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Fundamental frequency

About: Fundamental frequency is a research topic. Over the lifetime, 8941 publications have been published within this topic receiving 131583 citations.


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Journal ArticleDOI
TL;DR: In this paper, the effect of bending-twisting coupling on the fundamental frequencies is discussed for the cases of simply supported or clamped edges and the optimal laminate configuration is also obtained by using a mathematical programming method in which four lamination parameters are used as design variables.

70 citations

Journal ArticleDOI
J. Moorer1
TL;DR: A new method of tracking the fundamental frequency of voiced speech is described, shown to be of similar accuracy as the Cepstrum technique and to be faster than the SIFT algorithm.
Abstract: A new method of tracking the fundamental frequency of voiced speech is described. The method is shown to be of similar accuracy as the Cepstrum technique. Since the method involves only additions, no multiplication, it is shown to be faster than the SIFT algorithm. The basis of the method is searching for a minimum in the magnitude of the difference between a speech segment and a delayed speech segment. This is shown to be equivalent to selecting the comb filter which best annihilates the input signal.

69 citations

Proceedings ArticleDOI
17 Jul 2016
TL;DR: In this paper, the authors present three dynamic linear state space models of Modular Multilevel Converter (MMC) which are suitable for small-signal dynamic studies and controller design.
Abstract: This article presents three dynamic linear state space models of Modular Multilevel Converter (MMC) which are suitable for small-signal dynamic studies and controller design. The three models differ by the number of states (two, six and ten) and therefore are suitable for different applications based on the required accuracy. The 2nd and 6th order models ignore dynamics of the second harmonics and circulating current suppression control. The main challenges of dynamic analytical modelling of MMC are the non-linear multiplication terms in equations for modulating oscillating signals. The multiplication non-linear terms is therefore considered directly in the rotating DQ frame. This requires simultaneous modeling in zero sequence, fundamental frequency DQ and double fundamental frequency DQ2 frames. The proposed linear analytical models are implemented in state-space in MATLAB. The validity and accuracy of the models are verified against detailed 401 level MMC model in PSCAD/EMTDC in both: time and frequency domains. The results show very good accuracy for the 10th order model and decreasing accuracy for the lower order models.

69 citations

Journal ArticleDOI
TL;DR: In this paper, it is conjectured that pseudo-second spectrum contributions arising when evanescent waves become propagating above the cut-off frequency ω co = κ AG / ρ I can corrupt the frequency predictions of Timoshenko beam theory.

69 citations

Journal ArticleDOI
TL;DR: In this paper, a parametrization of the solution of the eigenvalue equation for lasing at odd harmonics is presented, and an explicit expression for FEL gain length, taking into account all essential effects.
Abstract: Harmonic lasing in a free electron laser with a planar undulator (under the condition that the fundamental frequency is suppressed) might be a cheap and efficient way of extension of wavelength ranges of existing and planned x-ray free electron laser (FEL) facilities. Contrary to nonlinear harmonic generation, harmonic lasing can provide much more intense, stable, and narrow-band FEL beam which is easier to handle due to the suppressed fundamental frequency. In this paper we perform a parametrization of the solution of the eigenvalue equation for lasing at odd harmonics, and present an explicit expression for FEL gain length, taking into account all essential effects. We propose and discuss methods for suppression of the fundamental harmonic. We also suggest a combined use of harmonic lasing and lasing at the retuned fundamental wavelength in order to reduce bandwidth and to increase brilliance of x-ray beam at saturation. Considering 3rd harmonic lasing as a practical example, we come to the conclusion that it is much more robust than usually thought, and can be widely used in the existing or planned x-ray FEL (XFEL) facilities. In particular, Linac Coherent Light Source (LCLS) after a minor modification can lase to saturation at the 3rd harmonic up to the photon energy of 25--30 keV providing multigigawatt power level and narrow bandwidth. As for the European XFEL, harmonic lasing would allow one to extend operating range (ultimately up to 100 keV), to reduce FEL bandwidth and to increase brilliance, to enable two-color operation for pump-probe experiments, and to provide more flexible operation at different electron energies. Similar improvements can be realized in other x-ray FEL facilities with gap-tunable undulators like FLASH II, SACLA, LCLS II, etc. Harmonic lasing can be an attractive option for compact x-ray FELs (driven by electron beams with a relatively low energy), allowing the use of the standard undulator technology instead of small-gap in-vacuum devices. Finally, in this paper we discover that in a part of the parameter space, corresponding to the operating range of soft x-ray beam lines of x-ray FEL facilities (like SASE3 beam line of the European XFEL), harmonics can grow faster than the fundamental wavelength. This feature can be used in some experiments, but might also be an unwanted phenomenon, and we discuss possible measures to diminish it.

69 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202344
2022101
2021236
2020335
2019421
2018375