Table of contents

During the past thirty years the hot-wire anemometer has enabled detailed experimental measurements in air flows to be recorded, analysed and subsequently published. In just over a decade the laser Doppler anemometer (LDA) has been conceived and developed into a valuable research tool. The introduction of LDA has now enabled reliable measurements to be achieved in water flows and consequently considerable effort has been directed towards this application. Due to this the imbalance in the published literature has been partially corrected. This review looks not in detail at the LDA but at the measurements which have been made, and additionally those which are now possible, in water flows.

A refractometer employing the phenomenon of total internal reflection of light has been designed for use at low temperatures. The instrument has been used to measure the refractive indices of argon, krypton and xenon at 546.1 nm in the temperature range 178 to 30K. The upper limit of the theoretical accuracy of the refractive index is +or-0.02% but the experimental uncertainty proved to be +or-0.1% maximum. This accuracy is comparable to that obtained using a spectrometer and the method of minimum deviation.

The design, construction and performance of a low-cost, current-regulated power supply suitable for operating a general-purpose cold-cathode discharge lamp are described. In the case of the many-lined molecular hydrogen spectrum (85-160 nm) the power dissipated by the supply is typically less than one-fifth of that of the lamp.

Diamonds intended for use as anvils in high-pressure devices for Raman and infrared spectroscopy must be selected carefully. For Raman use it is suggested that a useful criterion is whether or not the second-order spectrum of diamond can be seen above the accompanying fluorescence. Some type IIa stones are also suitable for Raman use and are superior to IIb stones in the infrared region above 2000 cm^-1.

A simple sample holder is described for the measurement of thermoelectric power and other conduction phenomena to be used with cylindrical metal samples, such as single crystals.

A modification which enables a twin-wire wave probe to measure the instantaneous slope of a water surface is described. Details are given of the design of a four-wire probe capable of measuring simultaneously two orthogonal components of surface slope and the surface elevation. Resolution of the slopes to find the direction of the maximum slope enables the direction of propagation of the wave to be deduced.

A photoelectron spectrometer designed specifically for measuring the angular distributions of valence shell electrons from gaseous molecules has been constructed. Positioning of the wide-angular-range analyser/detector is done with a potentiometric servo-system. The voltages for both this and the energy scan potential are derived from a small on-line computer, which also counts the signal pulses so that the instrument operation is fully automated. The same computer is used in the spectral analyses so that no manual recording or transfer of data is required. The performance of the spectrometer is illustrated by sample results obtained with argon.

A method of constructing a large Fabry-Perot type resonator for operation in the microwave region is described. Simple and moderately inexpensive techniques are used to fabricate the mirrors which are 1 m in diameter and have a radius of curvature of 10 m. Tests show that Q-factors in excess of 10⁵ may be observed at 10 GHz. The system is found to support resonances at frequencies over a wide bandwidth, namely 2-26 GHz.

Several asymmetrical corona gaps are investigated for rectification effects. The gaps are suitable for partial rectification in the kilovolt and microampere ranges. Rectification is better for narrow gapsand thin wire electrodes. The effect of the other electrode is investigated.

The system described uses an array of 50 FET switches to access the elements of either a linear array of silicon photodiodes or an array of pyroelectric detectors formed on a single sheet of PVF₂ plastic. Compensating capacitors are used to give 1% uniformity of response down the array. The two types of arrays are easily interchanged, giving a very flexible system. With suitable attenuation, the photodiode array can give a saturation signal-to-noise ratio of 100:1 in the range 0.4-1.1 mu m for all levels above 4 W m^-2 CW or 60 mJ m^-2 for 10 ns duration pulses. The pyroelectric array can give a saturation signal-to-noise ratio of 1300:1 for CW beams above 180 kW m^-2 or 260:1 for 10 ns pulses above 700 J m^-2 in the range 0.3-30 mu m. These figures are achieved without the prescanning usually necessary with other systems.

A thermoelectric detector is described for measuring the output power of a CO₂ laser from 1 to about 30 or 40 W. Its response time can be less than 1 s, with convenient sensitivity, adjusted according to the power range.

The author aims to identify theoretically and to measure electronically the basic dynamic performance parameters of the constant-temperature hot-wire anemometer. It is found that a well designed anemometer behaves as a third-order control system which allows for a two-parameter optimization of its dynamic response. The cut-off frequency of the anemometer and related dynamic parameters can be estimated by means of electronic square- and sine-wave tests.

The nonlinear theory for constant-temperature hot-wire anemometers is outlined in more detail than before. It is shown that the domain of nonlinear effects is restricted to velocity fluctuations above at least 12% of the mean velocity in a frequency range larger than 10% of the cut-off frequency of the anemometer. The nonlinear domain can be avoided in most cases by using an anemometer with good high-frequency capabilities, by using thin hot-wires and by proper tuning of the anemometer.

A method of producing a full colour representation of an NMR image from a monochrome storage oscilloscope is described. Variations in the proton density are displayed as changes in colour hue by decoding the image data into three sets of intensity information which correspond to the three primary colour separations of the image. These are displayed consecutively on the oscilloscope and recombined photographically on to colour film.

A low-cost system is described which permits the recording of up to eight channels of analogue information, with a frequency component not exceeding 1 Hz, on to an unmodified stereo cassette tape recorder. A digital recording technique is used and the information can be recovered either as analogue voltages or as digital data for computer processing.

High and homogeneous magnetic fields can easily be generated by superconducting solenoids. Superconducting split-coil magnets are both suitable for fields up to about 4.77*10⁶ A m^-1 (60 kOe) and sufficiently homogeneous over the sample (1 cm³) to permit wide-line NMR experiments. Moreover, the magnets are limited in size, i.e. smaller than 20 cm in diameter. The magnetic field is calculated for a general system of coils that possesses cylindrical symmetry and that also has a mirror plane perpendicular to the cylindrical axis. An expression for the homogeneity of the central field is derived. Two models of split-coil magnets are treated in detail: the L-coil and the N₄-coil. Due to the number of available free coordinates the homogeneity of the field can be corrected up to eighth order for these magnets. The results of the calculations for L- and N₄-coils are given graphically. Finally, the properties of an actually built magnet of the N₄ type are discussed.

A fully automatic optical system for determining the distribution of the volume emission coefficient of spectral lines and continua throughout the volume of a plasma is described. The system carries out measurements of specific intensity at a number of positions across the plasma for two orthogonal views of the plasma. By carrying out measurements for these two views it is possible to adopt an inversion procedure for obtaining the volume emission coefficient which takes into account small departures from cylindrical symmetry of the plasma. The volume emission coefficient can be used to determine the temperature distribution in the plasma and an example of the temperature distribution throughout an argon plasma is presented.

An experimental arrangement is described for measuring in situ in a nearly continuous way the reflectance R and transmittance T near normal incidence, as well as the electrical DC resistance of thin films throughout their deposition and subsequent heat treatment. It is then possible to determine the effective complex dielectric constant epsilon and the electrical DC resistivity rho as functions of the mass thickness of the deposit and to follow their evolution during film growth. The possibilities of the method are demonstrated by an application to thin films of gold.

A field-emission retarding-potential device is described which has been specifically designed to fit typical UHV surface research systems. The design and construction of the lens system are fully described. Its performance is demonstrated, both as an energy analyser for the field-emitted electrons and in the determination of the absolute, area-averaged work function of UHV-evaporated films of aluminium, copper, gold and silver. The values obtained for these metals are 4.26+or-0.02, 4.64+or-0.02, 5.37+or-0.02 and 4.46+or-0.02 eV respectively. In view of (i) the clean conditions of film growth, (ii) the proven purity of the films (by Auger electron spectroscopy), and (iii) the demonstrated reproducibility of the technique, it is claimed that these measurements have yielded the most reliable work function values yet available for thin films of the four metals studied.

A simple multipass 'cavity' accessory has been designed and built for the enhancement of absorption intensity and elimination of optical interference effects in the infrared spectroscopic examination and analysis of thin polymer films. Use of the accessory in conjunction with a Wilks MIRAN non-dispersive infrared analyser is illustrated by application to the spectroscopic analysis of propylene/ethylene copolymer films.

An analogue signal averager capable of subnanosecond time resolution is described. The circuit combines the time resolution of a sampling oscilloscope, the signal-averaging capabilities of a multichannel analyser and the processing power of a minicomputer into a single unit. The circuitry and computer program necessary to accumulate data in the computer memory and output the averaged data on an analogue display or plotting device are described. Although the circuitry described refers specifically to an interface to a PDP-11 computer, the design principles are readily adaptable to any minicomputer or microprocessor with at least 4k words of memory.

An apparatus is described which measures the strength of welds formed between contacts following capacitive switching closures and provides a relative measure of the ability of various contact materials to resist welding. Contact bounce is controlled by a simple mechanism which produces a constant, preset bounce time. Tests can be carried out using a range of closure velocities and peak discharge currents with reliable accuracy.