Sine wave

About: Sine wave is a research topic. Over the lifetime, 12183 publications have been published within this topic receiving 93013 citations. The topic is also known as: sinusoid.

A multiwavelength distance-measuring instrument for geophysical experiments

Abstract: A multiwavelength distance-measuring (MWDM) instrument that utilizes the dispersive nature of the atmosphere has been developed and tested. With this instrument there is no need for the usual meteorological observations and corrections. This MWDM instrument simultaneously measures the optical path length at three wavelengths, two in the optical region of the spectrum and one in the microwave region. The instrument calculates correction terms from the optical path length differences and then computes the corrected base line distance, the first-order effects of temperature, pressure, and water vapor fluctuations along the line thus being eliminated. Field testing demonstrated that the instrument was capable of making consecutive distance determinations with a standard deviation from the mean as small as 4 parts in 108. The long-term stability of the instrument was investigated from June 1974 to November 1974. The results showed a standard deviation of 1.3 parts in 107 when the data were fit to a sine wave of annual periodicity. The amplitude of this sine wave was 3 parts in 107, which was in good agreement with the predicted results of a two-dimensional thermoelastic model.

Sine waves and flicker fusion.

Abstract: The author reviews several phenomena occurring in sine wave flicker experiments, classifying them into low-frequency (below 10 cps) and highfrequency (above 20 cps) effects, and suggests that two different, kinds of mechanisms are needed to account for the behavior of amplitude sensitivity curves in these two frequency ranges. At low frequencies, the threshold modulation ratio is independent of the time-average luminance or adaptation level of the flickering stimulus (but decreases significantly with increasing field size); whereas at high frequencies, the threshold amplitude of the sinusoidal component alone (measured in retinal illuminance units) is independent of adaptation level. In the intermediate frequency band, a smooth transition occurs from one type of behavior to the other. These facts simplify the well-known calculation of classical flicker-fusion thresholds from sine-wave data (first demonstrated by de Lange). The present paper discusses such calculations in some detail, developing the concept of the sinusoidal equivalent stimulus and explicitly stating the reducibility hypothesis for various flicker-fusion waveforms. Additional equivalence tests are provided by periodic-flash experiments conducted for this purpose and reported here.

Instantaneous frequency and wave shape functions (I)

Abstract: Although one can formulate an intuitive notion of instantaneous frequency, generalizing "frequency" as we understand it in e.g. the Fourier transform, a rigorous mathematical definition is lacking. In this paper, we consider a class of functions composed of waveforms that repeat nearly periodically, and for which the instantaneous frequency can be given a rigorous meaning. We show that Synchrosqueezing can be used to determine the instantaneous frequency of functions in this class, even if the waveform is not harmonic, thus generalizing earlier results for cosine wave functions. We also provide real-life examples and discuss the advantages, for these examples, of considering such non-harmonic waveforms.

Elastic contact stiffness and contact resistance for the Weierstrass profile

Abstract: The Weierstrass series comprises a system of superposed self-affine sine waves that can be used to define a simple idealization of a two-dimensional fractal rough surface profile. The load–compliance relation for the contact of this profile with a rigid plane is here estimated using Westergaard's solution for the contact of a single sine wave with a plane and various approximations concerning the interaction of the different terms in the series. These approximations are compared with a numerical solution for the contact of the profile defined by the first few terms of the series. Once the load–compliance relation is established, the electrical contact resistance can be determined, using an analogy between the conduction and incremental elastic contact problems. The results show that these simple estimates give quite good predictions of the relations between load, compliance and contact resistance. They also confirm that these relations are largely determined by the coarse scale features of the surface profile, in contrast to the predictions of classical asperity model theories.

Pulse Width Modulated Inverters for AC Motor Drives

Abstract: The use of pulse width modulation techniques applied to thyristor inverters to obtain variable frequency-variable voltage waveforms is reviewed. A number of basic modes of modulation are analyzed; harmonic content and principles of wave generation are investigated and compared to conventional forms of synthesis. The prime advantage of such systems is to preserve a near sine wave envelope rather than to eliminate specific harmonics. This allows a potentially wider range of speed control by keeping the harmonics in fixed but small proportions relative to the fundamental frequency. The principal harmonics which are presen-t are those induced by pulse modulation; these normally can be filtered by the inherent delays of the motor.