Initial Development of a Portable Acoustic Array on a Large-Scale E-Textile Substrate
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Initial Development of a Portable Acoustic Array on a Large-Scale E-Textile Substrate K.A. Luthy, L.S. Mattos, J.C. Braly, E. Grant, J.F. Muth Center for Robotics and Intelligent Machines, Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC A. Dhawan, K. Natarajan, T. Ghosh, A. Seyam Department of Textile and Apparel Technology and Management, North Carolina State University, Raleigh, NC Abstract Electronic textiles offer possibilities for producing large-area sensors circuits on conformal substrates. To demonstrate this concept, a 5x4 element acoustic array was produced on a 3m x 1m fabric substrate. In the course of fabricating the acoustic array a variety of production issues were identified that impacted the performance of the prototype when experimental tests were carried out with this prototype acoustic array. Fabric-based acoustic array design and production, along with design issues related to scaling an acoustic array to handle larger numbers of microphones on large-area fabrics, are the focus of this paper. 1. Introduction The focus of this paper is the development of a portable acoustic array produced on a textile substrate. The research proved that it is possible to integrate the technologies of electronics and textiles (e-textiles) and produce large-area sensor arrays on fabric substrates. Primary advantages of these fabric-based large-area sensor arrays are: (1) their ability to conform to their surroundings, e.g., surfaces like a tent or a truck cover, (2) they can be camouflaged to suit their surroundings, (3) they are generally lightweight, easily deployed and easily transported. This paper highlights advantages of developing and applying e-textile acoustic arrays for use in tracking targets via beam-forming and triangulation to accurately locate targets. In developing this system researchers at NC State University, sponsored by the DARPA MTO Division and conjunction with Draper Laboratories, addressed several electronics and textile integration to successfully produce their portable acoustic array. Such issues included: producing designs for circuits that covered large areas, the formation of interconnects within the textile, maintaining signal integrity, the integration of electronic elements within the textile, and the development of algorithms and software specifically for portable acoustic arrays. 2. Acoustic triangulation and beam-forming methods Triangulation techniques are used to calculate the position of a sound source based on time delay measurements and on geometric relationships. Many acoustic triangulation algorithms exist, but they all are limited by the geometric arrangement of the acoustic array. If the acoustic array dimensions are small, it is difficult to precisely measure time delays associated with low frequency sound sources. Also, acoustic arrays with small dimensions do not allow for sensor redundancy, due to the lack of useful space to add additional sensors. For example, with a twodimensional array, only the relative azim
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