Recent advances in flexible force sensors and their applications: a review

In this paper, five sensing mechanisms including capacitive, piezoresistive, inductive, piezoelectric, and optical are reviewed in details with representative literature. Basic functions of flexible force sensors (such as normal force, shear force, shear angle, torsional angle, and rotational angle) with additional physical quantities (such as environmental temperature, gesture, vibration, and bending) are discussed and categorized clearly in this article. In addition, materials used in the flexible force sensors as electrodes, substrates, and deformable dielectrics are also highlighted and summarized. Furthermore, structural design, specifications of sensitivity, spatial resolution, dynamic window and cyclic life are unambiguously outlined. Meanwhile, key design considerations are listed and evaluated in this review to indicate major contributions to the characteristics of the flexible force sensors. Notable challenges, potential business, and examples of commercial players in the market are also listed. This article offers a stepping stone for those who plan to enter this fields by revisiting the outcomes from the past decades.