Solar Cells

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Book Reviews Surface-acoustic-wave passive interdigital devices D. P. Morgan (Ed.) Peter Peregrinus Ltd., 1976, 372pp. £9 in the UK, £10'50 overseas (excluding the Americas) Anyone with the time and energy to read carefully through this volume will certainly emerge as a world expert on surface-acousticwave passive interdigital devices. Not that I advise anyone to try it, for this is not a text book but a compilation of research papers, interspersed with an occasional review. It is meaty fare, to be approached and digested cautiously, not a light dessert to be swallowed in a mouthful. The editor has selected 74 papers covering: the theory and design of interdigital transducers; materials and propagation effects (including diffraction); bandpass filters; pulse-compression filters; delay lines; and phase-coded matched filters. There is also a very good bibliography of over 1300 entries which includes a range of subjects not covered by the printed papers. I think the choice of papers is good and gives a full and balanced view of the field although, understandably, there is a bias towards European—particularly IEE—sources. My only regret is that the editor has not been able to include any papers on the problems of fabrication, which so often set the limit on the performance of practical devices. This book is not for the general reader; it is a specialist work for those who wish to study the subject with some care. For them, the editor and publishers have done an excellent service in collecting a group of papers which give an authoritative account of the subject and which will remain useful for several years to come. R.F.MITCHELL

Solar cells Charles E. Backus (Ed.) IEEE Press, 1976, 504pp. (cloth bound) £7.70 (paperback)


Solar cells convert energy from the sun directly into electricity without moving parts or objectionable byproducts. Interest in the possible application of this space technology to terrestrial power generation has grown rapidly in recent years with the realisation of the limitations of fossil-fuel resources and the environmental and social costs of a proliferation of nuclear power stations. Prof. Backus's selection of significant papers from the solar-cell literature will serve as a convenient reference book for students, scientists and engineers working in this interesting field. The theoretician will find here the classic papers on the choice of optimum semiconductor, the theoretical limits of the efficiency of Si, Cu 2 S-CdS, Ga,-* A l x As-GaAs and other types of cell, achievements to date (1973) and prospects for further improvement. The electrical engineer is not so well served. The few papers on cell fabrication are limited to silicon, there is only one paper on solar-array design and none on related topics, such as cell interconnection and shielding. The main emphasis in the section on terrestrial applications is on the problem of reducing production costs by the necessary two orders of magnitude for large-scale power generation. The appended reprints from the 1973 workshop on this subject give a good insight into the American approach to possible solutions. The volume ends with a bibliography, which is justifiably claimed to be the most complete to date. It is to be hoped that this useful publication will be updated as and when further significant advances are made. F.C. TREBLE

Light emitting diodes A. A. Bergh and P. J. Dean Clarendon/Oxford University Press, 1976,591pp. £22 The. first publication on light-emitting diodes appeared in 1907 and over the subsequent years many thousands of papers have been published on these devices and the allied phenomenon of electroluminescence. It was not until 1962, when Henish published his book Electroluminescence, that an informed survey of the literature was available to guide researchers through the mass of publications. Since then, l.e.d.s have achieved considerable commercial importance and a new profusion of literature has appeared on the topic, including several books. However, until now, no author has had the tenacity to provide a really comprehensive review of this more up to date material. Bergh and Dean achieve this in a book which can only be described as a very remarkable publication, both in terms of its clarity and depth of treatment. The core of the book deals with those factors contributing to the main problem associated with l.e.d.s: that of overall efficiency. Initially the authors consider the intricacies of carrier injection and then deal with the light generation process itself. This latter topic is covered in a chapter constituting 273 pages and citing 596 references. The general impression on reading it is that not a single word is wasted. The treatise on efficiency is concluded by considering upconverting phosphors and the extraction of light from l.e.d. devices. Around this very detailed review are set chapters dealing with the photometry of l.e.d.s, material growth, production technology and device applications. These topics are with somewhat less rigorously, but they set the scene well for the main part of the work. I think this book must be classed as essential for the l.e.d. specialist, be he a device engineer or a research physicist. To the postgraduate student or a relative newcomer to the field, it will inevitably have less appeal, although if read selectively it still has much to offer. I feel that this book will be regarded as the standard text on the topic for many years to come A.R.PEAKER

Advances in magnetic materials and their applications IEE Conf. Pub/. 142, 1976, 165pp. £8-40in the UK, £9-80overseas (£5-50 to IEE members) Research and development in magnetic materials and their applications continue to be a major branch of science and technology. Although, in some areas, digital techniques and active linear circuits are beginning to compete in areas traditionally held by inductive components, e.g. small inductors and transformers, the role of magnetism as a whole flourishes. Major advances are being made in materials and the range of applications appears to be continually broadening. One consequence of this is that often new technologies, originating under the general heading of magnetism, soon graduate as separate subjects, giving rise to their own conferences and publication structures; examples are thin magnetic films, magnetic bubbles and magnetic recording. The main stream of advances in magnetism continues to find expression in broadly based conferences. This publication contains the proceedings of such a conference, aimed at providing a European forum at which recent advances could be presented. It contains 42 papers representing four main subjectdivisions:

magnetically soft materials; magnetic separation; transportation and levitation; and permanent magnet materials. The papers on magnetically soft materials include several on particular aspects of ferrites and thin films, but, in the main, they consist of reports of progress on silicon-iron and nickel-iron technology in the UK. High-gradient magnetic separation is one of those subjects which is rapidly emerging as a separate entity. The technique finds application in ore processing, raw-material benefication and in biochemical processing. The seven papers in this section, all but one from the UK, provide a good state-of-the-art report. Transportation and levitation, sometimes referred to as maglev, deals with the use of magnetism in advanced forms of transport, particularly where the vehicle is supported and propelled by magnetic fields, thus eliminating rolling friction. The papers describe progress mainly in the UK and Germany. One paper, from the Netherlands, describes a nontransport application; namely a magnetically suspended momentum wheel for satellite stabilisation. Finally, the group of papers on permanent magnets report on recent advances in rare-earth cobalt materials, as well as including contributions on ferrite magnets, magnetisation processes and a review of high-coercivity materials. IEE Conf. Publ. 142 gives a wide ranging view of the title subject, particularly in relation to work in the UK. The presentation is good but would have been better if the papers, which are printed continuously in the order of presentation, had been separated into subtitled divisions. E.C.SNELLING

Theory of electrical filters J. D. Rhodes Wiley, 1976,224pp. £10-50 After many publications in the circuit-theory field, this book will be welcomed by all followers of Prof. Rhodes. The limited length of papers and their rather mathematical content have always been a stumbling block to the practising design engineer, who would probably have applied his techniques if only they had been easier to understand. However, this book, as the title implies, is still mainly theoretical; but, within the text, the necessary 'short-cut' design formulas can be found. Prof. Rhodes's field is microwave-filter design where his major contribution has been in the realisation of filters with prescribed amplitude and phase characteristics, the so-called linear phase filters. The emphasis is on analytic solutions rather than numerical synthesis or design by tables. Early chapters give the standard textbook introduction to the approximation problem but use the scattering-matrix approach to obtain explicit formulas for element values (in terms of coupling coefficients). Consideration of simultaneous amplitude and phase approximations leads to realisations with coupling between nonadjacent resonators (most suitable for narrow-band filters). On amplitude approximation of distributed networks, the bandpass response associated with the interdigital filter is investigated, and explicit design formulas are given. After discussion on optimum amplitude and phase approximations, the synthesis of generalised interdigital filters (i.e. allowing coupling to exist between all of the wires) is considered, together with a practical example of its implementation. J.N.TORRY BOOK REVIEWS are continued on p.791