Smart epidermal electrophysiological electrodes:Materials,structures,and algorithms

Epidermal electrophysiological monitoring has garnered significant attention for its potential in medical diagnosis and healthcare,particularly in continuous signal recording.However,simultaneously satisfying skin compliance,mechanical properties,environmental adaptation,and biocompatibility to avoid signal attenuation and motion artifacts is challenging,and accurate physiological feature extraction necessitates effective signal-processing algorithms.This review presents the latest advancements in smart electrodes for epidermal electrophysiological monitoring,focusing on materials,structures,and algorithms.First,smart materials incorporating self-adhesion,self-healing,and self-sensing functions offer promising solutions for long-term monitoring.Second,smart meso-structures,together with micro/nanostructures endowed the electrodes with self-adaption and multifunctionality.Third,intelligent algorithms give smart electrodes a“soul,”facilitating faster and more-accurate identification of required information via automatic processing of collected electrical signals.Finally,the existing challenges and future opportunities for developing smart electrodes are discussed.Recognized as a crucial direction for next-generation epidermal electrodes,intelligence holds the potential for extensive,effective,and transformative applications in the future.

Multi-layered plate finite element models with node-dependent kinematics for smart structures with piezoelectric components

This article presents a type of plate Finite Element(FE)models with adaptive mathematical refinement capabilities for modeling laminated smart structures with piezoelectric layers or distributed patches.The p-version shape functions are used in combination with the higher-order Layer-Wise(LW)kinematics adopting hierarchical Legendre polynomials.Node-Dependent Kinematics(NDK)is employed to implement local LW models in the regions with piezoelectric components and simulate the global substrate structure with the Equivalent Single-Layer(ESL)approach.Through the proposed NDK FE models,the electro-mechanical behavior of smart structures can be predicted with high fidelity and numerical efficiency,and various patch configurations can be conveniently modeled through one set of mesh grids.Moreover,the effectiveness and efficiency of the NDK FE approach are assessed through numerical examples and its application is demonstrated.

Smart structures with embedded flexible sensors fabricated by fused deposition modeling-based multimaterial 3D printing

Smart structures have the advantages of high system integrity and diverse sensing capabilities.However,the labor-intensive and timeconsuming fabrication process hinders the large-scale adoption of smart structures.Despite recent attempts to develop sensorembedded structures using 3D printing technologies,the reported smart structures generally suffer from the complex fabrication process,constrained part size,and limited sensing modality.Herein,we propose a workflow to design and fabricate novel smart structures via multi-material fused deposition modeling(FDM)-based 3D printing.More specifically,conductive filaments with tailorable mechanical and elec-trical properties,e.g.piezoresistive effects,were developed.Additionally,the printing process was optimized for processing soft filaments with Young’s modulus around 2 MPa,resolving the issue of filament buckling.Furthermore,the potential applications of the proposed workflow were showcased using three design cases,i.e.biaxial strain sensor,smart tire,and cable-driven soft finger with multiple sensing capabilities.This workflow provides a cost-effective and rapid solution for developing novel smart structures with soft materials.

Study on interface failure of shape memory alloy(SMA)reinforced smart structure with damages

Shape memory alloy （SMA） reinforced smart structure can be used to make structural shape and strength selfadapted and structural damage self-restrained. Although SMA smart structures without damages were extensively studied, researches on SMA smart structures with damages have rarely been reported thus far. In this paper, thermo-mechanical behaviors of SMA fiber reinforced smart structures with damages are analyzed through a shear lag model and the variational principle, Mathematical expressions of the meso-displacement field and the stress-strain field of a typical element with damages are obtained, and a failure criterion for interface failure between SMA fibers and matrix is established, which is applied to an example. Results presented herein may provide a theoretical foundation for further studies on integrity of SMA smart structures.

MESO-MECHANICAL ANALYSIS OF SHAPE MEMORY ALLOY REINFORCED SMART STRUCTURE WITH DAMAGE

The mechanical behaviors of shape memory alloy （SMA） wires reinforced smart structure with damage were analyzed through the variational principle, a governing equation for the structure was derived, mathematical expressions for the meso-displacement field, stressstrain field of typical element with damage were presented, and a failure criterion for interface failure between SMA wires and matrix was established under two kinds of actuation which are dead-load and temperature, where the temperature is included in effective free restoring strain. In addition, there are some other composing factors in the failure criterion such as the interface properties, dynamical properties of SMA, initial debonding length L - l etc. The results are significant to understand structural strength self-adapted control and failure mechanism of SMA wires reinforced smart structure with damage.

LINEAR ACTIVE STRUCTURES AND MODES (Ⅰ) —BASIC CONCEPTS AND PROPERTIES

Some basic concepts about the active structures were firstly explained, and the main subjects to study in the field of active structure dynamics were synthesized. For the linear active structures, the annotations on the modes were done in detail. The physical meanings of the right and left eigenvectors were explained. The right eigenvectors are the modal shapes and the modal responses of an active structure depend on the left ones. The adjoint structure of an active structure was defined and the reciprocity theorem was interpreted. For two active structures, which are adjoint to each other and with the reciprocal gain-matrices, the right and left eigenvector are reciprocal. The relationship between an active structure and the corresponding passive structure is expressed with the transfer functions, which is employed to resolve the estimation problems.

The Parameters Selection of SMA Optically Activated and Its Application

Shape Memory Alloy (SMA) optically activated is the key technology of optical SMA activator.According to the shape memory mechanism of SMA,researches are done on the activating response time and light wavelength of activating source etc of SMA optically activated to approach the parameters selection of optical activation.SMA has the optimum efficiency in the range of 13 seconds to 27 seconds when SMA is illuminated continuously by wavelength of 675nm;The power of light wave has a low effect on SMA;The longer the activating wavelength,the quicker the response time of SMA activated.If the proper activating time and activating wavelength are adopted, and the structure deformation of composite material of SMA imbedded may be actively controlled,an ideal effect will be gotten.The research provides an evidence for the design of optical SMA activator and is of great significance to its application.The research on smart structure has a wide application prospect.

A refined finite element method for bending analysis of laminated plates integrated with piezoelectric fiber-reinforced composite actuators

This research presents a finite element formulation based on four-variable refined plate theory for bending analysis of cross-ply and angle-ply laminated composite plates integrated with a piezoelectric fiber-reinforced composite actuator under electromechanical loading. The four-variable refined plate theory is a simple and efficient higher-order shear deformation theory, which predicts parabolic variation of transverse shear stresses across the plate thickness and satisfies zero traction conditions on the plate free surfaces. The weak form of governing equations is derived using the principle of minimum potential energy, and a 4-node non-conforming rectangular plate element with 8 degrees of freedom per node is introduced for discretizing the domain. Several benchmark problems are solved by the developed MATLAB code and the obtained results are compared with those from exact and other numerical solutions, showing good agreement.

Recent advances in structural control research and applications in China mainland

The recent developments of theoretical research, model tests and engineering applications of structural control in China's Mainland are reviewed in this paper. It includes seismic isolation, passive energy dissipation, active and semi-active control, smart materials and smart structural systems. It can be seen that passive control methods, such as seismic isolation and energy dissipation methods, have developed into the mature stage in China. At the same time, great progress has been made in active and semi-active control, and smart actuators or smart dampers and smart structural systems. Finally, some future research initiatives for structural control in civil engineering are suggested. Keywords state-of-the-art review - structural control - seismic isolation - passive energy dissipation - active and semi-active control - smart material and smart structure Supported by : National Natural Science Foundation of China (Grant No. 50025821)

Nonlinear integral resonant controller for vibration reduction in nonlinear systems

A new nonlinear integral resonant controller（NIRC） is introduced in this paper to suppress vibration in nonlinear oscillatory smart structures. The NIRC consists of a first-order resonant integrator that provides additional damping in a closed-loop system response to reduce highamplitude nonlinear vibration around the fundamental resonance frequency. The method of multiple scales is used to obtain an approximate solution for the closed-loop system.Then closed-loop system stability is investigated using the resulting modulation equation. Finally, the effects of different control system parameters are illustrated and an approximate solution response is verified via numerical simulation results.The advantages and disadvantages of the proposed controller are presented and extensively discussed in the results. The controlled system via the NIRC shows no high-amplitude peaks in the neighboring frequencies of the resonant mode,unlike conventional second-order compensation methods.This makes the NIRC controlled system robust to excitation frequency variations.

Vibration shape testing of space sheet structure

The space sheet for a solar array structure is large in dimension, and flexible to induce complex distortion. It is difficult to measure the distortion. A large-scale flexible test prototype system is built for sheet structure vibration monitoring based on the vibration information of the solar array in space. The system provides an intelligent test method for flexible space structure with embedded sensors and non-visualization reinstruction. Multiple fiber Bragg grating （FBG） sensors are packaged and embedded into the structure with spatial division multiplexing （SDM） and wavelength division multiplexing （WDM）. The sensor interrogator distinguishes wavelength shifts that can be turned into curvature of the curve. The structure shape is reconstructed based on the curvature information and the arc-length, and then displayed. The experiment shows that the system has a high FBG sensitivity. The reconstruction algorithm is fast with high precision. The system has great potential for use in health monitoring of the space sheet structure.

Dynamic Modeling and Analysis ofWind Turbine Blade of Piezoelectric Plate Shell

This paper presents a theoretical analysis of vibration control technology of wind turbine blades made of piezoelectric intelligent structures.The design of the blade structure,which is made from piezoelectric material,is approximately equivalent to a flat shell structure.The differential equations of piezoelectric shallow shells for vibration control are derived based on piezoelectric laminated shell theory.On this basis,wind turbine blades are simplified as elastic piezoelectric laminated shells.We establish the electromechanical coupling system dynamic model of intelligent structures and the dynamic equation of composite piezoelectric flat shell structures by analyzing simulations of active vibration control.Simulation results show that,under wind load,blade vibration is reduced upon applying the control voltage.

A Multivariate Variational Principle for Piezoelectric Efect Problems

The mechanical electric coupling effect of piezoelectric materials and devices is discussed and a brief review on the evolution of the technique is presented.On such basis,as a first step toward the formulation of finite elements for analysis of piezoelectric devices,a multivariate variation principle is presented.As has been revealed by the present work,an important particularization thereof is the Allik Hughes functional.

Morphing wing flaps for large civil aircraft:Evolution of a smart technology across the Clean Sky program

Abstract Morphing wing structures are widely considered among the most promising technologies for the improvement of aerodynamic performances in large civil aircraft.The controlled adaptation of the wing shape to external operative conditions naturally enables the maximization of aircraft aerodynamic efficiency,with positive fallouts on the amount of fuel burned and pollutant emissions.The benefits brought by morphing wings at aircraft level are accompanied by the criticalities of the enabling technologies,mainly involving weight penalties,overconsumption of electrical power,and safety issues.The attempt to solve such criticalities passes through the development of novel design approaches,ensuring the consolidation of reliable structural solutions that are adequately mature for certification and in-flight operations.In this work,the development phases of a multimodal camber morphing wing flap,tailored for large civil aircraft applications,are outlined with specific reference to the activities addressed by the author in the framework of the Clean Sky program.The flap is morphed according to target shapes depending on aircraft flight conditions and defined to enhance high-lift performances during takeoff and landing,as well as wing aerodynamic efficiency during cruise.An innovative system based on finger-like robotic ribs driven by electromechanical actuators is proposed as morphing-enabling technology;the maturation process of the device is then traced from the proof of concept to the consolidation of a true-scale demonstrator for pre-flight ground validation tests.A step-by-step approach involving the design and testing of intermediate demonstrators is then carried out to show the compliance of the adaptive system with industrial standards and safety requirements.The technical issues encountered during the development of each intermediate demonstrator are critically analyzed,and justifications are provided for all the adopted engineering solutions.Finally,the layout of the true-scale demonstrator is presented,with emphasis on the architectural strengths,enabling the forthcoming validation in real operative conditions.

Innovative technologies in manufacturing,mechanics and smart civil infrastructure

An overview on converging technologies that are the primary drivers of the 4th Industrial Revolution is presented,followed by new developments in advanced manufacturing,nano-,information-technologies and smart civil infrastructure technologies.Convergence of these transformative technologies is discussed.Emphases are on advanced manufacturing,nano mechanics/materials,sensors,structural control,smart structures/materials,energy harvesting,multi-scale problems and simulation methods.

Forced vibration of smart laminated viscoelastic plates by RPT finite element approach

In this study,a finite element formulation based on the four-variable refined plate theory(RPT)is presented for forced vibration analysis of laminated viscoelastic composite plates integrated with a piezoelectric layer.To the best of the authors’knowledge,this is the first time that the proposed approach is extended for study of the dynamic behavior of the smart viscoelastic plate.The utilized RPT which works for both thick and thin plates predicts a parabolic variation for transverse shear stresses across the plate thickness.Considering a linear viscoelastic model for the substrate material,the relaxation module is predicted by the Prony series.Using Hamilton’s principle,the weak form equation is constructed and a four-node rectangular plate element is utilized for discretizing the domain.The Newmark scheme is employed for advancing the solution in time.A MATLAB code is developed based on the formulations and several benchmark problems are solved.Comparing the findings with existing results in previous studies confirms the accuracy and efficiency of the proposed method.The dynamic response of the smart viscoelastic plates under various electromechanical loads is investigated and the results show that the.vibration can be passively controlled by adding and actuating the piezoelectric layer.The damping effects of viscoelastic parameters on the results are investigated,too.

Field-dependent nonlinear piezoelectricity:a focused review

This contribution presents a multidisciplinary review of the so-called field-dependent nonlinear piezoelectricity.It starts with an introduction that poses the literature analysis framework,through defining this operational(that is oftenmet in practice)piezoelectric field-dependent nonlinearity.Indeed,the latter is a less known phenomenon although it is inherent to stress-free actuation responses of corresponding smart materials,actuators and structures.Then,related experimental observations from piezoelectric materials,actuator devices and smart structures tests are multidisciplinary surveyed for understanding the underlying mechanisms of the encountered field-dependent nonlinearity.Next,empirical material and numerical structural modelling and simulation approaches are critically reviewed from,respectively,the constitutive and finite element analysis points of view.Summary conclusions and few future directions for research are finally provided as a closure.It is worth mentioning that,although it is concise(retains only experiments and experimentally-correlated models and simulations),this critical review covers the last three decades period which is almost the whole age of the piezoelectric materials,actuators and smart structures research field.

In-plane corrugated cosine honeycomb for 1D morphing skin and its application on variable camber wing

A novel 0-Poisson＇s ratio cosine honeycomb support structure of flexible skin is proposed. Mechanical model of the structure is analyzed with the energy method, finite element method （FEM） and experiments have been performed to validate the theoretical model. The in-plane characteristics of the cosine honeycomb are compared with accordion honeycomb through analytical models and experiments. Finally, the application of the cosine honeycomb on a variable camber wing is studied. Studies show that mechanical model agrees well with results of FEM and experiments. The transverse non-dimensional elastic modulus of the cosine honeycomb increases （decreases） when the wavelength or the wall width increases （decreases）, or when the amplitude decreases （increases）. Compared with accordion honeycomb, the transverse non-dimensional elastic modulus of the cosine honeycomb is smaller, which means the driving force is smaller and the power consumption is less during deformation. In addition, the cosine honeycomb can satisfy the deform- ing requirements of the variable camber wing.

Piezoelectric Actuator Placement Optimization and Active Vibration Control of a Membrane Structure

The placement optimization of piezoelectric actuators and active vibration control of a membrane structure are studied in this paper. The classical linear quadratic regulator con- trollers are designed to suppress the unwanted vibration. Simulation results indicate that the optimal locations of piezoelectric actuators are affected deeply by the additional mass and stiff- ness of actuators, the computational efficiency of particle swarm optimizer is higher than that of genetic algorithm for this particular problem, and the control performance of optimally placed actuators is better than that of non-optimally placed actuators.

An artificial neural network model for multi-flexoelectric actuation of Plates

Flexoelectric effect can be used to design actuators to control engi-neering structures including beams,plates,and shells.Multiple flexo-electric actuators method has the advantage of less stress concentration and better control effect,but the mode-dependent optimal actuator locations could influence the flexoelectric actuation effect significantly.In this work,a neural network model is established to study the optimal combinations of multiple flexoelectric actuators on a rectangular plate.In the physical model,an atomic force micro-scope(AFM)probe was employed to generate an electric field gradient in the flexoelectric patch,so that flexoelectric control force and moment can be obtained.Multiple flexoelectric actuators on the plate was considered.Case studies showed that the flexoelectricity induced stress mainly concentrate near the probe,the size and shape of the flexoelectric patch have limited effect on the actuation,hence,only the actuator positions were choosing as the input of the ANN model.Using the prediction of the neural network model,the driving effect of a large number of actuators at different positions can be quickly obtained,and the optimal position of the actuator can be analyzed more accurately.