Hydraulically Coupled Dielectric Elastomer Actuators for a Bioinspired Suction Cup

Suction cups of cephalopods show a preeminent performance when absorbing irregular or flat objects. In this paper, an octopi-inspired suction cup, driven by hydraulically coupled dielectric elastomer actuators (HCDEAs), is proposed, which is considered to be controlled easily and have compact structure. To investigate the performance of suction cups, experiments have been conducted to clarify the effect of the pre-stretch ratio and chamber angle on suction forces. It could be seen that both factors have a complicated influence on suction forces, and the best performance obtained was a reasonable combination of the pre-stretch ratio and chamber angle. Here, we achieved a maximum suction force of 175 mN with λp = 1.2, α = 23° under a DC voltage of 3500 V. To enhance the capacity and adaptation of the suction cup, flat objects of various types of materials were introduced as targets. Experimental results displayed that for tested materials, including a dry/wet acrylic plate, CD, ceramic wafer, and aluminum plate, the suction cup showed outstanding performance of absorbing and lifting the target without any damage or scratch to them. Our research may serve as a guide to the optimal design and provide insights into the performance of the HCDEAs-actuated suction cup.

Analysis of Membrane Deploying Process Based on Miura Origami

Aiming at a series of characteristics of the membrane structure in the folded configuration during the deploying process, the initial defect of the membrane crease is introduced by proxy model, and to realize the study of the deploying process of the membrane. Based on the finite element method, the deploying process of the multi-element Miura membrane is simulated. And the stretch ratio, maximum mises stress, deployment rate, wrinkle deformation, etc. of membrane structure are discussed. The existence of creases can cause damage to the membrane surface, so the total length of the creases should be within an appropriate size range. By changing the number of elements and the longitudinal crease angle of the same size membrane respectively, the influence of the above two factors on the total crease length, storage volume and deploying process of the folded membrane is studied. The results show that when the longitudinal crease angle is 15°, the transverse and longitudinal displacements of the Miura folded membrane with different element numbers are not synchronized during the deploying process. By keeping the number of elements constant and increasing the angle of the longitudinal creases from 15° to 45°, the synchronization of the transverse and longitudinal displacements during the membrane deploying process is gradually enhanced. In addition, the experiment on the membrane deploying process verifies the reliability of the finite element simulation results.

A Compliant Micromechanism for Biaxially Stretching Biological Cells

Biological cells are known to respond to mechanical forces. Diverse biological phenomena such as tissue development and cancer are regulated by mechanical forces acting on cells. One such mechanical loading found in various tissues such as alveoli, pericardium, blood vessels, and urinary bladder is biaxial stretching. To study the effect of such a loading pattern, it is necessary to develop mechanical tools that can apply controlled biaxial stretching on cells. Here we present the design for such a device, a compliant micromechanism for biaxially stretching single cells. We first designed a compliant, double-input, biaxial stretching mechanism based on re-entrant structures. Various stretch ratios, defined as the ratio between deformations in orthogonal directions, could be obtained by changing the dimensions of this mechanism. Next, we derived an analytical expression relating the geometric parameters to the stretch ratio. This analytical expression was verified using finite element analysis. By numerically solving this expression, multiple designs for a desired stretch ratio were obtained. Furthermore, we converted our design into a single-input mechanism by coupling the double-input biaxial stretcher to a single-input gripper mechanism. Finally, we demonstrate the functioning of our design using a macroscale, 3D-printed version.

3D brain tumor segmentation using a two-stage optimal mass transport algorithm

Optimal mass transport (OMT) theory, the goal of which is to move any irregular 3D object (i.e., the brain) without causing significant distortion, is used to preprocess brain tumor datasets for the first time in this paper. The first stage of a two-stage OMT (TSOMT) procedure transforms the brain into a unit solid ball. The second stage transforms the unit ball into a cube, as it is easier to apply a 3D convolutional neural network to rectangular coordinates. Small variations in the local mass-measure stretch ratio among all the brain tumor datasets confirm the robustness of the transform. Additionally, the distortion is kept at a minimum with a reasonable transport cost. The original $$240 \times 240 \times 155 \times 4$$ 240 × 240 × 155 × 4 dataset is thus reduced to a cube of $$128 \times 128 \times 128 \times 4$$ 128 × 128 × 128 × 4 , which is a 76.6% reduction in the total number of voxels, without losing much detail. Three typical U-Nets are trained separately to predict the whole tumor (WT), tumor core (TC), and enhanced tumor (ET) from the cube. An impressive training accuracy of 0.9822 in the WT cube is achieved at 400 epochs. An inverse TSOMT method is applied to the predicted cube to obtain the brain results. The conversion loss from the TSOMT method to the inverse TSOMT method is found to be less than one percent. For training, good Dice scores (0.9781 for the WT, 0.9637 for the TC, and 0.9305 for the ET) can be obtained. Significant improvements in brain tumor detection and the segmentation accuracy are achieved. For testing, postprocessing (rotation) is added to the TSOMT, U-Net prediction, and inverse TSOMT methods for an accuracy improvement of one to two percent. It takes 200 seconds to complete the whole segmentation process on each new brain tumor dataset.

INTEGRATED DESIGN OF PHYSIOLOGICAL MULTI-PARAMETER SENSORS ON A SMART GARMENT BY ULTRA-ELASTIC E-TEXTILE

The performance of electronic textile (E-textile)-based wearable sensors is largely determined by the wire and electrode contacting stability to the body, which is a multi-discipline challenge for smart garment designs. In this paper, an integrated design of wearable sensors on a smart garment is presented to concurrently measure the multi-channel electrocardiogram, respiration, and temperature signals in different regions of the body. Sensors in separative probe-controller schemes are introduced with full-textile designs of the electrodes and signal transmission wires. An ultra-elastic structure of E-textile wire is proposed with excellent electrical stability, high stretch ratio, and low tension under body dynamics. A complete garment integration solution of the probes, wires, and the sensors is presented. The design is evaluated by comparing the signal quality in static and moderate body movements, which shows clinical level comparable precision and stability. The proposed design may constitute a general solution of distributed noninvasive physiological multi-parameter detection and monitoring applications.

Stochastic dynamics of dielectric elastomer balloon with viscoelasticity under pressure disturbance

Dielectric elastomers are widely used in many fields due to their advantages of high deformability, light weight, biological compatibility, and high efficiency. In this study, the stochastic dynamic response and bifurcation of a dielectric elastomer balloon (DEB) with viscoelasticity are investigated. Firstly, the rheological model is adopted to describe the viscoelasticity of the DEB, and the dynamic model is deduced by using the free energy method. The effect of viscoelasticity on the state of equilibrium with static pressure and voltage is analysed. Then, the stochastic differential equation about the perturbation around the state of equilibrium is derived when the DEB is under random pressure and static voltage. The steady-state probability densities of the perturbation stretch ratio are determined by the generalized cell mapping method. The effects of parameter conditions on the mean value of the perturbation stretch ratio are calculated. Finally, sinusoidal voltage and random pressure are applied to the viscoelastic DEB, and the phenomenon of P-bifurcation is observed. Our results are compared with those obtained from Monte Carlo simulation to verify their accuracy. This work provides a potential theoretical reference for the design and application of DEs.

Non steady-state intersonic cracks in elastomer membranes under large static strain

International audience Dynamic crack propagation in elastomer membranes is investigated; the focus is laid on cracks reaching the speed of shear waves in the material. The specific experimental setup developed to measure crack speed is presented in details. The protocol consists in (1) stretching an elastomer membrane under planar tension loading conditions, then (2) initiating a small crack on one side of the membrane. The crack speed is measured all along the crack path in both reference and actual configurations, including both acceleration and deceleration phases, i.e. non steady-state crack propagation phases. The influence of the prescribed stretch ratio on crack speed is analysed in the light of both these new experiments and the few previously published studies. Conclusions previously drawn for steady-state crack growth are extended to non steady-state conditions: stretch perpendicular to the crack path governs crack speed in intersonic crack propagation regime, and the role of the stretch in crack direction is minor.

Humidity Effect on Dynamic Electromechanical Properties of Polyacrylic Dielectric Elastomer: An Experimental Study

In this research, by utilizing the Very-High-Bond (VHB) 4905 elastomer, we carry out an experimental examination on the humidity effect on dynamic electromechanical performances of dielectric elastomers, including the dynamic response and viscoelastic creeping. Firstly, we experimentally analyze effects of the pre-stretch, peak voltage, waveform and frequency of the dynamic response of VHB 4905 elastomer under several ambient humidities. In general, the amplitude of dynamic deformation gradually adds up with the increasing humidity. Besides, it is found that the amplitude affected by different parameters shows diverse sensitivity to humidity. Subsequently, effect of humidity on the viscoelastic creeping of VHB 4905 is explored. The results demonstrate that, subject to different ambient humidities, the viscoelastic creeping under Alternating Current (AC) voltage is similar to that under Direct Current (DC) voltage. Furthermore, the equilibrium position of dynamic viscoelastic creep enlarges gradually with the humidity, regardless of voltage waveforms. For the dielectric elastomer with a pre-stretch ratio of 3, when the humidity increases from 20% to 80%, the increase of average equilibrium position of dynamic viscoelastic creep is larger than 1599%.

Fracture Kinematics and Holocene Stress Field at the Krafla Rift, Northern Iceland

In the Northern Volcanic Zone of Iceland, the geometry, kinematics and offset amount of the structures that form the active Krafla Rift were studied. This rift is composed of a central volcano and a swarm of extension fractures, normal faults and eruptive fissures, which were mapped and analysed through remote sensing and field techniques. In three areas, across the northern, central and southern part of the rift, detailed measurements were collected by extensive field surveys along the post-Late Glacial Maximum (LGM) extension fractures and normal faults, to reconstruct their strike, opening direction and dilation amount. The geometry and the distribution of all the studied structures suggest a northward propagation of the rift, and an interaction with the Húsavík–Flatey Fault. Although the opening direction at the extension fractures is mostly normal to the general N–S rift orientation (average value N99.5° E), a systematic occurrence of subordinate transcurrent components of motion is noticed. From the measured throw at each normal fault, the heave was calculated, and it was summed together with the net dilation measured at the extension fractures; this has allowed us to assess the stretch ratio of the rift, obtaining a value of 1.003 in the central sector, and 1.001 and 1.002 in the northern and southern part, respectively.