Showing papers on "Fundamental frequency published in 1991"

Some Observations of Chaotic Vibration Phenomena in High-Speed Rotordynamics

Abstract: Subharmonic response in rotordynamics may be encountered when a rotor is operated with its rotational centerline eccentric to that of a close clearance static part, so that local contact can take place during each orbit when the rotor is excited by residual unbalance. The rotor will tend to bounce at or near its fundamental frequency when the rotor is operated at or near a speed which is a whole number [n] times that frequency. Using a simple numerical model of a Jeffcott rotor mounted on a nonlinear spring, it is found that the vibratory response in the transition zone midway between adjacent zones of subharmonic response has all the characteristics of chaotic behavior. The transition from subharmonic to chaotic response has a complex substructure which involves a sequence of bifurcations of the orbit with variations in speed. This class of rotordynamic behavior was confirmed and illustrated by experimental observations of the vibratory response of a high-speed turbomachine, operating at a speed between 8 and 9 times its fundamental rotor frequency when in local contact across a clearance in the support system. A narrow region between zones of 8th order and 9th order subharmonic response was identified where the response had all the characteristics of the chaotic motion identified in the numerical model.

Effects of nonlinear loads on optimal capacitor placement in radial feeders

Abstract: The nonlinear portion of electrical loads has increased significantly in recent years. Harmonic currents injected by these loads into the distribution system should be considered when solving the capacitor placement problem in order to assure that the optimal solution does not result in excessive harmonic distortion. A voltage-dependent current injection load model is presented to determine voltage waveform characteristics and additional losses at harmonic frequencies. Computer simulations show that the optimal capacitor sizes and locations depend heavily on the load model used at fundamental frequency and on harmonic signals, especially when limits are imposed on voltage waveforms. >

Musical frequency tracking using the methods of conventional and “narrowed” autocorrelation

Abstract: In two recent papers, a description is given of a means of obtaining an arbitrarily narrow peak in the calculation of the autocorrelation function [J. C. Brown and M. S. Puckette, “Calculation of a narrowed autocorrelation function,” J. Acoust. Soc. Am. 85, 1595–1601 (1989)] or of a narrow valley in the calculation of an inverse autocorrelation [J. C. Brown and M. S. Puckette, “Musical information from a narrowed autocorrelation function,” Proceedings of the 1987 International Conference on Computer Music, Urbana, Illinois, 84–88 (1987)]. These calculations are applied to the determination of the fundamental frequency of musical signals produced by keyboard, wind, and string instruments. These results are compared to frequency tracking results obtained on these sounds with conventional autocorrelation. In so doing it is determined first whether the method of autocorrelation is well-adapted to the problem of tracking the frequency of musical signals, and, second, under what conditions “narrowed” autocorrelation is advantageous.

Estimating the frequency of a periodic function

Abstract: SUMMARY The problem of estimating the frequency and other parameters of a cyclical oscillation is considered, where the data consists of a periodic function observed subject to stationary additive noise. An estimation procedure is proposed and the asymptotic properties of the estimators established. Tests for unknown frequencies to be harmonics of a fundamental frequency are also developed and their asymptotic properties investigated. The procedures are applied to observations on the variable star S. Carinae.

Perception of concurrent vowels: effects of harmonic misalignment and pitch-period asynchrony.

Abstract: Three experiments examined the ability of listeners to identify steady-state synthetic vowel-like sounds presented concurrently in pairs to the same ear. Experiment 1 confirmed earlier reports that listeners identify the constituents of such pairs more accurately when they differ in fundamental frequency (f0) by about a half semitone or more, compared to the condition where they have the same f0. When the constituents have different f0’s, corresponding harmonics of the two vowels are misaligned in frequency and corresponding pitch periods are asynchronous in time. These differences provide cues that might aid identification. Experiments 2 and 3 determined whether listeners can use these cues, divorced from a difference in f0, to improve their accuracy of identification. Harmonic misalignment was beneficial when the constituents had an f0 of 200 Hx so that the harmonics of each constituent were well separated in frequency. Pitch-period asynchrony was beneficial when the constituents had an f0 of 50 Hz so t...

A new multiharmonic loading method for large-signal microwave and millimeter-wave transistor characterization

Abstract: A multiharmonic loading method for nonlinear microwave and millimeter-wave transistor characterization using six-port techniques is presented. The system allows independent load tuning of an excitation signal and its harmonics. Load-pull measurements on a MESFET which have been performed at the fundamental frequency f/sub 0/ and at the second (2f/sub 0/) and third (3f/sub 0/) harmonics are discussed. The results highlight the importance of such measurement in designing and modeling nonlinear devices and circuits. The experimental results are found to be directly applicable for optimizing efficiency and output power in high-power MESFET amplifiers and MESFET frequency multipliers. >

Simple efficiency maximizer for an adjustable frequency induction motor drive

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). >

Switched mode power supply for single-phase boost commercial AC users in the range of 1 kw to 10 kw

Abstract: A DC to AC power converter is disclosed which is connectable to a DC source, and including a first and second pair of switches which converts the DC source directly to AC by alternately switching between each of the first pair of switches at high frequency modulation, and between second pairs of switches alternately switching at each of the half cycles of the low frequency fundamental output voltage, for producing a positive pulse train and a negative pulse train A transformer boosts the source voltage to the desired high voltage of the output of the converter circuit A filter is connectable to an AC load and having a plurality of damping modes for extracting fundamental frequency from the output of the transformer, and having a control responsive to a signal for switching between damping modes A sine wave oscillator generates a sine wave at the fundamental frequency Feedback circuits maintain the AC output at the fundamental frequency

Low-distorted waveform generating method and waveform generator using the same

Abstract: Waveform data read out of a memory (12) is converted by a D/A converter (13) into an analog waveform, which is amplified by an amplifier (15), from which a waveform signal is generated. To cancel the generation of a distortion in the amplifier, a composite waveform composed of a distortion canceling signal waveform and a fundamental frequency signal waveform to be generated is written into the memory. To determine a distortion canceling signal, the fundamental frequency component in the signal waveform which is output from the amplifier when multi-sine waveform data is read out of the memory, is attenuated by a notch filter (17), and the signal waveform is converted by an A/D converter (18) to a digital multi-sine waveform, which is provided to a computation and control part (10) and subjected to a Fourier transform analysis to compute the amplitude and phase of each harmonic component. Further, the output of the amplifier when fundamental frequency sine waveform data is read out of the memory, is fed via the notch filter and the A/D converter to the computation and control part, wherein it is subjected to a Fourier transform analysis to compute the amplitude and phase of each distortion component. At the same time, the output of the amplifier is converted into digital waveform data without being applied to the notch filter and the data is subjected to a Fourier transform analysis in the computation and control part. By this, the amplitude and phase of the fundamental frequency component are computed. Based on the results of these Fourier transform analyses, the amplitude and phase of each frequency component of the distortion canceling signal are determined, which are used to compute composite waveform data composed of the distortion canceling signal and the fundamental frequency signal.

Estimation of fundamental frequency of musical sound signals

Abstract: In order to estimate the fundamental frequency (fO) of pseudoperiodical sounds with a wide band of possible fO, a theoretical model based on a maximum likelihood for fO is proposed. The model is simplified to make it fast enough for extensive tests. The resulting algorithm is tested on musical speech sounds. As a musical application, an instrument follower based on the algorithm and operating in real time is implemented. >

Motion detector unit

Abstract: A unit for detecting a moving person or object by means of doppler frequency shift. The unit comprises a microwave circuit board (1) accommodating an oscillator and a mixer, and an antenna board (2) carrying transmit (8) and receive (7) patch arrays. In the assembled unit the two boards (1, 2) are intimately secured together. Coupling between the microwave circuit and the antenna arrays is achieved by two slots (5, 6) resonant at the oscillator fundamental frequency, formed in the ground plane (4) of the microwave board (1). Feed striplines (9, 10, 17, 19) on the two boards lie orthogonal to and sandwich the slots (5, 6). The stripline/slot arrangement suppresses emission at the oscillator second harmonic frequency.

Frequency response analysis and modeling of measurement transformers under distorted current and voltage supply

Abstract: The time and frequency response of current and potential transformers (CTs and PTs) operating under fundamental frequency conditions are well known. However, in the presence of harmonic frequencies, these transformers can exhibit significant errors. The authors present CT and PT comprehensive frequency domain equivalent circuits which, in addition to previous study features, include the hysteresis and eddy current effects. Furthermore, a practical approach which calculates the stray capacitances is proposed. By comparing theoretical and practical results the importance of considering parameters which are usually ignored in such studies is highlighted. >

Intra-cavity high order harmonic laser

Abstract: An intra-cavity high order harmonic laser consists of a output coupler, total reflection mirror, and a laser medium disposed therebetween. The output coupler and the total reflection mirror form a resonator. At least two nonlinear crystals are disposed between the laser medium and the output coupler. One of the crystals acts as a frequency doubler, doubling the fundamental frequency of the laser and the other crystal acts as a frequency mixer or high order harmonic doubler in order to produce higher nth order harmonic (n≧2). The invention overcomes the disadvantages associated with producing a high order harmonic laser beam in low peak power lasers such as CW lasers.

Three phase AC-DC load and harmonic flows

Abstract: The validity of assuming that the fundamental frequency load flow conditions of an AC-DC conversion plant are unaffected by the presence of harmonics is questioned, and an algorithm is derived which is capable of determining the true load flow conditions in the presence of harmonics. The algorithm is unique in its three phase approach to the problem, which is essential if normally unfiltered uncharacteristic harmonics are to be represented. Results of a realistic and relevant test system are used to demonstrate the interaction which exists between the fundamental and harmonic frequencies in the power converter. >

System for cancelling phase noise in an interferometric fiber optic sensor arrangement

Abstract: A fiber optic sensor system for cancelling phase noise while it senses a measurand field is disclosed The system includes circuitry for developing a light beam that is frequency modulated at a fundamental frequency First and second unbalanced interferometers, having equal path imbalances, are responsive to the frequency modulated light beam for producing respective first and second optical outputs Detection circuitry is responsive to the fundamental frequency, the second harmonic of the fundamental frequency, and the first and second optical outputs for producing a plurality of sine and cosine signals containing phase difference and phase noise components A signal processor is responsive to the plurality of sine and cosine signals for cancelling the phase noise components and only producing output sine and cosine components of the difference in the phase shift between the first and second unbalanced interferometers The system can further include a demodulator for demodulating the sine and cosine components to produce an output signal proportional to the phase shift difference between the first and second unbalanced interferometers

Sine-Wave Amplitude Coding at Low Data Rates

Abstract: An analysis/synthesis system based on the sinusoidal speech model has been developed [1] In that system, the sine-wave amplitudes and frequencies are located by searching for the peaks of the magnitude of the short-time Fourier transform (STFT) of the input speech The phases are computed from the real and imaginary parts of the STFT at the measured frequencies The frequencies on successive frames are matched, used in a cubic phase interpolator and applied to a sine-wave generator Each sine wave is amplitude-modulated by the linear interpolation of the matched sine-wave amplitudes At a 10 ms frame rate, this system produces speech that is perceptually indistinguishable from the original [1] Since it is not possible to code all of the sine-wave parameters at low data rates, a system has been developed that codes the sine-wave frequencies by fitting a harmonic set of sine waves to the input waveform using a modified mean-squared error criterion [2], and codes the phase information implicitly using a voicing adaptive transition frequency to provide for a mixed voiced/unvoiced phase excitation model [3] Provided a postfilter is used at the synthesizer to attenuate the noise in the formant nulls, the speech synthesized by this system is of quite high quality having achieved a DAM score of 630 in the uncoded mode Since the fundamental frequency can be coded using ≈ 7 bits and the voicing measure can be coded using ≈ 3 bits, then the possibility exists for good speech quality at low data rates provided the sine-wave amplitudes can be coded efficiently In this paper the zero-phase, harmonic analysis/synthesis system and the post-filter design methodology will be described and then the various techniques that have been examined for coding the sine-wave amplitudes will be discussed

Frequency domain fluorometry using coherent sampling

Abstract: Apparatus and methods for measuring response of a chemical composition to light, as by frequency domain, phase angle, or modulation fluorometry and/or phosphorimetry. Pulsed light having a known fundamental frequency is applied to the composition thereby eliciting response light varying at the fundamental frequency and at harmonics thereof. The response light signal may be sampled according to a wave-skipping sampling scheme, and the sampled response signal may be transformed into a frequency domain representation, as by a digital fast Fourier transform technique. A reference signal derived from the excitation light may be similarly processed and the results used as a basis for comparison to derive properties of the chemical composition such as phase and modulation response of the composition to the fundamental and harmonic frequencies. The invention provides rapid monitoring and determination of luminescence characteristics. Multiple excitation frequencies may be applied simultaneously and the resulting response signals may be separated and separately sampled.

Antibody coated crystal chemical sensor

Abstract: A sensor for detecting the presence of a particular chemical by determining the absolute frequency shift in the oscillating frequency of an antibody-coated oscillator. Specific antibodies deposited on a high Q crystal oscillator detect the change in frequency as chemical particulates become trapped by the antibodies and change the effective mass of the crystal. In one embodiment, two oscillating crystals are used, one that has been coated with the antibodies, and one that is uncoated. This permits detection of frequency differences between the oscillating frequencies of the two crystals, thus eliminating pressure, temperature, and humidity corrections that conventionally must be made. The sensor maintains a high specificity by using antibodies that are specifically related to the chemical to be detected, while achieving relatively good sensitivity by using high Q oscillators, such as quart or sapphire, and eliminating drift problems due to temperature, pressure, and humidity. In a second embodiment, a single crystal is used having antibodies coated at specific nodal locations associated with harmonics of the fundamental frequency of oscillation of the crystal. Harmonic amplitudes are measured to determine the presence of the chemical of interest.

Method and apparatus for producing an electronic representation of a musical sound using coerced harmonics

Abstract: A technique for digitally processing a counterpart of a musical sound first transforms a set of time-domain samples of the sound into frequency-domain counterparts and then gradually coerces the frequency-domain counterparts into integer multiples of a fundamental frequency of the sound.

Nonuniform beams with harmonically related overtones for use in percussion instruments

Abstract: Beams used in certain percussion instruments with definite pitch such as marimba, xylophone, and vibraphone are undercut in order to bring the frequencies of the first few overtones into a harmonic relationship with the fundamental frequency. This paper addresses the problem of determining the optimal dimensions of the undercut so that the frequencies of modes 2 and 3 of transverse motion are harmonically related with that of the fundamental (mode 1). The undercut is assumed to have a parabolic shape described by two variable parameters related to its depth and width. The rest of the beam on each side of the undercut is assumed to be uniform. Seven pairs of optimal undercut parameters are found that bring the frequencies of the first three transverse modes into the harmonic (integer) ratios 1:3:6, 1:4:8–9, and 1:5:10–13. Calculations performed with and without taking into account the effects of rotary inertia and shear stress are compared against measurements taken from a set of experimental beams. The comparison shows that including the effects of rotary inertia and shear stress results in a better prediction of the optimal parameters of the undercut.

Analytic and synthetic pitch of two-tone complexes

Abstract: An experiment was performed in which subjects had to judge whether the pitch of two sequential sounds went up or down. The sounds were harmonic two‐tone complexes. They were constructed in such a way that the frequency of one harmonic remained fixed, the frequency of the other went up or down, and the missing fundamental moved in the opposite direction. Results show that, for partials of low harmonic order, most subjects tend to follow the frequency of the moving partial, whereas for partials of order 6 or higher, responses are divided more or less equally between tracking of the moving partial and tracking of the missing fundamental.

Method and apparatus for measuring and compensating nonlinear bitshift

Abstract: A method and device for use in measurement and compensation of nonlinear bitshift in nonlinear communication media such as magnetic and optical recording devices. The method and device are based on special bit patterns constructed to eliminate at least one harmonic of the fundamental frequency of the data pattern if all bits are communicated without any nonlinear bitshift. The presence of nonlinear bitshift is manifested by the appearance of the harmonic. By measuring the magnitude of the harmonic, the amount of nonlinear bitshift is determined, and compensation adjustment is then used to offset its effect on the data detection scheme.

Harmonically modified twelve-pole inverter

Abstract: Apparatus and method for a twelve-pole inverter for eliminating all of the relevant low-order harmonic component frequencies, except the fundamental for an AC output from a source of DC input voltage. The inverter circuit provides four separate three-phase sets of constantly phase displaced pole voltages from controlled six-pulse bridge inverter circuits. Additional phase displacements for straddled paired-sets of the pole voltages are introduced with a first and second predetermined phase displacement proportion of 2:1 or 15 degrees. One paired-set of pole voltages is input to a transformer configuration of a wye with a delta, and the other paired-set of pole voltages is input to a neutralizing transformer with a truncated delta paired configuration for low-order cancellation of harmonics. A phase separated composite output circuit connects series aiding and series opposing secondary winding components coupled from the two sets of paired transformer windings to provide coupled fundametal voltages with low-order odd harmonic components eliminated below twenty-three times the fundamental frequency.

Crystal oscillator with quartz vibrator having temperature detecting faculty, quartz vibrator for use therein, and method of measuring temperature using quartz vibrator

Abstract: A crystal oscillator for generating an output oscillation whose frequency is maintained constant independently of the variation of temperature including a first quartz vibrator arranged in a heating unit which includes a thermostat and vibrating at a fundamental frequency, a second quartz vibrator arranged also in the same heating unit and vibrating at a third overtone frequency, a frequency multiplying circuit for multiplying the fundamental frequency by three, a frequency comparator for comparing the fundamental frequency multiplied by three with the third overtone frequency to derive a frequency difference which represents a temperature of the thermostat, and a temperature controlling circuit for controlling the temperature setting of the thermostat in accordance with the detected frequency difference. Any one or both of the fundamental and third overtone oscillations may be derived as an output oscillation. The first and second quartz vibrators are constructed by a single common quartz substrate, a first pair of electrodes each applied on respective main surfaces of the quartz substrate, and a second pair of electrodes each applied on respective main surfaces of the quartz substrate.

Voltage and harmonic control of a multi-pole inverter

Abstract: Apparatus and method for eliminating or reducing to a filterable minimum the relevant harmonic frequencies which otherwise occur in an AC output voltage from a multi-phase static inverter circuit operating from a symmetrically notched source of DC input voltage. The inverter circuit is electronically switched and controlled to provide notched phase voltages with the notch positioning being optimally variably placed in the periodically occurring waveform and with a controlled interval of the notch for controlling the fundamental component independently of the source voltage, while substantially eliminating the 11th and 13th harmonic components of the fundamental output voltage. A harmonic neutralizing transformer circuit includes paired wye, delta, or wye-delta configurations is connected between the inverter circuit and a composite output transformer circuit which couples or connects paired windings of the harmonic neutralizing circuit. This provides an output voltage with cancelled remaining harmonics immediately adjacent to odd number multiples of six times the fundamental frequency.

Phase-locked millimeter-wave two-port second-harmonic Gunn oscillators

Abstract: Two-port harmonic oscillators have been developed which are suitable for voltage-controlled-oscillator (VCO) operation in frequency stabilized systems. Two oscillator designs are presented. The first has a fundamental frequency cavity located above the harmonic output cavity and the fundamental is coupled by means of the Gunn device bias-line filter. The second design is an in-line structure which uses a waveguide taper as the filter element separating the fundamental and harmonic frequency components. The latter design is a translation of the first oscillator concept onto a single plane, so that the prospect of an integrated monolithic version is conceivable. The performance of the oscillators is discussed, and a demonstration of their use in a heterodyne phase-locked loop control system is presented. >