Accurate analytical measurements in the atomic force microscope: a microfabricated spring constant standard potentially traceable to the SI

Calibration of atomic force microscope?(AFM) cantilevers is necessary for the measurement of nanonewton and piconewton forces, which are critical to analytical applications of AFM in the analysis of polymer surfaces, biological structures and organic molecules at nanoscale lateral resolution. We have developed a compact and easy-to-use reference artefact for this calibration, using a method that allows traceability to the SI (Système International). Traceability is crucial to ensure that force measurements by AFM are comparable to those made by optical tweezers and other methods. The new non-contact calibration method measures the spring constant of these artefacts, by a combination of electrical measurements and Doppler velocimetry. The device was fabricated by silicon surface micromachining. The device allows AFM cantilevers to be calibrated quite easily by the 'cantilever-on-reference' method, with our reference device having a spring constant uncertainty of around ± 5% at one standard deviation. A simple substitution of the analogue velocimeter used in this work with a digital model should reduce this uncertainty to around ± 2%. Both are significant improvements on current practice, and allow traceability to the SI for the first time at these nanonewton levels.     

脉冲式动态压力溯源方法研究

动态压力测试在工业领域应用越来越广泛,而可靠的校准技术则是动态压力量值准确的保障,溯源问题一直是制约动态压力校准技术发展的瓶颈。本文以基于激光干涉的可溯源动态压力测量方法为研究对象,针对液体脉冲压力的特点,建立基于牛顿第二定律的脉冲压力测量模型,对各影响因素引入的误差进行分析和测试,通过压力传感器校准试验完成激光干涉测量可行性验证和测量不确定度分析,实现脉冲压力的可靠溯源。     

基于频偏应答的ADCP流速现场校准方法研究

针对声学多普勒流速剖面仪(ADCP)现场校准困难的问题,介绍了一种基于频偏应答的ADCP流速现场校准方法。通过声信号应答器,设置回发信号相对于发射信号的频偏实现速度矢量的模拟,并以频率为溯源量,对ADCP发射的信号及应答器回发频偏信号进行频率校准,进而实现ADCP流速参数的现场校准。研制了一套基于频偏应答的ADCP流速现场校准装置,在实验室消声水池条件下,以四波束300kHz ADCP为校准对象,开展了1～2m/s的流速校准实验,进行不确定度分析。结果表明,该装置对流速校准的不确定度达到1％模拟流速＋7mm/s,验证了该校准方法的可行性。     

频率调制多普勒全场测速实验系统测试

频率调制多普勒全场测速技术是一种基于分子滤波和多普勒频移现象的流场速度测量方法,在高速、超高速及大尺度风洞流场测量方面潜力巨大.我们设计开发了采用CCD相机作为接收探头的FM-DGV实验系统,该系统主要包括激光器、片光光学系统、碘分子滤波器、图像采集相机、频率监测单元等.基于该系统进行了谐波幅值比和转盘线速度测试实验.实验结果表明,该实验系统工作正常,速度测量误差最大值小于2m/s.     

声学多普勒测速仪标校技术研究

为了提高声学多普勒测速仪输出速度的准确度,安装过程中测速基阵与载体之间的偏差角不可忽略,安装偏差角包括航向偏角,横摇角及纵摇角三类。介绍了一种三维空间上的多普勒标定技术,通过高精度的GPS导航仪以及多普勒测速仪对海底测速,利用速度比值差校准航偏角。通过纵向剖面的几何关系,从航偏角出发进而获得纵摇角和横摇角的大小,完成了三维方向上多普勒测速仪的校准,使多普勒测速仪坐标系与载体坐标系能够进行精确转换,从而提高了声学多普勒测速仪输出速度的准确度。外场试验较好地证明了该方法的有效性,分析结论看出在二维平面上,造成误差的原因主要在于安装偏角的航向偏角,而在三维空间上,尤其垂向速度,误差主要由纵摇角和横摇角产生。该方法可以快速地对三维安装偏角进行校准,运算量小,并且在对海水测速后续研究中可以形成一套体系。     

基于火箭橇试验的北斗接收机动态校准技术

提出一种基于火箭橇试验的北斗接收机动态校准技术,通过阐述动态校准过程,火箭橇试验标准弹道建立方法、接收机动态定位和速度误差评定方法、火箭橇试验外测参数的溯源及校准过程不确定度评定方法,建立了计量型可溯源的火箭橇试验系统,并对两款接收机校准结果进行了分析。结果表明火箭橇试验能够有效解决北斗接收机的高动态校准问题,具有一定的应用价值和扩展前景。     

激光多普勒效应微纳测量技术的研究

研究MEMS系统中可动构件(膜、梁、梳、面、弹簧)在承受压力、弯曲等机械负荷及热负荷下的性能，重要途经是测量其在各种条件下的运动量(振动、位移等)．提出了一种MEMS构件微小振动、位移测量系统，采用外差法激光多普勒技术，通过对信号的频谱分析，确定了信号处理单元的适宜频带宽度．对调相多普勒跟踪信号进行相干解调及频率／电压转换，可以实时地得到被测的速度、位移、加速度、频率等参量．实现的测量分辨力为20nm．     

一种解决BBADCP测速模糊的方法

宽带声学多普勒海流剖面仪采用重复相位编码信号和复协方差方法进行频移量的估计．具有较高的测速精度,但是在测速上具有速度模糊,在不改变原有的系统结构的基础上对宽带多普勒海流剖面仪的信号处理方法进行改进,提出采用回波自相关的第一个旁瓣的位置解决测速模糊的方法,并推导了计算公式。最后进行了数字计算和仿真。结果证明了这种方法的正确性和可行性。     

宽带可调谐光源瞬时波长测量方法研究

激光波长作为“米”基准的重要实现途径之一，其量值准确性在计量校准、精密测量以及光谱探测等领域具有十分重要的意义。目前基于标准物质吸收谱线的波长基准仅能用于单一波长的计量校准，对于宽带光源波长校准手段有限。本文开展宽带连续调谐激光波长校准技术研究，利用飞秒激光频率梳宽光谱、光频可溯源至原子频率标准、稳定性高的特点，对宽带调谐光源在调谐输出时的连续光波长进行测量，最终实现了1 nm带宽下可调谐激光器调谐输出过程中瞬时值的测量，并利用该结果对可调谐激光器在121 GHz带宽的调频非线性度进行了评价。     

动态力计量建模与分析方法综述

针对动态力计量中大规模复杂数据分析与处理难度大的问题,本文从原理性和实用性角度,系统地对动态力的标准激励源、校准仪表建模方法、动态时频域评价和测量不确定度评定等进行了综述讨论。梳理了数据建模和评价在动态力校准、量值溯源与传递等关键计量链路中的作用。为动态力计量数据评价机制的建立提供了一定的理论基础。     

空气声高声压的激光活塞法溯源技术研究

目前空气声高声压的溯源存在空白,本文基于激光-活塞发声器法,研究采用激光直接测量高声压下活塞振速的方式,实现了180 dB下高声压的溯源,并通过实验验证了理论公式和结果的一致性,为高声压的绝对溯源提供了技术方法,保障了高声压量值的准确可靠。     

Vacuum Pressure Measurement in Industrial Environments

High accuracy and reproducibility are the basis for outstanding product quality in the manufacturing of vacuum pressure gauges. Selective product and process controls supported by statistical process control (SPC) ensure success. Automated calibration processes traceable to the National Measuring Institute (NMI) are necessitated by the high product volume and the requirement for complete traceability. Even in industrial use under mostly non‐ideal surrounding conditions, the devices must deliver stable and accurate measured values in all production processes. Using the example of hot‐filament ionization gauges, it is shown how design modifications in the production process have reduced the measurement uncertainties of the devices from one generation to the next. In another example, the introduction of a second baffle in a capacitance diaphragm gauge, led to significant reductions in sensor drift.     

低压流场速度测量的不确定度分析

激光多普勒测速技术被广泛应用于流速测量领域。在搭建好的真空气流检测实验平台基础上,运用二维激光多普勒测速仪对真空腔室进行流速测量;为了减小测速系统的测量误差,对真空腔室流速测量不确定度的来源及评定进行了分析与说明,得到了真空腔室流速测量的合成相对标准不确定度和相对扩展不确定度。研究表明:LDV重复性测速和进气量估读引起的不确定度较大,而LDV系统误差和其它因素引起的不确定度较小。研究结果对后期真空腔室流速测量有一定指导意义。     

Laser Doppler vibrometer employing active frequency feedback

We present a heterodyne Michelson interferometer for vibration measurement in which feedback is used to obviate the need to unwrap phase data. The Doppler shift of a vibrating target mirror is sensed interferometrically and compensated by means of a voltage-controlled oscillator driving an acousto-optic modulator. For frequencies within the servo bandwidth, the oscillator control voltage provides a direct measurement of the target velocity. Outside the servo bandwidth, phase-sensitive detection is used to evaluate high-frequency displacements. This approach is of great interest for the frequently-occurring situation where vibration amplitudes at low frequency exceed an optical wavelength, but knowledge of the vibration spectrum at high frequency is important as well.     

仪表着陆信号发生器校准研究

仪表着陆信号发生器是仪表着陆系统机载设备的专用检测设备,目前国内还没有公开发布的关于仪表着陆信号发生器的国家或行业范围内的检定/校准技术标准。本文通过对仪表着陆系统原理进行剖析,从仪表着陆信号发生器工作特点入手,对航向信标、下滑信标、指点信标等信号特点进行分析,给出了计量特性,并基于频谱分析仪直接测量法给出了各项计量特性的校准方法,同时对频谱分析仪引入的测量不确定度进行了分析,用GUM法评定了扩展不确定度。结果表明,给出的校准方法可满足仪表着陆信号发生器关键参数的校准需求,使用频谱分析仪校准符合仪表着陆信号发生器各计量特性的量值溯源要求。     

A traceable calibration procedure for MEMS-based load cells

Characterizing the mechanical properties of materials and biological systems at the nanoscale requires accurate measurement of forces on the order of μN and less. Due to the scale of the measurements and size of the instrumentation, calibration of nanoscale devices presents a new challenge in metrology. In order to ensure accuracy of results, traceable calibrations must be performed on nanoscale instrumentation. Our group recently developed a novel MEMS-based high resolution load cell with force resolution on the order of μN. This paper reports on a simple method for traceably calibrating our device using dead weights that could be generalized to other MEMS-based load cells. In this article, fabrication of a MEMS load cell is detailed and we compare our calibrated force–displacement curves to a non-linear theoretical prediction, revealing errors as great as 29%.     

Frequency-locked light scattering: real-time Doppler velocimetry with closed-loop feedback control

Real-time measurement capability of a frequency-modulated filtered light-scattering- (FM FLS) Doppler velocimeter has been demonstrated. Doppler-shifted light from a frequency-modulated Ti:sapphire laser scattered from a supersonic flow is imaged through a potassium vapor cell and is detected by FM spectroscopy. The FM signal is used in closed-loop feedback control of the laser frequency to lock the Doppler-shifted scattered light to the resonance frequency of the filter. The difference between the filter resonance frequency and the laser frequency when the scattered light is frequency locked to the filter resonance is the flow-induced Doppler shift. Changes in flow velocity are tracked by changes in laser frequency, which is subsequently measured to obtain the Doppler shift. The frequency-locking capability of the technique was achieved with use of a simple analog controller. The random Doppler shift measurement errors (2varsigma) were approximately 20 MHz, which correspond to velocity measurement errors for the real-time measurement of less than 3% in a 10-Hz bandwidth.     

选带细化频谱分析在超声波流量测量中的应用

通过中频调制为基础提取流体速度方向信息,引入选带细化频谱分析技术对解调后多普勒信号进行高精度的频谱估计,该方法主要有三个方面的优点:能判断流速的方向;降低流速测量下限;提高了流速测量的动态响应速度、实时性以及稳定性.在此基础上,以数字信号处理器(DSP)为平台设计了超声流量计,实验分析表明1 024点ZOOM-FFT算法在选定频带范围内与16 384点FFT有相近的分辨率.     

Accurate and precise calibration of AFM cantilever spring constants using laser Doppler vibrometry

Accurate cantilever spring constants are important in atomic force microscopy both in control of sensitive imaging and to provide correct nanomechanical property measurements. Conventional atomic force microscope (AFM) spring constant calibration techniques are usually performed in an AFM. They rely on significant handling and often require touching the cantilever probe tip to a surface to calibrate the optical lever sensitivity of the configuration. This can damage the tip. The thermal calibration technique developed for laser Doppler vibrometry (LDV) can be used to calibrate cantilevers without handling or touching the tip to a surface. Both flexural and torsional spring constants can be measured. Using both Euler-Bernoulli modeling and an SI traceable electrostatic force balance technique as a comparison we demonstrate that the LDV thermal technique is capable of providing rapid calibrations with a combination of ease, accuracy and precision beyond anything previously available.