Table of contents

The author examines current practice in the multiprobe method of roundness measurements, and derives design strategies for improved measurement accuracy and reliability. The multiprobe method eliminates variable centring errors by combining displacement measurements made simultaneously at several points about the periphery of the workpiece. Discrete signal processing methods for reconstruction of the workpiece profile are described, and design guidelines are established to eliminate the detrimental effects of aliasing from the reconstruction process. The harmonic response of a three-probe arrangement is investigated, and methods are developed to avoid the unwanted suppression of harmonics. The advantages of a more complex multiprobe arrangement are discussed, and a novel harmonic reconstruction method used to avoid suppression, and to allow the detection of incorrect measurements by a redundancy technique.

A device is described which is used to measure very small mass losses of a target (typical mass 1 g) which is impacted by sand particles at velocities up to 80 m s^-1. In this adverse environment, ordinary gravitational mass measurement is not sufficiently sensitive, so the target is made part of a resonant system; the resonant frequency of this system is continually tracked with great accuracy, and this is used to obtain information about the mass loss of the target. Tracking is performed by forcing the system to oscillate at a frequency produced by an electronic voltage controlled oscillator (VCO); the phase difference between driving force and amplitude response is monitored with a new electronic device, and the frequency of the VCO adjusted to maintain phase quadrature. Under the conditions described, mass changes of 0.2 mg can be recorded: these correspond to changes in resonant frequency of 2 parts in 10⁵.

The alternative coupling of short-circuiting the secondary coil of a fluxgate sensor by connecting it to the inverting input of a current amplifier is shown to have significant advantages over the more conventional unloaded or second-harmonic tuned voltage coupling. The short-circuit output current impulses are independent of changes in the excitation level, and sensor performances is not degraded by cable and coil stray capacitances or by resistive loads from the feedback circuit. The current impulse amplitude is proportional to the average-to-minimum secondary self-induction ratio minus 1, and to a virtual current in the secondary coil corresponding to the external magnetic field.

The authors present the analysis of losses in lumped parameters resonators used for ESR spectroscopy at low microwave frequencies. The relative weight of electric and magnetic field losses has been evaluated as a function of frequency and sample conductivity. The theory has been tested at two frequencies (680 and 549 MHz) and with samples of different conductivity.

The authors demonstrate that for four-probe measurements the application of high-frequency, phase-sensitive modulation in pulsed magnetic fields yields the same sensitivity and signal-to-noise ratio that has so far been the privilege of DC magnetic fields. In this way the combination of phase-sensitive modulation and pulsed magnetic fields opens a new class of experiments in high-field magneto-spectroscopy.

A torque magnetometer has been developed and built in order to measure torque curves of magnetic materials. It is of the electromagnetic compensation type (counteracting coil in a magnetic field). Its main characteristic is that the magnetic field employed to obtain the counteracting torque in the coil is the same as that used to magnetise the sample. In this way one obtains a sensitive, simple and compact magnetometer.

A method for processing and analysing images of bacterial colonies growing on solid bacterial medium is presented. The procedure determines the position of single colonies, intended for further inoculum transfer by a specially designed life-science laboratory robot. The image processing and analysis of Streptomyces colonies are described. The procedure can be employed to isolate antibiotic producers for the pharmaceutical industry; a similar process can be used to automate methods of charting human genomic DNA.

The finite element method was used to compute numerically the distributions of the potential and field in the central region for the circular rod quadrupole. The differential equations of ion motion were solved numerically according to the above field at discrete points, without employing the usual analytical functions of the field. The phase-space dynamics has been developed and applied to the quadrupole field generated by four circular rods, an approximate quadrupole field. From the stability diagram obtained for the circular rod quadrupole, it is shown that the resolution of an analyser with circular rod electrodes will largely be limited owing to a blunted tip on the stability diagram and the increase of the width of the stable region for a scan line.

A target assembly has been developed for the irradiation of transmission electron microscope samples with high-energy protons. The chamber permits accurate dose and temperature measurement during irradiation to be made and gives maximum control over irradiation variables. Maximum power inputs so far obtained without significant rises in sample temperature (i.e 160 degrees C, the lower limit of the infrared monitoring system) are 450 W cm^-2 at 3 MeV and 1.5 kW cm^-2 at 18 MeV. This is achieved by careful chamber design and the use of heat-pipe technology.

Twenty-two EMI 9821B photomultipliers were tested to evaluate their performance down to -80 degrees C for use in a cosmic-ray experiment at the South Pole. The temperature coefficients of the individual tubes were measured using light from fast pulsed green LEDS. The temperature coefficients were found to have a large spread of values. Comparison measurements were made with scintillator light sources. All the tubes tested operated successfully down to the lowest temperatures.

A two-stage MCP ion detector for steady ion currents of the order of some pA and ion pulses of a pulse width between 10 and 500 ns is described. Detector current gain for Ne⁺ and H₂⁺ ions at an energy of 0.1 to 4 keV was found to be dependent on ion energy and species. In pulse current mode, linearity is maintained up to an output charge density of 1.9 nC cm^-2; the detector rise time is below 3.5 ns. For the first time an MCP ion detector is used at an ambient gas pressure of 10^-3 Pa to investigate ions emitted by a transient gas discharge. With an appropriate operating voltage the detector operated without degradation of performance for at least 500 hours. First measurements of ion species, ion-energy distribution function, ion current density and pulse shape of the axial ion pulse of a pseudospark discharge were performed.

Metastable noble gas atoms are produced by crossing a low-energy electron sheet beam with a jet of gas injected by an automotive fuel injector. A laser beam is directed at right angles through the wide dimension of the electron beam, and the gas jet is directed at a small (19 degrees ) angle to the laser beam. An electric field is used to extract photoionised atoms from the interaction region which are then detected in a time-of-flight (TOF) mass spectrometer. The apparatus has two novel features. First the metastable atoms are created directly in the interaction region where they are photoionised instead of being created in a discharge cell and transported as a molecular beam to the interaction region. This simplification eliminates at least one level of differential pumping and creates a relatively high density of metastable atoms. Because the low-energy electron gun which creates the metastable atoms can also be operated at higher energies, it can be used to ionise any atom or molecule present. In this mode the apparatus is self-diagnostic for system alignment and can readily detect the presence of impurities in the target gas.

A very small and highly sensitive flow velocity sensor has been designed and fabricated using silicon microelectronic technology. To determine the performance of this silicon sensor, comparisons with a conventional hot-wire sensor were made in a well defined two-dimensional turbulent flat-plate boundary layer at a constant Reynolds number of 4.2*10⁶. The silicon sensor was found to have spatial and frequency resolutions that make it suitable for turbulence measurements. In the investigated flow field the new silicon sensor measures profiles of the mean velocity and the turbulence intensity with the same accuracy as the hot wire.

Laser Doppler anemometer measurements using counter processors and requiring large shift frequencies are sensitive to small errors introduced by limited digital resolution as well as the method of clock pulse counting. Tests with at least one commercially available processor have shown the existence of a bias error induced by the clock pulse counter. This error has a significant effect on results for a low velocity flow component when a large shift frequency must be used for all components in order to avoid fringe bias. A correction method is proposed.

Wall shear rate was measured in the canine thoracic aortal in vivo by means of a hot-film anemometer and flush-mounted shear probe. Simultaneous measurement of blood temperature at the probe tip was accomplished by means of a thermistor film located close to the hot-film shear sensor on the probe tip. Blood temperature measurements were utilised to monitor the reversal of the thermal boundary layer produced by the heated shear sensor during blood flow reversal. Temperature data were utilised in an attempt to correct wall shear rates by adjusting the overheat ratio in response to the varying near wall temperature. Wall shear rate data and blood viscosity data were utilised to compute wall shear stress values. The average change in peak shear stress resulting from temperature corrections was 16%.

The efficient low-voltage bending properties of PZT bimorph wafers have been combined with conventional microelectronics techniques to produce a 37-hex-faceted deformable mirror 23 mm in diameter and 1 mm thick. Despite the high ratio of diameter to thickness, at 633 nm an overall flatness of better than one-half wave peak-to-valley (PV) and one-tenth wave RMS is attained under an active figure control of about 7 V per wave. Evaporative deposition of the electrical contact pattern eliminates mechanical coupling to the bimorph and allows the device to perform to frequencies in excess of 10 kHz.

A new low-cost streak camera readout system has been developed which offers the high signal-to-noise and dynamic range performance associated with photon-counting techniques coupled with 25 ps temporal resolution and the convenience of computer-based operation. The superior sensitivity of this system has enabled a study of luminescence processes in single and coupled GaAs quantum well samples to be made in the low-excitation regime and typical data are presented.

The measuring system consists of an ultrahigh vacuum evaporation set UW/S 350, automatic ellipsometer and a modular microcomputer system. This experimental set-up allows in situ measurement of ellipsometric parameters of thin layers in vacuum. The modular microcomputer system connected with the measuring set have recorded polarising elements readings and enables the optical constants of thin films to be determined.

A simple modification of a test-cell which enables the field dependence of the complex susceptibility of ferrofluids to be measured at fields up to 40 kA m^-1 is reported. The technique may be used for much larger fields.