Tunable piezoresistivity of low percolation threshold micro-nickel wires/PDMS conductive composite regulated by magnetic field

High-performance flexible pressure sensors with tunable piezoresistivity are proposed with percolative composites as a single sensing layer using micro-nickel (μNi) wires as the conductive filler and polydimethylsiloxane (PDMS) as the matrix. The μNi wires were dispersed in PDMS and cured in a magnetic field of 17 mT to align the μNi wires along the direction of the magnetic field. An ultra-low percolation threshold (0.31 vol%) has been achieved, which is more than an order of magnitude lower than the 4.79 vol% of the control sample without a magnetic field. The pressure sensor with microhump structures based on Ni@PDMS composites with a volume fraction of 0.6 vol% molded by sandpaper exhibited ultrahigh averaged sensitivity (8706 kPa⁻¹), a wide sensing range of 1 kPa to 120 kPa and a fast response time of ∼22 ms. The sensor was used to monitor different frequencies and flow rates of water flowing in a pump-driven system that mimics the pulsatile behavior of the coronary artery, and judge whether the graft vessel is blocked or not, showing high potential for application in clinical diagnosis.