Flexible tensile strain-pressure sensor with an off-axis deformation-insensitivity

The high demand for flexible force sensors with both strain and pressure sensing has attracted considerable attention for various application scenarios, such as electronic skins and smart prostheses. However, successful application of these sensors in real-world is challenging because the performance of the sensors can be severely degraded under applied off-axial deformations (e.g., bending and twisting) and it is also difficult to successfully decouple these signals due to electromechanical crosstalk. Here, we developed an integrated sensor patch (ISP) consisting of a strain sensor insensitive to pressure, bending and twisting, coupled with a pressure sensor insensitive to tension, bending and twisting. Benefiting from the serpentine structure and bionic design of strain sensor material, as well as the inherent rigidity properties of the piezoelectric ceramic, the resulting patch exhibits insensitivity to off-axis sensing with independent tensile strain and out-of-plane pressure sensing capabilities. The patch achieves a wide range of tensile strains (up to 160% with an apparent pressure coefficient of over 1.23) and a wide range of pressures (1 Pa to 100 kPa). We demonstrate that the wearable ISP can interact human gestures with the robotic hand in real time through a fully soft integrated glove and further continuously record wrist activity to verify tensile strain sensing independent of pressure mode. In addition, the ISP successfully captures the subtle strain of less than 20% of eye blinks and the ultra-low pressure of less than 1.2 kPa of unobtrusive exhalation force with low off-axis interference. Moving forward, this strategy of endowing sensors with off-axis sensing insensitivity and decoupled strain and pressure sensing has great potential in human-machine interface (HMI), virtual reality (VR)/augmented reality (AR) user interfaces, and other soft electronics fields.