Interlaced Circuits for Multidirectional Stretchable Electronics
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Interlaced Circuits for Multidirectional Stretchable Electronics Qiao Li, Xiaoming Tao and Tao Hua Institute of Textiles & Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong ABSTRACT Stretchable electronic circuits have the potential to the fields where electronics have to be conformable, deformable and stretchable into three dimensional surfaces. In this work, an “interlaced” structure is developed for multidirectional stretchable circuit. The shape of the conductor is loop-like configuration. A knitted structure is employed for the elastic substrate due to its flexibility, high stretchability, low cost and simple fabrication. The electro-mechanical behavior of the interlaced circuit is investigated in three different directions, i.e., 0-degree, 45degree, and 90-degree, respectively. A significant improvement in stretchability is achieved in 0degree direction. Then, a preliminary theoretical analysis is made in the electro-mechanical mechanism of the interlaced circuit. From the experimental investigation and theoretical analysis, it is found that the interlaced structure gives the conductor more freedom to move in the substrate, decreasing the stress concentration in the crest and trough parts of the loop when it is stretched. INTRODUCTION Recently, the demand of stretchable interconnects on three-dimensional surface is considerably increasing in many applications where the circuits are designed to be deformable, flexible, stretchable and minimally invasive into curvilinear shapes. Present-day stretchable interconnects are created by depositing metal films on rubber-like elastic substrates with out-of-plane wavy pattern [1, 2, and 3] or in-plane tortuous pattern [4, 5]. One vital issue for the pioneering designs is the adhesive fracture between the metal films and the elastic substrate [6] as the delaminated conducting line may lead to shorts, inducing electrical failure. This paper presents an “interlaced” integration (instead of bonding) between the conductor and the substrate using appropriate materials to improve the stretchability of the stretchable circuits while maintaining electrical integrity. The conductor is “interlaced” with the elastic substrate. The shape of the conductor is loop-like configuration. Knitted elastic substrate is proposed for high flexibility, stretchability, low cost and simple fabrication.
EXPERIMENT The conductor was silver coated nylon yarn composed of 24*2 filaments with a diameter of 0.2mm from Xiamen Unibest Import and Export Co., Ltd, China. From the SEM microphotographs in figure 1, the surface of every filament is very smooth. We used this conductor because it is flexible enough to be knitted into fabric-like structure and highly stretchable. A plain knitted fabric made by polyester multifilament was used as the elastic substrate. The dielectric constant of the polyester is 3.2, and it has been widely used in flexible circuit technology for a long period.
(a). Multi-filaments (b). Monofilament Figure 1. SEM images of silver coated ny
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