Pinecones use a 'material intelligence' of sorts to drive movement. Their scales open and close elastically due to hygroscopic expansion differences between their cell layers. This allows for repeatable motion without the use of active energy, a subject of particular interest as pressure grows to move away from energy-intensive and high-maintenance electromechanical systems.
Can we design a window shade like a pinecone scale?
From this mechanical logic of a pinecone: when a moisture-dependent material (wood) and a moisture-independent material (resin) are fabricated as a two-material bilayer, a change in moisture activates a material-wide bend.
Material bilayers can be calibrated to bend at a certain angle relative to their fastening seam. This is determined by the magnitude of the angle between the grain direction of the wood and the fastening seam. As this angle approaches 90 degrees, the bend effect becomes almost negligible.
Material bilayers can be calibrated to bend with either an increase, or decrease, in humidity. If a bilayer is fabricated in a low moisture environment, it will bend in high moisture. If a bilayer is fabricated in a high moisture environment, it will bend in low moisture. For example, the bilayer on the left in both of the above images was fabricated in a low moisture environment; where as the bilayer on the right in both images was fabricated in a high moisture environment.
Rather than fabricating a material-wide bilayer, it is also possible to fabricate a localized bilayer. This allows controlled bending along a predetermined axis, almost like a hinge.
Depending on the location and thickness of the hinge, the bend degree can be calibrated to relative humidity. As such, a bend in a bilayer can be programmed to activate at a certain relative humidity level, and with a certain degree.
From the above method, window shades can be fabricated and programmed to open at certain moisture levels. The image to the right shows the computational simulation of the left physical model.
Bilayer components can also be watered into opening, as is displayed above.
Can a wall become more dense as the weather changes?
When a moisture-dependent material (wood) and a moisture-independent material (resin) are fabricated as a two-material bilayer, a change in moisture activates a material-wide bend. Long bilayer strips bend quickly as a function of moisture changes, and bend in on themselves. In a contained system – for example, trapped within window panes – this bending phenomenon causes a stacking effect that simulates the activation of a shading mechanism.
The density, so to speak, of a window shade can be calibrated to the relative humidity within the enclosed window system, as illustrated above. As this bend effect is elastic, the stacking effect is reversible.
Using partitioning systems, it is also possible to control the form that a shading mechanism takes. For example, certain window portions can be activated at different times for different optical and thermal purposes.
The above images illustrate the range of optical transmission for given relative humidity levels within the enclosed window shading mechanism.
Can we use magnetic and tensile forces to amplify hygroscopic forces?
A bilayer material bend can be generated if the material properties of the respective layers differ. In this case, a hygroscopic (responsive to moisture) and non-hygroscopic (independent of moisture) layer are fastened to one another, inducing a bend. Compounding this bend effect, however, is an magnetic effect, as a series of magnets (opposite poles facing one another) are attached to each bilayer system.
As can be seen above, the difference in the displacement between the two hygroscopic bilayer systems is almost 50%. This (likely) represents the magnetic effect, compounding the hygroscopic bend between the two bilayers.
A similar amplification is seen to the left, however, instead of magnetic activation, the bilayer bend is being amplified with a tensile force. Two bilayer systems are fastened to one another using a string connection. As can be seen, this (likely) amplifies the hygroscopic bend effect by one third.
Work by Raphael Kay, Kevin Nitiema, with external guidance from David Correa (Waterloo)