Showing papers in "Measurement Science and Technology in 1991"
TL;DR: In this paper, a simple and practical procedure is described for the design of electrodes that produce well defined non-uniform electric fields for the study and application of negative dielectrophoresis.
Abstract: A simple and practical procedure is described for the design of electrodes that produce well defined non-uniform electric fields for the study and application of negative dielectrophoresis. Such electrode systems can be used to direct and assemble colloidal particles away from electrode edges, and this is demonstrated for the case of yeast cells.
255Â citations
TL;DR: In this article, a set-up has been devised to take two stereoscopic images of the flow simultaneously with only one camera, thus making automatic recording of three-dimensional (3D) velocity fields quite straightforward.
Abstract: The three components of the velocity field in a plane can be measured simultaneously by combining particle image velocimetry (PIV) and stereoscopy. A set-up has been devised to take two stereoscopic images of the flow simultaneously with only one camera, thus making automatic recording of three-dimensional (3D) velocity fields quite straightforward. Theoretical and practical considerations in implementing this stereoscopic PIV system are presented. The performance of the technique has been investigated by measuring several known displacements produced on a solid surface, and the application of the system to the measurement of the 3D velocity field in an acoustic streaming flow is presented.
226Â citations
TL;DR: In this article, the possibility of using a minimal volume photoacoustic cell to perform spectroscopy of samples is discussed, which allows one to obtain both absorption and transmission spectra with minimal experimental arrangement and cell machining requirements.
Abstract: The possibility of using a minimal-volume photoacoustic cell to perform spectroscopy of samples is discussed. It is shown that this alternative signal-to-noise-enhanced photoacoustic configuration allows one to obtain both absorption and transmission spectra with minimal experimental arrangement and cell machining requirements. The theoretical model is presented, the use of which is exemplified by a complete optical and thermal characterization of leaves.
138Â citations
TL;DR: In this paper, a gas sensor array with six metaloxide-semiconductor field effect transistors (MOSFETs) operating at elevated temperatures was exposed to two types of multiple-component gas mixture, one containing 5-65 ppm of hydrogen, ammonia, ethanol and ethylene in air and the other containing hydrogen and acetone in air.
Abstract: A very promising way of increasing the selectivity and sensitivity of gas sensors is to treat the signals from a number of different gas sensors with pattern recognition (PARC) methods. A gas sensor array with six metal-oxide-semiconductor field-effect-transistors (MOSFETs) operating at elevated temperatures was exposed to two types of multiple-component gas mixture, one containing 5-65 ppm of hydrogen, ammonia, ethanol and ethylene in air and the other containing hydrogen and acetone in air. The signals from the sensors were analysed with both conventional multivariate analysis, partial least-squares (PLS), and artificial neural network (ANN) models. The results show that both hydrogen and ammonia concentrations can be predicted with PLS models; the predictions were even better with ANN models. The predictions for ethanol and ethylene concentrations were, however, poor for both types of model. Hydrogen and acetone, from the two-component mixture, were best predicted from an ANN model.
121Â citations
TL;DR: In this paper, the authors describe the performance of capacitive transducers constructed with v-groove backplates and membranes of varying thicknesses, and give design criteria for producing transducers at well defined frequencies.
Abstract: Capacitive transducers provide a means of coupling ultrasound efficiently into air. Many investigations of these transducers have been reported but none have provided a reliable means of producing a transducer resonating at a specific frequency. The authors describe the performance of capacitive transducers constructed with v-groove backplates and membranes of varying thicknesses, and give design criteria for producing transducers at well defined frequencies.
115Â citations
TL;DR: The scanning beam illumination method as discussed by the authors provides a highly efficient method of illuminating flow fields for recording PIV (particle image velocimetry) images so that the instantaneous velocity profile of the whole flow field can be determined.
Abstract: The scanning beam illumination method provides a highly efficient method of illuminating flow fields for recording PIV (particle image velocimetry) images so that the instantaneous velocity profile of the whole flow field can be determined. The authors analyse the scanning beam technique and discuss its advantages over the more conventional pulsed illumination methods. The versatility of the scanning beam system is demonstrated with examples of its application to the study of both breaking water waves and pneumatic particle transport.
71Â citations
TL;DR: In this paper, a machine was designed and built that allows the winding of a layer of fibre rovings of precisely controlled thickness between the layers of wire, and a field of 58 T has been obtained in a 20 mm bore; in a 12 mm bore a maximum field of 669 T resulted in destruction of the coil.
Abstract: Coils for pulsed magnetic fields were developed using layer by layer reinforcement with fibre composite material The thickness of each individual layer of the reinforcement was optimized using a simple 'finite element' calculation method A machine was designed and built that allows the winding of a layer of fibre rovings of precisely controlled thickness between the layers of wire So far, a field of 58 T has been obtained in a 20 mm bore; in a 12 mm bore a maximum field of 669 T resulted in destruction of the coil
67Â citations
TL;DR: In this paper, a technique for measuring Mossbauer spectra of metallurgical slags with a spatial resolution of approximately 500 mu m was developed, using a 57Co source with high specific activity, the gamma-ray beam can be collimated from the conventional diameter of approximately 1 cm to a diameter of 500 m m.
Abstract: The authors have developed a technique for measuring Mossbauer spectra of metallurgical slags with a spatial resolution of approximately 500 mu m. Using a 57Co source with high specific activity, the gamma-ray beam can be collimated from the conventional diameter of approximately 1 cm to a diameter of 500 mu m. The sample is mounted in an epoxy resin, ground to a thin disc and then mounted on an x-y stage directly behind a lead shield with a 500 mu m hole. The authors studied a melt composition in the system FexO-Al2O3-SiO2 with 62 mol.% FeO. Five spectra at 298 K were recorded at increasing depths in the quenched slag, with one additional spectrum taken in a 10 mu m layer at the surface. The spectra can be fitted to two doublets with different linewidths. The relative areas of the doublets vary dramatically with depth, and indicate that the proportion of the glass phase is highest near the surface and lowest in the centre of the quenched slag.
66Â citations
TL;DR: In this article, a fully submersible capillary suction probe technique was developed for bubble size measurement in large-scale stirred vessel reactors, which uses a vacuum to continuously withdraw a small stream of gas-liquid dispersion through a short capillary tube with a funnel-shaped inlet.
Abstract: The authors describe a fully submersible capillary suction probe technique developed for bubble size measurement in large-scale stirred vessel reactors. The method uses a vacuum to continuously withdraw a small stream of gas-liquid dispersion through a short capillary tube with a funnel-shaped inlet. Photodetectors mounted on the tube are used to detect the bubble slugs, producing a binary-waveform type signal. The probe is interfaced to a high-speed data acquisition system controlled by a microcomputer, to allow storage of large amounts of data and fast processing. Some aspects of two-phase flow inside the capillary are discussed, as well as details of the probe calibration procedure. The automated bubble size measurement technique achieved very good reproducibility of results and very high rates of sampling from bubble sizes down to 0.3 mm diameter. Typical results obtained in a 1.0 m diameter stirred vessel are presented.
63Â citations
TL;DR: In this paper, an electrical capacitance method is described for the measurement of multi-interface levels of gas/liquid/solid, including the foam layer, using a novel multi-electrode capacitance sensing element.
Abstract: An electrical capacitance method is described for the measurement of multi-interface levels of gas/liquid/solid, including the foam layer. It uses a novel multi-electrode capacitance sensing element. A capacitance transducer based on the charge/discharge principle is used, which is stray immune and capable of operating at high frequencies to reduce the effects of the liquid conductivity on the measurement. The presence of foam is detected by processing the fluctuating component of the capacitance signal, which reflects the inherently unstable feature of the foam, whereas the multi-interface levels are reconstructed by processing the steady-state component of the measured capacitances.
63Â citations
TL;DR: In this paper, a modified Abbe refractometer for measuring the optical transmittance across a plane interface from a diffusely scattering turbid sample into a prism is described.
Abstract: The authors describe a modified Abbe refractometer for measuring the optical transmittance across a plane interface from a diffusely scattering turbid sample into a prism. When the prism refractive index exceeds that of the sample, a critical angle is present even when the sample contains particles which are wavelength sized or larger. Hence, the sample refractive index may be measured. However, measurements of transmittance near the critical angle show a poor definition of the critical angle for some samples, with a consequent loss of experimental precision in the refractive index. The method is applied to several polymer latex dispersions and some glass ballotini. For all lattices the measured refractive index varies linearly with latex volume fraction. For all dispersions except one the dependence of refractive index on volume fraction is in good agreement with the theory of refractive index based on Mie scattering by spherical particles.
TL;DR: An instrument for the reproducible measurement of polymerization shrinkage kinetics, constructed around a disc-shaped specimen sandwiched between two glass plates, is described in this paper, where the physical response of this measurement system, in relation to the characteristics of photo-polymerized materials, has been subject to an original detailed analysis and validation.
Abstract: An instrument for the reproducible measurement of polymerization shrinkage kinetics is described, constructed around a disc-shaped specimen sandwiched between two glass plates. Test specimens of light-activated resins were irradiated through the lower, rigid plate. The physical response of this measurement system, in relation to the characteristics of photo-polymerized materials, has been subject to an original detailed analysis and validation. The upper non-rigid plate was readily deflected by an increase of the adhesive stress from the polymerizing and shrinking sample. Deflection was measured by a LVDT transducer and computer recorded. Dimensional changes were confined to the specimen disc-thickness dimension, such that the fractional linear shrinkage approximated the volumetric shrinkage. Shrinkage data are reported for representative unfilled and composite resins. Equilibrium shrinkage magnitudes ranged from 1.3 to 7.9%. The kinetic behaviour was approximately characterized by an overall time constant, ranging from 12.5-27 s, associated with an exponential growth curve, although the initial shrinkage was nearly linear in time, for many materials, due to non-steady-state concentrations of polymer free radicals.
TL;DR: In this article, the sensor offset as a function of the ring rotation angle with respect to the detector coil has been studied for three different fluxgate sensors of the RingCore type, which consists of metallic glass ribbons which have been heat treated in different ways so that different magnetization curves and noise levels are obtained.
Abstract: The sensor offset as a function of the ring rotation angle with respect to the detector coil has been studied for three different fluxgate sensors of the ringcore type. The core material consists of metallic glass ribbons which have been heat treated in different ways so that different magnetization curves and noise levels are obtained. For the best core the offsets are rather low (a few nT) and only slightly dependent on the rotation angle.
TL;DR: In this paper, an active compensation technique for improving the performance of a mu-metal magnetically shielded room is presented, where active compensation is established by measuring the magnetic field inside the room by a SQUID magnetometer.
Abstract: An active compensation technique is presented for improving the performance of a mu -metal magnetically shielded room. Active compensation is established by measuring the magnetic field inside the room by a SQUID magnetometer. The output of this sensor is amplified and connected to a coil surrounding the room. The magnetic field generated in this way compensates the measured field inside the room. Active compensation was tested for magnetic fields in the vertical direction in a shielded room with one mu -metal shield. At low frequencies a shielding improvement of typically 40 dB was obtained. Measurements performed on a room with two mu -metal shields indicated that the attainable improvement is not limited by the amount of mu -metal applied in the room. The active compensation set-up is described in detail and experiments performed on the two magnetically shielded rooms are presented and discussed.
TL;DR: In this paper, two electrostatic probes have been tested simultaneously in the same plasma, where the passive and active probes were located on the midplane of a capacitively coupled RF plasma.
Abstract: Two electrostatic probes have been tested simultaneously in the same plasma. The passive design uses a distributed inductive chain to block RF signals from the probe tip. The tip itself is capacitively coupled to a secondary ring electrode of large area, which effectively drives the probe tip potential in phase with the plasma space potential. The active design substitutes an externally generated sinusoidal signal (synchronous with the plasma excitation) of controllable phase and amplitude for the signal from the ring. Both probes were located on the mid-plane of a capacitively coupled RF plasma. In most cases the passive probe is found to float more positive than the active one. Both probes give results in close agreement when the plasma excitation is predominantly sinusoidal. The passive probe has a broad-band response which enables its tip to follow more closely non-sinusoidal RF potentials in the plasma. The active probe is more expensive in terms of components external to the plasma chamber but is considerably simpler to construct.
TL;DR: In this article, a technique for the simultaneous determination of specific heat, thermal conductivity and thermal diffusivity of metals has been developed for a transient heat-flow type where the heating element serves both as a heat source and the temperature detector.
Abstract: A technique is developed for the simultaneous determination of specific heat, thermal conductivity and thermal diffusivity of metals. The method is of a transient heat-flow type where the heating element serves both as a heat source and the temperature detector. The experiment is arranged in such a way that the temperature development in the sample is close to adiabatic. The method has been tested on samples of pure iron (99.95% of purity), cast iron (SIS 2140) and austenitic stainless steel (SIS 2343). The results obtained were in an excellent agreement with the literature data for these materials. The accuracy of determination of specific heat has been additionally tested on an Al sample.
TL;DR: A critical evaluation of the state of the art in tactile sensing is presented to provide clues for the conception and design of artificial haptic systems capable of surface texture discrimination, stable object grasping, fine-form detection, hardness evaluation and thermal sensing.
Abstract: A critical evaluation of the state of the art in tactile sensing is presented. Various fields of application such as prosthetic and teleoperation are covered, but particular attention is paid to advanced robotics. Tactile sensing modalities are discussed in some detail through reference to basic issues of contact mechanics to provide clues for the conception and design of artificial haptic systems capable of surface texture discrimination, stable object grasping, fine-form detection, hardness evaluation and thermal sensing.
TL;DR: In this paper, the design of an open field site for the calibration of antennas in the frequency range 30-1000 MHz is described, followed by methods for calibrating the antenna factor of antennas.
Abstract: Testing electronic equipment for radiated emissions requires the accurate calibration of antennas. This in turn entails the use of a high-quality measurement site. The design of an open-field site for the calibration of antennas in the frequency range 30-1000 MHz is described. An antenna that is used as a primary standard must have a calculable antenna factor since there are uncertainties in quantifying the quality of the site and hence of setting up a known field. The design of a standard dipole antenna and the S-parameter characterization of its balun/matching network is described, followed by methods for calibrating the antenna factor of antennas.
TL;DR: The principles of aperture synthesis are outlined and the implementation of these principles in some algorithms is examined with reference to radio astronomy in this paper, where progress made in applying these techniques at optical frequencies in terrestrial and spacecraft instruments is briefly reviewed.
Abstract: The principles of aperture synthesis are outlined and the implementation of these principles in some algorithms is examined with reference to radio astronomy. Progress made in applying these techniques at optical frequencies in terrestrial and spacecraft instruments is briefly reviewed.
TL;DR: In this paper, the particle size and velocity in a gas-solid two-phase flow using the phase-Doppler technique based on transient recorder data processing and the cross-spectral density (CSD) function are improved in accuracy by introducing new complex interpolation functions to the discrete frequency lines.
Abstract: Measurements of the particle size and velocity in a gas-solid two-phase flow using the phase-Doppler technique based on transient recorder data processing and the cross-spectral density (CSD) function are improved in accuracy by introducing new complex interpolation functions to the discrete frequency lines. The improvements of the accuracy for size and velocity measurements are additionally based on the use of an external electronic unit, which is allowed to trigger the transient recorder near the peak of the envelope of the band-pass filtered bursts. This procedure could improve the signal-to-noise ratio of the processed part of the signal and hence the accuracy and data rate. A simultaneous measurement of the gas velocity is achieved by seeding the flow with small spherical glass beads which have the same refractive index as the dispersed phase particles. The identification of signals from these seeding particles-with a diameter less than 4 mu m-is based on the phase between the two signals.
TL;DR: The ring described allows a single microcomputer to control a number of remote digital interfaces, in a simple manner, as though they were connected directly to its input/output (I/O) bus.
Abstract: A ring interface bus has been developed for use in computer-controlled apparatus for making precise electrical measurements. To achieve a low uncertainty in the results of such measurements it is necessary to eliminate unintentional electrical disturbances in the quantities being measured. The ring described allows a single microcomputer to control a number of remote digital interfaces, in a simple manner, as though they were connected directly to its input/output (I/O) bus. The interfaces transfer data to and from measurement and control circuits required by the apparatus. The interfaces are grouped into outstations which, along with the controlling microcomputer, are connected in a ring by means of optical fibres which electrically isolate each outstation whilst providing bidirectional data transfer at 200 kbyte s-1. Care has been taken to eliminate or minimize both line-frequency interference and digital interference produced by an outstation. The ring has been applied successfully both to room-temperature metrology and to a cryogenic apparatus incorporating a SQUID detector.
TL;DR: In this article, a critical discussion is given of some of the experimental parameters involved in measurement of the three-, four-and five-fold differential cross sections obtained in (e,2e), ( e,(3-1)e) and (e-3e) experiments, respectively.
Abstract: A critical discussion is given of some of the experimental parameters involved in measurement of the three-, four- and five-fold differential cross sections obtained in (e,2e), (e,(3-1)e) and (e,3e) experiments, respectively. Features observed in the triple coincidence time-delay spectrum are attributed to fully accidental, semi-accidental or true triple coincidence events. Formulas are given that allow computation of the true coincidence rate, the percentage statistical error and the signal-to-background ratio, and to optimize the gas density-electron beam current product for any given experiment. The effective coincidence energy resolutions and transmission functions are defined, and their importance clearly demonstrated.
TL;DR: In this article, the authors present a wide bandwidth pulse transmission technique for the study of the interactions between near-plane-wave ultrasound and thin films (down to 50 mu m) of adhesive polymer set between glass substrates.
Abstract: The authors present a novel wide bandwidth pulse transmission technique for the study of the interactions between near-plane-wave ultrasound and thin films (down to 50 mu m) of adhesive polymer set between glass substrates. Acoustically thick transducers are clamped in coaxial alignment on either side of the glass substrates and short (less than 10 ns) acoustic transients are made to reverberate to and fro in the test bond. The signal received consists of time-resolvable and successively dispersed reverberations from the bond layer. It is digitized at 1 GHz and approximately corrected for the effects of transducer insertion and transient radiation coupling between the transducers. Frequency domain methods are then applied to estimate absorption coefficient, propagation velocity and the real and imaginary parts of the plane-wave elastic modulus, all as functions of frequency. Preliminary data obtained by this technique indicate that a number of adhesives display plane-wave velocity dispersion and absorption as a function of frequency that can be modelled by a relaxation process with a single time constant. A simple spring-dashpot model for an anelastic solid provides a mechanistic equivalent to the observed relaxation.
TL;DR: In this paper, two improved methods for hot-wire anemometer calibration in the low-speed range (15-95 cm/s) are described: a laminar pipe-flow method, and a shedding-frequency method.
Abstract: Two improved methods for hot-wire anemometer calibration in the low-speed range (15-95 cm/s) are described: a laminar pipe-flow method, and a shedding-frequency method. For the laminar pipe-flow method the calibration is performed in the exit plane of a fully-developed laminar pipe flow. For the shedding-frequency method the shedding frequency of a parallel mode cylinder wake is measured; the velocity is then obtained from a continuous Strouhal-Reynolds number relationship. Calibration results from the present methods were compared with each other and with results from a commercially available calibration jet. The present methods were demonstrated as a simple, but accurate means for low-speed hot-wire calibration.
TL;DR: In this article, a new interpolation procedure is introduced which accounts for variable peak width and is adaptive, to avoid the usual periodicities inherent to this interpolation problem, and the new estimators are compared with other commonly used methods using simulated LDA signals.
Abstract: The discrete Fourier transform (DFT) finds widespread use in laser anemometry for the estimation of frequency, phase and signal-to-noise ratio (SNR) of individual Doppler signals. Peak interpolation is a common method for increasing the accuracy of these estimates without significantly adding to the computational load. Many methods for peak interpolation do not account for large variations in the peak width due to signal length variations, and thus often result in biased SNR estimates and/or frequency estimates. A new interpolation procedure is introduced which accounts for variable peak width and is adaptive, to avoid the usual periodicities inherent to this interpolation problem. Estimators of frequency and SNR based on this interpolation are compared with other commonly used methods using simulated LDA signals. The new estimators are shown to be more accurate and robust.
TL;DR: In this article, the uncertainties in the parameters of the functional expression used to fit a set of experimental points, with both coordinates subject to error, are analytically determined by means of the least-squares canonical equations and the error propagation law only.
Abstract: By means of the least-squares canonical equations and the error propagation law only, the uncertainties in the parameters of the functional expression used to fit a set of experimental points, with both coordinates subject to error, are analytically determined.
TL;DR: In this paper, a single-beam thermowave technique is described, based on a two-frequency modulation of the laser beam used for both excitation and detection, which provides frequency conversion to the low-frequency region and phase sensitivity without applying the lock-in detection method.
Abstract: A single-beam thermowave technique is described, based on a two-frequency modulation of the laser beam used for both excitation and detection. The differential frequency content of the laser beam is used as a measure of the photothermal response. This technique provides frequency conversion to the low-frequency region and, to a certain degree, phase sensitivity without applying the lock-in detection method. By using a modulation set-up comprising two acousto-optical modulators and by applying a balance detector arrangement, an intermodulation content of 10-7 for zero response and a noise of 10-7 Hz-1/2 could be achieved. The new single-beam technique yields substantial evidence in the field of ion implantation and laser annealing of semiconductors, such as the dose of implanted species, annealing threshold, the defects generated by the ultrafast solidification and the homogeneity of the laser beam applied for irradiation.
TL;DR: In this article, an experimental system for the study of electron-molecule scattering at high resolution is described, where synchrotron radiation from the synchroron radiation source (SRS) at the SERC Daresbury laboratory is used to photoionize Ar at threshold (78.65 nm).
Abstract: An experimental system for the study of electron-molecule scattering at high resolution is described. Synchrotron radiation from the synchrotron radiation source (SRS) at the SERC Daresbury laboratory is used to photoionize Ar at threshold (78.65 nm). The resulting photoelectrons are formed into a beam of energy spread 3.5 meV (FWHM) and crossed with a Campargue-type supersonic molecular beam. The primary electron beam energy can be varied over the range 0.04-20.0 eV. An electrostatic hemispherical monochromator with a narrow acceptance cone (+or-6 degrees ) together with a position-sensitive detector provides energy analysis of the scattered electrons. In addition a second detector comprising a cascaded pair of microchannel plates and a high-voltage anode can record without energy analysis those electrons scattered over a much wider angular range (90+or-30 degrees ). The performance of the apparatus is illustrated with data on O2, N2, SF6, NO and CO2.
TL;DR: Digital radiography is progressively replacing conventional (film-based) radiographic techniques promising consistently high levels of image quality, more effective use of radiation and more efficient work practices.
Abstract: Digital radiography is progressively replacing conventional (film-based) radiographic techniques promising consistently high levels of image quality, more effective use of radiation and more efficient work practices. At the same time its introduction poses new challenges to those physical scientists who design radiological imaging systems and those who provide scientific/technical support to a clinical radiology service Scientific aspects of those digital X-ray imaging systems which are proving most successful are described. Physical measurement techniques developed to evaluate the imaging performance and radiation dose efficiency of clinical digital radiography systems are outlined. Directions in which digital X-ray imaging technology may evolve in the 1990s are discussed.
TL;DR: In this article, a W-band waveguide system is described which enables the complex permittivity of high-loss liquids to be measured accurately at a spot frequency of 90 GHz.
Abstract: A W-band waveguide system is described which enables the complex permittivity of high-loss liquids to be measured accurately at a spot frequency of 90 GHz. Mechanical restrictions are overcome by using an oversized rectangular cell. Data are presented and the experimental errors considered. The authors compare results found from an oversized rectangular waveguide cell with those from a standard circular waveguide cell and an E-band rectangular waveguide cell, operated at the upper limit of its frequency range. The results for a range of liquids are comparable within experimental errors.