Instrumentation for microwave frequency-domain spectroscopy of filled polymers under uniaxial tension

Artificially engineered multiphase heterostructures with high permittivity, high permeability and low dielectric and magnetic losses are desired for microwave applications. In addition, the direct conversion of electrical (and/or magnetic) energy to mechanical work through a material response is important for many practical applications. Thus, there is a need for sensitive and quantifiable techniques to probe how uniaxial strain affects the complex effective permittivity or magnetic permeability of particulate-filled polymers. We describe an apparatus for in situ studies of the effective electromagnetic properties of filled polymers under elongation. As currently configured, our new system will already be of significance to a wide variety of research, and in particular in the materials, automotive as well as aeronautical science. In this paper, we describe the design and operation of the measurement system. Two examples of preliminary observations of electromagnetic properties of filler reinforced polymeric materials under axial strain have been obtained and are presented to illustrate the utility of this instrumentation. On one hand, the effective permittivity of carbon-black-filled SBR (styrene-butadiene rubber) is discussed as a function of the carbon black volume fraction, frequency and extension ratio. On the other hand, we also show how the effective permeability of plasto-ferrite at microwave frequency changes due to external stress. This paper concludes with suggestions for possible research topics of current interest where the knowledge of material parameters under stress would be beneficial to the basic understanding of physical processes.