Each material is characterized by its dielectric properties, which determine how is it going to interact under the presence of an electromagnetic field. At present, whith the continuous development of new materials and functionalities, there are many applications in which it is crucial to precisely determine the dielectric properties of materials in static conditions. However, these properties change when the material undergoes a certain process. A new field of application of microwave sensors arises then, as they permit to characterize the dielectric properties of materials continuously and in real time while the process is running. The necessary information to monitor the process kinetics is provided by the sensors, and this allows for a deeper understanding of chemical reactions which take place during the process, and also it permits to develop new control functionalities. This is possible since changes in dielectric properties of materials can be directly correlated to the main material parameters such as moisture content, viscosity, degree of cure, etc.
In this work it is presented the analysis and optimization of microwave sensors, based both in waveguides and planar circuits, to perform the dielectric characterization of materials and the monitoring of some industrial processes. Some new design methods are developed in order to obtain the maximum sensitivity to the changes of the dielectric properties of  considered materials, and new analysis models are applied, which are more complete and accurate than the existing sensor models. This has allowed various applications to be succesfully developed and transferred to industrial and laboratory environments.