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META POPART – From top-left corner, proceeding clockwise: 1) Kirigami metamaterial drives the deformation of inflatable actuators; 2) Rotating square pattern when compressed in plane; 3) Cellular metamaterial makes fabric buckle out-of-plane; 4) Inclined porous metamaterials drives surface morphology when vacuumed;

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META POPART – From top-left corner, proceeding clockwise: 1) Kirigami metamaterial drives the deformation of inflatable actuators; 2) Rotating square pattern when compressed in plane; 3) Cellular metamaterial makes fabric buckle out-of-plane; 4) Inclined porous metamaterials drives surface morphology when vacuumed;

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The aftermath of destruction arising from debris impacting on a plasmonic hologram made of silver nanostructures.

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The aftermath of destruction arising from debris impacting on a plasmonic hologram made of silver nanostructures.

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The image displays different bone-like porous designs of metal 3D printed meta-biomaterial for medical implants. 3D printing offers a fascinating processing ability and design freedom that enabled the manufacturing of these intricate structures tailored to modulate both the mechanical and biological properties of Titanium implants in such a way that mimics the porous anatomy of human bone. Owing to their architected geometries, these meta-biomaterials present significant advantages over conventional structures due to their unique characteristics such as high strength-to-weight ratios and surface area-to-volume ratios which do not only tailor mechanical properties of typically stiff bio-metallic material to match that of the bone but they, also, facilitate biological functions by providing a porous media for nutrients transport and blood vessel growth. This would ultimately improve patient recovery and implant longevity offering exciting ‘meta’ opportunities for the healthcare sector to provide better patient care and efficient solutions which aim to elevate common problems associated with current practices in the medical implant industry.

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The image displays different bone-like porous designs of metal 3D printed meta-biomaterial for medical implants. 3D printing offers a fascinating processing ability and design freedom that enabled the manufacturing of these intricate structures tailored to modulate both the mechanical and biological properties of Titanium implants in such a way that mimics the porous anatomy of human bone. Owing to their architected geometries, these meta-biomaterials present significant advantages over conventional structures due to their unique characteristics such as high strength-to-weight ratios and surface area-to-volume ratios which do not only tailor mechanical properties of typically stiff bio-metallic material to match that of the bone but they, also, facilitate biological functions by providing a porous media for nutrients transport and blood vessel growth. This would ultimately improve patient recovery and implant longevity offering exciting ‘meta’ opportunities for the healthcare sector to provide better patient care and efficient solutions which aim to elevate common problems associated with current practices in the medical implant industry.

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Stretching of the Gaussian pulse in a layered nonlinear elastic metamaterial designed as an alternative layer of a linear and nonlinear elastic metallic material. The widths of linear and nonlinear layers are kept the same and that unit cell is repeated nearly 200-500 times. Note that, as the impedance of linear and nonlinear layers is the same, if material nonlinearity is not considered, no stretching and no higher harmonics, it’s just a linear wave propagation study. The widths of the layers are varied by maintaining the total length of the metamaterial same as shown in the image (?/?, ?, ??). Due to multiple local resonances, harmonic scattering, and cumulative harmonic generation, such an effect is observed. At ?/? width of a single layer, the wave received at the other end of the nonlinear metamaterial maintains its shape and generates higher harmonics. At ? width of a single layer, local harmonic resonance and harmonic scattering dominate more resulting in stretching of the wave. As the width of the single-layer increases to ??, the bulk wave gets delayed in the time domain due to cumulative harmonic generation.

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Stretching of the Gaussian pulse in a layered nonlinear elastic metamaterial designed as an alternative layer of a linear and nonlinear elastic metallic material. The widths of linear and nonlinear layers are kept the same and that unit cell is repeated nearly 200-500 times. Note that, as the impedance of linear and nonlinear layers is the same, if material nonlinearity is not considered, no stretching and no higher harmonics, it’s just a linear wave propagation study. The widths of the layers are varied by maintaining the total length of the metamaterial same as shown in the image (?/?, ?, ??). Due to multiple local resonances, harmonic scattering, and cumulative harmonic generation, such an effect is observed. At ?/? width of a single layer, the wave received at the other end of the nonlinear metamaterial maintains its shape and generates higher harmonics. At ? width of a single layer, local harmonic resonance and harmonic scattering dominate more resulting in stretching of the wave. As the width of the single-layer increases to ??, the bulk wave gets delayed in the time domain due to cumulative harmonic generation.

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One way to define a metamaterial is a material that exhibits properties not found in nature. This image represents a structure inspired by a natural metamaterial - Cellulose Ib.
Cellulose Ib, specifically from Norway spruce aka a Christmas tree, is auxetic at the molecular level. In the X-Y projection shown, the beams along X represent cellobiose chains, whereas the connecting spacers along Y represent hydrogen bonds that connect neighbouring chains to form a sheet. This model is deformed along Y, and the colours represent displacements with blue being the least and red representing the highest displacement. The shaded/grey model in the background shows the un-deformed version of this system, thus showing its auxetic behaviour as expansion is observed along both X and Y directions.
This model is part of a series of models developed to ultimately form a nature-inspired auxetic structure that derives its auxeticity from the molecular level. This would allow for chemical tuneability of such a material, thus finding applications in a wide range of sectors including automotive, biomedical, and aerospace.

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One way to define a metamaterial is a material that exhibits properties not found in nature. This image represents a structure inspired by a natural metamaterial - Cellulose Ib.
Cellulose Ib, specifically from Norway spruce aka a Christmas tree, is auxetic at the molecular level. In the X-Y projection shown, the beams along X represent cellobiose chains, whereas the connecting spacers along Y represent hydrogen bonds that connect neighbouring chains to form a sheet. This model is deformed along Y, and the colours represent displacements with blue being the least and red representing the highest displacement. The shaded/grey model in the background shows the un-deformed version of this system, thus showing its auxetic behaviour as expansion is observed along both X and Y directions.
This model is part of a series of models developed to ultimately form a nature-inspired auxetic structure that derives its auxeticity from the molecular level. This would allow for chemical tuneability of such a material, thus finding applications in a wide range of sectors including automotive, biomedical, and aerospace.

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Active noise control has been around since the pioneering work of Paul Lueg in 1936. The idea is to use active sources to prevent scattering of sound or to keep a closed region quiet. Over the last twenty years active metamaterials have become an important part of metamaterial science, leading to (amongst other things) what are now known as active cloaks. The idea is to distribute active sources in a way that both prevents scattering and keeps a region quiet. Achieving both of these feats is highly non-trivial! Furthermore knowing how to distribute sources spatially in three dimensions, whilst also calculating the required amplitudes of those sources is a highly complex computational challenge.
In our work we re-visited this problem and realised that distributing the active sources at the vertices of an imaginary Platonic solid surrounding the region that needs to be made quiet is highly effective and efficient. Why? One can exploit the rotational symmetry properties of the Platonic solids to show that we only need to find the required amplitude at one of the source locations in order to know the amplitudes at every other source location. This speeds up computations of the required amplitudes significantly.
The image illustrates the implementation of our active noise control technique in the case of acoustic scattering from a sphere. The bottom left image illustrates a cross-section of the pressure field due to scattering from a sphere due to plane wave incidence, without any active control. This is contrasted with the image in the bottom right, in which we have used the Platonic distribution of sources in the top right image to control the field. There is almost no scattering outside the active source region and almost complete quiet inside.
For more details see our current arxiv paper on this topic:
https://arxiv.org/abs/2109.14552

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Active noise control has been around since the pioneering work of Paul Lueg in 1936. The idea is to use active sources to prevent scattering of sound or to keep a closed region quiet. Over the last twenty years active metamaterials have become an important part of metamaterial science, leading to (amongst other things) what are now known as active cloaks. The idea is to distribute active sources in a way that both prevents scattering and keeps a region quiet. Achieving both of these feats is highly non-trivial! Furthermore knowing how to distribute sources spatially in three dimensions, whilst also calculating the required amplitudes of those sources is a highly complex computational challenge.
In our work we re-visited this problem and realised that distributing the active sources at the vertices of an imaginary Platonic solid surrounding the region that needs to be made quiet is highly effective and efficient. Why? One can exploit the rotational symmetry properties of the Platonic solids to show that we only need to find the required amplitude at one of the source locations in order to know the amplitudes at every other source location. This speeds up computations of the required amplitudes significantly.
The image illustrates the implementation of our active noise control technique in the case of acoustic scattering from a sphere. The bottom left image illustrates a cross-section of the pressure field due to scattering from a sphere due to plane wave incidence, without any active control. This is contrasted with the image in the bottom right, in which we have used the Platonic distribution of sources in the top right image to control the field. There is almost no scattering outside the active source region and almost complete quiet inside.
For more details see our current arxiv paper on this topic:
https://arxiv.org/abs/2109.14552

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