Research ArticleELECTRONICS

Bend, stretch, and touch: Locating a finger on an actively deformed transparent sensor array

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Science Advances  15 Mar 2017:
Vol. 3, no. 3, e1602200
DOI: 10.1126/sciadv.1602200
  • Fig. 1 Working principle and general properties.

    (A) Mutual capacitive coupling is simulated between two planar electrodes (shown in the inset without a finger). The coupling between electrodes is reduced by the presence of a finger, which acts as an electrode itself. (B) Finger approaching a pair of electrodes that are in the form of a loop and disc. The finger reduces the coupling between the electrodes (CM) by coupling itself with the projected field (CF is increased). (C) Two-dimensional array of loop-disc electrode pattern, with the loops on top. (D) Sensor array sitting above a forearm and a printed number pad. (E) Sensor array on an LCD with a video playing demonstrating transparency. Two edges of the sensor are indicated by the dashed lines. A third edge is just visible, extending perpendicular to the lower line. (F) Sensor array wrapped around a finger demonstrating conformity.

  • Fig. 2 Sensor fabrication and sensitivity.

    (A) Curing PDMS in a mold. (B) Plasma-bonding three layers forming perpendicular channels on top and bottom of the dielectric. (C) Injecting the monomer mixture inside the channels and polymerizing them to form the ionically conducting electrodes. (D) Map showing the localized change in capacitance due to a touch by a finger. (E) Change in capacitance due to a hovering finger at various distances from the top of the sensor. The change in capacitance upon approach of the finger is negative, as indicated.

  • Fig. 3 Touching while stretching and bending.

    (A) Plot showing the recorded displacement (7% strain) and capacitance of a single taxel in the sensor while being stretched by a sinusoidally varying displacement using a dynamic mechanical analyzer; the sharp drops in capacitance coincide with touch, while the sinusoidally varying changes are the result of the stretching. (B) Sensor in steady state. (C) Stable capacitance map for steady state. (D) Sensor folded in an anticlockwise direction. (E) Resulting small positive change in capacitance of the taxels along the axis of bend where capacitance increases with positive y axis. (F) Sensor being touched while being bent. (G) Negative change in capacitance map showing the taxel touched having a change in capacitance of 10%, reduced slightly by the change due to the bend where the capacitance decreases with positive y axis. (H) Sensor being bent in the clockwise direction. (I) Positive change in capacitance map showing the axis of bend and a similar response to that in (E).

  • Fig. 4 Swipe, multitouch, and augmented bend detection.

    (A) Swipe functionality of the sensor showing the negative change in capacitance following a movement across the row from left to right. (B) Detection of one (top), two (middle), and three (bottom) fingers simultaneously, demonstrating multitouch capability. (C) Diagram of the design and results from an augmented bend sensor (compared with the regular sensor with the neutral axis aligned with the dielectric), with the neutral axis aligned with the top electrode layer, which enhances the detection of bend (bottom left) but still enables the simultaneous detection of touch (bottom right).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/3/e1602200/DC1

    Effects of scaling on sensor

    Mechanical characterization: Cyclic loading

    fig. S1. Coplanar electrode capacitor with a finger.

    fig. S2. Finger on an array of capacitive sensors.

    fig. S3. Effect of scaling on change in capacitance along a row due to a touch at a single taxel.

    fig. S4. Steps of mechanical test.

    fig. S5. Plot showing change in capacitance in percentage due to a touch after cycles of 10% strain, followed by a buckling with a radius of curvature of 16 mm.

    movie S1. Video showing proximity detection.

    movie S2. Video showing the sensor being stretched and then being touched while being stretched.

    movie S3. Video showing the sensor being bent and a finger touching it while bending.

    movie S4. Video showing a finger moving across the sensor and the sensor’s response to it.

    movie S5. Video showing multiple fingers touching the sensor at multiple locations.

    movie S6. Video showing an accidental coffee spill on the sensor and continued functionality after wiping it clean.

    movie S7. Video showing a wrist gear made using this sensor and an LED grid under it to demonstrate potential use as part of a wearable device.

    Reference (38)

  • Supplementary Materials

    This PDF file includes:

    • Effects of scaling on sensor
    • Mechanical characterization: Cyclic loading
    • fig. S1. Coplanar electrode capacitor with a finger.
    • fig. S2. Finger on an array of capacitive sensors.
    • fig. S3. Effect of scaling on change in capacitance along a row due to a touch at a single taxel.
    • fig. S4. Steps of mechanical test.
    • fig. S5. Plot showing change in capacitance in percentage due to a touch after cycles of 10% strain, followed by a buckling with a radius of curvature of 16 mm.
    • Reference (38)

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • movie S1 (.mp4 format). Video showing proximity detection.
    • movie S2 (.mp4 format). Video showing the sensor being stretched and then being touched while being stretched.
    • movie S3 (.mp4 format). Video showing the sensor being bent and a finger touching it while bending.
    • movie S4 (.mp4 format). Video showing a finger moving across the sensor and the sensor’s response to it.
    • movie S5 (.mp4 format). Video showing multiple fingers touching the sensor at multiple locations.
    • movie S6 (.mp4 format). Video showing an accidental coffee spill on the sensor and continued functionality after wiping it clean.
    • movie S7 (.mp4 format). Video showing a wrist gear made using this sensor and an LED grid under it to demonstrate potential use as part of a wearable device.

    Files in this Data Supplement:

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