Radiofrequency replica of plasmonic nanosphere

U ovom radu analizirana je radiofrekvencijska struktura (RF replika) koja u potpunosti oponaša elektromagnetska svojstva plazmoničke nano-kugle u optičkom području frekvencija. Analizirane strukture su Stuartov i Bestov sferni rezonator koje su se do sada upotrebljavale samo u antenskoj tehnologiji. Elektromagnetska svojstva ovih RF replika istražena su teorijski, numeričkom punovalnom simulacijom pomoću metode konačnih razlika u vremenskoj domeni i mjerenjima na prototipovima u frekvencijskom području 100-500 MHz. Simulacijom i mjerenjima potvrđena je inverzija smjera vektora električnog polja unutar RF replika u usporedbi s vektorom električnog polja u okolnom prostoru, što je osnovno svojstvo plazmoničke kugle. Pokazalo se da polje ima uniformniju razdiobu unutar Bestovog rezonatora, što ga čini pogodnijim za izradu RF replike od Stuartovog rezonatora. U cilju testiranja upotrebljivosti ovako izrađenih RF replika u skaliranim plazmoničkim eksperimentima, izrađen je model plazmoničkog valovoda sastavljen od četiri Bestova rezonatora. Valovod je pobuđen pomoću kratkog dipola u transverzalnom i longitudinalnom modu, a mjerenjem razdiobe faze incidentnog vala utvrđeno je postojanje povratnog i direktnog vala što se u potpunosti slaže s teorijskim predviđanjima. Time je pokazano da se razvijene RF replike plazmoničkih kugli zaista mogu koristiti za istraživanje osnovnih EM svojstava budućih plazmoničkih struktura za vođenje vala i plazmoničkih metamaterijala bez potrebe za skupom nanotehnologijom.electromagnetic properties of a plasmonic nanosphere at optical frequencies is analysed. Two structures, based on well known small spherical antennas (Stuart and Best’ spherical resonators), are considered as the possible candidates for the RF replicas. The electromagnetic properties of these RF replicas are investigated analytically, numerically, and experimentally in 100-500 MHz RF frequency range. The basic property of a plasmonic sphere is the inversion of the electric field vector direction inside the sphere compared to the electric field vector direction outside the sphere. This phenomenon, is confirmed by FDTD simulations and the measurements on experimental RF replicas. It was found that the electric field inside Best resonator is more uniform than the electric field inside Stuart resonator. Thus, it appears that Best resonator is more suitable for the construction af an RF replica of plasmonic nanosphere. In order to test the possible application of developed RF replicas in scaled experiments, the prototype of RF plasmonic wavegude consisted of four Best resonators was constructed. The waveguide was excited in both transversal and longitudinal modes with the help of a short dipole. The phase of the incident electric field was scanned along the waveguide and the results revealed the existence of the backward and forward waves, which is consistent with the theorethical analysis. Therefore, it was shown that developed RF replicas of plasmonic nanospheres can indeed be used for the investigation of the basic electromagnetic properties of future plasmonic structures and metamaterials. This approach elegantly avoids the use of advanced and very expensive nanotechnology