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Frequency response
About: Frequency response is a research topic. Over the lifetime, 25705 publications have been published within this topic receiving 332249 citations.
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TL;DR: An important objective of this paper is to demonstrate the broad applicability of the proposed overall methodology by selected numerical examples including finite element models of structures with strongly nonlinear, non-conservative contact constraints.
73 citations
TL;DR: In this paper, the authors used numerical simulations to gain insight into the changes in the frequency response of the higher eigenmodes in bimodal and trimodal operation for different levels of sample stiffness and dissipative forces.
Abstract: We have recently implemented a trimodal tapping mode atomic force microscopy (AFM) imaging scheme for ambient air with which it is possible to simultaneously acquire topographical, phase and frequency shift contrast images. In implementing this method we have identified conditions, such as very low fundamental amplitude setpoints and very low oscillation amplitudes for the higher eigenmodes, for which the stability of the imaging process can be compromised. In this work we use numerical simulations to gain insight into the changes in the frequency response of the higher eigenmodes in bimodal and trimodal operation for different levels of sample stiffness, tip–sample dissipative forces, oscillation amplitudes for each of the eigenmodes and cantilever rest positions above the surface. Although we do not attempt to convey a complete dynamics picture of the system, the results provide general guidelines for the selection of conditions that lead to stable imaging as well as insight into the observed phase and frequency shift contrast, highlighting a few potential imaging artifacts. Our simulation results are in general agreement with our experimental observations.
73 citations
TL;DR: In this article, a bi-level damage detection algorithm that utilizes dynamic responses of the structure as input and neural network (NN) as a pattern classifier is presented, which is applied to an experimental model bridge to demonstrate the feasibility of the algorithm.
Abstract: A bi-level damage detection algorithm that utilizes dynamic responses of the structure as input and neural network (NN) as a pattern classifier is presented. The signal anomaly index (SAI) is proposed to express the amount of changes in the shape of frequency response functions (FRFs) or strain frequency response function (SFRF). SAI is calculated by using the acceleration and dynamic strain responses acquired from intact and damaged states of the structure. In a bi-level damage identification algorithm, first the presence of damage is identified from the magnitude of the SAI value. Then the location of the damage is identified using the pattern recognition capability of the NN. The proposed algorithm is applied to an experimental model bridge to demonstrate the feasibility of the algorithm. Numerically simulated signals are used for training the NN, and experimentally acquired signals are used to test the NN. The results of this example application suggest that the SAI based pattern recognition approach ...
73 citations
TL;DR: Using radio-frequency modulation spectroscopic techniques for interrogation of fiber Bragg-grating (FBG) structures, both static and dynamic strain measurements can be performed, with a noise-equivalent sensitivity of the order of 150 nepsilon/ radicalHz in the quasi-static domain and 1.6 nePSilon/radicalHz at higher frequencies.
Abstract: We demonstrate the possibility of using radio-frequency modulation spectroscopic techniques for interrogation of fiber Bragg-grating (FBG) structures. Sidebands at 2 GHz are superimposed onto the output spectrum of a 1560-nm DFB diode laser. The power reflected by an FBG is demodulated at multiples of the sideband frequency. The sideband-to-carrier beat signal is shown to be extremely sensitive to Bragg wavelength shifts due to mechanical stress. Using this method, both static and dynamic strain measurements can be performed, with a noise-equivalent sensitivity of the order of 150 ne/√Hz, in the quasi-static domain (2 Hz), and 1.6 ne/√Hz at higher frequencies (1 kHz). The measured frequency response is presently limited at 20 kHz only by the test device bandwidth. A long-term reproducibility in strain measurements within 100 ne is estimated from laser frequency drift referred to molecular absorption lines.
73 citations
TL;DR: In this paper, an improved formulation based on the Maxwell's equations in integral form is presented, which corresponds to the Helmholtz equation and reduces the numerical efforts in solving the large linear equation system considerably.
Abstract: The finite-difference method in the frequency domain is a powerful tool for analyzing arbitrarily shaped transmission-line discontinuities and junctions. An improved formulation based on Maxwell's equations in integral form is presented. It corresponds to the Helmholtz equation and reduces the numerical efforts in solving the large linear equation system considerably. The method is verified by comparison to previous work on microstrip. >
73 citations