Showing papers on "Harmonics published in 1979"

Acoustic harmonic generation due to fatigue damage in high‐strength aluminum

Abstract: It is shown that acoustic second harmonic generation is a useful tool for studying surface microcrack development during fatigue of a high‐strength aluminum alloy. A fundamental (5 MHz) surface acoustic wave (SAW) was transmitted across the gauge section of flexural fatigue specimens of Al 7075‐T6. The second harmonic amplitude was determined after several increments of fatigue, as a function of external load and the amplitude of the fundamental. It was found that the second harmonic signal is at a maximum close to zero external load and increases with progressing fatigue. Harmonic generation, attributable to microcracking at the surface, has been observed as early as 10–20% of the expended fatigue life. A simple analysis to obtain a coefficient of harmonic‐generation efficiency versus applied surface stress is described. This analysis considers the effect of changes in attenuation of the fundamental and harmonic waves associated with degree of surface microcrack opening as a function of surface stress. I...

Harmonic Load-Pull

Abstract: A unique operator-interactive load-pull system which allows independent tuning of a signal and its harmonics is presented. Various tuning techniques are described and data on MESFET's in amplifier and oscillator configurations is presented.

Second‐harmonic generation with Ga1−xAlxAs lasers and KNbO3 crystals

Abstract: Efficient second‐harmonic generation from pulsed Ga1−xAlxAs injection lasers operating at room temperature has been observed in KNbO3 crystals. The Al concentration x of the laser was chosen such that the output corresponds to the room‐temperature noncritical 90° phase‐matching wavelength λpm=860 nm for the nonlinear optical coefficient d32 of KNbO3. Up to 0.35‐mW peak harmonic power was obtained with a pulsed fundamental peak power of 785 mW incident on a 5.74‐mm‐long crystal.

The control of the magnetosphere by power line radiation

Abstract: Evidence is presented that radiated power line harmonics leak into high-altitude regions of the magnetosphere with sufficient intensity to control the starting frequencies of chorus emissions. OGO-3 data from three passes show that the starting frequencies of all measurable chorus emissions were within a few hertz of power line harmonics. It is also found that emissions detected over Western Europe were controlled by harmonics of 50 Hz; over the eastern United States and Canada by 60 Hz; and along the Alaska-New Zealand meridian by harmonics of both 50 and 60 Hz. These results indicate that man-made VLF noise plays an important role in the generation of chorus, one of the commonly observed forms of wave activity in the outer magnetosphere.

Field effect transconductance amplifiers

Abstract: The present invention relates to the field of amplifiers comprising one or more field effect devices as the active amplifying element and/or as load devices in amplifier circuits The drawbacks to using prior art techniques are many Very high voltage gains are not possible without power supply voltages which greatly exceed the drain-source voltage Further, prior amplifiers are relatively non-linear, and because the amplifier is unsymmetrical, the distortion of an AC input is also unsymmetrical, giving rise not only to high-third and other odd harmonics, but also high-second and other even harmonics Also, obviously, the output is highly sensitive to power supply fluctuations The present invention overcomes these deficiencies by providing a field effect transconductance amplifier having improved linearity and noise rejection characteristics to provide an amplifier output having excellent temporal coherence with the input signal The amplifiers utilize a series connection of two field effect devices, actual or emulated, preferably appropriately biased in a carrier velocity limited region to maximize linearity of the output A high level of rejection of power supply noise may be achieved by a third series field effect device Various embodiments including high gain and power amplifier embodiments are disclosed

Second harmonic generation in a laser plasma (review)

Abstract: A review is given of experiments carried out to date on the generation of laser radiation frequency harmonics in a plasma on exposure to neodymium, ruby, and CO2 lasers. A physical picture of second harmonic generation in a laser plasma is developed on the basis of an analysis of theoretical and experimental investigations. Experiments involving the spherical irradiation of solid targets carried out in the Kal'mar laser system made it possible to identify for the first time the processes taking place in the critical-density plasma region under conditions as close as possible to "thermonuclear". New methods are proposed for ultrafast diagnostics of a transient superdense plasma using the second harmonic radiation spectrum.

Double-Drift Beam Bunching Systems

Abstract: The double-drift beam bunching system consists of two bunchers that are separated in space, independently driven but phase-locked together. The second buncher to be encountered by the beam is driven at twice the frequency of the first. This system offers an attractive alternative to conventional one- and two-frequency systems since it's bunching efficiency is about twice that for a single frequency system and about 25% larger than that for a two-frequency system in which both harmonics are imposed on the same electrode. The independence of the two bunchers provides for greater ease in the adjustment and stabilization of the rf amplitudes and phase to the accuracy of ±1% and ±0.5° that is required. A double-drift system, designed to operate at 4.5 to 14 MHz, has been installed on the ORNL EN-tandem and evaluated using 16O, 32S, 58Ni, and 63Cu ion beams. Performance was in close agreement with predictions; about 60% of the dc beam was bunched into a phase angle of 6° of the fundamental frequency. A brief discussion of the principles of operation, predicted performance and practical design considerations are given. Results of a theoretical study of the dynamic focussing effects and energy-modulation imperfections of ungridded klystron bunchers are presented as approximate formulas.

Pitch extraction from corrupted harmonics of the power spectrum

Abstract: Unlike most frequency domain methods for pitch extraction, here the pitch is computed from a few selected high quality peaks in the spectrum, achieving greater reliability. A new approximate greatest common devisor (AGCD) algorithm is proposed to compute the fundamental frequency of a given set of corrupted harmonics. Authentic harmonic peaks ar4e obtained by logical filtering of the spectrum and the computed fundamental frequency is subjected to an error test using the best of the harmonic peaks. Thus the algorithm provides a voiced–unvoiced decision, as well as the pitch for voiced regions. The results are uniformly good for male and female voices, and error rates are comparable to those for the best algorithms reported in the literature.

Surface acoustic wave resonators utilizing harmonic frequencies

Abstract: A surface acoustic resonator including an interdigital transducer configured to generate acoustic waves at at least one harmonic frequency, and a pair of reflection gratings capable of essentially total reflection of the acoustic waves in both fundamental and harmonic modes of operation. One-port and two-port resonators are disclosed, capable of operation at fundamental and harmonic frequencies, to provide a higher frequency of operation without correspondingly higher resolution requirements for manufacturing processes. For single-mode operation at higher frequencies, the interdigital transducer and reflection gratings have different fundamental frequencies, and utilize harmonics of different order but the same actual frequency, such that the resonator functions at a single frequency, which may be, for example, the third harmonic with respect to the transducer fundamental frequency, and the second harmonic with respect to the reflection grating-fundamental frequency.

Composite filter for suppressing harmonic frequencies on electric power transmission lines

Abstract: AC to DC converters used in high-voltage direct-current power transmission lines produce objectionable harmonics. The composite filter herein described is actively tuned for the eleventh and thirteenth harmonics in addition to providing a low impedance path for the higher order harmonics, thereby eliminating such undesired harmonics so that they will not be transmitted over power lines where they can cause telephone interference, undesired heating of electrical equipment and other difficulties.

Fatigue detection utilizing acoustic harmonics

Abstract: Disclosed is a nondestructive test method for inspecting an object, including the steps of generating a surface acoustic wave at a first location on the object, detecting a harmonic of the generated wave at a second location on the object, and relating the characteristics of the detected wave to the remaining useful life of the object. The amplitude of the detected harmonic may be compared to standard amplitude values to predict the percentage of fatigue life remaining in the object, or the amplitude may be used to estimate the size and density of cracks in the object. Additionally, the harmonic wave may be detected for a range of stress values, the amplitude differential between the maximum harmonic amplitude and the minimum amplitude under compression calculated, and the differential related to the remaining useful life of the object.

Torque oscillations in traction drives with current-fed asynchronous machines

Abstract: An asynchronous machine supplied by an inverter with nonsinusoidal currents generates an internal torque, which is the superimposition of a constant torque with an oscillating torque is discussed. If the torque harmonics coincide with the mechanical resonances of the mechanical power transmission, a pulse-current modulation is needed in order to avoid problems. At a laboratory test set-up measurements have been performed. Some of the results are presented.

Using characteristic loci in the Hopf bifurcation

Abstract: The Hopf bifurcation theorem is used by physicists, biologists and others interested in oscillations in systems described by differential equations. This paper presents a version of the theorem applicable directly to feedback systems, using the method of characteristic loci in an interpretation which looks rather like a multiple-loop version of the graphical describing function method. Frequency, amplitude and stability of oscillations about an equilibrium state are predicted by an iterative process which starts with a 2nd-order harmonic balance and successively increases the number of harmonics taken into account. The results from each stage of the process are used to define a curve in the complex plane from which the results of the next stage can be read off; consequently, the user has a visual indication of the accuracy and rate of convergence. The main theoretical limitation is that the nonlinear elements in the system must be continuously differentiable at least once more than the order of the highest harmonic used, whereas the main practical limitation is that the formula for the curve becomes extremely complicated if more than about six harmonics are considered.

Harmonic levels and vowel roughness.

Abstract: In this study the effects of vowel roughness on the level of harmonics in test vowel spectra were investigated. Twenty normal-speaking adult males sustained productions of each of the vowels /u/, /...

Simulation of lower-hybrid heating in a nonuniform plasma slab

Abstract: A computer simulation study of the excitation of lower hybrid waves by external sources and the associated plasma heating is presented. A plasma slab with a nonuniform density profile is modeled with a two and one‐half dimensional electrostatic particle code. Both a finite‐length electrostatic antenna and a single wave exciter are considered. The frequency is chosen so that a wave conversion layer exists in the plasma. It is found that a narrow sheath is formed at the plasma edge and the dominant effect is surface electron heating within that region. Ponderomotive force effects as well as the nonlinear generation of harmonics and subharmonics also occur. A low amplitude lower hybrid wave is observed to be excited by the sources and propatates to the wave conversion layer where it is absorbed.

Velocity-induced harmonics for the thin-wire resistance thermometer

Abstract: The frequency and amplitude dependence of velocity-induced harmonics in thin-wire resistance thermometers are derived. The influence on the measured mean temperature and on the skewness is discussed.

Large signal analysis of the extended interaction oscillator

Abstract: Taking account of the space charge term and the effect of interaction gap length, we have derived a large signal model for the extended interaction oscillator (EIO) on the assumption that the axial RF electric field distribution is a rectangular Pulse train The conversion efficiency is calculated and analysed and the results are shown in detail for the typical situations Besides, the effect of space charge, the action of the space harmonics and the efficiency limitation are analysed and discussed

Nonlinear distortion in long wavelength AC bias recording

Abstract: Nonlinear distortion due to tape magnetization nonlinearity is analyzed for long wavelength ac bias recording. A normal distribution of particle switching fields is assumed in order to derive a transfer function. Harmonic components are computed by Fourier expansion, not only for idealized uniform magnetization but also for practical nonuniform magnetization throughout tape coating thickness. To calculate harmonics for nonuniform magnetization, the tape coating thickness is divided into thin layers. Even though the vertical magnetization component and the demagnetizing field effect are neglected, the computed results for nonuniform magnetization exhibit excellent quantitative agreement with experimental data.

On the cylindrical and spherical wave spectral content of radiated electromagnetic fields

Abstract: Simple expressions are derived for determining the number of significant cylindrical and spherical wave harmonics in the field of any antenna. They depend on the maximum radial extent a of the source and the distance r to the field point. The expressions show that very close to the source the number of significant harmonics in the field is potentially large, but it decreases with distance from the source. The number of significant harmonics, in general, approaches existing guidelines only for electrically large antennas and in the far field. The evaluated amplitudes of the harmonics in the fields of practical antenna models show that the expressions derived here give reasonably close bounds while the currently used guideline is not generally correct.

Extraction unit for fundamental wave signal

Abstract: PURPOSE:To extract effectively and definitely only fundamental components from an input signal by proviing a variable characteristic filter which allows fundamental frequency components of the input signal including higher harmonics to pass through and by controlling this filter with the output of a fundamental wave detection circuit CONSTITUTION:An input signal including a higher harmonic of a sound of a musical instrument performance is supplied to voltage control type variable characteristic filter 20 and fundamental wave detection circuit 22 via buffer 12 Circuit 22 is equipped with LPFs 23a, 23b with their frequencies set higher in sequence, whose output signals are detected by signal detection circuits 24a, 24b The sequence of the lowest-pass LPF 23a is supplied from circuit 24a to gate element 26a directly, but sequences of other LPFs 23b, 23c are inputted to gates 26b, 26c through AND circuits 25b, 25c , and 27, and inverters 28b, 28c and filter 20 is controlled by gate outputs Consequently, the output signal of the lowest-pass filter LPF allowing the input signal to pass through is generated and signals of other filter sequences are inhibited, so that only fundamental wave components will be extracted

A dynamic induction motor model including space harmonics

Abstract: An induction motor model is presented which can be used to compute dynamic characteristics and which includes both asynchronous and synchronous parasitic torque effects owing to space harmonics. A new transformation is given which eases computation and enables the stability of the synchronous parasitic torque to be determined. The model is applied to the computation of the direct on line starting characteristic for a four pole, three phase cage machine with 36 stator slots and 28 rotor slots.

Generation of high-power picosecond pulses of 218–316 nm wavelengths

Abstract: Generation, in a KDP crystal, of the sum frequencies of YAG:Nd3+ laser harmonics and the Stokes components of stimulated Raman scattering produced picosecond pulses of 218–316 nm wavelengths and 01–3 mJ energy

Simultaneous Dynamic Compensation of Stopbands and Multipurpose Location of Correction Lenses in the CERN PS Booster

Abstract: Three 3rd order stopbands, amongst them the structural 3Qv = 16 (= number of lattice periods), are compensated simultaneously for the first 100 msec of the acceleration cycle. The location of the correction multipoles was optimized for all relevant resonance harmonics. The ultimate QH-QV working area still being uncertain, all stopbands up to order four as well as 3rd order crossing point were considered when choosing the locations of the new sextupoles and octupoles, eight per type and ring. A solution providing ideal locations for pairs of lenses applying to almost all harmonics was found. Experiments dealing with compensation of 3QV = 16 are described. With simultaneous dynamic correction of 2QH + QV = 14, QH + 2QV 15 and 3QV = 16, high intensity beams of a transverse density hitherto unknown in the PS Booster were obtained.

Numerical simulation of type III solar radio bursts caused by high-density electron beam

Abstract: Numerical simulation for the type III solar radio bursts in meter wavelengths was made with the electron beam of a high number density enough to emit fundamental radio waves comparable in intensity with the second harmonic. This requirement is fulfilled if the optical thickness τ 1 for the negative absorption (amplification) becomes -23 to -25. Since τ 1 is roughly proportional to the time-integral of the electron flux of the beam, the intensity of the fundamental waves depends strongly on the parameters which determine the electron flux. Therefore, it is most unlikely that the harmonic pairs of type III bursts of the first and the second harmonics occur frequently with comparable intensities in a wide frequency range, say 200 MHz to 20 MHz, if we take the working hypothesis that the fundamental waves are caused by the scattering of electron plasma waves by thermal ions and amplified during the propagation along the beam. However, we cannot rule out the possibility that single type III bursts with short durations or group of such bursts are the fundamental waves emitted by the above mechanism, but only if the observed large size of the radio source can be attributed to the radio scattering alone.

Data processor with interference suppression system - has clock pulses generated in random or pseudo-random fashion to reduce harmonics

Abstract: The data processor is designed to reduce the risk of interference to frequency-selective circuits and devices, such as radio receivers, caused by harmonics of the synchronising clock-pulse frequency, without the use of expensive filters. It has applications in computers used in aircraft. The clock-pulse generator built into or separate from the data processor is frequency or phase modulated by means of a noise generator to provide random or stochastic timing of the pulses. This can be achieved by using the output of a shift-register which has feedback. Random variation of the pulse-width of successive pulses may be employed as an alternative.

Metal contacts and barrier layers sensing device - has light-weight operating sensor units connected by screened cables and uses sinusoidal oscillator

Abstract: The sensor has a sinusoidal oscillator. There is a harmonic suppressing filter and a transmitter aerial, a receiver with an aerial, a band-pass filter and a harmonic receiver, with display and supply units and amplifier. The receiver aerial is rotated by 90 deg. with respect to the transmitter aerial and a diplexer is used as a bandpass filter passing only the first and second harmonics; a two-channel mixer or two separate mixers are used for the first and second harmonics. There are two separate amplifiers, a digital signal processing unit and a display unit. The sensor is divided into a lighter sensor unit and operating unit connected by screened cables.