Variable frequency microwave curing: ADVANCED PROCESS FINDS OPTOELECTRONIC APPLICATIONS

摘要

Microwave ovens are found in almost every home in the United States. The two primary limitations of our home microwave ovens ― hot and cold spots in our food and arcing to metals (such as utensils and aluminum foil) are also potential concerns when the technology is applied to heating applications in the electronics manufacturing industry. However, these problems are largely related to the fixed-frequency (2.45 GHz) operation of such appliances in the home. Figure la shows a schematic representation of the electric field established in the cavity by a fixed-frequency microwave. Variable frequency microwave (VFM) is a patented microwave technology developed at Oak Ridge National Laboratory that does not suffer from these limitations. VFM technology sweeps a bandwidth of frequencies rapidly to increase the uniformity of microwave energy in comparison to fixed-frequency microwaves. VFM ovens are normally operated to sweep a bandwidth of about 1 GHz around a center frequency every 100 milliseconds. The center frequency can be selected from a variety of bunds― typically C-band (5.8 to 7 GHz) or X-band (7.3 to 8.7 GHz). The bandwidth of frequencies swept is broken up into 4,096 individual frequencies. Therefore, during operation of a VFM processing cycle, the microwave frequency launched into the cavity is changed approximately every 25 microseconds. Figure 1b shows a schematic representation of the microwave field in a VFM cavity. VFM technology eliminates hot and cold spots and allows the use of metals in the microwave ― major benefits to fiber optic and optoelectronic processing.