The future of microwave processing of materials appears to be strongest in specialty applications, and it will probably be of limited usefulness as a general method of producing process heat. Within the specialized areas, microwave processing has distinct advantages over conventional processing means. Microwave processing will not be applicable to all materials and in fact may be readily applicable only to certain types of materials.
The development of hybrid heating systems that optimally combine microwave sources with conventional sources to balance process variables such as required power, process flow time, tooling requirements, etc., represents a very promising, largely untapped area in process development. Hybrid heating may be provided actively, using a separate conventional heat source, or passively, using higher dielectric loss susceptors, insulation, or coatings that more readily absorb the incident power. Development of hybrid heating systems may be required for full realization of the benefits of microwave technology.
Most of the current research has focused on laboratory-scale, exploratory efforts. In order to realize the potential of microwave and hybrid processes, work is needed to scale-up process and system designs to large-batch or continuous processes. Process scaling includes model simulation, system design and integration, and an understanding of the costs and benefits involved in moving to production scale.
For particular materials, define the conditions under which microwaves provide uniform, stable processing. These may be developed through appropriate numerical modeling techniques and should be presented as processing charts that contain information on material properties, processing conditions, and specimen size and geometry. This modeling requires characterization of the thermal and physical properties of materials, including thermal conductivity and diffusivity, thermal expansion, and the temperature-dependent dielectric properties. Hybrid heating schemes, in which traditional heating is augmented with microwave heat, should be considered.
Emphasize research work that facilitates the transition of developmental processes to production scale. This may include materials property characterization, process simulation, control schemes, equipment prototyping, and pilot-scale production.
An important element of microwave process development and system design is the capability to model electromagnetic interactions. An understanding of the variation of dielectric properties with temperature and processing state is crucial for simulations and process modeling. Computer modeling can be used to optimize generator or applicator system design, establish