井下噪声的频谱分析

噪声是一种普遍存在于各种环境的有害因素。针对矿井下恶劣的环境,用噪声振动分析测试仪对井下的压风机、局扇和风锤的噪声信号进行数据采集及分析,得到压风机、局扇和风锤的最大噪声级强度分别为101.3、104.4和120 dB,并明确了噪声源的分布规律。用DSO-2902数字存储示波器分析得出了噪声的频谱成分和频谱结构:移动压风机的频率为20 Hz~3 kHz,局扇的频率为20 Hz~4.5 kHz,风锤的频率范围为20 Hz~10 kHz。     

A solid-mounted resonator-oscillator-based 4.596 GHz frequency synthesis

This paper describes a 4.596 GHz frequency synthesis based on a 2.1 GHz solid mounted resonator (SMR) voltage-controlled oscillator (VCO). The SMR oscillator presents a chip size lower than 2 mm(2), a power consumption of 18.2 mW, and exhibits a phase noise of -89 dBc/Hz and -131 dBc/Hz at 2 kHz and 100 kHz offset frequencies, respectively. The VCO temperature-frequency dependence is measured to be -14 ppm∕°C over a range of -20°C to 60°C. From this source, a low noise frequency synthesizer is developed to generate a 4.596 GHz signal (half of the Cs atom hyperfine transition frequency) with a phase noise of -81 dBc/Hz and -120 dBc/Hz at 2 kHz and 100 kHz from the carrier. The frequency synthesis output is used as a local oscillator in a Cs vapor microcell-based compact atomic clock. Preliminary results are reported and discussed. To the authors knowledge, this is the first development of a SMR-oscillator-based frequency synthesizer for miniature atomic clocks applications.     

变频循环泵振动噪声特性试验研究

为了较为系统地理解变频循环泵的振动噪声特性,以一台比转速为200和最高转速为5600r/min的变频循环泵为研究对象,在背景噪声小于16dB的半消音室和固有频率小于10Hz的振动试验台的试验条件下,对不同流量和转速下的船用循环泵振动噪声特性进行深入的试验研究。试验结果表明:循环泵的总体噪声水平低于66 dB(A),水力诱导的空气传递噪声小于3dB(A);噪声的主要激励频率为工频及谐波,总体结构振动烈度低于1.1mm/s,振动烈度与转速具有良好线性函数关系;结构振动烈度的大小排序为电机、法兰、电机座和泵体.     

A low phase noise microwave source for atomic spin squeezing experiments in 87Rb

We describe and characterize a simple, low cost, low phase noise microwave source that operates near 6.800 GHz for agile, coherent manipulation of ensembles of (87)Rb. Low phase noise is achieved by directly multiplying a low phase noise 100 MHz crystal to 6.8 GHz using a nonlinear transmission line and filtering the output with custom band-pass filters. The fixed frequency signal is single sideband modulated with a direct digital synthesis frequency source to provide the desired phase, amplitude, and frequency control. Before modulation, the source has a single sideband phase noise near -140 dBc/Hz in the range of 10 kHz-1 MHz offset from the carrier frequency and -130 dBc/Hz after modulation. The resulting source is estimated to contribute added spin-noise variance 16 dB below the quantum projection noise level during quantum nondemolition measurements of the clock transition in an ensemble 7 × 10(5) (87)Rb atoms.     

压电振子及流体对泵近场噪声的影响

研究了压电振子的弯曲振动形变及振动辐射噪声.首先建立压电泵压电振子振动方程,导出弯曲振动形变函数;提出用微平面活塞振动理论简化压电振子振动模型,推导了近场声压理论计算方程及泵内流体对泵噪声贡献量方程;最后把理论计算结果与试验结果进行比较分析,分别得出在不同频率下压电振子及泵内流体对泵噪声贡献的大小.在输入频率为50 Hz时,泵噪声的理论值为45 dB,实际值为37 dB,泵内流体对泵噪声的影响较大,实际值与理论值的相对误差为21.6%;在输入频率为120 Hz时,泵噪声的理论值为61 dB,实际值为62 dB,泵内流体对泵噪声的影响较小,实际值与理论值的相对误差为1.6%,证明了本研究所提出理论的正确性.     

短波频率合成器中DDS技术的具体应用与分析

介绍一种新型、实用的短波频率合成器。该频率合成器将直接数字频率合成器(DDS)技术和传统的锁相环(PLL)技术有机地结合起来,具有频率转换速度快、分辨率高、相位噪声低、可靠性高等优点。分析了DDS技术的工作原理及其在短波频率合成器中的应用,给出了具体方案及实施结果。     

A precision frequency synthesizer with direct digital synthesis for a low-field magnetic-resonance imager

A frequency synthesizer of the microwave spectrometer of a magnetic-resonance imager (MRI) with a 0.06-T intensity of the basic magnetic field is described. The synthesizer is based on a programmable logic integrated circuit and a direct digital synthesis microcircuit. The synthesizer is capable of operating in a range up to 70 MHz with a 3-μHz tuning step, allowing one to use it in MRI systems with a basic magnetic intensity of up to 1.5 T. The unit is intended to store up to 16348 frequency values in its random-access memory, and the switching is carried out by a logic signal, the source of which can be, e.g., a pulse train programmer of the microwave spectrometer. The frequency switching rate is 1 kHz and higher. The synthesizer is loaded through a USB 2.0 standard interface.     

Estimating the efficiency of digital filtering of periodic and impulse noise based on local statistics

This paper presents the results of modeling of several digital filtering algorithms of the ADC output codes for suppressing periodic and impulse noise signals and normal noise. The algorithms were tested in LabVIEW. It was shown that they provided real-time suppression of normal and impulse noise to a level from ?57 to ?63 dB.     

一种高精度直接数字式频率源的设计

直接数字频率合成(DDS)是近年来发展非常迅速的一种新型频率合成技术,它具有频率分辨率高、相位噪声低、频率转换时间短等特点。首先简要介绍DDS的工作原理及其性能,然后主要阐述如何利用AD9851芯片设计一个高精度直接数字式合成频率源。     

A low-noise microwave signal source

An ultrafast electron diffraction setup is described and requirements for a signal source are determined. Taking into account these requirements, a low-noise microwave signal source with a 6.2-GHz-frequency and ≥6-W power, and 6.1-GHz additional frequency and ≥5-mW power is designed. The phase noise level at the output frequency was no higher than −115 dB/Hz when the offset from the carrier was 10 kHz. The manufactured setup was supplied to the Max-Planck Institute (Garching, Germany), experiments were performed, and the first results were obtained.     

在DDS波形发生器中相位截尾噪声的分析和抑制

直接数字频率合成技术（DDS）是近年来发展迅速的一种新的频率合成技术。全数字化的结构赋予了它很多的优点：频率转换时间短，频率分辨率很高，输出相位连续，容易集成和易编程控制等，当然也就引进了数字化结构的缺点－－输出杂散在。本文对DDS波形发生器中由于相位截尾所产生的杂散进行分析，并提出抑制相位截尾噪声的方法，给出了实现方法和实验结果。     

A Digital Synthesizer of Ultralow Frequencies for Biophysical Investigations

The synthesizer forms pulses in a frequency range of 0.1–10 Hz with a control step of 0.1 Hz. The generated frequency is additionally controlled with the help of a built-in digital frequency meter. An operation mode used in electro-acupuncture after Voll is provided. In this mode, the device generates a 1.2-V dc voltage and a current of 5.5–11.25 A. An operation mode with high-frequency (23 MHz) filling of the generated pulses and controlled duty factor and polarity of the pulse sequence is also provided. The device can be controlled either manually from the front board or with the help of a microprocessor.     

一种频谱仪自适应调整扫描带宽的数字信号提取方法

介绍了混合模拟信号和噪声的情况下提取通信卫星数字信号的方法。由于信号频率、3d B带宽、信噪比和信号电平属于待测参数 ,因此需要程控频谱仪自适应地调整扫描带宽 ,以正确测量出数字信号的频率、3d B带宽和信噪比等特征。实践证明 ,该方法相对于人工读取频谱仪方法具有效率高、准确率高和实时性等优点。     

Simulation on a car interior aerodynamic noise control based on statistical energy analysis

How to simulate interior aerodynamic noise accurately is an important question of a car interior noise reduction. The unsteady aerodynamic pressure on body surfaces is proved to be the key effect factor of car interior aerodynamic noise control in high frequency on high speed. In this paper, a detail statistical energy analysis (SEA) model is built. And the vibra-acoustic power inputs are loaded on the model for the valid result of car interior noise analysis. The model is the solid foundation for further optimization on car interior noise control. After the most sensitive subsystems for the power contribution to car interior noise are pointed by SEA comprehensive analysis, the sound pressure level of car interior aerodynamic noise can be reduced by improving their sound and damping characteristics. The further vehicle testing results show that it is available to improve the interior acoustic performance by using detailed SEA model, which comprised by more than 80 subsystems, with the unsteady aerodynamic pressure calculation on body surfaces and the materials improvement of sound/damping properties. It is able to acquire more than 2 dB reduction on the central frequency in the spectrum over 800 Hz. The proposed optimization method can be looked as a reference of car interior aerodynamic noise control by the detail SEA model integrated unsteady computational fluid dynamics (CFD) and sensitivity analysis of acoustic contribution.     

2D数字伺服阀的简介

该文主要阐述了2D数字伺服阀的结构原理及工作原理,建立了电—机械转换器的数学模型,设计了2D数字伺服阀控制器。为了获得电—机械转换器及样阀的性能,对其进行了实验研究,实验结果表明,该电—机械转换器具有良好的频率特性,对应-3dB、-90°的频宽约为250Hz;2D数字伺服阀具有良好的静态、动态性能,其分辨率与滞环皆在1%以内,阀在25%满量程正弦输入信号下,对应-3dB、-90°的频宽约为130Hz。     

某机载雷达频综器相噪故障诊断与试验分析

针对某机载雷达的频综器在振动环境下相位噪声(相噪)相比静态环境下恶化明显,不符合动态指标要求的情况进行故障诊断和试验分析。通过相噪主要来源分析和振动特性试验,探明了振动环境下导致相噪恶化的主要原因,并提出改进方案。最后对改进后频综器的相噪水平进行试验评估,结果显示频综器的相噪全面达到指标要求,成功解决了该频综器在振动环境下相噪恶化的问题。     

平面电极型MEMS电化学地震传感器

针对传统电化学地震传感器的加工工艺成本高、一致性差等问题,设计了一种新的平面电极型微机电系统(MEMS)电化学地震传感器结构。建立了平面电极型MEMS电化学地震传感器的计算模型,通过Comsol多场耦合数值模拟分析方法,对影响传感器的结构参数如:电极宽度、电极间距、流道高度等进行了计算和优化。采用MEMS表面工艺和准LIGA工艺,制备了平面电极型MEMS电化学地震传感器。最后,与采用传统方法精密加工的MET2003器件进行了频率响应和微震动的对比测试。实验结果表明:与MET2003器件相比,平面电极型MEMS电化学地震传感器的带宽从1Hz扩展到了30Hz,两种器件的采集结果具有很好的相关性和一致性,相关系数为0.887,在1Hz处的噪声低于120dB。     

A direct digital synthesizer of compound wideband signals

Principles of construction and structural and circuit designs of direct digital synthesizers based on the method of direct digital frequency and signal synthesis are described. The block and circuit diagrams of the direct digital synthesizer of compound wideband signals are presented. This synthesizer is used to synthesize signals with the amplitude, frequency, and phase modulation in a frequency range from 0.001 to 200MHz.     

基于双DSP的噪声模拟试验系统研究

针对多参数复合环境试验系统中噪声环境的生成要求,提出了一种以双数字信号处理器(DSP)为核心的噪声环境模拟系统的控制结构.该系统与上位机通讯采用异步串口,DSP之间传输数据或命令采用同步串口.在对模糊PID算法进行深入分析和研究的基础上,利用该控制算法对测量噪声信号进行了频域控制,从而实现了噪声模拟系统的闭环自动控制....     

(Φ)6通径2D数字阀高频电-机械转换器的研究

为提高数字伺服阀的频率特性和响应速度,对弹射系统用(Φ)6通径,2D数字阀选用低惯量的两相混合步进电机作为其电-机械转换器,介绍了其工作原理并设计了2D数字伺服阀专用DSP控制器,用电流和位置双闭环算法对其性能进行了实验研究.实验结果表明,该电-机械转换器在幅值100%最大阀开口的阶跃信号输入下,上升时间为5 ms;正...