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Tri-axial plantar pressure sensor: design, calibration and characterization

A novel tri-axial plantar pressure sensor has been developed. This sensor simultaneously measures vertical plantar pressure and anterior-posterior and medial-lateral shear plantar pressures utilizing a central post, four parallel plates, and a commercial miniature pressure transducer. As a subject walks over the sensor, the central post is deflected and the shear pressures are measured utilizing capacitive sensing technology. The miniature pressure transducer (MPT) is simultaneously loaded to measure the vertical pressure. Each individual tri-axial plantar pressure sensor has the capability of measuring shear forces ranging from 0 to 15 N and vertical pressures ranging from 0 to 28 MPa. The shear component of the tri-axial pressure sensor has a sensitivity of 1.3 mV/g, a non-linearity of 8.3 %, and hysteresis of 7.3 %. The commercial vertical MPT has a sensitivity of 220 nv/V/psi, a non-linearity of 0.094%, and a hysteresis of 0.567%. An array of individual tri-axial plantar pressure sensors in the form of a platform will be developed to measure plantar pressure in patients. This pressure platform is placed on the surface of a walkway and is suitable for barefoot walking trials.