Table of contents

Mechanical surface profiling can be used not just for characterization of surface quality but also to measure the contour of the shape of micromachined structures. Here the surface features in vertical and horizontal directions are of the same order of magnitude, producing three problems: the movement of the stylus is in an arc of a circle; the stylus cone prevents the profiling of steep sidewalls; concave structures must have large aspect ratios relative to the aspect ratio of the convex stylus. This paper describes the correction of profiles which are distorted by the movement of the stylus in a circle arc and the profiling of steep sidewalls, by using a half-cone stylus tip and an inclined positioning of the specimen. However, the problem of high aspect ratios cannot be resolved easily because of the limited mechanical stability of a stylus with a small diameter and a large length.

CCD video cameras have been used extensively in recent years for image capture in fluid flow measurements with the particle image velocimetry (PIV) technique. Recent advances in CCD imaging technology have improved and extended the PIV technique to new applications, ranging from rotating machinery to 3D measurements. The progressive scan interline transfer CCD allows the time interval between two consecutive frames to be very small. Combined with frame straddling technique and the cross correlation analysis method, video cameras with such CCD design can be used for high-speed flow measurements, without the need for image shifting or image tagging methods to resolve directional ambiguity. Investigation of the pixel fill factor in CCD designs has indicated that the particle image diameter of two pixels or more is required to minimize the error in particle image location, which is important for accurate PIV measurements. Results of the investigation on a commercial video camera with the progressive scan interline transfer CCD design for its capability in high-speed flow measurements are presented. It is shown that this camera can achieve images for a time interval as small as s and for velocities of up to 250 m in the experiment.

A measurement study was performed to obtain a full-field quantitative description of a three-dimensional, two-phase bubbly flow. Particle image velocimetry (PIV), a whole-field, non-invasive velocity measurement technique, was utilized. PIV is capable of producing an instantaneous velocity map of steady-state and transient flows of a fluid seeded with microscopically small neutral density particles.

The objective of this investigation was to study the turbulence structure in a co-current bubbly flow. The obtained information will help to determine parameters needed for two-phase flow modelling. The study investigated the influence of bubbles on the surrounding flow field (bubble/flow interaction). A stereoscopic reconstruction technique was used to obtain three-dimensional velocity vector data from the recorded planar images. Radial distributions of volume-averaged turbulence intensities and Reynolds stresses were calculated. The volume-averaged turbulent kinetic energy within the measurement zone due to a rising bubble is presented.

A diode-laser sensor system has been developed to measure the concentrations of NO, O, CO, and in combustion gases using absorption spectroscopy and fast-extraction sampling techniques. Measured survey spectra of the NO 3 band (the R branch) and O lines from the band in the spectral region from 5556 to 5572 were recorded and compared with calculated spectra to select optimum transitions for detection of NO. Similarly, measured survey spectra of the O 3 band from 6535 to 6600 were used to identify optimum transitions for detection of O. High-resolution NO absorption measurements ((7.5) and (7.5) lines) were recorded in a fast-flow multipass cell containing probe-sampled combustion gases to determine NO concentrations in a laminar, premixed -air flame, seeded with . For fuel-lean conditions, the measured NO mole fractions corresponded to 68% of the injected . For fuel-rich conditions, the fraction of converted to NO decreased with increasing equivalence ratio. In additional experiments, CO, and absorption measurements (the R(13) line of the 3 band, the R(16) line of the band and the RQ(7, 8) line of the b band, respectively) were used to determine species concentrations above a laminar, premixed -air flame. Good agreement was found between measured CO, and concentrations and calculated chemical equilibrium values.

This paper describes work which has been carried out to investigate a rotating stereoscopic imaging system consisting of two line-scan cameras for measurement. Algorithms have been proposed and experimentally tested which allow three-dimensional co-ordinates to be derived from a defined object workspace. The use of stereoscopic imaging is not new; however, what is novel in this approach is the method used to produce panoramic images of the workspace surrounding the rotating line-scan camera. This system is particularly suited to applications which require the `all-round' observation of a scene. These include autonomous vehicle guidance and path-planning for complex manipulator manoeuvres. The results indicate that the positions of targets can be determined, at best, to a measurement accuracy of within mm in the X axis (horizontal), mm in the Y axis (vertical) and mm in the Z axis (range) at a camera-to-object range of 1.5 m.

We evaluated in this paper an improved technique for measuring gear transmission error (GTE) at high speed, by using low pulse per revolution optical encoders. The originality of this technique lies in the fact that highly precise, completely digital measurements of torsional vibration or transmission error (TE) at high speed are achievable by the use of low-price, basic optical components. The lengths of encoder pulses are estimated with a high-frequency timer (100 MHz): thus, it appears that the theoretical precision of this device depends only on the angular speed of shafts, not on the number of pulses per revolution of the encoder. In practice, the intrinsic encoder accuracy (namely the grating or electronic signal processing precision) directly affects precision measurements. Alternatively, the number of pulses per revolution of the encoder specifies the resolution.

We examined the possibility of calibrating encoders through using a specific test rig. The determination of corrective data assigned to each grating leads to an insignificant improvement of the precision measurement. The coherence from one revolution to another does not present any significant deterministic component. The overall precision achieved is less than 0.03 second of arc for each frequency of the power spectral density.

This calibration device only gives a good assessment of eccentricity induced by mechanical mounting of optical discs on a shaft, compared with the direct measurement on grating discs. The correlation between the two measurements is less than 3% of the magnitude of the relative eccentricity. Thus, the encoder technique seems to be a cheap and easy way to implement transmission error measurement on real mechanical systems with high precision and sufficient reliability.

The paper describes some design aspects of newly developed bimorphic piezoresistive humidity sensors. Their operation relies on the bimorphic bending of a polymer-coated diaphragm as a result of the humidity-induced swelling of the polymer. The mechanical bending is evaluated by means of piezoresistors located on the diaphragm, but physically separated from the polymer. This physical separation between the mechanical and the electrical transducer is expected to improve the reliability and long-term stability of the sensor devices. In order to evaluate the benefits and limitations of the piezoresistive humidity sensor, we have developed empirical models based on consistent material parameters to describe the sensor behaviour. Transfer functions correlating the sensor output voltage to the relative humidity have been developed assuming a zero-humidity offset voltage and a linear relationship between the voltage and the humidity. The transfer functions were validated by measurements on prototypes. The measurement accuracy and long-term stability of the sensors were found to be limited by the temperature sensitivity of the polymer's response function and by an initial voltage drift due to the relaxation of technologically induced mechanical stress. These undesired effects can, however, be reduced by means of electronic temperature compensation and controlled artificial ageing.

A highly selective ZnO: based thick-film hydrogen sensor has been developed. The surface morphological studies indicate that the average grain size increases with higher amounts of in ZnO. It is observed that the sensitivity increases with the grain size. A possible working model for the sensor is postulated. was mixed in ZnO in various weight percentages. These mixtures were screen printed on alumina substrate. The sensors operate at an operating temperature of C and their conductance increases linearly with the square root of the concentration of gas in ambient air. The response time of these sensors is around 20 s.

We have designed and developed a pulsed field magnetometer to measure the dynamic properties of magnetic dispersions commonly used in recording media. The instrument produces well defined single-shot field pulses of variable amplitude from 10 Oe to 1270 Oe, adjustable in steps of 10 Oe. Pulse widths of between and can be selected with a resolution of . The rise and fall times of the pulses are between and and are symmetrical throughout the range of field amplitudes and pulse widths. Results obtained from the instrument indicate that it is possible to distinguish between inherent particle switching and physical particle rotation, which is not possible when using conventional AC and DC magnetometers. It has also been found that the instrument may be used in on-line measurements to access the quality of magnetic pigment dispersions used for magnetic tape manufacture.

A nano-stabilization technique is developed for the observation of Ramsey fringes in low repetition rate Rydberg electron wavepacket experiments. The stabilization system consists of a CCD array monitoring optical interference fringes of a reference CW laser beam passing through a Michelson interferometer, a PID feedback circuit generating an error voltage, and a piezo responding to the error voltage to compensate for geometric fluctuations in the interferometer of nm with a response time ms. The proficiency of the stabilized interferometer is demonstrated in an experiment to observe Ramsey fringes in autoionizing Rydberg states of Xe.

A study of the vibration isolation system in scanning probe microscopes (SPMs) to reduce external noises in a wide range of frequencies is presented. For the low-frequency isolation case, a pneumatic system based on a cylindrical plastic tube with an elastic membrane for damping is studied. The theoretical model and the experimental results obtained from it to isolate noises above 2 Hz are discussed. For the high-frequency isolation, a design based on stacked metallic sheets, with cylindrical elastomers (viton) between them, is simulated. The effect of the elastomer geometry when it is used in a real case by means of the transfer function of the vibration system is discussed. From the results, we are able to predict and optimize the performance of SPMs with regard to noise isolation.

This paper describes the development of a new kind of two-dimensional high-resolution imaging integrated circuit. It is used in conjunction with micro-channel plate (MCP) electron multipliers. The electron detection array IC (EDAIC) consists of a two-dimensional array of charge sensing circuits each covered by its own m aluminium electrode on the IC surface. These electrodes are used to collect electronic charge from the MCP channel outputs. The sensors are arranged and accessed in a DRAM-like manner and can be configured to generate either an analogue or a digital output. The EDAIC device is a multiple, simultaneous, event detector suitable for medium-count-rate applications and was originally developed for use in an x-ray photoelectron spectrometer.

Transparent windows used to perform optical measurements in `difficult' samples such as natural waters in the environment and sewage streams in treatment plant inevitably become coated with chemically and/or biologically deposited films. These usually dominate the instrument's performance and reliability. We describe here a windowless measurement configuration, which avoids this fouling by supporting the water sample from below on an air bubble. By controlling the air pressure in the bubble with a fast pressure-modulator and feedback controller, the air-water meniscus' curvature is stabilized, and serves as a reliable optical interface to the liquid medium. Round menisci up to 8 mm in diameter have been stably controlled, with electronically regulated curvature. By periodically purging the bubble with air, long-term measurements of scattering and long-path absorption are possible, substantially free from fouling problems.

A new electrostatic positron beam has been constructed and tested. The energy range spans more than three decades, from less than 50 eV to more than 50 keV. The machine can operate in a low-energy mode (50 eV to 2 keV) with a beam diameter (FWHM) from 2.9 to 1.7 mm or in a high-energy mode (1 keV to 50 keV) with a FWHM from 1.4 to 1.0 mm. The transverse spot position on the target is very stable, with wandering being much smaller than the beam diameter. The apparatus transmission function is very flat, with an intensity change of only 30% when going from 10 eV to 50 keV. The product of moderation and optical transmission efficiency is , corresponding to 800-1000 with a 1 mCi source. The apparatus shows low noise in S-parameter measurements. The background of the high-energy wing of the annihilation line is also one of the best reported. Optical and constructional details are given.

This paper addresses questions of amplitude stability and laser frequency modulation with reference to carbon dioxide laser saturation spectra in the 10 m spectral region. We demonstrate a novel laser intensity stabilizer acting on the laser current supply, together with modulation and feedback loops operating up to 100 kHz. These permit routine phase locking of lasers and locking of lasers to saturated absorptions even when the latter are rather weak. Tuneable radiation can be obtained near the laser lines with a spectral purity much better than 1 kHz. Saturated absorption spectra can thus be obtained at linewidths of a few kilohertz over a dynamic range of , while the methods used have more general applicability.

A laser-based light source for circularly polarized VUV radiation generated by nonlinear sum-frequency mixing is described. By choosing an appropriate nonlinear resonant process a light flux of up to photons at a bandwidth smaller than 1.2 is achieved. The determination of the polarization state is performed by means of using a four-mirror analyser. A degree of circular polarization greater than 0.99 was found for several mixing processes. These properties make this instrument an ideal source for high-resolution spectroscopic studies of polarization-dependent photo-ionization or photoemission at photon energies up to 14 eV.

Heat flux gauges at a flat plate are designed suited to measure the heat transfer in transition boundary layers. The measuring technique employed (cold thin films) is convenient for transient experimental facilities (such as a Ludwieg tube). The development of a well defined and optimized sensor design is discussed.

A general method of model parameter estimation for irregularly sampled data is introduced, with special emphasis on estimation of the power spectral density. The main application is processing of data sets from a laser Doppler anemometer (LDA), for which often the mean data rate is low and the total data set duration is short. It is shown that the model parameter estimation can be quite effective under these conditions, resulting in consistent, bias-free estimates which exhibit very low variance. Simulations and experiments are used to examine the performance of the technique.

A new estimator is introduced for correlation functions between two or more channels of a laser Doppler anemometer. The estimator is based on a sample-and-hold reconstruction and resampling of each channel, thus eliminating the coincidence requirement between channels. The estimator is applicable to two-component or three-component laser Doppler anemometry (LDA), but is particularily interesting for two-point or multi-point LDA, where coincidence is practically non-existent. The estimator is fully derived in this paper and verified using simulated data sets. An appropriate transformation of coordinate systems is introduced for the case of a rotated or non-orthogonal measurement system.

Hot-wire anemometric measurements of non-isothermal flows require that temperature-compensation or correction systems should be applied. A basic method of temperature compensation in a constant temperature anemometric bridge circuit involves an additional compensating sensor being connected into the bridge. The resistance of the temperature-compensating sensor must be several times bigger than that of the anemometric sensor. That is one of the major limitations of those sensors. This paper presents some modification to the constant-temperature bridge system with temperature compensation. A compensating sensor of any resistance may be applied there. As a result, a wider group of measuring sensors may be used, which, in certain applications, may optimize measuring processes. This modification consists of transformation of the voltage supplying the compensating branch of the anemometric bridge. Special attention was given to the theoretical basis of temperature compensation. Schematic diagrams of the measurement circuits as well as one selected application of the new system for a low-frequency case have been presented.

The development of a novel slotting technique for the estimation of the autocorrelation function (ACF) of randomly sampled data has eliminated the major disadvantages of the Mayo algorithm. The reduced variance of the estimators in the vicinity of and the elimination of estimators greater than 1 has opened the possibility to approximate the ACF with a curve-fit, leading to a noise-free estimator of the power spectrum. In this paper we describe an analytical function, based on known properties of turbulence power spectra, which is suited to the approximation of the ACF from randomly sampled laser-Doppler anemometry (LDA) data with noise. Using simulated LDA data, based on both simulated and hot-wire measured turbulence signals, it is shown that the method estimates the power spectrum with an error of less than 25% over six decades of power. Application to various LDA data sets shows that the analytical function, derived from the spectral properties, is sufficiently flexible to describe ACFs from data sets of pipe flow, mixing layer flow, flow in stirred tanks and flows around airfoils. An extension of the technique could be in automatic incorporation of periodic components and compensation for data sets with a high velocity bias (turbulence intensities > 40%).

In this paper, a non-nulling calibration method using a seven-hole pressure probe in the range of at intervals both in yaw and in pitch planes is developed and reported. Calibration is carried out in two stages, low angles (for the maximum centre hole pressure) and high angles (other cases). On the basis of the maximum probe pressure reading, the calibration region is divided into seven zones; one central zone and six side zones. The calibration coefficients are derived for each zone. For interpolation, a localized two-variable polynomial is used at each point with the calibration data surrounding it. Zone extension is another useful feature developed here, in which each boundary point of every zone is extended to the nearest calibration point of the adjacent zone. By doing so, for a measuring point falling in between the boundaries of two adjacent zones, one employs the extended zone boundary data for fitting a polynomial. In addition to calibration data, additional data are acquired in the calibration tunnel. These data are used as measured data and calibration curves of suitable zones are used to derive flow parameters. In general, the interpolation errors in flow angles are found to be within and the errors in total and static pressures are within 0.5% and 1% of the dynamic pressure respectively.

More than 20 weighting functions proposed for DLTS are critically compared. It is shown that the variety of DLTS peak widths of different weighting functions was primarily due to the variety of shapes of the high-temperature side of the peak. A refinement of the classification scheme of the weighting functions is proposed. It is shown that the high-temperature side of the DLTS peak can be made independent of the weighting function, by considering the delay time between the end of the filling pulse and the beginning of the weighting function as an integral part of each weighting function. An optimum delay time (specific for each weighting function) is obtained by maximizing the figure of merit defined as the signal-to-noise ratio of the correlator divided by the DLTS peak width. Using the concept of optimum delay time, the functions can be classified into several groups according to their selectivity. The functions from one group differ only by their sensitivity, making it easy to select the functions with the best signal-to-noise ratios. In the second part of the paper, several misunderstandings concerning exponential correlators and double boxcars that frequently appear in the literature are revealed.

We show that accurate measurements of transmittance as a function of the wavelength can be used to calculate simultaneously the thickness, real and imaginary parts of the refractive index and dispersion coefficient of thin weakly absorbing plates. We test this method with the characterization of a freshly cleaved mica muscovite sheet.

This paper presents a new method for testing electrical steel sheet, based on measurements of the magnetic field distribution over the sheet surface. The tangential field value is measured with the aid of a permalloy magnetoresistive sensor. The field distribution is displayed in the form of a colour map, hence the method is called `magnetovision'. The repeatability of the maps is excellent. The most interesting new results of electrical steel investigations are presented. The system provides a versatile tool for non-destructive quality control and for the determination of the structural uniformity of electrical steel. Magnetovision, compared with other methods, seems to be especially useful for detecting the causes of steel quality deterioration.

The characterization of thermal systems can be performed by using thermal impedance measurements. Experimentally, this method requires simultaneous measurements of the variations in heat flux and the temperature of the measuring surface. The sensor, placed on the system to be characterized, induces a disturbance. For a slow change in thermal characteristics and for low frequencies, the disturbance due to the sensor is negligible. The low-frequency case has been studied in several works, but we show here that it is possible to extend the method to higher frequencies by taking the sensor disturbance into account. A model accounting for sensitivity to parameters shows that in a zone called `the middle frequency zone' the disturbance is limited to a resistive effect. This zone is studied in this work and concrete was tested under these conditions. Several tests were carried out on the same sample. The contact resistance was modified for each test and the method used led to a stable value of material effusivity.

The detection of humans for their own safety in an industrial environment is vital, especially with increases in the flexibility and velocity of automated working machines. A capacitive detector for the detection of humans in guarded zones has been designed. An electromagnetic model accounting for bodies of different permittivity in the vicinity of the sensor is described. Numerical calculations based on the electromagnetic model have been made and experimental measurements have been taken. An example shows how the electromagnetic model can be used to model the output of the person detector.

This paper describes a low-cost realization of a precision capacitance measurement instrument. The method is based on synchronous modulation and demodulation operating at a frequency of 100 kHz. A two-channel multiplying digital-to-analogue converter is used to generate a sinusoidal drive voltage and to perform multiplication with the demodulation signal. The modulation and demodulation signals are generated using a direct digital synthesizer, which is implemented using a field programmable gate array. Experimental results show a reproducibility of better than in the range from 50 pF to 600 pF.

Electrorotation (ROT) has been applied widely for determining the dielectric properties of cells (and bio-particles) with single-cell resolution. However a serious limitation of ROT has been the tedious manual measurements required. A new real-time PC-based machine vision algorithm and hardware implementation are presented that achieve measurements of cell rotational motion and analysis of ROT spectra. The system is equipped with a computer-controlled quadrature digital synthesizer and is capable of measuring a ROT spectrum of a single cell with the frequency range 1 kHz-200 MHz in less than 5 min, taking four measurement points per frequency decade. Laser tweezers are used to facilitate cell selection and positioning in order to maximize the flexibility and accuracy of the system. The performance of this system is characterized in terms of robustness, accuracy and linearity with respect to manual measurements of real spinning cells under the influence of a rotating electric field. The system is quite generally applicable to a wide variety of mammalian cell morphologies and optical appearances. Membrane capacitance values derived from automated ROT measurements averaged within 10% of those obtained from manual measurements.

The discharge excited atom beam source we designed uses a trigger electrode between a nozzle and skimmer to generate a metastable helium atom beam that is directly discharge pulsed. A pulsed discharge current up to 200 mA maintained between the needle cathode behind the nozzle and the skimmer anode produced an intense pulsed metastable helium atom beam equivalent to a continuous total flux of with mechanical chopping.

The constant-temperature hot-wire anemometer is in essence a dynamic system of third order. It is shown that this conclusion can be drawn from the scattered and controversial literature on higher order effects.

A resonator technique has been employed to measure the relative permittivity of single crystal squares of strontium titanate in the temperature range 20-300 K at microwave frequencies. We found that the method of metallization of the strontium titanate crucially affects the effective measured dielectric constant, with an air gap as small as giving a 50% error in the inferred value of at 20 K; as the gap size increases the corresponding error increases dramatically. This has important implications when using strontium titanate, or indeed any high-permittivity crystals, at cryogenic temperatures.

A control system for Langmuir-Blodgett (LB) film set-up has been developed based on the principle of microstepping of the stepper motors to drive the barriers and the substrate with precision and smooth motion. The stepper motors and the Wilhelmy plate used to measure the monolayer surface pressure are interfaced to a microcomputer for automatic operation. This home-made LB film set-up has been successfully used to fabricate LB films of cadmium arachidate of high crystalline quality.

Numerical coefficients for more complicated models than those discussed in the original paper are provided. These models can reduce the measurement uncertainty in moisture content for different cultivars of wheat of 10-19% moisture at temperatures from -1 to 42 °C to less than ±0.5% moisture with a 95% confidence interval.