Progress and prospects in flexible tactile sensors

Piezoresistivity and strain-sensing behaviour of poly(butylene adipate-co-terephthalate)/multiwalled carbon nanotube nanocomposites

Multiwalled carbon nanotubes (MWCNTs) at different concentrations, ranging from 0.5 to 10 wt%, as a conductive filler, were incorporated into poly(butylene adipate-co-terephthalate) (PBAT), a flexible biodegradable copolyester, via melt-mixing, followed by compression moulding. The electrical conductivity of the prepared nanocomposites was evaluated by considering their volume resistivity value. The volume resistivity values of the nanocomposites suggested a quite low percolation threshold between the MWCNT concentration of 0.5 and 1 wt%. The corresponding volume resistivity values of the nanocomposites in the range of (6.90 ± 3.16) × 105 Ω cm to (1.24 ± 0.41) × 101 Ω cm implied their suitability for strain-sensing applications. The change in the electrical resistance of the nanocomposites was measured simultaneously with tensile testing to evaluate their piezoresistivity. The deformation behaviour of the nanocomposites was correlated with relative resistance change (ΔR/R 0) via a cyclic-strain test to investigate the stability of their strain-sensing behaviour. A non-linear and exponential-like increment in the ΔR/R 0 values of the nanocomposites as a function of mechanical strain during tensile stretching confirmed their piezoresistivity. ΔR/R 0 values fitted well with an increase in applied mechanical strain from 2% to 8% during the cyclic-strain test, which revealed the low-strain sensing potential of the nanocomposites, provided by their stable and intact microstructure formed via continuous stretching and releasing during the test; this was further supported by the reproducibility of the ΔR/R 0 values in the cyclic-strain test with 7% applied strain in 15 cycles. Additionally, the uniformly extended net-like morphology of the nanocomposites with an entangled network of MWCNTs throughout the polymer matrix was revealed by their electron micrographs.

Increasing the sensor channels: a solution for the pressing offsets that cause the physiological parameter inaccuracy in radial artery pulse signal acquisition

Introduction: In studies of pulse wave analysis, single-channel sensors only adopt single temporal pulse signals without spatial information to show pulse-feeling patterns. Multi-channel arterial pulse signals, also named as three-dimensional pulse images (3DPIs), provide the spatial and temporal characteristics of radial pulse signals. When involving single or few-channel sensors, pressing offsets have substantial impacts on obtaining inaccurate physiological parameters like tidal peak (P2). Methods: This study discovers the pressing offsets in multi-channel pulse signals and analyzes the relationship between the pressing offsets and time of P2 (T2) by qualifying the pressing offsets. First, we employ a data acquisition system to capture 3DPIs. Subsequently, the errorT2 is developed to qualify the pressing offsets. Results: The outcomes display a central low and peripheral high pattern. Additionally, the errorT2 increase as the distances from the artery increase, particularly at the radial ends of the blood flow direction. For every 1 mm increase in distances between sensing elements and center sensing elements, the errorT2 in the radial direction escalates by 4.87%. When the distance is greater than 3.42 mm, the errorT2 experiences a sudden increase. Discussion: The results show that increasing the sensor channels can overcome the pressing offsets in radial pulse signal acquisition.