视觉电生理闪光参数测量误差研究

闪光参数准确与否对于视觉电生理检查结果有效性具有重要意义。针对视觉电生理闪光参数特点,建立了闪光测量系统等效电路模型,基于传递函数理论分析了闪光测量系统参数对闪光强度、时程和波形测量误差的影响,以氙灯和LED为实验对象研究了系统参数在测量不同类型闪光时的误差。提出了减小测量误差以及消除测量闪光强度和LED闪光时程理论误差的方法并进行了实验验证。采用所述方法在不同系统参数下测量LED闪光强度结果的标准差为0.17%,LED闪光时程结果标准差为0.07%,可认为基本不变,实验与理论分析结果吻合。     

Five-step phase-shifting algorithms with unknown values of phase shift

The presented work offers new algorithms for phase evaluation in interferometric measurements. Several phase-shifting algorithms with an arbitrary but constant phase-shift between captured intensity frames are proposed. These phase calculation algorithms need to measure five frames of the intensity of the interference field. The algorithms are similarly derived as so called Carré algorithm. The phase evaluation process then does not depend on the linear phase shift errors. Furthermore, the detailed analysis of the algorithms with respect to most important factors, which affect interferometric measurements, is carried out. It is also studied the dependency of the evaluation algorithms on the phase shift values, and the proposed phase calculation algorithms are compared with respect to the resulting phase errors. The influence of most important factors in the measurement and evaluation process was simulated as systematic and random errors using a proposed mathematical model.     

化学反应溶液介电特性同轴式在线测量装置

 为解决化学反应溶液腐蚀测量探头的问题,提出了一种能实现宽带在线测量且测量探头不直接接触化学反应溶液的测量装置,并用这种测量装置采用全波仿真软件得到了用于重构溶液等效介电系数的散射参量。同时在假定2%测量误差的情况下,采用遗传算法反演溶液的等效介电系数。化学反应溶液等效介电系数的重构结果与文献值吻合较好,其相对误差小于5%,表明该测量装置在化学反应溶液介电系数的宽带在线测量中具有明显优势。     

Selection of response measurement locations to improve inverse force determination

The forces obtained by inverse methods are prone to errors. These arise due to a combination of errors in the measurements and high condition numbers in the matrix of transfer functions to be inverted. Ill-conditioning of the frequency response function matrix causes measurement errors to be magnified significantly. When the condition numbers are small, the measurement errors simply propagate without much amplification. Due to modal behaviour of the structure, the condition numbers can vary significantly over the frequency range and with the spatial location of the response measurements. The spatial variation can be quite considerable across the structure. The potential for using this characteristic to improve force determination is explored in this paper as an alternative to matrix regularization methods. The aim is to reduce error magnification in inverse methods by an ‘optimal’ spatial distribution of response locations. A method is proposed which is based on the minimization of the average condition number across the frequency range. If many possible locations are available, however, this can involve excessive calculation. An approximate method is therefore proposed which results in consistently good location selection for use in inverse force determination but involves much less computational effort. The error reduction in reconstructed forces is found to be significant in numerical simulations on a simply supported plate and in validation experiments.     

Finite difference approximation errors in acoustic intensity measurements

The errors due to developmental finite difference approximations in the two-microphone acoustic intensity measurement technique are considered in this paper. Equations are developed which describe the errors in intensity measurements for point monopoles, dipoles, and lateral quadrupoles. High accuracy is shown possible with careful selection of measurement parameters for each of these sources. For a microphone separation of 8 mm approximation errors are shown to be less than 2 dB from 0 to 10 000 Hz. For the quadrupole source low frequency errors not present with other sources are demonstrated. A lower limiting frequency for intensity measurements is determined to prevent these low frequency errors.     

Comparison of different experimental methods for the assessment of the room’s acoustics

The paper presents the acoustics analysis of three different enclosed spaces. These spaces (rooms) have different geometrical shapes and sizes and serve for different purposes. The early decay time, reverberation time, clarity and center time are evaluated with Dirac, WinMLS, Aurora and Caracad software using simple, low-cost equipment. The listed acoustic parameters were determined using linear sine sweep and impulsive sources. Comparisons between experimental measurements, simulations and analytic results were done. The room impulse response measurement proved to be the most reliable method to evaluate the properties of different rooms even if the measurements are perturbed by non-idealities of the low-cost equipment.     

Thermal Modelling and Characterisation of Semiconductor Bolometers

A revised version of the Griffin & Holland ideal semiconductor bolometer model is presented and its use in determining bolometer properties and parameters from experimental load curve measurements is discussed. We show that degeneracy between some bolometer parameters can only be broken by model fitting a family of load curves over a range of bath temperatures, and that measurements with the bolometer blanked (zero absorbed radiant power) are essential for unambiguous determination of the main parameters. The influence of measurement errors on parameter recovery is analysed using synthetic noisy data sets.     

Measurement of dynamic properties of viscoelastic materials

A new method for measurement of viscoelastic properties of materials, based on the exact solution of the problem of the forced oscillations of a flat sample loaded by inertial mass, is proposed. The device for these measurements is described. The elasticity modulus and loss tangent are measured within the frequency range from 100 Hz to 10 kHz at relative deformation of a sample below 1%. The approximate formulas for calculation of viscoelastic properties are derived, and the conditions of their applicability are determined. The methods for expansion of the frequency range and measurement of materials with extremely high loss tangent are proposed. The proposed method is compared with the current Standard. It is shown that the new method has the higher accuracy and expanded range of parameter measurements, and the construction of device is easy and reliable, since it does not require the knowledge on the oscillation properties of vibration source. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 06-08-00193-a).     

An investigation of the recombination mechanisms associated with the X states in type II GaAs/AlAs superlattices

We present a new examination of the phonon modes participating in the recombination processes from type II GaAs/AlAs superlattices. This is achieved through the use of a novel Raman resonance at the type II band gap, which provides a very precise, in-situ measurement technique for the important phonon energies. These are compared with the energies of the phonon satellites appearing in the photoluminescence emissions, using external uniaxial stress to access, in turn, the optical properties of both the longitudinal and transverse X states. Not only do these measurements resolve an existing controversy in the assignment of one of these satellites, but they also demonstrate that two of the others are currently in error, and re-assignments are proposed.     

A statistical assessment of ambient electromagnetic field using body-worn multiaxial sensors

The electromagnetic field exposure of the population due to wireless communications originates from both down-link and up-link emissions. Although the main contribution comes generally from the latter (e.g., higher by three to five orders of magnitude for the 2G), the former must be considered as well, because they are continual, and as contributions can be competitive for some cases (e.g., in femtocells). Sensor and exposimeter networks (NW) can be deployed by the operators themselves (to enrich feedback information from their own NW) or by independent external stakeholders such as regulatory agencies or local authorities. When sensors are directly worn by a user, body proximity effects – notably the masking effect – can introduce significant errors in the ambient field measurement. A methodology of the statistical assessment of this harmful effect is proposed in this article. It is mainly based on electromagnetic simulations (and partly on measurements) of a triaxial sensor – composed of three orthogonal wideband probes devoted to the evaluation of the field components – placed at different positions of a set of whole body phantoms. The main original contribution of the proposed approach is that both the isolated sensor calibration procedure and the assessment of the measurement errors are based on statistical analyses accounting for the propagation environment. The quantitative results are obtained using statistical channel models for polarimetric and non-polarimetric measurements in various propagation scenarios. Some quantitative results examples are presented. Eventually, preliminary corrections schemes are proposed.     

The inaccuracy principle

The problem of joint measurement of incompatible observables is investigated. Measurements are represented by positive operator-valued measures. A quantitative notion of inaccuracy is defined. It is shown that within this framework joint inaccurate measurements are possible for arbitrary maximal projection-valued measures on finite-dimensional spaces. The accuracy of such measurements is limited, as is shown by an inaccuracy inequality we derive. This new type of uncertainty relation can be unambiguously interpreted as referring to measurement precision rather than preparative quality. Several recent experiments are seen to be realizations of such joint measurements.     

Optical Differentiation Phase Measurement Using the Bias Shifting Method

A new optical phase measurement method using a differentiation filter is proposed. The new method uses two images obtained by shifting the filter. This method has an advantage in that non-uniformity of the wavefront intensity does not produce errors. We present herein the theory of the newly proposed method and verify the theory by computer simulation. The effects of non-uniformity of the wavefront intensity, noise, and bias shifting length for errors are discussed. The system has been demonstrated for a plane wave and a spherical wave. For the proposed method, although the number of errors due to noise increases, the number of errors due to non-uniformity decreases. Therefore, the proposed method is useful for the phase measurement of a wavefront for which the intensity is not uniform. In addition, it improves the accuracy of the phase measurement system using a differentiation filter.     

Error Principle

The problem of characterizing the accuracy ofand disturbance caused by a joint measurement ofposition and momentum is investigated. In a previouspaper the problem was discussed in the context of the unbiased measurements considered by Arthurs andKelly. It is now shown that suitably modified versionsof these results hold for a much larger class ofsimultaneous measurements. The approach is a development of that adopted by Braginsky and Khalili in thecase of a single measurement of position only. Adistinction is made between the errors of retrodictionand the errors of prediction. Two error-errorrelationships and four error-disturbance relationships arederived, supplementing the uncertainty principle usuallyso-called. In the general case it is necessary to takeinto account the range of the measuring apparatus. Both the ideal case of an instrument havinginfinite range and the case of a real instrument forwhich the range is finite are discussed.     

Sensitivity of Elastic Properties to Measurement Uncertainties in Laryngeal Muscles With Implications for Voice Fundamental Frequency Prediction

This paper discusses the effects of measurement uncertainties when calculating elastic moduli of laryngeal tissue. Small dimensions coupled with highly nonlinear elastic properties exacerbate the uncertainties. The sensitivity of both tangent and secant Young's Modulus was quantified in terms of the coefficient of variation, which depended on measurement of reference length and cross-sectional area. Uncertainties in the measurement of mass, used to calculate cross-sectional area of a small tissue sample, affected Young's Modulus calculations when tissue absorption of the hydrating solution was not accounted for. Uncertainty in reference length had twice the effect on elasticity than other measures. The implication of these measurement errors on predicted fundamental frequency of vocalization is discussed. Refinements on isolated muscle experimental protocols are proposed that pay greatest attention to measures of highest sensitivity.     

Experimental modal substructuring to estimate fixed-base modes from tests on a flexible fixture

Fixed boundary conditions are often difficult if not impossible to simulate experimentally, but they are important to consider in many applications. In principle, modal substructuring or impedance coupling approaches can be used to predict the fixed base modes of a system from tests where the system has some other boundary condition if the motion at the connection point can be measured, but this approach can be highly sensitive to imperfections in the experimental measurements. This work presents two alternatives that reduce the sensitivity to experimental errors, capitalizing on recent works where additional degrees of freedom are used to improve the robustness of substructure uncoupling. The system of interest is tested while mounted on a stiff fixture, where some modes of the fixture inevitably interact with those of the system of interest. The modes of the system–fixture assembly are extracted using a modal test and then a modal substructuring approach is used to apply constraints to eliminate the motion of the fixture. Two types of constraints are proposed, one based on the modes of the fixture and the other on a singular value decomposition of the fixture motion that was observed during the test. Neither approach requires an estimate of the displacements or rotations at the points where the system of interest is connected to the fixture. The methods are validated by applying them to experimental measurements from a simple test system meant to mimic a flexible satellite on a stiff shaker table. A finite element model of the subcomponents was also created and the method is applied to its modes in order to separate the effects of measurement errors and modal truncation. The proposed method produces excellent predictions of the first several modes of the fixed-base structure, so long as modal truncation is minimized. The proposed approach is also applied to experimental measurements from a wind turbine blade mounted in a stiff frame and found to produce reasonable results.     

Mode shape expansion using perturbed force approach

A new approach for expanding incomplete experimental mode shapes is presented which considers the modelling errors in the analytical model and the uncertainties in the vibration modal data measurements. The proposed approach adopts the perturbed force vector that includes the effect of the discrepancy in mass and stiffness between the finite element model and the actual tested dynamic system. From the developed formulations, the perturbed force vector can be obtained from measured modal data and is then used for predicting the unmeasured components of the expanded experimental mode shapes. A special case that does not require the experimental natural frequency in the mode shape expansion process is also discussed. A regularization algorithm based on the Tikhonov solution incorporating the generalized cross-validation method is employed to filter out the influence of noise in measured modal data on the predictions of unmeasured mode components. The accuracy and robustness of the proposed approach is verified with respect to the size of measured data set, sensor location, model deficiency and measurement uncertainty. The results from two numerical examples, a plane frame structure and a thin plate structure, show that the proposed approach has the best performance compared with the commonly used existing expansion methods, and can reliably produce the predictions of mode shape expansion, even in the cases with limited modal data measurements, large modelling errors and severe measurement noise.     

Evaluation of diffraction errors in precise pulse-echo measurements of ultrasound velocity in chambers with waveguide

Ultrasound velocity measurements in medicine and biology usually are performed using relatively small measurement chambers. When the pulse-echo method is used, the presence of the reflector close to the transducer can cause essential diffraction errors. These errors may be reduced using an additional buffer rod as a waveguide between the transducer and the measurement chamber. The objective of the presented work was analysis of diffraction errors in measurement chambers with a buffer rod. The work was performed in two steps. In the first stage propagation of transient ultrasonic waves in a buffer rod was analysed using an axisymmetric finite element model. This approach enables all dimensions of the measurement chamber and the waveguide to be taken into account, but is less accurate in the time domain. In the second step the absolute values of diffraction errors were evaluated using a mixed analytic-numeric disk shaped transducer diffraction model. In this case only the dimensions of the waveguide and measurement chamber along the wave propagation direction were taken into account. Diffraction errors were calculated by simulating small changes of ultrasound velocity in the liquid under investigation. The simulation performed allowed optimisation of the dimensions of the measurement chamber and a buffer rod thus minimising measurement errors.     

Compensation of phase change on reflection in white-light interferometry for step height measurement

We present a method for compensating for the phase change on reflection in scanning white-light inteferometry that practically permits precise three-dimensional profile mapping of composite target surfaces that comprise multiple, dissimilar materials. The compensation method estimates the variation of phase change with the spectral distribution of the light source through a first-order approximation and then directly compensates for the measurement errors by performing two additional quasi-monochromatic phase-measuring interferometric measurements. Experimental results prove that the proposed compensation method is capable of reducing the measurement error in step height gauging to +/-5 nm or less.     

Period correction method for binary fringe defocused projection

Binary fringe defocused projection can resolve the problem caused by the nonlinear gamma of the projector. Owing to the intersecting axis measurement system, the broadening of the fringe period on the reference plane can cause measurement errors. Non-uniform periodical binary fringe defocused projection is utilized to overcome this problem. After appropriate defocused projection of non-uniform periodical binary fringe, uniform periodical sinusoidal fringe can be obtained on the reference plane. This method can prevent the nonlinear gamma effect and broadening of the fringe period, and filter high harmonics and high-frequency noise. Three-dimensional (3-D) shape measurement experiments of standard flat are performed with four-step phase-shift method. Experimental results demonstrate that the proposed method exhibits high measurement precision. Highly accurate 3-D measurements of large objects can also be performed with the proposed method.     

Air-dispersion measurement by second-harmonic heterodyne interferometry

Interferometers with long optical paths in air usually require knowledge and control of air dispersion. In addition, the measurements at several wavelengths and the dispersion properties of air allow errors caused by air turbulence to be compensated for. An innovative technique for air-dispersion measurement is described for long-baseline ground-based stellar interferometers. The technique combines second-harmonic interferometry and heterodyne detection to permit high-resolution measurement even for low optical powers. Experimental results show measurements of air dispersion in good agreement with the values predicted from the Edlén equation.