Near-field
optical binding force is an emerging new topic in the field of optical
manipulation and plasmonics. However, so far, all the studies of near-field
binding force and its counterintuitive reversal are only restricted
to dimer sets. In this work, we have studied extensively the idea
of near-field optical binding force and associated Lorentz force dynamics
for more than two objects, such as plasmonic tetramers over different
substrates. We have demonstrated that if closely positioned plasmonic
cube tetramers are placed only over the plasmonic substrate and the
circularly polarized light is impinged over them, all-optical control
between their mutual attraction and repulsion is possible because
of strong Fano resonance. In addition, the polarization state of light
controls the shifting of the extinction spectra and the binding force
reversal wavelength, making such nanostructures ideal for the polarization-dependent
optical switching device. The high magnitude of attractive and repulsive
binding forces has been obtained at the dark and bright resonant modes,
respectively, because of strong induced currents in the plasmonic
substrate. Because of its simple arrangement, our proposed tetramer
configuration may open a novel route for all-optical particle clustering,
aggregation, and crystallization, which can be verified by the simple
experimental setup.
In this paper, the enhancement of gain and bandwidth of a Minkowski fractal antenna (MFA) with defected ground structure is investigated. The antenna characteristics are studied for first and second iterations by considering complementary split ring resonators in the L-shaped modified ground plane. The dimensions of the MFA are optimized with computer simulation technology software and the fabricated antenna characteristics are measured using Vector Network Analyzer and Wave and Antenna Training System. From the simulation, the maximum gain of our proposed antenna has been found 5.2 dB. Both bandwidths obtained from simulation and measurement exceed 2 GHz. The results of simulation are in good agreement with measured ones. This proposed antenna is suitable for the applications of various 5G wireless communications.
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