Waveform | EPFL Graph Search

In electronics, acoustics, and related fields, the waveform of a signal is the shape of its graph as a function of time, independent of its time and magnitude scales and of any displacement in time. Periodic waveforms are those that vary periodically – they repeat regularly at consistent intervals. In electronics, the term is usually applied to periodically varying voltages, currents, or electromagnetic fields. In acoustics, it is usually applied to steady periodic sounds — variations of pressure in air or other media. In these cases, the waveform is an attribute that is independent of the frequency, amplitude, or phase shift of the signal. The term can also be used for non-periodic signals, like chirps and pulses. The waveform of an electrical signal can be visualized in an oscilloscope or any other device that can capture and plot its value at various times, with suitable scales in the time and value axes. The electrocardiograph is a medical device to record the waveform of the electric signals that are associated with the beating of the heart; that waveform has important diagnostic value. Waveform generators, that can output a periodic voltage or current with one of several waveforms, are a common tool in electronics laboratories and workshops. The waveform of a steady periodic sound affects its timbre. Synthesizers and modern keyboards can generate sounds with many complicated waveforms. Simple examples of periodic waveforms include the following, where is time, is wavelength, is amplitude and is phase: Sine wave: . The amplitude of the waveform follows a trigonometric sine function with respect to time. Square wave: . This waveform is commonly used to represent digital information. A square wave of constant period contains odd harmonics that decrease at −6 dB/octave. Triangle wave: . It contains odd harmonics that decrease at −12 dB/octave. Sawtooth wave: . This looks like the teeth of a saw. Found often in time bases for display scanning.

Direct observations of X-rays produced by upward positive lightning

Marcos Rubinstein, Antonio Sunjerga, Farhad Rachidi-Haeri, Thomas Chaumont

X-rays have been observed in natural downward cloud-to-ground lightning for over 20 years and in rocket-triggered lightning for slightly less. In both cases, this energetic radiation has been detected during the stepped and dart leader phases of downward n ...

2024

Step detection in power system waveforms for improved RoCoF and frequency estimation

Mario Paolone, Asja Derviskadic, Guglielmo Frigo, Alexandra Cameron Karpilow

The evaluation of the signal frequency and Rate of Change of Frequency (RoCoF) from voltage or current waveforms is used for critical grid control, monitoring and protection applications. However, when step changes in the amplitude or phase of the signal o ...

ELSEVIER SCIENCE SA2022

Study of the enhanced electricity output of a sliding droplet-based triboelectric nanogenerator for droplet sensor design

Jürgen Brugger, Xia Liu, Wei Xu, Xiaopeng Li

Triboelectric nanogenerators are establishing themselves as promising candidates for realizing high-efficient energy harvesting from largely available droplets. However, the conventional droplet-based liquid-solid triboelectric nanogenerator (DLS-TENG) has ...

2022