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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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Patent
07 Jun 1990
TL;DR: In this paper, a two frequency system with constructive reflection of energy at fundamental frequency back to the resonant circuitry, and with isolation of fundamental frequency energy from the output load is provided.
Abstract: An oscillator operational in the millimeter wave and microwave range, including frequencies greater than 60 GHz, is provided with reduced phase noise by enhancing Q of the resonant circuitry by reactively terminating fundamental frequency oscillation and increasing stored fundamental frequency energy in the resonant circuitry. A two frequency system is provided with constructive reflection of energy at fundamental frequency back to the resonant circuitry, and with isolation of fundamental frequency energy from the output load. Energy to the output load is obtained from the in-situ generated second harmonic of the active element. Phase noise is reduced by enhancing Q by more than an order of magnitude.

56 citations

Journal ArticleDOI
N. Miller1
TL;DR: An algorithm that determines the fundamental frequency of sampled speech by segmenting the signal into pitch periods, which processes both male and female speech, provides a voiced-unvoiced decision, and operates in real time on a medium speed, general purpose computer.
Abstract: This paper presents an algorithm that determines the fundamental frequency of sampled speech by segmenting the signal into pitch periods. Segmentation is achieved by identifying those samples of the waveform corresponding to the beginning of each pitch period. The segmentation is accomplished in three phases. First, using zero crossing and energy measurements, a data structure is constructed from the speech samples. This structure contains candidates for pitch period markers. Next, the number of candidate markers within this structure is reduced utilizing syllabic segmentation, coarse pitch frequency estimations, and discrimination functions. Finally, the remaining pitch period markers are corrected, compensating for errors introduced by the data reduction process. This algorithm processes both male and female speech, provides a voiced-unvoiced decision, and operates in real time on a medium speed, general purpose computer.

56 citations

Journal ArticleDOI
TL;DR: A potentially unstable limestone column (∼1000 m3, Vercors, French Alps) delineated by an open rear fracture was continuously instrumented with two three-component seismic sensors from mid-May 2009 to mid-October 2011 as discussed by the authors.
Abstract: A potentially unstable limestone column (∼1000 m3, Vercors, French Alps) delineated by an open rear fracture was continuously instrumented with two three-component seismic sensors from mid-May 2009 to mid-October 2011. Spectral analysis of seismic noise allowed several resonance frequencies to be determined, ranging from 6 to 21 Hz. The frequency domain decomposition (FDD) technique was applied to the ambient vibrations recorded on the top of the rock column. Three vibration modes were identified at 6, 7.5 and 9 Hz, describing the upper part of corresponding modal shapes. Finite element numerical modelling of the column dynamic response confirmed that the first two modes are bending modes perpendicular and parallel to the fracture, respectively, while the third one corresponds to torsion. Seismic noise monitoring also pointed out that resonance frequencies fluctuate with time, under thermomechanical control. For seasonal cycles, changes in frequency are due to the variations of the bulk elastic properties with temperature. At daily scale, increase in fundamental frequency with temperature has been interpreted as resulting from the rock expansion inducing a closure of the rear fracture rock bridges, hence stiffening the contact between the column and the rock mass. Conversely, the rock contraction induces a fracture opening and a decrease in resonance frequency. In winter, when the temperature drops below 0 ◦C, a dramatic increase in fundamental frequency is observed from 6 Hz to more than 25 Hz, resulting from ice formation in the fracture. During spring, the resonance frequency gradually diminishes with ice melting to reach the value measured before winter.

56 citations

Journal ArticleDOI
TL;DR: The removal of harmonic noise, spikes, self-potential drift, tapered windowing and the uncertainty estimation allows for doubling the usable range of TDIP data to almost four decades in time, and will significantly advance the science and the applicability of the IP method.
Abstract: The extraction of spectral information in the inversion process of time-domain (TD) induced polarization (IP) data is changing the use of the TDIP method. Data interpretation is evolving from a qualitative description of the subsurface, able only to discriminate the presence of contrasts in chargeability parameters, towards a quantitative analysis of the investigated media, which allows for detailed soil- and rock-type characterization. Two major limitations restrict the extraction of the spectral information of TDIP data in the field: i) the difficulty of acquiring reliable early-time measurements, in the millisecond range and ii) the self-potential drift in the measured potentials distorting the shape of the late time IP responses, in the second range. Recent developments in TDIP acquisition equipment have given access to full waveform recordings of measured potentials and transmitted current, opening a breakthrough for data processing. For measuring at early times, we developed a new method for removing the significant noise from powerlines contained in the data through a model-based approach, localizing the fundamental frequency of the powerline signal in the full-waveform IP recordings. By this, we cancel both the fundamental signal and its harmonics. Furthermore, a novel and efficient processing scheme for identifying and removing spikes TDIP data is developed. The noise cancellation and the de-spiking allow the use of earlier and narrower gates, down to a few milliseconds after the current turn-off. Furthermore, tapered windows are used in the final gating of IP data, allowing the use of wider and overlapping gates for higher noise suppression without signal distortion. For measuring at late times, we have developed an algorithm for removal of the self-potential drift. Usually constant or linear drift-removal algorithms are used, but these algorithms fail in removing the background potentials due to the polarization of the electrodes previously used for current injection. We developed a drift-removal scheme that model the polarization effect and efficiently allows for preserving the shape of the IP responses at late times. Uncertainty estimates are essential in the inversion of IP data. Therefore, in the final step of the data processing, we estimate the data standard deviation based on the data variability within the IP gates and the misfit of the background drift removal Overall, the removal of harmonic noise, spikes, self-potential drift, tapered windowing and the uncertainty estimation allows for doubling the usable range of TDIP data to almost four decades in time (corresponding to four responses in frequency), and will significantly advance the science and the applicability of the IP method. (Less)

56 citations

Journal ArticleDOI
TL;DR: In this article, a self-adjustable variable mass dampers (SAVM-TMD) is proposed for controlling human-induced vibrations of footbridges, which is capable of varying its mass and retuning its frequency on the basis of the acceleration ratio between the primary system and TMD.
Abstract: Summary Tuned mass dampers (TMDs) represent a quite mature technology for controlling human-induced vibrations of footbridges, when they are tuned to the primary structure's fundamental frequency. However, the TMD is very sensitive to even a small change in the tuning ratio. This paper proposes a novel TMD named self-adjustable variable mass TMD (SAVM-TMD), which is capable of varying its mass and retuning its frequency on the basis of the acceleration ratio between the primary system and the TMD. The accelerations are obtained from two acceleration sensors, and the frequency adjustment is achieved by using a microcontroller and actuating devices. The acceleration ratio limit value should be set in the microcontroller firstly, and when the adjustment begins, the microcontroller will retune the TMD to a reasonable frequency region, under a specific harmonic excitation. The SAVM-TMD can be regarded as a passive control device capable of adjusting its frequency. The performance of SAVM-TMD is studied via both experimental studies and numerical simulations under different pedestrian excitations. It is found that the SAVM-TMD is effective in reducing the response and improving the equivalent damping ratio of the primary system when the structural frequency changes, with little power consumption. The results obtained from the experimental studies and the numerical simulations agree with each other very well. More pedestrian vibration situations are studied in the numerical simulations, and the results also show that the SAVM-TMD has excellent performance in controlling human-induced vibrations.

55 citations


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