Frequency‐dependent attenuation and velocity characteristics of nano‐to‐micro scale, lossy, magnetite‐rich materials

Abstract

ABSTRACTIn many situations, the magnetic properties of sub‐surface materials are often considered unimportant when compared to their ‘dielectric’ characteristics (i.e., the permittivity and conductivity). However, if significant amounts of magnetic minerals exist, such as magnetite, hematite, maghemite, etc., then the relaxation phenomena of these magnetically lossy minerals can have a significant effect on the complex apparent permittivity of the materials. In this paper, the apparent complex permittivity, attenuation and propagation characteristics of a range of nano‐to‐micro scale quartz/magnetite mixtures are investigated with the aim of determining how the lossy magnetic minerals affect the propagation of ground‐penetrating radar waves in the near‐surface environment. In addition, the investigated results are compared to popular ‘dielectric‐based’ mixing models (such as the complex refractive index model – CRIM) where the performance of the model is evaluated in terms of its appropriateness for practical situations. The results indicate that even with relatively low amounts of magnetite, the magnetic materials can have a considerable effect on the attenuation, wave propagation velocity and interface reflectivity and that the current non‐linear complex mixing models (such as CRIM) are inadequate for the description of nano‐to‐micro scale, magnetically lossy mixtures.