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Electromagnetic Radiation Made Simple

January 1997

Authors:

Hans G. Schantz

Geeks and Nerds Corporation

The traditional methods of visualizing electromagnetic radiation focus on locating ''kinks'' in the electric field lines. This method can be used only for very simple situations, such as an accelerating point charge. In this talk, I will present an alternate method that focuses on the magnetic field lines. I will show how this method can be used to obtain a qualitative picture of even more complicated radiating systems, such as dipoles."

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Electromagnetic

Radiation

Made Simple

Hans Gregory Schantz

Session G11: Physics Topics in the Undergraduate Course and

Computational Physics

Room 4, Renaissance

1997 APS/AAPT Joint Meeting

Washington, D.C.

Sponsored by:

Outline:

• Visualizing Fields: A History

• The Jefimenko Form of the Biot-Savart Law

• Examples:

Electric Dipole

Magnetic Dipole

Quadrupole Moment

• Visualizing Energy Flows - The Origin of Radiation

Visualizing Fields: A History

Michael Faraday - Originated field line concept (~1825)

Heinrich Hertz 1893 [See also Marion & Heald p. 242]

J.J. Thompson (1902)

“I cannot refrain from again expressing my

conviction of the truthfulness of the

representation, which the idea of lines of

force affords in regard to magnetic action.”

Experimental Researches in Electricity,

Vol. 3 §3234

Radiation From an Accelerated Charge

Electromagnetic Radiation (1912) G.A. Schott

Contemporary Source: Electricity & Magnetism (1985)

Purcell

Conclusion: The usual methods for

visualizing radiation rely on the “kink” in

the electric field line to identify the

radiation component of the electric field.

The Jefimenko Form of the Biot-Savart Law

[Oleg D. Jefimenko, Electricity and Magnetism, 1966]

[David J. Griffiths & Mark A. Heald, Am. J. Phys. 59 111-117 (1991)]

 



BJ x Jx=+



































o

xxc tdV

4

1

2



TWO “Right-Hand-Rules” for Magnetic Fields

Induction Component Radiation Component

Electric Dipole Radiation

Top View (Magnetic Radiation Field):

Side View (Magnetic Radiation Field):

 



I

vs. Distance []

 

I

vs. Distance []

Magnetic Dipole Radiation

Magnetic radiation polarized perpendicular to plane of loop

A Final Defense Oral Question

[Courtesy John A. Wheeler]

A solenoid is radially compressed by a sudden explosion.

Describe the radiation that will be emitted.

Knowing that the radiation is directed outward, the

Poynting vector may be used to solve for the orientation of

the electric field.

The electric field has the familiar quadrupole configuration.

Visualizing the Energy Flow About A

Decelerating Charge

[Hans Gregory Schantz "The flow of electromagnetic energy in the decay of

an electric dipole." Am. J. Phys. 63 No. 6, 513-520 (June 1995)]

[Travis Norsen and Hans Gregory Schantz, “Decelerating charges don’t

radiate; their magnetic fields do,” Submitted to Am. J. Phys.]

The Magnetic Field Around a Decelerating Charge

Space-time Diagram of the Energy Flow

About a Point Charge with Constant

Deceleration

Axes have units of

cv

ao

Summary

The magnetic radiation right-hand-rule allows quick and

easy qualitative predictions of the form of the

radiation fields.

Dispersion and UWB antennas

Conference Paper

Full-text available

Jun 2004

Hans G. Schantz

This paper discusses the phenomenon of dispersion in UWB antennas and presents a simple model to evaluate the time domain radiated fields from an antenna structure. This model allows a quick assessment of dispersion.

ResearchGate has not been able to resolve any references for this publication.

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The flow of electromagnetic energy in the decay of an electric dipole

June 1995 · American Journal of Physics

Hans G. Schantz

In a typical dipole decay, the induction magnetic field and the radiation magnetic field are in opposing directions. The former is dominant close to the decay, and the latter is dominant far away. Thus, there exists a surface on which these two components cancel each other, so that the magnetic field reverses direction. Because the magnetic field changes direction, so also will the Poynting ... [Show full abstract] vector field, provided the electric field is reasonably well behaved. This defines a "causal surface," within which electromagnetic energy will collapse, and outside which the electromagnetic energy will radiate away. I present a simple example, the decay of a point electric dipole, to argue that the radiated energy comes, not necessarily from the accelerating charges themselves, but from the energy stored in the far field.

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A multi-perspective examination of the physics of electromagnetic radiation

January 2001

Three different perspectives of electromagnetic radiation are presented here. The first employs the electric-field kink model, the second is based on a technique called FARS (Far-field Analysis of Radiation Sources), and the third uses time-domain solutions obtained from the TWTD (Thin-Wire Time Domain) model. The kink model demonstrates quali-tatively that radiation is produced by "wriggling" a ... [Show full abstract] charge. The latter two provide more quantitative results, showing that radiation for a straight dipole can come not only from the source region and ends but also from along its length.

Conference Paper

Full-text available

Planar elliptical element ultra-wideband dipole antennas

February 2002 · AP-S International Symposium (Digest) (IEEE Antennas and Propagation Society)

Hans G. Schantz

This note introduces a new class of planar ultra-wideband (UWB) dipoles that use elliptical elements. These antennas offer good dipole performance over nearly two octaves in frequency. Unlike more traditional broadband dipole elements that must be around a quarter-wavelength to radiate efficiently, planar elliptical UWB dipoles still exhibit a -10 dB return loss for a 0.20λ element size, and ... [Show full abstract] remain 50% efficient (-3 dB return loss) for a 0.14λ element size. A wide variety of techniques including exponential and Klopfenstein tapers, and an energy flow analysis all converge to an element axial ratio of about 1.5:1 being optimal.

Conference Paper

Fresh look at Lorenz-like system

August 2016

In this paper we consider the charged particle which moves by a trajectory describing by the Lorenz-like system of equation. Of course, because of non-zero acceleration this particle can be considered as a source of electromagnetic radiation. Such a radiation allows to investigate the system under consideration in the case when the system as itself is unobservable. This fact allows to obtain an ... [Show full abstract] interesting result as well as to take a fresh look at the chaotic systems that describe by the Lorenz-like system of equations.