Modulation of dielectric properties in low-loss polypropylene-based composites at GHz frequencies: theory and experiment

Abstract

Polymer composites with high dielectric constant and low loss tangent are highly regarded as substrates for modern high-speed electronics. In this work, we analyze the high-frequency dielectric properties of two types of composites based on polypropylene infused with high-dielectric-constant microparticles. Two types of fillers are used: commercial ceramics or titanium oxide (TiO2) with different concentrations. The key observation is that adding the fillers causes an increase of dielectric constants by around 100% (for highest loading) up to 4.2 and 3.4, for micro-ceramics and TiO2 based composites, respectively. Interestingly, for the TiO2 composite, the loss tangent depends on the filler loading volume, whereas the other composite has a slightly increasing tendency, however, being at the level ~ 10–3. To explain the experimental results, a theoretical model determined by microwave reflection and transmission through a representative volume element is proposed, which allows the investigation of the impact of volume ratio, grain shape, aggregation, and size on the loss tangent and permittivity evolution. This approach could be used for modeling other low dielectric loss materials with inclusions.

Effect of the Alumina Particle Filler Structure and Particle Size on the Dielectric Constant and Dielectric Loss in the Millimeter-Wave Band

“…26 They reported that the composite law is valid for the dielectric constant but not for the dielectric loss in certain cases. 27 A comparison was made with 10 and 30 wt % additions for the other fillers.…”

“…The dielectric constant and dielectric loss of alpha alumina at 18 GHz were 8.5 and 3 × 10 –3 , respectively, according to the split-spot measurement . They reported that the composite law is valid for the dielectric constant but not for the dielectric loss in certain cases . A comparison was made with 10 and 30 wt % additions for the other fillers.…”