Instantaneous Radiation from Time-Varying Electric and Magnetic Dipoles

TL;DR

This paper investigates the instantaneous radiation from time-varying electric and magnetic dipoles in the time domain, revealing new insights and corrections to conventional models, with implications for metamaterials and temporally modulated emitters.

Contribution

It introduces a near-field method based on electromotive force to analyze instantaneous radiation, providing corrections to traditional far-field approaches and aligning with numerical simulations.

Findings

Corrective terms for instantaneous radiation derived

Near-field approach aligns with numerical simulations

Implications for time-varying metamaterials and emitters

Abstract

Radiation from magnetic and electric dipole moments is a key subject in theory of electrodynamics. Although people treat the problem thoroughly in the context of frequency domain, the problem is still not well understood in the context of time domain, especially if dipole moments arbitrarily vary in time under action of external forces. Here, we scrutinize the instantaneous power radiated by magnetic and electric dipole moments, and report findings that are different from the conventional understanding of their instantaneous radiation found in textbooks. In contrast to the traditional far-field approach based on the Poynting vector, our analysis employs a near-field method based on the induced electromotive force, leading to corrective terms that are found to be consistent with time-domain numerical simulations, unlike previously reported expressions. Beyond its theoretical value, this work may also have significant impact in the field of time-varying metamaterials, especially in the study of radiation from subwavelength meta-atoms, scatterers and emitters that are temporally modulated.