Toroidal Dipole Mode Observation In Situ

Abstract

Besides classical dipole moments, the metaparticles are characterized by toroidal dipole moments that are important for numerous applications ranging from strong field localizations to anapole modes and the dynamic Aharonov–Bohm effect. On the other hand, the toroidal and electric dipole radiation are undistinguished by external observers due to identical radiation patterns. Therefore, the importance of toroidal dipole moments in multipole expansion is questioned by many researchers. However, a long‐awaited unanswered question is—what is going on inside a toroidal metamolecule and is its near‐field distribution distinct from the electric dipole field? Herein, the toroidal dipole mode is experimentally confirmed in situ by proof‐of‐concept measurements of electric and magnetic fields inside properly fabricated water metamolecules with toroidal topology in the microwave frequency range.

Seeing the Unseen: Experimental Observation of Magnetic Anapole State Inside a High‐Index Dielectric Particle

“…The study of the magnetic field distribution inside the water cylinder prototype was done with the help of near‐field scanning procedure. [ 34 ] A transmitting horn antenna was used to mimic the plane wave and excited the structure. The antenna was connected to the first port of the VNA and located 2 m away from the water cylinder.…”

“…Our investigation was performed in MW frequency range, where we used water as a dielectric material of the particle. Recently, water has been used as a dielectric in several applications [33,34] since its permittivity is high and characterized by small dielectric loss in the low part of the MW range. [35,36] Moreover, in addition to far-field measurements, we are also able to directly measure the electromagnetic field distribution inside the water and identify key features associated with the magnetic anapole state derived from the analytical solution.…”

Water-based devices for advanced control of electromagnetic waves

“…147 For efficient excitation, such resonant modes require complex structures. A MS composed of clusters of four cylindrical water inclusions was demonstrated to exhibit a toroidal dipole around 1 and 2.5 GHz, 32,76 see Figs. 10(a)-10(d).…”

“…In 2015, inspired by Rybin et al 17 as well as Popa and Cummer, 18 Andryieuski et al demonstrated for the first time the possibilities with exploiting water's dynamic properties in microwave all-dielectric metasurfaces (MSs). 19 This launched a series of publications on water-based (WB) microwave devices, such as tunable metamaterials (MMs) [20][21][22][23] and MSs, [24][25][26][27][28][29][30][31][32][33] as well as MS reflectors, [34][35][36][37][38] MS absorbers, and many more; [72][73][74][75][76][77][78][79] see Table I for a thorough overview. While the recent efforts on WB MSs have certainly given new life to water as an interesting microwave material, it must be mentioned that its use within the area of microwave antennas, with the first antenna dating back to 1999, 80 has been around for many years and still constitutes an active research field; see Table I for more details on particular antenna types.…”

Pseudo-anapole regime in terahertz metasurfaces

“…Toroidal and electric dipoles radiate with identical radiation patterns, while they have different current configurations in their origin [11,12]. Nevertheless, the Cartesian multipole expansion of poloidal currents flowing along torus meridians demonstrates that radiating intensity of electric dipole moment is zero, though intensity of toroidal moment prevails in the system [13].…”