Table of contents

The main purpose of this review is to expound results related to the production of ordinary sound waves by electrical discharges. Work on different kinds of discharge especially glow, arc and 'true' corona are presented and classified according to the relative importance of different acoustic source terms, namely the 'heat' term and the 'force' term. Related fields such as lightning and thunder are also dealt with. Different applications are presented but emphasis is given to 'plasma' loudspeakers. Fields in which knowledge is not well established are also outlined.

Describes the microwave properties of a sapphire loaded superconducting cavity resonator. The authors report measurements of energy confinement, evanescent field scale lengths and radiation losses. They report high quality factors, in excess of 10⁹ at cryogenic temperatures, for a resonator based on a sapphire element mounted inside a superconducting cavity. From the measured properties we show that resonators of this type have potentially valuable applications as ultra-high-stability oscillators, high-Q filters and as low phase noise frequency sources.

For pt.III see ibid., vol.18, p.1269 (1985). X-ray distributions in targets inclined to the electron beam have been established using both tracer measurements and Monte Carlo calculations. The data are used to extend the Love-Scott II correction for quantitative electron-probe microanalysis so that it can also deal satisfactorily with tilted specimens.

Presents a general technique for the generation of a chosen field distribution in a cylindrical region by controlling the individual currents of an arbitrary number of coils. The use of a least-squares approximation based on the Chebyshev polynomials has permitted the achievement of uniform accuracy over a large fraction of the coil assembly.

A spectroscopic study has been made on various mixtures of the mercurous halides HgX(X=F, Cl, Br, l) photodissociated from the mercuric salts by ArF excimer laser excitation at 193 nm. The combination of two or more different halides of mercury within a laser cavity, operating under similar conditions to the single HgX lasers, is a logical step forward in extending the tuning range within the visible spectrum. The effect of such mixtures upon the laser absorption bands for both photolytically pumped and electrically excited laser emission and the production of interhalogen compounds and their effect on laser emission is discussed. For certain mixtures, a continuous fluorescence emission band was observed from 420 nm to 560 nm with further emission at 340 nm. It was deduced that mixed laser emission would occur in four bands: 340 to 343 nm, 440 to 445 nm, 493 to 510 nm and 533 to 565 nm; this has been confirmed by recent laser measurements.

A novel pulse compression scheme, based on a combination of two non-waveguide liquid-filled cells and two focusing elements, is described. It is demonstrated experimentally that a 15 ns long pulse from a dye laser can be compressed to 2 ns with good conversion efficiency. Theoretical modelling confirms the observed behaviour and indicates that the compression can be improved further in lower loss media.

A time of flight pulse technique has been used for the measurement of the ratio of radial diffusion coefficient to mobility (D_r/ mu )_d for electron swarms in helium, argon, neon and krypton. The experimental range for helium and argon is 56.5<E/N<5650 Td (where E/N is the ratio of electrical field to gas number density), whilst the experimental range for neon and krypton is 1.41<E/N<5650 Td. The values of (D_r/ mu )_d increase with increasing E/N to a maximum value and then decrease in value. The values vary from 6.52 to 21.7 V in helium, 6.40 to 16.4 V in argon, 1.23 to 28 V in neon and 5.24 to 13.3 V in krypton. The results in helium and argon show good agreement with the result of Lakshminarasimha et al. (1977) obtained by using a steady-state technique over an experimental range which extended up to E/N=1300 Td. There are no experimental results in neon and krypton for comparison. The present results have been compared with theoretical values computed by various workers using the Boltzmann and Monte Carlo technique. Good agreement can generally be obtained between selected theoretical and the experimental results for the entire E/N region.

The influence of the stress/strain curve shape on the cracking of a brittle elastic material is analysed in terms of the energy balance theory of fracture mechanics. Both r-shaped and J-shaped elastic curves are investigated. For some cracking tests, for example the trouser tear and lubricated cutting tests, the shape of the stress/strain curve is found to have little effect on the crack extension force; this is determined mainly by the fracture surface energy of the material. However, in other tests such as tension, the shape of the stress/strain curve does influence the fracture stress, but not by a large amount when compared with the effect of reinforcement. Whether an r-shaped or J-shaped curve leads to a higher fracture stress depends on such factors as the fracture energy and the size of the pre-existing crack. It thus appears that no general statement can be made about the effect of the shape of the stress/strain curve upon the crack resistance of materials, contrary to views expressed previously in the literature.

A simplified version of differential thermal analysis has been developed resulting in an inexpensive apparatus for determining the latent heat of fusion of phase change materials. The experimental results performed with three samples show that the present method yields results which agree within 5% with the measurements of sophisticated differential scanning calorimetry apparatus.

The injection of photo-excited electrons from bis(4-dimethylaminophenyl)-squaraine into (4-butoxycarbonyl-9-fluorenylidene)malononitrile was studied by using the xerographic discharge technique. The present study has demonstrated for the first time that electrons can be injected from a squaraine into an electron transport layer. The photoinjected current data, analysed in terms of Schottky emission model, indicate that the injection barrier height at the squaraine/BCMF interface is 0.24 eV.

A generalisation of the distribution function of the surface charge density with respect to the surface curvature is given. It is used to calculate the field intensity at any point in an electrostatic field with arbitrary boundary conditions, thus a general formula to solve electrostatic and other boundary value problems is derived. Calculations using the formula are convenient, accurate and permit an analysis of the effect of the physical parameters. This method when supplemented by data derived from experiments using an analogue technique can be used to solve very complex boundary value problems in technology, instead of using numerical methods.

The contact charging of insulators is often investigated by contacting the insulators with metals. However, the use of solid metal contactors introduces difficulties due to the hardness of the metal, the uncertain area of contact, and charge accumulation which occurs when contacts are repeated. These difficulties can be avoided by the use of liquid metals to contact the insulator. This paper reports an investigation of the use of liquid metals as contactors in contact-charging experiments. Liquid gallium may be more suitable for some measurements than mercury because, as the Appendix shows, the work function of mercury changes with time but that of gallium does not.

So far, knowledge about the dielectric properties, especially the loss factor, of ice at microwave frequencies has been unsatisfactory. In this work the authors report on new measurements made over the frequency range from 2 to 100 GHz by a resonator method (2-10 GHz) and a radiometer method (10-100 GHz). Measurements were made with pure and with slightly saline (10 to 13 p.p.m.) ice. The results agree with the assumption of a single minimum of the dielectric loss at 2 to 4 GHz. For pure ice the data are a natural link between the measurements of Westphal made below 1 GHz and the far-infrared spectrum. The influence of small impurities on the dielectric loss is compared with the behaviour of sea ice, and it is found that the same linear relationship with salinity can be applied to both cases.

Measurements of secondary electron emission coefficient and surface work function phi are reported for polyacrylonitrile (PAN) and polytetrafluoroethylene (PTFE) in the virgin and chemically modified forms. A single pulse method was used for SEE measurements and a retarding field method for estimating the work function. Doping of PTFE with alkali metals (Na and Li) and pyrolysis of PAN at 300 degrees C led to an increase in the surface conductivity. The processing of the surface effectively increased the SEE yield in these polymers. Electrical conductivity and XPS results were used to explain the chemical structures of modified polymers.

The authors have studied sintered bimodal distributions of spheres (size ratio 1:4). They discuss the preparation and the characterisation of these model porous structures where the porosity can be adjusted by varying the ratio of sphere diameters, the volume ratio as well as the rate of sintering. They study the formation factor (effect resistivity of the pore fluid) and permeability of the materials as a function of porosity. A comparison with a previous work by Wong, Koplik and Tomanic (1984) on sintered monosize distributions of spheres leads to the definition of an effective length scale for their problem. It is defined by an average on the grain geometry and is independent of the porosity. They also discuss other candidate length scales using measurements of formation factor and permeability.

BaTiO₃ positive temperature coefficient of resistance (PTCR) ceramics were prepared using commercially available BaTiO₃ which was doped with 0.4 mol.% Ho to make it semiconducting. The samples were sintered in air at 1320 degrees C and while cooling to room temperature, different samples were annealed at 1220 degrees C for various periods ranging from 0 to 27 h. The annealing process was found to result in the formation of a resistive grain boundary region in series with the space charge layer. Dielectric measurements in the audio- and radio-frequency regions revealed that the resistive layer did not diffuse throughout the entire grain bulk, even during the longest annealing period. It was also found that annealing at 1220 degrees C results in (i) an increase in the value of rho _max, (ii) a reduction in the temperature corresponding to rho _max and (iii) an increase in the steepness of the resistivity-temperature plots in the region of the transition from low to high resistance. These changes were explained in terms of an increase in the acceptor state density.

The Shockley-Read-Hall (SRH) theory of electron-hole recombination at single level traps has been modified to include bands of trap levels inside the energy gap. The variation in excess-carrier lifetime in the base region of an n-p junction solar cell with temperature, illumination level and dopant concentration has been calculated on the basis of this model. Wherever possible the results are compared with the experimental findings.

The author reports on an extensive study of energy deficit measurements of the energy distribution of the ion beam emitted by a gallium liquid metal ion source in an attempt to resolve the controversy arising from the unusually wide divergence of findings by different workers. The controversy can be conceivably resolved in terms of misalignment of the liquid cone, whereby different parts of the beam enter the energy analyser at different times. Coupled to this is an alteration of the work function of the retarding electrode of the energy analyser by contaminants, such as the liquid metal itself, or its oxides, altering in turn the value of the critical energy deficit for surface field ionisation. A detailed investigation is also made for the region of emission current below 1 mu A-a region rarely investigated by the vast majority of researchers, but a most important one from the point of view of the emission mechanism, as well as from an applications' standpoint. Finally, the reasons for the scatter observed in energy spread measurements are considered, and only a tentative explanation can be given, related to ion source misalignment; this misalignment arises from the fact that the liquid cone does not always form at the centre of the apex region of the supporting needle.

The angular locations of maxima and minima in light scattered by infinite cylinders of refractive index 1.46+0.0i are presented. Earlier literature in which similar graphs are presented would appear to contain errors and may therefore by misleading to those working in the area of fibre-sizing.

Using a stainless steel discharge chamber embodying a point-sphere electrode system, filled with hexane, a critical region was detected together with corona, disturbance, treeing and arc discharge. The critical region is located in the highest field concentration with radiationless transitions predominating. This region is the critical precursor of breakdown in the liquid. The critical region is ellipsoidal and, for a gap length of 4.32 mm employed here, has a major axis of 152 mu m.

The condensation characteristics of antimony in the presence of an oxygen glow discharge were studied as a first step in the understanding of how to obtain high-quality antimony-doped tin oxide films deposited by activated reactive evaporation (ARE). It was found that the antimony condensation characteristics are modified by the presence of an oxygen glow discharge such that antimony condenses as an oxide at a temperature greater than 300 degrees C; at such a temperature there would be no antimony condensation if the oxygen glow discharge was not present. The oxide film produced in this way has a refractive index of around 2, an optical band gap of around 4 eV and it is amorphous. The oxide is probably Sb₂O₄ or Sb₂O₅ rather than Sb₂O₃, because Sb₂O₃ is known to be more volatile than antimony.