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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.


Papers
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Journal ArticleDOI
TL;DR: This paper investigates the extraction of acoustic signatures from small boats using a passive sonar system and shows the HEAT algorithms ability to extract these signatures.
Abstract: This paper investigates the extraction of acoustic signatures from small boats using a passive sonar system. Noise radiated from a small boats consists of broadband noise and harmonically related tones that correspond to engine and propeller specifications. A signal processing method to automatically extract the harmonic structure of noise radiated from small boats is developed. The Harmonic Extraction and Analysis Tool (HEAT) estimates the instantaneous fundamental frequency of the harmonic tones, refines the fundamental frequency estimate using a Kalman filter, and automatically extracts the amplitudes of the harmonic tonals to generate a harmonic signature for the boat. Results are presented that show the HEAT algorithms ability to extract these signatures.

53 citations

Journal ArticleDOI
TL;DR: In this paper, the authors quantified and modeled the relative frequency drop affecting low-rise modern masonry buildings and discussed the damping variations based on two experimental data sets: Pseudo-dynamic tests at ELSA laboratory in the frame of the ESECMaSE project and in situ forced vibration tests by EMPA and EPFL.
Abstract: The knowledge of fundamental frequency and damping ratio of structures is of uppermost importance in earthquake engineering, especially to estimate the seismic demand. However, elastic and plastic frequency drops and damping variations make their estimation complex. This study quantifies and models the relative frequency drop affecting low-rise modern masonry buildings and discusses the damping variations based on two experimental data sets: Pseudo-dynamic tests at ELSA laboratory in the frame of the ESECMaSE project and in situ forced vibration tests by EMPA and EPFL. The relative structural frequency drop is shown to depend mainly on shaking amplitude, whereas the damping ratio variations could not be explained by the shaking amplitude only. Therefore, the absolute frequency value depends mostly on the frequency at low amplitude level, the amplitude of shaking and the construction material. The decrease in shape does not vary significantly with increasing damage. Hence, this study makes a link between structural dynamic properties, either under ambient vibrations or under strong motions, for low-rise modern masonry buildings. A value of 2/3 of the ambient vibration frequency is found to be relevant for the earthquake engineering assessment for this building type. However, the effect of soil–structure interaction that is shown to also affect these parameters has to be taken into account. Therefore, an analytical methodology is proposed to derive first the fixed-base frequency before using these results. Copyright © 2010 John Wiley & Sons, Ltd.

53 citations

Journal ArticleDOI
TL;DR: In this article, a general high precision triangular plate bending finite element has been extended to the free vibration analysis of laminated skew plates by deriving the consistent mass matrix in explicit form.

53 citations

Patent
26 Sep 1974
TL;DR: In this paper, a frequency synthesizer is described which can provide rational fractional frequencies between harmonics, where a cycle swallower is provided to occasionally abruptly shift the phase of the oscillator output.
Abstract: A frequency synthesizer is disclosed which can provide frequencies which are rational multiples of a fundamental reference frequency. The synthesizer includes a voltagecontrolled oscillator in a phase-locked loop with the reference frequency. A modulo-N counter is included to allow synthesis of harmonics of the reference frequency. To obtain rational fractional frequencies between harmonics a ''''cycle swallower'''' is provided to occasionally abruptly shift the phase of the oscillator output. The swallowing rate is determined by the contents of a storage register which is pre-loaded with a representation of the desired frequency. The contents of this storage register are periodically loaded into and accumulated in an accumulator which generates an overflow signal to the cycle swallower whenever the accumulated value exceeds its maximum storage capacity. In response to the average rate of phase shifting by the swallower, the loop stabilizes when the oscillator frequency is equal to the desired rational multiple of the reference frequency.

53 citations

Journal ArticleDOI
TL;DR: In this paper, gallium arsenide (GaAs) Gunn diodes having active lengths of 1.8-2.6 µm, bonded into commercially available packages, were operated in full-height waveguides in the V-, E-, and W-(WR-10) bands, using coaxial-bias circuits with a disc-post resonator to provide the required resonance at their fundamental frequency in the range from about 25-65 GHz.
Abstract: Pulsed and CW measurements in the range 26-110 GHz were performed on gallium arsenide (GaAs) Gunn diodes having active lengths of 1.8-2.6 µm, bonded into commercially available packages. The diodes were operated in full-height waveguides in the V-(WR-15), E-(WR-12), and W-(WR- 10) bands, using coaxial-bias circuits aud a disc-post resonator to provide the required resonance at their fundamental frequency in the range from about 25-65 GHz. Frequency and power measurements were performed up to 110 GHz on the fundamental, second, and third harmonics. The main emphasis of this experimental investigation has been the study of frequency changes caused by changes made in the various parameters of the disc, post, diode, diode package, and embedding waveguide sections.

53 citations


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