摘要:

When a flat sheet of dielectric is in an open resonator, its surfaces do not coincide with the curved wavefronts of the electric field. For calculations, the specimen may be imagined to be composed of a specimen having curved faces plus a thin concave lens, whose refractive index must be supposed to vary with the position of the lens in the field. The results of measurements, using specimens of polystyrene and of alumina, show that a satisfactory theory can be developed on this basis, leading to values of refractive indexnagreeing with those of the earlier theories. The new theory, however, predicts slightly different beam widths, which have been confirmed by measurement.

DOI:10.1049/ip-a-1.1983.0064

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The generation of static electricity during the transport of low-conductivity materials is a well known phenomenon. Until recently, large-scale experimentation has been the principal means by which the electrostatic conditions associated with the charging of processes have been assessed. Furthermore, the wide range of materials which exhibit differing charging characteristics, together with the various sizes of containers in common use, makes conclusions drawn from one arrangement difficult to apply to others. Consequently, there is an increasing need, at the initial stage of industrial storage facility design, to assess the effect of the electrostatic conditions arising from the transport of these materials. In the paper, mathematical models were developed and numerical solution methods proposed, for typical storage installations. In addition, the results of experiments have been reported which substantiate the methods employed and numerical techniques used. Despite the diversity of materials involved and the widely differing scales of experimentation, the finite-element method is shown to be a feasible and accurate means of assessing these conditions in typical fluid and powder storage situations. Furthermore, because these numerical techniques have been used in a pseudointeractive manner, with ongoing experimentation, they have permitted the process of charging and relaxation mechanisms, which has hitherto been experimentally unobtainable in the practical situations encountered in industry, to be more fully understood.

DOI:10.1049/ip-a-1.1983.0066

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Twelve different metals, having oxide films of a few nanometres, were used as the cathode for a single 4 A arc in air at atmospheric pressure, about 30 μm long and of duration between 3.8 ns and 3.5 μs, and the surface was then examined by scanning electron microscopy. Three groups of metals were distinguished; those having semiconducting oxide leading to scattered craters; those with insulating oxide leading to dense cratering and considerable melting; and those with volatile oxide leading to little or no cratering. The growth with increasign arcing time of the circular areas containing these craters was measured and found to be remarkably similar, and, in the light of this, various aspects are examined. A number of simple models of the cathode region for these arcs are outlined. These include an examination of the gaseous and solid-state regions of the cathode fall and mechanisms of producing the high electric field required within the oxide, for electron emission by positive-ion charging or plasma jet biasing, and possible effects of microinclusions. Different assumptions about the current-density distribution are examined. It is concluded that positive-ion bombardment is likely to cause electron emission for aluminium cathodes, but that further work is needed for other metals.

DOI:10.1049/ip-a-1.1983.0067

出版商:IEE    

年代:1983

数据来源: IET

摘要:

An automated ‘arc and spark’ test method has been developed for economical high-voltage testing of vacuum interrupters, taking into consideration both the physics of vacuum breakdown and realistic service conditions. Each breakdown test is preceded by a well defined but variable switching operation. Test control and evaluation by a computer provide fast and economic execution, even of large series of complex tests. Short descriptions of devices for breakdown detection and prebreakdown field emission current measurement are added. The presented test method concerns the dielectric performance of an open interrupter, but not its dielectric recovery at current interruption.

DOI:10.1049/ip-a-1.1983.0068

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The paper describes experiments on blowflies and fruitflies in electrostatic fields. At a high enough field strength, yet not so high as to cause flashover, the insect becomes paralysed; however, if the field is quickly removed the insect eventually regains control and can fly away apparently unharmed. This occurs whether the insect is originally in contact with one of the electrodes or in flight between the electrodes. It is suggested that the nervous system is affected by conduction currents resulting from corona discharges due to local field enhancement at irreugularities on the insects' bodies.

DOI:10.1049/ip-a-1.1983.0069

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The population of the world is increasing and is almost certain to reach six billion by the year 2000. In many countries, the standard of living is deplorably low so that more than half the present world population cannot do much more than exist. In some countries, they are getting even poorer and, if the population goes on increasing, are in danger of starvation. This depressing situation can only be averted by improved agriculture, on the one hand, and more and better engineering, on the other. If only to increase agricultural production, more engineering is needed to provide irrigation, fertilisers, agricultural machinery and transportation to the densely populated areas where it is needed. To improve the quality of life beyond the subsistence level, even in the simplest manner, will require production of consumer goods, public utilities and transportation many times greater than are available now. In addition, the growth of big cities and conurbations in developing countries will require capital development of housing and public utilities, as well as leisure facilities on a large scale. All of these activities involve engineering and, because the engineering problems are dependent on the local enviroment, professional engineers will always be needed for their successful solution. The task of raising the quality of life in the less developed countries, when population is increasing by 3% a year or more, is so immense that the greatest ingenuity is required to ensure that our limited resources of materials, tools and skills are exploited in the most effective manner. This means that we need, not only more qualified engineers, but better ones, and particularly more engineering leaders who can see large and complex projects through to a successful conclusion in the most difficult conditions. Although such leaders are more likely to be born, rather than made, they must still have the education and training to make them resourceful in emergencies, experience wide enough to give them critical judgement to do what is best in difficult circumstances, and the determination to combat inefficiency wherever it may arise. Above all they must have integrity and a sense of mission to do their best for their clients, whether they be world organisations or small communities, powerful corporations or struggling private companies, multimillionaires or subsistence farmers. The customer may know best but not the client, because, if he die, he would have no need to employ a professional engineer. The professional engineer must for ever be striving to improve his technical ability, and this he will only achieve by widening his experience and carrying out every job he takes on as well as he possibly can. He must treat all men without fear or favour and always put the public interest before his personal ambitions. This does not mean that he should not be entreprenurial: far from it, for if he beleives his work is good, whom does it profit if it goes unheeded, and so he must do his utmost to exploit it for the benefit of others. If he profits from this exploitation, he is fortunate, but if he is unsuccessful he must carefully consider the reasons and try again. In the end, it is only the engineers who can ensure the success of the project or the quality of the product, and, if they fail, we are all the poorer or, worse, there will be some dreadful disaster.

DOI:10.1049/ip-a-1.1983.0070

出版商:IEE    

年代:1983

数据来源: IET

摘要:

A personal case history of the problems of establishing a small high-technology company to manufacture and develop specialised microwave components that had originated in the author's academic research is presented in the paper. Part-time involvement grew rapidly into full-time commitment and, within three years, to the attraction of venture capital and a major expansion into the USA. The special nature of each stage is outlined, with special mention of the recurrent problem of control of cash flow. Recent Government initiatives have made it easier for small companies, but these potential creators of national wealth deserve more encouragement, and three measures are suggested. The paper is a summary of a lecture given at the Institution of Electrical Engineers, Savoy Place, London, on the 22nd March 1983, and the chair was taken by Mr. H. Tomlinson. It was a joint meeting of the Management & Design and the Electronics Division. The lecture was based on one given by the author a year previously at the North Midlands Centre.

DOI:10.1049/ip-a-1.1983.0071

出版商:IEE    

年代:1983

数据来源: IET