Additive manufacturing of electromagnetic multifunctional composites

Date
2015
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University of Delaware
Abstract
Electromagnetic multifunctional composites merge the excellent structural performance of structural composites with additional functionality such as sensing, communication, or electromagnetic interference protection. The multifunctionality aspect of these devices increases the functional capability of structures and can reduce weight, size, and cost. Often left addressed in the development of these structures, is the scalability and practicality of fabricating devices over large surface areas. In this dissertation, scalable methods of fabricating embedded electromagnetic devices are explored using highly scalable additive manufacturing techniques. Both screen printing and microdispensing of silver conductive inks are used to demonstrate common devices found in electromagnetic systems. Specifically, transmission line feeds, frequency selective surfaces, high impedance surfaces, and antennas are demonstrated and fabricated within woven fabric structural composites. Through these devices, the electromechanical tradeoffs of embedded printed conductors were explored. It was found that silver conductive inks that were screen printed onto glass woven fabrics experienced a reduction of conductivity and an increase in electrical path length. Additionally, the mechanical shear strength and delamination resistance of a composite decreased compared to a baseline when printed with a continuous plane of conductive ink. At higher frequencies, screen printed, embedded frequency selective surfaces compared well against devices fabricated with copper clad polyimide. The high scalability of screen printing pairs well with the patterning of frequency selective surfaces over large structures. Microdispensing of silver conductive inks was also explored as a higher quality method of depositing silver inks onto woven fabrics. The high turnover of additive manufacturing allowed for rapid processing of multiple antenna design iterations in a short time period. In addition, microdispensing allows for the deposition of higher conductivity, lower viscosity inks that were difficult to deposit onto woven fabrics via screen printing. The resulting antenna showed high conductivity, within an order of magnitude of copper, and excellent radiation performance. A final device was demonstrated using multimaterial additive manufacturing that combined an embedded antenna and high impedance surface fabricated within a single machine. A method for predicting the dielectric properties of geometrically controlled polycarbonate substrates was determined. This method was used to fabricate multiple substrates with varying dielectric properties using a single material. Additionally, the co-deposition of silver conductive ink and polycarbonate was used to additively manufacture both the embedded antenna and high impedance ground plane. The measured antenna showed improved performance when radiating above the high impedance surface relative to a continuous conducting surface at the same distance.
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