Patent ID: 6730894
Filing Date: 2004-05-04
Classification: H02M,H05B

Abstract:
A method for heating a workpiece using a radio frequency (RF) field, the method comprising the steps of:providing an RF signal having a frequency and a first voltage level to a circuit having an initial resonant frequency, wherein the RF signal and the circuit are used in producing the RF field; determining an estimate of the initial resonant frequency of the circuit after providing the RF signal to the circuit; setting the frequency of the RF signal to the determined estimate of the resonant frequency; increasing the voltage level of the RF signal from the first voltage level to a second voltage level after determining the estimate of the initial resonant frequency; and tracking the resonant frequency of the circuit at least during a portion of a period during which the workpiece is being heated, wherein the tracking step comprises the steps of sensing power applied to the circuit, sensing power reflected from the circuit, and modifying the frequency of the RF signal so that the frequency of the RF signal tracks the resonant frequency.