What
to write this month? No new interesting topics and not in a mood for writing. Since
I have made an oath like I will post one writing each month I had to find
something. Opened YouTube as usual scrolled down and found one interesting
video in the “nature video” channel. The video was about- spinning seeds
inspire floating electronics. I have seen this before- I said. Yes, one of my friends
have shared a link on this in the student community group. I watched the video
and wanted to see the original paper. So, went to nature.com and downloaded the
article and started reading. Blend of few subjects, but not complicated. Struggled
bit to understand the technical side but the concept was clear. Here, in this
post I like to discuss about that article.
Inspiration
from Seeds
Seeds
of many plants are designed in such a way to disperse to a longer distance by exploiting
the air flow for the controlled free fall. Botanists have even categorised the
seeds based on the character of motion-gliders, helicopters, parachuters,
flutters/spinners. Inspired from the helicopter motion of certain seeds Professor
Rogers developed 3D fliers that doesn’t use any motor or engine, simply exploiting
the airflow. The team studied the aerodynamics of wind dispersed seeds and fabricated
the fliers by optimising the design parameters like wing diameter, type and porosity
so that it - when dropped from a height, falls at a slow velocity in a
controlled manner while having interaction with the surrounding air for the
longest possible time.
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This above
image compares the sizes and morphologies of wind dispersed seeds with that of
microflier. Here the fliers are fabricated inspired from the helicopter types- Diptocarpus
alantus and Tristellateia seeds
Fliers of different
sizes
The team had developed fliers with
microscale (smaller than 1 mm; microfliers), millimeter-scale (about 1 mm; mesofliers),
and macroscale (larger than >1 mm; macrofliers). These devices can be combined
with sensors for environmental monitoring, power sources, antennas for wireless
communications and embedded memory to store data.
Photograph and optical micrograph of three different 3D microfliers, [2, H, 1.2], [3, H, 0.6] and [3, M, 0.4]; left, resting on the tip of a finger; and right, shown at higher magnification
A simple identifying nomenclature includes (i) a number to indicate the number of wings, (ii) a letter to describe the shape of wings (R = ribbons, M = membranes, PM = porous membranes and H = hybrid, a combination of ribbons and membranes), and (iii) a number to define the 3D aspect ratio (for example, height divided by width).
Fabrication
3D layouts of the devices were created using the state-of-the-art planar processing and lithographic techniques. A layer of a shape-memory polymer (SMPs; a mixture of epoxy monomer; a material that return to its original shape when a particular stimulus is applied) is bonded to a prestrained elastomer substrate (a rubber like material) at specific sites. Releasing the strain generates compressive forces on these 2D materials, and the shape memory effect fixes the fliers into the 3D shape.
The overall 3D architectures of the devices, aspect ratio (ratio of height to width- small, 3D; large, 3D+) and the number and shape of the aerodynamic surfaces can vary by controlling the location of bonding sites and adjusting the magnitude of strain release.
Mechanical simulation results for the geometrical transformation of ten different 2D precursors (grey; 2D, bottom row) into corresponding 3D structures with modest (green; 3D, middle row) and large (green; 3D+, top row) aspect ratios.
Terminal
velocity
Computational fluid dynamics (CFD) simulations and analytical approaches were used to find the underlying aerodynamics of the fliers and their behaviour with the surrounding air. They found that the flow field of microfliers and mesofliers are laminar and that of microfliers are turbulent, implying that the scale has major effect on the terminal velocity. To check the effect of porosity, perforating holes were introduced in the structural component to create parachute-type feature. This reduced the terminal velocity eventually, but having smaller effect on macrofliers than in microfliers. By contrast, the effects of curvature and tilt angle in the blades have greater effect on macrofliers than on microfliers.
They also found that the interaction
with the environmental factors like altitude, humidity, temperature or
molecular structure of the air alter the behaviour of these devices.
This
graph compares the terminal velocity of 3D porous mesoflier, green bar (one type of flier they developed) with
that of several other tiny objects. It is clearly noticeable that the 3D porous
mesoflier have a very lower terminal velocity of 28cms-1
Different designs
Like
seeds, these 3D platforms can transport payloads with passive or active
functionality. 3D mesofliers were made without electronics which is capable of
responding to pH. This design uses a colour indicator based on anthocyanin infiltrated
into a polycarbonate membrane.
Exploded
schematic illustration and images of a colorimetric mesoflier that responds to
local pH b, Colour responses of the device at two different pH values.
Electronics can be easily integrated that support semiconductor devices based on silicon nanomembranes the active material.
Optical
micrographs of 3D electronic mesofliers [3, M, 0.4] and [3, H, 0.75] with
silicon nanomembrane (NM) nMOS transistors and diodes as payloads.
Photograph of a 3 × 3 array of 3D electronic mesofliers [3, M, 0.4] with Si NM nMOSFET payloads. Note- nMOSFET is a transistor
The team also designed a macroscale
flier (with a diameter of 5mm) as shown below that contained a simple circuit
to detect airborne particles and can be used as a battery-free wireless device
for atmospheric measurements. The circuit consists of a controller, sensor and
a coil for wireless power transmission.
This research provides a foundational understanding of the 3D fliers and establishes a set of unusual capabilities in aerial dispersal of advanced device technologies. Among all the environmental factors wind still remains the important consideration to be investigated further. Also, gliders and parachuters represent alternative platforms that can be further studied since they are not discussed here.
So, that’s the end of the story I will
be attaching the link of the original article and the YouTube video I watched.
I will end this post by showing one comment that came under the video.
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