Shuhai Jia

Dynamic electromechanical performance of viscoelastic dielectric elastomers

Because of their viscoelasticity, dielectric elastomers (DEs) are able to produce a large time-dependent electromechanical deformation. In the current study, we use the Euler-Lagrange equation to characterize the influence of temperature, excitation frequency, and viscoelasticity on the dynamic electromechanical deformation and stability of viscoelastic dielectrics. We investigate the time-dependent dynamic performance, hysteresis, phase diagram, and Poincare map associated with the viscoelastic dissipative process. The results show that the dynamic response has strong temperature and frequency dependencies. It is observed that the natural frequency of the DE decreases with increasing temperature and the maximal amplitude increases at higher temperatures. At relative low frequencies, the amplitude is very small and the viscoelasticity has a significant effect on the oscillation of the system. Furthermore, the results show that the viscoelasticity has a relatively major influence on the dynamic performance for DEs that have very low relaxation times.

Experimental study on the dynamic response of in-plane deformation of dielectric elastomer under alternating electric load

Recently, dielectric elastomer actuators (DEAs) have garnered remarkable attention mainly due to their ability of large deformation. Previously, the dynamic responses of out-of-plane deformations of inflated and clamped dielectric elastomer (DE) membranes were experimentally investigated, and a quasi-static model of large deformation concerned with the configuration was derived. However, the research work on the time-varying response of in-plane deformation of DE is insufficient. In this paper, we studied the dynamic response of the in-plane deformation of a dielectric elastomer membrane under a pure-shear state. We experimentally analysed how this response was affected by the peak voltage, frequency, pre-stretching, and signal waveform. The deformation equilibrium position of the membrane drifted severely during vibration, which may be attributable to the high viscoelasticity of the membrane and may lead to issues when designing precise instruments. We also studied how the peak voltage, frequency, pre-stretching, and waveform affected this viscoelastic drifting.

Phase-error analysis and elimination for nonsinusoidal waveforms in Hilbert transform digital-fringe projection profilometry

The nonlinear intensity response of a digital fringe-projection-profilometry (FPP) system causes the captured fringe patterns to be nonsinusoidal waveforms, which results in phase error and therefore measurement error. The theoretical analysis of the phase error due to the nonsinusoidal waveforms in Hilbert transform FPP is performed. Based on the derived phase-error expression, a cubic spline-smoothing method is proposed to eliminate the nonsinusoidal phase error. Experiments show that the proposed algorithm can be used for effective phase-error elimination in practical Hilbert transform FPP.

Recovery of absolute height from wrapped phase maps for fringe projection profilometry

A novel multi-frequency fringe projection profilometry is presented in this paper. Fringe patterns with multiple frequencies are projected onto an object by a digital micro-mirror device projector. The approach involves an improved Fourier transform profilometry method with an additional π phase shifting stage and hence the acquisition of two source images. A peak searching algorithm is then employed to obtain the real height profile of the object together with a mathematical proof of this algorithm. In our method, the height of each point on the object is measured independently and the phase unwrapping procedure is avoided, enabling the measurement of objects with large depth discontinuities, where the phase unwrapping is difficult. The measurement result is given to validate the method in the paper. Our technique has great potential in industrial applications where the measurement of objects with complex shape and large discontinuities is needed.

Modeling of dielectric elastomer as electromechanical resonator

Dielectric elastomers (DEs) feature nonlinear dynamics resulting from an electromechanical coupling. Under alternating voltage, the DE resonates with tunable performances. We present an analysis of the nonlinear dynamics of a DE as electromechanical resonator (DEER) configured as a pure shear actuator. A theoretical model is developed to characterize the complex performance under different boundary conditions. Physical mechanisms are presented and discussed. Chaotic behavior is also predicted, illustrating instabilities in the dynamics. The results provide a guide to the design and application of DEER in haptic devices.

Graphene-Based Polymer Bilayers with Superior Light-Driven Properties for Remote Construction of 3D Structures

3D structure assembly in advanced functional materials is important for many areas of technology. Here, a new strategy exploits IR light‐driven bilayer polymeric composites for autonomic origami assembly of 3D structures. The bilayer sheet comprises a passive layer of poly(dimethylsiloxane) (PDMS) and an active layer comprising reduced graphene oxides (RGOs), thermally expanding microspheres (TEMs), and PDMS. The corresponding fabrication method is versatile and simple. Owing to the large volume expansion of the TEMs, the two layers exhibit large differences in their coefficients of thermal expansion. The RGO‐TEM‐PDMS/PDMS bilayers can deflect toward the PDMS side upon IR irradiation via the cooperative effect of the photothermal effect of the RGOs and the expansion of the TEMs, and exhibit excellent light‐driven, a large bending deformation, and rapid responsive properties. The proposed RGO‐TEM‐PDMS/PDMS composites with excellent light‐driven bending properties are demonstrated as active hinges for building 3D geometries such as bidirectionally folded columns, boxes, pyramids, and cars. The folding angle (ranging from 0° to 180°) is well‐controlled by tuning the active hinge length. Furthermore, the folded 3D architectures can permanently preserve the deformed shape without energy supply. The presented approach has potential in biomedical devices, aerospace applications, microfluidic devices, and 4D printing.

Aided manufacturing techniques and applications in optics and manipulation for ionic polymer-metal composites as soft sensors and actuators

Abstract Recently, ionic polymer-metal composites (IPMCs), which are becoming an increasingly popular material, have been used as soft actuators because of their inherent properties of light weight, flexibility, softness, especially efficient transformation from electrical energy to mechanical energy with large bending strain response under low activation voltage. This paper mainly focuses on a review on optical and micromanipulation applications of IPMCs as soft actuators. After presenting the general mechanism of sensing and actuating in IPMCs, recent progresses are discussed about the preparation process and practical technologies, especially for aided manufacturing techniques defined as the methods to fabricate IPMC into all kinds of shapes in terms of the demands, which are reviewed for the first time. Then, a number of recent IPMC applications for optical actuators, grippers and catheters are reviewed and investigated in this paper. Further developments and suggestions for IPMCs are also discussed. Extensive previous researches are provided for references in detail.

The application of multi-frequency fringe projection profilometry on the measurement of biological tissues.

A volume of research has been performed on the optical surface profilometry in the field of biomedicine and the optical system with the phase-measuring method becomes the main emphasis of the research. In this research, a brand new fringe projection profilometry with multiple frequencies is described for measuring the biological tissue. A pork liver, as an object, is regarded as a human organ and a DMD projector is used to generate the multi-frequency fringe patterns. The wrapped phase maps are obtained by means of the five-step phase shifting method and calculated via a peak searching algorithm in which the process of measuring the point on the surface of the object is independent so that the step of unwrapping the phase can be avoided. The final results given are acceptable which confirm this method and suggest its enormous potential for the biomedical measurements.

Constitutive relation of viscoelastic dielectric elastomer

In this paper, we present a modified model describing the constitutive relation of viscoelastic dielectric elastomer (DE). The uniform uniaxial tension-recovery experiment was carried out at different stretching rates. Based on Yeoh hyper-elastic model, model-fitting approach is put forward to obtain the relationship between parameters of Yeoh model and stretching rate, thus the modified model was obtained. From the approximate relationship between harmonic motion and uniform reciprocating motion, the stress—strain curve in the recovery process was also identified through the hysteresis between stress and strain. The modified model, with concise form and evident physical concept, can describe the strong nonlinear behavior between deformation and mechanical stress of the material in a common stretching rate range (from 0.01s−1 to 0.8s−1 at least). The accuracy and reliability of the modified model was examined.

Highly Stretchable Core–Sheath Fibers via Wet-Spinning for Wearable Strain Sensors

Lightweight, stretchable, and wearable strain sensors have recently been widely studied for the development of health monitoring systems, human-machine interfaces, and wearable devices. Herein, highly stretchable polymer elastomer-wrapped carbon nanocomposite piezoresistive core-sheath fibers are successfully prepared using a facile and scalable one-step coaxial wet-spinning assembly approach. The carbon nanotube-polymeric composite core of the stretchable fiber is surrounded by an insulating sheath, similar to conventional cables, and shows excellent electrical conductivity with a low percolation threshold (0.74 vol %). The core-sheath elastic fibers are used as wearable strain sensors, exhibiting ultra-high stretchability (above 300%), excellent stability (>10 000 cycles), fast response, low hysteresis, and good washability. Furthermore, the piezoresistive core-sheath fiber possesses bending-insensitiveness and negligible torsion-sensitive properties, and the strain sensing performance of piezoresistive fibers maintains a high degree of stability under harsh conditions. On the basis of this high level of performance, the fiber-shaped strain sensor can accurately detect both subtle and large-scale human movements by embedding it in gloves and garments or by directly attaching it to the skin. The current results indicate that the proposed stretchable strain sensor has many potential applications in health monitoring, human-machine interfaces, soft robotics, and wearable electronics.