Showing papers on "Harmonic published in 1981"

Second-harmonic detection with tunable diode lasers — Comparison of experiment and theory

Abstract: A series of experiments are carried out by current modulating a tunable diode laser, and slowly ramping the wavelength to scan weak absorption lines in gases at pressures ranging from 2 to 60 Torr. A lock-in amplifier detects the second harmonic (2f) of the modulation frequency, and the experimental 2f signals are compared with theory. Detailed measurements are made on Lorentzian, Voigt, and Gaussian line profiles, over a wide range of modulation amplitudes. Excellent agreement between experiment and calculation is obtained in all cases. This quantitative understanding enables one to derive true lineshapes and linewidths of very weak absorption lines from measurements of 2f lineshapes only. Results are applicable to trace gas detection using tunable diode lasers, and to other areas of spectroscopy and magnetic resonance where harmonic detection techniques are routinely employed to monitor weak signals.

Surface-enhanced Second-harmonic Generation

Abstract: Second harmonic generation at a silver-air interface was enhanced due to surface roughness by a factor of 10{sup 4} The local field enhancement is believed to be responsible for the effect An unusually broad luminescence background extending far beyond the antiStokes side of the second harmonic was also observed

Numerical Methods for Harmonic Analysis on the Sphere

Abstract: : This report presents some numerical methods for estimating spherical harmonic coefficients from data sampled on the sphere. The data may be given in the form of area means or of point values, and it may be free from errors or affected by measurement 'noise'. The case discussed to greatest length is that of complete, global data sets on regular grids (i.e., lines of latitude and longitude, the latter, at least, separated by constant interval); the case where data are sparsely and irregularly distributed is also considered in some detail. The first section presents some basic properties of spherical harmonics, stressing their relationship to two-dimensional Fourier series. Algorithms for the evaluation of the harmonic coefficients by numerical quadratures are given here, and it is shown that the number of operations is the order of N cubed for equal angular grids, where N is the number of lines of latitude, or 'Nyquist frequency', of the grid. The second section introduces a quadratic measure for the error in the estimation of the coefficients by linear techniques. This is the error measure of least squares collocation, which is a method that can be used for harmonic analysis. Efficient algorithms for implementing collocation on the whole sphere are described. a formal relationship between collocation and least squares adjustment is used to obtain an alternative form of the collocation algorithm that is likely to be stable with dense data sets and, with a minor modification, can be used to implement least squares adjustment as well. The basic principle is that for regular grids the variance-convariance matrix of the data consists of Toeplitz-circulant blocks, so it can be both set up and inverted very efficiently.

Nonlinear visual responses to flickering sinusoidal gratings.

Abstract: Over a range of high temporal and low spatial frequencies, counterphase flickering gratings evoke the so-called frequency-doubling illusion, in which the apparent brightness of the grating varies at twice its real spatial frequency. The form of the nonlinearity that causes this second-harmonic distortion of the visual response was determined by a cancellation technique. The harmonic distortion can be measured as a function of amplitude (or contrast) by adding to the flickering grating a real, nonflickering, double-frequency component with the amplitude and phase required to cancel the illusory second harmonic. Harmonic distortion curves obtained in this way imply that the nonlinearity is of the form |s|p, where s is the stimulus pattern (without its dc component) and p is close to 0.6. If p = 1, or if the absolute value is not taken, this expression predicts distortion curves that differ significantly from the experimental results. Hence neither rectification nor compression alone is sufficient to account for the second-harmonic distortion; both are required.

Visible harmonic emission as a way of measuring profile steepening

Abstract: First observed visible harmonics of CO/sub 2/-laser-irradiated plane and microballoon targets are reported. For intensities >5 x 10/sup 14/ W/cm/sup 2/, the harmonic production efficiency is constant over several visible harmonics with a cutoff at a high harmonic number. Two-dimensional particle simulations performed where there is a highly steepened density profile show a flat spectrum for high harmonics, with a cutoff at the harmonic where the upper density shelf is underdense. Harmonics thus offer a means of measuring the upper density shelf and its dynamics.

Rectangular harmonic analysis applied to the geomagnetic field

Abstract: Spherical harmonic analysis of the earth's magnetic field is limited in the resolution that can be obtained. This limitation is caused by inadequacies of computers and of available data sets. The fundamental wavelength in spherical harmonic analysis is the circumference of the earth. To resolve wavelengths as short as 100 km would require a spherical harmonic analysis carried out to a degree and order 400 involving 160,800 coefficients. This is impractical even with modern computers. This limitation of spherical harmonic analysis can be overcome by using rectangular harmonic analysis in successively smaller areas so that the data are more fully utilized. Rectangular harmonic analysis is illustrated for data from Europe and then again for a subset of the data from a smaller area of Europe. The magnetic field at 15 observatories for the smaller area can be computed to an rms residual of only 7 nT for all three components using two sets of rectangular harmonic coefficients and the AWC/75 world chart model. Rectangular harmonic analysis and spherical harmonic analysis are complementary.

1981 Analysis and Control of Harmonic Current in Systems with Static Power Converters

Abstract: In the last 50 or 60 years, the development of rectifier and semiconductor technology has led to new products and applications for drives in all industries. These semiconductor converters produce harmonics in the ac power system. With the widespread application of these economical power supplies, problems are arising that should be approached from a logical standpoint and preventive measures taken. The theory of the problem and the solution to it is discussed.

Fundamental frequency extracting system

Abstract: A system for extracting the fundamental frequency or pitch of complex waves such as voice, musical instruments or other audio signals. Separate channels extract the fundamental frequency component when it is present in successively wider frequency bands, the frequency intervals between which are equal or less than an octave. Control signals generated in response to the presence of the fundamental components in any lower frequency channel inhibit each of the higher frequency channels thereby reducing the possibility of an overtone being detected as a fundamental frequency component of the complex wave.

Brownian motion of harmonic systems with fluctuating parameters: III Scaling and moment instabilities

Abstract: We examine the stability properties of equilibrium moments of all orders for the damped mechanical oscillator with a delta correlated fluctuating frequency. A Markovian master equation is derived startimg from a frequency fluctuation process with finite correlation time τc and the limit τc→0 is taken. To approach this limit systematically, the oscillator and frequency fluctuation parameters are expressed in terms of a dimensionless scaling parameter. We derive exact integer moment transport equations in the limit of vanishing correlation time. These equations, and hence the moments, depend only on the second cumulant of the frequency fluctuations and not on the higher cumulants. The conjecture of Bourret et al.1) that for given frequency fluctuations, however weak, all moments beyond a certain order diverge is proved. We therefore conclude that the equilibrium distribution of the oscillator displacement and momentum cannot be Gaussian. A simple algebraic relation is established between the order of the lowest unstable moments and the system parameters.

Resonance frequency shift of an acoustic chamber containing a rigid sphere

Abstract: The resonance frequency shift of an acoustic rectangular chamber due to the presence of a rigid sphere has been measured for l = 1,2 modes as a function of sphere size and position. The frequency shift is the results of volume exclusion and wave scattering. An analytical Green’s function calculation was used to explain the data, providing excellent agreement between the measured and the calculated values. Also reported are similar measurements for a thin disk and the ratio of second harmonic to fundamental pressure as a function of sphere position. The measurement shows that the sphere reduces the first harmonic content, with sharply peaked suppression minima at specific sphere positions.

A Wideband, Backshort-Tunable Second Harmonic W-Band Gunn-Oscillator

Abstract: Today W-Band (75...110 GHz) Gunn-oscillators are mostly built as 2nd harmonic oscillators. Because the fundamental frequency is below cutoff of the waveguide system, a backshort affects the output frequency only slightly. For the same reason, power combining and varactor tuning is extremely difficult. This paper presents design and performance of a more than 15 GHz backshort tunable 2nd harmonic 90 GHz oscillator. Using a common waveguide cavity, designed for both the fundamental and the 2nd harmonic frequency, this oscillator is easily backshort and varactor tunable. It is also well suited for "in line" power combiners. Results for a three diode combiner are given. Finally, a varactor tuned 2 diode combiner with a tuning range of 1.5 GHz is presented.

PWM Systems in Power Converters: An Extension of the ``Subharmonic'' Method

Abstract: In this paper the extension of the subharmonic method for pulse-width modulation (PWM) systems, in the case in which the ratio between modulating and carrier wave amplitudes can be varied from 0 to ?, is studied in an analytical way. This method allows us to obtain an inverter output waveform variable continuously from a nearly sinusoidal to a square wave and to increase somewhat the amplitude of the fundamental output wave without a significant worsening of the harmonic content, a feature particularly useful for drives with wide speed variations or which need an optimized use of dc power supply.

Performance and Design of Microwave FET Harmonic Generators

Abstract: Experimental measurements of the power gain of a 4- to 8-GHz frequency doubler, employing a single-gate GaAs MESFET device and a microstrip circuit, are reported. The measured performance provides design guidelines, and is explained in terms of FET characteristics. In particular, the multiplication gain is largest when the FET is biased near pinchoff.

Digital Simulation of Distribution System Frequency-REsponse Characteristics

Abstract: A new digital computer program developed for harmonic analysis of multi-phase networks is described. The program-the Distribution Feeder Harmonic Analysis (DFHA) Program-is designed to conveniently model distribution systems to determine frequency-response characteristics. Results of simulations performed for two different distribution systems are compared with actual harmonic measurements on the systems. Simulation accuracy is evaluated and guidelines are presented for modeling a distribution system and performing the digital harmonic analysis.

Protective relay methods and apparatus

Abstract: Differential protective relay methods and apparatus which include a differential current function supervised by both a harmonic restraint function and a voltage change function. The voltage change function determines whether or not the differential current function requires harmonic restraint supervision, preempting such supervision when it is not required, to enable faster trip decisions to be made by the differential current function.

Operating modes of millimetre wave transferred electron oscillators

Abstract: The harmonic content of both GaAs and InP millimetre wave transferred electron oscillators has been measured using a Michelson interferometer. The operating modes of these devices as a function of active length and frequency have thus been identified. Additionally, the higher frequency capabilities of InP as a millimetre wave oscillator material have been demonstrated.

Cyclotron harmonic maser

Abstract: A cyclotron resonance maser configuration is proposed which may allow operation at the higher cyclotron harmonics. Instability growth rates at the higher harmonics are shown to be significant when coupling between transversely- and longitudinally-polarized waves occurs at the electron beam boundary, for radiation propagating across the static magnetic field. With experimental parameters well within practical ranges, oscillation in a single device, tunable from about 100 to 1000 GHz, is shown to be possible.

Dayside electron cyclotron harmonic emissions

Abstract: Observations of waves exhibiting an often complex frequency banding related to the electron gyrofrequency were first reported in 19701. Later observations2–5 showed that the spectral content of these electrostatic electron cyclotron harmonic waves is highly variable6,7, including single frequency emissions between the electron gyrofrequency Ωe and its first harmonic, multiple bands between consecutive harmonics of Ωe, and emissions in a single band far above the electron gyrofrequency8–10. These observations have led theorists to investigate both the linear instability which generates the waves11–15 and various wave–particle14,16 and wave–wave17–18 interactions in which they may be involved. The consensus seems to be that at least two plasma components with different temperatures are required to destablilize electron cyclotron harmonic waves. We adopt this view here and test our present knowledge of electron cyclotron harmonic instabilities against the observed reality. To do this we use simultaneous observations of wave spectra and electron distribution functions, available in the GEOS 1 data from 25 August 1977 (see ref. 15). From these we present the wave event and then use the measured particle fluxes to derive a model distribution function, providing the input to a computer program which solves the plasma dispersion relation. From the computed temporal growth rates and group velocities, the total amplification of waves which are unstable within a limited volume of space is estimated.

Measuring Voltage and Current Harmonics on Distribution Systems

Abstract: This paper describes the instrumentation systems and test methodologies used for simultaneously measuring voltage and current harmonic magnitudes at the harmonic source and remote-feeder locations on each of two distribution systems. Results of two sets of field tests are presented. Recommendations are offered for measuring distribution system harmonics.

A Fundamental Study on Frictional Noise : (5th Report, The influence of random surface roughness on frictional noise)

Abstract: Experimental and theoretical studies have been done on the frictional noise without lubrication when a steel rod is pressed in the radial direction on a rotating thick disk with periodic corrugation surface. When the surface roughness becomes larger, various resonances are observed in the frictional noise and acceleration because of the nonlinearity such as loss of contact between the rod and the disk. That is higher harmonic resonances, subharmonic resonances, higher-subharmonic resonances of the fundamental lateral natural frequency of the rod, the fundamental and higher harmonic resonances of the higher mode of the rod are observed. Moreover, the differential and additional harmonic resonances of the fundamental and 2nd lateral natural accelerations of the rod are also observed with a long rod. The calculated results by considering the corrugation surface roughness as the external force almost agree with the experimental results. However, subharmonic, higher-subharmonic and differential and additional harmonic resonances do not occur so remarkably as those in experimental results.

Harmonic generation using a surface of metal particles

Abstract: Metal ellipsoidal particles are deposited on an ordered array of silicon dioxide posts. Each of the particles has dimensions that are less than the wavelength of a fundamental beam to be used in the generation of second harmonic radiation. The rows of particles in the ordered array are spaced at a distance that is less than one-half of the fundamental wavelength and greater than one-half of the second harmonic wavelength.

PWM Inverter circuit

Abstract: This invention relates to a pulse width modulated inverter circuit having an output signal with reduced harmonic content. The inverter circuit includes a first circuit that provides a filtered fundamental pulse width modulated signal. A second circuit is electrically coupled to the first circuit to receive the signal and sum therewith a controlled signal and the filtered fundamental pulse width modulated signal. The second circuit thereby providing the output signal with reduced harmonic content.

New method for digital-computer evaluation of convertor harmonics in power systems using state-variable analysis

Abstract: A detailed assessment of the frequency-domain approach normally used for evaluation of convertor harmonics is presented, limitations and inaccuracies are identified, and the need for an improved method is established. The theoretical basis of a new method, which simulates the individual switching processes within each convertor, is described. The method uses a modified state-variable approach to automatically formulate the 3-phase network equations, which are then linked with the convertor equations to give a time-domain solution. The computer program developed is capable of analysing power systems with interconnected components of any desired configuration, and the simultaneous operation of several convertor loads may be studied. When the time-domain solution reaches a periodic condition, the harmonic components are evaluated using a special-purpose Fourier-analysis program. The computed results of selected cases are presented to demonstrate the inherent accuracy of the method and to show its potential usefulness for other applications

Propagation and absorption of the extraordinary mode at frequencies around the second harmonic of the electron cyclotron frequency in a high density plasma

Abstract: The perpendicular propagation and absorption of the (fast) extraordinary mode is analyzed for frequencies around the second harmonic of the electron cyclotron frequency and plasma densities such that omega p/ omega c is about 1. It is shown that mode conversion into an electrostatic Bernstein wave is, in principle, possible for these densities. In most practical cases, and in particular in those where a WKB analysis applies, the wave energy is almost completely absorbed in the resonant layer around omega =2 omega c.

Method and means for detecting decay in wood

Abstract: A method and apparatus for detecting degradation in wood by applying acoustic waves along the wood grain and measuring the bandwidths and frequencies or standing wave resonances induced in the wood as the frequency of the applied waves is varied. Good quality wood exhibits a substantially harmonic relationship between the frequencies at which resonances occur and the bandwidths of the resonances are relatively small.

Electronic musical instrument of a formant synthesis type

Abstract: A musical tone is synthesized by frequency modulation which realizes a desired fixed formant. A first accumulator repeatedly adds a constant corresponding to a center frequency of the fixed formant at a regular time interval to generate phase angle data of a carrier. A second accumulator repeatedly adds a constant corresponding to a fundamental frequency of a selected note at a regular time interval to output a carry out signal each time the accumulated value has exceeded a predetermined modulo number. By resetting the first accumulator repeatedly by this carry out signal, the phase angle data of the carrier is brought into a harmonic relation with the fundamental frequency. By effecting frequency modulation using this phase angle data of the carrier and the fundamental or harmonic frequency of a selected note, a musical tone in which harmonic components of the selected note are controlled in accordance with the desired fixed formant is synthesized. A third accumulator repeatedly adds a constant corresponding to a modulating frequency peculiar to the desired fixed formant at a regular time interval. Contents of the third accumulator are repeatedly reset by a carry out signal from the second accumulator. As a result, the output of the third accumulator is brought into a harmonic relation with the selected note and therefore is suitable for use as phase angle data of a modulating frequency in the frequency modulation.