Broadband Characterization of Bulk and Thin Magnetic Composites Using Stripline Structures

We present two broadband characterization techniques to extract the RF (50 MHz-4.5 GHz) permeability of bulk and thin magnetic composite materials. Both techniques are based on broadband stripline structures with the permeability determined from S-parameter measurements. For bulk samples, a tapered stripline fixture, supporting transverse electromagnetic (TEM) waves, is employed. As this approach is not suitable for thin material samples (thickness t < 1 mm), a microstrip line fixture is proposed along with a new permeability de-embedding technique. Compared with conventional microstrip line methods, this approach is found to be accurate for thin samples with small surface areas (less than 1 cm x 1 cm). The validity of the techniques is demonstrated by measuring a bulk ferrite slab and a thin patterned ferrite composite with in-plane anisotropy.