Showing papers on "Harmonic published in 1980"

Non-equilibrium Transitions in Sub/Second Harmonic Generation

Abstract: In this, the first of two papers on the subject, we present an analysis of a non-linear optical system with a mode coupled to its second harmonic, exhibiting a rich variety of non-equilibrium steady-state transitions. Here we use a semiclassical analysis to examine the steady states and their stability, and thus predict the existence of various instabilities. We find that this system exhibits both first- and second-order phase transition-like behaviour, as well as having a hard mode transition. The application of this system as a switching device is also considered.

The nonlinear capillary instability of a liquid jet. Part 1. Theory

Abstract: Nonlinear capillary instability of an axisymmetric infinite liquid column is investigated with an initial velocity disturbance consisting of a fundamental and one harmonic component. A third-order solution is developed using the method of strained co-ordinates. For the fundamental disturbance alone, the solution shows that a cut-off zone of wavenumbers (k) exists such that the surface waves grow exponentially below the cut-off zone, linearly in the middle of the zone (near k = 1), and an oscillatory solution exists for wavenumbers above the boundary of the zone. For an input including both the fundamental and a harmonic, all wave components grow exponentially when the fundamental is below the cut-off zone. Using a Galilean transformation, the solution is applied to a progressive jet issuing from a nozzle. The jet breaks into drops interspersed with smaller (satellite) drops for k 0·65. It is shown theoretically that the formation of satellites can be controlled by forcing the jet with a suitable harmonic added to the fundamental.

A systematic theoretical study of harmonic vibrational frequencies: The ammonium ion NH4+ and other simple molecules

Abstract: Analytic gradient techniques have been used to predict the harmonic vibrational frequencies of HCN, H2CO, H2O, CH4 and NH4+ at several levels of molecular electronic structure theory. Basis sets of double zeta, double zeta plus polarization, and extended plus polarization quality have been used in conjunction with self‐consistent‐field and configuration interaction methods. For the four spectroscopically characterized molecules, comparison with theory is particularly appropriate because experimental harmonic frequencies are available. For the 16 vibrational frequencies thus considered, the DZ SCF level of theory yields average errors of 166 cm−1 or 8.0%. The DZ+P SCF results are of comparable accuracy, differing on the average from experiment by 176 cm−1 or 8.3%. With the extended basis set, the comparable SCF frequency errors are only slightly less. The explicit incorporation of correlation effects qualitatively improves the agreement between theoretical and experimental harmonic vibrational frequencies....

Theory and Simulation of the Gyrotron Traveling Wave Amplifier Operating at Cyclotron Harmonics

Abstract: An analytical expresion for the efficiency of the gyrotron traveling wave amplifier is derived for the case of nonfundamental cyclotron harmonic interaction. It scales the efficiency with respect to the modes and parameters of operation. This relation, together with a general linear dispersion relation, also derived in the present paper, gives the characteristics and optimum operation conditions of the gyrotron traveling wave amplifier.

Harmonic Pollution on Power Systems - A Change in Philosophy

Abstract: Static power converters have increased in number and uses in the past decade, and there has been an increased use of static power capacitors for improving power factor. These two trends have set, the stage for possibly uncontrolled harmonic resonances on industrial power systems. Some example of some problems are given and some practices are recommended, in line with a new IEEE standard, that will minimize the chance of harmful resonant conditions.

Beam Dynamics in a Double RF System

Abstract: The addition of a higher harmonic RF system to the main system allows a control of the synchrotron frequency, the spread in synchrotron frequency and the bunch length. Adjustment of the higher harmonic system so as to reduce the slope of the RF wave to zero at the bunch centre leads to a longer bunch and a greatly increased spread in synchrotron frequency. This increases the Landau damping against: longitudinal coupled bunch instabilities. The motion of single particles in this highly non-linear potential is calculated numerically as well as analytically (by making some approximations). The dependence of the synchrotron frequency on amplitude and the forms of the synchrotron oscillations and the RF bucket are calculated. Finally the bunch shape and the distribution of particles in Qs are calculated for electron bunches.

Radiation from a strongly turbulent plasma: Application to electron beam‐excited solar emissions

Abstract: The emission of radiation at the plasma frequency and at twice the plasma frequency from beam‐excited strong Langmuir turbulence, for the case of low‐density high‐velocity warm beams, is considered. Under these conditions, Langmuir wave packets undergo (direct) collapse in a time short compared with one e folding of a beam mode. The wave packet energy density threshold for collapse depends only on the beam temperature and velocity, not on the beam density. Upper and lower limits on the volume emissivity for harmonic emission from these collapsing wave packets are found. Within most of this range, the emissivity is large enough to account for observations of second harmonic radiation during type III solar radio wave bursts. The radiation at the fundamental is many orders of magnitude larger than predicted by weak turbulence theory.

Measuring fluorescence decay times by phase-shift and modulation techniques using the high harmonic content of pulsed light sources

Abstract: In the present work we discuss the possibility to measure fluorescence lifetimes by coupling pulsed excitation with phase-shift and amplitude-modulation detection techniques We show that, because of the high harmonic content of narrow light pulses, the sample may be considered as simultaneously excited with a set of modulation frequencies up to the GHz region with noticeable power By measuring then the phase-shift and modulation ratio of fluorescence with respect to the exciting light in the high-frequency region, impressive time resolutions may be achieved On the other hand, since we dispose of a wide range of modulation frequencies, the problem of the multiexponential decay may be easily handled and has an exact analytical solution, provided the signal-to-noise ratio is good enough We anticipate the possibility to introduce cross-correlation methods in order to perform the experiment in the very-low-frequency region A short discussion about the notion of time resolution for this kind of measurement is also included

Optimum Voltage and Harmonic Control PWM Techniques for Three-Phase Static UPS Systems

Abstract: Pulsewidth modulation (PWM) is frequently employed with static ac power supplies to control the amplitude and harmonic content of load voltage However, published work on the subject of PWM techniques has mainly dealt with variable-speed ac drive applications Consequently, PWM techniques compatible with constant frequency and constant (load) voltage applications, such as uninterruptible power supply (UPS) systems, have been largely ignored Several known and novel PWM techniques suitable for three-phase static UPS systems are analyzed, and attempts are made to evaluate them Optimum techniques are subsequently selected on the basis of the low-order harmonic attenuation obtained with each technique and the number of thyristor commutations (per cycle) required to implement each technique

Harmonic reduction in d.c.-ripple reinjection

Abstract: A d.c.- ripple reinjection principle is described which reduces the harmonic content produced by static convertors. It is shown by theory and experiment that, using this principle, a six-pulse convertor configuration can be made to operate as a twelve-pulse convertor from the point of view of a.c. and d.c. system harmonics. The reinjection circuit includes a feedback convertor in series with the d.c. output. This convertor provides automatic adjustment of the reinjected current as the load changes and improves the efficiency of the overall system.

Long duration aperiodic musical waveform generator

Abstract: This is an electronic organ which economically simulates long duration aperiodic musical waveforms, such as the clash of cymbals. It employs the digital waveform generation technique, in which successive instructions are read out of a memory to determine the amplitude of the waveform at successive sample points. To save memory capacity, the memory addresses are rescanned; and to avoid audible discontinuities the scan direction recirculates numerically back and forth across the address field. Despite the bidirectionality of the scan, monotonic decreases in amplitude and in higher harmonic content are achieved. The monotonic decrease in amplitude is accomplished by impressing an exponentially declining envelope upon the digitally generated amplitudes. The monotonic decrease in higher harmonic content is accomplished by preventing the rescan from returning to a memory region of greater harmonic content after it has once entered a region of lesser harmonic content.

Rectifier Harmonics in Power Systems

Abstract: The effect of rectifier harmonic currents on power systems is described. Rectifiers and inverters require nonsinusoidal waves of current. These current waves are made up of a number of sine waves which are harmonics of the fundamental wave. These harmonic currents can excite resonant circuits causing them to ``ring'' and produce large oscillating currents. Criteria as to possible problem areas are discussed and illustrated with case studies. Examples of application of filters to ``trap'' these harmonic currents are included.

Voice band multiplex transmission system

Abstract: A system for simultaneously transmitting over the same voice circuit a voice signal and input information other than the voice. First and second sine-wave signals which do not bear any harmonic relation to each other in the band of the voice circuit are simultaneously frequency modulated by the input information, and the modulated outputs are superimposed on the voice signal and transmitted. On the receiving side, the pitch frequency of the voice signal is extracted from the received signal, and the pitch frequency and its integral multiples are removed from the received signal to remove a voice component. At this time, at least one of the first and second sine-wave signals is detected. One of these detected outputs is made to have the same frequency as the other frequency. The converted frequency and the detected frequency are demodulated to obtain the original input information.

Brownian motion of harmonic systems with fluctuating parameters: I. Exact first and second order statistics of a mechanical oscillator

Abstract: Exact first and second order statistics of a damped mechanical oscillator with a fluctuating frequency and driven by a fluctuating force are obtained. All the cumulants of the fluctuating frequency are assumed to be delta correlated, while those of the driving force are of arbitrary form. The oscillator results depend only on the first and second order statistics of the driving force and on the coefficients of the first and second cumulants of the frequency fluctuations. Thus neither the higher order statistics of the driving force nor the coefficients of the higher cumulants of the frequency fluctuations need to be specified. When the fluctuating quantities are both delta correlated, the dynamics of the correction functions are shown to be independent of the frequency fluctuations.

Spreading noise generated by load supporting elements

Abstract: Noise generated by load supporting elements of an apparatus (e.g., tread of a tire) having a plurality of repeating design cycles is spread over a broad frequency spectrum. This is accomplished by designing load bearing elements in accordance with the following procedure. First, determining the maximum number of repeating design cycles which may be placed about the apparatus; Second, selecting a maximum pitch ratio; Third, determining the appropriate number of harmonic segments into which the apparatus can be divided; Fourth, determining the size of each of the harmonic segments and the number of design cycles for each of the harmonic segments; Fifth, arranging the various design cycles in each of the harmonic segments so that the wave length of the predominant modulation frequency of the segment corresponds to the fundamental length of that segment.

A wide-band electromagnetic exploration method—Some theoretical and experimental results

Abstract: Theoretical electromagnetic (EM) responses of a conductive circular cylinder in a conductive half‐space are obtained for a frequency range between 10 Hz and 30 kHz. The results show that the spectral characteristics can be used to determine the subsurface configuration of a target body, particularly in terms of its depth. Laboratory experiments using a wide‐band sweep‐frequency source provide support for the theoretical prediction of the spectral behavior. The experiment employed a harmonic EM source continuously sweeping logarithmically from 4 kHz to 4 MHz over a graphite slab submerged in a conductive solution. The results suggest that a wide‐band EM spectral profile displayed in a frequency‐distance space may provide many intuitive interpretation schemes which may not be possible with a single or discrete frequency profile.

Non-linear optical device with a composite waveguide and radiation source using such a device

Abstract: Non-linear optical devices incorporating an integrated waveguide on a substrate, also relating to a non-linear optical device utilizing a passive layer covering the integrated waveguide making it possible by increasing the effective index ranges of the fundamental and harmonic radiations to obtain a phase matching for two propagated modes having an increased overlap integral value. The invention is more particularly applicable to frequency doubling making it possible to obtain a visible radiation source from a primary source functioning in the very-near infrared region.

Harmonic generation in organ pipes, recorders, and flutes

Abstract: A simplified treatment is given of the mechanism of sound production in musical instruments driven by air jets, which is sufficiently explicit that semiquantitative predictions can be made about the effects of certain variables upon the harmonic structure of the sound produced. In particular it is found that the amplitude of the even harmonics, generally, and of the second harmonic, particularly, is quite critically dependent upon the offset of the pipe lip from the symmetry plane of the jet. A completely symmetrical relationship (zero offset) reduces the generated amplitude of the second harmonic by a large factor. Experimental results with an adjustable organ pipe are found to confirm these predictions. The implications of these results for the voicing of organ pipes and recorders and for subtle tonal variation in flute playing are briefly discussed.

Propagation of plane, cylindrical, and spherical finite amplitude waves

Abstract: A numerical solution to the generalized Burgers' radial wave equation has been developed which allows one to calculate stepwise the harmonic content of a finite amplitude wave in the frequency domain for the case of plane, cylindrical, or spherical geometries. The finite amplitude wave may have any initial harmonic content and the attenuation coefficient of each harmonic is independently adjustable. Remaining in the frequency domain allows much larger steps than conventional programs which alternate between the time and frequency domain. The algorithm is used to verify the farfield behavior of spherical waves as predicted by D. A. Webster [J. Acoust. Soc. Am. 64, S33(A) (1978)] and to investigate the effect of a large second harmonic attenuation coefficient on the generation of a shock wave.

Strong Langmuir turbulence as a source of radio emission

Abstract: Two mechanism for generation of electromagnetic radiation by strong Langmuir turbulence were investigated: radiation of the plasma frequency and at the second harmonic of the plasma frequency. Expressions were obtained for the electromagnetic-radiation power in these two cases. The presented theory is used for a quantitative explanation of type III solar radio bursts.

Stabilization circuit for a digitally operated laser

Abstract: Compensation for variation of a semiconductor laser threshold position is based on the utilization of the rectifying property of such lasers near threshold. A small amplitude test signal is applied to the laser close to threshold and a distortion component at a harmonic of the test signal frequency is isolated from a voltage or current analog generated from the laser light output. Depending on the order of the harmonic, the characteristic of this distortion component has a maximum value (even harmonic) or is zero valued (odd harmonic) when the threshold current is applied to the laser. If the laser threshold position changes, a feedback circuit resets the bias current applied to the laser to a value close to but just below, the threshold position. The test signal can also be used to compensate for change in laser slope efficiency to avoid any variation in signal power output at a fixed modulation level.

Small amplitude non-linearities in the mechanical response of an asynchronous flight muscle

Abstract: Sinusoidal length deformations were applied to bundles of one to three fibres from glycerol-extractedLethocerus flight muscle under conditions of high calcium activation (pCa=6) and in the absence of phosphate. The mechanical response was found to be significantly non-linear under these conditions for amplitudes of the order of 0.05% and greater. The non-linearity was analysed into harmonic components by Fourier analysis, data for this being collected and stored in a computer. The largest harmonic components were found to be the first and second; these components were particularly prominent at frequencies close to those producing maximum phase shift between length and fundamental tension amplitude. At very low amplitudes (<0.02%) the non-linearities became very small and could not be readily detected. At this very low amplitude the fundamental could be considered as the linear response to the length change; it had a much sharper frequency dependence than previously recorded fromLethocerus flight muscle. The variation of the response with imposed conditions has been studied.

Harmonic saturated spectroscopy for improved atomic detection.

Abstract: A novel method for improved cw laser-induced atomic fluorescence detection that we call harmonic saturated spectroscopy takes advantage of the nonlinear response of an optically saturated atomic system to reject background sources of interference. A reduction in background and an improved SNR are demonstrated for sodium detection in an air–acetylene flame. The dependence of the harmonic signal on intensity, excitation waveform, and depth of modulation was also investigated.

Discharge lamp energization circuit, particularly for audio and supersonic frequency operation of high-pressure discharge lamps

Abstract: Discharge lamp energization circuit to operate a discharge lamp 1 over two electronic switches 10, 11, for example high-voltage, high-current switching transistors, which alternately apply a d-c voltage connected across two capacitors 4, 5, in opposite polarity, to the lamp circuit. The capacitors have the same value, and the lamp circuit includes a serially connected inductance. The electronic switching transistors are supplied from a frequency constant square-wave generator 16, at frequency high with respect to power line frequency, for example within the audio or supersonic range, e.g. 7.5 kHz. A separate ignition or starting circuit may be provided or the series inductance 2 and a capacitor 20 connected in parallel with the lamp may form a series resonance circuit tuned to a low odd harmonic (3, 5 7) of the lamp operating frequency.

Method and apparatus for recovering a signal from a charge transfer device

Abstract: Relatively noise-free information signals are recovered from a charge transfer device by demodulating sideband components of the output signal of the device at a selected harmonic of the pulse output frequency of the device. In a further refinement of the invention, the relative duty cycles between the clock signals employed to operate the device and the output signal from the device are chosen such that a minimum of power from the clock signals is present at the selected harmonic.