On electromagnetic wave ignited sparks in aqueous dimers

• Published in: Physics of plasmas Vol. 28; no. 10
• Main Authors: Lin, M. S., Liu, L. C., Barnett, L. R., Tsai, Y. F., Chu, K. R.
• Format: Journal Article
• Language: English
• Published: 01.10.2021
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/5.0062014

The dimer under study is a dielectric structure formed of two identical sub-units. Dimer interactions with electromagnetic waves are widely studied in connection with electromagnetic properties of complex systems. The dimer in the form of two closely spaced grapes is also a subject of high public interest because its gap region sparks curiously in a household microwave oven. A recent paper presented the first scientific interpretation of this long-standing puzzle. It attributed the sparking phenomenon to an electromagnetic hotspot in the gap created by electromagnetic resonances in the dimer. This study has opened up a fertile ground for further research as well as motivating the current study on an independent mechanism. Our simulation and experimental results consistently point to an electrical origin for the sparks. The triggering mechanism is a two to three orders-of-magnitude buildup of localized electric field in the narrow gap, which results from the mutual enhancement of polarization charges on opposite sides of the gap. Consequently, sparks are observed at the frequency of 27 MHz, at which no electromagnetic resonance in the dimer is possible. Results also indicate a broad frequency range of the electrical mechanism, which persists even when the dimer is in strong electromagnetic resonance with the first few higher-order modes. These quantitative characterizations of basic dimer properties, in particular the broad frequency range of the polarization-charge enhancement effect, may be helpful for the understanding of collective behavior of multi-particle systems under electromagnetic radiations.