Science Fair Project Encyclopedia

Science Fair Project Encyclopedia Contents Page

Spectral density

In physics, the spectral density, or more correctly the power spectral density (PSD) of a given bandwidth of electromagnetic radiation is the total power in this bandwidth divided by the specified bandwidth.

Spectral density is usually expressed in watts per hertz (W/Hz).

There exist both power and energy spectral densities. The energy spectral density is defined as

$\Psi_x(f) = \left| X(f) \right|^2.$

Note that the total energy in the frequency domain equals the total energy in the time domain:

$\int \left| x(t) \right|^2\, dt = \int \Psi_x(f)\, df.$

This is a result of Parseval's theorem.

Practically, for discrete-time signals, the PSD is calculated using the FFT. One example is Welch's method.

External links

Power Spectral Density Function - from Wolfram Research's "Time Series Documentation"

Categories: Physics

Science Fair Project Encyclopedia Contents Page

10-26-2009 08:16:03
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details

All Science Fair Projects