Progresses in Tensile, Torsional, and Multifunctional Soft Actuators

The microvalve is one of the most important components in microfluidics. With decades of development, the microvalve has been widely used in many industries such as life science, chemical engineering, chip, and so forth. This paper presents a comprehensive review of the progress made over the past years about microvalves based on different actuation mechanisms. According to driving sources, plenty of actuation mechanisms are developed and adopted in microvalves, including electricity, magnetism, gas, material and creature, surface acoustic wave, and so on. Although there are currently a variety of microvalves, problems such as leakage, low precision, poor reliability, high energy consumption, and high cost still exist. Problems deserving to be further addressed are suggested, aimed at materials, fabrication methods, controlling performances, flow characteristics, and applications.

/pdf/actuation-mechanism-of-microvalves-a-review-g5ryvu4dso.pdf

Actuation Mechanism of Microvalves: A Review.

Liquid infiltration is an efficient way to densify carbon nanotubes (CNTs) and was used to strengthen CNT fibres in the method of array spinning. Rather than the volatility, the dipole moment of solvent plays a more important role in determining the densification level. The fibres densified by highly polar but non-volatile solvents such as N , N -dimethylformamide, dimethyl sulphoxide, and N -methyl-2-pyrrolidone were 100–200 MPa stronger than those by ethanol and acetone. Ethylene glycol is the most efficient solvent due to its two polar OH groups and improved the fibre strength to 1.45 GPa. Long chain or cross-linked polymers like polyvinyl alcohol, polyimide, and bismaleimide (BMI) were introduced into CNT fibres by infiltration with aid of polar solvents. These polymers reinforced the fibres significantly, as they can connect non-neighboring CNTs and benefit the load transfer. The strongest CNT/BMI fibre was 2.38 GPa in strength and 110 GPa in modulus.

Enhancement of carbon nanotube ﬁbres using diﬀerent solvents and polymers

To improve the security, robustness and imperceptibility of watermark schemes, a novel watermark scheme is devised by fusing multiple watermark techniques, including lifting wavelet transform, discrete cosine transform, discrete fractional angular transform and singular value decomposition. To solve the false positive problem in various SVD-based watermark schemes, transform domain encryption is utilized and the embedding component of watermark instead of the whole watermark is embedded into the host image. Furthermore, the particle swarm optimization algorithm is used to optimize the scaling factors and the parameter of the improved discrete fractional angular transform. The proposed watermark scheme is tested by several attacks, such as JPEG compression, low-pass filtering, Histogram equalization, contrast enhance, and etc. Simulation results demonstrate that the proposed watermark scheme is superior in the aspects of security, robustness and imperceptibility.

Secure and robust watermark scheme based on multiple transforms and particle swarm optimization algorithm

In the past decade, with the rapid development of wearable electronics, medical health monitoring, internet of things and flexible intelligent robots, flexible pressure sensors have received unprecedented attention. As a very important kind of electronic components for information transmission and collection, flexible pressure sensor has gained a wide application prospect in the fields of aerospace, biomedical and health monitoring, electronic skin and human-machine interface. In recent years, MXene has attracted extensive attention because of its unique two-dimensional layered structure, high conductivity, rich surface terminal groups and hydrophilicity, which has brought a new breakthrough for flexible sensing. Thus, it has become a revolutionary pressure sensitive material with great potential. In this work, the recent advances of MXene-based flexible pressure sensors is reviewed from the aspects of sensing type, sensing mechanism, material selection, structural design, preparation strategy and sensing application. The methods and strategies to improve the performance of MXene-based flexible pressure sensors are analyzed in details. Finally, the opportunities and challenges faced by MXene-based flexible pressure sensors are discussed. This review will bring the research and development of MXene-based flexible sensors to a new high level, promoting the wider research exploitation and practical application of MXene materials in flexible pressure sensors. This article is protected by copyright. All rights reserved.

Recent Advances in Flexible Pressure Sensors Based on MXene Materials.

Piezoresistive pressure sensors with electromagnetic interference (EMI) shielding and high sensitivity are highly preferred in the field of human motion and physiological signal monitoring. Inspired by the pod structure, we prepare the thermoplastic polyurethane electrospinning membrane (TPUEM) composite with MXene and poly (styrene-co-methacrylic acid)@polypyrrole nanospheres (PPNs) sandwiched structure by vacuum filtering and spraying. Due to excellent EMI shielding property of MXene and the special structure of the composite, the MXene/PPNs/MXene/TPUEM shows a good EMI shielding function (SET = 20.2 dB). This indicates that the composite has the ability to avoid to some extent the interference of electromagnetic radiation generated by nearby circuits and micro-electrical components. Benefiting from the excellent negative piezoresistive characteristics of the pressure sensor assembled by the MXene/PPNs/MXene/TPUEM, it exhibits a high-sensitivity of 177.3 kPa−1, a wide sensing range (0–30.4 kPa), and a rapid response time of 137 ms. Importantly, the sensor shows an excellent ability to accurately monitor human activities including joint flexions, voice recognition, and pulses. The MXene/ PPNs/MXene/TPUEM will have application prospects in the design of multifunctional smart wearable devices. 

Multifunctional Ti3C2Tx MXene/nanospheres/Ti3C2Tx MXene/thermoplastic polyurethane electrospinning membrane inspired by bean pod structure for EMI shielding and pressure sensing

The design, analytical modelling, finite element analysis (FEA), and experimental characterization of a microelectromechanical system (MEMS) out-of-plane (vertical) translational piezoelectric lead–zirconate–titanate (PZT) bimorph actuator supported on Archimedes' spiral tethers are presented. Three types of bimorph actuators with different electrode patterns (with spiral tethers half actuated, fully actuated with uniform polarity, or fully actuated with reversed polarity) are designed and modelled. The two actuators with the highest predicted performance (half actuated and fully actuated with uniform polarity) are implemented and characterized. Both designs are fabricated by commercial processes and are compatible with integration into more complex MEMS systems. Analytical modelling and FEA are used to analyze and predict the actuators' displacements and blocking forces. Experimental measurements of the deflections and blocking forces of actuators with full uniform actuation and half actuation validate the design. At an applied voltage of 110 V, the out-of-plane deflections of the actuators with half actuation and full uniform actuation are measured at about 17 µm and 29 µm respectively, in good agreement with analytical predictions of 17.3 µm and 34.2 µm and FEA predictions of 17.1 µm and 25.8 µm. The blocking force for devices with half-actuated tethers is predicted to be 12 mN (analytical) and 10 mN (FEA), close to the experimental value of 9 mN. The blocking force for devices with full uniform actuation is predicted to be 23 mN (analytical) and 17 mN (FEA), as compared with 15 mN in experiments.

https://iopscience.iop.org/article/10.1088/0960-1317/26/12/124005/pdf

Compact, planar, translational piezoelectric bimorph actuator with Archimedes’ spiral actuating tethers

https://iopscience.iop.org/article/10.1088/1361-6463/aaf198/pdf

Low-cost, additively manufactured electron impact gas ionizer with carbon nanotube field emission cathode for compact mass spectrometry

As the largest organ in human body, skin provides the important sensory channel for humans to receive external stimulations based on touch. By the information perceived through touch, people can feel and gain the properties of objects like weight, temperature, textures, and motion etc. In fact, those properties are nerve stimuli to our brain received by different kinds of receptors in the skin. Mechanical, electrical and thermal stimuli can stimulate these receptors and cause different information to be conveyed through the nerves. Technologies for actuators to provide mechanical, electrical or thermal stimuli have been developed. These include static or vibrational actuation, electrostatic stimulation, focused ultrasound and more. Smart materials such as piezoelectric materials, Carbon nanotubes, shape memory alloys play important roles in providing actuation for tactile sensation. This paper aims to review the background biological knowledge of human tactile sensing in order to give an understanding of how we sense and interact with the world through the sense of touch, as well as the conventional and state-of-the-art technologies of tactile actuators for tactile feedback delivery.

The application of smart materials in tactile actuators for tactile information delivery

A novel Fabry–Perot (F–P) interferometer model based on the ultra-small gradient-index (GRIN) fiber probe is investigated. The signal arm of the F–P interferometer is organically combined with the ultra-small GRIN fiber probe to establish the theoretical model of the novel F–P interferometer. An interferometer experimental system for vibration measurements was built to measure the performance of the novel F–P interferometer system. The experimental results show that under the given conditions, the output voltage of the novel interferometer is 3.9 V at the working distance of 0.506 mm, which is significantly higher than the output voltage 0.48 V of the single-mode fiber (SMF) F–P interferometer at this position. In the range of 0.1–2 mm cavity length, the novel interferometer has a higher output voltage than an SMF F–P interferometer. Therefore, the novel F–P interferometer is available for further study of the precise measurement of micro vibrations and displacements in narrow spaces.

Research on a Novel Fabry⁻Perot Interferometer Model Based on the Ultra-Small Gradient-Index Fiber Probe.

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