High performance shape memory polyurethane synthesized with high molecular weight polyol as the soft segment

Shape memory polyurethanes (SMPUs) are typically synthesized using polyols of low molecular weight (MW~2,000 g/mol) as it is believed that the high density of cross-links in these low molecular weight polyols are essential for high mechanical strength and good shape memory effect. In this study, polyethylene glycol (PEG-6000) with MW ~6000 g/mol as the soft segment and diisocyanate as the hard segment were used to synthesize SMPUs, and the results were compared with the SMPUs with polycaprolactone PCL-2000. The study revealed that although the PEG-6000-based SMPUs have lower maximum elongations at break (425%) and recovery stresses than those of PCL-based SMPUs, they have much better recovery ratios (up to 98%) and shape fixity (up to 95%), hence better shape memory effect. Furthermore, PEG-based SMPUs showed a much shorter actuation time of < 10 s for up to 90% shape recovery compared to typical actuation times of tens of seconds to a few minutes for common SMPUs, demonstrated their great potential for applications in microsystems and other engineering components

Review on biomedical sensors, technologies, and algorithms for diagnosis of sleep-disordered breathing: Comprehensive survey

This paper provides a comprehensive review of available technologies for measurements of vital physiology related parameters that cause sleep disordered breathing (SDB). SDB is a chronic disease that may lead to several health problems and increase the risk of high blood pressure and even heart attack. Therefore, the diagnosis of SDB at an early stage is very important. The essential primary step before diagnosis is measurement. Vital health parameters related to SBD might be measured through invasive or non-invasive methods. Nowadays, with respect to increase in aging population, improvement in home health management systems is needed more than even a decade ago. Moreover, traditional health parameter measurement techniques such as polysomnography are not comfortable and introduce additional costs to the consumers. Therefore, in modern advanced self-health management devices, electronics and communication science are combined to provide appliances that can be used for SDB diagnosis, by monitoring a patient's physiological parameters with more comfort and accuracy. Additionally, development in machine learning algorithms provides accurate methods of analysing measured signals. This paper provides a comprehensive review of measurement approaches, data transmission, and communication networks, alongside machine learning algorithms for sleep stage classification, to diagnose SDB

Flexible Surface Acoustic Wave Humidity Sensor with on Chip Temperature Compensation

AbstractThis paper reports the development of flexible surface acoustic wave (SAW) based humidity sensors on polyimide substrate. The SAW devices have two resonant peaks, named the A0 and S0 Lamb modes, which have different temperature coefficients of frequency. Graphene oxide (GO) is used as the sensing layer owing to its large surface area and hydrophilcity to water. The sensors show high sensitivity up to 145.83ppm/%RH, comparable to those on rigid substrates, and fast response time of 4.4s. The sensitivity increases with the increase of GO thickness and resonant frequency. By utilizing the S0 mode as the temperature reference, a SAW Humidity-sensor with an on chip temperature compensation capability is demonstrated. The humidity sensors also show the ability to work under severe bending condition, demonstrated its great potential for flexible/wearable applications

Nebulization using ZnO/Si surface acoustic wave devices with focused interdigitated transducers

Propagation of surface acoustic waves (SAWs) on bulk piezoelectric substrates such as LiNbO3 and quartz, exhibits an in-plane anisotropic effect due to their crystal cut orientations. Thin film SAW devices, such as those based on ZnO or AlN, offer potential advantages, including isotropic wave velocities in all in-plane directions, higher power handling capability, and potentially lower failure rates. This paper reports experimental and simulation results of nebulization behaviour for water droplets using ZnO/Si surface acoustic wave devices with focused interdigital transducers (IDTs). Post-deposition annealing of the films at various temperatures was applied to improve the quality of the sputtering-deposited ZnO films, and 500 °C was found to be the optimal annealing temperature. Thin film ZnO/Si focused SAW devices were fabricated using the IDT designs with arc angles ranging from 30° to 90°. Nebulization was significantly enhanced with increasing the arc angles of the IDTs, e.g., increased nebulization rate, reduced critical powers required to initialise nebulization, and concentration of the nebulised plume into a narrower size of spray. Effects of applied RF power and droplet size have been systematically studied, and increased RF power and reduced droplet size significantly enhanced the nebulization phenomena

Advancement of electroadhesion technology for intelligent and self-reliant robotic applications

The growing need for automation in industries has foreseen drastic advancements in the development of soft robotics in the areas of navigation systems, textiles, healthcare, and biometric monitoring. Electroadhesion (EA) based robotic applications benefit from ultra-low power consumption, low maintenance, choices in versatile surfaces, sustainable life cycles, applicability in harsh and vacuum environments, and exteroceptive/proprioceptive abilities. It is of scientific and technological importance to comprehend the sequence of developments in working mechanisms, modeling, and materials to explore its full potential for future intelligent robotics systems. This review provides an all-inclusive roadmap of EA technology from its inception to unprecedented developments and complex relationships across multi-disciplines viz robotics, solid and fluid mechanics, electrostatics, haptics, space technologies, nanotechnology, and IoT

Triboelectric effect based instantaneous self-powered wireless sensing with self-determined identity

Sensors are the foundation of modern Internet of Things, artificial intelligent, smart manufacturing etc, but most of them require power to operate without spontaneous unique identifiable function. Herein we propose a novel instantaneous force-driven self-powered self-identified wireless sensor based on triboelectric effect to meet the huge demand of true self-powered wireless sensors. The device consists of a microswitch controlled triboelectric nanogenerator (TENG) in parallel with a capacitor-inductor oscillating circuit, and a wireless transmitter. The system is fully powered by the output of the TENG to generate a resonant frequency containing sensing and device identity information, which is then coupled to the transmitter for realizing a long-range wireless communication. The device, with the multiple functions of energy harvesting, sensing, identity generation and wireless signal transmission, is a standalone device, which responds to each trigger without losing sensing information. It eliminates the requirement of electric components for traditional wireless communication, such as rectification circuit, energy storage units, microprocessor, wireless communication chip, etc. Thus, we developed a true self-powered identifiable wireless sensor with great potential for widespread applications

Emulsion Electrospinning of Polytetrafluoroethylene (PTFE) Nanofibrous Membranes for High-Performance Triboelectric Nanogenerators

Electrospinning is a simple, versatile technique for fabricating fibrous nanomaterials with the desirable features of extremely high porosities and large surface areas. Using emulsion electrospinning, polytetrafluoro­ethylene/polyethene oxide (PTFE/PEO) membranes were fabricated, followed by a sintering process to obtain pure PTFE fibrous membranes, which were further utilized against a polyamide 6 (PA6) membrane for vertical contact-mode triboelectric nanogenerators (TENGs). Electrostatic force microscopy (EFM) measurements of the sintered electrospun PTFE membranes revealed the presence of both positive and negative surface charges owing to the transfer of positive charge from PEO which was further corroborated by FTIR measurements. To enhance the ensuing triboelectric surface charge, a facile negative charge-injection process was carried out onto the electrospun (ES) PTFE subsequently. The fabricated TENG gave a stabilized peak-to-peak open-circuit voltage (<i>V</i>_oc) of up to ∼900 V, a short-circuit current density (<i>J</i>_sc) of ∼20 mA m^–2, and a corresponding charge density of ∼149 μC m^–2, which are ∼12, 14, and 11 times higher than the corresponding values prior to the ion-injection treatment. This increase in the surface charge density is caused by the inversion of positive surface charges with the simultaneous increase in the negative surface charge on the PTFE surface, which was confirmed by using EFM measurements. The negative charge injection led to an enhanced power output density of ∼9 W m^–2 with high stability as confirmed from the continuous operation of the ion-injected PTFE/PA6 TENG for 30 000 operation cycles, without any significant reduction in the output. The work thus introduces a relatively simple, cost-effective, and environmentally friendly technique for fabricating fibrous fluoropolymer polymer membranes with high thermal/chemical resistance in TENG field and a direct ion-injection method which is able to dramatically improve the surface negative charge density of the PTFE fibrous membranes

Hierarchical nanotexturing enables acoustofluidics on slippery yet sticky, flexible surfaces

The ability to actuate liquids remains a fundamental challenge in smart microsystems, such as those for soft robotics, where devices often need to conform to either natural or three-dimensional solid shapes, in various orientations. Here, we propose a hierarchical nanotexturing of piezoelectric films as active microfluidic actuators, exploiting a unique combination of both topographical and chemical properties on flexible surfaces, while also introducing design concepts of shear hydrophobicity and tensile hydrophilicity. In doing so, we create nanostructured surfaces that are, at the same time, both slippery (low in-plane pinning) and sticky (high normal-to-plane liquid adhesion). By enabling fluid transportation on such arbitrarily shaped surfaces, we demonstrate efficient fluid motions on inclined, vertical, inverted, or even flexible geometries in three dimensions. Such surfaces can also be deformed and then reformed into their original shapes, thereby paving the way for advanced microfluidic applications