Electromagnetic shielding effectiveness and microwave properties of expanded graphite-ionic liquid co-doped PVDF

Polymer-based dielectric materials exhibiting high permittivity and high dielectric loss can be preferred in electromagnetic interference shielding due to providing lightweight and better corrosion characteristics as compared to heavy metals. In this work, modified carbon black (CB), graphite (GR) and expanded graphite (e-GR) are incorporated with an ionic liquid; 1-Butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) in a polyvinylidene fluoride (PVDF) matrix in form of their binary alloys. Electromagnetic shielding effectiveness (SE) and complex permittivity/permeability characteristics of synthesized materials are investigated and measured both in X and Ku band waveguides. The addition of the [BMIM]BF4 into material is observed to enhance ionic conductivity as well as polarizability of the designed composites. The ionic liquid (IL) comprising and IL-free e-GR based composites are measured to give minimum 32.7 dB and 28.1 dB shielding effectiveness along X-band, and minimum 39.5 dB and 35.5 dB shielding effectiveness along Ku-band frequency ranges for materials having 3.00 mm sample thicknesses, respectively. In comparison with the modified CB and GR, the e-GR exhibits better dispersion and superior SE values in the PVDF matrix. In addition to homogeneity observations obtained from scanning electron microscope (SEM), an electromagnetic approach to check homogeneity of the synthesized composites is proposed to the literature, which compares shielding effectiveness values per unit thickness (dB/mm) calculated from S-parameter measurements with vector network analyzer (VNA) and calculated from permittivity/permeability values being extracted with Nicolson-Ross-Weir (NRW) algorithm. The homogeneity of composites is found sufficient, and more than 9.5 dB/mm and 11.5 dB/mm shielding effectiveness for IL e-GR composite are obtained at X and Ku-bands, respectively.

Automated summary

Polymer-based dielectric materials with modified carbon black, graphite, and expanded graphite incorporated with an ionic liquid were investigated for their electromagnetic shielding effectiveness. The addition of the ionic liquid enhanced the ionic conductivity and polarizability of the composites. The e-GR showed better dispersion and superior shielding effectiveness compared to modified CB and GR in the PVDF matrix. The homogeneity of the composites was found to be sufficient, with IL e-GR achieving over 9.5 dB/mm and 11.5 dB/mm shielding effectiveness at X and Ku-bands, respectively.