纳米金悬浮液中射频吸收的物理限制
On the physical limitations for radio frequency absorption in gold nanoparticle suspensions
摘要：
本文研究了金纳米颗粒悬浮液中射频吸收的物理限制。一个典型的球形几何被认为是由一个球形的胶体金纳米粒子的悬浮液，其特征在于作为一个任意的被动介电材料，这是沉浸在一个任意的有损介质。考虑到周围介质的趋肤效应，定义了相对加热系数和相应的最佳近场激励。对于小颗粒悬浮液的最佳激励是一个明确的渐近表达式很容易得到的电偶极子场。然后证明，最佳介电常数函数产生的最大吸收内的球形悬浮是一个共轭匹配相对于周围的有损材料。对于由弱电解质溶液组成的周围介质，然后可以容易地在单个频率下实现最佳共轭匹配，例如，通过调整对应于电泳粒子加速机制的Drude模型的参数。因此，共辄匹配也可以被认为产生最佳等离子体共振。最后，一个凸优化方法被用来调查的无源材料的可实现性，以近似所需的共轭匹配在有限的带宽。所提出的方法一般米氏理论的关系，以及近似的超材料进行了讨论。数值例子来说明加热的最终潜力在一个现实的情况下，在微波政权。
英文摘要：
This paper presents a study on the physical limitations for radio frequency absorption in gold nanoparticle suspensions. A canonical spherical geometry is considered consisting of a spherical suspension of colloidal gold nanoparticles characterized as an arbitrary passive dielectric material which is immersed in an arbitrary lossy medium. A relative heating coefficient and a corresponding optimal near field excitation are defined taking the skin effect of the surrounding medium into account. For small particle suspensions the optimal excitation is an electric dipole field for which explicit asymptotic expressions are readily obtained. It is then proven that the optimal permittivity function yielding a maximal absorption inside the spherical suspension is a conjugate match with respect to the surrounding lossy material. For a surrounding medium consisting of a weak electrolyte solution the optimal conjugate match can then readily be realized at a single frequency, e.g., by tuning the parameters of a Drude model corresponding to the electrophoretic particle acceleration mechanism. As such, the conjugate match can also be regarded to yield an optimal plasmonic resonance. Finally, a convex optimization approach is used to investigate the realizability of a passive material to approximate the desired conjugate match over a finite bandwidth. The relation of the proposed approach to general Mie theory as well as to the approximation of metamaterials are discussed. Numerical examples are included to illustrate the ultimate potential of heating in a realistic scenario in the microwave regime.
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