SwitchBack: an on-body RF-based gesture input device

We present SwitchBack, a novel e-textile input device that can register multiple forms of input (tapping and bi-directional swiping) with minimal calibration. The technique is based on measuring the input impedance of a 7 cm microstrip short-circuit stub consisting of a strip of conductive fabric separated from a conductive fabric ground plane (also made of conductive fabric) by a layer of denim. The input impedance is calculated by measuring the stub's reflection coefficient using a simple RF reflectometer circuit, operating at 900MHz. The input impedance of the stub is affected by the dielectric properties of the surrounding material, and changes in a predictable manner when touched. We present the theoretical formulation, device and circuit design, and experimental results. Future work is also discussed.

[1]  H. A. Wheeler.  Transmission-Line Properties of a Strip on a Dielectric Sheet on a Plane , 1977 .

[2]  Thad Starner,et al.  The Textile Interface Swatchbook: Creating graphical user interface-like widgets with conductive embroidery , 2010, International Symposium on Wearable Computers (ISWC) 2010.

[3]  A. A. Moreira,et al.  Belt antenna for wearable applications , 2009, 2009 IEEE Antennas and Propagation Society International Symposium.

[4]  Patrick Baudisch,et al.  Modular and deformable touch-sensitive surfaces based on time domain reflectometry , 2011, UIST.

[5]  Jan O. Borchers,et al.  Pinstripe: eyes-free continuous input on interactive clothing , 2011, CHI.

[6]  Maggie Orth,et al.  Smart fabric, or "wearable clothing" , 1997, Digest of Papers. First International Symposium on Wearable Computers.

[7]  R. Kaul,et al.  Microwave engineering , 1989, IEEE Potentials.

[8]  Leah Buechley,et al.  A Construction Kit for Electronic Textiles , 2006, 2006 10th IEEE International Symposium on Wearable Computers.

[9]  Halley Profita,et al.  Textile Interfaces: Embroidered Jog-Wheel, Beaded Tilt Sensor, Twisted Pair Ribbon, and Sound Sequins , 2012, 2012 16th International Symposium on Wearable Computers.

[10]  Albrecht Schmidt,et al.  Evaluating capacitive touch input on clothes , 2008, Mobile HCI.

[11]  Zamora,et al.  Electronic textiles: a platform for pervasive computing , 2003, Proceedings of the IEEE.

[12]  Balasundar I Raju,et al.  3-D finite-element models of human and monkey fingertips to investigate the mechanics of tactile sense. , 2003, Journal of biomechanical engineering.

[13]  R. Langley,et al.  Dual-Band Wearable Textile Antenna on an EBG Substrate , 2009, IEEE Transactions on Antennas and Propagation.

[14]  S. S. Stuchly,et al.  Analysis of a Microstrip Covered with a Lossy Dielectric , 1980 .

[15]  N. Spyrou,et al.  In vivo dielectric properties of human skin from 50 MHz to 2.0 GHz. , 1988, Physics in medicine and biology.