There are several microwave techniques and probes available for characterizing inner properties of materials [1]. Microstrip patches operating in cavity modes are well suited for determining the dielectric properties of materials. A microstrip patch can be characterized by its resonant frequency and quality factor (Q-factor) when operating in free-space. When the patch is covered by another material whose dielectric properties (real and imaginary parts) are different than that of free-space, resonant frequency and Q-factor of the patch will change. The changes in these two parameters are then related to the real and imaginary parts of the material permittivity. Subsequently, the permittivity of the material is related to its moisture content, density, temperature, grain size, etc. via available dielectric mixing models [2]. Such a device can be placed inside a material temporarily (snow pack for avalanche prediction) or permanently (concrete structures for water content and crack detection).