Computational design of composite EMI shields through the control of pore morphology

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Research Letter

Computational design of composite EMI shields through the control of pore morphology Avi Bregman, and Alan Taub, Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, USA Eric Michielssen, Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, MI 48109, USA Address all correspondence to Avi Bregman at [email protected] (Received 30 May 2018; accepted 8 August 2018)

Abstract A model-guided design methodology for polymer composite electromagnetic (EM) interference shields is presented. The approach utilizes measurement of intrinsic complex EM parameters, predictive modeling of absorbing geometries in the COMSOL environment, and subsequent fabrication using 3D printing and compression molding. The viability of the first two steps in the approach was confirmed using a commercially available conductive nano-filled polymer composite filament, as well as a model system from the literature. Initial results suggest that the addition of periodically placed air-filled pores within the conductive polymer composite can lead to lower reflection loss and higher absorption bandwidths.

Introduction With the advent of ubiquitous telecommunication networks and the expansive development of wireless electronics operating in the gigahertz (GHz) regime, “electromagnetic pollution” has risen to unprecedented levels.[1] Electromagnetic interference (EMI) arises when spurious or intended electromagnetic (EM) signals radiated by electronic circuits interfere with the normal operation of surrounding equipment.[2] Research pertaining to EMI shields has been conducted since the 1940s, and there currently exist many commercial options to reflection and absorb EM energy to minimize the occurrence of EMI.[3] An emerging approach to absorbance dominated EMI shielding is the use of conductive polymer composite foams. As compared with non-porous materials, foams exhibit lower density, lower percolation thresholds, and higher EMI shielding efficiency (SE) that is largely dominated by absorption.[4–6] The porous morphology decreases the impedance mismatch between air and the shield allowing a larger portion of the incident EM wave to penetrate into the shield where it can be absorbed and dissipated.[7] However, foamed polymer composites have shielding characteristics that are highly dependent on the morphology of the finished foam, which is in turn highly sensitive to the specific conditions of the foaming process.[8,9] Developing optimized polymer foam composites is a complex process that requires the screening of many different factors including material compositions, foaming temperature, foaming time, and depressurization rate, to name a few. This work focuses on the development of a new methodology for designing and producing periodic porous EMI shields that begin with intrinsic EM property measurement, continues with finite element modeling using these parameters to identify

the optimal geometries, ends with fabricating the desired composite using 3D printing or compression molding. We dem