Patent ID: 7457344
Filing Date: 2008-11-25
Classification: H05B

Abstract:
1. Apparatus for electric induction heating or melting of an electrically conductive material, the apparatus comprising: a susceptor associated with a heat absorbing process that absorbs heat by conduction or radiation from the susceptor; an active induction coil surrounding a first section of the susceptor, the active induction coil connected to an ac power supply to form an active circuit and to generate a first magnetic field, the first magnetic field magnetically coupling with the susceptor substantially in a first section of the susceptor; a pair of passive induction coils, each of the pair of passive induction coils located adjacent to opposing ends of the active induction coil and respectively surrounding second and third sections of the susceptor, each of the pair of passive induction coils exclusively connected in parallel with at least one capacitance element to form a passive circuit, the first magnetic field magnetically coupling with each of the pair of passive induction coils to generate a second and third current in each of the pair of passive circuits, the second and third currents generating second and third magnetic fields respectively, the second and third magnetic fields magnetically coupling with the susceptor substantially in the second and third sections of the susceptor respectively, the impedance of each of the pair of passive circuits selected so that each of the passive circuits has a different resonant frequency different from any resonant frequency of the active circuit; and a control system for selectively changing the output frequency of the ac power supply to change the amount of induced power in the active circuit and each of the pair of passive circuits.