Table of contents

The original work of Kang et al (2004 Meas. Sci. Technol.15 1104–12) presents a scheme for correcting optical distortion caused by the curved surface of a droplet, and illustrates its application in PIV measurements of the velocity field inside evaporating liquid droplets. In this work we re-derive the correction algorithm and show that several terms in the original algorithm proposed by Kang et al are erroneous. This was not evident in the original work because the erroneous terms are negligible for droplets with approximately hemispherical shapes. However, for the more general situation of droplets that have shapes closer to that of a sphere, with heights much larger than their contact-line radii, these errors become quite significant. The corrected algorithm is presented and its application illustrated in comparison with that of Kang et al.

We propose a 2D displacement control system with sub-nanometric repeatability on position over the millimetre travel range on both axes. It could be useful for nanofabrication processes or other applications related to the nanotechnology community. In our case, the apparatus is planned to be used in atomic force microscopes and lithography systems as a sample-holding device. The method is based on a heterodyne interferometric sensor and a home-made high frequency phase-shifting electronic board. This paper presents the complete mechanical system and gives experimental results showing a repeatability of 0.5 nm over a moving range of 5 mm.

The Korea Research Institute of Standards and Science (KRISS) has developed a 100 N m deadweight torque standard machine. The machine consists of a torque arm, an air bearing, six weight stacks, a main body and a control system. It can be operated almost fully automatically. The machine can generate torque from 0.1 N m to 110 N m with a relative expanded uncertainty of 5.0 × 10⁻⁴ for 0.1 N m to 1 N m and 5.0 × 10⁻⁵ for 1 N m to 110 N m. The machine was compared with a 2 kN m deadweight torque machine. In the comparison, the relative deviation was less than 5 × 10⁻⁵, the declared expanded uncertainty of the torque standard machines, and therefore we confirmed the accuracy of the machine.

Doppler optical coherence tomography (DOCT) was applied to non-invasive monitoring of multi-dimensional velocity profiles within complex geometry vessels. The effect of channel geometry on the flow dynamics at different inlet flow rates was studied. We investigated the flow dynamic regime arising at the junction of T- and Y-shaped samples and vessels with aneurism. We show that at constant input volume flow rate, the distribution of flow velocities measured along a cross-sectional plane orthogonal to the inlet arm, located at 20 mm off the junction, exhibited stationary and laminar behaviour. A non-homogeneous distribution of flow velocity along a junction cross-section plane is presented. Finally, we demonstrate the feasibility of DOCT for mapping the velocity profiles along the vessels' junction with a spatial resolution of about 10 × 10 × 10 µm³ and a minimum detectable velocity of about 2 mm s⁻¹.

Electrical capacitance tomography (ECT) and electromagnetic induction tomography (EMT) attempt to visualize the distributions of materials with different permittivity and conductivity/permeability, aiming to reveal electrical and magnetic characteristics of an object, by measuring electrical capacitance and electromagnetic inductance on the periphery of the object. In ECT, capacitances of pairs of electrodes placed around the periphery are measured and in EMT, mutual induction of pairs of coils is measured. In this paper, a dynamic imaging technique is developed for ECT and EMT with a linearized Kalman filter to improve the temporal resolution of images. The inverse problem is treated as a state estimate. A Kalman estimator is used to obtain the material distribution. Experimental results demonstrate that the dynamic imaging technique can improve the spatio-temporal resolution of both ECT and EMT.

In this work we describe a small, low cost conductivity, temperature and depth (CTD) system for measurements of salinity in coastal waters. The system incorporates three low cost expendable sensors, a novel planar four-electrode conductivity cell, a planar resistive temperature device and a piezoelectric pressure sensor. The conductivity cell and the resistive temperature device were fabricated using novel printed circuit board (PCB) microelectromechanical (MEMS) techniques combined with a new thin-film material, liquid crystal polymer (LCP). Printed circuit board techniques allow for mass production of the sensors, thereby lowering the cost of the system. The three sensors are packaged so that they are independent of one another and can be quickly replaced if bio-fouled or damaged. Deployments in Bayboro Harbor, St Petersburg, FL demonstrate that the novel CTD systems are capable of obtaining highly resolved in situ salinity measurements comparable to measurements obtained using commercially available instruments. The estimated accuracies for the conductivity, temperature and pressure sensors are ±1.47%, ±0.546 °C and ±0.02 bar, respectively. This work indicates that a small, low cost CTD system with expendable/replaceable sensors can be used to provide accurate, precise and highly resolved conductivity, temperature and pressure measurements in a coastal environment.

The amplitude–frequency dependences of a dielectric layered semi-ball resonator placed in a high loss liquid were studied experimentally and theoretically. It was determined that at definite relations between real and imaginary parts of complex permittivity of high loss liquid the electromagnetic field extrusion effect was observed. The extrusion effect means that the region of strongest E-field becomes displaced when the surrounding liquid has high loss, and may end up inside the resonator. Such an effect takes place when the resonator is immersed into the liquid with real and imaginary parts of complex permittivity that are much greater than 1 and the imaginary part is higher than the real one. Liquids with various real and imaginary parts of complex permittivity were studied. The existence conditions for the electromagnetic field extrusion effect were found. The influence of this effect on the measurement of complex permittivity of a high loss liquid using a sapphire layered semi-ball resonator was observed.

We have developed a method to obtain the ratio error and phase displacement of a single-stage current transformer (CT) by measuring four parameters in a CT equivalent circuit. The method was applied to CTs under test with a primary current in the range 10–20 000 A and a secondary current of 5 A. By determining the errors of the CTs under test using this method, the ratio error and phase displacement of the standard CTs used as a reference in a CT test system could be obtained. This implies the establishment of a traceability chain of a national standard for CTs. The ratio error and phase displacement of the standard CTs obtained in this study are consistent with those measured at the Physikalisch-Technische Bundesanstalt in Germany using the same standard CTs within an expanded uncertainty (k = 2) in the overall primary current range investigated.

A fully automated system has been developed for voltage calibrations where fast programmability and extremely low uncertainties are required. This system is based on a binary Josephson junction array with a smallest segment of one single junction. As an important application, the linearity of the 10 mV range of a digital nanovoltmeter was determined with a standard uncertainty better than 1 nV. As a further application of the fast programmability of the binary Josephson system, the standard uncertainty of voltage ratios measured by an -digit digital voltmeter in quantum Hall measurements was measured to be 10 × 10⁻⁹.

We examine the effect of varying the temperature points on MEMS inertial sensors' noise models using Allan variance and least-squares spectral analysis (LSSA). Allan variance is a method of representing root-mean-square random drift error as a function of averaging times. LSSA is an alternative to the classical Fourier methods and has been applied successfully by a number of researchers in the study of the noise characteristics of experimental series. Static data sets are collected at different temperature points using two MEMS-based IMUs, namely MotionPakII and Crossbow AHRS300CC. The performance of the two MEMS inertial sensors is predicted from the Allan variance estimation results at different temperature points and the LSSA is used to study the noise characteristics and define the sensors' stochastic model parameters. It is shown that the stochastic characteristics of MEMS-based inertial sensors can be identified using Allan variance estimation and LSSA and the sensors' stochastic model parameters are temperature dependent. Also, the Kaiser window FIR low-pass filter is used to investigate the effect of de-noising stage on the stochastic model. It is shown that the stochastic model is also dependent on the chosen cut-off frequency.

An experimental methodology is developed for gas temperature measurements in highly radiating environments. It consists of a suction thermocouple apparatus and associated heat transfer model for determining the gas temperature from shielded thermocouple readings by radiation, convection and conduction dimensionless correlations. The apparatus and methodology are calibrated and applied to measure gas flow temperatures in a tubular furnace with wall temperatures up to 1223 K. Results are compared with predictions by CFD simulations.

We report on the hydrogen sensing property of Pd-capped Mg–Pd alloy thin films which were prepared by dc magnetron sputtering. Pd-capped Mg_0.9Pd_0.1 films of thicknesses 10 nm Pd and 40 nm Mg–Pd show a good hydrogen sensing property for hydrogen-containing atmosphere at room temperature. Their sensing range is from 40 ppm to 4% hydrogen in Ar. These films are supposed to be candidates for a low-cost room temperature hydrogen sensor.

A heterodyne interferometric ellipsometer, with no moving parts and a transverse Zeeman laser, is demonstrated. The modified Mach–Zehnder interferometer characterized as a separate frequency and common-path configuration is designed and theoretically analyzed. The experimental data show a fluctuation mainly resulting from the frequency mixing error which is caused by the imperfection of polarizing beam splitters (PBS), the elliptical polarization and non-orthogonality of light beams. The producing mechanism of the frequency mixing error and its influence on measurement are analyzed with the Jones matrix method; the calculation indicates that it results in an error up to several nanometres in the thickness measurement of thin films. The non-orthogonality has no contribution to the phase difference error when it is relatively small; the elliptical polarization and the imperfection of PBS have a major effect on the error.

Recently, a new method was proposed to measure nonlinear distortions in weak nonlinear systems using specially designed broadband excitation signals (odd random phase multisines). During one single experiment, the output response level, the noise level and the level of the nonlinear distortions are simultaneously measured. We implement this method in an opto-acoustic set-up which allows us to measure vibrations with high accuracy. To demonstrate the method, we present results obtained on the membrane of an earphone speaker and a latex membrane. On the earphone good agreement is found between measurements of the produced sound field and the actual membrane vibration using heterodyne interferometry. The results show that heterodyne vibrometry can be used to detect nonlinear distortions which are up to 80 dB below the output level in an acoustically driven system.

We have demonstrated the feasibility of using the nano force calibrator (NFC), consisting of a microbalance and a nano-stage, as a calibration device, which can accurately determine normal spring constants (k) of various atomic force microscope (AFM) cantilevers with traceability to the Système International d'Unités (SI units). From very compliant (k < 0.1 N m⁻¹) to stiff (k > 10 N m⁻¹) cantilevers, three types of commercial levers with different shapes (beam and V) and operating modes (contact and tapping) were chosen to test NFC calibration performances. We have found that all types of levers could be well characterized by the NFC even when a small force (approximately 500 nN) was used to calibrate a soft cantilever (k < 0.1 N m⁻¹). We declared the relative standard uncertainty of the spring constant calibration of our method to be better than 1%, based on calibration results and uncertainty analysis. Because of its small calibration uncertainty, the NFC is recommendable for accurate calibration of AFM cantilevers and as a reference method for assessing other popularly used calibration methods.

The behavior of a liquid drop constrained between two rigid plates is studied. The problem is solved numerically in the following cases: (1) the free oscillations of the drop when the plates are motionless; (2) the forced oscillations when the upper plate makes a translational vibration in the normal direction. The possibility of viscosity and surface tension determination in such experiments is shown.

Optical coherence tomography has become an important tool for medical imaging and increasingly for quantitative metrological applications. As a consequence detection sensitivity is highly valued. In this paper, we introduce a novel post-processing technique for digitally stabilizing and spectrally averaging optical coherence tomography datasets in order to enhance detection sensitivity. We demonstrate sensitivity gains of 18 dB when the algorithm is applied to data from a high-speed Fourier domain system.

Electrical impedance tomography (EIT) is a technique for reconstructing the conductivity distribution of an inhomogeneous medium, usually by injecting a current at the periphery of an object and measuring the resulting changes in voltage. The conjugate gradient (CG) method is one of the most popular methods applied for image reconstruction, although its convergence rate is low. In this paper, an advanced version of the CG method, i.e. the Schur conjugate gradient (Schur CG) method, is used to solve the inverse problem for EIT. The solution space is divided into two subspaces. The main part of the solution lies in the coarse subspace, which can be calculated directly and its corresponding correction term with a small norm can be solved in the Schur complement subspace. This paper discusses the strategies of choosing parameters. Simulation results using the Schur CG algorithm are presented and compared with the conventional CG algorithm. Experimental results obtained by the Schur CG algorithm are also presented, indicating that the Schur CG algorithm can reduce the computational time and improve the quality of image reconstruction with the selected parameters.

We developed a fast read-out electronics for a gamma ray computed tomography radiation detector for measurements of two-phase flow distributions in rapidly rotating hydrodynamic machines. The electronics operates with a gamma ray detector comprising 320 single scintillation detector elements working in pulse counting mode. Digital pulses corresponding to gamma or x-ray absorption events in the scintillation crystals are counted with electronics implemented fully parallel in field programming gate array (FPGA) electronics. Data from these counters can be transferred to the measurement PC via a USB 2.0 interface. The design aim for the data acquisition electronics was to acquire data that then could be reconstructed as tomograms with 2 mm spatial resolution from objects rotating as fast as 1200 rpm. This requires approximately 800 tomographic projections during a single revolution in 50 ms. This aim has been achieved with an optimized read-out electronics that is able to transfer the data of all detector counters within 23 µs to the PC. As an example, in this paper we demonstrate the capability of the measurement system to reconstruct gas distributions in the turbine region of a stirred tank reactor at a stirrer speed of 1200 rpm.

In a simulation experiment, we study the feasibility of single-view coded source neutron transmission tomography for imaging water density in fuel cells at the NIST neutron imaging facility. In standard two-dimensional transmission tomography, one reconstructs a spatially varying attenuation image based on many projections or views of an object. Here, we consider the limiting case where only one view is available. Rather than parallel beam sources, the projection data are produced by multiple pinhole sources. For a high-count case where the object is near the sources and the object magnification is approximately 200, and attenuation varies very smoothly in the object, we demonstrate that a penalized maximum likelihood method yields a reconstruction of attenuation that has a fractional root-mean-square prediction error of 5.8%. We determine the regularization parameter in the penalized likelihood method using a statistical learning method called two-fold cross-validation. As the object-to-source distance increases and object magnification in the detector plane decreases, the quality of the reconstruction deteriorates. At the NIST neutron imaging facility, the object magnification in a single-view coded source neutron imaging experiment would be only about 4. Due to this low magnification, even for the favorable case considered where attenuation varies very smoothly and we observe high-count projection data, we conclude that single-view coded source neutron transmission tomography is not a promising method for quantifying the spatial distribution of water in a fuel cell. (Contributions by staff of NIST, an agency of the US Government, are not subject to copyright.)

Microbridge samples of length 134–368 µm and width 20 µm, composed of a Cr film of 150 nm thickness sputter-deposited on a silicon substrate, were fabricated by the MEMS (microelectromechanical systems) technique. The profile of 'buckled' beams was measured by the white light interference technique and only the middle and the boundary of the beams are shown in the results. From the length and amplitude, the full profile of the beams was fitted and residual strain in the film was deduced. The fitted results correspond well with the experimental results and the residual strain is about 5.826 × 10⁻³.

This study evaluates the effect of loading on closed crack openings on eddy current signals caused by the crack. Three plate specimens having a fatigue crack and another three specimens having stress corrosion cracking are prepared. Four-point bending of the specimens is carried out to introduce compressive stress to close the opening of the cracks. Then eddy current signals due to the crack are gathered using a plus point type probe. The bending was conducted with a variable load; the eddy current signals remain almost unchanged regardless of the loading.

Temperature measurement of cutting tools used in machining processes has great technological importance, and it is interesting in a large number of industrial applications because wear is directly related to this variable. The influence of emissivity on the temperature measurement using radiation thermometers and the dependence of the measured temperature on the emissivity as a function of the surface roughness and the oxidation state is studied in this paper. Emissivity is measured using the direct radiometric method for uncoated P10 tungsten carbide inserts. Theoretical temperature shifts produced by changes in emissivity are estimated for several types of radiation thermometers, and these shifts are compared to the experimental temperature measurements carried out in the orthogonal turning process of cylindrical samples of 42CrMo4 steel with different machinability grades.

Recent studies confirmed the feasibility of interventional whole body hyperthermia (IWBH) through directly heating the blood flow via minimally invasive heating needles. Among the factors to determine successful IWBH, a most challenging task is to in situ monitor the temperatures of the heating needle and the blood running across it. In this paper, an indirect method was developed which can approximately measure the temperatures of the needle while performing its heating role. Meanwhile, the information acquired in the simulated experiments and theoretical analyses was combined to evaluate the temperature variation of the blood during IWBH. Finally, the measurement errors of this method were discussed and the significance of adopting IWBH for efficiently raising the body-core temperature was demonstrated. This study also raised quite a few new fundamental issues related to the heat transfer of large blood vessels.

A low-cost direct solar radiation detector (DSRD) has been designed, characterized and calibrated. The detector was made of a simple silicon diode and then characterized with respect to spectral response, polar response and environmental stability. It was calibrated by using an Eppley normal incidence pyrheliometer (NIP) mounted on an Eppley power driven sun tracker (ST) whose axis is parallel to the Earth's axis of rotation. The DSRD and the NIP were mounted together on the ST. The results indicate that the DSRD follows the NIP very closely and can therefore be used in its place. The correlation between the DSRD and the NIP data is good with a correlation factor close to unity and a root mean square value close to zero.

The well-known problem of fitting a straight line to data with uncertainties in both coordinates is revisited. An algorithm is developed which treats x- and y-data in a symmetrical way. The problem is reduced to a one-dimensional search for a minimum. Global convergence and stability are assured by determining the angle of the straight line with respect to the abscissa instead of the slope. As opposed to previous publications on the subject, the complete uncertainty matrix is calculated, i.e. variances and covariance of the fitting parameters. The algorithm is tested using Pearson's data with York's weights. Although the algorithm is implemented in MATLAB, implementation in a different programming language is straightforward using the formulae presented. An application example is given, a calibration line for dosimetry based on electron spin resonance of alanine is investigated.

A novel compact dual-wavelength measurement system for absorbance chemical sensing incorporating digital lock-in amplifiers is reported. Its main innovation is the introduction of a reference wavelength to correct the possible non-specific optical changes of the system. The performance of the instrumentation has been tested on a laboratory setup and with integrated optical absorbance sensors.

In many applications, the detection of a visually obscured magnetic target is followed by the characterization of the target, i.e. localization and magnetic moment estimation. Effective target characterization may reduce the detection false alarm rate as well as direct the searcher toward the target. We address the characterization of a static magnetic target by a three-axis fluxgate magnetometer installed on a stabilized mobile platform. The magnetometer readings are contaminated by magnetic noise, which results in a low signal-to-noise ratio. We formulate the problem as an over-determined nonlinear equation set using a magnetic dipole model for the target and use simulated annealing (SA) in order to rapidly find a good approximation to the global optimum of this equation set. Computer simulations demonstrate high accuracy of the SA method in localizing the target and estimating its magnetic moment in the presence of high-level noise. The high accuracy of the SA method is also exemplified in tests employing real-world magnetic signals. In addition to its high accuracy, the SA method is very rapid, making it appropriate for real-time practical applications.

The mean pressure over a receptor placed at a small distance from a circular source is calculated in order to estimate the effect of diffraction when the medium is transparent or slightly absorbing. The deviation relative to the propagation without diffraction is written in the form of a simple integral of the radial wave vector. The source and receiver are considered of the same size, but the expression for different diameters is given. Approximate analytical expressions are derived when the diffraction effect is small, i.e., when the source is much larger than the wavelength. The analytical expressions are used to show that diffraction corrections can easily be performed in a standard pulsed echo experiment.

Two laboratory-based near infrared systems were compared for the purpose of quantifying kaolinite within Weipa bauxites. The two systems were based on different instrument technologies, a Bruker MPA (multi-purpose analyser) FTNIR (Fourier transform near infrared) instrument, and a Foss Model 6500 pre-dispersive grating instrument. Systems were compared in terms of accuracy, robustness, sample throughput and ease of use. The MPA-based system was superior in terms of accuracy (root mean squared error of prediction (RMSEP) = 0.88%m/m), throughput and ease of use. The Model 6500 had an advantage of offering the most robust measurement with greater time stability and lower errors in repeated and repacked measurements. However, addition of a small number of temporally displaced and repacked samples in the calibration set improved robustness of the MPA system, matching the Model 6500.

This paper presents new methodologies for measuring the hand tremor of surgeons. A means to measure and evaluate the surgeon hand tremor in real time during operating practice can serve to assess the ergonomics of operating conditions. Tremor information is also important for determining surgical performance, particularly in microsurgical tasks. Micro-surgeons often work continuously for several hours with the most complex part occurring toward the end of the procedure. During these procedures the surgeon often uses a binocular microscope and is working at the threshold of perception and manual tool point control. The resulting performance is sensitive to hand tremor. In this paper, maximum tremor amplitude was determined by integrating the acceleration signals measured from three-axis piezoelectric accelerometers. New methods of removing the drift in the acceleration signals through empirical mode decomposition, and of determining the maximum tremor amplitude through proper orthogonal decomposition are presented. An experimental calibration demonstrates that the average error between the maximum tremor calculated by the proposed new method and the measured amplitude is below 5%. The paper also presents the results of the new techniques applied in the operating room in practice. Some of the tasks investigated focused on tool control in microsurgery.

We present a novel, remote technique for measuring in situ and in real time (every 2 s) the spectral emissivity of particles at λ = 3.95 µm, in optically thick combustion environments. The novelty lies in the use of spectral information in the mid-IR (the blackbody emission profile of the 4.3 µm CO₂ band and the gray emission profile of particles between 3.8 and 4.1 µm) to determine the physical and brightness temperatures of the gas–particle medium, from which particle emissivity can be calculated. The retrieved particle emissivity at 3.95 µm is a reasonable average of total particle emissivity between 1 and 15 µm. Thus, CFD researchers who work with radiation sub-models may use this technique to obtain in situ emissivities at different locations, with a portable, rugged and inexpensive device. A small prototype was built with off-the-shelf components: standard light collection optics, a grating spectrometer and a linear-array pyroelectric detector. The particle emissivity is calculated from the asymptotic solution of the radiative transfer equation for optically thick media with isotropic scatterers. Results from a proof-of-concept test at a full-scale, coal-fired boiler 10 m above the top row of burners showed an average particle emissivity of 0.41 and an average gas temperature of 1533 K. Intrinsic and prototype error as well as the impact of temperature gradients in the line of sight of the instrument are discussed.

The increasing prevalence of elemental thermocouples, Au/Pt and Pt/Pd, in place of those using alloys of platinum and rhodium, has dramatically reduced measurement uncertainties at temperatures above the range of platinum resistance thermometers, to the extent that the single largest contribution to the uncertainty budget is often that due to the inhomogeneity of the Seebeck coefficient in the thermoelements along the length. This uncertainty must be estimated as an upper limit because the temperature gradient experienced by the thermocouple during calibration may be very different to that used in the field. In the worst case uncertainties of hundreds of mK are possible, although often the profiles are quite similar and the uncertainties are much lower than this. Here a method is presented for quantitatively determining the uncertainty in emf arising from inhomogeneity, by employing an experimentally determined sensitivity as a function of distance along the thermocouple, and numerically evaluating the effect of this sensitivity by considering its influence on all possible linear temperature gradients that the thermocouple can experience. It is then possible to determine the uncertainty due to the inhomogeneity within a desired confidence interval.

A new approach is proposed for the characterization of Agilent 16380A-type four-terminal-pair (4TP) air dielectric capacitance standards, which in the present study ranged from 1 pF to 1000 pF up to 30 MHz. The main objective is to determine all residual parameters of the four-terminal-pair capacitor (C_4TP) defined in previous investigations. The key feature of this study is to find all resonance frequencies of C_4TP up to 500 MHz using 4TP impedance and admittance values calculated from scattering parameter measurements employing a vector network analyzer. Inductive residual parameters of C_4TP are calculated from these resonance frequencies, and capacitive residual parameters are measured by using a 1 kHz capacitance bridge.

The consistency of magnetic Barkhausen noise (MBN) measurements under applied sinusoidal magnetic field control and sinusoidal magnetic circuit flux control was investigated under variable circuit permeability conditions. A U-core electromagnet was used to provide the alternating magnetic excitation. The magnetic circuit permeability was changed by varying excitation magnet lift-off and by using samples with known magnetic anisotropy. By controlling the circuit magnetic flux, measured as the flux in one of the U-core poles near the sample, MBN measurements were found to be consistent and independent of the excitation magnet lift-off in both a Si–Fe steel sample and an interstitial free (IF) steel sample at peak sample flux densities greater than 1.16 T and 0.29 T respectively. Consistency within a 95% confidence level was demonstrated for lift-off values of 0.6 mm or less, with decreasing sensitivity to lift-off observed at higher fluxes. MBN anisotropy measurements were also performed using both field control and flux control. Under field control conditions a component of the anisotropy signal was found to be dependent on the magnetic circuit permeability. This permeability dependence was absent when using flux control. The results demonstrated that flux control should be used when performing MBN measurements on samples where lift-off may be an issue, as values obtained will have less dependence on the excitation magnet characteristics than when field control is used.

This paper proposes a new method for correcting spurious displacement vectors obtained by using particle image velocimetry. Unlike methods that generate and use statistics from neighboring vectors toward outlier identification, a bootstrapping process is employed to generate statistics for each component. The mode-ratio criterion, defined as the normalized absolute value of the difference between the mode of the generated statistics and the actual value on the field, is used to identify and tag spurious components. The bootstrapping process is repeated to generate new statistics from the untagged components. This process is then repeated multiple times. The resulting mode field is used as the correction field. Two different displacement fields, each with a different error type, are artificially generated to evaluate the performance of the method. The evaluation is done by measuring the deviation between the resulting mode field and the perfect component field. The method is then tested on a real turbulent jet flow, obtained from www.pivchallenge.org, and the effect of the spatial gradient is discussed.

In this paper, an electrical and optical layered sensor is proposed as a new, non-invasive sensing method for the measurement of ingredients in liquid, particularly in the food industry. In the proposed sensor, the optical properties of the liquid are measured by a light-emitting diode (LED) and a photodiode, and the electrical properties are measured by indium tin oxide (ITO) film electrodes with the transparent conductive properties arranged on the surfaces of the LED and the photodiode. Thus, the electrical and optical properties in the same space of the liquid can be simultaneously measured at a single sensor. To test the sensor experimentally, two parameters of a liquid—such as concentrations of red color and sodium chloride (NaCl) between 0.1% and 0.5% in distilled water—were estimated using measurement values of the electrical and optical properties obtained with the proposed sensor. In addition, it was found that two other parameters of a liquid, such as coffee and milk concentrations between 0.1% and 1.0% in distilled water, could also be estimated with the proposed sensor. The measurement values of optical properties with and without the ITO film and those of electrical properties using an ITO film electrode and a stainless-steel film electrode were also compared. The results suggested that it is possible to measure both optical and electrical properties using the proposed sensor, although there are still some problems such as the surface resistance and transmittance of the ITO film that must be addressed.

The design of a novel scheme long-period fiber grating (LPFG) film sensor is presented. The sensor is composed of a long-period grating coated with sol–gel derived films, which are sensitive to the surrounding medium (gases). Based on the coupled-mode theory, a four-layered numerical model has been developed to study the characteristics of the transmissivity of the LPFG film sensor. By analyzing the relationship between the sensitivity S_n and the thin film optical parameters (thickness h₃ and refractive index n₃) and the fiber grating parameters (the grating period Λ, the core index change σ and the grating length L), the optimal design parameters of the LPFG film sensor can be obtained. Data simulation shows that the resolution of the refractive index of this LPFG film sensor is predicted to be 10⁻⁸. Experimentally, a long-period fiber grating film sensor for the detection of C₂H₅OH was fabricated, and a preliminary gas-sensing test was performed. The results indicate that a novel optical film sensor scheme with structure optimization has higher sensitivity.

Cosmic rays, mostly composed of high energy muons, continuously hit the Earth's surface (at sea level the rate is about 10 000 m⁻² min⁻¹). Various technologies are adopted for their detection and are widespread in the field of particle and nuclear physics. In this paper, cosmic ray muon detection techniques are assessed for measurement applications in engineering, where these methods could be suitable for several applications, with specific reference to situations where environmental conditions are weakly controlled and/or where the parts to be measured are hardly accessible. Since cosmic ray showering phenomena show statistical nature, the Monte Carlo technique has been adopted to numerically simulate a particular application, where a set of muon detectors are employed for alignment measurements on an industrial press. An analysis has been performed to estimate the expected measurement uncertainty and system resolution, which result to be strongly dependent on the dimensions and geometry of the set-up, on the presence of materials interposed between detectors and, ultimately, on the elapsed time available for the data taking.

The main content dealt with in this paper is to present a new apparatus and a new method that can measure multiple mechanical properties through a single test in principle, which can be used for handle evaluation for textile materials. The comprehensive handle evaluation system for fabrics and yarns (CHES-FY) is a kind of apparatus that is capable of measuring mass, bending, friction and tensile behavior just through one pulling-out test, and is able to characterize the handle of fabrics, whose measurement principle and structure of the CHES-FY system in mass and bending steps are analyzed in the present paper. The shape of a hung fabric was captured by a digital camera, and its weight was calculated. Then, a three-point bending in principle was utilized to model and analyze the bending properties of the fabric, and the corresponding formula was obtained for calculating the bending rigidity of the fabric. The comparisons of mass and bending rigidity based on 17 fabrics have been conducted by using CHES-FY, electronic balance and KES-FB2, respectively. The measured results show that there are high correlations between the three measuring systems for fabrics. It indicates that the approach using CHES-FY is feasible and accurate in measuring and characterizing mass and bending rigidity.

Following the first part of this series, the friction and stretching steps of the comprehensive handle evaluation system for fabrics and yarns (CHES-FY) are studied in this paper. By analyzing the friction and stretching principle and the structure of the CHES-FY, theoretical analyses and modeling of the friction between a fabric and a surface were made and the corresponding formula for the frictional coefficient was obtained; then, theoretical models of tensile characteristics were also constructed and corresponding formulae for tensile elastic constants with friction action were obtained. Comparisons of frictional coefficient and tensile elastic constant values between experimental results and theoretical prediction were conducted, and the results of the correlation coefficient show good agreement. It indicates that the method for measuring the frictional coefficient and tensile elastic constant was good at characterizing the frictional and tensile behavior of fabrics. It can be concluded that the theoretical models of friction and tensile properties are effective in characterizing the friction and tensile properties of fabrics, and the CHES-FY is feasible and accurate in measuring the friction and tensile properties of fabrics.

This paper evaluates uncertainty contributors for frequency response function (FRF) measurements obtained through impact testing. The FRF is an important estimator for the structural dynamics of tool-holder–spindle-machine assemblies and is used as an input to analyses of milling dynamics. Therefore, it is of interest to determine the confidence in the measurement results. In this work, we present a bivariate uncertainty analysis that considers statistical variations, imperfect calibration coefficients for the hammer and transducer, misalignment between the intended and actual force direction during impact and mass loading (when using an accelerometer). The complex-valued FRF can be expressed by its real and imaginary parts, which are potentially correlated. This correlation is included in the bivariate analysis. An ellipsoid-shaped confidence region (at each frequency) is defined in the complex plane; the size and orientation of this region is determined from the individual input uncertainties. The scalar, total uncertainty is then determined using an eigen analysis of the FRF covariance matrix. Experimental results are provided.

The problem of determining the particle size range in the visible spectrum is studied. The forward-scattering corrections are considered in the spectral extinction measurements. The monomodal and bimodal particle size distributions are retrieved in the independent model and dependent model algorithms, respectively. The constrained least-squares inversion method developed by Phillips and Twomey is applied in the independent model, and the genetic algorithm (GA) optimization method is employed in the dependent model. In the independent model, it is found that the particle size distributions can be retrieved very well in the size range from 0.1 µm to 12 µm for latex particles dispersed in water. The light scattering will enter the Rayleigh scattering region for particles below 0.1 µm and the diffraction scattering region for particles above 12 µm. The relation between the size range and relative refractive index of particles is also investigated. In the dependent model, the GA method can be successfully applied to retrieve the particle size distribution with high stability in the range from 0.01 µm to 350 µm for water particles dispersed in air even in the case where the bimodal distributions are retrieved.

Shearography is a full-field interferometric speckle technique used to determine displacement derivatives. Measurement of surface strain is possible using shearography if six components of displacement gradient are calculated. This can be achieved using shearography instrumentation that incorporates at least three measurement channels combined with two orthogonal shear directions. This paper presents a laser shearography instrument that utilizes coherent imaging fibre bundles to port four spatially multiplexed speckle images to a single CCD camera via a shearing Michelson interferometer. The four images are spatially multiplexed onto the sensor of a CCD camera. Wrapped phase maps are derived from the recorded speckle interferograms using temporal phase stepping. The unwrapped phase maps are combined with the measurement channel sensitivity vectors using a matrix operation to determine the required displacement derivatives. Results from an out-of-plane displacement of a flat aluminium plate are presented and compared with a computational model. Results from a second test object that show in-plane and out-of-plane strain components are also shown.

This paper discusses two probability density functions related to continuous wave (CW) phase demodulation systems such as those used in optical sensing. In the first case, we show that if the input intensity noise in the quadrature streams of the demodulator is Gaussian, then the induced phase noise is approximately Gaussian. If, however, the noise in both in-phase and quadrature streams is correlated, then the intensity induced phase noise exhibits a periodic dependence on the input phase and follows new asymmetric density distributions. We give expressions for the mean and variance for both processes.

The form measurement and gauge repeatability and reproducibility (R&R) of a micro-hole using a coordinate measurement machine (CMM) with a combination of optical and contact sensors were conducted in this study. The micro-holes, about 160 µm in diameter and 0.9 mm in depth, were fabricated using the electrical discharge machining process for diesel fuel injectors. The shape and size of micro-holes are important for the desired spray pattern, fuel economy and exhaust emission of diesel engines. In this study, the setup of the measurement machine and the procedure to determine the contact points are presented. Five form characteristics, the cylindricity, diameter, roundness, straightness and taper, of the micro-hole are analyzed from measurement points. The gauge R&R test is conducted to determine the micro-hole form measurement capability and to calculate the tolerance specifications for each characteristic that the CMM is capable of measuring. An example to quantify the change in the shape of the micro-holes before and after the abrasive flow machining is presented.

A moving-coil designed micro-mechanics tester, named as MicroUTM (universal testing machine), is in-house developed in this paper for micro-mechanics tests. The main component is a moving coil suspended in a uniform magnetic field through a set of springs. When a current passes through the coil, the electromagnetic force is proportional to the magnitude of the current, so the load can easily be measured by the current. The displacement is measured using a capacitive sensor. The load is calibrated using a Sartorius BP211D analytical balance, with a resolution/range of 0.01 mg/80 g or 0.1 mg/210 g. The displacement is calibrated using a HEIDENHAIN CT-6002 length gauge with an accuracy of ±0.1 µm. The calibration results show that the load range is ±1 N and the displacement range is ±300 µm. The noise levels of the load and displacement are 50 µN and 150 nm, respectively. The nonlinearity of the load is only 0.2%. Several in-plane load tests of the MEMS micro-cantilever are performed using this tester. Experimental results, with excellent repeatability, demonstrate the reliability of the load measurement as well as the flexible function of this tester.

This paper presents the development and evaluation of a smart flow measurement system based on an integrated thermal flow sensor that implements a heater and two pairs of thermopiles, symmetrically situated on both sides of the heater. A specially designed interface circuit monitors and controls sensor operation, allowing three different operational modes: constant voltage (CV), constant power (CP) and constant temperature (CT). It also simultaneously monitors the heater resistance and the thermopile signal. Communication with a PC is implemented through a USB connection, and a developed Java program controls the system and data representation and storage. Transfer rates in the order of 20 000 sps are achieved, which allow detailed flow monitoring. For system evaluation, flow measurements were performed in both the calorimetric and hot-wire principles with the three different modes of operation and the corresponding results are presented comparatively. Flow velocity was determined by different sensor signals (heater resistance and power, thermopile signal) and the related sensitivities were extracted. Furthermore, it was verified that the system could detect the flow direction as well as the transition point from laminar to turbulent region.

This paper presents a new method for on-line monitoring of the liquid level and water content of brake fluid using an enclosed reference probe as the capacitive sensing part. The probe has an enclosed cavity at the end which is designed to hold fresh brake fluid as an on-line reference. Three capacitances formed by four electrodes are used for the liquid level, water content and reference measurement and form the mutual calibrating output functions of the sensing probe. The liquid level measurement is calibrated to the permittivity changes by the capacitance for water content measurement. At the same time, the water content measurement is calibrated to temperature changes and variety of fluids by the capacitance of the reference measurement. Therefore, once the permittivity characteristics of brake fluids are experimentally modeled, the proposed method has a self-calibration ability to influence factors including temperature, water content (to liquid level measurement) and variety of brake fluids without an additional sensor supported by database as in conventional intelligent sensor systems. The design and implementation method are discussed with a prototype probe developed and tested. The permittivity characteristics of brake fluid samples are discussed. The calibration method and errors analysis are presented. The method presents a different way to construct a smart sensor which is useful in brake fluid condition monitoring and also other liquid measurement applications.

The switched reluctance motor has been receiving attention recently after the availability of power electronics devices, for its robustness, simple construction and a high torque/mass ratio. The electromagnetic characteristic measurement for the motor has been widely researched and reported despite nonlinear behavior of the motor. The electromagnetic characteristic data are being used as look-up tables for modeling and simulation purposes. However, for dynamic simulation, mechanical parameters such as friction coefficients and moment of inertia are equally important. There has not been much work done to measure the parameters as mostly they are provided by the manufacturer of mechanical parts (the motor etc) which are not accurate for the entire mechanical system, when they are coupled. A few measurement methods have been used widely to measure the mechanical parameters but the important friction constants such as Coulomb friction constant were neglected. This paper introduces a new technique which was derived from the classical viscous plus Coulomb friction model for all the mechanical parameter measurements including the Coulomb friction. The results obtained were verified using experimental data.

Fluxgate magnetometers have a long heritage of measuring the magnetic fields aboard space missions to all regions of the solar system. Fluxgate sensors have the stability, mass and resolution required for the space environment. However, future missions demand reductions in the mass and power of the electronics associated with these sensors and electronics designs which can survive the harsh radiation environment of space. Here a new design concept and first results are presented for a fluxgate magnetometer which combines the benefits of digital detection and digital feedback control with the low-noise amplification provided by tuning the sensor. It is also compatible with a mass optimized sensor using common sense/feedback windings. This design has been developed from the analogue design used for the Double Star mission. Moving the field extraction from the analogue to the digital domain reduces the component count and therefore the mass. The use of sigma–delta analogue-to-digital and digital-to-analogue conversion architecture embedded in a field programmable gate array offers the possibility of realizing a complete design able to operate up to a total ionizing dose of radiation of 100 krad without shielding.

An opto-digital imaging system for counting and analysing tracks on a LR-115 detector is described. One batch of LR-115 track detectors was irradiated with Am-241 for a determined period and distance for linearity test and another batch was exposed to radon gas. The laser-illuminated etched track detector area was imaged, digitized and analysed by the system. The tracks that were counted on the opto-digital system with the aid of media cybernetics software as well as spark gap counter showed comparable track density results ranging between 1500 and 2750 tracks cm⁻² and 65 tracks cm⁻² in the two different batch detector samples with 0.5% and 1% track counts, respectively. Track sizes of the incident alpha particles from the radon gas on the LR-115 detector demonstrating different track energies are statistically and graphically represented. The opto-digital imaging system counts and measures other track parameters at an average process time of 3–5 s.

Clarification is provided for certain expressions quoted in Hedlund and Pendrill (2006 Meas. Sci. Technol.17 2767–72).

In this comment, we provide a critique of the article published by R Wajman et al (2006 Meas. Sci. Technol.17 2113–8) with regard to 3D electrical capacitance tomography. Moreover, we further examine the sensor design and image reconstruction employed by Wajman et al, and we provide criteria for a robust direct 3D imaging system. References to pioneering and related work on 3D electrical capacitance direct imaging are also included.

The original authors respond to the preceding comment.

The authors unintentionally omitted to mention that parallel work on 3D ECT has been developed by Warsito and Fan (2003) but using the artificial neural networks to 3D image reconstruction (where our group concentrated on algebraic methods) and that the rectangular shape of electrodes was also used by Warsito and Fan (2003) but in a twin-plane sensor (where our group used three or more planes).

Reference Warsito W and Fan L S 2003 Development of three-dimensional electrical capacitance tomography Proc. 3rd World Congress on Industrial Process Tomography (Banff, Canada, 2–5 September 2003) pp 391–6

Figure 18(a) on page 2540 is incorrect (figure 17(a) was repeated). The correct figure 18(a) is shown below.

Figure 18. (a) Detector time signal (position: 5 mm, 80 kHz modulation frequency).