A flexible 2D piezoresistive shear and normal force sensor array for pressure mapping applications

Abstract

Biology, information science, and material science are considered to be the fastest growing and the hottest research areas in the 21st century. The collection, transmission, and processing of information are the pillars of modern information technology. Sensor technology, also considered the source of information technology, is the foundation for the development of modern science, and it has been widely applied in various disciplines. Micromachined sensors and actuators have been studied and industrially produced for more than twenty years. However, the obtention of information pertaining to normal and shear force acting on non-planar surfaces has been a significant challenge for a long time. The current study aims at developing an effective method to fabricate the flexible force sensor. To achieve this, the work should be focused on the following objectives: 1) To study the feasibility of the proposed method for building the force sensor; 2) To develop an effective technique to fabricate normal and shear force sensor samples with comparable qualities. In the existing report, we propose a two-dimensional normal and shear force sensor array by using liquid metal alloy as the strain gauge. For the realization of the sensor, Polydimethylsiloxane (PDMS) is used as a substrate, which makes the sensor flexible. Each sensing element comprises two symmetric piezoresistive sensing cells. They are screen-printed on the cavity of PDMS substrate with tilt angle around 30° such that they are sensitive to the shear force. The serpentine design enables the increase in the resistance of the metal gauge wire to reduce the self-heating effect from joule heating caused by the application of an electrical current. By using liquid metal alloy as gauge material, the sensor can detect large forces without fracturing the sensor wires. The liquid metal sensing cells deform with the elastic body, therefore, shear and normal forces can be detected based on the resistance changes of the liquid-metal strain gauge. The line width of the strain gauge is around 100 ~ 200 μm, and the force range of the sensor element is between 0 to 20 N. The results show that the sensor array has a lower hysteresis effect when applying force at lower speed.