Showing papers on "Harmonic published in 1969"

A circular-harmonic computer analysis of rectangular dielectric waveguides

Abstract: This paper describes a computer analysis of the propagating modes of a rectangular dielectric waveguide. The analysis is based on an expansion of the electromagnetic field in terms of a series of circular harmonics, that is, Bessel and modified Bessel functions multiplied by trigonometric functions. The electric and magnetic fields inside the waveguide core are matched to those outside the core at appropriate points on the boundary to yield equations which are then solved on a computer for the propagation constants and field configurations of the various modes. The paper presents the results of the computations in the form of curves of the propagation constants and as computer generated mode patterns. The propagation curves are presented in a form which makes them refractive-index independent as long as the difference of the index of the core and the surrounding medium is small, the case which applies to integrated optics. In addition to those for small index difference, it also gives results for larger index differences such as might be encountered for microwave applications.

Stability Analysis of a Rectifier-Inverter Induction Motor Drive

Abstract: A stability study of a rectifier-inverter induction motor drive system is performed by neglecting the harmonic content of the stator voltages and applying Nyquist stability criterion to the small- displacement equations obtained by linearization about an operating point. This investigation reveals that system instability can occur over a wide speed range if the system parameters are improperly selected. It appears that the method of analysis presented in this paper is sufficient to predict stability of practical rectifier-inverter induction motor drive systems. Also, with slight modifications, this method of analysis can be applied to rectifier-inverter systems which supply reluctance-synchronous machines or synchronous machines.

LARGE NONLINEAR OPTICAL COEFFICIENT AND PHASE MATCHED SECOND HARMONIC GENERATION IN LiIO3

Abstract: The second harmonic of a Nd laser has been produced in LiIO3 in a phase matching direction of 30° to the c axis with high conversion efficiency. The nonlinear optical coefficient t31 is among the highest so far reported for phase matchable substances using λ = 1.06 μ. LiIO3 can be grown from water solutions with excellent optical quality.

Physical modeling of the step recovery diode for pulse and harmonic generation circuits

Abstract: A simple charge-controlled switching model describes most fundamental aspects of the step recovery diode. However, it is shown that switching speed and the associated loss are related to the width of the i layer and to the doping level. A switching model appropriate for general computer use is given, and examples of its application are shown in pulse and harmonic generator circuits.

Analysis and Simplified Representations of a Rectifier-Inverter Induction Motor Drive

Abstract: Simplified representations of a rectifier-inverter induction motor drive system are established and verified by comparing the results obtained from a computer study using these representations to those obtained using a detailed simulation of the system. It is shown that when all harmonic components are neglected the static drive system may be conveniently represented in the synchronously rotating reference frame. The computer simulation resulting from this type of representation can be readily implemented, and in many cases it will predict the system performance with sufficient accuracy. Also, in the analysis leading to these simplified representations, the operation of the inverter is analytically expressed in the synchronously rotating reference frame with the harmonic components due to the switching in the inverter included. These equations of transformation may be used to advantage in describing the interaction between the filter and the induction motor.

Data modulator employing sinusoidal synthesis

Abstract: Multitone data-transmitting apparatus employing sinusoidal synthesis with harmonic cancellation. A multitone data transmitter employs relative phase displacements between plural digital waveforms all of which are representative of a tone to be transmitted and a weighted summing network for summing the plural waveforms so as to cancel undesirable harmonics of the frequency tone to be transmitted. In the illustrated FSK modulator, four square waves having relative phase shifts of pi /4 radians are given suitable summing weights so as to cancel the third and fifth harmonic of any selected one of the FSK tones.

Topside ray trajectories near the upper hybrid resonance

Abstract: Ray trajectories near the upper hybrid resonance show both similarities to and important differences with calculations near the resonance at the plasma frequency. As long as the upper hybrid frequency is less than the second harmonic of the electron cyclotron frequency, ray paths almost identical to those calculated near the plasma frequency can return energy to a satellite moving through the topside ionosphere. An additional type of ray path is also found. When the upper hybrid is greater than the second harmonic, the returning ray paths are not found. This is consistent with the observed resonance strength. The possibility of return paths near the frequency where the Bernstein mode disappears is also found.

Effect of Adsorbed Surface Layers on Second-Harmonic Light from Silver

Abstract: It has been found that atomically clean silver surfaces generate approximately four times as much harmonic light as those subjected to adsorption. Existing theories of the nonlinear optics of metals, which are based on bulk properties, must therefore be modified to account for the surface contribution. It is hypothesized that an electric dipole contribution to the nonlinear polarization may account for the present result.

Stabilized mode-locked laser arrangement

Abstract: It has been observed that the pulse-train output of a modelocked Nd:YA1G laser exhibits a 180* phase instability. As a result it is not possible to achieve long term stable operation of such a laser by abstracting from the output pulse train a signal whose frequency corresponds to the axial-mode fundamental beat frequency. However, the phase of the second harmonic of this fundamental beat frequency which may be abstracted from the output pulse train does not exhibit such a 180* phase instability. Accordingly this second harmonic signal can be utilized as a discriminant from which a fundamental signal may be derived. In turn this derived fundamental signal is applied to drive an intracavity phase modulator. In this way the laser is stabilized in its mode-locked state by feedback techniques despite the aforementioned phase-instability characteristic.

Rigorous Bounds for Thermodynamic Properties of Harmonic Solids

Abstract: A procedure for obtaining rigorous bounds to thermal properties of harmonic solids from moments of the frequency distribution is presented, and methods for improving these bounds when low‐frequency expansion coefficients for the frequency distribution function are known are described. The technique is demonstrated by application to a face‐centered‐cubic crystal with nearest‐neighbor interactions, and extremely precise bounds for the thermal properties are obtained.

High efficiency klystron amplifier

Abstract: A klystron amplifier yielding above 65 percent efficiency at the 100 kW power level at a frequency of 800 MHz will be described. The high efficiency is obtained by using a novel combination of second harmonic and fundamental frequency cavities in the buncher system.

High-efficiency operation of a Gunn oscillator in the domain mode

Abstract: An examination of the problem of obtaining high-efficiency operation of a Gunn oscillator is given in this paper. The results are based on an assumed form of I-V characteristic of the Gunn diode, the ideal voltage and current waveforms being found for high-efficiency operation. The theory for a square wave of current through and voltage across the diode is worked out in detail and shown to predict the experimental results well. It is shown that a voltage waveform consisting of only a fundamental and second harmonic component could give efficiencies in the 20-28 percent range, as much as a factor of 3 larger than for a simple sinusoid. This is a reasonable approximation to the ideal voltage waveform, which is a half sinusoid of voltage. In this paper the charge and discharge time of the domain is neglected. An estimate of these times is given in the Appendix, and it is shown that the efficiency theory should be relevant to operation with diodes for which nL \gg 10^{12} cm-2. The theory may also describe certain types of "LSA mode" operation.

Phase locked loop

Abstract: An oscillator in a spacecraft transponder or repeater is frequency stabilized by a phase locked loop with reference signal therefor having a frequency (N/M) F being received in the repeater from a ground station. The reference signal is processed in the repeater and returned to the ground station where it is monitored to detect when the pull-in range of the loop is exceeded. When this condition is detected, the frequency of the reference signal is swept in the ground station until the frequency of the reference signal and frequency of the signal of the oscillator in the repeater is within said pull-in range. The oscillator frequency F is divided by M and the phase comparator includes a first tuned input circuit to respond to a frequency (N/M) F, a second turned input circuit to respond to the nth harmonic of the frequency F/M and a phase error detecting circuit to produce a control signal used to stabilize the frequency of the oscillator.

Nonlinear Effects and Turbulent Behavior in a Beam-Plasma Instability

Abstract: Continuing experimental studies of beam‐plasma interactions in a magnetic field have shown an assortment of nonlinear effects to be present during a well‐developed instability. Observations have been made of: the vanishing of the spatial growth rate; electron cross‐field diffusion in synchronism with the unstable electric field; generation of harmomics of the fundamental interaction frequency up to the seventh; similarities in the spatial behavior of all seven harmonics; and the existence of a wavenumber power spectrum whose average behavior over the domain of the harmonic peaks is proportional to k−5±0.5, in agreement with certain theories of plasma turbulence. The data suggest that the large‐amplitude fundamental electric field is the driving force for the nonlinearity that generates the harmonics, and that the fundamental, and the harmonics as well, represent waves traveling with a phase velocity equal to that of the slow space‐charge wave on the electron beam. An interpretation is offered in terms of ...

A General Approach to Harmonic Current Generation by HVDC Converters

Abstract: A general approach to the computation of current harmonics is presented for the ac side of HVDC transmission installations considering both normal and abnormal harmonics that can arise from harmonic distortion of the supply waveform and perturbations in the control firing pulses. Attention is given to 12- pulse converter operation and to alternative types of automatic control. A comprehensive digital computer program is described and examples of computed harmonics are given.

Analysis and Simplified Representations of Rectifier - Inverter Reluctance-Synchronous Motor Drives

Abstract: Methods of analyzing six-step and pulse-width- modulated (PWM) types of rectifier-inverter reluctance-synchronous motor drive systems are set forth. In this development the harmonic components due to the switching of the rectifier are neglected, and the operation of the inverter is expressed in a reference frame rotating in synchronism with the fundamental frequency of the inverter output voltages. In the case of the PWM inverter, the Fourier series expansion of a pulse train is used to express the operation of this type of inverter in the synchronously rotating reference frame. Simplified representations are obtained by neglecting the harmonics due to the inverter switching. These simplified representations are verified by comparing the results obtained from a computer study using these representations to those obtained using a detailed simulation of the system. The analysis set forth and the simplified representations that are developed can be used to determine small-displacement system stability, as well as provide a simple and direct technique of predicting the dynamic and steadystate performance of these involved systems. Moreover, the equations established for the PWM inverter can also be used in conjunction with an induction motor drive.

Time‐variant spectra of violin tones

Abstract: Harmonic analyses of several violin tones have been performed by computer. Each sound is represented by a finite series of harmonic‐amplitude and phase‐spectrum components varying with time. Graphical representations of spectra being explored are: (1) individual plots of fundamental‐frequency harmonic amplitudes (both linear and dB), and relative phases as functions of time; (2) line‐spectra movies with harmonic amplitude changes slowed 20:1; (3) spectrograms with vertical frequency scale, horizontal time scale, and darkness indicating amplitude. Spectrum analysis can be performed synchronously with the fundamental or asynchronously at a base frequency much lower than the fundamental, with advantages for each method. Completeness of harmonic analysis is demonstrated by examples of tones resynthesized using smoothed versions of harmonic‐amplitude and pitch curves. For storage purposes, synthetic tones typically require 500 to 800 parameter‐time coordinates per 1 sec of sound. Over all, the violin tones ana...

Performance and design of induction motors with square-wave excitation

Abstract: The paper investigates the reasons for loss of efficiency when conventional induction motors are supplied with square-wave voltages. A method of analysis using harmonic travelling current-density waves is developed and methods of design are described to produce induction motors with comparable efficiency and output to those of sinusoidally fed machines. The air-gap flux densities in these motors are discussed, and experimental values of iron losses are given to compare with conventional machines.

Distribution pattern of cochlear harmonics.

Abstract: This study is designed to determine whether or not traveling waves accompany harmonic distortion products generated in the cochlea, and also to describe the amplitude distribution of these nonlinear components. Cochlear microphonics were monitored with the differential electrode technique from the first and third turns of guinea pig cochleas. Cancellation of the distortion components was attempted by introducing bone‐conducted pure tones of the frequency of the harmonic and of controllable magnitude and phase. It was demonstrated that harmonic components can never be canceled simultaneously throughout the cochlea. It was shown that the reason for this inability to cancel is that harmonics are not distributed in the cochlea as their own frequency would indicate, but instead they are prominent in the region where their fundamentals are strong.

Equivalent Circuits for Single-Phase Squirrel-Cage Induction Machines with both Odd and Even Order MMF Harmonics

Abstract: The special winding connections used in certain dual voltage or multiple-speed single-phase induction motors lead to large, even order MMF harmonics. The calculation procedures used to evaluate machines of this type must include proper representation of these harmonics. This paper develops the general describing equations for a two-phase machine with arbitrary MMF distributions. These equations are then specialized to yield harmonic equivalent circuits for steady-state operation. Proper interconnection of these harmonic circuits yields equivalent circuits representing actual machine windings. Examples are given, including circuits for representation of consequent pole windings. A numerical example of a machine operating with only its north poles excited is also included.

LSA oscillator waveforms for high efficiency

Abstract: The efficiency of an LSA oscillator can be increased by adding the second harmonic for dc bias electric fields up to 12 kV/cm. For higher bias fields, a third-harmonic content seems to be preferable. With second harmonic present, 30 percent efficiency appears possible at 11 kV/cm dc bias.

Digital waveform generator

Abstract: A digital waveform generator is provided for synthesizing a digital waveform having only the fundamental and prescribed harmonic components present. Additionally, a frequency translation system is provided for selecting a band of frequencies from a given input spectrum and to translate it, either erect or inverted, to a new frequency band. This system is application to both N-path filters or modulators and to R-C digital filters.

Acoustic detection apparatus

Abstract: 1,268,640. Acoustic detection of gas bubbles in blood. NATIONAL RESEARCH DEVELOPMENT CORP. 29 May, 1969 [31 May, 1968], No. 26072/68. Heading H4D. Apparatus for detecting decompression bubbles in a diver's blood comprises a transducer for application to his skin to transmit an acoustic wave of predetermined frequency through the blood, and acoustic detection means tuned to respond to acoustic waves of a related frequency generated in the blood due to non-linearity of its acoustic propagation characteristics. In one arrangement, a transmitting transducer coupled to the liquid is energized by an oscillator via an amplifier and a narrow-band filter tuned to the oscillator fundamental frequency. The same or a spaced separate skincontacting transducer is used as a receiver and is connected to an amplifier and amplitudeindicating device via a filter tuned to a harmonic (e.g. the second) or sub-harmonic of the transmitted frequency. The amplitude of the received acoustic signal at the fundamental frequency may additionally be monitored. Spurious pick-up at the desired harmonic or sub-harmonic frequency, due to non-linearity of the transducer or transducers, can be cancelled by initial adjustment of a phase-shifter and attenuator connected across the transmitter filter, the transducer(s) being arranged in air or applied to a person with bubble-free blood. In a modification the transmitted acoustic signal has two distinct frequency components and the receiver arrangement is tuned to detect the sum or difference frequency generated by the non-linearity.

A non-linear theory of acoustoelectric gain and current in piezoelectric semiconductors: II

Abstract: General expressions are developed for the dependence of acoustoelectric gain and current on the electron density distribution associated with an acoustic wave propagating through a piezoelectric semiconductor. The results are valid for nearly-periodic travelling waves with arbitrary harmonic content. It is shown that the frequency and magnitude of the peak gain can both tend to zero as the acoustic wave amplitude increases and the electrons bunch more strongly.

Frequency shifts observed in the Alouette II cyclotron harmonic plasma resonances

Abstract: The cyclotron harmonic plasma resonances observed by Alouette II were investigated using a technique that yielded frequency measurements with an accuracy of the order of 1 kHz. The resonances observed near f H and 2f H experience frequency shifts of the order of +2 percent and +0.5 percent, respectively, when f N /f H ≈3 where f N is the electron plasma frequency and f H is the electron cyclotron frequency. The resonances observed above the upper hybrid frequency approach the true frequency values of nf H as n increases; beyond about n=5 the observed cyclotron harmonic resonant frequences are consistent with a single value of f H which agrees with model magnetic field calculations within the estimated 0.2 percent reliability of this field. The frequency shifts observed previously for these resonances on the Alouette I data are attributed to magnetic contamination from the Alouette I spring steel, antennas. A comparison of the earlier Alouette I results with the-present Alouette II results indicates that the bulk of the original excitation volume associated with the higher cyclotron harmonic resonances is confined to a region considerably less than one antenna-length in radius from the antenna, that the size of this region decreases with increasing harmonic number n; and that it increases significantly as the radiating antenna becomes parallel to the direction of the earth's magnetic field.

Nonlinear analysis of the avalanche transit-time oscillator

Abstract: The nonlinear operating characteristics of the avalanche transit-time oscillator are studied by means of Fourier-series representation. For optimum operation, the oscillator must be designed such that start-oscillation conditions are satisfied simultaneously at the first and the second harmonic of the desired oscillation frequency. Under those conditions the oscillation frequency does not depend on the dc bias current; the signal level increases smoothly with bias current. For large signals, the diode exhibits negative resistance for frequencies substantially below the avalanche frequency; the oscillation frequency therefore may be below the avalanche frequency corresponding to the dc bias current required for large-signal operation. A condition for attaining large-signal operation is that the product of drift-zone capacitance and total load resistance must be small compared to the oscillation period; this condition also yields small starting currents. The output power at the oscillation frequency is obtained explicitly in terms of diode and external circuit parameters. The maximum attainable output power is limited by parasitic series resistance and by permissible RF voltage swing as compared to dc bias voltage. The best power-impedance product is obtained by choosing the transit angle equal to 0.74 π. In practice, it may be advantageous to choose a smaller value for the transit angle, in order that the tuning condition for the second harmonic may be more easily satisfied. The dc-to-RF conversion efficiency in principle is linearly proportional to the dc current density; the maximum efficiency again is limited by parasitic series resistance and by permissible RF voltage swing.