A simplification technique for s-parameter calculations within partially loaded resonant cavities

Wireless sensor networks are being deployed for engine health monitoring on marine vessels, which enables longer periods of time between engine servicing while reducing the risk of component failure. Due to the nature construction of such vessels this type of wireless sensor network must be able to operate within a highly resonant environment. To ensure reliability of suitable communication systems electromagnetic modelling can be performed. Several techniques are available for such modelling including ray tracing, finite element method, method of moments, and FDTD based methods. Each has its own relative merits and disadvantages including, material characterisation, computational time and required memory. This work considers a technique for reducing the numerical complexity of finite element method calculations within a resonant cavity under normal and partially flooded scenarios. Computational resources required to calculate electromagnetic fields within a cavity scenario when water is present are considerably higher than for the equivalent empty model. Simulations have been experimentally validated using a cylindrical four port resonant cavity (see Figure 1) having internal dimensions of 1 m x 0.2 m. Two methods are presented to reduce this additional computational burden. Consider the cavity shown rotated by 90° and filled with 100mm of water. Firstly we consider a 55 mm thick slab of water below which we use an open boundary, allowing us to ignore the cavity below this point. Secondly we consider a very thin layer of water (0.1 mm thick) representing the surface of the water above an open boundary.