Multimode Microwave Systems
Author: langfeng1 Time: 2017-12-07
Design of industrial microwave oven is complicated due to several considerations such as load type, heating uniformity and hot/cold spots. Varith J. et al. (2007) presented a design of multimode circular microwave cavity at 2.45 GHz as a section of multimode microwave oven. Industrial microwave ovens are available both at 915 MHz and 2.45 GHz frequencies. Microwave oven at 915 MHz has an advantage of higher penetration depth than that of 2.45GHz. The potential application of microwave bandwidth of 2.45 GHz is increasing because it is not limited to application of the industrial microwave generator but also available for household microwave generator modification. Thostenson E.T. et al. (1999) has given an overview of microwave applicators and processing systems. The design of the applicator is critical to microwave heating because the microwave energy is transferred to materials through the applicator. The temperature fields within the material undergoing microwave heating are inherently linked to the distribution of the electric fields within the applicator.
Common microwave applicators include waveguides, traveling wave applicators, slow wave applicators, single mode cavities, and multi-mode cavities. For heating and material processing applications, resonant applicators, such as single mode and multi-mode applicators and non-resonant waveguides are most popular. Resonant cavities are commonly used because of their high field strengths. The type of applicator used in a microwave processing system depends on the application and type of material to be processed. Single mode, multi-mode, and variable frequency multi-mode processing systems are commercially available and are being used for different microwave processing applications. Multimode cavities can be used for processing large sized objects and are suitable for batch operations and therefore most industrial microwave processing systems employ multimode cavity. Multimode cavity is widely used as an applicator in microwave processing because of low cost, simple construction and adaptability to wide range of heating loads. To achieve more uniform electric field distribution and higher heating power multiple microwave inputs can be added in a microwave cavity. That means it is possible to couple two or more low power microwave generators (< 1 kW) in series to generate higher heating power in a multimode microwave cavity. The waveguide port arrangement is done so as to obtain uniform field distribution and low coupling between two generators. Different locations of waveguide ports were simulated and cavity was optimized to obtain low coupling and uniform field distribution.