Showing papers on "Fundamental frequency published in 2001"

A theoretical investigation of average H/V ratios

Abstract: SUMMARY The mode summation method and a finite difference technique are applied to investigate the spectral ratio between the horizontal and vertical components (H/V ratio) of ambient vibrations and to explore the variation of the resonance frequency and the amplitude and shape of polarization as a function of the structure and the source positions. Layered structural models are used by assuming a large number of sources distributed around a receiver, with shallow source depths that are randomly assigned. We identify stable parts of the H/V ratios that are independent of the source distance and are dominated by the ellipticity of the fundamental-mode Rayleigh wave in the frequency band between the fundamental frequency of resonance of the unconsolidated sediments and the first minimum of the average H/V ratio. The ellipticity in this frequency band is determined by the layering of the sediments. The numerical simulations are compared with observations at a site where the thickness and velocity structure of the unconsolidated sediments are known from S-wave and surface wave measurements. Two methods are applied to compute the H/V ratio, the classical method in the frequency domain and a method based on frequency–time analysis that allows us to locate P–SV wavelets in the time-series. The main problem in comparing synthetics with observations is the contribution of SH waves in the observed H/V ratios. We propose a method to minimize these effects and the effects of the superposition of different incoming P–SV waves. An inversion scheme is applied to the stable parts of the observed H/V ratio, based on a genetic algorithm, to retrieve the S-wave velocity structure from a single ambient vibration record.

A novel current-tracking method for active filters based on a sinusoidal internal model [for PWM invertors]

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 fundamental frequency component signal. It is applied to a single-phase pulsewidth modulation inverter and active filter. The validity is confirmed by simulation and experimental results.

Coding of the fundamental frequency in continuous interleaved sampling processors for cochlear implants

Abstract: In this study the perception of the fundamental frequency (F0) of periodic stimuli by cochlear implant users is investigated. A widely used speech processor is the Continuous Interleaved Sampling (CIS) processor, for which the fundamental frequency appears as temporal fluctuations in the envelopes at the output. Three experiments with four users of the LAURA (Registered trade mark of Philips Hearing Implants, now Cochlear Technology Centre Europe) cochlear implant were carried out to examine the influence of the modulation depth of these envelope fluctuations on pitch discrimination. In the first experiment, the subjects were asked to discriminate between two SAM (sinusoidally amplitude modulated) pulse trains on a single electrode channel differing in modulation frequency ( deltaf = 20%). As expected, the results showed a decrease in the performance for smaller modulation depths. Optimal performance was reached for modulation depths between 20% and 99%, depending on subject, electrode channel, and modulation frequency. In the second experiment, the smallest noticeable difference in F0 of synthetic vowels was measured for three algorithms that differed in the obtained modulation depth at the output: the default CIS strategy, the CIS strategy in which the F0 fluctuations in the envelope were removed (FLAT CIS), and a third CIS strategy, which was especially designed to control and increase the depth of these fluctuations (F0 CIS). In general, performance was poorest for the FLAT CIS strategy, where changes in F0 are only apparent as changes of the average amplitude in the channel outputs. This emphasizes the importance of temporal coding of F0 in the speech envelope for pitch perception. No significantly better results were obtained for the F0 CIS strategy compared to the default CIS strategy, although the latter results in envelope modulation depths at which sub-optimal scores were obtained in some cases of the first experiment. This indicates that less modulation is needed if all channels are stimulated with synchronous F0 fluctuations. This hypothesis is confirmed in a third experiment where subjects performed significantly better in a pitch discrimination task with SAM pulse trains, if three channels were stimulated concurrently, as opposed to only one.

Evaluation of frequency tracking methods

Abstract: This paper presents an analysis of proposed methods for tracking the fundamental power frequency to see if they have the performance necessary to cope with the requirements of future protection and control equipment and are robust enough to cope with the more demanding nature of modern power system conditions. The analysis shows that the linear estimation of phases, decomposition of single phase into orthogonal components and discrete Fourier transform perform extremely well but they all suffer from a periodic error in the estimated frequency if it departs from the assumed frequency. This can be cancelled using a low pass filter although it would introduce delays and obscure any real oscillations in the fundamental frequency. Alternatively, averaging over three phases could be used but higher harmonics in the oscillation of the estimation would be present.

Removal of decaying DC in current and voltage signals using a modified Fourier filter algorithm

Abstract: Protecting transmission lines frequently involves applying distance relays. Protective relays must filter their inputs to reject unwanted quantities and retain signal quantities of relevant interest. Accuracy and convergent speed of filter algorithm are essential for protective relays. A widely applied filter algorithm, the discrete Fourier transform (DFT) can easily remove integer harmonics using simple calculation. However, the voltage and current signals contain serious harmonics and decaying DC during the fault interval. In addition, the decaying DC and higher order harmonics seriously decrease the precision and convergence speed of fundamental frequency signal from DFT. In this investigation, the authors derive a novel algorithm which combines the appropriate analog low pass filter and modified full cycle DFT (FCDFT) or half cycle DFT (HCDFT) algorithm to remove the decaying dc in a voltage or current signal. Using the Electromagnetic Transients Program (EMTP) simulates the transient responses of transmission lines during the fault period. Applying the proposed algorithm in distance relays effectively suppresses the decaying DC and quickly decomposes the accurate fundamental frequency components.

Effects of frequency-shifted auditory feedback on fundamental frequency of long stressed and unstressed syllables.

Abstract: Twenty-four normally speaking subjects had to utter the test word /tatatas/ with different stress patterns repeatedly. Auditory feedback was provided by head-phones and was shifted downwards in frequency during randomly selected trials while the subjects were speaking the complete test word. If the first syllable was long stressed, fundamental frequency of the vowel significantly increased by 2 Hz (corresponding to 25.5 cents) under frequency-shifted auditory feedback of .5 octave downwards, whereas under a shift of one semitone downwards a trend of an increase could be observed. If the first syllable was unstressed, fundamental frequency remained unaffected. Regarding the second syllable, significant increases or a trend for an increase of fundamental frequency was found in both shifting conditions. Results indicate a negative feedback mechanism that controls the fundamental frequency via auditory feedback in speech production. However, within a syllable a response could be found only if the syllable duration was long enough. Compensation for frequency-shifted auditory feedback still is quite imperfect. It is concluded that control of fundamental frequency is rather important on a suprasegmental level.

Parallel control of the UPS inverters with frequency-dependent droop scheme

Abstract: This paper presents a control approach for paralleling the UPS inverters with no control interconnection. The reference voltage of the inverter is generated to simulate a reactor connected between the inverter and the load at the fundamental frequency. The intention is to control the real and reactive power sharing of the inverters with the Q-V and P-/spl omega/ droop scheme without connection of a true transfer reactor. At the harmonic frequency the reference voltage turns to simulate a resistor, aiming that the load harmonic current can be shared equally and the voltage distortion is low. Two 1 kVA inverters are setup for demonstrating the effectiveness of the proposed approach.

Multi-phase electric motor with third harmonic current injection

Abstract: Significantly increased torque is provided from a motor having a stator with a core and at least two three-phase windings wound on the core The two windings are separated spatially by 30 electrical degrees Power is provided to the two windings by two power supplies which each provide power at the same fundamental frequency and with a component at the third harmonic of the fundamental, with the power provided from one power supply shifted in time by 30° of the fundamental frequency with respect to the power provided by the other power supply The additional third harmonic component reduces the effective peak flux density, allowing an increase in the fundamental component of flux to allow an increase in effective torque, with the third harmonic component also providing additional torque

Novel oscillator incorporating a compact microstrip resonant cell

Abstract: A novel transistor oscillator incorporating a compact microstrip resonant cell (CMRC) as its terminating resonance is proposed. Adjusting the dimensions of the cell, it is possible that the fundamental frequency can be positively fed back and the second harmonic negatively fed back at the input port of the oscillator. The fundamental output is enhanced with the second harmonic being suppressed. The output power of the proposed CMRC oscillator is 14.7 dBm at 2.5 GHz with 27.1 dB rejection of the second harmonic, outperforming the conventional microstrip termination with a 40% size reduction.

Exploring the temporal mechanism involved in the pitch of unresolved harmonics

Abstract: This paper continues a line of research initiated by Kaernbach and Demany [J. Acoust. Soc. Am. 104, 2298–2306 (1998)], who employed filtered click sequences to explore the temporal mechanism involved in the pitch of unresolved harmonics. In a first experiment, the just noticeable difference (jnd) for the fundamental frequency (F0) of high-pass filtered and low-pass masked click trains was measured, with F0 (100 to 250 Hz) and the cut frequency (0.5 to 6 kHz) being varied orthogonally. The data confirm the result of Houtsma and Smurzynski [J. Acoust. Soc. Am. 87, 304–310 (1990)] that a pitch mechanism working on the temporal structure of the signal is responsible for analyzing frequencies higher than ten times the fundamental. Using high-pass filtered click trains, however, the jnd for the temporal analysis is at 1.2% as compared to 2%–3% found in studies using band-pass filtered stimuli. Two further experiments provide evidence that the pitch of this stimulus can convey musical information. A fourth experiment replicates the finding of Kaernbach and Demany on first- and second-order regularities with a cut frequency of 2 kHz and extends the paradigm to binaural aperiodic click sequences. The result suggests that listeners can detect first-order temporal regularities in monaural click streams as well as in binaurally fused click streams.

Fundamental frequency estimation based on the joint time-frequency analysis of harmonic spectral structure

Abstract: In this paper, we propose a new scheme to analyze the spectral structure of speech signals for fundamental frequency estimation. First, we propose a pitch measure to detect the harmonic characteristics of voiced sounds on the spectrum of a speech signal. This measure utilizes the properties that there are distinct impulses located at the positions of fundamental frequency and its harmonics, and the energy of voiced sound is dominated by the energy of these distinct harmonic impulses. The spectrum can be obtained by the fast Fourier transform (FFT) however, it may be destroyed when the speech is interfered with by additive noise. To enhance the robustness of the proposed scheme in noisy environments, we apply the joint time-frequency analysis (JTFA) technique to obtain the adaptive representation of the spectrum of speech signals. The adaptive representation can accurately extract important harmonic structure of noisy speech signals at the expense of high computation cost. To solve this problem, we further propose a fast adaptive representation (FAR) algorithm, which reduces the computation complexity of the original algorithm by 50%. The performance of the proposed fundamental-frequency estimation scheme is evaluated on a large database with or without additive noise. The performance is compared to that of other approaches on the same database. The experimental results show that the proposed scheme performs well on clean speech and is robust in noisy environments.

Gigahertz surface acoustic wave probe for chemical analysis

Abstract: This paper considers the propagation of high frequency 0.1–2.6 GHz surface acoustic wave pulses in aqueous solutions of pure water, glycerol and protein. The GHz frequency components of the pulse are used to provide the highest operating frequencies so far reported and also to construct the first acoustic absorption spectrum associated with the evanescent field. Acoustic generation is sourced from a single non-linear SAW device that provides a series of harmonic frequencies, simultaneously. The received power level is determined from digital samples of the received pulse waveform. The power leaked into glycerol solutions at the fundamental frequency was found to be 50% smaller for pulses, than for continuous acoustic waves, an effect that could be related to the equilibration of the evanescent field. Increasing the concentration of the glycerol solutions or time exposed to the protein (IgG) solution, showed that the power losses from the surface acoustic wave pulse were broadly consistent with the behaviour of transverse shear mode sensors. Atomic force microscope measurements of the bare device revealed that the morphology of the silica overlayer was uniformly granular, whereas adsorbed protein films formed non-contiguous islands. Confirmation of the presence of the IgG film was obtained from quantitative X-ray photoelectron spectroscopy. An 8 gigasample per second digitising oscilloscope running a fast Fourier transform routine captured the acoustic absorption spectrum, and revealed a smooth characteristic for the glycerol and IgG, although for the latter, frequencies beyond 500 MHz were associated with an irregular spectrum. These multiple frequency measurements of the solid–liquid interface provide evidence that when the penetration depth and film thickness are similar, disruption of the predicted exponential form of the evanescent wave occurs, as indicated by the fluctuations seen in the absorption spectrum recorded. These preliminary results have shown that multiple frequency operation of single non-linear SH-SAW devices is possible, and an evanescent interfacial absorption spectrum can be obtained. By extending the measurement technique it may be possible to obtain additional information about the structure and composition of the solid–liquid interface.

Fast frequency-domain pitch estimation

Abstract: A method for estimating a pitch frequency of an audio signal includes computing a first transform of the signal to a frequency domain over a first time interval (42), and computing a second transform of the signal of the frequency domain over a second time interval (44), which contains the first time interval. A line spectrum of the signal is found, based on the first and second transforms, the spectrum including spectral lines having respective line amplitudes and line frequencies. A utility function (130) that is periodic in the frequencies of the lines in the spectrum is then computed. This function is indicative (158), for each candidate pitch frequency in a given pitch frequency range, of a compatibility of the spectrum with the candidate pitch frequency. The pitch frequency of the speech signal is estimated responsive to the utility function (176, 178).

Psychophysical estimates of cochlear phase response: masking by harmonic complexes.

Abstract: Harmonic complexes with identical component frequencies and amplitudes but different phase spectra may be differentially effective as maskers. Such harmonic waveforms, constructed with positive or negative Schroeder phases, have similar envelopes and identical long-term power spectra, but the positive Schroeder-phase waveform is typically a less effective masker than the negative Schroeder-phase waveform. These masking differences have been attributed to an interaction between the masker phase spectrum and the phase characteristic of the basilar membrane. To explore this relationship, the gradient of stimulus phase change across masker bandwidth was varied by systematically altering the Schroeder-phase algorithm. Observers detected a signal tone added in-phase to a single component of a masker whose frequencies ranged from 200 to 5000 Hz, with a fundamental frequency of 100 Hz. For signal frequencies of 1000-4000 Hz, differences in masking across the harmonic complexes could be as large as 5-10 dB for phase gradients changing by only 10%. The phase gradient that resulted in a minimum amount of masking varied with signal frequency, with low frequencies masked least effectively by stimuli with rapidly changing component phases and high frequencies masked by stimuli with more shallow phase gradients. A gammachirp filter was implemented to model these results, predicting the qualitative changes in curvature of the phase-by-frequency function estimated from the empirical data. In some cases, small modifications to the gammachirp filter produced better quantitative predictions of curvature changes across frequency, but this filter, as implemented here, was unable to accurately represent all the data.

Two-stage chaotic Colpitts oscillator

Abstract: A novel version of the chaotic Colpitts oscillator is proposed. It contains two bipolar junction transistors coupled in series. The resonance loop consists of an inductor and three capacitors. The two-stage oscillator, compared with the classical circuit, enables the fundamental frequency of chaotic oscillations to be increased by a factor of three. The PSpice simulations performed with 9 GHz threshold frequency transistors demonstrate that the highest fundamental frequencies of chaotic behaviour are 1 and 3 GHz for the classical and the two-stage Colpitts oscillator, respectively.

Frequency response of the thyristor controlled series capacitor

Abstract: This paper introduces the application of a new method based on Fourier series expansion, to derive the frequency response of a thyristor controlled series capacitor (TCSC). The theory and the numerical approach are presented and the results are reported. Although this method is solely applied to the TCSC device in this context, it is completely general and may well be applied to any type of switched power device. The analysis shows the behavior of a TCSC at frequencies other than fundamental frequency. Such information is very important for sub-synchronous resonance (SSR) as well as other harmonic related studies.

Reconciling frequency selectivity and phase effects in masking.

Abstract: The effects of auditory frequency selectivity and phase response on masking were studied using harmonic tone complex maskers with a 100-Hz fundamental frequency. Positive and negative Schroeder-phase complexes (m+ and m−), were used as maskers and the signal was a long-duration sinusoid. In the first experiment, thresholds for signal frequencies of 1 and 4 kHz were measured as a function of masker bandwidth and number of components. A large difference in thresholds between the m+ and m− complexes was found only when masker components were presented ipsilateral to the signal over a frequency range wider than the traditional critical band, regardless of the absolute number of components. In the second experiment, frequency selectivity was measured in harmonic tone complexes with fixed or random phases as well as in noise, using a variant of the notched-noise method with a fixed masker level. The data showed that frequency selectivity is not affected by masker type, indicating that the wide listening bandwid...

Dual-frequency ultrasonic array transducer and method of harmonic imaging

Abstract: An ultrasonic transducer, method, and system are disclosed for performing ultrasonic harmonic imaging in a medium or a living body. The ultrasonic transducer consists of a linear array of alternating long and short elements. A first set of transducer elements is for transmitting and receiving at a fundamental frequency, and a second set of transducer elements is for receiving second harmonic or subharmonic echoes, each set operating at their respective center frequencies. This dual-frequency ultrasonic transducer is coupled to an ultrasound system wherein transmit beamforming is done at the fundamental frequency, and receive beamforming is done at the second harmonic or subharmonic frequency. When receive beamforming at the fundamental frequency is added, the method enables parallel fundamental, harmonic, compound, and difference imaging. These methods may be utilized to improve ultrasonic harmonic imaging of hard-to-image patients by optimizing the transmission of fundamental-frequency ultrasound beams and the receiving of second harmonic or subharmonic echoes, while minimizing harmonic distortion and signal losses.

Passive external radio frequency filter for Langmuir probes

Abstract: A tunable passive circuit is introduced for radio frequency (rf) filtering of Langmuir probes used to measure plasma properties. The circuit produces a high impedance between the probe tip and ground so that the probe tip follows potential fluctuations in the plasma so that the probe bias voltage with respect to the plasma is constant on the time scale of rf fluctuations. Filtering is implemented at the fundamental frequency (13.56 MHz in this case) and the second and third harmonics. Representative probe traces and electron energy distribution functions from an inductively coupled plasma are presented to demonstrate filter performance.

Cable connector assembly with an equalization circuit board

Abstract: An equalization card is provided for a cable assembly carrying high speed data signals. The cable assembly includes a cable with conductors, a plug mounted on the cable and a socket receiving the plug. An equalization card is removeably received within the plug. The equalization card conveys data signals over data paths between the plug and receptacle. The circuit board attenuates frequency components below at least one half of the fundamental frequency of the data rate, without introducing equalization attenuation into frequency components below a second harmonic of the fundamental frequency. The circuit components maintains a substantially constant attenuation level for frequency components of the data signal below a predefined frequency cutoff that is less than the second harmonic of the fundamental frequency of the data rate.

H/V technique for site response analysis. Synthesis of data from various surveys

Abstract: H/V techniques are very attractive tools for estimating local site effect characteristics. They consist in computing the spectral ratio between the horizontal and the vertical components of a signal. For the receiver function, or RF method, the signal is an earthquake. whereas it is composed of ambient noise for the NN method. The classical transfer function method, called SR here, is based on the spectral ratio of an earthquake recording between one site and a reference. The aim of this paper is to collect experimental results (44 sites) and compare values worthy of note obtained from the H/V and the SR techniques. For several typical sites, we first illustrate that, when a clear peak arises on an SR curve, it also exists, at the same frequency for RF or NN curves. But there is no correlation between the two kinds of curves except for the low frequency part (below the first peak) where a fuzzy relationship seems to exist. Finally,we show that NN and RF techniques determine, very accurately, the fundamental frequency of alluvial sites, below which there is no amplification. In most cases, they also provide a lower bound (in amplitude) and bandwidth (in frequency) estimates for peak amplification.

Light modulation at molecular frequencies

Abstract: It is well known that a carrier and two sidebands, depending on their relative phases, correspond to a frequency ~FM! or amplitude modulated ~AM! signal. Light is most often modulated by driving the dielectric constant of a material so as to produce phased sidebands with a frequency spacing of, at most, 150 GHz. In this Rapid Communication, we describe AM and FM light with a sideband spacing, and therefore modulation frequency, equal to the fundamental vibrational frequency of molecular deuterium (2994 cm '90 THz). We believe that this is a first step toward the synthesis of subfemtosecond pulses with prescribed temporal shape. As a light source for this experiment, we use a recently developed collinear Raman generator @1,2#. This light source produces a comb of ~at present! 17 sidebands spaced by about 2994 cm and extending from 2.94 mm in the infrared to 195 nm in the vacuum ultraviolet. The light source is based on the off-resonance adiabatic excitation of a Raman mode with a coherence that is sufficiently large that the importance of phase matching is negated and generation occurs collinearly. Although it was expected that sidebands obtained from such a source are mutually coherent, until now it was not clear if the relative phase among the sidebands remained the same across their temporal and spatial profiles. It is this uniform mutual coherence among the sidebands that allows the synthesis of AM and FM light, and in the future may lead to the generation of subfemtosecond pulses. In this work we separate out and use only three sidebands ~1.06 mm, 807 nm, and 650 nm! from the Raman comb. Frequencyor amplitude-modulated light is obtained by manually adjusting the relative phases of these sidebands. To detect this modulation, we make use of the fact that a Raman transition is driven by the near resonance component of the temporal envelope of the applied light intensity. These sidebands may be phased so that this component is either zero ~FM!, or maximized ~AM!. We note that it is essential that three sidebands be used in an experiment of this type. If two sidebands are used, as in coherent anti-Stokes Raman spectroscopy @3#, then the magnitude of the envelope is independent of phase. Our experimental setup is shown in Fig. 1. To construct the Raman generator, we use two transform-limited laser pulses at wavelengths of 1.0645 mm and 807.22 nm, such that the ~tunable! laser-frequency difference is approximately equal to the fundamental vibrational frequency in D2. The first laser is a Quanta-Ray GCR-290 Q-switched injectionseeded neodymium-doped yttrium aluminum garnet

Simultaneous fundamental and harmonic ultrasonic imaging

Abstract: An ultrasonic diagnostic imaging system and method are described for performing fundamental frequency and second harmonic frequency imaging simultaneously Transmit bursts are employed which include a first waveform component optimized for fundamental imaging and a second waveform component optimized for harmonic imaging The first waveform component may be centered in the transducer passband, and the second waveform component may be located on the opposite side of the center of the transducer passband from its second harmonic frequency, for instance Echoes received from the bursts are separated into fundamental and harmonic components and used to form separate fundamental and harmonic images or blended fundamental/harmonic images