Fig. 2: Design features of a multi-axial sensor.

a Schematic illustration of a tri-layered cantilever strain gauge (PI/Au/PI) on glass with a cavity, and b microscopic image of Au trace of the strain gauge. c Cross-sectional schematic illustration of the multi-axial sensor. d FEA results of the multi-axial sensor under a pressure of 10 kPa and a shear stress of 10 kPa. e Photograph of top view of the multi-axial sensor consisting of four cantilevers without a soft cover. f Schematic illustration and (g) photograph of three-axis testing machine, including XYZ-axis actuator and XYZ-axis load cell to apply and measure pressure and shear stress.