Micro-robot fish with SMA Biomimetic Fin

Wang and collaborators wrote an article on the design of cuddle fish like biomimetic fin using shape memory alloy wires.  A link to the abstract for this article is given here:  http://www.sciencedirect.com/science/article/pii/S0924424708001283.  The design of a biomimetic fishtail has utilization in the underwater vehicles, since fishtails create a greater propulsive efficiency.  Also, there may be uses in the areas of microsurgery or underwater exploration that requires a narrow vehicle.  The inspiration comes from the cuddlefish fin which works through a combination of jet propulsion at high speed and fin undulatory/oscillation at low speed.  The fin of the cuddlefish consists of a 3 layered-structure.

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The structure on the left is of the cuddlefish fin and on the right is of the biomimetic fin.  The biomimetic fin is made of an elastic substrate (plastic and/or rubber silicone) with skin containing embedded shape memory alloy wires attached to it.  The SMA wires acts as transverse muscle fibers by providing a lateral compressive force.  While, the elastic substrate stores elastic energy.

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The biomimetic fin is incorporated into the micro-robot fish as seen in the picture above in the assembled and unassembled forms.  The motion of the fish is controlled by batteries and a control circuit.  The resulting fish structure can swim forward and turn.

Interactive “Living” Wall

This artwork is a wall made from smart foils which fold open like flower petals in response to human behavior.  These smart foils unfold in response revealing voids.  The artwork is named Lotus and was self-commissioned by Studio Roosegaarde.  The project link is found here:  http://www.studioroosegaarde.net/project/lotus/info/.  It present a merging of architecture and nature and interactive design.  A video of the Lotus Dome in action and some more detailed description is given here:  http://www.emptykingdom.com/featured/lotus-dome/.

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Biomimetic Chromatophores

Collaborators at the University of Bristol presented an article in the journal of Bioinspiration and Biomimetics on creating a structure that simulates chromatophores.  The ability to replicate this behavior in artificial skin type structure creates new possibilities in the areas of active camouflage, thermal regulation, and active photovoltaics.  The link for the article is given here:  http://iopscience.iop.org/1748-3190/7/3/036009/pdf/1748-3190_7_3_036009.pdf.  This study uses a type of elctroactive polymer called dielectric elastomers to create the chromatophore-like material.  These elastomers have demonstrated actuation strains comparable to biological muscle with fast response times.  The study looks at mimicking two types of chromatophores:  cephalopod chromatophores and zebrafish melanophores.

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Achieving the functionality of the cephalopod chromatphores was done through implementing a planar membrane of dielectric elastomer that allows for radial expansion or contraction.  The picture on the left above shows a single artificial “planar” type chromatophore and on the right shows a cluster of artificial “planar” type chromatophores.  Both pictures depict the contracted and relaxed states of the artificial chromatophore.  The article also depicts a “negative” chromatophore, one that squeezes in similar to the way the iris of your eye becomes larger making your pupil smaller.

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Zebrafish melanophores work through the local translocation of fluids, such as inks.  This functionality was achieved using diaphragm of dielectric elastomers.  The picture above depicts the artificial melanophore which is made up of two dielectric pumping elements.  Both types of artificial chromatophores show promise in applications related to artificial skin.

Kinetic Rain

Here is an interesting work by the German design collective ART+COM.  This sculpture is located in Singapore’s Changi Airport.  The sculpture consists of raindrops made of lightweight aluminium covered by copper and suspend by motor-driven steel wires.  The length of the wires changed based on computer controlled choreography.  A link describing the work is given here:  http://www.artcom.de/en/projects/project/detail/kinetic-rain/.

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Material with Embedded Responsiveness

A recent article by Achim Menges and Steffan Reichert was published in Architectural Design journal titled  Material Capacity:  Embedded Responsiveness.  The link to the abstract is given here:  http://onlinelibrary.wiley.com/doi/10.1002/ad.1379/abstract.  This article discusses the development of biomimetic materials that require no external energy input (mechanical, electrical, ect.) to respond, but respond based on humidity control.  This idea exploits two characteristics typically seen in plant materials, anisotropy and hygroscopicity.  (Hygroscopicity is the ability to take on moisture from the atmosphere when dry and release moisture to the atmosphere when wet.  Therefore, the substances maintains a moisture equilibrium with the surrounding relative humidity.)  The material created is based on the concept of a confer cone.

Confer Cone

 

This picture is of a confer cone.  The confer cone is the seed carrying part of the tree and the seeds are released by opening its scales.  The cone opens when it is dry and closes when it is wet due to its hygroscopic structure.  Note wood is a hygroscopic structure because water can be absorbed and chemically bonded to the cellulose and hemicelluloses on a molecular level.  This water within the cell wall is bound water as opposed to free water within the cell lumen.  When bound water is removed, the distance between microfibrils within the cell tissue is reduced which increases strength and reduces overall dimension.

 

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This paper describes the creation of a humidity responsive veneer composite element made from simple quarter-cut maple veneer.  The result is depicted above with the picture on the left of a full-scale responsive system and on the right of a responsive system that can adapt its shape by being based on a 4, 5, 6, or 7-sided polygon.  Note of a rise in relative humidity from 40-70% the system geometry becomes a highly curved shape.  The authors state that design of the responsiveness of these structures can be changed by adjusting the following parameters:  fibre directionality, layout of the natural and synthetic composite, length to width to thickness ratio, geometry of the element, and humidity control during construction phase.  The resulting full-scale design could be utilized as a weather-proof skin.

Biomimetic Fabrics

"Bastard Hogberry Plant"

A photo of a “bastard hogberry” plant

Harvard University in collaboration with the University of Exeter has created a new material inspired by the “bastard hogberry”.  This plant changes its color and the fiber that the collaborator’s invented mimics this change in the fact that it changes color when stretched.  A picture of the phonotic fibers is given below:

Phonotic Fibers

The photonic fibers are made by wrapping multiple layers of polymer around a glass core, which is later etched away. The thickness of the layers determines the apparent color of the fiber, which can range across the entire visible spectrum of light. (Image courtesy of Mathias Kolle.)

The upper cells within the seed skin of the bastard hogberry contain a repeating curved pattern which yields color through interference of light waves.  There are multiple layers of cells in the seed coat made from a highly regular cylindrically layered architecture.  Hence the researchers processed the fabric by using a thin glass fiber and wrapping the polymer around them.

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An article published on this material is found in Advanced Materials here:  http://onlinelibrary.wiley.com/doi/10.1002/adma.201203529/abstract.  Also, a brief synopsis of the work is given here:  http://wyss.harvard.edu/viewpage/413/.

Shape Memory Alloy Paper/Fabric Movements

Felt with Embedded SMA Felt with Embedded SMA with Current Applied   photo

This post is an extension of the previous post regarding material experimentation and shape memory alloys on September 17, 2013.  I am working on replicating Jei Qi’s work at the MIT Hi-Low Tech lab.  The above picture depicts the results of applying shape memory alloy onto a felt surface.  A video of the movement is given here:   http://youtu.be/z23Ah9FKpCU.  The felt seems to have some residual plastic deformation after the electrical current is not being send through the SMA.  The third picture is of wool felt which has greater stiffness than the regular felt and was not able to move at all using the SMA.

Paper Folding with SMA

This picture depicts the results of the paper folding with the shape memory material.  A video of the movement is given here:  http://youtu.be/hssL3ho4AZI.  The paper exhibits no plastic deformation because it returns to the original shape completely.  Other notable results are the amount of movement depends on the length of the wire.