Micro-Electro-Mechanical-Fiber Devices for Touch-sensing

By Freddy White on March 24, 2017

How functional can fibers become? In their recent Journal of Physics D: Applied Physics Paper, published as part of our Emerging Leaders special issue, Fabien Sorin et al investigate. To hear more in the authors’ own words, read on.

Smart textiles and advanced fabrics will play an increasingly important role in the functionalization of our environment via health monitoring, sensing or energy harvesting. Beyond the integration of small devices within fabrics, the future of smart textiles and garments will rely in part on the functionalization of each fiber forming the fabric. Therefore, developing innovative techniques for the fabrication of fibers with multi-material and complex architectures is vital for the development of the next generation of advanced textiles.

The thermal drawing technique, also used to fabricate optical fibers, can be exploited to this end. Compared to other fiber processing approaches, thermal drawing relies on the deformation at high viscosity of a macroscopic preform that represents a scaled up version of the targeted fiber. One key attribute of the technique is the ease of creating such a preform at the millimeter level, by the simple and straightforward assembly of a wide range of materials within complex architectures. The subsequent thermal drawing results in a fiber with sub-micrometer features in its cross-section, uniformly maintained over kilometers of fiber length. Thermally drawn fibers capable of electronic, optoelectronic, piezoelectric, or energy harvesting functions have been demonstrated with this approach.

In this work, we exploited for the first time the integration of freely movable domains in the fiber cross-sectional structure to fabricate a cantilever-like touch-sensing micro-electro-mechanical-fiber (MEMF) device. The device consists of a thin conducting polymer composite sheet above a conducting bus, as showed in the SEM picture in Figure 1. Under mechanical pressure, the conducting sheet can bend and be brought in contact with the bus, generating an electrical signal that can reveal the pressure. Via modeling the interplay between surface tension and viscosity during processing, we show that the feature sizes of the sheet and the bus can be chosen such that the deformation time constant associated with the reflow and capillary breakup is much longer than its processing time, resulting in a perfect preservation of the cross-section.

Figure 1: Proof of concept “piano device”. By connecting a fiber segment to a voltage divider circuit the device extracts the electrical resistance and hence the position of the touch. Image adapted from Tung Nguyen-Dang et al 2017 J.Phys. D: Apply. Phys. 50 144001

Our device demonstrated the capacity of multipoint detection and localization of touch along the entire fiber length with sub-millimeter resolution, in excellent agreement with our model. The fiber exhibited a response bandwidth of close to 20 kHz that remained unaltered after loading cycles at 200 Hz. Beyond the simplicity and scalability of the fabrication process, MEMF devices are the first one-dimensional touch-sensing systems, superseding two-dimensional grids at a very low energetic consumption and with a high resolution. As a proof of concept, we made a “piano device” by connecting a fiber segment to a voltage divider circuit to extract the electrical resistance, hence the position of the touch (see Figure 1). This highly flexible, robust and sensitive fibers represent significant opportunities for smart textiles and wearable electronics.

Biography:

Professor Fabien Sorin studied Physics at Ecole Polytechnique in France, and obtained his PhD from the department of Materials Science at the Massachusetts Institute of Technology (MIT), Cambridge, USA. After 3 years at the Research Laboratory of Electronics at MIT, he joined the company Saint-Gobain as a research scientist in Aubervilliers, France. In 2013, he joined the Ecole Polytechnique Fédérale de Lausanne (EPFL, Switzerland) as an assistant professor in the Institute of Materials. His research interests lie in investigating innovative materials, fabrication methods, and nanoscale device architectures to integrate advanced photonic and electronic functionalities within one-dimensional fibers and two-dimensional flexible and stretchable substrates.

Tung Nguyen Dang is a PhD student in the group led by Prof. Fabien Sorin at EPFL. His research interests lie in the field of the surface and interface of materials, as well as in the fabrication of micro/nano-structure on large-are substrates. Prior to his doctoral study, he graduated from the Ecole Polytechnique in Paris (BS. and MSc.), and was a research engineer in Saint-Gobain, working on the coating of smart windows via sputtering.

Alexis Page is a PhD student in the group led by Prof. Fabien Sorin at EPFL. His research interests lie in the electronic and rheological properties of nanocomposites, as well as in their application in functional devices. Prior to his doctoral study, he graduated from the Ecole Polytechnique in Paris (BS. and MSc.) and the University of Cambridge (Master’s degree in materials science).

This work is licensed under a Creative Commons Attribution 3.0 Unported License. Image adapted from Tung Nguyen-Dang et al 2017 J. Phys. D: Appl. Phys. 50 144001. (C) IOP Publishing, All Rights Reserved.