Explanation
In physics, the signal is usually a wave, such as an electromagnetic wave, random vibration, or an acoustic wave. The spectral density of the wave, when multiplied by an appropriate factor, will give the power carried by the wave, per unit frequency, known as the power spectral density (PSD) of the signal. Power spectral density is commonly expressed in watts per hertz (W/Hz).
For voltage signals, it is customary to use units of V2Hz−1 for PSD, and V2sHz−1 for ESD.
For random vibration analysis, units of g2Hz−1 are sometimes used for acceleration spectral density.
Although it is not necessary to assign physical dimensions to the signal or its argument, in the following discussion the terms used will assume that the signal varies in time.
Read more about this topic: Spectral Density
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