单次飞行事件噪声等值线计算新方法的研究

针对现行单次飞行事件噪声等值线计算中存在的需要布点、插值繁琐等缺点,提出单次飞行事件噪声等值线的分段函数计算模型,将航迹各分段产生的噪声等值线表示成函数形式.该模型具有在计算单次飞行事件噪声影响等值线时不需要布点、程序设计简单等优点.根据某型飞机的基础飞行数据,将分段函数模型与常规模型的计算结果进行了对比,结果表明两种...     

两个宽带噪声矢量场模型的空间相关特性

针对宽带噪声矢量场的空间相关特性问题,文章讨论了各向同性噪声模型和表面噪声模型。在高频近似条件下,根据射线声学理论和简谐平面行波满足的欧拉公式,采用时域建模方法分别建立了宽带各向同性噪声和表面噪声矢量场模型。给出了噪声场相关函数的积分表达式和竖直方向空间相关系数的解析表达式。数值分析结果表明,相较于窄带噪声矢量场,宽带噪声矢量场各分量空间相关系数振荡幅度更小,随空间两点间距的增大更快地趋近于零;噪声源指向性对表面噪声场竖直方向上的空间相关特性的影响显著。相较于已有的宽带噪声空间相关系数计算方法,文中模型无需使用傅里叶合成方法,可通过时域建模直接获得宽带噪声空间相关函数。     

航空发动机风扇噪声经验预测方法分析

随着飞机广泛使用的涡轮风扇发动机涵道比的不断提高,风扇噪声在飞机总噪声中占有越来越突出的地位.因此介绍用于预测风扇噪声水平的三种经验模型:Heidmaan模型,Konto-Janardan-Gliebe模型及Hough-Weir模型.编写风扇噪声经验预测方法程序并计算飞机降落过程中某航空发动机风扇的远场噪声水平.三种模型计算结果对比表明,Heidmann模型预测值普遍较大,Hough-Weir模型与上述两种模型趋势稍有不同.     

统计能量分析在汽车车内噪声分析中的应用

建立了用于汽车车内高频噪声分析的整车SEA模型，介绍了工程设计中车身子系统SEA模型和整车噪声传递路径分析方法的应用，最后以分析实例说明了统计能量分析在汽车车内噪声性能设计中的适用性和准确性。     

多反馈带通滤波电路自噪声分析及仿真

为降低电路自噪声,研究了多反馈带通滤波电路,建立了电路自噪声模型,分析了各元器件对输出噪声的影响,给出了噪声功率频谱密度计算公式,通过Multisim噪声仿真及实测数据验证了模型的正确性。     

高速列车轮轨滚动噪声的理论预估

本文以高速列车噪声控制问题为背景，建立了一种轮轨滚动噪声的理论预估模型，并用已有实验结果验证了本模型的可行性，接着又利用该模型分析了轮轨系统参数对滚动噪声的影响。     

高速列车运行产生的轮轨噪声预测

随着列车运营速度的提高，轮轨噪声是非常重要的噪声源。为了预测和控制高速列车在受到轮轨表面粗糙度和轮轨结构表面的不连续几何缺陷等激起的轮轨噪声，本文综合应用了车辆-轨道耦合动力学理论、随机振动理论和声辐射理论，建立了轮轨噪声预测模型，开发了相应的预测软件WRNOISE，通过与已有的轮轨噪声预测模型TWINS、STTIN及实测数据的比较，研究表明：（1）本文所建模型的计算结果与TWINS模型的结果在噪声主频上是一致的，并且变化趋势也是一致的，这充分验证了本文所建模型的正确性。（2）跟STTIN模型相比，WRNOISE模型在预测车轮和钢轨噪声时更加充分，考虑了车轮的辐板和钢轨轨腰横向振动噪声的贡献。（3）跟有砟和无砟轨道路基区段噪声实测结果相比，WRNOISE模型计算结果与实测结果有一定差异，但从轮轨噪声辐射主导频率看，变化趋势基本一致。     

潜艇辐射噪声声源级经验公式修正

潜艇辐射噪声的声源级大小会直接影响潜艇的隐蔽性，潜艇的辐射噪声与航速密切相关。分析了目前主要模型的不足，在此基础上对其中一个模型进行了改进。新模型考虑了临界航速的影响，兼顾了不同潜艇类型噪声大小差别较大的特点。仿真结果表明：该模型更好地符合潜艇噪声随航速变化的实际情况，更具有普遍适用性。     

边界噪声检测耦合差分曲率驱动的脉冲噪声图像降噪

目的提出边界识别噪声检测耦合差分曲率驱动扩散模型的脉冲噪声图像降噪算法,用于高密度(≥50%)脉冲噪声的消除。方法基于传统边界识别噪声检测BDND,定义噪声像素分类规则,设计新的边界识别噪声检测M-BDND机制;定位噪声边界,精确识别噪声像素点,形成噪声区域与完好区域;利用噪声像素点的周边信息形成掩码,对其进行修复,有效填补噪声像素点,而在完好区域只将像素点进行复制;构造了差分曲率驱动扩散模型控制噪声像素区域的扩散过程,完成图像复原,并对该模型进行了数值分析。结果与当前图像降噪技术相比,对于等密度随机值脉冲噪声而言,提出算法的误检率与虚警率更低;在噪声密度高达90%时,仍然具有可接受的降噪效果,能够更好地保留原图的边缘与细节特征,且复原图像的一维行距像更好,与真实图像的吻合程度高。结论该算法可用于高密度脉冲噪声的图像降噪处理。     

汽车刹车装置摩擦噪声的试验研究

本文对刹车时发出的尖叫摩擦噪声的机理进行了研究。通过对不同工况下摩擦噪声及振动的测量和频谱分析，以及对刹车装置动力学模型的分析与研究表明：尖叫摩擦噪声是由摩擦引发的高频自激振动所致。同时还探讨了这种噪声产生的原因及不同工作条件对其影响的规律。     

Residual phase noise measurements of VHF, UHF, and microwavecomponents

The results of residual phase noise measurements on a number of VHF, UHF, and microwave amplifiers, both silicon (Si) bipolar junction transistor (BJT) and gallium arsenide (GaAs) field effect transistor (FET) based, electronic phase shifters, frequency dividers and multipliers, etc., which are commonly used in a wide variety of frequency source and synthesizer applications are presented. The measurement technique has also been used to evaluate feedback oscillator components, such as the loop and buffer amplifiers, which can play important roles in determining an oscillator's output phase noise spectrum (often in very subtle ways). While some information has previously been published related to component residual phase noise properties, it generally focused on the flicker noise levels of the devices under test, for carrier offset frequencies less than 10 kHz. The work reported herein makes use of an extremely low noise, 500 MHz surface acoustic wave resonator oscillator (SAWRO) test source for residual phase noise measurements, both close-to-and far-from-the-carrier. Using this SAWRO-based test source at 500 MHz, we have been able to achieve a measurement system phase noise floor of -184 dBc/Hz, or better, for carrier offset frequencies greater than 10 kHz, and a system flicker phase noise floor of -150 dBc/Hz, or better, at 1 Hz carrier offset. The paper discusses the results of detailed residual phase noise measurements performed on a number of components using this overall system configuration. Several interesting observations related to the residual phase noise properties of moderate to high power RF amplifiers, i.e., amplifiers with 1 dB gain compression points in the range of +20 to +33 dBm, are highlighted     

Low phase noise operation of microwave oscillator circuits

In this paper, we describe a theoretical basis, leading to new results, on the general conditions to be fulfilled by oscillator circuits to achieve a very low phase noise. Three main conditions must be fulfilled by a transistor oscillator circuit to reach the minimum phase noise. The energy stored in the resonator must be maximum. Its transfer to the controlling voltage port of the transistor current source must be first maximized. A possible conversion noise at the transistor output port will be also minimized by maximizing the energy transferred to that port. The proposed method has been applied to an experimental oscillator set up with a PHEMT transistor. A state-of-the-art phase noise of -80 dBc/Hz at 100 Hz offset from carrier with a 1/f(3) slope has been measured at room temperature with a 9.2 GHz, oscillator. The application of these new results to free-running oscillator circuits with one-stage then multistage transistor amplifiers demonstrate clearly the validity of the design method. The efficiency of this design method and its ease of use represent a real breakthrough in the field of low noise transistor oscillator circuit design.     

偏相干分析在风洞噪声源识别中的应用

噪声源识别对噪声控制具有重要意义。在建立多输入/单输出系统噪声模型,分析介绍噪声源贡献量测量及偏相干分析技术的基础上,给出偏相干函数的条件谱计算公式。针对0.55 m×0.4 m航空声学风洞,拟定噪声测试方案。结合噪声测试数据,表明风洞主要噪声源识别的有效性。     

Measurement and analysis of a microwave oscillator stabilized by a sapphire dielectric ring resonator for ultra-low noise

Phase-noise measurements are presented for a microwave oscillator whose frequency is stabilized by a whispering gallery mode sapphire ring resonator with Q of 2x10(5). The nature of the mode, which involves little metallic conduction, allows nearly full use of the very low dielectric loss in sapphire. Several mode families have been identified with good agreement with calculated frequency predictions. Waveguide coupling parameters have been characterized for the principal (lowest frequency) mode family, for n=5 to n =10 full waves around the perimeter. For a 5-cm wheel resonator in a 7.6-cm container, Q-values of above 10(5) were found at room temperature for all of the modes in this sequence. Coupling Q-values for the same modes ranged from 10(4) (n =5) to 10(5) (n=10) for a WR112 waveguide port at the center of the cylinder wall of the containing can. Phase noise measurements for a transistor oscillator locked to the n=10 (7.84-GHz) mode showed a 1/f(3) dependence for low offset frequencies, and a value of L(f)=-55 dB/Hz at an offset of 10 Hz from the carrier. The oscillator shows phase noise below the previously reported for any X-band source.     

NIM相位噪声测量系统的改造

介绍NIM(中国计量科学研究院)相位噪声测量系统的组成,讨论HPE5501B在微波信号源相位噪声测量中的应用,即将HPE5501B的测量频段由1.6GHz扩展到18GHz的方法,并给出测量系统噪声本底的计算方法及典型测量结果     

光学测量系统信噪比优化方法研究

在光学测量中常常受低信噪比问题的影响,导致测量结果的不确定度增大。近红外波段双向反射分布函数（BRDF）的测量由于红外信号强度偏弱,易受环境干扰,面临的低信噪比问题尤其突出。光学测量系统的信噪比问题一般产生自探测系统,对于红外测量系统来说,经常使用斩波器、锁相放大器进行弱信号测量,但同时也引入了噪声问题。因此,本文针对近红外波段BRDF测量信噪比问题,从探测器、斩波器、锁相放大器三部分着手,分析噪声来源并针对性地提出抑制方法与优化措施,以提升信号信噪比。优化后的测量系统较优化前抗噪声能力提高,可重复性由优化前的2.1%提升到1.6%。     

基于波束形成方法的货车车外加速噪声声源识别

综合基于波束形成的噪声源识别方法和外场车外加速噪声测量技术,构建一套完整的针对运动声源的车外加速噪声外场声源识别测试系统,给出了相应的测试计算流程与方法。利用该系统完成货车车外加速噪声声源识别试验,确定发动机为该货车车外加速噪声的主导噪声源,且对应最大噪声时刻发动机转速为２４００ｒ／ｍｉｎ。进一步的发动机噪声源识别结果表明：涡轮增压器、发电机、气缸盖罩是其主要噪声辐射源。     

Wideband on-wafer noise measurement setup for noisecharacterization of active devices in the low VHF band

This paper addresses a new wideband on-wafer measurement test set designed for noise characterization of microwave active devices over the frequency range of 300 kHz to 150 MHz. Noise parameters obtained from the multiple impedance technique on a GaAlAs/GaAs heterojunction bipolar transistor (HBT) from 300 kHz to 70 MHz are reported and compared with low-frequency noise data. Investigation of the excess noise sources of III-V HBT's is performed well above the 100 kHz frequency limit of standard dynamic signal analyzers and noise modeling of these devices is reported     

Optimization of an ultra low-phase noise sapphire--SiGe HBT oscillator using nonlinear CAD

In this paper, the electrical and noise performances of a 0.8 /spl mu/m silicon germanium (SiGe) transistor optimized for the design of low phase-noise circuits are described. A nonlinear model developed for the transistor and its use for the design of a low-phase noise C band sapphire resonator oscillator are also reported. The best measured phase noise (at ambient temperature) is -138 dBc/Hz at 1 kHz offset from a 4.85 GHz carrier frequency, with a loaded Q/sub L/ factor of 75,000.