microstrip microwave integrated circuits (MIC's) is described. Following a comparison of the optical and millimeter approaches to this circuit technique, a discussion of transmission lines and components for millimeter wavelengths is presented. System applications are also described.     

模拟乘法器概述

对实现模拟乘法运算的各种方法进行了概括介绍,并对这些方法的优缺点进行了比较,然后对生产模拟乘法器的厂家及其代表产品进行了介绍。最后从电路设计和工艺角度简单地介绍了某些性能的改进。     

Size Effect in the Measurement of Microwave Permeability of Ferrites (Correspondence)

In the usual method of measuring the tensor permeability of ferrites at microwave frequencies, a small sample of the material is placed in a suitable cavity, and the change in resonant frequency and Q of the cavity, caused by the presence of the ferrite, are measured. The measured quantities are related to the quantities of interest-real and imaginary parts of permeability-by equations derived through perturbation theory.     

Differential Phase Shift at Microwave Frequencies Using Planar Ferrites (Short Papers)

It is generally believed that planar ferrites are not useful in differential-phase-shift devices operated below resonance. A configuration of planar ferrite is suggested, which Ieads to appreciable differential phase shift on application of very small magnetic fields.     

微波光子成像雷达技术发展综述

随着隐身化、无人化以及微型集群化目标的快速发展,精确获取目标形状和形态的情报需求,对微波成像雷达提出了大带宽和多频段的现实要求。得益于微波光子技术的低相噪、大带宽、宽调谐等显著优势,微波光子成像雷达技术已得到快速发展。本文对微波光子成像雷达研究现状进行了总结,对其典型系统架构和主要工作原理进行了研究分析,进一步结合系统能力优势给出了主要应用方向和相关成像实验结果,最后提出了进一步发展仍需解决的问题。     

Parallel Component µ /sub z/ of Partially Magnetized Microwave Ferrites

A formula for the parallel component µ /sub z/ of the microwave permeability tensor in the partially magnetized state is derived. The theory is in good agreement with the experimental results.     

X波段移相器用微波锂铁氧体材料的制备

对钛置换锂铁氧体进行了理论计算,在此基础上通过控制 Ｆｅ 含量,添加 Ｃａ、 Ｖ 离子及高压氧气退火等工艺,制备出了性能优良的微波铁氧体材料。     

Satellite News Gathering : An Overview

This paper begins with a brief history of satellite communication, with particular regard to the early Ku-Band satellites and reviews some of the many experiments conducted by different organizations.     

Microwave biological effects: An overview

Although most investigators accept the fact that "high power density" of microwaves can result in pathophysiological manifestations of a thermal nature, some reports have suggested that "low power density" microwave (MW) energy can affect neural and immunologic function in animals and man. Most of these reports have emanated from the USSR and other Eastern European countries. Since most reported "low-level" effects relate to behavioral and central nervous system changes, studies are needed to determine the nature and mechanism(s) of the nervous system's reactions, if any, to electromagnetic fields and to investigate the degree to which the individual's performance capabilities may be affected. Because of their important integrative and regulatory functions, the neuroendocrine and central nervous system should receive attention as possible sensitive areas. Neurochemical assays and immunologic reactivity could indicate basic mechanisms of interaction. A critical review of studies into the biological effects of MW's indicates that many of the investigations suffer from inadequacies of either technical facilities and energy measurement skills or insufficient control of the biological specimens and the criteria for biological change. There is a great need for systematic and quantitative comparative investigations, using well-controlled experiments. This should be done by using sound biomedical and biophysical approaches at the various organizational levels from the whole animal to the subcellular level on an integrated basis, with full recognition of the multiple associated and interdependent variables. Above all there is a need for scientific competence and integrity. It is important to maintain a proper perspective and assess realistically the biomedical effects of microwave exposure, so that the worker or general public will not be unduly exposed nor will research, development and benficial utilization of this energy be hampered or unecessarily restricted.