Flexible Fringe Effect Capacitive Sensors with Simultaneous High‐Performance Contact and Non‐Contact Sensing Capabilities

Abstract

To mimic human touch sensing, robotics must be able to leverage multiple sensory inputs. Previously, to achieve both proximity and pressure sensing, most approaches have required using two separate sensors, each with their corresponding electronics, limiting the achievable density. More recently, sensors with multifunctional pressure and proximity capabilities have been realized at the cost of compromised pressure sensing. Presented here is a new design for a multifunctional interdigitated fringe field capacitive pressure sensor with a pyramid microstructured dielectric layer that has proximity‐sensing capabilities (noncontact mode) while also sensing pressure (contact mode) as strongly as an equivalent parallel plate capacitive sensor of the same size. In contact mode, both sensors have a response time of less than 20 ms and can respond to loads lighter than 0.5 Pa. Further, the interdigitated fringe field sensor can clearly distinguish between the two sensing modes, as well as between conductive and nonconductive materials in the noncontact mode. Finally, we use the interdigitated fringe field sensor to demonstrate both proximity and high‐sensitivity pressure sensing on a robotic gripper.

Recent Progress on Flexible Capacitive Pressure Sensors: From Design and Materials to Applications

“…Prof. Z. Bao group from Stanford University showed the first demonstration of flexible capacitive pressure sensors using the shape and size optimization, pillar orientations, and combination of micro‐pillers and micro‐bumps technique. [ 104,105,110,135 ]…”

Post-surgical wireless monitoring of arterial health progression

“…In this case, we used a capacitive pressure sensor where the electrodes are planar to capitalize on the capacitive fringe field. We previously demonstrated both computationally and experimentally that fringe-field sensors are capable of proximity sensing by objects disrupting the fringe field (Ruth et al, 2020a). In this case, we used an interdigitated electrode design to increase the number of fringing capacitances, thus increasing the strength of the electric field and consequently the proximity sensing sensitivity.…”

“…This is important because depending on the diameter of the artery and its location in the body, the sensor may only come in partial contact with the artery when surgically implanted. We use pyramidal elastic microstructures since they significantly increase sensor sensitivity compared to bulk material and other microstructure shapes (Figure 1E) (Mannsfeld et al, 2010;Ruth et al, 2019Ruth et al, , 2020aRuth et al, , 2020bRuth and Bao, 2020).…”

“…We use a polyimide substrate (thickness 80 mm), which has demonstrated in vitro and in vivo biocompatibility (Hiebl et al, 2010;Richardson et al, 1993;Sun et al, 2009). We chose a lower-modulus PDMS (23:1) for the pressure-responsive element because of its biocompatibility, low compressive modulus for high pressure sensitivity, and negligible pressure response hysteresis (Beker et al, 2020;Ruth et al, 2020a). In this work, we found non-statistically significant differences in terms of tissue inflammation between PDMS, polyimide, poly(octamethylene maleate (anhydride) citrate (POMaC), and control at 1 week and 12 weeks (Figure S1; Tables S1 and S2).…”

“…The resonance frequency of the LC circuit is determined by the value of capacitance (C) and inductance (L). In our previous work, the capacitive pressure sensor had an initial capacitance of 1.79 G 0.15 pF (Ruth et al, 2020a). We then designed a miniaturized antenna coil with the dimensions <1 mm 3 1 mm for minimally invasive surgery.…”