Fig 1.
Schematic representation of process used to fabricate inkjet-printed SWCNT thin film on PDMS substrate using aqueous SWCNT ink.
Fig 2.
Measurement of finger joint motion using fabricated strain sensor.
(a) The 18-mm-long middle segment of the strain sensor was placed directly over the 3rd MCP joint. (b) The hand was placed next to a conventional goniometer (protractor), and the subject was told to flex his fingers at the MCP joint level at predetermined angles of 20°, 45°, 60°, and 90°. (c) A variable resistor was used to measure the change in the resistance between two electrodes during flexion movement of the MCP joint.
Fig 3.
(a) Schematic illustration of SWCNT-PDMS substrate (SWCNT thin film indicated in dark gray), (b) SEM image of SWCNT thin film, (c) relationship between resistance change and time for sensor under 80% strain, and (d) piezoresistive response over 1000 loading–unloading cycles under 60% strain.
Fig 4.
Microstructure of SWCNT strain sensor (a) just after fabrication, (b) after 100 cycles under 80% strain, and (c) after 100 cycles under 120% strain.
Fig 5.
Initial resistance of the sensor at different states; (a) 60°C, (b) 25°C, (c) 25°C with high humidity. Resistance values are marked in yellow; temperature values are marked in red. (d) Resistance variations of SWCNT-based strain sensor under 80% strain (black circles: before water spraying, red circles: after water spraying).
Fig 6.
Changes in resistance in various ranges of joint movements.
Relative changes in resistance are plotted versus time for the flexion and extension movements of the MCP joint. Here, Ra: initial value of resistance in resting state (neutral position of MCP joint) and Rb: resistance value at predetermined flexion angle.
Fig 7.
Relationship between change in sensor length and angle of MCP joint for subject no. 12 shown as an example.
(a) High linearity of the correlation (R2 = 0.9751, p = 0.000) between the MCP joint flexion angle (x-axis) and the change in the length of the strain sensor (y-axis) is observed when the finger is flexed 20 times each at 20°, 45°, 60°, and 90°. (b) High linearity of the correlation (R2 = 0.9475, p = 0.000) between the MCP joint flexion angle and the change in the length of the strain sensor is also observed when the 3rd MCP joint is flexed 20 times at random angles between 0° and 90°.