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

QCM Measurements of RH with Nanostructured Carbon-Based Materials: Part 2-Experimental Characterization

In this series of two papers, the humidity sensing of a carbon nanotube (CNT) network-based material is transduced and studied through quartz crystal microbalance (QCM) measurements. To this aim, quartzes functionalized with different amounts of sensing material were realized, exposed to different humidity levels, and characterized. In this second paper, the experimental results are presented and discussed. The sensing mechanisms are elucidated exploiting the theory presented in the first paper of this series. The presented results show that the investigated material functionalization induces a large response of QCM to humidity in terms of resonant frequency even at low RH levels, with a sensitivity of about 12 Hz/%RH (at RH &lt; 30% and room temperature and 10 ug of deposited SWCNT solution) and an increase in sensitivity in the high RH range typical of nanostructured film. Regarding the response in terms of motional resistance, a large response is obtained only at intermediate and high humidity levels, confirming that condensation of water in the film plays an important role in the sensing mechanism of nanostructured materials

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

Theory of band gap bowing of disordered substitutional II-VI and III-V semiconductor alloys

For a wide class of technologically relevant compound III-V and II-VI semiconductor materials AC and BC mixed crystals (alloys) of the type A(x)B(1-x)C can be realized. As the electronic properties like the bulk band gap vary continuously with x, any band gap in between that of the pure AC and BC systems can be obtained by choosing the appropriate concentration x, granted that the respective ratio is miscible and thermodynamically stable. In most cases the band gap does not vary linearly with x, but a pronounced bowing behavior as a function of the concentration is observed. In this paper we show that the electronic properties of such A(x)B(1-x)C semiconductors and, in particular, the band gap bowing can well be described and understood starting from empirical tight binding models for the pure AC and BC systems. The electronic properties of the A(x)B(1-x)C system can be described by choosing the tight-binding parameters of the AC or BC system with probabilities x and 1-x, respectively. We demonstrate this by exact diagonalization of finite but large supercells and by means of calculations within the established coherent potential approximation (CPA). We apply this treatment to the II-VI system Cd(x)Zn(1-x)Se, to the III-V system In(x)Ga(1-x)As and to the III-nitride system Ga(x)Al(1-x)N.Comment: 14 pages, 10 figure