Figure 1. Overview of the gesture-recognition wristband (GRW):
a) Configuration of the proposed GRW. b) Schematic illustration of a
single nanofiber-based pressure-sensor unit. c) Cross section of the
wrist with GRW. d) Photograph of the GRW.
One key to the success of the GRW in this work is its highly sensitive
NFPSU, as shown in Figure 1b . It consists of a filmy
optical-nanofiber sensor, a soft liquid sac, and a rigid
three-dimensional (3D)-printed resin shell. The optical nanofiber,
serving as a light waveguide to detect skin deformation with high
sensitivity, is U-shaped for increased compactness and is encapsulated
by polydimethylsiloxane (PDMS) films (length: 21 mm; width: 14 mm;
thickness: 200 μm) to form a filmy optical nanofiber sensor. A soft
liquid sac (length: 27 mm; width: 23 mm; thickness: 2.5 mm) filled with
glycerol is sealed by the filmy optical nanofiber sensor; it is used to
transfer the applied pressure due to skin deformation to the optical
nanofiber. The rigid 3D-printed resin shell is designed to isolate the
sensor from mechanical stimuli other than those generated by finger
movements. The sac base (length: 6 mm; width: 6 mm; thickness: 200 μm)
penetrates the hole in the center of the resin shell to contact the skin
surface and collect pressure signals. To analyze the relationship
between hand gestures and the related tendon movements, two NFPSUs are
positioned on the dorsal wrist (back side) and one on the volar wrist
(palm side), respectively (Figure 1c ). Using only these three
NFPSUs, twelve typical hand gestures can be recognized. To make the GRW
suitable for testers with different physiques, we used elastic straps to
connect the three NFPSUs as shown in Figure 1d . Each NFPSU has
dimensions 3×2.5×0.3 cm3 (comparable to a coin) and
can be comfortably worn on the wrist.