Showing papers in "Measurement Science and Technology in 2004"

Recent advances in the use of infrared thermography

Abstract: Infrared thermography transforms the thermal energy, emitted by objects in the infrared band of the electromagnetic spectrum, into a visible image. This feature represents a great potentiality to be exploited in many fields, but this technique is still not adequately enclosed in industrial instrumentation because of a lack of adequate knowledge; at first sight, it seems too expensive and difficult to use. The aim of the present paper is to shortly overview existing work and to describe the most relevant experiences devoted to the use of infrared thermography in three main fields, i.e. thermo-fluid dynamics, technology and cultural heritage, which have been performed in the department the authors belong to. Results may be regarded from two points of view, either as validating infrared thermography as a full measurement instrument, or as presenting infrared thermography as a novel technique able to deal with several requirements, which are difficult to perform with other techniques. This study is also an attempt to give indications for a synergic use of the different thermographic methods and sharing experiences in the different fields.

Recent trends in electrochemical DNA biosensor technology

Abstract: Recent trends and challenges in the electrochemical methods for the detection of DNA hybridization are reviewed. Electrochemistry has superior properties over the other existing measurement systems, because electrochemical biosensors can provide rapid, simple and low-cost on-field detection. Electrochemical measurement protocols are also suitable for mass fabrication of miniaturized devices. Electrochemical detection of hybridization is mainly based on the differences in the electrochemical behaviour of the labels towards the hybridization reaction on the electrode surface or in the solution. Basic criteria for electrochemical DNA biosensor technology, and already commercialized products, are also introduced. Future prospects towards PCR-free DNA chips are discussed.

Microstructure fibres for optical sensing in gases and liquids

Abstract: A novel water-core microstructure fibre design allows nearly ideal guidance for aqueous sensing applications. The total internal reflection by a microstructured silica–air cladding provides robust confinement of light in a fluid-filled core, if the average cladding index is sufficiently below the index of water. Numerical results show dramatically improved loss and overlap of light with the sample, compared to evanescent-field fibres, indicating a direct improvement of sensor performance. A strategy for the improvement of evanescent-wave gas sensors is also discussed.

Holographic particle image velocimetry: from film to digital recording

Abstract: Holographic particle image velocimetry (HPIV) offers potentially the best solution to volumetric measurements of the three-dimensional velocity fields in complex flows. However, the traditional film-based HPIV measurement is rather cumbersome, limiting its use to only a handful of groups worldwide. The newly emerged digital HPIV revolutionizes flow measurement science by providing a practical 3D velocimetry tool. It commands simple hardware that is similar to regular two-dimensional particle image velocimetry (PIV), yet it provides continuous (time-series) three-dimensional, three-component flow field data. Not only is the need for chemical processing eliminated, but also the cumbersome optical reconstruction is completely replaced by numerical reconstruction algorithms. Several breakthroughs have led to the development of the first practical and integrated digital HPIV systems. To explain the transition from film to digital recording, fundamental issues in HPIV are reviewed in this paper. Axial accuracy in HPIV measurement is ultimately limited by an inherent depth-of-focus problem, while information capacity is limited by inherent speckle noise. Information capacity is an important concept in HPIV, comprising the maximum acceptable seeding density multiplied by the sample volume depth along the optic axis. Both the axial accuracy and the information capacity are limited by the effective hologram aperture. The pursuit of a large hologram aperture in the past has resulted in further complexity in film-based HPIV systems. Digital HPIV, on the other hand, enjoys great simplicity of implementation and operation. A digital HPIV is also far more compact and rugged compared to existing film-based HPIV systems, making it suitable for duplication and commercialization. However, since digital sensors suffer from inferior pixel resolutions compared to films, the effective hologram aperture is much smaller in digital HPIV than that achievable in film-based HPIV. Alleviating this problem, digital HPIV also presents new possibilities in data processing such as the use of the complex amplitude of the reconstructed light wave to improve depth sensitivity and signal-to-noise ratio. Two examples of digital HPIV systems and measurement results are given. We believe digital HPIV can revitalize holographic particle imaging and bring it into the mainstream in much the same way that digital PIV brought PIV into widespread use a decade ago.

Octopus, a fast and user-friendly tomographic reconstruction package developed in LabView?

Abstract: A new software package called Octopus was developed for tomographic reconstruction of parallel beam projection data and fan beam data. It was written entirely in LabView®. It has a full graphical user interface and a high level of automation while allowing every processing step to be manually controlled. Octopus displays some unique features such as dual-energy tomography for element-sensitive investigations. Most importantly it features distributed reconstruction over a network using a server–client architecture with negligible network delays reducing reconstruction times almost proportionally to the number of clients. Octopus runs independently in a Windows® environment.

Measurement of the refractive index of liquids at 1.3 and 1.5 micron using a fibre optic Fresnel ratio meter

Abstract: A fibre optic technique based on the Fresnel reflection from the fibre tip is used for measurements of the refractive indices of various liquids at wavelengths of 1310 and 1551 nm. Reflection signals from liquid?fibre interface are compared with reflection signals from air?fibre interface to obtain the refractive index. Values of refractive indices for distilled water measured by this technique compare very well with known values at both wavelengths only if the fibre effective waveguide index is used. Applying the double-pulse measurement technique, it is shown that a measurement resolution of about 2.5 ? 10?5 can be achieved.

PIV optimization for the study of turbulent flow using spectral analysis

Abstract: Particle image velocimetry (PIV) is a measurement technique which is well adapted to the study of the structure of turbulent flows, as it allows us to obtain quantitative information on the spatial structure of the velocity field. This contribution presents an experimental approach to characterize the measurement noise of a PIV system and the spatial response of such a method. This approach is based on a specific spectral analysis of the velocity vector field deduced from several PIV experiments. This study was done in two steps. The first step was to measure the noise level of PIV and to determine a model for the PIV transfer function from a series of displacement fields measured in a quiet liquid. This model shows the effect of the interrogation window size and introduces a spectral noise density which is constant for a given recording set-up. The second step was to compute spectra from velocity fields obtained in a turbulent boundary layer in a plane parallel to the wall. These spectra show that PIV behaves as a band pass filter. This series of experiments allows us to build a model for the prediction of the PIV spectrum knowing the real one. This model confirms that the PIV noise is white. It allows us to optimize the interrogation window size in order to obtain the best compromise between the spectral response and the spatial resolution. The rms value of the noise can be estimated from the noise density, allowing us to quantify the measurement accuracy. The improvement of sub-pixel window shift is also discussed, leading to a small decrease in the noise level. An analysis is proposed to identify the main sources of noise: particles cut by the border of the interrogation window, isolated particles, etc.

Holographic particle image velocimetry

Abstract: Holography is truly the key to three dimensions in particle image velocimetry, i.e.?the measurement of all spatial components of the velocity vector - and this over a deep measuring field. Sophisticated instruments have been designed that successfully tackle practical problems such as the low scattering efficiency of particles, the inferior depth resolution or the aberrations and distortions in the reconstruction. Furthermore, efficient strategies are introduced to interrogate the holographic storage and process the huge amount of data towards a final flow field representation. Recently, phase-sensitive metrology, familiar in many fields of experimental mechanics, has been examined for use in particle velocimetry. Suitable methods are holographic and speckle interferometry or the optical processing of data for three-dimensional correlation. While in these techniques the power of optics is unrivalled, the practical advantage of video and digital techniques over photographic recording is obvious. The electronic version of speckle interferometry (ESPI/DSPI) is a well-established method used in laser metrology and has received further exploitation for applications in flow analysis recently. Finally, the state-of-the-art of digital particle holography is reviewed to allow estimates of its future in experimental flow analysis.

A digital holographic microscope for complete characterization of microelectromechanical systems

Abstract: Digital holographic microscopy (DHM) can be described as a non-invasive metrological tool for inspection and characterization of microelectromechanical structures (MEMS). DHM is a quick, non-contact and non-invasive technique that can offer a high resolution in both lateral and vertical directions. It has been employed for the characterization of the undesired out-of-plane deformations due to the residual stresses introduced by technological processes. The characterization of these deformations is helpful in studying and understanding the effect of residual stress on the deformation of a single microstructure. To that end, MEMS with different geometries and shapes, such as cantilever beams, bridges and membranes, have been characterized. Moreover, DHM has been applied efficiently to evaluate variations of the structure profile due to some external effects. As an example, the characterization of a cantilever subjected to a thermal process has been described. The results reported show that DHM is a useful non-invasive method for characterizing and developing reliable MEMS.

High-speed scanning stereoscopic PIV for 3D vorticity measurement in liquids

Abstract: A scanning stereo particle image velocimetry (SSPIV) system was developed to measure the three-dimensional (3D) distribution of three-component (3C) velocity in a turbulent round jet. A laser light sheet produced with a high-repetition-rate pulsed Nd:YLF laser was scanned by an optical scanner in a direction normal to the sheet. Two high-speed mega-pixel resolution C-MOS cameras captured the particle images illuminated by the light sheet, and the stereoscopic PIV method was adopted to acquire the 3D-3C velocity distribution of turbulent water flow. A water jet formed by a round nozzle with an exit diameter of D = 5 mm was diagnosed by the current technique. The jet Reynolds number was set at Re ≈ 1000, and the streamwise location of the measurement was fixed at approximately x = 45D. A measurement volume (~100 × 100 × 100 mm3) containing 50 velocity planes was scanned in 0.22 s, which was sufficiently short to capture the instantaneous vortical structures. The residue of the continuity equation (divergence) was approximately 7% of rms vorticity on the centreline of the jet. The iso-vorticity surfaces clearly depict vortical structures in the jet shear layer.

Long-period grating Michelson refractometric sensor

Abstract: This paper presents a single-probe Michelson interferometer that uses mode coupling in a long-period grating to establish the two optical paths in a single optical fibre. The interferometer phase shift depends on the refractive index of the material that surrounds the fibre probe, with the phase sensitivity directly proportional to the probe length. A simple phenomenological model explains the experimental results obtained with a liquid level sensor and a refractive index sensor. Its temperature sensitivity depends on the type of fibre that constitutes the probe. With a 45 mm long fibre probe, it is −2.5 and 12.8 degrees °C−1 for normal single mode fibre (SMF28) and germanium–boron co-doped fibre (PS1500), respectively.

A nonlinear image reconstruction algorithm for electrical capacitance tomography

Abstract: We present a total-variation-based image reconstruction algorithm for electrical capacitance tomography. This is a nonlinear iterative algorithm designed to minimize both the data error and the total variation of the permittivity, with iterations updated by the projected Gauss?Newton steps. We present numerical examples to illustrate the effectiveness of the algorithm in reconstructing permittivity images from both noise-free and noisy capacitance data.

High-speed micro-PIV measurements of transient flow in microfluidic devices

Abstract: This paper reports a new technique of micro-resolution particle image velocimetry (PIV). To investigate transient phenomena in a microfluidic device, a high-speed micro-PIV technique was developed by combining a high-speed camera and a continuous wave (CW) laser. The technique was applied to a micro counter-current flow, consisting of water and butyl acetate. The velocity fields of water in the micro counter-current flow were visualized for a time resolution of 500 µs and a spatial resolution of 2.2 × 2.2 µm2. Using the micro-PIV technique, the vortex-like motions of fluorescent particles around the water–butyl acetate interface were captured clearly.

Adsorptive pressure-sensitive coatings on porous anodized aluminium

Abstract: A novel pressure-sensitive luminescent coating on porous anodized aluminium is developed. A method of making the coating is described in detail. The coating is a thin anodized aluminium layer, which is formed onto the surface of aluminium by an electro-chemical process. The luminophore is adsorbed directly onto the surface of the layer via chemical or physical adsorption. This coating is suitable for measuring unsteady pressure fields due to its fast-responding characteristics. The time response of the present coating is evaluated theoretically and experimentally. Four kinds of luminophore, tris(4,7-diphenylphenanthroline)ruthenium(II) ([Ru(dpp)3]2+), tetrakis(4-carboxyphenyl)porphyrin (TCPP), platinum tetrakis(4-carboxyphenyl)porphyrin (PtTCPP), and pyrene butylic acid (PBA), have been tested on their response to a step change in pressure. A pressure jump apparatus and a shock tube were utilized to generate a pressure discontinuity. Some static characteristics were also tested. The theoretical analysis shows that the present coating should have a time response in the order of microseconds due to its porous structure. The time response depends not only on luminescence lifetime, which imposes an ultimate limit on the time response, but also on the thickness of the anodized aluminium layer, because oxygen permeation to the pores existing on the anodized aluminium layer can be described as a diffusive phenomenon. The effective diffusion coefficient is estimated to be approximately 5 × 10−6 m2 s−1. Experimental results show that all the tested coatings except the PtTCPP coating have a response time of less than 1 ms. Only the PBA coating shows a substantial photodegradation. The response time of the [Ru(dpp)3]2+ coating is longer than 20 µs, and depends on the thickness of the anodized aluminium layer. The response time of the TCPP coating, on the other hand, is less than 10 µs, and is independent of the thickness of the layer. This independence suggests that the arrangement of the luminophore on the surface of the anodized aluminium layer affects the time response.

A 'smart' bed for non-intrusive monitoring of patient physiological factors

Abstract: In this paper we present the results of research aimed at the development of a 'smart' bed to non-intrusively monitor patient respiration, heart rate and movement using spatially distributed integrating multimode fibre optic sensors. The research is focused upon allowing more automation of patient care, an especially important matter for the elder population, which is a rapidly growing fraction of much of the world population today. Two spatially integrating fibre optic sensors were investigated, one of which was based on inter-modal interference and the other on mode conversion. The sensing fibre was integrated into a bed and test subjects were monitored in different positions. The sensor outputs were then correlated with subject movement, respiration rate and heart rate. The results indicated that the inter-modal sensor could detect patient movement and respiration rate while the mode conversion sensor could detect patient movement, respiration rate and heart rate. Results and analysis of the research are presented and future research activities discussed.

Frequency scanning interferometry in ATLAS: remote, multiple, simultaneous and precise distance measurements in a hostile environment

Abstract: ATLAS is the largest particle detector under construction at CERN Geneva. Frequency scanning interferometry (FSI), also known as absolute distance interferometry, will be used to monitor shape changes of the SCT (semiconductor tracker), a particle tracker in the inaccessible, high radiation environment at the centre of ATLAS. Geodetic grids with several hundred fibre-coupled interferometers (30 mm to 1.5 m long) will be measured simultaneously. These lengths will be measured by tuning two lasers and comparing the resulting phase shifts in grid line interferometers, (GLIs) with phase shifts in a reference interferometer. The novel inexpensive GLI design uses diverging beams to reduce sensitivity to misalignment, albeit with weaker signals. One micrometre precision length measurements of grid lines will allow 10 μm precision tracker shape corrections to be fed into ATLAS particle tracking analysis. The technique was demonstrated by measuring a 400 mm interferometer to better than 400 nm and a 1195 mm interferometer to better than 250 nm. Precise measurements were possible, even with poor quality signals, using numerical analysis of thousands of intensity samples. Errors due to drifts in interferometer length were substantially reduced using two lasers tuned in opposite directions and the precision was further improved by linking measurements made at widely separated laser frequencies. © 2004 IOP Publishing Ltd.

Quantitative visualization of flow inside an evaporating droplet using the ray tracing method

Abstract: Liquid droplets possess many practically important applications and academically interesting issues. Accurate flow data are necessary to correlate the hydrodynamic characteristics with the physicochemical processes occurring inside a droplet. However, the refraction of light at the droplet surface makes it difficult to measure the flow field inside the droplet accurately. To resolve this problem, two correction methods based on the ray tracing technique are employed. One is the image mapping method and the other is the velocity mapping method. For this, a mapping function between the image plane and the object plane is derived. The two correction methods are applied to the flow inside evaporating droplets of different ethanol concentrations for measuring their velocity fields, using a PIV method. The results obtained with the two methods are nearly identical. The major differences between the original results and the corrected results are found in the locations of the vortex centres and the magnitude of velocity vectors. Between the two correction methods, the velocity mapping method is recommended, because it is more convenient and recovers a greater number of velocity vectors, compared with the image restoration method.

High-pressure adsorption measurements. A comparative study of the volumetric and gravimetric methods

Abstract: In this paper, we propose a comparative study between a volumetric apparatus and a gravimetric one, which were developed for the acquisition of high-pressure adsorption isotherms. The volumetric apparatus is able to perform measurements in the temperature range 278?323 K and in the pressure range 0?4000 kPa. We provide a complete report on the experimental errors due to the mass balance calculation based on pressure?volume?temperature measurements. The same analytical study has been achieved for a gravimetric apparatus (temperature range: 223?393 K, pressure range: 0?10?000 kPa). The comparison comments are based on experimental data obtained for the system: activated carbon (CENTAUR Chemviron Carbon)?nitrogen. It appears that for such a system exhibiting quite low adsorbed quantities, important discrepancies may appear if the measurements are not properly achieved. Minimizing the experimental errors for the two experimental techniques leads to an average observed deviation (relative error) between the two methods equal to 3% in the whole measurement range.

Dual luminophor pressure-sensitive paint: III. Application to automotive model testing

Abstract: Porphyrins play key roles in natural energy conversion systems, including photosynthesis and oxygen transport. Because of their chemical stability, unique optical properties and synthetic versatility, porphyrins are well suited as chemical sensors. One successful application is the use of platinum porphyrin (PtP) in pressure-sensitive paint (PSP). Oxygen in the film quenches luminescence, and oxygen pressure was initially monitored by measuring the ratio of I(wind-off)/I(wind-on). But this ratio is compromised if there is model motion and if the paint layer is inhomogeneous. Furthermore it requires careful monitoring and placement of light sources. Moreover, this method is seriously affected by temperature. The errors caused by model motion and temperature sensitivity are eliminated or greatly reduced using dual luminophor paint. This paper illustrates a successful application of a dual luminophor PSP in auto model testing. The PSP is made from an oxygen sensitive luminophor, Pt tetra(pentafluorophenyl)-porpholactone, which provides Isen, and Mg tetra(pentafluorophenyl)porphine, which provides temperature-sensitive paint (TSP) as the pressure-independent reference. The ratio PSP/TSP in the FIB polymer produced ideal PSP measurements with a very low-temperature dependence of −0.1% °C−1.

A neuro-wavelet method for multi-sensor system integration for vehicular navigation

Abstract: The last two decades have shown an increasing trend in the use of navigation technologies in several applications including land vehicles and automated car navigation. Navigation systems incorporate the global positioning system (GPS) and the inertial navigation system (INS). While GPS provides position information when there is direct line of sight to four or more satellites, INS utilizes the local measurements of angular velocity and linear acceleration to determine both the vehicle's position and attitude. Both systems are integrated together to provide reliable navigation solutions by overcoming each of their respective shortcomings. The present integration schemes, which are predominantly based on Kalman filtering, have several inadequacies related to sensor error models, immunity to noise and observability. This paper aims at introducing a multi-sensor system integration approach for fusing data from an INS and GPS hardware utilizing wavelet multi-resolution analysis (WMRA) and artificial neural networks (ANN). The WMRA is used to compare the INS and GPS position outputs at different resolution levels. The ANN module is then trained to predict the INS position errors in real time and provide accurate positioning of the moving vehicle. The field-test results have demonstrated that substantial improvements in INS/GPS positioning accuracy could be obtained by applying the proposed neuro-wavelet technique.

An investigation on airflow in disordered nasal cavity and its corrected models by tomographic PIV

Abstract: Knowledge of airflow characteristics in nasal cavities is essential to understand the physiology and pathology aspects of nasal breathing. Several studies have utilized physical models of the healthy nasal cavity to investigate the relationship between nasal anatomy and airflow. Since the final goal of these works is their contribution to the diagnosis and treatment of nasal diseases, therefore, the next step in this topic must be followed by the studies for disordered nasal cavities. In this paper, airflows in normal and abnormal nasal cavities and surgically created models, which simulate surgical treatment, are investigated experimentally by PIV. High-resolution computerized tomogram data and careful manipulation of the model surface by the ear, nose and throat doctor provide more sophisticated nasal cavity models. The correlation based correction PIV algorithm with window offset is used for PIV flow analysis. Average and RMS distributions in sagittal and coronal sections are obtained for inspiratory and expiratory nasal airflows. Comparisons in nasal airflows for both normal and abnormal cases are also examined. Airflow characteristics that are related to the abnormalities in the nasal cavity are proposed. In the case of simulations of surgical operations, velocity and RMS distributions in coronal section change locally, this may cause some difficulties in physiologic functions of noses and may hurt mucosal surface.

Simultaneous measurement of temperature and velocity using two-colour LIF combined with PIV with a colour CCD camera and its application to the turbulent buoyant plume

Abstract: In this present paper, a method for simultaneously measuring the temperature and the velocity in a planar cross-section of fluid flow with a colour CCD camera is described. This technique combines the laser-induced fluorescence (LIF) and particle image velocimetry (PIV). The temperature is evaluated by the two-colour LIF technique using red and green images of the colour CCD camera, while the velocity is obtained from two sequential blue images by PIV. It is found that the temperature sensitivity of the present technique is almost the same as that of the standard two-colour LIF technique by two monochrome CCD cameras with optimum filter setting, but it provides a simple and convenient system for simultaneous measurement of temperature and velocity in thermal flows. The uncertainty in the temperature measurement is found to be a function of concentration ratios of the fluorescent dyes in the two-colour LIF technique and it increases with an increase in the number of tracer particles for velocity measurement. This technique is successfully applied to the simultaneous measurement of temperature and velocity in the turbulent buoyant plume. The statistical properties of the plume, such as mean and turbulence characteristics of the plume as well as turbulent heat fluxes are evaluated in the initial region of the buoyant plume.

A novel time–frequency-based 3D Lissajous figure method and its application to the determination of oxygen saturation from the photoplethysmogram

Abstract: We present a novel time–frequency method for the measurement of oxygen saturation using the photoplethysmogram (PPG) signals from a standard pulse oximeter machine. The method utilizes the time–frequency transformation of the red and infrared PPGs to derive a 3D Lissajous figure. By selecting the optimal Lissajous, the method provides an inherently robust basis for the determination of oxygen saturation as regions of the time–frequency plane where high- and low-frequency signal artefacts are to be found are automatically avoided.

Sensing characteristics of plastic optical fibres measured by optical time-domain reflectometry

Abstract: A new method based on photon counting is utilized to investigate sensing characteristics of plastic optical fibres (POF) using the optical time-domain reflectometry technique. The responses of POF under various disturbances including small-radius bending, clamping, axial strain, etc, are measured and discussed. The sensing characteristics of POF are then expressed via reflection and transmission loss due to the disturbances. This provides basic data for developing a distributed sensor using POF. The result shown here implies the possibility of discriminating different types of disturbances using their specific responses.

Cyclic variability measurements of in-cylinder engine flows using high-speed particle image velocimetry

Abstract: In this paper we present full-field flow measurements for cyclic variability analysis within in-cylinder flows. A high-speed particle image velocimetry system has been developed with a framing rate of 13.5 kHz to allow single pulse multiple frame cross-correlation processing. This framing rate produced velocity vector maps at approximately 1° crank angle temporal resolution for engine speeds up to 2000 rpm. A novel processing scheme employing the temporal product of correlation functions is shown to increase vector validation rates enabling a statistical flow analysis. Velocity data have been obtained over 15 engine cycles for two engine conditions to demonstrate the operation of the instrumentation and processing algorithms. The data obtained show that changing the axial swirl level via the inlet port geometry has a significant effect on the cyclic variability of the flow in the latter half of the compression stroke. The technique allows the acquisition and processing of the flow data within a single working day representing orders of magnitude time and cost savings compared to using single point optical velocimeters.

Variable threshold outlier identification in PIV data

Abstract: This paper describes a variable threshold technique that can be applied to any particle image velocimetry (PIV) post-analysis outlier identification algorithm which uses a threshold such as the local median or the cellular neural network techniques. Although these techniques have been shown to work quite well with constant thresholds, the selection of the threshold is not always clear when working with real data. Moreover, if a small threshold is selected, a very large number of valid vectors can be mistakenly rejected. Although careful monitoring may alleviate this danger in many cases, that is not always practical when large data sets are being analysed and there is significant variability in the properties of the vector fields. The method described in this paper adjusts the threshold by calculating a mean variation between a candidate vector and its eight neighbours. The main benefit is that much smaller thresholds can be used without suffering catastrophic loss of valid vectors. The main challenge in obtaining this threshold field is that it must be based on a filtered field to be representative of the underlying velocity field. In this work, a simple median filter which requires no threshold was used for preliminary rejection. A local threshold was then calculated from the mean difference between each vector and its neighbours. The threshold field was also filtered with a Gaussian kernel before use. The algorithm was tested and compared to the base techniques by generating artificial velocity fields with known numbers of spurious vectors. For these tests, the ability of the algorithms to identify bad vectors and preserve good vectors was monitored. In addition, the technique was tested on real PIV data from the developing region of an axisymmetric jet. The variable threshold versions of these algorithms were found to be much less susceptible to erroneously rejecting good vectors. This is because the variable threshold techniques extract information about the local velocity gradient from the data themselves. The user-adjustable parameters for the variable threshold methods were found to be more universal than the constant threshold methods.

Continuous wavelet transform analysis of projected fringe patterns

Abstract: 3D profile measurement of an object is studied experimentally by using a standard fringe projection technique consisting of a CCD camera and a digital projector. The height profile of the object is calculated through the phase change distribution of the projected fringes from the phase and phase gradient of the wavelet transform. Experimental results for the Fourier transform profilometry algorithm are compared with the results of wavelet analysis.

Validation of an analytical solution for depth of correlation in microscopic particle image velocimetry

Abstract: Because the entire flowfield is generally illuminated in microscopic particle image velocimetry (microPIV), determining the depth over which particles will contribute to the measured velocity is more difficult than in traditional, light-sheet PIV. This paper experimentally and computationally measures the influence that volume illumination, optical parameters, and particle size have on the depth of correlation for typical microPIV systems. First, it is demonstrated mathematically that the relative contribution to the measured velocity at a given distance from the object plane is proportional to the curvature of the local cross-correlation function at that distance. The depth of correlation is then determined in both the physical experiments and in computational simulations by directly measuring the relative contribution to the correlation function of particles located at a known separation from the object plane. These results are then compared with a previously derived analytical model that predicts the depth of correlation from the basic properties of the imaging system and seed particles used for the microPIV measurements. Excellent agreement was obtained between the analytical model and both computational and physical experiments, verifying the accuracy of the previously derived analytical model.

Expulsion detection system for resistance spot welding based on a neural network

Abstract: Resistance spot welding is one of the most important welding procedures. Therefore, a strong emphasis is placed on the quality of the welds. One of the phenomena that causes the deterioration in quality is the eruption of molten material, the so-called expulsion. Expulsion can be avoided with appropriate parameter selection. The problem, however, lies in the fact that the best quality welds are made with parameters just below the expulsion area. Therefore, for any successful control scheme an efficient and dependable expulsion detection is needed. A linear vector quantization (LVQ) neural network system is proposed to achieve this goal. The network is analysed with different sensor combinations and different materials. The results show that the LVQ neural network is able to detect the expulsion in different materials. The experiment also points to the welding force signal as the most important indicator of the expulsion occurrence.

Sievert-type apparatus for the study of hydrogen storage in solids

Abstract: We report on a Sievert-type experimental apparatus for the study of hydrogen storage in metals forming the hydride phase. The apparatus is realized by only using commercial components and allows the study of the hydrogen absorption and desorption kinetics as well as the determination of the pressure–composition (P–C) diagram of the material–hydrogen system. The apparatus can operate over a wide range of temperature, 300–700 K, and H2 pressures, 1–80 bar. The H2 storage efficiency can be measured with a good accuracy ~3%. The experimental errors in the hydrogen absorption and desorption kinetics are ~1% and 6%, respectively.