ABSTRACT
Microwave sensors are based on the interaction between microwaves and matter. Microwave sensors utilize electromagnetic fields and devices internally operating at frequencies starting from approximately 300 MHz up to the terahertz range. This interaction may be in the form of reflection, refraction, scattering, emission, absorption, or change of speed and phase. In this chapter, it is shown that this principle can be used for humidity sensor development. A description of the various approaches to the development of microwave humidity sensors can be found. The main focus is on considering transmission and resonant and impedance humidity sensors. It is important to note that constructively, microwave humidity sensors are fundamentally different from conventional solid-state humidity sensors. The performances of developed humidity sensors, as well as their advantages and disadvantages, are also considered in this chapter.
