Showing papers on "Fundamental frequency published in 2000"

Modes of vortex formation and frequency response of a freely vibrating cylinder

Abstract: In this paper, we study the transverse vortex-induced vibrations of an elastically mounted rigid cylinder in a fluid flow. We use simultaneous force, displacement and vorticity measurements (using DPIV) for the first time in free vibrations. There exist two distinct types of response in such systems, depending on whether one has a high or low combined mass–damping parameter (m*ζ). In the classical high-(m*ζ) case, an ‘initial’ and ‘lower’ amplitude branch are separated by a discontinuous mode transition, whereas in the case of low (m*ζ), a further higher-amplitude ‘upper’ branch of response appears, and there exist two mode transitions.To understand the existence of more than one mode transition for low (m*ζ), we employ two distinct formulations of the equation of motion, one of which uses the ‘total force’, while the other uses the ‘vortex force’, which is related only to the dynamics of vorticity. The first mode transition involves a jump in ‘vortex phase’ (between vortex force and displacement), ϕvortex, at which point the frequency of oscillation (f) passes through the natural frequency of the system in the fluid, f ∼ fNwater. This transition is associated with a jump between 2S [harr ] 2P vortex wake modes, and a corresponding switch in vortex shedding timing. Across the second mode transition, there is a jump in ‘total phase’, phis;total , at which point f ∼ fNvacuum. In this case, there is no jump in ϕvortex, since both branches are associated with the 2P mode, and there is therefore no switch in timing of shedding, contrary to previous assumptions. Interestingly, for the high-(m*ζ) case, the vibration frequency jumps across both fNwater and fNvacuum, corresponding to the simultaneous jumps in ϕvortex and ϕtotal. This causes a switch in the timing of shedding, coincident with the ‘total phase’ jump, in agreement with previous assumptions.For large mass ratios, m* = O(100), the vibration frequency for synchronization lies close to the natural frequency (f* = f/fN ≈ 1.0), but as mass is reduced to m* = O(1), f* can reach remarkably large values. We deduce an expression for the frequency of the lower-branch vibration, as follows:formula herewhich agrees very well with a wide set of experimental data. This frequency equation uncovers the existence of a critical mass ratio, where the frequency f* becomes large: m*crit = 0.54. When m* < m*crit, the lower branch can never be reached and it ceases to exist. The upper-branch large-amplitude vibrations persist for all velocities, no matter how high, and the frequency increases indefinitely with flow velocity. Experiments at m* < m*crit show that the upper-branch vibrations continue to the limits (in flow speed) of our facility.

Detection of bridge tap using frequency domain analysis

Abstract: A method for detecting the presence of a bridge tap and other types of fault in a transmission line. Initially, test signals of predetermined frequencies are transmitted into a transmitting end of the transmission line. The test signals are received at a receiving end of the transmission line and the amplitudes of the received signal are measured. A frequency response of the transmission line is computed based on the measured amplitudes. The frequency response is then analyzed for the presence of a frequency-domain signature that corresponds to one of the detectable types of fault. The presence of a bridge tap or another type of fault is identified based on the detected frequency-domain signature. The frequency-domain signature associated with a bridge tap can comprise a set of one or more attenuation dips in the frequency response, with each attenuation dip corresponding to a local minima in the frequency response. The length of the bridge tap can be estimated based on a fundamental frequency of the set of harmonically related attenuation dips. Also, the location of the bridge tap in the transmission line can be estimated by performing a time domain reflectometer (TDR) test.

A novel current tracking method for active filters based on a sinusoidal internal model

Abstract: A new current control method based on the internal model principle in control theory is proposed. It introduces a sinusoidal internal model into the control system. It does not use any coordinate transformations. The method can be used for tracking an arbitrary number of harmonics; a DC component or a fundamental frequency component signal. It is applied to a single-phase PWM inverter and active filter. The validity is confirmed by simulation and experimental results.

Ultrasonic harmonic imaging with adaptive image formation

Abstract: An ultrasonic diagnostic imaging system receives fundamental frequency, harmonic contrast, and tissue harmonic echo information for image processing. The fundamental and harmonic signal content of the echo information is analyzed and the relative content of an output signal is adjusted as necessary to take advantage of the different characteristics of the different types of echo information present in the echo signal. The ultrasound system can produce images which are an adaptive blend of fundamental, tissue harmonic and harmonic contrast echo information.

A frequency domain method for the measurement of nonlinearity in heterodyne interferometry

Abstract: This paper presents a method for the measurement of nonlinearity in heterodyne interferometry which utilizes the frequency spectrum of the output of the photodetector for the direct measurement of the magnitudes of the first and second harmonic nonlinearities. The underlying theory and the experimental technique are discussed. Results showing the application of this technique for the determination of the influence of the azimuthal alignments of the polarization beamsplitter, the analyzer and measurement retroreflector are presented. The applicability of the technique to the in situ optimization of an interferometer system is demonstrated. It is shown that using this technique an interferometer system can be optimized to reduce the first-harmonic nonlinearity to below 0.5 nm p-p and the second harmonic nonlinearity to 2 nm p-p. This method is contrasted with other methods and the advantages conferred by the elimination of an external reference and the phase measuring electronics are highlighted.

Modeling of tension modulation nonlinearity in plucked strings

Abstract: A nonlinear discrete-time model that simulates a vibrating string exhibiting tension modulation nonlinearity is developed. The tension modulation phenomenon is caused by string elongation during transversal vibration. Fundamental frequency variation and coupling of harmonic modes are among the perceptually most important effects of this nonlinearity. The proposed model extends the linear bidirectional digital waveguide model of a string. It is also formulated as a computationally more efficient single-delay-loop structure. A method of reducing the computational load of the string elongation approximation is described, and a technique of obtaining the tension modulation parameter from recorded plucked string instrument tones is presented. The performance of the model is demonstrated with analysis/synthesis experiments and with examples of synthetic tones.

Techniques for Automatic Music Transcription

Abstract: The scheme of the monophonic transcription system implemented here, is illustrated in figure 1. If the fundamental frequency of a harmonic signal is calculated, and the resulting track is visualised, it can be noticed that, for most of the duration of the notes, the pitch remains approximately constant. This relation, so clear to the eye, requires some comment. In order to implement some grouping criteria and rules for sounds, emphasis should be given to the similarity in human perception between image and sound [2]. Important clues can be obtained by observing carefully the plot of the pitch track.

Method and apparatus for flow imaging using coded excitation

Abstract: In performing flow imaging using coded excitation and wall filtering, a coded sequence of broadband pulses (centered at a fundamental frequency) is transmitted multiple times to a particular transmit focal position, each coded sequence constituting one firing. On receive, the receive signals acquired for each firing are supplied to a finite impulse response filter which both compresses and bandpass filters the receive pulses, e.g., to isolate a compressed pulse centered at the fundamental frequency. The compressed and isolated signals are then high pass filtered across firings using a wall filter. The wall-filtered signals are used to image blood flow and contrast agents.

Analysis, design, and implementation of a random frequency PWM inverter

Abstract: Random pulse width modulation (RPWM) approaches can make the harmonic spectrum of inverter output voltage be continuously distributed without affecting the fundamental frequency component, and thus the acoustic noise and mechanical vibration of an inverter-fed AC motor drive are greatly reduced. However, the analysis and design of the RPWM mechanisms are generally not so trivial for practical engineers that their applications are limited. In this paper, a random frequency PWM (RFPWM) inverter and its practical design procedure are presented. First, the effects of the attributes of a random signal on the inverter output harmonic spectrum distribution characteristics are analyzed using an intuitive concept, then based on which, the quantitative design. Simulink simulation and implementation of the proposed RFPWM inverter are introduced. The proposed RFPWM inverter is employed to power an indirect field-oriented induction motor drive. The simulated and measured results indicate that the uniform random distribution of inverter output harmonic spectrum and thus smaller acoustic noise and mechanical vibration are obtained by the proposed RFPWM scheme.

Effects of the salience of pitch and periodicity information on the intelligibility of four-channel vocoded speech: Implications for cochlear implants

Abstract: Recent simulations of continuous interleaved sampling (CIS) cochlear implant speech processors have used acoustic stimulation that provides only weak cues to pitch, periodicity, and aperiodicity, although these are regarded as important perceptual factors of speech. Four-channel vocoders simulating CIS processors have been constructed, in which the salience of speech-derived periodicity and pitch information was manipulated. The highest salience of pitch and periodicity was provided by an explicit encoding, using a pulse carrier following fundamental frequency for voiced speech, and a noise carrier during voiceless speech. Other processors included noise-excited vocoders with envelope cutoff frequencies of 32 and 400 Hz. The use of a pulse carrier following fundamental frequency gave substantially higher performance in identification of frequency glides than did vocoders using envelope-modulated noise carriers. The perception of consonant voicing information was improved by processors that preserved periodicity, and connected discourse tracking rates were slightly faster with noise carriers modulated by envelopes with a cutoff frequency of 400 Hz compared to 32 Hz. However, consonant and vowel identification, sentence intelligibility, and connected discourse tracking rates were generally similar through all of the processors. For these speech tasks, pitch and periodicity beyond the weak information available from 400 Hz envelope-modulated noise did not contribute substantially to performance.

Hybrid active filter for harmonically unbalanced three phase three wire railway traction loads

Abstract: This paper investigates a hybrid active/passive topology and control strategy appropriate for removing harmonics caused by unbalanced nonlinear loads. Unbalanced loads such as railway traction loads may use static compensators to balance the fundamental frequency components. The harmonic currents produced by this combination are unlikely to be balanced. Purely passive structures are not sensitive to this harmonic imbalance, however some active structures are. Controllers aimed at balanced three phase loads using synchronous transformations will not remove all of the harmonic components. The controller presented in this paper uses harmonic sequence components to detect both balanced and unbalanced components and reduce both harmonic components to zero.

Influence of peripheral resolvability on the perceptual segregation of harmonic complex tones differing in fundamental frequency.

Abstract: Two experiments investigated the influence of resolvability on the perceptual organization of sequential harmonic complexes differing in fundamental frequency (F0). Using a constant-stimuli method, streaming scores for ABA-... sequences of harmonic complexes were measured as a function of the F0 difference between the A and B tones. In the first experiment, streaming scores were measured for harmonic complexes having two different nominal F0s (88 and 250 Hz) and filtered in three frequency regions (a LOW, a MID, and a HIGH region with corner frequencies of 125-625 Hz, 1375-1875 Hz, and 3900-5400 Hz, respectively). Some streaming was observed in the HIGH region (in which the harmonics were always unresolved) but streaming scores remained generally lower than in the LOW and MID regions. The second experiment verified that the streaming observed in the HIGH region was not due to the use of distortion products. Overall, the results indicated that although streaming can occur in the absence of spectral cues, the degree of resolvability of the harmonics has a significant influence.

A simple circuit synthesis method for microwave class-F ultra-high-efficiency amplifiers with reactance-compensation circuits

Abstract: A class-F amplifier circuit by which the transistor load impedance, for even-order higher harmonics, can be kept “zero” and that for odd-order higher harmonics can be kept “open” without affecting the impedance at the fundamental frequency has been developed. This circuit basically consists of transmission lines with lengths equal to a half wavelength and a quarter wavelength at the fundamental frequency where the residual reactance at the fundamental frequency, due to the higher harmonic-frequency circuits, is compensated. Using this circuit, a microwave heterojunction bipolar transistor amplifier was designed using a harmonic-balance simulator. The designed power-added efficiency was more than 90%. The output waveforms, a dynamic load line, and the input/output power response were evaluated.

A broadband and miniaturized V-band PHEMT frequency doubler

Abstract: In this work, we present the design and measured performances of a V-band frequency doubler fabricated using 0.15 /spl mu/m GaAs pseudomorphic HEMTs and the three-dimensional (3-D) MMIC technology. Thank to the use of an improved 180/spl deg/ rat-race hybrid, the frequency doubler exhibits high spectral purity over a large bandwidth. Isolation better than 30 dB is achieved on a frequency range from 31.736 GHz and fundamental frequency rejection better than 35 dB is achieved between 31.5 GHz and 37.5 GHz. Conversion loss measured at 32.5 GHz is 8.5 dB for an input power of 14 dBm. Both the broadband spectral purity and the small size of 1 mm/sup 2/ make it suitable for the realization of high-quality and widely tunable V-band frequency sources. For the future developments of millimeter-wave wireless communication systems, it offers good perspectives toward the fabrication of single-chip V-band transceiver including the frequency source.

Ultrasonic pulse inversion harmonic separation with reduced motional effects

Abstract: Pulse inversion harmonic separation is performed utilizing echoes from three or more pulses of alternating phase or polarity. Temporally different echoes of opposite phase or polarity are combined in pairs, which are in turn combined to form partial sums and a final sum in which fundamental frequency signal components are substantially eliminated. Preferably the signals are normalized to a common reference level. The inventive technique can be performed by a filter structure using weighting coefficients exhibiting a Gaussian variation.

Tone features for speech recognition

Abstract: Robust acoustic tone features are achieved first by the introduction of on-line, look-ahead trace back of the fundamental frequency (F0) contour with adaptive pruning, this fundamental frequency serves as the signal preprocessing front-end. The F0 contour is subsequently decomposed into lexical tone effect, phrase intonation effect, and random effect by means of time-variant, weighted moving average (MA) filter in conjunction with weighted (placing more emphasis on vowels) least squares of the F0 contour. The phrase intonation effect is defined as the long-term tendency of the voiced F0 contour, which can be approximated by a weighted-moving average of the F0 contour, with weights related to the degree of the periodicity of the signal. Since it is irrelevant from lexical tone effect, therefore it is removed by subtraction of the F0 contour under superposition assumption. The acoustic tone features are defined as two parts. First is the coefficients of the second order weighted regression of the de-intonation of the F0 contour over neighbouring frames, with window size related to the average length of a syllable and weights corresponding to the degree of the periodicity of the signal. The second part deals with the degree of the periodicity of the signal, which are the coefficients of the second order regression of the auto-correlation, with lag corresponding to the reciprocal of the pitch estimate from look-ahead tracing back procedure. These weights of the second order weighted regression of the de-intonation of the F0 contour are designed to emphasize/de-emphasize the voiced/unvoiced segments of the pitch contour in order to preserve the voiced pitch contour for the semi-voiced consonants. The advantage of this mechanism is, even if the speech segmentation has slightly errors, these weights with look-ahead adaptive-pruning trace back of the F0 contour served as the on-line signal pre-processing front-end, will preserve the pitch contour of the vowels for the pitch contour of the consonants. This vowel-preserving property of the tone features has the ability to prevent model parameters from bias estimation due to speech segmentation errors.

Spectral characterization of jitter, shimmer, and additive noise in synthetically generated voice signals.

Abstract: Alteration of the harmonic structure in voice source spectra, taken over at least two periods of the waveform, may occur due to the presence of fundamental frequency (f0) perturbation, amplitude perturbation, additive noise, or changes within the glottal source signal itself. In order to make accurate inferences regarding glottal-flow dynamics or perceptual evaluations based on spectral measurements taken from the acoustic speech waveform, investigation of the spectral features of each aperiodic component is required. Based on a heuristic development involving a consideration of the partial sum of the Fourier series taken for two periods of a jittered, shimmered, and (additive, random) noise-contaminated signal, the corresponding spectral characteristics are hypothesized. Subsequent to this, the Fourier series coefficients are calculated for the two periods in order to test the hypotheses. Definite spectral differences are found for each aperiodic component; based on these findings differential quantitative spectral measurements are suggested. Further supportive evidence is obtained through use of Fourier transform and periodogram-averaged calculations. The analysis is carried out on synthetically generated glottal-pulse waveforms and on radiated speech waveforms. A discussion of the results is given in terms of voice aperiodicity in general and in terms of their implication for future studies involving human voice signals.

Stochastic modeling of spectral adjustment for high quality pitch modification

Abstract: We present a new algorithm for adjusting the magnitude spectrum when the fundamental frequency (F/sub 0/) of a speech signal is altered. The algorithm exploits the correlation between F/sub 0/ and the magnitude spectrum of speech as represented by line spectral frequencies (LSFs). This correlation is class-dependent, and thus a broad classification of the input is achieved by a Gaussian mixture model (GMM). The within-class dependencies of LSFs on F/sub 0/ values are captured by constructing their joint probability densities using a series of GMMs, one for each speech class. The proposed system is used for post-processing the pitch modified signal. Perceptual tests showed that the addition of this post-processing system improves the naturalness of the pitch modified signal for large pitch modification factors.

Chaotic behavior in bubble formation dynamics

Abstract: We constructed an experimental apparatus to study the dynamics of the formation of air bubbles in a submerged nozzle in a water/glycerin solution inside a cylindrical tube. The delay time between successive bubbles was measured with a laser-photodiode system. It was observed bifurcations, chaotic behavior, and sudden changes in a periodic regime as a function of the decreasing air pressure in a reservoir. We also observed dynamical effects by applying a sound wave tuned to the fundamental frequency of the air column above the solution. As a function of the sound wave amplitude, we obtained a limit cycle, a flip bifurcation, chaotic behavior, and the synchronization of the bubbling with sound wave frequency. We related some of the different dynamical behaviors to coalescent effects and bubble sizes.

Jitter measurement apparatus and its method

Abstract: A signal under measurement is converted into a digital signal by an AD converter, and a band-pass filtering process is applied to the digital signal to take out only components around a fundamental frequency of the signal under measurement. A data around a zero-crossing of the components around the fundamental frequency is interpolated to estimate a timing close to a zero-crossing point. A difference between adjacent timings in the estimated zero-crossing timing sequence is calculated to obtain an instantaneous period data sequence. A period jitter is obtained from the instantaneous period data sequence.

Robust fundamental frequency estimation using instantaneous frequencies of harmonic components.

Abstract: ICSLP2000: the 6th International Conference on Spoken Language Processing, October 16-20, 2000, Beijing, China.

Miniaturized artificial-transmission-line monolithic millimeter-wave frequency doubler

Abstract: Millimeter-wave signals are typically generated by frequency multiplication in modern single-chip or multichip module (MCM) systems. Consequently, the multiplication efficiency, spurious rejection, and size of the frequency multiplier ultimately limit the integration level and cost of these systems. This paper points to the size reduction of millimeter-wave frequency doublers by evaluating artificial transmission lines (ATL's) as a means to minimize the size of the low-impedance shunt stubs. As a result, we developed a 40-GHz frequency doubler, which used only 0.6-mm/sup 2/ area on a monolithic microwave integrated circuit. Despite the area minimization, the doubler exhibited state-of-the-art conversion loss of 1 dB over 10% bandwidth and rejected the fundamental frequency signal by more than 20 dB over 25% bandwidth. Reported herein is the novel simulation of the frequency doubler with active harmonic loads. Included in this paper are theoretical evaluation and simulation of ATL's with models for lumped components and verification of the results by electromagnetic simulation. Due to the high efficiency, low area requirement, and over 20-dB rejection of the fundamental signal, this miniaturized ATL frequency doubler can be used as a building block in the generation of local-oscillator signals in single-chip and MCM millimeter-wave systems.

Plane harmonic waves in piezo-thermoelastic materials

Abstract: The present paper is aimed at to study the propagation of plane harmonic waves in homogeneous anisotropic piezo­ thermoelastic materials afte r deriving the secular equation. [t is found th at four dispersive modes are possible. The low and high frequency approximations for the propagation speeds and attenuation coefficients have been obtai ned fo r quas i­ longit udinal (QL), quasi-transverse (QT), and quasi-thermal (T-mode). The limiting cases of th e frequency equation have also been di sc ussed. The analytical results obtained have been computed numerically for cadmium selenide material (6 mm class) of hexagonal symmetry. The piezo-thermoelastic material response entails an interaction of three major fields, namely, mechanical , thermal and electric in the macro physical world. One of the applications of the piezo-thermoelastic materi al is to detect the responses of a structure by measuring the electric charge, sensing or to reduce excessive re­ spo nses by applying additional electric forces or thermal forces, actuating. If sensing and ac tuating can be integrated smartly, a so-called intelligent structure can be designed. The piezoelectric materials are also often used as resonators whose frequencies need to be precisely controlled. Because of the coupling between the thermoelectric and pyroelectric effects, it is im­ portant to quantify the effect of heat dissipation on the propagation of waves at low and high-frequencies . A thermo-piezoelectricity theory was first proposed by Mindlin'. He also derived governing equations of a thermo-piezoelectric plate 2 • The physical laws for the thermo-piezoelectric materials have been explored by Nowacki 3 . 5 . Chandrasekharaiah 6 .? has generalized Mindlin's theory of thermo-piezoelectricity to account for the finite speed of propagation of thermal distur­ bances. Several investigators 8 . '4 have studied the propagation of waves in plates, cylinders and general three-dimensional bodies that are made of thermo­ piezoelectric materials. Tauchert' 5, has recently ap­ plied thermo-peizoelectricity theory to composite pl ates. Tang and XU' 6 derived the general dynamic equations, which include mechanical, thermal and electric effects, based on the anisotropic composite laminated plate theory. They also obtained analytical dynamical solutions for the case of general forces acting on a simply supported piezo-thermoelastic laminated plate and harmonic responses to temperature variation and an electric field has been examined as a special case. Yang and Batra' ? stu died th e effect of heat conduction on shift in the frequencies of a freely vibrating linear piezoelectric body with the help of two perturbation methods. It is shown that the first order effect on frequencies is to shift them by a small imaginary number thereby signifying that the effect of energy dissipation due to heat conduction is to reduce the amplitude of vibration. The aim of present paper is to study the propaga­ tion of plane harmonic waves in homogeneous aniso­ tropic linear piezo-thermoelastic mate ri als after de­ riving the secular equation. It is found that four dis­ persive modes are possible. The low and high­ frequency approximations for the propagation speeds and attenuation coefficients have been obtained for quasi - longitudinal (QL), quasi - transverse (QT), and quasi - thermal (T-mode). The limiting cases of th e frequency equation have also been discussed . The analysis done in the paper in based on the theory of algebraic functions as developed by Ahlfors' 8. A similar approach was used by Chadwick'9 and Sharma and Sidhu 20 to study the plane harmonic thermoelastic waves in anisotropic solids in the context of coupled and generalized theories of thermoelasticity, respec­ tively.

Method and apparatus for harmonic imaging using multiple focal zones

Abstract: A method and apparatus for performing harmonic imaging. Each transmit focal zone in the near-field is interrogated by two or more transmit firings of different phase, while each transmit focal zone in the far-field is interrogated by a single transmit firing. On receive, the respective near-field vectors are summed, thereby substantially cancelling the fundamental signal components while isolating the (sub)-harmonic signal components. In the far-field, the single transmit firing has a fundamental frequency f0. A filter isolates the signal component having a passband centered at a (sub)-harmonic frequency, e.g., 2f0. The near-field and far-field receive vectors at each scan angle are then stitched together to form a composite vector.