High-Performance Interface Electronic System for a 13 $\,\times\,$13 Flexible Biomechanical Ground Reaction Sensor Array Achieving a Gait Ground Velocity Resolution of 100 $\mu{\rm m/sec}$

This paper describes a high-performance interface electronics system design for a high-density flexible biomechanical ground reaction sensor array (GRSA). The prototype system can be incorporated into a personal boot heel to measure real-time ground force, shear strain, and sole deformation associated with a human bipedal locomotion, thus providing zero-velocity correction to an inertial measurement unit placed in a close proximity. This approach can greatly reduce inertial error accumulation and improve positioning accuracy. The sensing electronics consist of a front-end multiplexer that can sequentially connect individual sensing nodes from a 13 × 13 GRSA to a capacitance-to-voltage converter followed by a 12-bit algorithmic ADC with a sampling rate of 66.7 k-samples/s. The entire sensor array can be scanned within 10 ms. The GRSA employs capacitive sensing scheme and is fabricated using PDMS deformable dielectric layer. The integrated sensing electronics are fabricated in XFAB 0.35 μm CMOS process and dissipate 3 mW power. The overall system sensing resolution is limited by electrical interferences coupled through long interconnect traces between a GRSA and an electronic sensing module. Dynamic and static pressure testing shows the prototype system functionality achieving a gait ground velocity sensing resolution of 100 μm/s.