Inductive heating of conductive nanoparticles

Abstract

This paper presents an analysis and some interesting observations regarding the classical electromagnetic background to the heating of gold nanoparticles (GNPs) in the radio frequency spectrum. Here, it is assumed that the related dipole effects are based solely on homogeneous conducting nanospheres that are immersed in an lossy medium. From this point of view it is concluded that the effect of using a capacitive coupling i.e., a strong electric field to induce electric dipoles can be disregarded unless the volume fraction of the GNPs is unrealistically high, or if there are some other electric dipole mechanisms present which are not taken into account here, such as e.g., with nanospheres coated with ligands providing an electrophoretic movement and associated resonances. On the other hand, a simplified quasi-magnetostatic analysis indicates that an inductive heating (induced eddy currents inside the metal particles) based on magnetic coupling may have the potential to significantly increase the heating locally provided that the supplied magnetic field can be made sufficiently strong at radio frequency. This paper presents a near field optimization approach to study the electromagnetic heating of conductive nanoparticles. An optimization problem is formulated where the power absorption inside the nanoparticles is maximized subjected to power constraints related to the skin effect in the surrounding medium. The analysis shows that when the exterior medium is modelled as salty water the skin effect in the bulk material will render the simple principle of inductive heating of GNPs practically useless at 13.56 MHz.