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Polymeric Electromagnetic Metamaterials created by flow-induced Structure PRINTing

Periodic Reporting for period 1 - PEM-SPrint (Polymeric Electromagnetic Metamaterials created by flow-induced Structure PRINTing)

Reporting period: 2021-02-01 to 2022-07-31

The increasing miniaturization and integration of numerous components in electronic devices and the booming use of wireless technologies leads to an explosion in the amount of electromagnetic waves and resulting crosstalk. In addition, with the recent 5G mobile network, a major challenge is to enhance the range of the electromagnetic waves, which could be accomplished by suitable wave bending around obstacles. To make these upcoming technologies viable for the future, a novel class of materials is needed. These materials need to fulfil two major requirements namely processability into complex and customized shapes and local interactions with selected electromagnetic waves. The aim of this research is to develop polymeric multi-phasic electromagnetic metamaterials generated by a novel processing method, i.e. flow-induced structure printing. The novel method will make it possible to create 3-dimensional materials having substructures that are up to 100 times smaller than the dimension of the printer nozzle. By using polymeric materials with conductive and magnetic inclusions, 3D structures will be generated that allow to induce electromagnetic metamaterial responses such as wave bending or complete absorption. To enable these groundbreaking developments in material design and processing, fundamental understanding should be generated on the relations between microstructure and electromagnetic properties in 3D structured materials with conductive and magnetic inclusions combined with their flow-induced structure development.
As part of WP1, an experimentally validated finite element tool was developed that allows to predict the shielding performance of 3D-printed polymer nanocomposite shields comprising architectured shapes and (location-dependent) electromagnetic properties. Challenges included (1) re-writing functions and subroutines to solve the 2D Helmholtz equation, (2) validation of the model based on vector network analyzer-based measurements on single PMMA-CNT layers of varying thickness and CNT content, (3) improving the analysis of the aforementioned measurement data and (4) developing and efficient and stable strategy to solve the highly non-linear and coupled system of 6 field variables. In addition, a 1D analytical model was constructed in MATLAB by making use of transfer-matrix theory for verification of the 2D FE model. Perfect agreement between the analytical and FE model predictions was found. However, there is, for a significant number of cases, a discrepancy between the measured shielding performance of the single layers and that predicted by theory. To the best of our current knowledge, this can be attributed to uncertainty in the measured permittivity values of the PMMA-CNT material and is currently being addressed. Next, a parametric study was conducted via the 1D and 2D model to explore the role of the distribution of electromagnetic properties and interface geometry on shielding performance. As part of WP2, a commercial 3D filament printer is transformed into a device able to extrude and mix curable nanocomposite inks. Using open source information and firmware combined with separate motherboards and add-ons, the printer has been equipped to achieve these functionalities. Most problems occurred with electronics and software (eg compatibility of different components, requirement of functionalities not possible with the standard firmware, …). The printer modification allowing to create gradient structures is now functional. However, we would still like to improve the transition speed from one material to the other. In addition, a material screening, mostly of silicones filled with conductive particles, is performed to determine the prerequisites for suitable inks. A problem that often occurs is aggregation of nanoparticles, which blocks the tubing and the printing nozzle. This is currently the limiting factor for the performance of the printed materials.
The overall objective of the proposed research is to develop polymeric multi-phasic EM metamaterials using several unexplored regions of the design space, namely gradients and anisotropy in 3D inclusion geometries, composition and porosity. To reach this goal, a novel 3D printing methodology, flow-induced structure printing, will be developed. This method will produce hierarchical structures that contain gradients or microscopic substructures within each printed layer of macroscale 3D printed objects. Thereby, the lengthscales of the substructures (micrometer range) will be much smaller than that of the printed layer and the printed macroscale object. This will be made possible by introducing static mixers designed for flow-induced structuring in the nozzle of an extrusion-based printer. Fundamental studies of the flow-induced structuring process and the roles of rheology and interfacial dynamics in this process will lead to deeper understanding of the relationships between the flow properties and resulting micro-structures within 3D printed macro-objects. Thereby, innovative static mixer designs will be developed to generate novel substructure geometries. Hence, hierarchically structured materials with target shapes can be generated with one continuous production process. The main goals of the proposed research are:
- a modelling framework that constitutes a rational design strategy for multi-phasic EM metamaterials for different applications focussing on generating novel geometries that exploit the 3rd dimension (WP1)
- fundamental understanding of the relations between geometrical and compositional parameters of the EM metamaterials and their EM behaviour (WP1 and WP5)
- fundamental understanding of the flow-microstructure-dielectric/magnetic properties relations for suspensions with magnetic and conductive particles (WP2)
- fundamental understanding of the stability of interfaces (with or without complex rheology in the bulk and at the interface) in different flow conditions (WP3)
- a methodology for flow-induced structuring and subsequently flow-induced structure printing of suspensions containing conductive and/or magnetic particles and using novel approaches to reach small length scales within large structures (WP2, WP3 and WP4)
- polymeric multi-phasic electromagnetic metamaterials with hierarchical structures and gradients in composition, microstructure and porosity (WP2, WP3, WP4 and WP5)