In microwave extraction systems (MES), heating is achieved through two mechanisms: ionic conductivity and dipole rotation.
The microwave extraction process
The electromagnetic field generated by microwave radiation causes the ions in the solvent to migrate, and the resistance to this ionic conduction results in frictional forces, which heat the solution. The electromagnetic field also causes the reorientation of dipoles, which further contributes to the heating of the solvent. This conversion of electromagnetic energy into heat is characteristic and unique to the process of microwave heating. In conventional processes, energy is transferred to the material via convection, conduction and radiation from the surrounding material, whereas in EMI, microwave energy results in direct molecular interaction with the electromagnetic field and, consequently, in the heating of the material exposed to the energy.