# What is an electromagnetic pulse?

Is an electromagnetic pulse a plain electromagnetic wave with one peak?

• Typically a pulse will be a wave packet – John Rennie Dec 30 '14 at 9:16
• What is a "plain" electromagnetic wave? – Rob Jeffries Dec 30 '14 at 10:16
• Is a simple wave with only one peak.Look at my answear below. – elias2010 Dec 30 '14 at 10:22
• @JohnRennie Hi, the first sentence of the wiki link on wave packet is rather strange: "In physics, a wave packet (or wave train) is a short "burst" or "envelope" of localized wave action that travels as a unit."... localized? Doesn't this imply that we cannot know the exact wavelength of wave packets then? (due to Heisenberg uncertainty), or such reasonings do not apply here? thanks – user929304 Dec 30 '14 at 12:09
• @user929304: yes, you're spot on. If you Fourier transform a wave packet you'll find it has a range of frequencies. Only an infinite plane wave has a perfectly defined frequency. I'm sure there's a question on this topic on the site somewhere ... – John Rennie Dec 30 '14 at 12:12

It could also be a chirp.

A chirp is a signal in which the frequency increases ('up-chirp') or decreases ('down-chirp') with time. In some sources, the term chirp is used interchangeably with sweep signal.1 It has also been called quadratic-phase signal. It is commonly used in sonar and radar

Electromagnetic wave solutions to Maxwell's equations have the form $\vec{E} = \vec{E_0} f (\vec{k}\cdot \vec{r} - \omega t)$, where $f$ can be any mathematical function and $\vec{E_0} \cdot \vec{k} = 0$.

In the case of an electromagnetic pulse, a plausible function that could represent a Gaussian pulse propagating along the x-axis would be: $$\vec{E} = E_{0} \exp [(kx -\omega t)^2/2\sigma^2]\ \vec{j},$$ where $\sigma$ would represent the dispersion of the pulse.

Other suitable functions could be obtained to suit the geometry/situation at hand. The wiki page on electromagnetic pulses illustrates some other, more complex, possible functions.

" An electromagnetic pulse (EMP), also sometimes called a transient electromagnetic disturbance, is a short burst of electromagnetic energy. Such a pulse may occur in the form of a radiated electric or magnetic field or conducted electrical current depending on the source, and may be natural or man-made. An electromagnetic pulse is a short burst of electromagnetic energy. Its shortness means that it will always be spread over a range of frequencies. Pulses are typically characterised by: The type of energy (radiated, electric, magnetic or conducted). The range or spectrum of frequencies present. Pulse waveform: shape, duration and amplitude. The last two of these, the frequency spectrum and the pulse waveform, are interrelated via the Fourier transform and may be seen as two different ways of describing the same pulse.!Here are some examples:   Types of EMP Lightning electromagnetic pulse (LEMP). The discharge is typically an initial huge current flow, at least mega-amps, followed by a train of pulses of decreasing energy. Electrostatic discharge (ESD), as a result of two charged objects coming into close proximity or even contact. Meteoric EMP. The discharge of electromagnetic energy resulting from the passage of a meteoroid (known specifically as an electrophonic bolide) through the Earth's atmosphere. " Source: Wikipedia

• 1-Rectangular pulse 2-Double exponential pulse 3-Damped sinewave pulse – Al.Ka Dec 30 '14 at 9:56
• Most of this is directly copied from the wikipedia page en.wikipedia.org/wiki/Electromagnetic_pulse and should be properly acknowledged as such. Passing off the work of someone else as your own is called plagiarism. – Rob Jeffries Dec 30 '14 at 10:14
• You are correct Rob, my bad! – Al.Ka Dec 30 '14 at 10:26
• Even though i never said that this is my work. – Al.Ka Dec 30 '14 at 10:32
• Omitting to say that something is someone else's work is implicitly claiming that it is your own. Directly quoted material should be indicated as such and properly cited. This is as true on a web page as for any other public document. Submitting this as a piece of work at a UK University (and I would hope most others) would result in a mark of zero and disciplinary action. I have added quotes and a link to avoid copyright issues. en.wikipedia.org/wiki/Wikipedia:Copyrights – Rob Jeffries Dec 30 '14 at 10:47

According to mainstream theory,a single photon is a plain (one peak) wave.If this is true,then an EM pulse (usually produced by a nuclear explosion) will be a large single photon.But it is not.It is a big number of photons released within a short time period.The visible part of them makes the flash.Pulse is figured with one peak.The area under the curve corresponds to the amount of photons.

• what is the "mainstream theory" you are referring to? And what is a "large photon"? – glS Dec 30 '14 at 10:55
• Wave theory.The large photon considered as wave has long width (amplitude).Considered as particle it has large size. – elias2010 Dec 31 '14 at 10:06
• 1. "Wave theory"? What do you mean? classical electrodynamics? semi-classical (non second-quantized) quantum mechanics? QED? Please be specific. 2. width and amplitude are two very different things, and to consider a "single photon" you must use the context of quantum mechanics, in which you can't just take a particle with "long width and amplitude" – glS Dec 31 '14 at 10:11
• The word "mainstream" includes all aspects you mentioned above.None of these describes the single photon as a simple wave with one peak?I don't think so. – elias2010 Dec 31 '14 at 21:23