A Polymer-Based Capacitive Sensing Array for Normal and Shear Force Measurement

Abstract

In this work, we present the development of a polymer-based capacitive sensing array. The proposed device is capable of measuring normal and shear forces, and can be easily realized by using micromachining techniques and flexible printed circuit board (FPCB) technologies. The sensing array consists of a polydimethlysiloxane (PDMS) structure and a FPCB. Each shear sensing element comprises four capacitive sensing cells arranged in a 2 × 2 array, and each capacitive sensing cell has two sensing electrodes and a common floating electrode. The sensing electrodes as well as the metal interconnect for signal scanning are implemented on the FPCB, while the floating electrodes are patterned on the PDMS structure. This design can effectively reduce the complexity of the capacitive structures, and thus makes the device highly manufacturable. The characteristics of the devices with different dimensions were measured and discussed. A scanning circuit was also designed and implemented. The measured maximum sensitivity is 1.67%/mN. The minimum resolvable force is 26 mN measured by the scanning circuit. The capacitance distributions induced by normal and shear forces were also successfully captured by the sensing array.

Experimental and numerical estimations into the force distribution on an occlusal surface utilizing a flexible force sensor array

“…A number of miniaturized force sensors fabricated using micro-electromechanical system (MEMS) technologies have been developed on flexible substrates, such as polyimide (PI) (Engel et al, 2003), polydimethylsiloxane (PDMS) (Lee et al, 2008) and polyvinylidene fluoride (PVDF) (Wang and Huang, 2000), for measuring force distribution over a surface. Flexible sensor arrays have been widely used as tactile sensors for measuring contact force and grab force (Cheng et al, 2010;Chuang et al, 2008). Alternatively, optical force sensors have also been used for the normal and shear force measurements (Huang et al, 2007).…”

Large deformation mechanics of a soft elastomeric layer under compressive loading for a MEMS tactile sensor application

“…Many MEMS based tactile sensor have been designed and fabricated [1,18,19,20,21]. In these sensors, silicondiaphragm structures are frequently used for measuring contact forces [22,23,24,25].…”

“…The electrodes are usually embedded in gel (PDMS) [1,18,20,21,26,27] in pair arrangements for sensor capacitance measurements. As established elsewhere [28,29] the capacitance between two electrodes is proportional to the electrode overlapping area while inversely proportional to the spacing distance between electrodes.…”

Dielectric Elastomer Sensors

“…The electronic conductors used as compliant electrodes in sensors mainly include carbon-based electrodes [11,34], metallic thin films [35], composites of conducting materials and elastomers (or rubber fiber mats) [36], conducting films (indium-tin oxide (ITO)-coated poly (ethylene terephthalate (PET)) [37] and liquid conductors [38].…”