Negative Transient Flux in the near Field of a Subwavelength Source

Xiao Li, Pengqi Li, Ming Hui Lu, Mathias Fink*, Guancong Ma*

*Corresponding author for this work

Research output: Contribution to journalJournal articlepeer-review

1 Citation (Scopus)
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The emission of waves by a small source is a generic wave problem that has long been thought to be well studied. Here, we report the experimental observation that the energy flux of an outgoing sound wave emitted by a deep-subwavelength-sized source can become negative, which indicates the backward flow of energy. Such a negative transient flux exists, even in a homogenous medium, but is only observable in the time domain and in the extreme near field of the source. By wave-impedance analysis, we show that such a phenomenon is fundamentally rooted in the geometry of the wavefield itself and, hence, is generic. Our findings have implications in the time-dependent emission, absorption, and scattering of waves.

Original languageEnglish
Article numberL011004
JournalPhysical Review Applied
Issue number1
Publication statusPublished - 23 Jul 2021

Scopus Subject Areas

  • Physics and Astronomy(all)


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