Measurement of velocity mismatch in traveling-wave electrooptic modulators

For traveling-wave electrooptic modulators, we describe an experimental method to determine the sign and magnitude of velocity mismatch between electrical and optical wave. To this end the waves are counterpropagated and frequencies yielding modulation nulls are determined. Such a measurement does also reveal dispersion of the modulator structure.     

Measurement of small-signal parameters in traveling-wave tube theory

An experimental procedure is described which allows the accurate determination of parameters needed to calculate the small-signal gain of traveling-wave tubes using the equivalent transmission-line model of Pierce. A movable electromagnetic probe is used to measure the gain per unit wavelength along the helix and the attenuator and also to measure the initial loss. From these data the gain parameter C' and the space-charge parameter Q'C' are determined simultaneously. The value of C' enables the growth parameter x' to be obtained from the gain per unit wavelength. Excellent agreement with theory has been obtained for the variation of C' and Q'C' with beam-to-helix radius ratio b/a and with perveance, and for the variation of the growth parameter x' with C' and Q'C'. The change of initial loss with helix voltage for various C' and Q'C' has been verified. Finally the growth parameter in the attenuator has been found to be positive, as expected from field theory as well as the equivalent transmission-line model.     

Spin transport and microwave self-oscillations in magnetic heterostructures with giant magnetoresistance

The phenomena of spin transport and spin-transfer torque between layers of a magnetic hetero-structure with conducting and tunneling interlayers, which can lead to switching of micromagnetic states in the structure??s layers and microwave generation, are considered. The features of spin transport in the field-emission mode for magnetic tunnel structures and problems of the current generation of spin waves in the magnetic film during local spin pumping are discussed. The possibility of the phase locking of the system of nanogenerators on a common magnetic platform and prospects for using nanogenerators based on the effect of spin transport in microwave communication engineering are analyzed.     

Measurement of transistor high-frequency current gain

An approach commonly used in instruments to test the high-frequency current gain of transistors consists of driving the base with a calibrated current source and measuring the collector current with a very low resistance meter. The major shortcomings of such instruments are their insufficient accuracy and their limited range of quiescent test conditions. However, a thorough analysis of this method demonstrates the possibility of reducing the measurement error, in the most unfavorable case, to less than 4.5 per cent as well as the possibility of extending the test conditions to 10µv, 10µa. These improvements were obtained as a result of the development of such features as a source impedance of 50K Ω at 100 Mc, a collector load of 1 Ω and a very low capacitance socket.     

Longitudinal mode control in giant pulse lasers

We have introduced longitudinal mode selection into a giant pulse laser to obtain single mode output from the laser. Some advantages of achieving longitudinal mode control in a giant pulse laser are noted. The methods of mode control used are described. These include orienting various reflecting surfaces in the laser cavity, cooling the ruby laser crystal, and introduction of a saturable dye in the cavity. Methods of measuring the mode structure are given. Results of these measurements with varying degrees of mode control are described in detail. Under some conditions it is possible to obtain essentially single mode behavior from the giant pulse laser.     

Measurement of the electron velocity-field characteristic in modulation-doped structures using the geometrical magnetoresistance method

We describe a method for measuring the electron mobility, velocity, and sheet carrier concentration in modulation-doped structures as functions of electric field through the use of the geometrical magnetoresistance effect. Because the geometry of the structures is identical to that of ungated FET's, these measurements are well suited for studying the electron velocity in MODFET's. We see that the mobility quickly decreases from its low field value with increasing electric field and observe significant electron injection from the contacts. The electron velocity increases to about 1.4 × 10⁷cm/s at 3000 V/cm at 77 K before domain formation prevents accurate measurements at higher fields.     

Measurement of intermodulation and a discussion of dynamic range in a ruby traveling-wave maser

This paper reports measurements of intermodulation in a ruby traveling-wave maser. The power level at frequency 2f2-f1was measured when strong signals at frequencies f1and f2were applied to the maser. In agreement with theoretical predictions, the intermodulation level was found to be extremely weak. Results of the measurement can be expressed as P(2f2- f1) = 2P(f2) - P(f1) - 95 where f1=4110 Mc, f2=4140 Mc and the powers are measured in dbm. The pertinent characteristics of traveling-wave masers are summarized in a concluding Section.     

Au/Fe磁性多层膜在纳米颗粒转化过程中的电磁物性在线测量方法

通过对当前磁性颗粒膜巨磁阻效应的一般研究方法的讨论,分析了当前已存在方法的不足之处,提出了一种利用离子束混合技术在线制备纳米颗粒膜的实验方法,该方法的特点是能够在磁性多层膜转化为纳米颗粒膜的过程中在线测量磁阻和霍尔系数。本文详细介绍了该方法的实施过程,提供了相关的实验结果,证明了该种方法的可行性,并初步讨论了此种方法的应用前景。     

Relativistic effects in the traveling-wave amplifier

A relativistically correct large-signal theory is developed for the analysis of high-power, axially symmetric traveling-wave amplifiers in order to investigate the physical phenomena involved in the interaction process. The nonlinear integro-differential system equations are developed from the Lorentz force equation, the one-dimensional equivalent circuit equation, the wave equation, and the continuity of charge relation. These equations are applied to two electron stream models: a ring model which permits the effects of nonlaminar flow and space-charge forces to be evaluated, and a disk-electron model in which these effects are ignored. The ring model space-charge fields are obtained from the appropriate Green's function for Poisson's equation in a moving frame of reference. Numerical solutions are presented and discussed with major emphasis on the disk-model solutions. The principal results are that the gain per unit length decreases with increasing beam velocity, the circuit phase velocity for optimum power output approaches the dc beam velocity u0, asu_{0}/capproaches unity, and the conversion efficiency is almost independent of u0for the synchronous case. The linearized one-dimensional theory of the traveling-wave tube is also discussed. Several of the large-signal results are predicted from the small-signal theory.     

Measurement of mode splitting in asymmetric Y-junctions

A measurement procedure is presented for the determination of mode splitting (or mode sorting) in asymmetric Y-junctions. This procedure avoids measurement errors introduced by bends, tapers, small damages in the waveguides outside the coupling region, variation in fiber-chip coupling, etc. It is based on the analysis of the normalized coupled power in an optical coupler in which a mode splitter is used. The method is illustrated with a mode splitter on lithium niobate. A value of 29.2±0.5 dB for the suppression of the unwanted mode is found, showing the applicability of the procedure     

Measurement of mode partition in DFB lasers

Some DFB (distributed feedback) laser diodes have a satellite mode beside a main DFB mode even if FP modes are suppressed. In this paper, the mode partition noise is presented for several DFB lasers operating in multilongitudinal modes. The results show that under modulation at 140 Mbit/s, the mode partition coefficient k²of multimode DFB lasers is very small and at most 0.02 while that of FP lasers biased at the threshold level is 0.03 to 0.12. The numerical evaluation of the mode partition effect in two-mode DFB lasers suggests that a 20- dB suppression of the satellite mode power is enough to achieve a repeater spacing of over 100 km in the 280 Mbit/s fiber-optic transmission system with less than 0.1-dB power penalty.     

Analysis of high-frequency thermal noise of enhancement mode MOS field-effect transistors

The high-frequency thermal noise in the drain and the gate of an enhancement mode MOS field-effect transistor was analyzed by using the transmission line model of the channel. The analysis gave the mean squared noise current generators of the drain and the gate and their correlation. The correlation coefficient of the drain and the gate noise was zero for zero drain voltage and was 0.395j at saturation. The noise figure of the MOS field-effect transistor was calculated from the result of the analysis. The high-frequency noise characteristics of an MOS field-effect transistor were similar to those of a junction gate field-effect transistor.     

Ni过渡层对Co/Cu/Co三明治膜微结构及巨磁电阻性能的影响

本文利用原子力显微镜对具有不同厚度Ｎｉ过层的Ｃｏ５．０ｎｍ／Ｃｕ３．５ｎｍ／Ｃｏ５．０ｎｍ三明治在各个制备阶段样品的表面形貌进行了系统的研究,并结合Ｘ射线衍射的结果,发现Ｎｉ过渡层可以使Ｃｏ／Ｃｕ／Ｃｏ三明治的界面平整,并形成强的（１１１）织构,从而导至瓣巨磁电阻值增大和矫顽力减少。电阻率的分析是表明过厚的Ｎｉ过渡层由于分流效应的存在会削弱材料的巨磁电阻值。     

Efficiency improvement of the traveling-wave interaction process

Experimental evidence that conventionally designed, uniform-period traveling-wave amplifiers are potentially highly efficient devices is presented. Experiments with a traveling-wave re-entrant cavity tube and with a two-helix tube show that substantial improvement is possible when the RF energy of the so-called beam of a saturated traveling-wave tube is used. Tests reported here on the two-helix tube realized efficiencies greater than 43 percent.     

A revision of the traveling-wave monopole model

Two time-domain electromagnetic emanation models are introduced into emission security (EMSEC) researches. The standing-wave dipole model can be easily gotten from some other references. But the traveling-wave monopole model addressed by Rothwell cannot be applied directly. A charge release coefficient C/sub q/(t) is introduced into this model, which makes the model more adaptive. Near-zone and far-zone fields are discussed of the revised traveling-wave monopole model through an example.     

Theory of space-harmonic traveling-wave interactions in semiconductors

Strong coupling can be obtained between slow space-charge waves in thin biased semiconductors and long-wavelength microwave fields, if the semiconductor is overlaid with an insulated periodic mosaic of tiny metal stripes. Microscopic field perturbations are represented by a set of slow space-harmonic waves traveling in opposite directions, with a standing-wave interference pattern which matches the periodicity of the mosaic. When the carrier drift velocity is approximately synchronized with one of the space-harmonic waves, interaction is enhanced, space-charge waves may be induced, negative-resistance effects may appear, and power may be coupled from the semiconductor into external microwave networks. Theory indicates that the principle can be used to obtain microwave amplification or oscillation in thin biased layers of normal semiconductors such as silicon or germanium. It may also be possible to couple efficiently in this way to traveling Gunn-effect domains in extensive thin layers of gallium arsenide.     

Measurement of high-frequency equivalent circuit parameters of junction and surface barrier transistors

Methods are described for the determination of the high-frequency parameters of junction and surface barrier transistors and involve, in addition to the knowledge of the usual low-frequency parameters, measurement of the product of Ccand the extrinsic base resistancer_{b0},r_{b0}itself, and the alpha cutoff frequency fα. A previously described method is used to determine the productr_{b0}C_{c}, but new methods are described for the measurement ofr_{b0}and fα. The measurements are of "bridge" type, involving simple circuit adjustments for a response null at a single frequency. Typical experimental results are given for transistors having fαvalues as high as 85 mc, Ccvalues down to 2.3 pF andr_{b0}ranging from 45 to 400 ohms. The limits quoted for fαand Ccrefer to surface barrier transistors. Comparison with results derived by alternative methods of measurement show good agreement.     

Generation of high-frequency power oscillation by astable mode arcing with SCR switched inductor

High-frequency high-power oscillation can be generated by a two-terminal and feedback oscillator. In the former, the negative resistance portion is separated from the frequency determining part so these can use a solid-state negative resistance switching device. However, the power output capability is limited in single-stage operation. Using an inductor-switched SCR device, an arc can be established and maintained by astable mode of operation actuating itself as negative resistance for the two-terminal oscillator. With proper selection of circuit parameters, arc geometry, and core material, an efficient sinusoid can be generated and power amplification stages can be avoided as well as circuit Q adjustment for good waveform at the cost of output power.