Showing papers on "Harmonics published in 1973"

Generalized Techniques of Harmonic Elimination and Voltage Control in Thyristor Inverters: Part I--Harmonic Elimination

Abstract: This paper considers the theoretical problem of eliminating harmonics in inverter-output waveforms. Generalized methods are developed for eliminating a fixed number of harmonics in the half-bridge and full-bridge inverter-output waveforms, and solutions are presented for eliminating up to five harmonics. Numerical techniques are applied to solve the nonlinear equations of the problem on the computer. The uneliminated higher order harmonics can be easily attenuated by using filter circuits in the output stage of the inverter. The results show the feasibility of obtaining practically sinusoidal output waveforms, which are highly desirable in most inverter applications.

Spatial correlation in arbitrary noise fields with application to ambient sea noise

Abstract: Explicit expressions are developed for the cross‐spectral density between pairs of sensors and the wavenumber‐frequency spectrum projected onto the line joining these sensors, when they are placed in arbitrary positions in noise fields which are described by an arbitrary directional distribution of uncorrelated plane waves. The approach is to expand the directional distribution in spatial harmonics. Each harmonic leads to a corresponding term, with the same coefficient, in series representations for the cross‐spectral density function and the wave‐number‐frequency spectrum. The approach particularly attractive when the field can be adquately represented by a relatively small number of harmonics. Both two‐ and three‐dimensional fields are considered. The approach is applied to the vertical directionality of ambient sea noise and is related to some existing models of ambient sea noise. Some new models are presented. Results are compared with reported experimental data and found to be in good agreement over a wide frequency range.

A method for analyzing waves in structures consisting of metal strips on dispersive media

Abstract: A method for analysis of wave propagation on structures consisting of periodic metal strips is presented. The method is an extension of earlier theories based on Legendre polynomial expansions of the electric field. The extension allows analysis of strips on any material or layers of materials, provided the electromagnetic properties can be expressed in terms of a wavenumber-dependent permittivity. Layers of dielectrics, piezoelectrics, semiconductors, and metals are typical of the materials of practical interest in connection with surface wave acoustics. Strip configurations such as interdigital transducers, multistrip directional couplers and reflectors, and strip coupled amplifiers can be analyzed by the present approach. Prescriptions for calculating the amplitudes of the space harmonics of the electric field strength are given. Closed-form expressions for strip current and voltage are developed.

Monolithic solid state travelling wave tunable amplifier and oscillator

Abstract: A travelling wave amplifier of signals in the millimeter wavelength range consists of a monolithic solid state waveguide structure wherein space harmonics of the input electromagnetic energy wave (signals) are generated due to periodic corrugations of the guide's top surface. The waveguide structure includes a current conductive layer supportive of a stream of electrons with an electron velocity ve, the stream of electrons being located where the amplitude of the spatial first harmonic is a maximum. The corrugation periodicity L is selected so that the equality ve = K ( omega /2 pi ) L is satisified. In the equality, omega is the angular frequency of the input wave and K is a factor which is not less than and on the order of one.

Cyclotron Internal Ion Source with DC Extraction

Abstract: This paper describes a method for increasing the intensities for heavy ion beams accelerated in isochronous cyclotrons at high harmonics (h?5) of the orbit frequency. Normally, only small intensities are obtained at high harmonics because of the low effective accelerating voltage between the ion source and the puller electrode. We have developed and tested a dc ion extraction system for the Oak Ridge Isochronous Cyclotron (ORIC). Use of the dc extraction system has increased beams of 4OAr3+ on the 5th harmonic and 2ONel+ on the 7th harmonic from nanoamperes to microamperes.

Fourier Analysis of Zooecial Shapes in Fossil Tubular Bryozoans

Abstract: Fourier harmonic amplitudes provide exact characterization of the cross-sectional morphology of fossil tubular bryozoans. The Fourier method resolves a complex zooecial shape into multiple shape components (harmonics), which can be treated as individual morphologic variables. Shape elongation caused by varying zooecial orientation affects only the value of the second harmonic. Fourier harmonic coefficients reveal small changes in model shapes involving different numbers of neighboring zooecia, thickening of zooecial walls, and acanthopore variation. The number (between three and six) of neighboring zooecia controls the gross zooecial shape, as reflected in the third to the sixth harmonic. The sixth harmonic reflects the closest packing of zooecia within a colony, and its mean correlates with the colonial growth form and number of mesopores. Monticules represent the budding centers of a colony: zooecial chambers decrease in maximum diameter and become more densely packed away from the monticules. Ontogenetic changes, from the budding of new zooids to the closest packing of mature individuals, involve variation in gross zooecial form, revealed in the amplitudes of the second to the sixth harmonic. Harmonics above the sixth reflect small-scale sculpturing of the zooecial margin. The mean harmonics of different taxa suggest that Fourier values can be used for multivariate phenetic differentiation. The mean spectra of different growth forms indicate that variation in the second and sixth harmonics results from ontogenetic differences and nonmutational response to external stresses. Comparison of intrageneric variability and intracolonial variability shows that the second and sixth harmonics vary more widely among genetically identical individuals than among evolving taxa, even though the morphologies they reflect have been used as major bio-characters in bryozoan systematics. The higher numbered harmonics, especially the seventh, carry evolutionary information.

Observation of plasma heating due to parametric instabilities at the upper hybrid and at the cyclotron harmonic frequencies

Abstract: Strong plasma heating is observed in external electric fields near the upper hybrid frequency or near the electron cyclotron harmonics. It is shown that the fast plasma heating is associated with the presence of the parametric instability of Bernstein waves, ionacoustic waves, and lower hybrid waves.

Lunar physical librations and laser ranging

Abstract: The analysis of lunar laser ranging data requires very accurate calculations of the lunar physical librations Libration terms are given which arise from the additive and planetary terms in the lunar theory The large size of the recently discovered terms due to third degree gravitational harmonics will allow some of these harmonics to be measured by laser ranging to the moon Numerical integration promises to be an effective method of calculating librations Comparison of numerical integrations with analytic series indicates that the calculation of the series due to third and fourth degree harmonics is not yet as accurate as the more extensively developed second degree terms-

Emission of coherent microwave radiation from a relativistic electron beam propagating in a spatially modulated field

Abstract: Intense electromagnetic radiation has been observed from the interaction of an intense relativistic electron beam and a spatially modulated magnetic field. An efficiency of conversion of electron kinetic energy into microwave radiation of the order of 1% has been achieved, with total rf power radiated greater than 30 MW. A parametric study has shown that the device has not reached saturation over the range of parameters tested. The experimental results show that the new device differs from conventional generators in several respects. For example, the frequency and the bandwidth of the rf radiation can be tuned over a wide range and the power at the harmonics of the fundamental frequency (∼ 1010 Hz) is the same order of magnitude as the power in the fundamental. Infrared radiation has also been observed; more than 1 MW has been found even for wavelengths under 10 μm.

Influence of Third Harmonic Circulating Currents in Selecting Neutral Grounding Devices

Abstract: It has long been recognized that third harmonic currents can and often do appear in the neutral of industrial generators. This paper will review the causes of such currents and the effects these currents have in the power system. The common methods of neutral grounding will be discussed with regard to circulating harmonic currents.

Harmonic Generation of Acoustic Surface Waves in Bi 12 GeO 20 and LiNbO 3

Abstract: Harmonic generation of acoustic surface waves has been observed experimentally in different laboratories on quartz, lithium niobate, and bismuth germanium oxide sub- strates and a phenomenological model containing one non- linear elastic constant has been proposed to explain the spatial variation of each observed harmonic on a LiNb03 delay line. In this paper we describe how the surface wave nonlinearities of different materials can be quantitatively compared. Using laser light deflection the growth with distance of the second harmonic was measured in LiNb03 and Bi12GeOzo for fun- damental frequencies of 50 and 100 MHz and of the second, third, and fourth harmonics in LiNb03 for a fundamental of 150 MHz. A one-dimensional, single-parameter model is used from which is obtained a system of coupled differential equa- tions describing the harmonic growth. This system is solved numerically as an initial value problem and a value of the single-parameter found for each material which gave good agreement between the measured data and the model pre- dictions. The parameter values found differ by an order of magnitude in the two materials, LiNb03 being the more strongly nonlinear.

Analysis of Induction Motor Drives with a Nonsinusoidal Supply Voltage Using Fourier Analysis

Abstract: A method of analysis of induction motor performance with nonsinusoidal supply is presented. It is based on the Fourier analysis of the impressed voltage waveform. Equivalent circuits for the various harmonics are derived, and the resultant harmonic currents are calculated. Experimental verification of the method is obtained by calculating the current waveform from the Fourier components and comparing it with oscillograms. Experimental data obtained from a cycloconverter and different types of inverters are used and show good agreement with calculated results. Evaluation of different schemes of power control and effects of a rapid variation of slip frequency are examined.

Method and apparatus for reducing distortion in multicarrier communication systems

Abstract: There is disclosed a method and apparatus for multiplexed transmission of a plurality of signals such as television programs through a communication system such as a coaxial cable containing one or more repeater amplifiers in a manner such as to reduce distortion below levels heretofore attainable. The system utilizes harmonically related coherent carriers ("HRC") all of which are generated from a master oscillator functioning as a system frequency synchronizer (and preferably having a frequency of 6 MHz) in order to make intermodulation frequencies in the system zero beat with the carriers to avoid the visual effects of picture degradation from such intermodulation or beat frequencies. The term "beat frequency" is herein used synonymously with "intermodulation frequency" to mean the frequencies of all intermodulation products including the harmonics. In addition to providing harmonically related coherent carriers, the relative phases of these carriers are adjusted in order to minimize or reduce their combined peak to peak amplitude. Reduction of peak amplitudes reduces excursions along the transfer curve for the amplifiers and permits operation on the linear portion of the amplifier and cable system instead of in the nonlinear range. In addition to avoiding the visual effects of beat frequencies, distortion products are also thereby actually reduced below values heretofore predicted or attained.

Unified analysis of fan stator noise

Abstract: A theory is developed which predicts the acoustic radiation of an axial‐flow fan stator due to interaction with rotor viscous wakes. Calculations are compared in detail with experimental data. Both the harmonic and broadband noise‐spectrum components are calculated from a unified model using methodology from the theories of random pulse amplitude modulation, PAM, and pulse position modulation, PPM. The stator is modeled as a circular array of pulsed dipoles. The amplitude and arrival time of each pulse are random variables whose means correspond to the values calculated from harmonic rotor‐stator interaction theory. The standard deviations of these random variables are measures of the turbulence levels in the blade wakes. For the model proposed the solution is exact: when PAM is imposed on a periodic stator source, new broadband energy is generated whose spectrum shape is similar to the envelope of harmonics at high frequencies and the harmonic radiation is unchanged; however, when PPM occurs, new broadband energy is radiated but at the expense of harmonic energy. At frequencies significantly above duct cutoff it is shown for a fixed stator solidity that the spectrum is essentially independent of the number of stator vanes.

Communicating over power lines

Abstract: An audiofrequency signal is applied to a power amplifier having an output impedance of considerably less than an ohm that is coupled through a network comprising at least a capacitor that presents a low impedance to this audiofrequency signal and much higher impedance to energy at the 60 Hz power frequency to a power line to provide an amplified signal that is transmitted to a receiver separated from the transmitter by at least one distribution transformer and having a high pass filter for rejecting the 60 Hz power frequency and a number of harmonics thereof while transmitting the audiofrequency signal. The system is especially advantageous for using ordinary power lines for transmitting information in connection with automatic meter reading.

Implementation of combined footage stops in a computor organ

Abstract: Combined footage stops are implemented in a computor organ of the type wherein musical notes are produced by computing successive sample point amplitudes of a musical waveshape and converting the amplitudes to sound as the computations are performed in real time. Each waveshape amplitude is obtained by evaluating those Fourier components comprising an incomplete set of harmonics for a first footage voice, and the fundamental and several low order odd harmonics of a voice of lower footage. In a preferred embodiment, an incomplete 8-foot harmonic series is employed, together with the first four odd harmonics of a 16-foot series. The 8-foot harmonics correspond in frequency to even harmonics of the 16-foot series. The missing 8-foot components are "reinstated" by the listener's ear. As a result, the combined voice is perceived just as though separate, complete spectra had been used to generate the waveshape. To implement shorter footage stops, certain of the 8-foot harmonics are excluded from the waveshape computation. For combined voices including shorter footage stops, the sum of the harmonic coefficients associated with the concurrently selected stops are used in the component calculations.

Experiments using a superconducting point-contact harmonic mixer near 1 THz

Abstract: Experiments are described in which simple and relatively reliable point-contact Josephson junctions were used to generate and mix harmonics (up to the 50th) of microwave klystron frequencies with emissions from a hydrogen cyanide laser operating at 891 GHz. Data are presented illustrating the variation of the intermediate frequency signal with DC bias current through the junction and incident radiation power levels, and the results compared, where possible, with a simple qualitative theory of Josephson mixing. Details are also given of experiments in which such a mixer was used to phase-lock a klystron to the laser, enabling the laser frequency to be accurately and continuously monitored.

Harmonic and power factor compensation means and method for power systems controlled by a non-linear device

Abstract: The fundamental frequency power factor is improved and a practical reduction in significant harmonic current is made in electrical power systems where the power to the load is controlled by a non-linear device, such as a saturable reactor, by using series inductive-capacitive filters to filter the significant harmonic current to act as a shunt for harmonic current in conjunction with a supply line inductive reactance. The resonant frequency of each filter is less than the frequency of the harmonic current and the impedance of each said inductivecapacitive filter is a net inductive reactance. The capacitive element of the filter provides a leading power factor component to compensate for the lagging power factor component imposed on the supply system by the non-linear control device.

Optimum control system for minimizing harmonic effects in HVDC power converters

Abstract: A real-time system for reducing the effects of harmonics reflected onto the a. c. supply line of a High Voltage Direct Current power converter by continuous measurement of various current and voltage fundamental, harmonic and d. c. components as reflected onto the supply line, calculation of an overall harmonic performance index based upon the necessary ones of the measured components, and on-line control of the firing angles at which various switching functions occur in the HVDC power converter to optimize the value of the performance index.

Characteristics and Performance of KNbO3-YAlG/Nd Intracavity Second Harmonic Generation

Abstract: The intracavity second harmonic generation of YAlG/Nd laser using KNbO3 single crystal was demonstrated and it was compared with that using Ba2NaNb5O15 crystal KNbO3 was found to be suitable for this application because of (1) its large conversion efficiency, ie (d2/n3)KNbO3 =08±01(d2/n3)Ba2NaNb5O15 , (2) its resistance to damage by intense green light output, and (3) its very low optical loss coefficients at the fundamental and the harmonic wavelengths (about 025%/cm at 106 µm) About 90% conversion of the optical second harmonics was obtained The thermal conductivity of KNbO3 was found to be larger than that of Ba2NaNb5O15 due to the increasing crystal temperature caused by the internal laser power

The physical librations of the moon, including higher harmonic effects

Abstract: The equations of the physical libration of the moon are developed using a representation of the earth-moon orbit as a Kepler ellipse referred to the lunar equator and expanding the lunar potential in terms of these Kepler elements. The Improved Lunar Ephemeris is used to calculate solar perturbations, and a linear integration of all effects arising from lunar gravitational harmonics through the fourth degree is performed. Aside from unobservable constant offsets of the principal axes, the main effects of the higher harmonics on longitude are: 10-sec six-yearly (argument omega), 1.2-sec three-yearly, 0.5-sec annual, and 0.1-sec monthly; on pole direction they are on the order of 0.5-sec six-yearly and 1.0-sec monthly. The higher harmonics must hence be taken into account in analyzing ranging data of 10 cm accuracy.

An Analysis of Helicopter Rotor Modulation Interference

Abstract: In satellite-to-helicopter communications, interference exists on the incoming signal when the receiving antenna is located below the rotor blades. A bound is established for the performance of a coherent fixed-tone ranging system operating at L band in this interference environment. The scalar diffracted field beneath the rotating blades, at L band and above, is found to satisfy the criterion of Fresnel diffraction, and is computed using the techniques of Fourier optics. The diffracted field is expressed in terms of a narrow-band signal. The amplitude and phase components are calculated from a Fourier Series expansion using the FFT algorithm. The significant harmonics of the phase component of the interference combine with the baseband of the narrow-band, phase-modulated ranging signal. This results in CW interference, and in rearrangement of the first-order, sideband, ranging-tone channel powers. The degradation in ranging accuracy is evaluated by computing the signal-to-interference (SIR) ratio for a set of ranging tones. The post-detection (SIR)PD at the output of the correlator is shown to be a function of the amplitude of the phase harmonics of the interference, the relative difference between the ranging tone and interference center frequencies (a function of rotor speed), the rangetone modulation indices, and the post-detection filter noise bandwidth.

Nonlinear Dielectric Constants in Barium Titanate

Abstract: An apparatus for detecting small second and third harmonics due to the dielectric nonlinearity is devised. A reactance filter network is used to obtain pure sine wave voltage and high detection sensitivity. The higher harmonic level applied to the crystal is suppressed to the order of 5×10 -7 times below the fundamental voltage. This apparatus is used for measuring the nonlinear dielectric constants of BaTiO 3 single crystals above and below the Curie point (120°C). The experimental results show that the coefficient of the P 4 term in the Devonshire's equation increases gradually with increasing temperature, which is against the previous result reported by Drougard et al.

Fractional‐harmonic frequency pairs in nonlinear systems

Abstract: Under proper conditions, the response of two coupled nonlinear oscillators, driven by a sinusoidal input, contains a pair of fractional‐harmonic frequency components. The frequencies f1 and f2 of the fractional‐harmonic pair correspond approximately to the resonance frequencies of the system, and the sum f1 + f2 equals the driving frequency. Conditions for the occurrence of fractional harmonics are examined by an analysis that relates them to a pair of coupled Mathieu equations. Fractional‐harmonic components were observed in several nonlinear electrical, mechanical, and acoustical systems. The observations are consistent with qualitative predictions of the analysis.