Human Exposure Design Considerations For Machine Directed Microwave Dryers For Drying Ink On Paper Webs For The Inkjet Printing Industry

The use of microwave energy at 2.45GHz for dielectric heating purposes is well known, and is the technology used within microwave ovens that are found in millions of homes. In addition, the use of microwave energy for industrial drying applications, such as drying wood and drying slices of potatoes for producing potato chips, for example, has been demonstrated [1]-[2]. However, it is also of interest to consider the use of microwave energy for drying other kinds of loads, such as inks on moving paper webs which are encountered within the inkjet printing industry. This paper addresses human exposure design considerations for a microwave dryer that is designed for drying ink on a fast moving paper web. The microwave dryer is comprised of several WR340 waveguides that are placed side-by-side, such that the broad sides of each waveguide are shared by adjacent waveguides. Slots must be supported by each waveguide to enable the paper web to pass through the dryer, and to support the drying process, while not causing the propagating E-field inside the dryer to collapse. Due to the potential fluttering of the propagating paper web within the dryer, the heights of the input and output slots that enable the paper to enter and exit the dryer cannot be arbitrarily small, while the need for ambient air to flow into the dryer also places constraints on the geometrical sizes of other apertures. Two-dimensional FDTD simulations of the dryer are used to estimate the performance of the microwave dryer from a human exposure perspective that leads to some novel structures of RF chokes that can be used to meet a 5mW/cm²emissions limit for controlled exposure, 5cm from the equipment, while also contributing to the drying process. These chokes are based upon the use of carbon materials. The proposed RF chokes can produce attenuation levels between 8.1dB and 45.8dB, depending upon their construction.