scholarly journals Mechanical metamaterials at the theoretical limit of isotropic elastic stiffness

Nature ◽  
2017 ◽  
Vol 543 (7646) ◽  
pp. 533-537 ◽  
Author(s):  
J. B. Berger ◽  
H. N. G. Wadley ◽  
R. M. McMeeking
Keyword(s):  
Elastic Stiffness ◽  
Theoretical Limit ◽  
Mechanical Metamaterials

scholarly journals Elasticity Approach to Predict Shape Transformation of Functionally Graded Mechanical Metamaterial under Tension

Materials ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3452
Author(s):  
Mohammad Javad Khoshgoftar ◽  
Ali Barkhordari ◽  
Sajjad Seifoori ◽  
Mohammad Javad Mirzaali
Keyword(s):  
Elastic Stiffness ◽  
Theory Of Elasticity ◽  
Functionally Graded ◽  
Unit Cell ◽  
Uniaxial Tensile ◽  
Geometrical Parameters ◽  
Design Strategies ◽  
Shape Transformation ◽  
Complex Deformation ◽  
Mechanical Metamaterials

The re-entrant structures are among the simple unit cell designs that have been widely used in the design of mechanical metamaterials. Changing the geometrical parameters of these unit cell structures, their overall elastic properties (i.e., elastic stiffness and Poisson’s ratio), can be simultaneously tuned. Therefore, different design strategies (e.g., functional gradient) can be implemented to design advanced engineering materials with unusual properties. Here, using the theory of elasticity and finite element modeling, we propose a fast and direct approach to effectively design the microarchitectures of mechanical metamaterials with re-entrant structures that allow predicting complex deformation shapes under uniaxial tensile loading. We also analyze the efficiency of this method by back calculating the microarchitectural designs of mechanical metamaterials to predict the complex 1-D external contour of objects (e.g., vase and foot). The proposed approach has several applications in creating programmable mechanical metamaterials with shape matching properties for exoskeletal and soft robotic devices.

New Aspects in the Design of Electron Optical Magnification Systems

1972 ◽  
Vol 30 ◽  
pp. 606-607
Author(s):  
Willem H.J. Andersen
Keyword(s):  
Electron Microscope ◽  
Imaging System ◽  
Chromatic Aberration ◽  
Research Tool ◽  
Energy Losses ◽  
Objective Lens ◽  
Theoretical Limit ◽  
Optical Magnification ◽  
Chromatic Aberrations ◽  
High Degree

Electron microscope design, and particularly the design of the imaging system, has reached a high degree of perfection. Present objective lenses perform up to their theoretical limit, while the whole imaging system, consisting of three or four lenses, provides very wide ranges of magnification and diffraction camera length with virtually no distortion of the image. Evolution of the electron microscope in to a routine research tool in which objects of steadily increasing thickness are investigated, has made it necessary for the designer to pay special attention to the chromatic aberrations of the magnification system (as distinct from the chromatic aberration of the objective lens). These chromatic aberrations cause edge un-sharpness of the image due to electrons which have suffered energy losses in the object.There exist two kinds of chromatic aberration of the magnification system; the chromatic change of magnification, characterized by the coefficient Cm, and the chromatic change of rotation given by Cp.

“Getting High Resolution Out of A High Voltage Microscope”

1980 ◽  
Vol 38 ◽  
pp. 822-825
Author(s):  
David J. Smith
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
High Voltage ◽  
Theoretical Limit ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
High Voltage Electron ◽  
Technological Advances ◽  
Potential Improvement ◽  
Lower Voltage

The initial attractions of the high voltage electron microscope (HVEM) stemmed mainly from the possibility of considerable increases in electron penetration through thick specimens compared with conventional 100KV microscopes, although the potential improvement in resolution associated with the decrease in election wavelength had been fully appreciated for many years (eg. Cosslett, 1946)1, even if not realizable in practice. Subsequent technological advances enabled the performance of lower voltage machines to be brought closer to the theoretical limit, to be followed in turn by more recent projects which have been successful, eventually, in achieving even higher resolution with dedicated higher voltage instruments such as those at Kyoto (500KV)2, Munich (400KV)3, Ibaraki (1250KV)4 and Cambridge (600KV)5. It does not necessarily follow however that the performance of journal high voltage microscopes can be easily upgraded, retrospectively, to the same level, as will be discussed in detail below.

Multi-Scale Aeroelastic Analysis of Wings with Lattice-Based Mechanical Metamaterials

2021 ◽  
Author(s):  
Natsuki Tsushima ◽  
Ryo Higuchi ◽  
Hitoshi Arizono ◽  
Masato Tamayama
Keyword(s):  
Multi Scale ◽  
Mechanical Metamaterials ◽  
Aeroelastic Analysis

scholarly journals Hierarchical mechanical metamaterials built with scalable tristable elements for ternary logic operation and amplitude modulation

2021 ◽  
Vol 7 (9) ◽  
pp. eabf1966
Author(s):  
Hang Zhang ◽  
Jun Wu ◽  
Daining Fang ◽  
Yihui Zhang
Keyword(s):  
Structural Diversity ◽  
Cell Number ◽  
Structural Elements ◽  
Ternary Logic ◽  
Stable States ◽  
One Dimensional ◽  
Logic Operation ◽  
Artificial Materials ◽  
Mechanical Metamaterials ◽  
Unit Cells

Multistable mechanical metamaterials are artificial materials whose microarchitectures offer more than two different stable configurations. Existing multistable mechanical metamaterials mainly rely on origami/kirigami-inspired designs, snap-through instability, and microstructured soft mechanisms, with mostly bistable fundamental unit cells. Scalable, tristable structural elements that can be built up to form mechanical metamaterials with an extremely large number of programmable stable configurations remains illusive. Here, we harness the elastic tensile/compressive asymmetry of kirigami microstructures to design a class of scalable X-shaped tristable structures. Using these structure as building block elements, hierarchical mechanical metamaterials with one-dimensional (1D) cylindrical geometries, 2D square lattices, and 3D cubic/octahedral lattices are designed and demonstrated, with capabilities of torsional multistability or independent controlled multidirectional multistability. The number of stable states increases exponentially with the cell number of mechanical metamaterials. The versatile multistability and structural diversity allow demonstrative applications in mechanical ternary logic operators and amplitude modulators with unusual functionalities.

scholarly journals Sensitivity Based Selection of an Optimal Cable-Driven Parallel Robot Design for Rehabilitation Purposes

Robotics ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 7
Author(s):  
Ferdaws Ennaiem ◽  
Abdelbadiâ Chaker ◽  
Juan Sebastián Sandoval Arévalo ◽  
Med Amine Laribi ◽  
Sami Bennour ◽  
...  
Keyword(s):  
Pareto Front ◽  
Parallel Robot ◽  
Elastic Stiffness ◽  
Upper Limb Rehabilitation ◽  
Daily Life Activities ◽  
System A ◽  
The Monte Carlo Method ◽  
Genetic Algorithm Method ◽  
Limb Rehabilitation ◽  
Selection Of

This paper deals with the design of an optimal cable-driven parallel robot (CDPR) for upper limb rehabilitation. The robot’s prescribed workspace is identified with the help of an occupational therapist based on three selected daily life activities, which are tracked using a Qualisys motion capture system. A preliminary architecture of the robot is proposed based on the analysis of the tracked trajectories of all the activities. A multi-objective optimization process using the genetic algorithm method is then performed, where the cable tensions and the robot size are selected as the objective functions to be minimized. The cables tensions are bounded between two limits, where the lower limit ensures a positive tension in the cables at all times and the upper limit represents the maximum torque of the motor. A sensitivity analysis is then performed using the Monte Carlo method to yield the optimal design selected out of the non-dominated solutions, forming the obtained Pareto front. The robot with the highest robustness toward the disturbances is identified, and its dexterity and elastic stiffness are calculated to investigate its performance.

scholarly journals Digital logic gates in soft, conductive mechanical metamaterials

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Charles El Helou ◽  
Philip R. Buskohl ◽  
Christopher E. Tabor ◽  
Ryan L. Harne
Keyword(s):  
Integrated Circuits ◽  
Electronic Materials ◽  
Polymer Networks ◽  
Conductive Polymer ◽  
Network Connectivity ◽  
Logic Gates ◽  
Boolean Logic ◽  
Digital Logic ◽  
Mechanical Metamaterials ◽  
Logic Operations

AbstractIntegrated circuits utilize networked logic gates to compute Boolean logic operations that are the foundation of modern computation and electronics. With the emergence of flexible electronic materials and devices, an opportunity exists to formulate digital logic from compliant, conductive materials. Here, we introduce a general method of leveraging cellular, mechanical metamaterials composed of conductive polymers to realize all digital logic gates and gate assemblies. We establish a method for applying conductive polymer networks to metamaterial constituents and correlate mechanical buckling modes with network connectivity. With this foundation, each of the conventional logic gates is realized in an equivalent mechanical metamaterial, leading to soft, conductive matter that thinks about applied mechanical stress. These findings may advance the growing fields of soft robotics and smart mechanical matter, and may be leveraged across length scales and physics.

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