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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 article, the experimental characterization of low-frequency dispersion (i.e., long-term memory effects) affecting microwave GaN HEMTs is carried out by adopting a new nonlinear measurement system, which is based on lowfrequency multiharmonic signal sources.
Abstract: In this paper, the experimental characterization of low-frequency dispersion (i.e., long-term memory effects) affecting microwave GaN HEMTs is carried out by adopting a new nonlinear measurement system, which is based on low-frequency multiharmonic signal sources. The proposed setup, which has been fully automated by a control software procedure, enables given source/load device terminations at fundamental and harmonic frequencies to be synthesized. Different experimental results are provided to characterize well-known effects related to low-frequency dispersion (e.g., knee walkout and drain current collapse) and to demonstrate the validity of assumptions commonly adopted for electron device modeling.

72 citations

Journal ArticleDOI
TL;DR: In this paper, a new method of efficiency maximization that utilizes sensing of the third-harmonic component of air-gap flux is proposed, which is used to determine the resulting instantaneous position of the fundamental component of the air gap flux and, consequently, the torque and flux-producing components of the stator current.
Abstract: A new method of efficiency maximization that utilizes sensing of the third-harmonic component of air-gap flux is proposed. This signal is used to determine the resulting instantaneous position of the fundamental component of the air gap flux and, consequently, the torque- and flux-producing components of the stator current. In addition, the third harmonic signal is also used to determine the rotor speed. Hence, the output power of the machine can be calculated with only a single sensor wire attached to the neutral point of the machine. The flux-producing component can be readily adjusted to produce the minimum input power for a fixed amount of output power (fixed speed). >

72 citations

Journal ArticleDOI
TL;DR: In this article, a new pseudo-dynamic approach based on standing shear and primary waves propagating on a visco-elastic backfill overlying rigid bedrock subjected to both harmonic horizontal and vertical acceleration is presented.
Abstract: Seismic active soil thrust, soil pressure distribution and overturning moment are obtained in closed form using a new pseudo-dynamic approach based on standing shear and primary waves propagating on a visco-elastic backfill overlying rigid bedrock subjected to both harmonic horizontal and vertical acceleration. Seismic waves respect the zero stress boundary condition at the soil surface, backfill is modeled as a Kelvin–Voigt medium and a planar failure surface is assumed in the analysis. Effects of a wide range of parameters such as amplitude of base accelerations, soil shear resistance angle, soil wall friction angle, damping ratio are discussed. Results of the parametric study indicate that amplitude of the horizontal base acceleration and soil shear resistance angle are the factors most influencing active pressure distribution whereas the presence of the vertical acceleration always results in a quite small increase in seismic active thrust. Damping ratio is important mainly close to the fundamental frequency of shear wave where seismic active thrust is maximum. Unlike the original pseudo-dynamic approach the effect of a different frequency for S-wave and P-wave is considered in the analysis. Seismic active thrust is found to increase when the frequency of P-wave is greater than that of S-wave. The results obtained by the proposed approach are found to be in agreement with previous studies, provided that the seismic input is adapted to include amplification effects.

72 citations

Proceedings ArticleDOI
03 May 1982
TL;DR: It is shown in particular that the comb method is computationally more efficient, gives a better fundamental frequency resolution, and can use smaller duration windows for the initial spectral analysis.
Abstract: Most reliable methods of detecting pitch in the speech signal are based on the assumed periodicity found in the voiced speech spectrum (cf. the cepstrum method). Due to recent hardware developments, this approach is becoming more attractive since the prerequired harmonic analysis can now be easily performed in real time. The spectral comb correlation, a new method based on spectral analysis, was recently introduced (5). Rather than performing a second spectral analysis on the log power spectrum, this approach relies on the correlation between the power spectrum and a spectral comb with "teeth" of decreasing amplitude and variable teeth intervals. The maximum of this correlation function is obtained when the width of the teeth intervals corresponds to the periodicity of the spectrum. The spectral comb method is compared to the cepstrum on both theoretical and experimental levels. It is shown in particular that the comb method is computationally more efficient, gives a better fundamental frequency resolution, and can use smaller duration windows for the initial spectral analysis.

72 citations

Journal ArticleDOI
TL;DR: In this paper, a set of differential equations governing the fluid flow and fluid-membrane coupling are obtained for a valveless micropump working at high frequencies, and an approximate analytical solution is derived under the action of an external sinusoidal excitation force.
Abstract: Through flow field simplification, a set of differential equations governing the fluid flow and fluid–membrane coupling are obtained for a valveless micropump. The dimensional analysis on the equations reveals that the ratio of the inertial force of the fluid to the viscous loss is dependent on the size ratios among internal elements of the pump. For a micropump working at high frequencies, these two forces possess the same order of magnitude, and this phenomenon is independent of the excitation frequency and fluid type. For the liquid medium, the inertial force of the fluid is around O(102)–O(103) times as that of the plate membrane, and is also larger than the elastically deformed force of the plate when the excitation frequency is close to the plate fundamental frequency. For the case where there is no pressure difference between the inlet and the outlet, an approximate analytical solution is derived for the micropump under the action of an external sinusoidal excitation force. It shows that a phase shift lagging the excitation force exists in the vibration response. For certain combinations of micropump size and fluid–solid density ratios, the phase shift can come to 90° at a specific excitation frequency ω* due to the action of fluid inertia. Away from ω*, the phase shift becomes smaller. The amplitude response of coupling vibration changes nonlinearly with the excitation frequency and reaches maximum at another frequency ω** ≠ ω*. Due to the nonlinearity of viscous loss, resonance does not seem to occur at any frequency. To obtain a larger average flux, the two loss coefficients of the nozzle should be minimized while their difference should be maximized. Under the action of the fluid inertia, there exists an optimal working frequency (equal to ω*) at which the average flux is maximum. This optimal frequency is dependent on the size of the micropump, the material properties of the plate, the fluid properties and has no relation with the excitation force. For the case where a pressure difference between the inlet and the outlet exists, a constraint condition between the excitation force and the pressure difference is obtained.

72 citations


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