The evaluation of the dielectric constants and loss tangents for different structural foams in wet and dry conditions

Summary form only given. In this research, the evaluation of the dielectric constant and loss tangent of different structural foams such as Rohacell HF 71 and EC71 will be discussed. In addition to these foams being used as structural foams for aircraft, radomes, etc., they can also be used as substrates for microwave devices and antennas, so knowing both their mechanical characteristics as well as their electrical characteristics can be quite important. Dielectric constant and loss tangent measurements for the different foams were done under both dry conditions and under wet conditions. For the wet conditions, the foams were subjected to a constant relative humidity over a period of 17 days to simulate an environment in which the foams were considered to be saturated with moisture. In addition to the humidity testing, different densities of one type of foam, such as HF71, were tested to see how the different densities affected both the dielectric constant and loss tangent. Our tests were performed in rectangular waveguide from 1.7 GHz to 26.5 GHz so that the electrical characteristics were known over a wide frequency band. Waveguide TRL calibration kits and material test kits were designed at the University of Mississippi and fabricated for this testing. This research is important because not only are these materials increasingly used as radomes and in shielding environments, but since they can also be utilized as substrates, it is necessary to know these materials´ electrical properties so that they can be used throughout the design process for antennas and microwave circuits by importing their electrical parameters into design software. All of the materials tested were measured on the Agilent PNA network analyzer at the University of Mississippi. In the presentation, a brief discussion of the design and fabrication of the TRL test fixtures will be shown, followed by a discussion of the measurement setup and material parameter extraction technique. Finally, the - esults obtained for the different foams will be presented and comparisons between different densities of the same foam type and comparisons of foams in the wet and dry conditions will be discussed.