Frequency Response Of Structures Research Articles

The Frequency Response of Some Trimmed Passive Distributed RC Low-Pass Networks

An improved element, derived from the admittance parameters of a uniform distributed RC network, is proposed for use in a finite element simulation program. Its superiority over the simple RC element in the modeling of trimmed distributed RC structures is demonstrated. The improved element has been used to analyze the effects of single trim cuts, double trim cuts, and L-shaped trim cuts upon the performance of uniform distributed RC networks. The frequency response of top-hat type structures with various geometries has also been examined, together with the effect of a trim cut upon their frequency response.

Analysis of frequency response and noise of CCD structures

Analysis of frequency response and noise of CCD structures

A Comparison of Methods for Measuring the Frequency Response of Mechanical Structures with Particular Reference to Machine Tools

The measurement of the frequency responses of machine tool structures is necessary because of the association between frequency response and chatter with consequent limitation of productivity. Various alternative techniques have been suggested. The paper describes comparative measurements of the frequency response of two systems using several techniques. The techniques examined were (1) Sinuoidal excitation with digital analysis, frequency incremented manually. (2) Slowly swept sinusoidal excitation with analogue analysis. (Traditional method). (3) Fast swept sinusoidal excitation with digital analysis. (4) Impulse excitation with digital analysis. (5) Band-limited random excitation with digital analysis. The results show the fast swept sinusoidal and impulse methods to be the most satisfactory.

Novel laplace transform techniques in structural dynamic analysis

The objective of any vibration testing method and analysis is the determination of the dynamic response of a structure. Irrespective of the form and nature of the force applied to the structure, the behaviour of the structure with frequency is generally sought and a number of methods exist for obtaining the frequency response of structures. Up to the present these methods made use of the Fourier transform. The author, following earlier published work [1], presents a novel method for the frequency analysis of structures. This method makes use of the Laplace transform and presents many advantages over existing methods. Formal mathematical relationships are established and applied to systems of a limited number of degrees of freedom and also to continuous structures. Furthermore, by following the procedure described in reference [2], it is shown how the method may be used either in the transient excitation case or the random force one. Finally, the analysis techniques developed are applied to transient tests on systems and continuous structures.

Dynamics of non-circular stiffened cylindrical shells

The objective of this study is to assess the effect of non-circularity, i.e. spatially varying curvature, on the dynamics of stringer stiffened cylindrical shell structures. The transfer matrix method is used to study the effect of varying curvature on the normal modes and the frequency response of such structures. To obtain these results the transfer matrix for a varying curvature shell in conjunction with the transfer matrix techniques for stiffened circular structures are applied. A previously developed exact solution for the panel transfer matrix, where the curvature varies exponentially, is used in computing the numerical results. Responses of increasing curvature and decreasing curvature structures are compared with those of the circular structure.

Frequency response of structures and the effects of noise on its estimates from the transient response

Transient testing techniques have been extensively used in determining the behaviour of a dynamic system and as a means of obtaining its frequency response.This paper deals with the determination of the frequency response of structures by transient testing techniques and is focused on the effects of extraneous noise on the estimate of the frequency response function.The deterministic approach of estimating the frequency response function of a structure by taking the Fourier transform of its transient response is shown to yield very poor results when noise is present either as additional excitation to the structure or at the response.Probabilistic theory is thus necessarily employed in the analysis of the transient response of the structure. The study shows that noise present at the response of a system affects the estimates of its frequency response function derived by considering either the power spectral density function of the response or the autocorrelation function of the response.The theoretical study is completed by the development of a novel analysis technique by which accurate estimates of the frequency response function of the structure may be obtained from transient tests carried out under noisy environmental conditions.

Evaluation of the dynamic characteristics of structures by transient testing

Transient methods of measuring the frequency response of structures may be used now that the digital computer is established as a means of analysing transient data. The spectral properties of the rapid frequency sweep are well defined and it is shown that this type of forcing function is extremely suitable for transient tests on structures. Methods of deriving the frequency response function from rapid frequency sweep tests are discussed and possible sources of error are investigated. Results from practical tests show how the method may be used to derive the frequency response characteristics of built-up structures.

Design considerations of a graded-base transistor with improved emitter-base breakdown voltage

Diffusion techniques are employed in transistor technology for cases where, for instance, a graded impurity profile improves the frequency response of alloyed structures, or for accurate control in the manufacture of very narrow base regions. This practice leads generally to a very low emitter-base breakdown voltage due to the high impurity density facing the emitter.This limitation can be overcome by insertion of a layer of high resistivity between the emitter and the graded base. The current flow equations of such a structure are derived for the case when charge neutrality prevails over a considerable part of the interposed layer, and the somewhat lowered frequency response is calculated. The signal delay time due to this neutral layer is shown to be proportional to (current density)−½, so that the emitter has to be adequately forward-biased. Several devices with varying design aims are evaluated, and numerical calculations of their performance, e.g. lower current density limits, are made. The modified small-signal input impedance is derived, and the layer is shown to be capacitive owing to its fluctuating charge storage. Transient response from the point of view of charge storage is also evaluated.