Broadband Electromagnetic Properties of Engineered Flexible Absorber Materials

Flexible and stretchable materials have attracted significant interest in wearable electronics and bioengineering fields. Recent developments also incorporate embedded microwave circuits and systems with engineered flexible materials that operate over a broad frequency range (& AP;1-100 GHz). Herein, a simple flip-chip technique is used to evaluate frequency-dependent electromagnetic properties of flexible materials and applied to evaluate engineered microwave absorbers based on self-biased barium hexaferrite composites. On-wafer error correction and de-embedding techniques are applied to determine broadband electromagnetic properties of the material-loaded transmission lines by placing the materials on top of coplanar waveguide transmission lines. Finite-element simulations along with broadband measurements were employed to estimate the electromagnetic material properties. To demonstrate, flexible polydimethylsiloxane (PDMS) composites are fabricated with barium hexaferrite nanoparticles and complex permittivity and permeability of the composites are quantified under zero magnetic field bias up to 110 GHz. Frequency-dependent composite permeability is fitted to models describing the ferromagnetic resonance of the self-biased barium hexaferrite nanoparticles in polydimethylsiloxane, and constituent nanoparticle properties are estimated using the Maxwell-Garnett mixing model. This study paves the way to exploit a wide range of engineered materials in flexible, wearable, and biomedical electronics applications and presents a convenient methodology to extract important broadband electromagnetic properties of nanoparticles for customized electromagnetic applications.