Flexible Ultra-Thin Nanocomposite Based Piezoresistive Pressure Sensors for Foot Pressure Distribution Measurement

Abstract

Foot pressure measurement plays an essential role in healthcare applications, clinical rehabilitation, sports training and pedestrian navigation. Among various foot pressure measurement techniques, in-shoe sensors are flexible and can measure the pressure distribution accurately. In this paper, we describe the design and characterization of flexible and low-cost multi-walled carbon nanotubes (MWCNT)/Polydimethylsiloxane (PDMS) based pressure sensors for foot pressure monitoring. The sensors have excellent electrical and mechanical properties an show a stable response at constant pressure loadings for over 5000 cycles. They have a high sensitivity of 4.4 kΩ/kPa and the hysteresis effect corresponds to an energy loss of less than 1.7%. The measurement deviation is of maximally 0.13% relative to the maximal relative resistance. The sensors have a measurement range of up to 330 kPa. The experimental investigations show that the sensors have repeatable responses at different pressure loading rates (5 N/s to 50 N/s). In this paper, we focus on the demonstration of the functionality of an in-sole based on MWCNT/PDMS nanocomposite pressure sensors, weighing approx. 9.46 g, by investigating the foot pressure distribution while walking and standing. The foot pressure distribution was investigated by measuring the resistance changes of the pressure sensors for a person while walking and standing. The results show that pressure distribution is higher in the forefoot and the heel while standing in a normal position. The foot pressure distribution is transferred from the heel to the entire foot and further transferred to the forefoot during the first instance of the gait cycle.

Microfluidic Wearable Devices for Sports Applications

“…Moreover, Rajendran (2021) discerned a correlation between athletes’ psychological challenges and gait imbalances [ 133 ]. By monitoring athletes’ gait distribution, potential psychological impediments can be identified, paving the way for optimized competitive performance.…”

Rational Design of Flexible Mechanical Force Sensors for Healthcare and Diagnosis

“…However, it remains challenging to improve the sensors performance from multiple aspects simultaneously and realize the on-demand design of mechanical force sensors for specific application scenarios. As shown in Figure 1 , many applications in healthcare and diagnosis are opened up by developments of flexible mechanical force sensors, including pulse wave [ 110 , 111 , 112 , 113 , 114 , 115 ] and muscle softness detection [ 116 ], ICP and IOP measurement [ 117 , 118 , 119 ], throat and cardiac activity monitoring [ 55 , 120 ], abdomen and pulse diagnoses [ 121 , 122 ], as well as force sensing in orthotics [ 123 , 124 ], orthodontics [ 125 ] and skin-prosthesis interface [ 64 ]. While many excellent reviews of flexible pressure sensors can be found in the literature [ 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 , 135 , 136 , 137 , 138 , 139 , 140 , 141 , 142 ], they focus mainly on the working mechanisms, material selections and device performances.…”

Soft CNT-Polymer Composites for High Pressure Sensors

“…To measure pressures in the range of 1–100 atm (approximately 0.1–10 MPa), an elastomer with a high Young’s modulus is needed to avoid complete compression within the pressure range, while sensors implementing Polydimethylsiloxane (PDMS) as the matrix have had success with implenting sensors over a wide range of pressures [ 14 , 15 , 16 , 17 ], and the pressure range of interest in this work far exceeds what PDMS is capable of. The maximum Young’s modulus of PDMS (as a function of the monomer to curing agent ratio) has been shown to be 2–3 MPa [ 18 , 19 ].…”