Electrical Characterization of Transmission Lines on Nonwoven Textile Substrates
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Electrical Characterization of Transmission Lines on Nonwoven Textile Substrates Carey R. Merritt1, Burcak Karaguzel2, Tae-Ho Kang1, John M. Wilson1, Paul D. Franzon1, H. Troy Nagle1, Behnam Pourdeyhimi2, Edward Grant1 1 College of Engineering 2 College of Textiles North Carolina State University, Raleigh, NC 27695 ABSTRACT The focus of this paper is the electrical characterization of coplanar waveguide (CPW) transmission lines that are printed onto nonwoven textile substrates using conductive inks, to determine their suitability for wide-band applications, e.g. digital signaling. The conductive ink line characterization tests included the defining of DC and Time-Domain Reflectometry metrics. The transmission line test samples were screen printed onto two different types of nonwoven textile substrates using two different conductive inks, i.e. inks with different viscosities. Tests showed that the variations in the continuity of the transmission lines varied, giving rise to geometrical variations in the CPW structure; and in the characterization of the same.
INTRODUCTION Electronic Textiles for wearable computing present considerably greater challenges to researchers than those presented by a traditional printed circuit board (PCB). According to Marculescu et al. [1] an electronic textile must be flexible, unobtrusive, robust, small, inexpensive, washable, biocompatible with human skin, and aesthetically acceptable, yet very few wearable computing devices exhibit any of these desired characteristics. Most wearable computing devices are bulky, non-conformal, expensive, and cannot be washed without removing complex electronics [1]. Electronic textiles are mostly made conductive through weaving or knitting conductive yarns into the fabric during their fabrication [1, 2, 3]. The geometrical limitations associated with the conductive lines also increases the difficulty of integrating electronic components into clothing since they lack the footprint patterns of the electronic components that are normally found in traditional PCB’s [1], requiring designers to develop alternate means of assembly [3]. Our research adopts the technologies used in the polymer thick film (PTF) industry and adapts and applies them to our nonwoven textiles project. Instead of weaving or knitting conductive yarns with fabrics, we are screen printing conductive inks onto nonwoven textile substrates. In order to determine the capabilities of these inks as they have been printed onto the nonwoven substrates, the electrical properties of the printed conductive traces are investigated. This first paper reports on the tests that were carried out to determine the suitability of this approach for use in wide-band applications. These tests include measuring the DC resistance and Time-Domain Reflectometry (TDR) metrics of the conductive traces.
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Table I. Screen Printing Parameters Mesh 250ss Emulsion 25.4 μm Mesh Angle 90º Squeegee Durometer 70 Print Pressure 275.8 kPa (40 PSI) Print/Flood Speed 3.5 cm/s Snap-off 76.2 μm SCREEN PRINTING CON
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