晶振减振系统的分析

锁相频率源中,晶振作为参考信号对相噪有着重要的影响。在振动条件下,晶振和锁相频率源输出频率的相位噪声恶化。本文详细分析了振动与相位噪声之间的关系。并得到了减振系统的数学模型,经试验验证根据该模型设计的减振系统能有效的减小振动条件下锁相频率源相位噪声的恶化。     

基于反共振原理的管路吸振器调谐方法

针对船用管路线谱振动传递的抑制问题,提出一种基于反共振原理的管路吸振器调谐方法。该方法利用吸振器带来的反共振物理特性,通过调谐动力吸振器固有频率,改变管路振动传递函数的反共振区域,使需要抑制的线谱频率处于该区域,从而改变管路振动传递特性,实现振动抑制。首先,介绍采用动力吸振器抑制管路线谱振动传递的策略。随后,针对船用管路提出动力吸振器的结构形式及其安装方式。其次,利用结构波理论,阐述基于反共振原理的调谐方法以及调谐步骤。最后,通过实验验证吸振器对某实船管路线谱振动传递的抑制性能。实验结果显示,调谐后的吸振器引入了反共振区域,有效降低了该线谱振动的传递。     

基于声振传递的飞行器噪声振动环境预示方法研究

针对高速飞行器飞行条件下的噪声、振动环境恶劣、复杂、难预示的问题,提出了基于声振传递的飞行器飞行条件下的噪声、振动环境预示方法。采用数值仿真、脉动压力风洞试验或工程分析等方法,获取飞行器在典型工况下的舱外脉动压力场;通过噪声试验或声振耦合仿真分析的方法,得到飞行器声振传递特性;根据获得的舱外脉动压力和声振能量传递特性,结合具体飞行参数得到实际飞行条件下的飞行器声振预示环境。采用该方法对某飞行器开展了振动环境预示研究,经地面及飞行试验验证振动环境量级预示精度可达1.6 dB。提出的基于声振传递的飞行声振环境预示方法可以广泛应用在导弹、火箭等飞行器的精细化环境设计中,对于提高飞行器总体性能、环境适应性和飞行可靠性具有重要的工程意义。     

动力吸振器对有轨电车弹性车轮的减振降噪影响分析

为了评价有轨电车弹性车轮动力吸振器的减振降噪效果,通过实验室测试方法对动力吸振器进行振动噪声测试,并结合理论和仿真来分析其降噪特性。首先,在半消声室分别测试弹性车轮在有无动力吸振器情况下的振动声辐射,测试结果表明：动力吸振器对弹性车轮轴向振动有明显的抑制作用。径向激励下,动力吸振器的降噪量为0.6 dB(A),轴向激励下,动力吸振器的降噪量为2.6 dB(A)。进而,基于动力吸振原理探究动力吸振器的降噪性能,并结合测试图纸建立动力吸振器有限元模型,分析表明：动力吸振器在车轮固有频率2 066 Hz、2 245 Hz和3 837 Hz处降噪效果较好,原因是降噪频率差值在2 %以内,调谐频率和理论最优频率相吻合。动力吸振器在车轮固有频率899 Hz处降噪效果较差,其降噪频率差值为6.26 %,由于调谐减振频率偏离最优同调条件,导致降噪性能的恶化。     

船舶设备激励源载荷转换方法及应用

设备激励源是分析船舶振动噪声特性的输入条件,对其获取方法研究具有重要价值。介绍以自由振速为桥梁的不同安装环境下船舶设备激励源特性转换关系,建立利用台架试验数据估算实船安装环境下设备激励源特性的工程应用方法,并给出应用流程。通过典型船用设备激励源特性测试和计算,提出振动测点布置原则和数据测试要求。设备机脚和基座的振动速度计算结果和实船测试结果吻合良好,表明所采用的船舶设备激励源特性转换方法可应用于船舶振动噪声工程问题分析。     

相位调谐对行星齿轮系统辐射噪声影响的研究

考虑齿轮啮合相位因素得到相位调谐前后各传动齿轮齿数配比,应用集中质量法建立行星齿轮传动系统的动力学模型,计算齿轮箱轴承支撑动载荷。建立单级行星齿轮传动系统齿轮箱的三维几何模型,将动载荷作为激励施加于齿轮箱轴承支撑处,通过有限元法计算得齿轮箱的模态频率和振动响应。在Virtual.lab中建立齿轮箱的边界元模型并导入齿轮箱振动位移响应作为边界条件,应用直接边界元法计算得到相位调谐前后齿轮箱辐射噪声。对比试验结果表明,相位调谐方法可有效地降低噪声,证明相位调谐方法降噪的可行性。     

负压条件下爆炸罐内爆炸引起筒体振动及噪声特性

为了研究负压条件下容器内爆炸引起的振动及噪声特性,研制一套34.8 L抽真空爆炸罐装置。实验用单发8号工业雷管作为爆炸源,采用NuBox8016型爆破振动测试仪、SZ4A型噪声振动测试仪分别测试筒体振动速度及爆炸噪声声压级,并使用快速傅里叶变换(fast Fourier transform,FFT)以及经验模态分解(empirical mode decomposition,EMD)方法对振动信号进行分析。结果表明,随着真空度的提高,筒体峰值振动速度、爆炸噪声声压级均呈下降趋势。当筒体内真空压力为-99 kPa时,爆炸产生的有害效应得到有效衰减,与常压条件相比,峰值振动速度衰减70.0%,最大噪声声压级降低18.3%。通过FFT变换及EMD分解,发现筒体主振频率随着真空度提高,主振频率也随之提高,高贡献率的imf分量个数呈现增多趋势。该实验结果与分析对探究负压条件下爆炸振动及其噪声信号衰减规律,以及真空爆炸工程应用等具有重要指导意义。     

基于机械作动器的振动主动控制实验研究

基于一种新型的可调机械式主动消振器进行控制算法和实验研究,引入一种相位跟踪控制算法,该控制算法可自动识别系统激励力与作动器消振力的相位差,以实现最终消振目的.在实验室环境下,建立结构振动主动消振实验系统,并进行实验研究.实验结果表明,该控制算法在没有预先获得振源结构动力特性的情况下,能实现相位的在线调节,取得很好的消振效果.     

集中驱动式电动车噪声特性分析与试验研究

为了研究电动汽车噪声特性及机理,在分析电动汽车噪声源的基础上进行了整车声振特性台架试验,运用频谱分析、阶次分析和偏相干分析相结合的方法对试验数据进行处理,分析了辅助系统的噪声频域特性,对比了正驱工况和倒拖工况下动力总成振动噪声特性,明确了动力总成噪声对车外噪声的贡献。研究结果为电动汽车整车振动噪声特性优化改善提供了试验支持。     

一种飞行模拟机运动系统的抖振特效建模方法

运动系统是构建飞行模拟机虚拟环境的主要分系统之一,抖振特效模拟是提高运动系统仿真度的重要研究内容。采用正弦加随机振动的基本模型,结合飞机试飞数据中的振动统计数据——加速度功率谱密度,建立抖振特效生成模型。研究基于加速度功率谱密度的抖振参数估计方法,实现正弦分量、随机分量参数的计算。分析典型飞行状态下的振动数据特性,研究抖振特效特征影响参数的提取方法,实现全飞行状态下的抖振特效生成。以抖振参数和特征影响参数为驱动,提出了抖振特效的建模方法。实验结果表明,该方法能有效实现飞行模拟机系统中的抖振特效仿真。同时,也为虚拟现实技术其他应用中振动环境的构建提供一定的借鉴意义。     

用参量法通过LiNbO3晶体产生太赫兹的理论设计

按照参量振荡器的基本原理,从理论上设计了一个太赫兹参量振荡器。根据动量守恒、能量守恒条件以及相位匹配条件,应用铌酸锂(LiNbO3)晶体,给出了理论设计过程。画出了频率在太赫兹波段,波长与折射率的关系曲线,分析了太赫兹参量振荡器的非共线相位匹配条件,确定了晶体形状及其切割角、输出太赫兹波的可调谐范围,并画出了晶体为铌酸锂时相应的曲线,根据有效的输出功率,最后设计出最佳的太参量振荡器的结构。     

A novel microcomputer temperature-compensating method for an overtone crystal oscillator

In this paper, a novel microcomputer temperature-compensating method for an overtone crystal oscillator (MCOXO) is presented. In this method, a ceramic oscillator is chosen, and its output frequency is mixed with the output frequency of an overtone crystal oscillator. A crystal filter is used to suppress the spurious mixing products. A microcomputer is used to control the switch capacitance array that is connected to the ceramic oscillator circuit. The frequency deviation of the crystal oscillator is directly compensated by the output frequency of the ceramic oscillator. As a result, the method is able to overcome the disadvantages of frequency stability degradation and phase noise deterioration that are provoked by adding inductance or frequency multiplication in traditional compensating approaches. At the same time, this method is able to compensate a quite wide frequency range and many types of oscillators, not just crystal oscillators. The experimental compensating results show that, using this method, the frequency-temperature stability of a 100 MHz 5th overtone temperature-compensated crystal oscillator can achieve /spl les/ /spl plusmn/2/spl times/10/sup -6/ for 0-70/spl deg/C.     

An Improved 5 MHz Reference Oscillator for Time and Frequency Standard Applications

An improved 5 MHz reference oscillator for use in time and frequency standards has been developed. This oscillator, using an improved crystal unit, reaches a long term drift rate of less than 1×10-11 per day in a few days. The design includes precautions for reduction of effects of conducted electrical noise on the output frequency. Modular design of functional circuits provides ease of manufacture and uniformity of the product. Stabilized temperature control circuits have been utilized to provide improved oven performance. The oscillator has been tested for the effects on frequency and phase stability of power supply variation, changes in thermal environment, modulation by electrical noise, and mechanical vibration. Phase noise within the range of 100 Hz through 5.0 kHz varies from -120 dB to -125 dB.     

Phase noise measurements of 10-MHz BVA quartz crystal resonators

In this paper, we review a new piece of equipment that allows one to characterize the phase noise of crystal resonators using a phase bridge system with carrier suppression. This equipment allows one to measure the inherent phase stability of quartz crystal resonators in a passive circuit without the noise usually associated with an active oscillator. We achieved a system noise floor of approximately -150 dBc/Hz at 1 Hz and -160 dBc/Hz, at 10 Hz. A SPICE characterization of the carrier suppression system is given. An investigation of the phase modulation (PM) noise in 10 MHz BVA, SC-cut quartz crystal resonator pairs is presented.     

Expected quality factor of a simple tuned oscillator

A positive feedback system oscillating under self-sustained mode is shown to have an extremely high gain. Modeled as one port, the expected Q is much higher than the loaded Q-factor of the resonator. With just thermal noise present, random phase/frequency deviation is linear. Centered about the oscillator frequency omega/(0), noise frequency on both sides is more amplified with decreasing separation distance. Ultimately, frequency pulling may result in synchronous locking with hysteresis, which occurs because a real oscillator displays a truncated limiting curve. Once locked onto a signal, smaller levels are ignored. A new approach to the design and characterization of a simple tuned oscillator is offered: According to the phenomenon of injection locking, there exists an expected quality factor relating the shape of the truncated limiting curve to an ideal curve. In this paper, synthesis and innovative analytical methods of academic interest are revealed: 1) application of the transducer loss method is revised to establish a new method for oscillator characterization; 2) a transparent method of normalizing a two-port network in the presence of white noise is developed; and 3) in quartz crystal controlled oscillators, characterization of the noise originating from an equivalent noise-resistance determined from parameter of the quartz crystal is proposed. It is shown that the two-port model can also be approximated on a one-port basis. In conclusion, a sample of closed-form estimation of expected Q-factor order of magnitude of piezoelectric resonator oscillators is calculated.     

Predicting phase noise in crystal oscillators

In order to predict the phase noise in crystal oscillators an enhanced phase-noise model has been built. With this model, the power spectral densities of phase fluctuations can be computed in different points of the oscillator loop. They are calculated from their correlation functions. The resonator-caused noise as well as the amplifier-caused noise are taken into account and distinguished. To validate this enhanced model, the behavior of a batch of 10 MHz quartz crystal oscillators is observed and analyzed. The tested batch has been chosen in a facility production. Their associated resonators have been selected according to the value of their resonant frequency and their motional resistance. Open-loop and closed-loop measurements are given. The phase noise of the overall oscillator working in closed loop is provided by the usual active method. Theoretical and experimental results are compared and discussed.     

Broad tuning ultra low phase noise dielectric resonator oscillators using SiGe amplifier and ceramic-based resonators

This paper describes the design of very low noise, tunable, X-band dielectric resonator oscillators (DROs) demonstrating phase-noise performance of -135 dBc/Hz at 10 kHz offset. SiGe transistors are used for the oscillator sustaining amplifiers that offer a circulating power of 12 dBm and a gain of 5.4 dB per stage as well as a low flicker noise corner of 40 kHz. A variety of resonator configurations utilising BaTiO₃ resonators are presented demonstrating unloaded Qs from 10 000 to 22 000. These resonators are optimised and coupled to the amplifiers for minimum phase noise where Q_L/Q₀ = 1/2, and hence S₂₁ = -6 dB. To incorporate tuning with low additional phase noise, a phase shifter is also investigated. The theory for the low noise oscillator design is included; experimental results demonstrate close correlation with the theory.