TY - JOUR
T1 - Negative Transient Flux in the near Field of a Subwavelength Source
AU - Li, Xiao
AU - Li, Pengqi
AU - Lu, Ming Hui
AU - Fink, Mathias
AU - Ma, Guancong
N1 - Funding Information:
The authors thank Nanjing Particle Acoustics Technology Co. Ltd. for technical supports with the PU probe. G.M. thanks Ping Sheng for discussions. This work is supported by the Hong Kong Research Grants Council (Grants No. 12302420, No. 12300419, No. 22302718, and No. C6013-18G), the National Natural Science Foundation of China (Grants No. 11922416 and No. 11802256), and Hong Kong Baptist University (Grant No. RC-SGT2/18-19/SCI/006).
Publisher Copyright:
© 2021 American Physical Society.
PY - 2021/7/23
Y1 - 2021/7/23
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=85112617474&partnerID=8YFLogxK
U2 - 10.1103/PhysRevApplied.16.L011004
DO - 10.1103/PhysRevApplied.16.L011004
M3 - Journal article
AN - SCOPUS:85112617474
SN - 2331-7019
VL - 16
JO - Physical Review Applied
JF - Physical Review Applied
IS - 1
M1 - L011004
ER -