J Comput Electron DOI 10.1007/s10825-017-1065-9 Yagi–Uda nanoantenna For NIR domain Jutika Devi 1 · Pranayee Datta 1 © Springer Science+Business Media, LLC 2017 Abstract Single component metal nanoparticles, such as Ag and Au, have surface plasmon resonance wavelengths in the visible region having a weak dependence on particle size. For double component (core/shell) nanoparticles, by proper tuning the core size and shell thickness, a wide variation in optical radiation characteristics as well as in surface plas- mon resonance wavelength up to Near-Infrared (NIR) region can be achieved. These aspects encourage one to model an optical Yagi–Uda antenna adopting core/shell nanopar- ticles as feed element, reflector and directors. In this paper, adopting the COMSOL Multiphysics software, we design all core/shell Yagi–Uda nanoantennas in the NIR domain. SiO 2 /Au core/shell nanoparticles are taken as antenna ele- ments for the proposed antenna, whose surface plasmon resonance wavelength can be shifted to the NIR region by tuning the core to shell size ratio in a particular size band. The optimized directivity and gain for this antenna is achieved with only one reflector and one director, thus making it ultra- compact, cost-effective and simple in structure. This type of very highly directional Yagi–Uda nanoantenna can be used in medical science such as in targeted drug delivery and in wireless optical communication. Keywords Surface plasmon resonance · Plasmonic core/shell nanoparticle · Yagi–Uda nanoantenna · Near- Infrared · Targeted drug delivery Electronic supplementary material The online version of this article (doi:10.1007/s10825-017-1065-9) contains supplementary material, which is available to authorized users. B Jutika Devi jutika.electronics@gmail.com 1 Nanoscience and Nanotechnology Division, Department of Electronics and Communication Technology, Gauhati University, Guwahati, Assam 781014, India 1 Introduction Theoretical investigation of the radiation characteristics of single element nanoantenna comprising of single component Au or Ag nanoparticle has been a topic of intense research in the recent years [1–3]. Rapid progress has been made in the modeling and design of single element nanoantennas and their applications in various fields such as communi- cation, quantum optics, bio-sensors, photovoltaic devices, information processing, imaging, linear and nonlinear opti- cal processes etc. [4–7]. The strongly enhanced intensity of the Surface Plasmon Resonance (SPR) of noble metal nanoparticles at optical frequencies makes them excellent absorbers as well as scatterers. Apart from the single element nanoantenna comprising of single component nanoparticles, core/shell plasmonic nanoparticles (double component), in which nanoparticles of one material (dielectric/metal) are coated with a thin layer of another material (metal/dielectric), have received particular attention, nowadays, as antenna in the optical domain due to property of higher tunability of SPR wavelength as well as radiation characteristics. By properly tuning the core/shell size ratio, the radiation characteristics viz. intensity, directionality, phase and polarization of the scattered light can be modified, which opens up new possibil- ities of applicability of the scattered light in various domains. First, in 1999, Oldenburg et al. [8, 9], from Mie scattering theory, obtained that for SiO 2 /Au core/shell nanoparticles of core radius (60 ± 6) nm and shell thickness (11 ± 4) nm, the dipole plasmon resonance occurs at 830 nm, whereas for core radius (135 ± 6) nm and shell thickness (15 ± 4) nm, the dipole resonance peak shifts to 1350 nm. Among all modes (dipole, quadrupole, octopole etc.), dipole resonance peak having the highest scattering intensity is of the greatest sig- nificance from the application point of view. 123