Here r  , r  and  are the relative permeability, permittivity, and conductivity respectively. ko denotes the wave number. Although the heat generation rate varies spatially inside the nanoparticle due to the non-uniform electric field, the heat spreads out "instantaneously" as the thermal conductivity of Auis much higher than that of the medium. A very small value of the Biot number (Bi ~ 0.00001) validates the lump capacitance approximation as per which the temperature of the nanoparticle can be considered constant throughout the volume with respect to the time scale of the process. So the total heat generation per unit time can be conveniently expressed as: