Hydrodynamic modeling of nano-dipole antennas: A theoretical approach

In this work, we introduce a new concept of plasmonic nanoantenna: the Hydrodynamic Nano-Dipole Antenna (HNDA), based on the hydrodynamic model of the electron gas. Conventional optical plasmonic antennas, typically studied within the local Drude approximation, can concentrate and manipulate light by coupling incident radiation to localized surface plasmon resonances in metallic nanostructures. In contrast, our approach is based on the excitation of bulk plasmons as propagating modes. These bulk modes are longitudinal in nature, originate from the nonlocality of the hydrodynamic model, and offer new possibilities for signal transmission at the nanoscale. Our study provides closed-form solutions for the potential, electric field, and induced charge under time-harmonic monopole and dipole excitations. Special attention is given to nanoantennas of length l=nλ/2, for which directional far-field radiation patterns are derived and analyzed. Using material parameters for doped indium antimonide (InSb), we demonstrate the feasibility of such antennas operating in the terahertz (THz) regime. Overall, these results establish the HNDA both as a new theoretical paradigm in nonlocal plasmonics and as a practical building block for THz nanophotonics, with potential applications in compact spectroscopy, on-chip communications, and active nanodevices.