Grape thermography maps electric fields in microwave Mie resonators at centimetre scale

The arXiv preprint reports polarization-controlled free-space excitation of single grapes and dimers, with infrared thermography capturing internal heating that matches simulated electric-dipole and magnetic-dipole resonances while diverging from magnetic-field patterns. Sample size comprised multiple grape pairs across 2.45 GHz excitation; the key limitation is the assumption that water-dominated dielectric response in grapes exactly replicates high-index solid resonators without accounting for ionic conductivity variations. This approach bypasses probe perturbation that has historically blocked subwavelength field mapping in microwave photonics. Prior work on grape sparking focused only on plasma ignition thresholds, missing the axial-polarization dependence now shown to localize the inter-grape hotspot. The dimer results indicate that field enhancement reaches maxima only when the connecting axis aligns with the incident electric field, offering a control parameter absent from earlier observational reports. Extension to engineered aqueous structures could accelerate design of microwave sensors and wireless power couplers. Next steps include quantitative validation against full-wave simulations on non-spherical geometries and integration with temperature-dependent permittivity models to tighten error bounds below 10 percent.