Shear-Force Sensors on Flexible Substrates Using Inkjet Printing

Abstract

Printing techniques are a promising way of fabricating low-cost electronics without the need for masking and etching. In recent years, additive printing techniques, such as inkjet and screen printing, have been adopted to fabricate low-cost and large-area electronics on flexible substrates. In this work, a three-axial normal and shear force sensor was designed and printed that consists of four miniaturized, printed capacitors. The partially overlapping electrodes are arranged in a manner, so that force sensitivity in orthogonal directions is achieved. A silicone rubber is used as an elastic dielectric and spacer between the two electrodes. The base unit of this sensor has been fabricated using inkjet printing and characterized for normal and shear forces. The force response was investigated in a force range from 0.1 N to 8 N, the normal-force sensitivity was determined to be Sz=5.2 fF/N, and the shear-force sensitivity was Sy=13.1 fF/N. Due to its sensing range, this sensor could be applicable in tactile sensing systems like wearables and artificial electronic skins.

Recent Advances in Printed Capacitive Sensors

“…When the array of sensors was characterized, displaying each of the array element in a different orientation, the shear force sensitivity to normal forces is quadrupled while the one to shear forces is doubled. The performances were comparable to previous sensors in the literature with the peculiarity that only additive deposition techniques with cost-effective materials were employed in this work [99]. Another example of a printed capacitive pressure sensor on a flexible substrate was described by Joo et al [100].…”

An Atlas for the Inkjet Printing of Large-Area Tactile Sensors

“…Inkjet printing technologies have been widely used for the development of flexible electronics as they offer a fabrication alternative to lithography-based approaches [ 68 , 98 ], introduce the use of new intrinsically stretchable inks [ 39 , 97 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 ], and avoid the challenges related to the brittleness of traditional materials used to manufacture tactile sensors [ 7 , 82 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 ,…”

“…Inkjet printing technology facilitates the utilization of a variety of flexible substrates for various designs [ 31 ]. Polyethylene terephthalate (PET) is widely used as a flexible substrate for inkjet-printed capacitive sensors [ 100 , 129 , 137 , 142 ]. Furthermore, printed electronics on paper allows the implementation of flexible sensors, and it has been used to manufactured printed capacitive sensors in [ 99 , 130 , 131 ].…”

Printed flexible mechanical sensors

“…Fabrication of flexible mechanical sensors by printing technologies have emerged as a versatile, economical, and enabling approach. For instance, various types of mechanical sensors (e.g., force, [33][34][35] pressure, [36][37][38][39][40] and strain [41][42][43][44][45][46] ) can be produced by leveraging many 2D/3D printing techniques including but not limited to screen printing, [47][48][49][50][51] inkjet printing, [52][53][54][55][56] direct ink writing (DIW), [57][58][59] digital light processing (DLP), [60][61][62] and fused filament fabrication (FFF). [63][64][65][66] The additive nature of printing technologies also largely reduces the fabrication cost and time; 67,68 in addition, fabrication by printing enabled the production of flexible mechanical sensors with excellent performance.…”