High-Sensitivity\nFlexible Sponge Sensor Capable of\nSensing Tiny Pressures with a Surface Microstructure

Piezoresistive sensors are widely used because of their\nsimple\nfabrication process and low cost, and their performance is usually\nimproved via a single method, such as creating microstructures or\nadjusting material mechanical properties. In this study, when the\ntwo methods are combined, a high-sensitivity flexible sponge sensor\ncapable of sensing tiny pressures with surface hemispheres was designed,\nand mathematical models for its sensing response caused by compression\ndeformation were established. Hydroxylated carbon nanotubes (CNT-OH)\nmodified with carbon nanotubes (CNTs) were filled in a polydimethylsiloxane\n(PDMS) matrix, along with a poreformer, and poured into a mold to\nobtain a CNT-OH/PDMS sponge piezoresistive layer with a hemispherical\narray on its surface. The deformation equation of the piezoresistive\nlayer under external pressure, the function of the contact area between\nthe surface hemispherical array and the electrode, and the sensitivity\nmodel of the sensor were subsequently established. The effects of\nthe material porosity and diameter of the surface hemispherical array\non the performance of the sensor were investigated. An increase in\nthe material porosity and a decrease in the hemispherical diameter\nof the piezoresistive layer are helpful for improving the sensitivity\nof the sensor and its ability to detect tinier pressure. The measurement\nrange and response time of the sensor are determined mainly by the\nmechanical properties of the piezoresistive layer material. These\nexperimental results were consistent with our theoretical conclusions.\nThis sensor can accurately detect the number of seeds sown by agricultural\nseeders each time and can identify the frequency of human vocal cord\nvibrations, pulse beats, and wrist movements.