Highly sensitive capacitive pressure sensors for robotic applications based on carbon nanotubes and PDMS polymer nanocomposite

Flexible tactile pressure sensor arrays based on multiwalled carbon nanotubes (MWCNT) and polydimethylsiloxane (PDMS) are gaining importance, especially in the field of robotics because of the high demand for stable, flexible and sensitive sensors. Some existing concepts of pressure sensors based on nanocomposites exhibit complicated fabrication techniques and better sensitivity than the conventional pressure sensors. In this article, we propose a nanocomposite-based pressure sensor that exhibits a high sensitivity of 25&thinsp;%&thinsp;N−1, starting with a minimum load range of 0–0.01&thinsp;N and 46.8&thinsp;%&thinsp;N−1 in the range of 0–1&thinsp;N. The maximum pressure sensing range of the sensor is approximately 570&thinsp;kPa. A concept of a 4×3 tactile sensor array, which could be integrated to robot fingers, is demonstrated. The high sensitivity of the pressure sensor enables precision grasping, with the ability to sense small objects with a size of 5&thinsp;mm and a weight of 1&thinsp;g. Another application of the pressure sensor is demonstrated as a gait analysis for humanoid robots. The pressure sensor is integrated under the foot of a humanoid robot to monitor and evaluate the gait of the robot, which provides insights for optimizing the robot's self-balancing algorithm in order to maintain the posture while walking.</p

Flexible piezoresistive sensor matrix based on a carbon nanotube PDMS composite for dynamic pressure distribution measurement

A highly flexible, piezoresistive sensor matrix based on a carbon nanotube (CNT) polymer composite is developed for pressure distribution measurement applications. With an overall height of about 400&thinsp;µm, the sensors can measure pressure directly, without any deformation elements, such as a cantilever or a deformation membrane. The measurement range is from 2.5 to 640&thinsp;kPa. Both the position and the pressure of the applied load can be measured and visualized as a resistance change. The relative resistance measurement deviation of the data acquisition system is lower than 3&thinsp;% for the resistance range of 610Ω to 380&thinsp;kΩ. This corresponds to a systematic deviation of pressure measurement of less than 3&thinsp;% in the measurement range. Besides the measurement of pressure, different sizes of loads can be detected as well. The developed fast and compact measurement system allows dynamic pressure measurement, such as gait analysis when used in an insole application.</p

Quantifying the contributing factors towards signal fatigue in nanocomposite strain sensors

With unparalleled sensitivities, nanocomposites are believed to be key components in future bodily sensor and healthcare devices. However, there is a lack in understanding of how repeated strain cycles effect their electromechanical performance and what measures can be taken to accommodate changes in measurement using modelling and signal processing. Here, the author examines published cyclic data from a wide range of nanocomposite strain sensors. From the datasets, the author reports a near universal scaling in electromechanical signal with cycle number (C) as a result of the Mullin’s effect. Using a modified model based on Basquin’s law of fatigue, for all nanocomposites, signal was found to following a nearly identical C-0.1 power law scaling with cycle number. Using the presented model, the author demonstrated that a critical conditioning cycle number for a nanocomposite at which a steady state signal occurs, known as the endurance limit, can be predicted. Endurance limit was reported to be highly dependent on the scaling exponent noted in the cyclic data

Synthesis of polyvinyl alcohol (PVA) infiltrated MWCNTs buckypaper for strain sensing application

Buckypaper (BP)/polymer composites are viewed as a viable option to improve the strain transfer across the buckypaper strain sensor by means of providing better interfacial bonding between the polymer and carbon nanotubes (CNTs). Multiwall carbon nanotubes (MWCNTs) BP/polyvinyl alcohol (PVA) composites were fabricated by a sequence of vacuum filtration and polymer intercalation technique. The optimized conditions for achieving a uniform and stable dispersion of MWCNTs were found to be using ethanol as a dispersion medium, 54?µm ultrasonic amplitude and 40?min sonication time. FTIR analysis and SEM spectra further confirmed the introduction of oxygenated groups (-COOH) on the surface of MWCNTs BP and the complete infiltration of PVA into the porous MWCNTs network. At MWCNTs content of 65 wt. %, the tensile strength, Young's modulus and elongation-at-break of PVA-infiltrated MWCNTs BP achieved a maximum value of 156.28?MPa, 4.02?GPa and 5.85%, improved by 189%, 443% and 166% respectively, as compared to the MWCNTs BP. Electrical characterization performed using both two-point probe method and Hall effect measurement showed that BP/PVA composites exhibited reduced electrical conductivity. From the electromechanical characterization, the BP/PVA composites showed improved sensitivity with a gauge factor of about 1.89-2.92. The cyclic uniaxial tensile test validated the high reproducibility and hysteresis-free operation of 65-BP/PVA composite under 3 loading-unloading cycles. Characterization results confirmed that the flexible BP/PVA composite (65 wt. %) with improved mechanical and electromechanical properties is suitable for strain sensing applications in structural health monitoring and wearable technology, as an alternative choice to the fragile nature of conventional metallic strain sensors