PEEC Models of Printed Antennas in Condition Monitoring Applications Covered by Dielectrics with Temperature-Dependent Permittivity

In wireless condition monitoring systems the antenna serves as a critical part of the data transmission link. A condition monitoring application usually pose a challenging environment for an antenna system, as they are often found in harsh machine environments. As conventional antennas usually are designed for free-space operation and for some design temperature range, the presence of additional materials and their temperature variation are commonly not accounted for. In this paper an attempt to highlight the impact of materials' temperature-dependence, in their electrical properties, on printed antenna characteristics is presented. Partial element equivalent circuit models of a common printed antenna design are developed. By incorporating temperature-dependent permittivity models of pure water, and a mixture of an industrial lubricant and water, the impact on the antenna's resonant behavior is demonstrated. The numerical examples highlight that the temperature variation in the permittivity of materials surrounding the printed antenna may impact the antenna characteristics enough to be considered in the design, if a degradation in performance is not an option.