Electromagnetic radiation and the self-field of a spherical dipole oscillator

Masud Mansuripur, Per K. Jakobsen

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


For an oscillating electric dipole in the shape of a small, solid, uniformly polarized, spherical particle, we compute the self-field as well as the radiated electromagnetic field in the surrounding free space. The assumed geometry enables us to obtain the exact solution of Maxwell's equations as a function of the dipole moment, the sphere radius, and the oscillation frequency. The self-field, which is responsible for the radiation resistance, does not introduce acausal or otherwise anomalous behavior into the dynamics of the bound electrical charges that comprise the dipole. Departure from causality, a well-known feature of the dynamical response of a charged particle to an externally applied force, is shown to arise when the charge is examined in isolation, namely, in the absence of the restraining force of an equal but opposite charge that is inevitably present in a dipole radiator. Even in this case, the acausal behavior of the (free) charged particle appears to be rooted in the approximations used to arrive at an estimate of the self-force. When the exact expression of the self-force is used, our numerical analysis indicates that the impulse response of the particle should remain causal.

Original languageEnglish (US)
Pages (from-to)693-703
Number of pages11
JournalAmerican Journal of Physics
Issue number9
StatePublished - Sep 1 2020

ASJC Scopus subject areas

  • Physics and Astronomy(all)


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