There are still challenges in the precise control of microwave energy for the industrial production, one of which is the effective inhibition of microwave hotspots or thermal runaway during microwave radiation, which has become a long-standing problem for improving heating uniformity and further expanding applications. Nevertheless, the evolution process and the underlying mechanism of microwave hotspots in high-dielectric dimers within different applied dielectrics are not fully understood due to the difficulty of internal temperature measurement. In this Letter, an optical indirect observation method has been proposed to characterize the hotspots distribution inside the applied dielectric. The grapes with high relative permittivity have been selected, which are easy to cut and absorb microwave, to conduct an in situ investigation of microwave hotspots evolution for dimers in a domestic microwave oven using the thermal and optical imaging. The results show that with the increase in the relative permittivity of applied dielectric, the starting of microwave plasma is prevented, and the focused hotspots disappear. Most significantly, the heating uniformity of dimers in water is improved by about ten times compared to that in air. The reduction of the calculated focused energy density near the contact point verifies the weakening effect of applied dielectric on the microwave cooperative resonance of dimers and explains the experimental phenomenon. These findings can be directly applied to inhibit the formation of focused hotspots for dimers or even multi-particle systems during the microwave processing and also provide a better understanding for cooperative interaction of Mie resonances.

中文翻译：

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应用电介质对二聚体诱导的微波等离子体和聚焦热点的抑制作用

工业生产对微波能量的精确控制仍然存在挑战，其中之一是有效抑制微波辐射过程中的微波热点或热失控，这已成为提高加热均匀性和进一步扩大应用的长期难题。然而，由于内部温度测量的困难，不同应用介质中高介电二聚体中微波热点的演化过程和潜在机制尚不完全清楚。在这封信中，提出了一种光学间接观察方法来表征所应用电介质内的热点分布。选用相对介电常数高的葡萄，易切割易吸收微波，使用热成像和光学成像对家用微波炉中二聚体的微波热点演变进行原位研究。结果表明，随着外加介质的相对介电常数的增加，微波等离子体的启动受到阻碍，聚焦热点消失。最重要的是，与空气中相比，二聚体在水中的加热均匀性提高了约十倍。接触点附近计算的聚焦能量密度的降低验证了施加的电介质对二聚体微波协同共振的削弱作用并解释了实验现象。