Microwave resonances in aqueous monomer and dimers

Abstract

The highly-localized and intense electromagnetic hotspots afforded by plasmonic resonances in nano-scaled metallic objects have led to many exciting biomedical applications. The equivalence between nanoplasmonic hotspots, and those due to morphology-dependent resonances in high-index dielectrics is a promising avenue of nanophotonic research. In the microwave frequency regime water is such a material (n~9), and thus cm-sized aqueous dielectric objects can become resonant to few-GHz light from microwaves, WiFi, and other communication-band sources. We are using experimental, analytical, and computational approaches for studying hotspots in aqueous dimers. Experimentally, we use a household microwave oven, grape-sized hydrogel beads, and thermal imaging to demonstrate a transition from dipole-like resonance in isolated spheres to intense hotspots at the nexus of dimers. We computationally identify a host of fundamental resonances in spherical monomers that hybridize to yield either/both internal and point-of-contact dimer modes. We demonstrate that an intuitive vector-field addition approach intuitively identifies which resonances are most likely to combine to form an axial hotspot in the dimer. The usefulness of this approach is confirmed with 3D FEM simulations.