Highly sensitive and broadband meta-mechanoreceptor via mechanical frequency-division multiplexing.

Bio-mechanoreceptors capable of micro-motion sensing have inspired mechanics-guided designs of micro-motion sensors in various fields. However, it remains a major challenge for mechanics-guided designs to simultaneously achieve high sensitivity and broadband sensing due to the nature of resonance effect. By mimicking rat vibrissae, here we report a metamaterial mechanoreceptor (MMR) comprised of piezoelectric resonators with distributed zero effective masses featuring a broad range of local resonances, leading to near-infinite sensitivity for micro-motion sensing within a broad bandwidth. We developed a mechanical frequency-division multiplexing mechanism for MMR, in which the measured micro-motion signal is mechanically modulated in non-overlapping frequency bands and reconstructed by a computational multi-channel demodulation approach. The maximum sensitivity of MMR is improved by two orders of magnitude compared to conventional mechanics-guided mechanoreceptors, and its bandwidth with high sensitivity is extendable towards both low-frequency and high-frequency ranges in 0-12 kHz through tuning the local resonance of each individual sensing cell. The MMR is a promising candidate for highly sensitive and broadband micro-motion sensing that was previously inaccessible for mechanics-guided mechanoreceptors, opening pathways towards spatio-temporal sensing, remote-vibration monitoring and smart-driving assistance.

Online Piecewise Convex-Optimization Interpretable Weight Learning for Machine Life Cycle Performance Assessment.

Machine life cycle performance assessment is of great significance to use a health index to inform the time of incipient fault initiation in a normal stage and realize fault identification and fault trending in a performance degradation stage. However, most existing works consider using unexplainable model parameters and historical data to build models and infer their off-line parameters for machine life cycle performance assessment. To overcome these limitations, an online piecewise convex-optimization interpretable weight learning framework without needing any historical abnormal and faulty data is proposed in this article to generate a piecewise health index to practically implement machine life cycle performance assessment. Firstly, based on a separation criterion, the first submodel in the proposed framework is built to detect the time of incipient fault initiation. Here, the piecewise health index generated by the first submodel is continuously updated by on-line monitoring data to timely detect the occurrence of any abnormal health conditions. Secondly, once the time of incipient fault initiation is informed, online updated model weights are highly correlated with fault characteristic frequencies and informative frequency bands for immediate fault identification. Simultaneously, the second submodel integrated with monotonicity and fitness properties in the proposed framework is triggered to generate the piecewise health index to realize overall monotonic fault trending. The significance of this article is that only online monitoring data are used to continuously update interpretable model weights as fault frequencies and informative frequency bands to generate the proposed piecewise health index so as to practically realize machine life cycle performance assessment. Two run-to-failure cases are studied to show the effectiveness and superiority of the proposed framework.

Identification of Sparse Volterra Systems: An Almost Orthogonal Matching Pursuit Approach.

This paper considers identification of sparse Volterra systems. A method based on the almost orthogonal matching pursuit (AOMP) is proposed. The AOMP algorithm allows one to estimate one non-zero coefficient at a time until all non-zero coefficients are found without losing the optimality and the sparsity, thus avoiding the curse of dimensionality often encountered in Volterra system identification.

Three new categories of hypoglycaemic agents and various cardiovascular diseases: A meta-analysis.

WHAT IS KNOWN AND OBJECTIVE: New hypoglycaemic agents consist of dipeptidyl peptidase four inhibitors (DPP4is), glucagon-like peptide one receptor agonists (GLP1RAs) and sodium-glucose cotransporter two inhibitors (SGLT2is). We aimed to define the association between each category of these new hypoglycaemic drugs and various cardiovascular diseases. METHODS: Large randomized trials comparing DPP4is, GLP1RAs or SGLT2is with placebo were included. Outcomes of interest were 95 kinds of cardiovascular diseases. Meta-analysis was conducted to generate pooled risk ratio (RR) and 95% confidence interval (CI). RESULTS AND DISCUSSION: Twenty-one large randomized trials were included in this meta-analysis. Compared with placebo, SGLT2is were associated with the lower risks of hypertension (RR 0.67, 95% CI 0.49-0.93), atrial fibrillation (RR 0.78, 95% CI 0.67-0.91), bradycardia (RR 0.60, 95% CI 0.40-0.89) and heart failure (RR 0.74, 95% CI 0.68-0.80); GLP1RAs were associated with the lower risk of peripheral arterial occlusive disease (RR 0.73, 95% CI 0.56-0.97) and with the higher risk of deep vein thrombosis (RR 2.12, 95% CI 1.32-3.4), while DPP4is were associated with the lower risk of peripheral ischaemia (RR 0.57, 95% CI 0.37-0.89). WHAT IS NEW AND CONCLUSIONS: Our meta-analysis revealed that SGLT2is were associated with the lower risks of hypertension, atrial fibrillation, bradycardia and heart failure; GLP1RAs were associated with the lower risk of peripheral arterial occlusive disease and with the higher risk of deep vein thrombosis, while DPP4is were associated with the lower risk of peripheral ischaemia. These findings propose that each category of these new hypoglycaemic agents should be avoided or preferred in patients at high risks of specific cardiovascular diseases.

Millimeter-Wave Bat for Mapping and Quantifying Micromotions in Full Field of View.

Echolocating bats possess remarkable capability of multitarget spatial localization and micromotion sensing in a full field of view (FFOV) even in cluttered environments. Artificial technologies with such capability are highly desirable for various fields. However, current techniques such as visual sensing and laser scanning suffer from numerous fundamental problems. Here, we develop a bioinspired concept of millimeter-wave (mmWave) full-field micromotion sensing, creating a unique mmWave Bat ("mmWBat"), which can map and quantify tiny motions spanning macroscopic to µm length scales of full-field targets simultaneously and accurately. In mmWBat, we show that the micromotions can be measured via the interferometric phase evolution tracking from range-angle joint dimension, integrating with full-field localization and tricky clutter elimination. With our approach, we demonstrate the capacity to solve challenges in three disparate applications: multiperson vital sign monitoring, full-field mechanical vibration measurement, and multiple sound source localization and reconstruction (radiofrequency microphone). Our work could potentially revolutionize full-field micromotion monitoring in a wide spectrum of applications, while may inspiring novel biomimetic wireless sensing systems.

Biomimetic Water-Repelling Surfaces with Robustly Flexible Structures.

Biomimetic liquid-repelling surfaces have been the subject of considerable scientific research and technological application. To design such surfaces, a flexibility-based oscillation strategy has been shown to resolve the problem of liquid-surface positioning encountered by the previous, rigidity-based asymmetry strategy; however, its usage is limited by weak mechanical robustness and confined repellency enhancement. Here, we design a flexible surface comprising mesoscale heads and microscale spring sets, in analogy to the mushroomlike geometry discovered on springtail cuticles, and then realize this through three-dimensional projection microstereolithography. Such a surface exhibits strong mechanical robustness against ubiquitous normal and shear compression and even endures tribological friction. Simultaneously, the surface elevates water repellency for impacting droplets by enhancing impalement resistance and reducing contact time, partially reaching an improvement of ∼80% via structural tilting movements. This is the first demonstration of flexible interfacial structures to robustly endure tribological friction as well as to promote water repellency, approaching real-world applications of water repelling. Also, a flexibility gradient is created on the surface to directionally manipulate droplets, paving the way for droplet transport.

Flexibility-Patterned Liquid-Repelling Surfaces.

Droplets impacting solid surfaces is ubiquitous in nature and of practical importance in numerous industrial applications. For liquid-repelling applications, rigidity-based asymmetric redistribution and flexibility-based structural oscillation strategies have been proven on artificial surfaces; however, these are limited by strict impacting positioning. Here, we show that the gap between these two strategies can be bridged by a flexibility-patterned design similar to a trampoline park. Such a flexibility-patterned design is realized by three-dimensional projection micro-stereolithography and is shown to enhance liquid repellency in terms of droplet impalement resistance and contact time reduction. This is the first demonstration of the synergistic effect obtained by a hybrid solution that exploits asymmetric redistribution and structural oscillation in liquid-repelling applications, paving the rigidity-flexibility cooperative way of wettability tuning. Also, the flexibility-patterned surface is applied to accelerate liquid evaporation.

Electrically Activated Soft Robots: Speed Up by Rolling.

Soft robots show excellent body compliance, adaptability, and mobility when coping with unstructured environments and human-robot interactions. However, the moving speed for soft locomotion robots is far from that of their rigid partners. Rolling locomotion can provide a promising solution for developing high-speed robots. Based on different rolling mechanisms, three rolling soft robot (RSR) prototypes with advantages of simplicity, lightweight, fast rolling speed, good compliance, and shock resistance are fabricated by using dielectric elastomer actuators. The experimental results demonstrate that the impulse-based and gravity-based RSRs can move both stably and continuously on the ground with a maximum speed higher than 1 blps (body length per second). The ballistic RSR exhibits a high rolling speed of ∼4.59 blps. And during its accelerating rolling process, the instantaneous rolling speed of the robot prototype reaches about 0.65 m/s (13.21 blps), which is much faster than most of the previously reported locomotion robots driven by soft responsive materials. The structure design and implementation methods based on different rolling mechanisms presented can provide guidance and inspiration for creating new, fast-moving, and hybrid mobility soft robots.

Liquid repellency enhancement through flexible microstructures.

Artificial liquid-repellent surfaces have attracted substantial scientific and industrial attention with a focus on creating functional topological features; however, the role of the underlying structures has been overlooked. Recent developments in micro-nanofabrication allow us now to construct a skin-muscle type system combining interfacial liquid repellence atop a mechanically functional structure. Specifically, we design surfaces comprising bioinspired, mushroom-like repelling heads and spring-like flexible supports, which are realized by three-dimensional direct laser lithography. The flexible supports elevate liquid repellency by resisting droplet impalement and reducing contact time. This, previously unknown, use of spring-like flexible supports to enhance liquid repellency provides an excellent level of control over droplet manipulation. Moreover, this extends repellent microstructure research from statics to dynamics and is envisioned to yield functionalities and possibilities by linking functional surfaces and mechanical metamaterials.

Randomized resonant metamaterials for single-sensor identification of elastic vibrations.

Vibrations carry a wealth of useful physical information in various fields. Identifying the multi-source vibration information generally requires a large number of sensors and complex hardware. Compressive sensing has been shown to be able to bypass the traditional sensing requirements by encoding spatial physical fields, but how to encode vibration information remains unexplored. Here we propose a randomized resonant metamaterial with randomly coupled local resonators for single-sensor compressed identification of elastic vibrations. The disordered effective masses of local resonators lead to highly uncorrelated vibration transmissions, and the spatial vibration information can thus be physically encoded. We demonstrate that the spatial vibration information can be reconstructed via a compressive sensing framework, and this metamaterial can be reconfigured while maintaining desirable performance. This randomized resonant metamaterial presents a new perspective for single-sensor vibration sensing via vibration transmission encoding, and potentially offers an approach to simpler sensing devices for many other physical information.

Self-Compensating Liquid-Repellent Surfaces with Stratified Morphology.

Artificial liquid-repellent surfaces have recently attracted vast scientific attention; however, achieving mechanical robustness remains a formidable challenge before industrialization can be realized. To this end, inspired by plateaus in geological landscapes, a self-compensating strategy is developed to pave the way for the synthesis of durable repellent surfaces. This self-compensating surface comprises tall hydrophobic structural elements, which can repel liquid droplets. When these elements are damaged, they expose shorter structural elements that also suspend the droplets and thus preserve interfacial repellency. An example of this plateau-inspired stratified surface was created by three-dimensional (3D) direct laser lithography micro-nano fabrication. Even after being subjected to serious frictional damage, it maintained static repellency to water with a contact angle above 147° and was simultaneously able to endure high pressures arising from droplet impacts. Extending the scope of nature-inspired functional surfaces from conventional biomimetics to geological landscapes, this work demonstrates that the plateau-inspired self-compensating strategy can provide an unprecedented level of robustness in terms of sustained liquid repellency.

Three-Dimensional Printed Surfaces Inspired by Bi-Gaussian Stratified Plateaus.

Wettability of artificial surfaces is attracting increasing attention for its relevant technological applications. Functional performance is often achieved by mimicking the topographical structures found in natural flora and fauna; however, surface attributes inspired by geological landscapes have so far escaped attention. We reproduced a stratified morphology of plateaus with a bi-Gaussian height distribution using a three-dimensional direct laser lithography. The plateau-inspired artificial surface exhibits a hydrophobic behavior even if fabricated from a hydrophilic material, giving rise to a new wetting mechanism that divides the well-known macroscopic Wenzel and Cassie states into four substates. We have also successfully applied the plateau-inspired structure to droplet manipulation.

Bioinspired Variable Stiffness Dielectric Elastomer Actuators with Large and Tunable Load Capacity.

This article proposes a bioinspired variable stiffness dielectric elastomer actuator (VSDEA) that is inspired by the leaf habit of monocots. The VSDEA is a fully flexible strip with a curved cross section and a tip dielectric elastomer minimum energy structure (DEMES). An arc fixture is used to clamp the strip that imitates the connection mode between the leaf and the cylindrical stem of the monocot. When applying voltage on the tip DEMES, the transverse curvature of the strip is changed, and then, the bending stiffness of the VSDEA can be tuned. Effects of applied voltage and important design parameters on the bending behavior of the VSDEA are experimentally studied in detail. The results show that the bending stiffness of the VSDEA approximately decreases linearly with the increase of applied voltage, which is very advantageous for stiffness control. The load capacity of the VSDEA is enhanced due to the bioinspired clamping mechanism and can be tuned by the applied voltage. It can also be found from the tested VSDEA prototypes that, when the applied voltage ranges from 0 V to 5.6 kV, the maximum relative stiffness and critical load changes reach about 71.8% and 75.6%, respectively. The maximum stiffness and critical load are, respectively, 157.8 N/m and 889.9 mN, which are two orders greater in magnitude than general DEMESs; as a result, this VSDEA can bear a payload 139 times its weight. It demonstrates that the bioinspired VSDEA can be useful for soft robots, vibration control, and morphing applications.

Bi-Gaussian Stratified Wetting Model on Rough Surfaces.

Wetting mechanisms on rough surfaces were understood from either a monolayer or a multiscale perspective. However, it has recently been shown that the bi-Gaussian stratified nature of real surfaces should be accounted for when modeling mechanisms of lubrication, sealing, contact, friction, acoustic emission, and manufacture. In this work, a model combining Wenzel and Cassie theories was put forward to predict the static contact angle of a droplet on a bi-Gaussian stratified surface. The model was initially applied to numerically simulated surfaces and subsequently demonstrated on hydrophilic steel and hydrophobic self-assembled monolayer specimens with preset bi-Gaussian stratified topographies. In the Wenzel state, both the upper and the lower surface components are fully wetted. In the Cassie state, the upper component is still completely wetted, while the lower component serves as gas traps and reservoirs. By this model, wetting evolution was assessed, and the existence of different wetting states and potential state transitions was predicted.

High-performance optical coherence velocimeter: theory and applications.

We proposed a high-performance optical coherence velocimeter (OCV) based on broadband optical interference which achieves spatial resolution from interference cancellation or enhancement of different components of the broadband light. There is a challengeable issue for OCV that the interference fringes become blurred when the velocity of detected object is relatively large, hindering the pace of OCV application in high-velocity field. To resolve this, the relationship between blurry coefficient and OCV system parameters (e.g., exposure time, central wavelength, bandwidth of source) was derived. It was found that blurry coefficient changed with oscillatory decay form and reached the minimum at each order blurry velocity. It showed that maximum measurable velocity of OCV systems could reach 10th order blurry velocity. The measurement of vibration of the loudspeaker driven by a function signal generator was employed to experimentally verify the velocity measurement performance of the system. The experiment demonstrated that the developed OCV can provide large velocity measurement ranges from static to 25.2 mm/s with nanometer-level precision and maximum measurable vibration frequency of up to 50 kHz. However, in theory, the theoretical maximum measurable velocity can be up to 1.06 m/s for current OCV configuration. The OCV has high precision, large dynamic range, and high-velocity measurement capability, making it attractive for applications in mechanical structure vibration monitoring and acoustic measurement.

Tunable micro- and nanomechanical resonators.

Advances in micro- and nanofabrication technologies have enabled the development of novel micro- and nanomechanical resonators which have attracted significant attention due to their fascinating physical properties and growing potential applications. In this review, we have presented a brief overview of the resonance behavior and frequency tuning principles by varying either the mass or the stiffness of resonators. The progress in micro- and nanomechanical resonators using the tuning electrode, tuning fork, and suspended channel structures and made of graphene have been reviewed. We have also highlighted some major influencing factors such as large-amplitude effect, surface effect and fluid effect on the performances of resonators. More specifically, we have addressed the effects of axial stress/strain, residual surface stress and adsorption-induced surface stress on the sensing and detection applications and discussed the current challenges. We have significantly focused on the active and passive frequency tuning methods and techniques for micro- and nanomechanical resonator applications. On one hand, we have comprehensively evaluated the advantages and disadvantages of each strategy, including active methods such as electrothermal, electrostatic, piezoelectrical, dielectric, magnetomotive, photothermal, mode-coupling as well as tension-based tuning mechanisms, and passive techniques such as post-fabrication and post-packaging tuning processes. On the other hand, the tuning capability and challenges to integrate reliable and customizable frequency tuning methods have been addressed. We have additionally concluded with a discussion of important future directions for further tunable micro- and nanomechanical resonators.

Modeling of the through-the-thickness electric potentials of a piezoelectric bimorph using the spectral element method.

An efficient spectral element (SE) with electric potential degrees of freedom (DOF) is proposed to investigate the static electromechanical responses of a piezoelectric bimorph for its actuator and sensor functions. A sublayer model based on the piecewise linear approximation for the electric potential is used to describe the nonlinear distribution of electric potential through the thickness of the piezoelectric layers. An equivalent single layer (ESL) model based on first-order shear deformation theory (FSDT) is used to describe the displacement field. The Legendre orthogonal polynomials of order 5 are used in the element interpolation functions. The validity and the capability of the present SE model for investigation of global and local responses of the piezoelectric bimorph are confirmed by comparing the present solutions with those obtained from coupled 3-D finite element (FE) analysis. It is shown that, without introducing any higher-order electric potential assumptions, the current method can accurately describe the distribution of the electric potential across the thickness even for a rather thick bimorph. It is revealed that the effect of electric potential is significant when the bimorph is used as sensor while the effect is insignificant when the bimorph is used as actuator, and therefore, the present study may provide a better understanding of the nonlinear induced electric potential for bimorph sensor and actuator.