Magnetic and dielectric properties of magneto-dielectric materials consisting of oriented, iron flake filler within a thermoplastic host

Materials that contain both an electric permittivity and magnetic permeability > 1 are currently being investigated for use as substrates to aid in antenna miniaturization. For such applications these materials, called "magneto-dielectrics", need to be low in weight, low in loss, and high in permeability. In order for these materials to be implemented within the large volume of antennas that are produced every year, they must be easy and cost effective to manufacture in bulk quantities.;An experimental procedure for fabricating magneto-dielectric materials based upon flake-like iron inclusions was developed. In order to minimize loss and maximize permeability, thin flakes with a high aspect ratio must be oriented parallel to the magnetic field. A high yield method for fabricating flakes from an iron powder precursor is discussed. Samples consisting of the iron flakes oriented within a low loss thermoplastic host were produced through several common plastics manufacturing techniques. These techniques were evaluated for their ability to orient the flakes within the plane of interest.;The electrical and magnetic properties of the magneto-dielectric samples were studied. The transport properties of permeability, dielectric constant, and loss were found as a function of the filler's aspect ratio, volume fraction, and orientation distribution. It was found that forming iron powder into flakes increases the permeability by reducing the demagnetization factor of the shape. The change to higher aspect ratio filler also increased the dielectric constant and the dielectric loss due to greater instances of inter-particle conduction. Insulating the flakes with a low dielectric coating greatly reduced the dielectric constant and the loss.;The measured composite properties were compared with several existing transport models. The Wu-McCullough model was found to be the most accurate in predicting the transport properties, but only when an accurate description of the microstructure was known. Therefore great effort was applied to precisely identifying microstructure parameters such as flake aspect ratio and orientation.