Design of a microwave applicator for nanoparticle synthesis

This paper presents the design and realization of a microwave applicator at 2.45 GHz for the synthesis of gold nanoparticles. The particles are dissolved in N,N-dimethylformamide (DMF). The heating rate is approximately 8 K/s to achieve a short crystallization time. For a proper applicator design it is necessary to know the dielectric properties of DMF. Therefore, the complex permittivity of DMF at 2.45 GHz is measured in a temperature range from 20 degrees C to 80 degrees C. The final applicator design is presented together with simulation results for the electric and thermal field distributions. The calculation of the temperature distribution is done with Comsol Multiphysics and considers mutual coupling between the electric and thermal field. To avoid overheating, a thermal controller is developed to control microwave power in dependency of the liquid's temperature. Finally, measurement results for matching and achieved heating rate are presented.