Time-domain radiation and absorption by subwavelength sources

Radiation by elementary sources is a basic problem in wave physics. The authors show that the time-domain energy flux radiated from electromagnetic and acoustic sub-walength sources exhibits remarkable features. In particular, a subtle trade-off between source emission and absorption underlies the mechanism of radiation. This behavior should be observed for any kind of classical waves, thus having broad potential implications. They discuss the implication for sub-wavelength focusing by time reversal with active sources.