Hydrodynamic Modeling of Nano-Dipole Antennas: A Theoretical Approach

In this work we introduce a new concept of plasmonic nanoantenna: the HydrodynamicNano-Dipole Antenna (HNDA), based on the hydrodynamic model (HDM) of the electrongas. Conventional optical plasmonic antennas, typically studied within the local Drudeapproximation, can concentrate and manipulate light by coupling incident radiation to lo-calized surface plasmon resonances in metallic nanostructures. In contrast, our approachis based on the excitation of bulk plasmons as propagating modes. These bulk modesare longitudinal in nature, originate from the nonlocality of the hydrodynamic model, andoffer new possibilities for signal transmission at the nanoscale. Our study provides closed-form solutions for the potential, electric field, and induced charge under time-harmonicmonopole and dipole excitations. Special attention is given to nanoantennas of lengthl = nλ /2, for which directional far-field radiation patterns are derived and analyzed. Usingmaterial parameters for doped indium antimonide (InSb), we demonstrate the feasibility ofsuch antennas operating in the terahertz (THz) regime. Overall, these results establish theHNDA both as a new theoretical paradigm in nonlocal plasmonics and as a practical build-ing block for THz nanophotonics, with potential applications in compact spectroscopy,on-chip communications, and active nanodevices.