Showing papers on "Sine wave published in 1969"

Quantitative interpretation of transient electromagnetic fields over a layered half space

Abstract: The transient fields from a finite horizontal loop excited by a half sine wave current pulse have been computed numerically for a particular source receiver configuration at a height of 100 meters above a layered ground. The amplitude of the vertical component of the magnetic field has been chosen for the interpretation. Curves of apparent conductivity vs. time, plotted during the off-time of the signal, show that layering is easily resolved, that resonance effects are present and that polarization effects are detectable for certain types of polarization.

Dispersive Pulse Propagation Parallel to the Interfaces of a Laminated Composite

Abstract: This paper presents a theoretical analysis of the geometric dispersion of transient stress waves in a linearly elastic laminated composite. The loading is a uniform pressure of step-function time-dependence, applied to a half space. The laminates are perpendicular to the half-space boundary. The mathematical treatment is borrowed from the theory of wave propagation in rods. Fourier transforms are applied to time and the coordinate in the propagation direction. Inversion of the spatial transform by residues yields a formal solution in the form of an infinite series of integrals. Each of these integrals is the contribution to the transient response from a mode of sinusoidal wave propagation. Application of the saddle-point technique for long-time asymptotic approximation indicates that the low-frequency portion of the integral from the first mode gives the dominant contribution, called the head-of-the-pulse approximation. The form of the expression for the head-of-the-pulse approximation leads to the definition of a characteristic dispersion time τ. Since τ is a single quantity which describes the dispersion of the wave, it simplifies parametric studies. A closed-form algebraic expression for τ is presented, which has a simple dependence on the propagation distance and spacing of the laminates. Numerical examples for boron-epoxy and glass-epoxy laminates are given.

Digital Generation of Low-Frequency Sine Waves

Abstract: Generation of approximately sinusoidal waveforms by a digital method is described. Very low frequencies (below 1 Hz) are easily obtained without the use of large inductors or capacitors, and the method is fully compatible with integrated circuit techniques. A process equivalent to nonrecursive digital filtering is used to remove the majority of harmonics from a binary waveform generated by a feedback shift register, leaving the fundamental together with only a few high-order harmonics of small amplitude.

Modulation of a General Periodic Object with Triangular Waveform by a Narrow Rectangular Aperture with Amplitude Filters

Abstract: Imagery of a general periodic triangular wave object formed by an aberration-free narrow rectangular aperture (slit) with tapered illumination, has been investigated. The system is assumed to be operating in incoherent light. Results have been presented for the far field intensity distribution in the diffraction images and the general triangular wave response of the system. An object function which gives a wave response nearly similar to that of sine wave has been pointed out.

Static transfer switching system

Abstract: A static transfer system includes a first switch for connecting a normally used AC source to a lead and a second switch for connecting a standby source to the lead. A sensor is connected to an AC sine wave reference source for comparing at every instant of time the normal AC sine wave signal to the reference source signal and feeding an error signal to a logic circuit at any instant in time when the normal source signal falls below the reference signal. The logic circuit is effective to instantaneously connect the load to the standby source and disconnect the load from the normal source irrespective of the load power factor, and to reconnect the load to the normal source and disconnect the standby source from the load when the normal source is again capable of handling the load.

Chopper-type alternating current regulator employing amplitude sensor and zero crossing detector

Abstract: A FAST RESPONSE TIME VOLTAGE REGULATOR WHICH WILL MAINTAIN THE AMPLITUDE OF AN ALTERNATING CURRENT VOLTAGE CONSTANT OVER A RELATIVELY WIDE RANGE OF FREQUENCIES. THIS IS ACCOMPLISHED BY CHOPPING THE INPUT ALTERNATING CURRENT VOLTAGE AT A FREQUENCY MUCH HIGHER THAN THAT OF THE ALTERNATING CURRENT VOLTAGE TO BE REGULATED, AND THEREAFTER FILTERING THE CHOPPER WAVEFORM TO RECONSTRUCT A TRUE SINE WAVE. BY SENSING THE AMPLITUDE OF THE FILTERED OUTPUT AND BY VARING THE "ON" AND "OFF" TIMES OF THE CHOPPER AS A FUNCTION OF VARIATIONS IN AMPLITUDE, SAID AMPLITUDE CAN BE MAINTAINED CONSTANT.

Modulation of a General Periodic Object with Triangular Transmission Profile by an Annular Aperture Using Incident Incoherent Light

Abstract: Expressions for the intensity distribution in the diffraction images of a general triangular wave-object have been obtained. The diffracting aperture considered is an aberration-free annular aperture. The circular aperture system appears as a particular case when the obstruction ratio is zero. Use of incoherent light has been assumed throughout. General triangular wave response of such systems to spatial frequencies in the object has been plotted and the object function, which gives a wave response nearly similar to that of the sine wave, has been pointed out.

Effective Dynamic Properties of a Fiber‐Reinforced Material and the Propagation of Sinusoidal Waves

Abstract: A theoretical study is presented on the propagation of a plane sinusoidal wave through a material that is reinforced with parallel fibers in one direction. The wave propagates in a direction normal to the fibers, and both fiber and matrix are made of linear elastic materials. An integral formulation for the scattered‐wave solution of an isolated fiber is used to study the multiple scattering in an infinite slab of the composite material. The transmitted and reflected waves from the composite and from a homogeneous slab are shown to be similar. By matching the two sets of results, formulas expressed in terms of the isolated‐fiber solution are derived for the wave speed, the effective density, and the modulus of the composite. In general, the effective density and modulus so defined are complex numbers and depend on the wave frequency. This fact indicates the possible existence of dissipation and dispersion in the composite under dynamic loadings. A series solution is presented for a composite containing ci...

Transient signal propagation through an inhomogeneous plasma

Abstract: The propagation of a transient electromagnetic field through a cold, isotropic, lossless, inhomogeneous plasma is considered. The electron density of the plasma decreases exponentially in the direction of propagation. For incident transient signals whose Laplace transforms are regular at infinity and whose only singularities are poles, the transient electric field propagated through the plasma can be expressed as a sum of exponential waves at discrete complex frequencies. The characteristic frequencies of the inhomogeneous plasma are related to the zeros of the modified Bessel function of the first kind of fixed argument and variable order. When the Laplace transform of the incident signal is not well-behaved at infinity, approximate methods may be used to evaluate the transient electric field. The propagation of a step sine wave and of a quasi-monochromatic Gaussian pulse are considered. It is found that for plasmas characteristic of reentry boundary layers, the effect of the plasma layer on dispersion is very small. The principal effect of the layer is to attenuate a signal propagated through it.

Image of a General Periodic Bar Pattern through an Aberration-Free Annular Aperture

Abstract: The image of a periodic bar pattern formed by a diffraction-limited annular aperture with incoherent incident light has been investigated theoretically. Results for the irradiance distribution in the image and the rectangular-wave response have been obtained. Three typical values of the central obscuration ratio are considered and the value of bar width that gives a rectangular wave response nearly equal to that of sine wave is identified.

Wide-band doubler and sine wave quadrature generator

Abstract: A wide-band signal quadrature and second harmonic generator comprising a voltage-controlled phase shifter which provides an output representing a phase-shifted sine input signal. The input signal and the phase shifter''s output are multiplied by a multiplier whose output, after integration, is used to control the illumination levels of photoresistors in the phase shifter so that the output of the phase shifter is the cosine of the sine input signal. The multiplier''s output when phase lock is achieved is the second harmonic of the sine input signal. The photoresistors in the phase shifter have large dynamic ranges of resistance changes to enable the generator to operate over a wide band of input signal frequencies.

Apparatus for varying the angular direction of a concentrated acoustic beam

Abstract: A SYSTEM FOR CONTROLLING THE DIRECTION OF PROPAGATION, AND FOR ANGULARLY DEFLECTING, A CONCENTRATED ACOUSTIC BEAM PRODUCED BY A LINEAR ARRAY OF ACOUSTIC SINE WAVE TRANSMITTERS, THE SYSTEM CONTROLLING THE DIRECTION OF THE CONCENTRATED ACOUSTIC BEAM BY ESTABLISHING A CONSTANT PHASE RELATIONSHIP BETWEEN THE SINE WAVE SIGNALS APPLIED TO EVERY ADJACENT PAIR OF TRANSMITTERS AND EFFECTING AN ANGULAR DEFLECTION OF THE CONCENTRATED BEAM BY ESTABLISHING A PREDETERMINED FREQUENCY DIFFERENCE BETWEEN THE WAVES APPLIED TO EVERY ADJACENT PAIR OF TRANSMITTERS.

Reliability of image evaluation techniques.

Abstract: A carefully controlled experiment was conducted to compare the modulation transfer function measurements, for a high performance photographic system, obtained with an automated edge gradient analysis technique and with a semimanual sine wave analysis procedure. These results and other experimentation have determined that image evaluation techniques can be reliably applied to determine modulation transfer functions of optical and photographic systems out to 200 cycles/mm.

Stroboscopic interferometric holography

Abstract: Means and method for stroboscopic interferometric holography consisting of passing the laser beam which is used to illuminate the object through a Pockels cell and pulsing the Pockels cell by means of a pulse which is derived from, and therefore synchronized with, a sine wave generator whose output is used to vibrate said object. The pulse duration and its phase position with respect to the sine wave are variable. A double-image hologram is made consisting of a stroboscopic (pulsed) exposure at the positive peak of the sine wave and at either the zero value or the negative peak, resulting in a hologram of the object including a gross interference fringe pattern. The hologram can then be converted to a conventional photograph. A second technique includes rotation of the object through a small angle before the second image is made.

Synchronous reluctance motor

Abstract: A synchronous reluctance motor particularly useful as a clock drive motor. The motor includes a stator having an airgap and a rotor having spaced teeth of magnetic material which travel in a circular path and pass through the airgap of the stator. A magnetic flux is established periodically in the stator airgap in timed relation to an approaching tooth. The timing is such that flux buildup in the airgap occurs when an approaching tooth is closer to the airgap than a receding tooth, and the flux is approximately zero when the tooth is at the center of the airgap. Hence, there is no retarding force on a tooth as it leaves the airgap. The pulsating flux is established, in one embodiment, by a power source which supplies periodic current pulses to the stator winding. In another embodiment, the power source has a sinusoidal wave form, and a magnetic shunt paralleling the stator airgap converts the sinusoid into a series of current pulses for energizing the stator winding.

Phase comparator providing dc output as a function of variable phase between two inputs

Abstract: A phase discriminator for producing a DC voltage which varies in magnitude and polarity according to the sense and extent of the phase displacement between two recurring signals which may vary in phase relation to one another. The first signal may, for example, be a train of pulses and the second signal may be a recurring sinusoidal wave. A tristate DC signal producing circuit is controlled by the two signals and its output is supplied to an averaging filter.

New method of measurement of diode junction parameters

Abstract: An experimental technique for measuring the two parameters i 0 and n of the diode equation i=i_{0}[\exp (qV/nkT)-1] has been developed The technique consists of determining n from the ratio of two average currents resulting from two sine waves being impressed-across the diode Then the value of n is used to determine an amplitude of sine wave to relate i 0 to the average current through a simple multiple The values of n and i 0 obtained by this method were compared with the same quantities obtained from the slope and intercept of a log i versus v plot Standard deviation between methods of measuring n was 0028 Standard deviation between methods of measuring log i 0 was 001

Essential Nonlinearity of Phase-Sensitive Detector Characteristics

Abstract: The effect of essential nonlinearity of phase-sensitive detector characteristics is studied and determined theoretically in detail, assuming that the input signal is a sine wave in the presence of additive narrow-band Gaussian noise. Minimum, maximum, and limiting values of nonlinearities of detector characteristics as functions of the input signal-to-noise ratio and the phase angle between the input signal and the reference wave are determined by means of computer-aided analysis. A set of curves that can be used to evaluate in detail the essential nonlinearities of detector performance and characteristics over a wide range of operating conditions and significant parameters is presented. Particular emphasis is placed on the determination of optimum detector operating conditions for minimum essential nonlinearities in wide-band Fourier-transform high-resolution nuclear magnetic-resonance and electron-spin-resonance spectrometers.

Code tone pulse train data transmitting and receiving system using sine wave gating

Abstract: Method and apparatus for transmitting data through the medium of ordinary telephone lines and handsets. Character information is generated in the form of gated sine wave tone bursts of a fixed audio frequency compatible with the telephone system, wherein the character information is contained in the number of continuous sine wave cycles in each tone burst. The sharp rise and decay times normally associated with pulse transmission, and consequent ringing and interference with reserved frequency areas, are avoided by substantially zero crossover initiation and termination of each tone burst, and PDM distortion is minimized by a combination of partial modulation, substantial on time-tooff time, and optimum frequency selection for harmonic and subharmonic rejection by telephone system rolloff.

Acoustic Pulse Distortion in Thermally Relaxing Liquids

Abstract: Pulse propagation in a thermally relaxing liquid is studied theoretically. First, Whitham's theory of wave propagation in systems governed by more than one velocity is utilized to obtain qualitative information. Second, Laplace transform solutions are obtained for particle velocity and pressure for rectangular and Gaussian pulses as well as semi‐infinite sine wave. Detailed numerical calculations are included.

Improvements in or relating to electrical oscillators

Abstract: 1,141,952. Frequency generating circuits. AIRMEC Ltd. 19 Jan., 1968 [19 Jan., 1967], No. 2979/67. Heading H3F. A frequency generating arrangement comprises an oscillator providing a first frequency, indicator means providing a measure of that frequency, and frequency-dividing means reducing the frequency to an accurate submultiple from which an output signal is produced, whereby the indicator means can be used to determine the output frequency without a full cycle of said output frequency having to be completed. A driving oscillator 10, preferably of sine wave output, produces a direct output on terminal 18 and also drives the first in a series chain of frequency dividers 12. Each of the dividers 12 comprises a cyclic counter type circuit and produces a second output signal whose amplitude at any given instant is proportional to the number of cycles counted since the preceding zero count. These second outputs from counters 12 are fed to an adding circuit 13 which generates a staircase waveform each step of which represents one count in the frequency dividers. Adder 13 feeds a phase inverter 14 producing an inverted staircase waveform which with that from adder 13 is fed to an electronic switch 15 which operates in synchronism with the frequency dividers to select alternate cycles of the two staircase waveform inputs to produce an essentially triangular waveform. The steps of this are smoothed and the waveform converted to sinusoidal form in a shaping circuit 16 which also renders the peak amplitude independent of frequency. Attenuator 17 enables the final output amplitude to be varied. The Specification also describes the use of the arrangement in measuring phase-shift in a circuit under test (Fig. 2, not shown).

Capacitance and dissipation factor measuring apparatus having coherent detectors

Abstract: A dielectric meter for measuring electrical characteristics of a dielectric sample having resistive and capacitive components in which a variable-frequency oscillator has a sine wave output coupled through an integrator with a 1-watt transfer characteristic into a sample; the output of the sample being coupled through an operational amplifier to the input of a first coherent detector and through a limiter to the input of a second coherent detector; the first coherent detector having a reference input comprising an inphase square wave signal from the variablefrequency oscillator and the second coherent detector having a reference input comprising a quadrature square wave signal output coupled from the variable-frequency oscillator; the output of the first coherent detector having an amplitude directly proportional to the capacitor component of the sample and the output of the second coherent detector being passed through a tangent function generator yielding a loss tangent dissipation factor.

Improvements in Control Circuits for Static Convertors

Abstract: 1,170,248. Converting. ENGLISH ELECTRIC CO. Ltd. 4 May, 1967 [6 May, 1966], No. 20279/66. Heading H2F. [Also in Division G3] In a circuit for controlling the conduction angle of controlled rectifiers in a converter, a sawtooth voltage is developed, the slope or frequency of which is dependent on the error between the required and actual output of the converter, firing pulses being developed from the sawtooth voltage so as to reduce said error and a control circuit for ensuring that the firing angle is within predetermined minimum and maximum limits. The invention is applicable to control of a three-phase bridge (Fig. 1, not shown) of mercury pool or thyristor rectifiers in an HVDC transmission system or in a D.C. motor control system for a rolling mill. The controlled quantity may be D.C. voltage, current or power; A.C. power or phase angle or speed of a D.C. motor. As shown in Fig. 2, the upper and lower limits of the firing angle a are determined in blocks 15 to which is fed a sine wave derived from the A.C. side which is delayed at 35 by 5 degrees then squared at 36 and differentiated at 37 to provide positive pulses corresponding to the desired minimum firing angle. These pulses trigger a bi-stable circuit 38, the output of which is fed to an AND circuit 39. The input sine wave is also fed to a phase reversal circuit 41 followed by a 10 degrees advance at 42 before being squared at 43 and differentiated at 44, the resulting positive pulses occurring at the desired maximum firing angle and are fed to AND circuit 39. A D.C. amplifier 19 determines the difference between the actual output and the required output (as set on potentiometer 20) and control the rate of rise of output voltage of a Miller integrator 21. When the output of integrator 21 reaches a threshold level, bi-stable circuit 22 is triggered so as to allow the AND gate 23 to pass the output of bi-stable circuit 38 via an OR circuit 24 to a pulse generator 25, 26, the output of which resets the integrator 21 and is distributed by a ring counter 16 and OR circuit 46 to the control electrodes of the six main rectifiers. The firing angle is thus determined by the slope of the output from integrator 21 (or frequency of pulses derived therefrom) which in turn depends on the error between required and actual output quantities. A separate control circuit 15 is provided for each main converting element, co-operating with a single firing pulse generator 14 which thus operates at six times the supply frequency when employed with a three-phase bridge system. Minimum firing angle.-If potentiometer 20 is set so as to demand a converter output greater than its maximum, the output from integrator 21 rises rapidly to its threshold value and allows AND gate 23 to pass a pulse at the time of the minimum firing angle (5 degrees). Integrator 21 is thus reset at this time. Maximum firing angle.-If potentiometer 20 is set in an attempt to provide an exceptionally low output (e.g. when operating as an inverter), the output from amplifier 19 is so low that the output from integrator 21 never reaches the threshold imposed by bi-stable circuit 22. The AND circuit 23 is thus never opened and a firing pulse is developed from the maximum firing angle pulse produced in circuit 44. This pulse is fed via OR circuit 24 to trigger the main converting elements and to reset integrator 21.

Synthesis Techniques for a Class of SSB-AM-PM Signals

Abstract: This paper develops synthesis techniques for a particular type of single-sideband sinusoidal carrier which is phase modulated by a subcarrier. Mathematical expressions for signal efficiency, sensitivity of design to parameter variation, and ratio of peak to average power are derived and incorporated in a computer program. Given the desired power ratios for modulated signal components, the program solves for the corresponding modulation parameters and evaluates signal efficiency, design sensitivity, and peak to average power ratio. A sample signal design is presented for clarity.

Improvements in and relating to Electro-Motive Apparatus.

Abstract: 1,154,141. Control of stepping motors. NATIONAL RESEARCH DEVELOPMENT CORP. 9 Jan., 1967 [10 Jan., 1966], No. 1131/66. Heading H2J. A servo system comprises a stepping motor 13 and has error indicator 23 whose output represents the magnitude and sense of a difference in the angular positions of shafts 21, 24. Signals from a device 17, which detects the angular position of rotor 11, are combined with signals from the indicator 23 whereby field coils 14, 15, 16, are energized in sequence to turn the rotor in a direction tending to reduce the error. A signal from branch A of the detector 17 is amplified, rectified, and the resultant pulses are then fed to a bi-stable device 34 producing signals of opposite sign which tend to drive the rotor in one direction or the other. A servo amplifier 35 receives the error signal from the indicator 23 and is also connected to a sawtooth generator 36, the outputs on leads 47, 46, representing the sum and difference respectively of the error and sawtooth signals. These resultant signals are fed through resistors 37, 38, to diodes 39, 40, which also receive the signals from the device 34. The combined signals are isolated by the diodes, amplified, and then applied to trigger circuit 44 having a constant output when its input exceeds a given level, but providing no output below that level. During time intervals when the circuit 44 is effective, amplifier 18 energizes the field coil 14. The operation of branches B, C, of the detector 17 and similar to that of the branch A. When the sense of the servo error signal changes, the signals on lines 46, 47, are interchanged to reverse the motor. As the error signal increases in magnitude, the duration of the pulses passed by the trigger circuit 44 is increased. In a modification, the generator 36 may be replaced by a sine wave generator. The detector 17 may comprise a metal disc which is mounted on shaft 12 and has an asymmetric shape with regard to its axis of rotation. High frequency currents are produced in the disc by means of a fixed ring which is supplied from a H.F. source and is capacitively coupled with the disc. As the disc is rotated, pulses are cyclically induced in metal strips which are circumferentially spaced around the axis of rotation. In an alternative form of detector 17, the shaft 12 carries a flat ring which is divided into magnetic and non-magnetic parts. Iron cores carrying coils are spaced symmetrically around the ring, each core having a central coil which is fed with alternating-current, and two outer coils which are connected in opposition.

Methods of multiplexing sampled data and apparatus therefore

Abstract: 1,173,607. Multiplex pulse signalling; data transmission systems. H. A. NORBY. 24 Nov., 1966 [24 Nov., 1965], No. 52709/66. Headings H4L, H4P and H4R. In a multiplex transmission system a number of carriers are used which are constituted by phase synchronous series of bipolar pulses. In order that the channels shall be orthogonal, and therefore free from cross-talk, the bipolar pulses must have equal area positive and negative portions and the pulses of each series of periodicity greater than the least must be symmetrical about the mid-points of the periods of the pulses of each series of lesser periodicity. In the described embodiments the carriers may be sine waves each of frequency twice that of the next lower frequency carrier or, as shown in Fig. 11, the highest frequency carrier, in channel A, may be a sine wave, the next highest frequency carrier, in channel B, a waveform consisting of two positive halfcycles followed by two negative half-cycles of the highest frequency carrier, the next highest frequency carrier, channel C, four positive half-cycles followed by four negative half-cycles of the highest frequency carrier, the next highest, channel D, eight positive and eight negative and so on. Information is carried by reversing the polarity of selected ones of the series of bipolar pulses and also by varying the amplitude of the pulses. Information is recovered from the multiplex modulated signals by multiplying the received signal with a square wave having the same period as the carrier to be demodulated and then integrating over the period of that carrier, the resulting signal being of a sign which depends on whether or not that bipolar pulse period was inverted and the amplitude being proportional to the transmitted amplitude of the bipolar pulse. For the transmission of digital information one digit position may be used to control the phase reversal of the bipolar pulse while further digits are converted to analogue form and modulate the amplitude of a bipolar pulse. Transmitter, Fig. 1, comprises an oscillator VCO phase locked to an external clock source and whose output is divided down to provide a series of signals each half the frequency of the previous signal and which, after filtering so that only the fundamental remains, provide the channel carrier frequencies. Channels A and B provide simple information channels and so their outputs are modulated first by phase reversal according to the digit stream d or d/2 and then in amplitude by the outputs of the digital to analogue converters fed with the remaining digits of the digit streams to be transmitted. Channel C may be used for synchronization by removing the digit stream d/4 and applying a quadrature version r 1 /4 of this channels normal carrier r/4 together with the carrier from channel B to the balanced gate. If this channel is to be used for normal data transmission the data is applied to the exclusive " OR " logic together with the r 1 /4 carrier. The resulting modulated carriers are added in adding amplifier A and the resulting signal fed to the line. Receiver, Fig. 2. The incoming signal, after equalization and gain adjustment to compensate transmission losses, is applied to a timing generator in order to extract switching signals r, r/2 and r/4 of the same period as the channel carrier bipolar pulses, which are applied to balanced modulators X together with the input signals. The modulator outputs are fed to the gated integrators which integrate over the period of the appropriate channel carrier to derive the channel modulation, in polarity and amplitude, which is fed to the analogue to digital converters in order to derive the transmitted digital signal, the integrator being reset at the end of each bipolar pulse period. By combining the phase reversals of the demodulated signal with the input signal in logic circuits and balanced modulator signals are derived to effect a g.c. of the input signal and phase locking of the timing generator. A receiver for the signals shown in Fig. 11 is described with reference to Fig. 12 (not shown), and comprises a gated integrator, the charge on which is stored and reset at the end of each half period of the highest frequency carrier. The value of the charge is converted to digital form and fed to a digital computer which combines the integrator outputs appropriately in order to extract the data signals corresponding to each multiplexed channel. In an alternative form of demodulator, Fig. 13, the signal is applied to a number of gated integrators in each channel and the signal input of each integrator is phase reversed by a respective switching waveform so that, in each channel, a maximum value will appear at the output of that integrator corresponding to the particular digit sequence transmitted during that signal period on that channel. In channel A eight orthogonal digit sequences are possible, in channel B four, and in channel C two, with D providing a reference signal. The maximum likelihood detector compares the output of the integrators in the respective channel to decide which digit sequence was transmitted, and connects the appropriate integrator output to the analogue to digital converter corresponding to that channel.