BIOMIMICRY OF
BIOLOGICAL OPTICAL DEVICES
Introduction
The article begins with the introduction of biomimicry. People have always been inspired by nature and engineers are no exception! Throughout history, structures, systems, and materials developed by engineers have had roots in natural structures, systems, and materials. Biomimicry is a developing field that involves physical,chemical,biological,computing and economical aspects which are multifunctional.
Introduction
The article begins with the introduction of biomimicry. People have always been inspired by nature and engineers are no exception! Throughout history, structures, systems, and materials developed by engineers have had roots in natural structures, systems, and materials. Biomimicry is a developing field that involves physical,chemical,biological,computing and economical aspects which are multifunctional.
It shows how
engineering in biomimicry is comprised of of 3 substages:
1)Bioinspiration
2)Biomimetics
3)Bioreplication
Bioinspiration as the word describes is designing a new structure that shows functional similarity to the natural aspect from which it was inspired without reproducing the biological structure responsible for that function.
For instance, helicopters hover and so do bumblebees, but their mechanisms for hovering are entirely different.
Biomimetics is the replication of the biological structure responsible for the specific functionality and herein lies the difference.
Bioinspiration is basically devicing a new method/structure to perform the same function and biomimetics is artificial replication of the structure performing a specific function.
Bioreplication whereas is the the exact replication of the responsible biological structure.
All three methodologies of engineered biomimicry – bioinspiration, biomimetics, and bioreplication – are represented in current research on harvesting solar energy. Both processes,anti-reflective surfaces and increased field of view inspired by plants and certain insects respectively, are being investigated for solar cells.
CONCEPTS
Applying the first method of bio-inspiration, artificial photosynthesis has been mentioned as a method of conversion of solar energy to electrical energy.It is a process based on photosynthesis used by plants which uses water,sunlight and carbon dioxide to create glucose sugar. Now instead of producing glucose,artificial photosynthesis creates fuel out of the same raw materials which is commonly ethanol.Here we combine water and carbon dioxide in presence of sunlight using a photocatalyst which is typically grapheme or silicon. Then it comes together to make fuel.
Fuel created by this process also releases carbon dioxide which can again be used to create fuel by the same method.
The process mentioned in the research paper is by the use of photoelectrochemical cell.In this case,water is split into hydrogen and oxygen. Hydrogen, which burns cleanly ,can be used as a fuel. In this method, the major problem is the identification of right materials to achieve efficient conversion which also has been find a solution.
The solution mentioned in the paper is use of dye sensitized solar cells.DSSCs are in fact much cheaper to manufacture than traditional silicon solar cells, and the technology was developed to provide low-cost solar energy.
The materials like iron oxide, or titanium dioxide, used in this method will never be commercial in their current form, or perhaps even in an improved form, because their solar conversion efficiency is just too low. In ordinary dye-sensitised solar cells, which are already commercialised, dye molecules capture visible light and the cell converts it into electricity. For cheap kitchen chemistry solar cells, the dye-sensitised cells are really pretty good and remarkably robust considering they have a dye in them that you think is not going to be stable. The dye molecules turn over billions of times and remain stable for years. If some of the same principles could be applied to artificial photosynthesis, we might have a practical device.
2)Biomimetics
3)Bioreplication
Bioinspiration as the word describes is designing a new structure that shows functional similarity to the natural aspect from which it was inspired without reproducing the biological structure responsible for that function.
For instance, helicopters hover and so do bumblebees, but their mechanisms for hovering are entirely different.
Biomimetics is the replication of the biological structure responsible for the specific functionality and herein lies the difference.
Bioinspiration is basically devicing a new method/structure to perform the same function and biomimetics is artificial replication of the structure performing a specific function.
Bioreplication whereas is the the exact replication of the responsible biological structure.
All three methodologies of engineered biomimicry – bioinspiration, biomimetics, and bioreplication – are represented in current research on harvesting solar energy. Both processes,anti-reflective surfaces and increased field of view inspired by plants and certain insects respectively, are being investigated for solar cells.
CONCEPTS
Applying the first method of bio-inspiration, artificial photosynthesis has been mentioned as a method of conversion of solar energy to electrical energy.It is a process based on photosynthesis used by plants which uses water,sunlight and carbon dioxide to create glucose sugar. Now instead of producing glucose,artificial photosynthesis creates fuel out of the same raw materials which is commonly ethanol.Here we combine water and carbon dioxide in presence of sunlight using a photocatalyst which is typically grapheme or silicon. Then it comes together to make fuel.
Fuel created by this process also releases carbon dioxide which can again be used to create fuel by the same method.
The process mentioned in the research paper is by the use of photoelectrochemical cell.In this case,water is split into hydrogen and oxygen. Hydrogen, which burns cleanly ,can be used as a fuel. In this method, the major problem is the identification of right materials to achieve efficient conversion which also has been find a solution.
The solution mentioned in the paper is use of dye sensitized solar cells.DSSCs are in fact much cheaper to manufacture than traditional silicon solar cells, and the technology was developed to provide low-cost solar energy.
The materials like iron oxide, or titanium dioxide, used in this method will never be commercial in their current form, or perhaps even in an improved form, because their solar conversion efficiency is just too low. In ordinary dye-sensitised solar cells, which are already commercialised, dye molecules capture visible light and the cell converts it into electricity. For cheap kitchen chemistry solar cells, the dye-sensitised cells are really pretty good and remarkably robust considering they have a dye in them that you think is not going to be stable. The dye molecules turn over billions of times and remain stable for years. If some of the same principles could be applied to artificial photosynthesis, we might have a practical device.
THE ARTIFICIAL LEAF
This new system can use pure carbon dioxide in gas form, or carbon dioxide captured from the air—which means it could be carbon-neutral, introducing no additional greenhouse gases into the atmosphere.
System uses a pair of catalysts to split water into oxygen and hydrogen, and feeds the hydrogen to bacteria along with carbon dioxide. The bacteria, a microorganism that has been bioengineered to specific characteristics, converts the carbon dioxide and hydrogen into liquid fuels. Allowing the bacteria themselves to capture carbon dioxide from the air,results in an efficiency of 3 to 4 percent—still significantly higher than natural photosynthesis.
Bio-inspired nanostructured materials in solar cells have improved performance. Bio-mimetically textured coatings for solar cells have been shown to reduce optical reflectance(anti-reflective) and increase optical absorbance over a broad spectral range.
Conventional solar devices require an antireflective coating to reduce the reflection loss at the interface between the air and the cell. However, the standard antireflective dielectric coating only works for a limited spectral range and incident angle of the radiation, and so there is a specific need to find materials with better antireflective properties.
Nature can provide inspiration for solving many technological and scientific problems, and in this case, the corneas of some night-flying moths have inspired antireflective structures for solar cells.
Moths' eyes are composed of well-aligned nanoscale pillar arrays that reflect very little light at night. These nanostructures collectively function as a dielectric buffer (i.e., an intermediate refractive index) at the air-medium interface. As a result, moths' eyes are antireflective for a broad wavelength range, regardless of the incident angle of radiation. Therefore, structures inspired by moths' corneas are very desirable for collecting solar radiation, which contains a broad spectrum and an incident angle that changes during the day.
Similar anti-reflective structures occur in the wings of some flies and moths,giving them a transparent appearance.The advantages of these anti-reflective surfaces lie in their ability to efficiently collect light.The applications of such surfaces are far-reaching,one example being in regards to efficient solar panels for energy.
Anti-reflection using liquid crystals-A liquid crystal device in which the liquid crystal is sandwiched between electrode-substrates. At least one of the electrode-substrates includes a transparent electrode having a refractive index changing successively in the direction of thickness to reduce the light to be reflected by the transparent electrode.
Photonic structures-Optical reflection, or in other words the loss of reflection, from a surface becomes increasingly crucial in determining the extent of the light-matter interaction. The simplest example of using an anti-reflecting (AR) surface is possibly the solar cell that incorporates an AR coating to harvest sunlight more effectively. Researchers have now found ways to mimic biological structures, such as moth eyes or cicada wings, which have been used for the AR purpose by nature herself. These nanoscopic biomimetic structures lend valuable clues in fabricating and designing gradient refractive index materials that are efficient AR structures. The reflectance from a selected sub-wavelength or gradient index structures have come down to below 1% in the visible region of the spectrum and efforts are on to achieve broader bands of such enhanced AR regime. In addition to the challenge of broader bands, the performance of AR structures is also limited by factors such as omnidirectional properties and polarization of incident light.
An astonishing variety of natural photonic structures exists: a species of Brittlestar uses photonic elements composed of calcite to collect light, Morpho butterflies use multiple layers of cuticle and air to produce their striking blue colour and some insects use arrays of elements, known as nipple arrays, to reduce reflectivity in their compound eyes.
Compound lenses fabricated by a bio-replication technique offer similar promise for reduced reflectance by increasing the angular field of view.
Each compound eye of a house fly comprises several cylindrical eyelets called ommatidia that are arrayed on a curved surface. Light propagating along the axis of an ommatidium is collected to form an image, but light propagating in other directions and reaching an ommatidium is absorbed by its dark side wall. The first phase requires the numerical simulation of light interacting with the air-silicon interface.
A simplified two-dimensional bioinspired texturing of the exposed face was considered as the first step of this phase. Results indicated that the bioinspired textured solar cell exhibits light-coupling efficiency. A Nano4 technique has been developed to manufacture multiple high-fidelity replicas of a single biotemplate. The technique can produce multiple replicas simultaneously of multiple biotemplates.
CONCLUSION
This article has therefore brought together the subjects of bioinspiration ,biomimetics and bioreplication as a probable solution for harvesting solar energy in a cost effective way.This field is in its infancy but has experienced several breakthroughs by means of bioinspired engineering. Bioinspired engineering is anyways more advantageous than conventional methods as we saw in the article.
Since it is a developing field we expect more of discoveries that could change the world and in this case solve the problem of fossil fuel consumption.
REFERENCES
Engineered biomimicry for harvesting solar energy: bird’s eye view
Raul J.Martin-Palma and Akhlesh Lakhtakia
http://www.tandfonline.com/doi/abs/10.1080/19475411.2012.663812?needAccess=true#aHR0cDovL3d3dy50YW5kZm9ubGluZS5jb20vZG9pL3BkZi8xMC4xMDgwLzE5NDc1NDExLjIwMTIuNjYzODEyP25lZWRBY2Nlc3M9dHJ1ZUBAQDA=
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