Showing papers in "Measurement Science and Technology in 1995"
TL;DR: In this paper, the authors proposed a super-resolution method for high-image-density particle image velocimetry (PIV), which combines correlation analysis of the group of particles in a spot with sub-interrogation-spot particle tracking.
Abstract: The spatial resolution of conventional high-image-density particle image velocimetry (PIV) is determined by the size of the interrogation volume, which is typically a fraction of a millimetre. An improved method of PIV analysis is proposed in which the ultimate resolution of PIV is determined by the smaller of the mean spacing between particles and the displacement of the particles between light pulses. Since these distances must be smaller than the interrogation spot size in the high-image-density limit, the new procedure is referred to as super-resolution. The method combines correlation analysis of the group of particles in a spot with sub-interrogation-spot particle tracking. The theory of the procedure is described and evaluated using Monte Carlo simulations. The feasibility of enhancing resolution significantly is demonstrated by re-analysing turbulent flow PIV data reported by Urushihara et al. (1993). The in-plane resolution has been improved from 250 to 100 mu m.
258 citations
TL;DR: Theoretical and experimental studies of cross correlation techniques applied to non-restrictive velocity measurement of pneumatically conveyed solids using ring-shaped electrodynamic flow sensors are presented in this article.
Abstract: Theoretical and experimental studies of cross correlation techniques applied to non-restrictive velocity measurement of pneumatically conveyed solids using ring-shaped electrodynamic flow sensors are presented. In-depth studies of the electrodynamic sensing mechanism, and also of the spatial sensitivity and spatial filtering properties of the sensor are included, together with their relationships to measurement accuracy and the effects of solids' velocity profiles. The experimental evaluation of a 53 mm bore sensing head is described, including trials using a calibrated pneumatic conveyor circulating pulverized fuel and cement. Comparisons of test results with the mathematical models of the sensor are used to identify important aspects of the instrument design. Off-line test results obtained using gravity-fed solids flow show that the system repeatability is within +or-0.5% over the velocity range of 2-4 m s-1 for volumetric concentrations of solids no greater than 0.2%. Results obtained in the pilot-plant trials demonstrate that the system is capable of achieving repeatability better than +or-2% and linearity within +or-2% over the velocity range 20-40 m s-1 for volumetric concentrations of solids in the range 0.01-0.44%.
200 citations
TL;DR: Development in optical systems, signal processing, data processing and in the application of LDA systems are reviewed, with particular emphasis on examining how well present instruments meet the changing needs of the fluid mechanics community.
Abstract: The availability of new optical and electronic components and the increasing demands on measurement accuracy have led to a continuous development of the laser Doppler measurement technique in recent years. This article reviews the developments in optical systems, signal processing, data processing and in the application of LDA systems. Particular emphasis is placed on examining how well present instruments meet the changing needs of the fluid mechanics community and what improvements would be desirable in the near future.
162 citations
TL;DR: In recent years, the problems tackled by experimentalists and theoreticians in fluid dynamics have grown considerably as discussed by the authors, and powerful computers allow modelling of very complex flow fields, such as nonstationary flows, their spatial structures and their development in time.
Abstract: In recent years, the problems tackled by experimentalists and theoreticians in fluid dynamics have grown considerably. Sophisticated flow facilities like large size or high speed wind tunnels are the basis for ambitious experiments, and powerful computers allow modelling of very complex flow fields. Interest has turned to nonstationary flows, their spatial structures and their development in time. An ultimate aim is to measure and understand the evolution of turbulence.
138 citations
TL;DR: In this article, a new iterative procedure for re-building the second image, based on velocity gradients of particles due to displacement, rotation and shear, has been proposed, which has been shown to be considerably more accurate for simulated uniform, recirculating and bi-axial shearing flows, and has been applied to the case of natural convection due to a heated horizontal cylinder.
Abstract: The standard cross correlation technique frequently used in particle image velocimetry to extract velocity vectors necessitates the assumption that the velocity gradients inside the interrogation area are negligible However, the procedure is generally video-based, so such an assumption may no longer be valid This is particularly so in re-circulation zones, in which the distortion between images can be dramatic A new iterative procedure for re-building the second image, based on velocity gradients of particles due to displacement, rotation and shear, has been proposed This improved cross correlation algorithm has been shown to be considerably more accurate for simulated uniform, re-circulating and bi-axial shearing flows, and has been applied to the case of natural convection due to a heated horizontal cylinder
123 citations
TL;DR: In this article, a method is described for measuring the specular optical reflectance R( phi ) of the interface between a fluid and a glass prism, the incident and reflected light being in the glass, and the angle of incidence phi being varied about the critical angle.
Abstract: A method is described for measuring the specular optical reflectance R( phi ) of the interface between a fluid and a glass prism, the incident and reflected light being in the glass, and the angle of incidence phi being varied about the critical angle. Transparent, absorbing and some turbid fluids give R( phi ) dose to theoretical predictions, and experimental reflectance data are analysed to give the real (n') and imaginary (n") refractive indices of the fluid. Other turbid fluids gave R( phi ) data that differed strongly from theoretical expectation. This is attributed to heterogeneity of the fluid on the optical wavelength scale, and problems of refractometry for such fluids are discussed.
118 citations
TL;DR: The discovery of highly active piezoelectric polymer materials was first reported in 1969 and an enormous amount of research work has been conducted, mainly aimed at discovering the structure and properties of these fascinating materials with the further aim of improving their pyroelectric behaviour.
Abstract: The discovery of highly active piezoelectric polymer materials was first reported in 1969. Since then an enormous amount of research work has been conducted, mainly aimed at discovering the structure and properties of these fascinating materials with the further aim of improving their piezoelectric and pyroelectric behaviour. An equally vast amount of literature devoted to applications of these polymers has appeared and even a cursory glance at all this shows that they have been applied as the basis for a wide range of devices. The subject has now reached a degree of maturity and in the nondestructive testing field, there is perhaps a 'niche market' emerging for transducers based on polyvinylidene fluoride and its derivatives. In certain areas such as miniature under water hydrophones, piezoelectric polymers have become the material of choice. This being so, it is appropriate to review the subject.
116 citations
TL;DR: In this paper, a three-axis fluxgate magnetometer was used in the Earth's field mapping satellite named OErsted, which is based on stress-annealed metallic glass ribbons as core materials.
Abstract: The experiments and theoretical considerations leading to the construction of a high-performance three-axis fluxgate magnetometer are described. The magnetometer will be used (1996) in the Earth's field mapping satellite named 'OErsted'. The fluxgate sensors are based on stress-annealed metallic glass ribbons as core materials. It is shown that very simple physical models can be used to explain the fluxgate mode of operation, thereby making it easy to calculate the overall sensor performance from first principles. Special attention is drawn to the core excitation current which is analysed on the basis of nonlinear electrical circuitry. It is furthermore shown that the ring-core demagnetizing field obeys a simple cosine law which permits the calculation of the sensor sensitivity with high accuracy. The sensitivity, that is the signal-to-noise ratio, is ultimately determined by the sensor noise which is about 15 pT RMS (0.06-10 Hz), corresponding to a noise power density (1/f noise) of 6.2 pT Hz-1/2 at 1 Hz. The actual magnetometer operating range and sensitivity is determined by the 1 bit resolution of the Earth's field represented by the output from the 18 bit AD converted used in the instrument (+or-65536 nT with 0.5 nT resolution). The maximum attainable bandwidth is half the sensor excitation frequency (1/2*15 kHz) but the OErsted magnetometer bandwidth is limited to 250 Hz. The thermal stability of the sensor has been measured to be better than 1 nT in the temperature range -20 to +60 degrees C.
106 citations
TL;DR: The development of Doppler global velocimetry from its inception to its use as a flow diagnostics tool is described in this paper, which traces the evolution from an elementary one-component laboratory prototype, to a full three-component configuration operating in a wind tunnel at focal distances exceeding 15 m.
Abstract: The development of Doppler global velocimetry is described from its inception to its use as a flow diagnostics tool. Its evolution is traced from an elementary one-component laboratory prototype, to a full three-component configuration operating in a wind tunnel at focal distances exceeding 15 m. As part of the developmental process, several wind tunnel flow field investigations were conducted. These included supersonic flow measurements about an oblique shock, subsonic and supersonic measurements of the vortex flow above a delta wing, and three-component measurements of a high-speed jet.
95 citations
TL;DR: In this article, the design and construction of a 50 mm bore laboratory gas gun capable of velocities up to 1000 m s-1 was described, and the performance of the gun was compared with the analytical interior ballistics model of Pidduck and Kent.
Abstract: The design and construction of a 50 mm bore laboratory gas gun capable of velocities up to 1000 m s-1 is described. The performance of the gun is compared with the analytical interior ballistics model of Pidduck and Kent. The adaptation for one-dimensional plate impact experiments, the instrumentation employed and the capabilities of the system are described, and some examples of experimental results obtained are given.
89 citations
TL;DR: In this article, a two-colour fixed filter near-infrared spectrometer in conjunction with a simple ratio circuit was used for sorting polyethylene terephthalate and polyvinyl chloride.
Abstract: This paper describes a simple device for automated sorting of post-consumer plastic waste. It is shown that rapid and reliable identification of certain polymers can be achieved by using a simple two-colour fixed filter near-infrared spectrometer in conjunction with a simple ratio circuit. The effectiveness of the proposed method is demonstrated in sorting of polyethylene terephthalate and polyvinyl chloride. A sensor based on this identification method is inexpensive to build and provides the necessary speed and performance required by the recycling industry.
TL;DR: In this article, the exact single-particle detection efficiencies of a microchannel plate (MCP) detector were determined by photo-ionization of atoms or molecules, and the ionized heavy particles were detected in coincidence with the resulting electrons.
Abstract: Absolute single-particle detection efficiencies of a microchannel plate (MCP) detector were determined by photo-ionization of atoms or molecules. The ionized heavy particles were detected in coincidence with the resulting electrons. This method allows the determination of detection efficiencies without a knowledge of the absolute event rates. We obtained the detection efficiencies for the ions H2+, D2+, HD+, H+, D+ and Ar+ in the impact energy range 0-5 keV. The detection efficiencies saturate above 3 keV and reach generally 41%. This value seems to reflect mainly the physically effective area of the MCP.
TL;DR: A measurement system for high-sensitivity and accurate permittivity measurements has been built in order to investigate dielectric spectroscopy as a basis for an easier-to-maintain system, which can replace some of the traditional instrumentation systems.
Abstract: Traditional quality measurement systems in the petroleum-related industry are complex in structure and difficult to maintain. A measurement system for high-sensitivity and accurate permittivity measurements has been built in order to investigate dielectric spectroscopy as a basis for an easier-to-maintain system, which can replace some of the traditional instrumentation systems. The permittivity measurement system has been designed and tested for low-permittivity and low-loss fluids in the frequency range from 1 kHz to 5 GHz. In the lower part of the frequency range impedance measurements are used, and in the higher range reflection coefficient measurements are employed. The characteristics of the measurement cells are optimized to give high sensitivity. High-accuracy permittivity measurements are obtained by calibration with several known fluids. Temperature control and careful experimental routines ensure good repeatability. Estimated overall uncertainty and presented measurement results on low-permittivity and low-loss oils and reference fluids confirm the performance of the system.
TL;DR: In this article, the change in the AC impedance characteristics of poly-N-(2-pyridyl)pyrrole in the presence of three different volatile chemicals was investigated, in order to determine whether measurement of multifrequency parameters could be used as the basis of chemical discrimination.
Abstract: Electrically conducting polymers have previously been used for the detection of vapours and gases by measuring the reversible change in their DC resistance. The sensors have very broad chemical specificity with higher sensitivity to polar chemicals. The change in the AC impedance characteristics of poly-N-(2-pyridyl)pyrrole in the presence of three different volatile chemicals was investigated, in order to determine whether measurement of multifrequency parameters could be used as the basis of chemical discrimination. The results demonstrate quantification of concentration and discrimination between the chemicals tested on the basis of capacitance, conductance, resistance and dissipation factor as a function of frequency. This technique may be generally applied for discrimination between many chemical species.
TL;DR: In this article, the design and construction of a computer-controlled beam transport system and its application to slow positron implantation spectroscopy is described, including the facility to vary the positron beam energy, observe visually the associated spatial movement of the beam profile, and change the beam position so as to hit the sample centrally at all energies selected.
Abstract: The design and construction of a computer-controlled beam transport system and its application to slow positron implantation spectroscopy is described. The control features include the facility to vary the positron beam energy, observe visually the associated spatial movement of the beam profile, and change the beam position so as to hit the sample centrally at all energies selected. This procedure allows the automatic collection of annihilation gamma ray energy spectra and calculation of lineshape parameters as a function of incident positron energy. Examples of such measurements for metallic and semiconductor samples are used to illustrate the performance of the system.
TL;DR: In this paper, the authors describe the design, construction and use of a new swept frequency pulsed magnetic resonance spectrometer that is particularly suitable for measurements of NMR in magnetically ordered materials but has also been used for ESR, NQR and conventional NMR.
Abstract: We describe the design, construction and use of a new swept frequency pulsed magnetic resonance spectrometer that is particularly suitable for measurements of NMR in magnetically ordered materials but has also been used for ESR, NQR and conventional NMR. It includes computer control, digital pulse generation, measurements over the range 10-1000 MHz in one sweep, and calibration of signal and pulse power. The spectrometer can also be used to track the change of the NMR frequency of a sample, e.g., as a function of temperature.
TL;DR: In this paper, a four-electrode potentiostat-galvanostat is described for electric measurements of membranes in controlled potential and current conditions or measurements of transmembrane potential.
Abstract: The use of four-electrode systems in the studies of electric phenomena occurring in membranes makes it possible to reduce errors caused by electrode and electrolyte resistance. A four-electrode potentiostat-galvanostat is described in this paper. It allows for electric measurements of membranes in controlled potential and current conditions or measurements of transmembrane potential. The method of selection of the operation mode of the system is described.
TL;DR: In this paper, the effects of pre-stressing during winding and thermal stresses are calculated and discussed, and it is shown that under some conditions, elastic-plastic cycling leads to a stable state, whereas in others this results in runaway deformation that leads to coil destruction after a few cycles.
Abstract: Stresses and strains in the mid-plane of a pulsed magnet are analytically calculated by solving the system of equations describing the displacement in each layer of the coil. Nonlinear stress-strain characteristics and the propagation of plastic deformation are taken into account by sub-dividing each layer of the coil in the radial direction and changing the elastic-plastic matrix at each transition point. The effects of pre-stressing during winding and thermal stresses are calculated and discussed. Two coils that have been tested up to 60-70 T fields are described as examples. It is shown that, under some conditions, elastic-plastic cycling leads to a stable state, whereas in others this results in runaway deformation that leads to coil destruction after a few cycles.
TL;DR: In this paper, a modification to the conventional split Hopkinson pressure bar system is described, which virtually eliminates these oscillations, resulting in a smooth loading pulse and a significant improvement in the interpretation of the stress-strain behaviour.
Abstract: The conventional split Hopkinson pressure bar system for materials testing at high strain rates produces loading pulses that have a high level of oscillation superimposed on their approximately trapezoidal shape. These oscillations, which are a consequence of the short risetime of the loading pulse produced by the impact of a projectile, cause difficulty in the interpretation of the stress-strain results obtained by such a system. A modification to the conventional system is described, which virtually eliminates these oscillations, resulting in a smooth loading pulse and a significant improvement in the interpretation of the stress-strain behaviour. The modification involves placing a pre-loading bar before the two main bars of the conventional system. By suitable choice of pre-loading bar material with lower strength than the main bars, the high-frequency oscillations resulting from the projectile impact are attenuated as the pulse travels along the pre-loading bar; the loading pulse entering the main loading bar is then smooth with virtually no oscillations. Results for copper and steel test specimens are presented, which illustrate the significant advantages that the three-bar technique has over the conventional method in producing unambiguous stress-strain data.
TL;DR: In this article, a planar optical waveguide is coupled with a thin-layer cell which is connected to a flow injection analysis system, which is coated with indium tin oxide and modified with covalently attached glucose oxidase.
Abstract: Light generated by luminol electrochemiluminescence is coupled into a simple planar optical waveguide and is collected with a photomultiplier tube and a photon counter unit. The waveguide is mounted to a thin-layer cell which is connected to a flow injection analysis system. The waveguide is coated with indium tin oxide and modified with covalently attached glucose oxidase. The range of detection for glucose is 0-10 mM (correlation coefficient r = 0.9974), with a detection limit of 0.3 mM.
TL;DR: In this paper, an acousto-optic tunable filter (AOTF) is used to control the wavelength of a p-polarized light beam incident on a gold-coated diffraction grating.
Abstract: In this work the construction of a wavelength-tunable optical sensor with a fixed angle of incidence, incorporating an acousto-optic tunable filter (AOTF) is described. The AOTF is used to control the wavelength of a p-polarized light beam incident on a gold-coated diffraction grating. A surface plasmon resonance (SPR) is observed as a deep minimum in the intensity of the reflected beam as the incident wavelength is incremented. Slight modification of this arrangement allows measurement of the differential reflectivity profile with respect to wavelength. By locking to the zero differential corresponding to the SPR reflectivity minimum and monitoring the AOTF drive frequency (typically about 100 MHz) the SPR minimum position is then measured to within a precision of 0.0005 nm. The sensitivity of this system was found to be equal to a change in the refractive index of a gas of 1*10-6. Furthermore, by adding a chemically active overlayer to the system a concentration of 0.01 ppm NO2 in N2 was detected.
TL;DR: In this paper, the authors describe the use of the open photoacoustic cell (OPC) to obtain the thermal effusivity of transparent liquid samples and demonstrate the usefulness of the OPC configuration.
Abstract: In this paper we describe the use of the open photoacoustic cell (OPC) to obtain the thermal effusivity of transparent liquid samples. The samples used to demonstrate the usefulness of the OPC configuration were distilled water, diffusion pump fluid oil, amaranth seed oil, car oil, glycerol and some solvent liquids, such as trichloroethylene, isopropanol, white gasoline and ethanol.
TL;DR: In this paper, a new compact interferometric sensor was proposed for displacement measurement which utilizes the output intensity undulation caused by the optical feedback effect of a frequency modulated laser diode (LD).
Abstract: We propose a new compact interferometric sensor for displacement measurement which utilizes the output intensity undulation caused by the optical feedback effect of a frequency modulated laser diode (LD). In order to stabilize the undulation signal, the relationship between the feedback rate and the oscillation behaviour of the LD was investigated experimentally. The results revealed that the undesired higher order undulation could be suppressed by a low feedback rate. In addition, a new current modulation technique for the LD was developed for improving the performance of the signal processing based on a pseudo-heterodyne scheme. By these improvements, the measurement range was extended to several tens of centimetres with resolution of under 25 nm. Two sensor systems were combined for the measurement of a two-dimensional displacement of a spherical retro-reflector.
TL;DR: In this article, an automated measuring system is described which enables the complex microwave permittivity of liquids to be determined at particular frequencies and a special cell design offers the possibility of precisely measuring a range of liquids from low to high loss.
Abstract: An automated measuring system is described which enables the complex microwave permittivity of liquids to be determined at particular frequencies. A special cell design offers the possibility of precisely measuring a range of liquids from low to high loss. Constructional details of the sample cell are presented together with a system diagram of the microwave apparatus and a description of the analysis of primary data. Possible experimental errors are considered and results for measurements in the XN- and Ku-waveguide bands (5.3-8.4 and 12.5-18 GHz) are discussed.
TL;DR: In this article, the development of a prototype liquid level sensor using a thin walled cylinder vibrating in a circumferential mode and thin film piezo-electric polymer transducers is presented.
Abstract: The development of a prototype liquid level sensor using a thin walled cylinder vibrating in a circumferential mode and thin film piezo-electric polymer transducers is presented. Vibration characteristics of the fluid loaded cylinder are analysed with a finite element model incorporating the 'added mass' concept. The model is shown to predict the prototype sensor performance. It is also demonstrated that a series of non-dimensional graphs of the modal characteristics of empty cylinders can be used to predict the performance of this family of level sensors and provide a valuable design tool in the selection of suitable cylinder dimensions.
TL;DR: In this paper, a five-velocity-component LDV system was designed to make five nearly simultaneous velocity component measurements: coincident instantaneous U, V, W components of the velocity at one point and two V velocity components at two nearby locations.
Abstract: A five-velocity-component LDV system was designed to make five nearly simultaneous velocity component measurements: coincident instantaneous U, V, W components of the velocity at one point and two V velocity components at two nearby locations. The research is aimed at examining the relations among measured velocity components in order to investigate the near wall turbulence structure of 3D turbulent boundary layers (3DTBLs) and aid in the development of new turbulence models for 3D subsonic pressure-driven turbulent boundary layer (TBL). To map the relations between the 'sweeps' and 'ejections' of near wall turbulent fluid, two V measurement points can be traversed within a selected domain. In order to map the velocity field for given V measurement locations, a U, V, W measurement point is traversed in a domain defined by the two V measurement points. At the same time, the system can make measurements throughout the whole boundary layer to investigate other phenomena. Data from this system show that the uncertainties are low and the repeatibility of measurements is excellent. Data presented include the mean and fluctuation velocities, shear stresses, some of the triple velocity fluctuation correlations and some auto and cross correlation coefficients obtained at one measurement station of a high Reynolds number 3DTBL flow.
TL;DR: In this paper, the feasibility and first results of a near sensor digitalization of fluxgate signals (digital fluxgate magnetometer) are presented, and a completely redesigned magnetometer experiment for applications on planetary surfaces is presented.
Abstract: The feasibility and first results of a near sensor digitalization of fluxgate signals (digital fluxgate magnetometer) are presented. Applying the usual magnetometer electronics we have substituted the analogue section by a digital processing unit (DPU). The 2f0 signal is digitized at its second harmonic and mean values are online phase-sensitively calculated. Based on this development we present a completely redesigned magnetometer experiment for applications on planetary surfaces. Sensor and electronics including serial interface have to be in one housing, its weight is less than 150 g and the number of electrical connections is limited to four (power lines+serial link). Applications for the digital magnetometer on Earth are also discussed.
TL;DR: In this article, the CO2 and H2O vapour content in the plume from a 55 m smoke stack and the temperature of these gases were obtained by comparing the measured emission spectra with those modelled using the HITRAN atmospheric transmission database.
Abstract: Techniques for obtaining quantitative values of the temperatures and concentrations of remote hot gaseous effluents from their measured passive emission spectra have been examined in laboratory experiments and on field trials. These emission spectra were obtained using an adapted FTIR spectrometer with 0.25 cm-1 spectral resolution. The CO2 and H2O vapour content in the plume from a 55 m smoke stack and the temperature of these gases were obtained by comparing the measured emission spectra with those modelled using the HITRAN atmospheric transmission database. The spatial distributions of CO2, CO and unburnt CH4 in a laboratory methane flame were reconstructed tomographically using a matrix inversion technique.
TL;DR: In this article, the design of high-purity magnetic field shim coils for NMR and MRI laboratory solenoid magnets is discussed based on unique recursion relations for the coefficients of the most important expansion component.
Abstract: The design of high-purity magnetic field shim coils for NMR and MRI laboratory solenoid magnets is discussed. The individual shim consists of several current carrying elements which have the form of a circle or circular arc. The influence of the needed connecting conductors can usually be neglected. The magnetic field components of the mentioned elements can be expressed in terms of spherical harmonics. The design is based on unique recursion relations for the coefficients of the most important expansion component. Using the Monte Carlo method, the procedure of optimizing the element positions is illustrated for an X-shim design. The results obtained by measuring the field of the implemented shim are compared with those of the theoretical evaluation.
TL;DR: In this paper, a four-electrode capacitance-to-period converter for bilayer lipid membranes is described, where the capacitance measurement consists of cyclically charging and discharging the measured capacitance with a constant current regarding its absolute value.
Abstract: A four-electrode capacitance-to-period converter designed for capacitance measurements of bilayer lipid membranes is described. The capacitance measurement consists of cyclically charging and discharging the measured capacitance with a constant current, regarding its absolute value. The voltage of the studied capacitor is triangularly shaped. The cycle duration is proportional to the input capacitance. Capacitance measurement with a four-electrode system makes it possible to reduce considerably the errors caused by electrode and electrolyte impedance. It is possible to use high-resistance microelectrodes. The system makes it possible to measure the capacitance at an imposed polarization potential; the voltage oscillates about that value during the measurement. This makes it possible to measure the membrane capacitance as a function of polarization potential. An example is cited of using the capacitance-to-period converter in a computer-controlled measuring system.