高功率因数低空载损耗AC／DC电源的研究

介绍了一种宽输入、低空载损耗的90W AC／DC电源。电路由两级组成：以L6561为核心的功率因数校正(PFC)；以L5991A为核心的DC／DC反激变换器。它的主要优点是轻载时通过L5991A的变频功能降低开关工作频率，减小开关损耗，并通过外部电路的设计关掉L6561的PFC功能，从而达到轻载时减少电路的功率损耗的目的。实验表明在空载时，整个电路的输入功率小于1W。     

基于单周期控制的软开关AC／DC变换器

提出了一种软开关单周期控制AC／DC变换器，以Boost电路工作在电流断续状态为例，分析了该电路的工作原理。仿真结果表明，该电路在整个输入电压范围内都能保持软开关特性，达到了高功率因数和高效率的目的。     

基于同步整流的多路输出变换器

提出了基于同步整流技术的多路输出后置调节方法，以实现各路输出电压的高精度自动稳压控制，并详细分析了电路的工作过程和主要参数的设计。仿真分析和实验表明；该方法具有电路结构简单、控制方便、输出电压稳定、精度高等优点，是一种实用的多路输出实现方案。     

LC滤波的三相桥式整流电路网侧谐波分析

对于广泛使用的三相桥式整流电容滤波电路，在直流侧接入电抗器是提高电路输入功率因数降低谐波电流的有效方法。通过分析得出了电路各项输入指标与参数间的理论关系式，为电路分析设计提供了有效的工具。仿真与实验证明了结论的正确性。     

电流源高频交流环节AC/AC变换器研究

提出了基于反激F1yback变换器的电流源高频交流环节AC/AC变换器电路结构与拓扑族。该电路结构由输入周波变换器、高频储能式变压器、输出周波变换器以及输入、输出周波变换器构成，能够将一种不稳定畸变的交流电变换成问频率稳定的正弦交流电压；该电路拓扑族包括单四象限功率开关式、推挽式、半桥式、全桥式等四种电路。以单四象限功率开关式电路拓扑为例，分析研究了这类变换器工作模式、稳态原理与电压瞬时值反馈控制策略，给出了变换器的外特性曲线、关键电路参数设计准则。原理试验结果证实了这类变换器新概念的正确性与先进性。     

扩展PLC控制系统I／O点的方法探讨

在PLC控制系统设计中，通过合理地高计硬件电路和软件编程，可有效地减少PLC的I／O点数，弥补I／O点不足的问题。本文以SIEMENS S7-200PLC为例，从硬件电路、软件编程、硬件与软件结合三个方面探讨PLC系统I／O点数的扩展方法。可以降低成本，提高系统的性价比比，具有一定的实用价值。     

正向型多谐振DC－DC变换器的不足与改进

分析了正向型多谐振ＤＣ－ＤＣ变换器的不足，并提出了改进电路。实验结果表明，改进电路降低了原有电路存在的高电压应力，从而提高了变换器的效率。     

通信用正激式DC／DC模块电源设计

简述ＤＣ／ＤＣ电源模块设计中常用的正激式电路的原理，并由此提高一款效率更高、体积更小、更简洁、无箝位绕组的改进型电路。同时给出了测试数据以供参考。     

多灯管并联电子镇流器的研究

从开关器件应力，多支灯管工作的可行性等角度，介绍和分析了电子镇流器的电路拓扑，提出了一种新的电路LCLC吕并联谐振变换器，介绍了其工作原理并给出了实验结果。     

LIM331与PIC16F73单片机的连接与驱动

介绍了一种应用WF转换器LM331芯片组成的A／D转换电路，它具有接线简单，价格低廉，转换精度高等特点，而且LM331芯片在转换过程中不需要软件程序驱动，与AD574等需要软件程序控制的A／D转换电路相比，使用方便。     

七频段金属外壳手机天线的设计

提出了一种应用在金属外壳手机终端上,实现了-6dB以下的带宽为800~960 MHz,1 710~3 000 MHz频段的天线设计。为了保证辐射性能和所需带宽,在金属的手机外壳的短边上开宽为2mm的U型槽,在馈电处采用电容匹配和一个可切换的电路接地枝节实现GSM850/900 (824~960 MHz),DCS/PCS/UMTS2100(1 710~2 170 MHz),LTE2300/2500 (2 300~2700 MHz)七个频段的覆盖。手机尺寸为152 mm×72 mm×6.8 mm,天线的净空区域为7 mm×70 mm。通过实物测试,手机天线的辐射效率,在低频824~960 MHz频段中为38%~46%,在1 710~2 700 MHz中,辐射效率为可达38%~64%。该天线具有很好的辐射性能,适合应用于金属外壳的移动终端中。     

Biological effects of narrow band pulsed electric fields

This paper describes the process of narrow band pulsed electric fields (NPEFs) and its effect on mammalian cells. The NPEF consists of a pulse modulated sinusoidal wave (PMSW), which allows delivery of well-defined electric fields in terms of frequency, field strength and deposition energy to the biological systems. 100 mus long sinusoidal electric fields with a frequency of 0.02, 2 or 50 MHz and field strengths of up to 2 kV/cm are applied to CHO cells with variation in the DNA density in the cells investigated by means of Acridine Orange assay. The experiments indicate that 50 MHz fields cause DNA degradation without cell membrane defects, while 0.02 MHz fields lead to an increase in membrane permeability which is similar to the effect known as electroporation. The intermediate frequency of 2 MHz influences both the membrane and DNA. It is demonstrated that the MHz range narrowband electric fields with the amplitude level of 1 kV/cm cause intracellular effects in mammalian cells.     

2Mb/2 MHz参考时钟转换设备的系统设计与实现

讨论了2Mb/2MHz参考时钟转换设备的基本性质，应用、系统结构及其实现。     

瞬态过程分析测试系统

介绍一种基于ＰＣ机的瞬态过程分析测试系统，该系统可用于爆炸、光脉冲、振动和材料破坏等各种非周期性随机信号的分析测试；系统采样速度四档可调，最高可达２０ＭＨｚ，其它分别为１０ＭＨｚ，５ＭＨｚ和２．５ＭＨｚ，以适用于不同速度的信号，采用数据存储与计算机复用存储器技术，计算机可马上对所采集的数据进行处理，免去数据传送的过程，用存储器页面管理虚存技术，解决了大数据量存储问题；用交叉存储技术，解决了存储器速     

基于有限元法的高频开关电源PCB地线设计电磁兼容分析

本文提出一种通过在高频开关电源PCB关键信号附近进行地线网格设计的方法,来减少高频开关电源PCB的辐射电磁干扰。基于有限元方法,分别对高频开关电源地线设计前后的PCB进行近场仿真,仿真结果表明在所选频点120MHz、150MHz、200MHz、600MHz处的近场辐射参数值均变小偏移,且在120MHz频点近电场强度降幅达到3．6374×10v／m,在600MHz近磁场强度降幅达到80％,强度明显减弱。得出在高频开关电源PCB设计时进行合理的设计地线,可以很好地改善开关电源的电磁兼容性。     

NMR microscopy of single neurons at 500 MHZ

Previous NMR microimaging studies at 360 MHz have demonstrated a clear differentiation between the nucleus and cytoplasm in isolated single neurons. In particular, theT ₂ of the cell nucleus is 2.5 times larger than that of the cytoplasm. In order to determine the magnitude of possibleT ₂ ^* influences on these observations, images of single cells have been obtained at 500 MHz using spin-echo and line-narrowing sequences. Comparison of the images acquired by the two sequences, and of the spin-echo images at 360 and 500 MHz, imply that anyT ₂ ^* contributions are relatively small. Consequently, the measuredT ₂ differences in spin-echo imaging represent a true difference in theT ₂ relaxation in the two cellular compartments.     

任意频点双混频时差测量方法及仪器的研究

介绍了采用双混频时差法研制的任意频点比对测量系统,媒介频标采用DDS代替了传统的调偏振荡器,采用双混频时差法原理,研发一种1~30 MHz频率范围内任意频点的时差、频差比对分析系统。系统比对测量频率1~30MHz,采样时间100 ms~106s;本底噪声(1 s)为5MHz/10MHz优于5×10-13,其他频点优于1×10-12。测量系统通过软件算法可以测量稳定度、准确度、相位差、老化率。     

Channel Characterization for Indoor Power-Line Networks

Power-line networks are promising mediums by which broadband services can be offered, such as Internet services, voice over Internet protocol, digital entertainment, etc. In this paper, an analysis of delay spread, coherence bandwidth, channel capacity, and averaged delay in the frequency bands up to 100 MHz for typical indoor power-line networks are studied. Earlier studies for indoor power-line networks considered frequencies up to 30 MHz only and earlier works have shown that at these frequency bands, the data rates are generally low and are inefficient for digital entertainment in comparison with wireless local-area networks standards, such as IEEE 802.11 n. In this paper, it is shown that at 100 MHz, the average channel capacity for typical indoor power-line networks can be up to 2 Gb/s and it is found that by increasing the number of branches in the link between transmitting and receiving ends, the average channel capacity decreases from 2 Gb/s to 1 Gb/s (when the number of branches was increased by four times for a power spectral density of -60 dBm/Hz). At the same time, the coherence bandwidth decreased from 209.45 kHz to 137.41 kHz, which is much better than the coherence bandwidths corresponding to 30-MHz systems. It is therefore recommended to operate the indoor power-line networks at 100-MHz bandwidths for a wide variety of broadband services.     

Indoor Power-Line Communications Channel Characterization up to 100 MHz—Part II: Time-Frequency Analysis

Estimations of coherence bandwidth and time-delay parameters from wideband channel sounding measurements made in the 30 kHz-100 MHz band in several indoor environments are described in and taken back in this paper. Powerline communications (PLC) modems rather see a channel which starts almost from 2 MHz . A comparison between coherence bandwidth and time-delay parameters estimated in both frequency bands 30 kHz-100 MHz and 2 MHz-100 MHz is elaborated in this paper. Results are intended for applications in high-capacity indoor power-line networks. The investigation is aimed to show that the PLC channel studies in a band starting from a frequency lower than 2 MHz distorts the real values that an implementer should take, as the PLC modem see only the frequencies from 2 MHz. The coherence bandwidth and the time delay parameters are estimated from measurements of the complex transfer functions of the PLC channels. For the 30 kHz-100 MHz frequency band, the 90 th percentile of the estimated coherence bandwidth at 0.9 correlation level stay above 65.5 kHz and below 691.5 kHz. It was observed to have a minimum value of 32.5 kHz. The maximum excess delay spread results show that 80% of the channels exhibit values between 0.6 s and 6.45 s. And a mean rms delay spread of 0.413 s is obtained. The passage to the 2 MHz-100 MHz frequency band induced an increase of the coherence bandwidth, whose min value is brought back to 43.5 kHz, and an important reduction of the time delay parameters: The min, max, mean, and standard deviation values of the maximum excess delay are almost divided by 2. For the twice frequency bands, this paper studies, also, the variability of the coherence bandwidth and time-delay spread parameters with the channel class , and thus with the location of the receiver with respect to the transmitter, and finally relates the rms delay spread to the coherence bandwidth.     

FeCoSiB单层和FeCoSiB/Cu/FeCoSiB多层磁弹性膜应力阻抗性能研究

用磁控溅射法在玻璃基片上制备了FeCoSiB单层膜和FeCoSiB/Cu/FeCoSiB多层膜,并进行磁场退火热处理以消除残余应力和形成磁场织构.薄膜的磁性能采用振动样品磁强计(VSM)进行测试,采用HP4275A型阻抗分析仪在200kHz～10MHz频率范围内测试了薄膜的应力阻抗(SI)效应.结果表明,磁场退火热处理可形成感生磁各向异性以及提高薄膜的SI效应,在10MHz测试频率下,FeCoSiB薄膜的△Z/Z可达1.5%,而FeCoSiB/Cu/FeCoSiB的可达8%.随着测试频率下降到1MHz时,薄膜的SI效应显著下降.