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IEEE SENSORS JOURNAL, VOL. 12, NO. 8, AUGUST 2012

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Design and Fabrication of Soft Artificial Skin Using Embedded Microchannels and Liquid Conductors Yong-Lae Park, Member, IEEE, Bor-Rong Chen, Member, IEEE, and Robert J. Wood, Member, IEEE

Abstract— We describe the design, fabrication, and calibration of a highly compliant artificial skin sensor. The sensor consists of multilayered mircochannels in an elastomer matrix filled with a conductive liquid, capable of detecting multiaxis strains and contact pressure. A novel manufacturing method comprised of layered molding and casting processes is demonstrated to fabricate the multilayered soft sensor circuit. Silicone rubber layers with channel patterns, cast with 3-D printed molds, are bonded to create embedded microchannels, and a conductive liquid is injected into the microchannels. The channel dimensions are 200 µm (width) × 300 µm (height). The size of the sensor is 25 mm × 25 mm, and the thickness is approximately 3.5 mm. The prototype is tested with a materials tester and showed linearity in strain sensing and nonlinearity in pressure sensing. The sensor signal is repeatable in both cases. The characteristic modulus of the skin prototype is approximately 63 kPa. The sensor is functional up to strains of approximately 250%. Index Terms— Artificial skin, eutectic gallium indium (EGaIn), pressure sensing, soft sensors, strain sensing.

I. I NTRODUCTION

T

HE DEVELOPMENT of highly deformable artificial skin (Fig. 1) with contact force (or pressure) and strain sensing capabilities [1] is a critical technology to the areas of wearable computing [2], haptic interfaces, and tactile sensing in robotics. With tactile sensing, robots are expected to work more autonomously and be more responsive to unexpected contacts by detecting contact forces during activities such as manipulation and assembly. Application areas include haptics [3], humanoid robotics [4], and medical robotics [5]. Different approaches for sensitive skin [6] have been explored. One of the most widely used methods is to detect structural deformation with embedded strain sensors in an

Fig. 1. Soft artificial skin prototype showing its stretchability and deformability.

Manuscript received January 16, 2012; revised April 13, 2012; accepted May 1, 2012. Date of publication May 22, 2012; date of current version June 13, 2012. This work was supported in part by the Wyss Institute for Biologically Inspired Engineering, Harvard University, and the National Science Foundation Grant CNS 0932015. This is an expanded paper from the IEEE SENSORS 2011 Conference. The associate editor coordinating the review of this paper and approving it for publication was Prof. Boris Stoeber. Y.-L. Park is with the Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115 USA (e-mail: ylpark@wyss.harvard.edu). B.-R. Chen was with the School of Engineering and Applied Science, Harvard University, Cambridge, MA 02138 USA. He is now with Biosensics LLC, Cambridge, MA 02139 USA (e-mail: brchen@post.harvard.edu). R. J. Wood is with the School of Engineering and Applied Science, Harvard University, Cambridge, MA 02138 USA, and also with the Wyss Institute for Biologically Inspired Engineering, Harvard University, Boston, MA 02115 USA (e-mail: rjwood@eecs.harvard.edu). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/JSEN.2012.2200790

artificial skin. Highly sensitive fiber optic strain sensors have been embedded in a plastic robotic finger for force sensing and contact localization [7], [8] and in surgical and interventional tools for force and deflection sensing [9], [10]. Embedded strain gauges have been used in a ridged rubber structure for tactile sensing [11]. Detecting capacitance change with embedded capacitive sensor [12] arrays is another approach for tactile sensing, as shown in a human-friendly...
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