Recent Development of Flexible Tactile Sensors and Their Applications

Abstract

With the rapid development of society in recent decades, the wearable sensor has attracted attention for motion-based health care and artificial applications. However, there are still many limitations to applying them in real life, particularly the inconvenience that comes from their large size and non-flexible systems. To solve these problems, flexible small-sized sensors that use body motion as a stimulus are studied to directly collect more accurate and diverse signals. In particular, tactile sensors are applied directly on the skin and provide input signals of motion change for the flexible reading device. This review provides information about different types of tactile sensors and their working mechanisms that are piezoresistive, piezocapacitive, piezoelectric, and triboelectric. Moreover, this review presents not only the applications of the tactile sensor in motion sensing and health care monitoring, but also their contributions in the field of artificial intelligence in recent years. Other applications, such as human behavior studies, are also suggested.

Conducting Polymers for the Design of Tactile Sensors

“…The four types of operation principles currently used in tactile sensor application are piezoresistive, piezocapacitive, piezoelectric, and triboelectric [ 103 ]. These working mechanisms describe the tactile sensor operation that detects mechanical external stimuli.…”

“…It is the internal generation reaction of an electric field according to a change in dipole moment. The most important factor in this effect is the change in polarization under the action of an external force [ 103 ]. The triboelectric effect specifies contact electrification that occurs when a particular material is charged, after being separated from the surface of another material.…”

Shielded soft force sensors

“…Capacitive sensors are, however, very susceptible to the motion or simply the presence of nearby objects, as well as to low-level electromagnetic (EM) interference. Despite numerous studies and the well-known effect of external interference, existing soft capacitive sensors lack the electromagnetic shielding needed to allow operation near moving conductors, motors, or other source of time-varying electric fields 19 , 20 . This restricts the use of soft capacitive sensors to laboratory settings with carefully controlled environments.…”

3D-printed elastomer foam-based soft capacitive pressure sensors

“…Whilst several types of touch sensors have been explored, the ones working on the capacitive transduction method are most popular due to their simple structures and readout electronics [10]. Capacitive-based sensors offer high sensitivity for static or quasi-static contacts in the low-pressure range, which is typically needed in object handling [10][11][12][13]. To improve the conformability, soft and stretchable capacitive touch sensors have also been reported recently using elastomeric materials as dielectric or stretchable substrates [14][15][16][17][18][19].…”