摘要:

The paper shows how the variational principle can be used to analyse the generation of ultrasonic surface waves by an infinite interdigital array of electrodes on the surface of a piezoelectric material. The method is used to analyse the behaviour of such an array deposited on a piezoelectric ceramic. Representation of surface-wave generation by an approximate electrical equivalent circuit is discussed, and the variation of piezoelectric coupling factor with the electrode width/gap ratio is computed for the fundamental resonant frequency, and the third and fifth harmonics. Bulk-wave generation is also treated in some detail.

DOI:10.1049/piee.1971.0163

出版商:IEE    

年代:1971

数据来源: IET

摘要:

Anechoic rooms are widely used in industrial testing and research on acoustic transducers and materials. The paper describes a chamber, designed and built at the University of Bradford for the dual purpose of research and teaching. The chamber designed was of necessity of small inside dimensions, and this fact dictated that the lining material had to be of high efficiency in order to leave the maximum usable internal volume. The acoustic properties of fibrous absorbers are discussed and a description of the methods used to classify fibrous material is given. The results of tests on several fibrous absorbers are presented, and the development of a highly efficient exponentially graded density configuration, using natural wool fibres or their equivalent, is described. The methods adopted in the Bradford University chamber to incorporate this favourable lining method are illustrated. The authors conclude by showing that the chamber, built as described, provides a highly satisfactory and economical solution to the problem.

DOI:10.1049/piee.1971.0164

出版商:IEE    

年代:1971

数据来源: IET

摘要:

A unified theory is formulated for the determination of the functional behaviour in the frequency domain of the propagation constant of electromagnetic waves which may exist in a uniform inhomogeneous waveguide which contains a linear time-invariant passive medium. By applying the constraints of linearity and time invariance to a bounded uniform medium, it is shown that the propagation coefficient in the transformed frequency domain is solely a function of the complex frequency variablep. The additional physical constraints of reality and passivity are shown to imply that the propagation constant γ belongs to a special class of functions which have been termed ‘nonzero real functions’. If the waveguide is also dissipationless, γ becomes a ‘symmetrical nonezero real function’ possessing symmetry about the axisp=jω. In restricted geometries for the cross-section of the guide, additional constraints on γ may exist and, as an example, a rectangular waveguide partially loaded with dielectric material is cited. A qualitative discussion on closed microstrip lines and circular waveguides containing dielectric rods is also included.

DOI:10.1049/piee.1971.0165

出版商:IEE    

年代:1971

数据来源: IET

摘要:

A technique is described which offers the potential of achieving wide-angle beam steering with fixed parabolic reflectors. The technique involves a primary-feed device with an aperture field distribution which can be adapted to match the distorted field distributions resulting from a parabolic reflector when an off-axis plane wave is incident. To provide an adaptation without deterioration of the system signal/noise ratio, which requires only a movement of the primary feed along a given locus and an adjustment of noninteracting phase shifters, the primary feed carries out a spatial Fourier transformation of the intercepted fields. The technique has been implemented in an experimental X band antenna and beam steering of ±15 beamwidths achieved with negligible distortion of the directional pattern and less than 0.5 dB loss in gain.

DOI:10.1049/piee.1971.0166

出版商:IEE    

年代:1971

数据来源: IET

摘要:

It is well known that the noise figure of a receiving system is directly proportional to the conversion power-loss ratio of the mixer. The paper is concerned with a mixer circuit whose loss, under certain conditions, can theoretically approach zero. A current-driven lattice mixer, using four matched semiconductor diodes, is analysed in detail, assuming a diode law as observed in practice. The design formulas are derived under matched conditions for the conversion power loss and the input and load impedances of the mixer. These formulas are expressed as functions of the termination at the image frequency, the diode quality factor and the local-oscillator current drive. It is finally concluded that losses below 1 dB are theoretically possible in a mixer using a lattice configuration of practical diodes. This conclusion is supported by the results obtained, mainly at low frequencies, using experimental circuits constructed for exploratory purposes.

DOI:10.1049/piee.1971.0168

出版商:IEE    

年代:1971

数据来源: IET

摘要:

A solution to the problem of halogen separation in linear tungsten-halogen lamps burning at arbitrary angles to the horizontal is presented. Two major advances in the technology of these lamps are reported. These are an understanding of the precise physical mechanism of halogen separation, and the advent of new forms of halogen compounds which permit the use of highly reactive halogens, such as bormine and chlorine, without excessive filament damage. By combination of these two areas of research, a universal-burning lamp has been developed, and is reported here.

DOI:10.1049/piee.1971.0169

出版商:IEE    

年代:1971

数据来源: IET

摘要:

The paper employs a ladder-network method for calculating the voltages and currents at the lamp junctions in a major road-lighting scheme. The lighting circuit is dealt with in unit lengths of one mile, and, (partly to demonstrate the method), use is made of a step-up transformer at the supply point with simple chokes at the lamp positions. Only by the use of circuit theory can the minimal size of cable become known, and the paper suggests that an increase in the supply voltage might further assist in reducing the size and cost of the cable, at the same time giving the lamp designer greater scope in the development of more efficient lamps. Planning the lighting scheme in unit lengths would necessarily introduce a measure of standardisation, with resulting economy. Further economies might be made possible by the use of low-cost conductors in road-lighting circuits, and by the use of cheaper joints and looping techniques which such conductors could bring in their train. Consequent upon the enforced use of crash barriers, a simple procedure for laying cables on the centre reservation of motorways is put forward in the paper.

DOI:10.1049/piee.1971.0170

出版商:IEE    

年代:1971

数据来源: IET

摘要:

A comparison is made of the validity and practical utility of five different methods, used to varying extents in practice, of accounting for the effect of rotor skew in predicting the performance characteristics of cage induction motors. It is shown that, of the two methods which are theoretically valid, the one commonly used is the less practical for computing the combined effect of mutual and leakage fluxes under conditions of magnetic saturation. It should be superseded by the other equally valid method, which is shown here to deal more directly with the internal electromagnetic conditions of the motor. With regard to the remaining three methods, it is demonstrated that although all are fundamentally invalid, one of them has practical utility as a simple expedient for inherently taking a preliminary account of the stray load and increased magnetic-saturation effects experienced with skewed cage induction motors.

DOI:10.1049/piee.1971.0171

出版商:IEE    

年代:1971

数据来源: IET

摘要:

It has been suggested that the solution of the relevant nonlinear differential equation would show that decreasing the interbar resistance at the central coreplates of the rotor of a cage induction motor results in a decrease of the interbar-current loss, with a consequent decrease of the stray loss. It is demonstrated here that such a conclusion is not necessarily true. Under certain circumstances, a decrease of the interbar resistance at the central coreplate can result in an increase of the stray loss. In particular, a specific linear change of the interbar resistance from each corestack end to its centre is assumed, and a plot obtained of the interbar loss with varyingmeaninterbar resistance. Surprisingly, when other linear changes are considered, the maximum loss remains the same, but occurs at different values of the mean interbar resistance. A discussion is given of the practical implications.

DOI:10.1049/piee.1971.0172

出版商:IEE    

年代:1971

数据来源: IET

摘要:

A theoretical and practical study is given of reluctance motors having rotors constructed from axially laminated anisotropic cores, as proposed in an earlier paper. The experimental work has led to the development of a practical motor of high performance, capable of a large maximum output without detriment to overall performance or stability. In addition, the broad field of reluctance motors and their features are reviewed, and an attempt is made to integrate developments. A full bibliography is provided.

DOI:10.1049/piee.1971.0173

出版商:IEE    

年代:1971

数据来源: IET