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Evolving random fractal Cantor superlattices for the infrared using a genetic algorithm.

Bossard JA, Lin L, Werner DH - J R Soc Interface (2016)

Bottom Line: Fractal geometry, often described as the geometry of Nature, can be used to mimic structures found in Nature, but deterministic fractals produce structures that are too 'perfect' to appear natural.Furthermore, we introduce fractal random Cantor bars as a candidate for generating both ordered and 'chaotic' superlattices, such as the ones found in silvery fish.We present optimized superlattices demonstrating broadband reflection as well as single and multiple pass bands in the near-infrared regime.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering, The Pennsylvania State University, 211A Electrical Engineering East, University Park, PA 16802, USA jab678@psu.edu.

No MeSH data available.


Related in: MedlinePlus

Random fractal Cantor superlattice comprised alternating a-Si and SiO2 layers on a glass substrate optimized by a GA to have broadband mid-IR reflectivity from 3 to 5 µm. (a) Fractal growth and superlattice structure. (b) Simulated scattering magnitudes at normal incidence. (c) Simulated scattering magnitudes at 30° off-normal incidence. (Online version in colour.)
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RSIF20150975F7: Random fractal Cantor superlattice comprised alternating a-Si and SiO2 layers on a glass substrate optimized by a GA to have broadband mid-IR reflectivity from 3 to 5 µm. (a) Fractal growth and superlattice structure. (b) Simulated scattering magnitudes at normal incidence. (c) Simulated scattering magnitudes at 30° off-normal incidence. (Online version in colour.)

Mentions: For the first a-Si and SiO2 design, the same cost function was used as for the theoretical superlattice. However, the total thickness range was limited to between 5 and 40 µm, and instead of optimizing the permittivity for the two dielectric materials, the GA optimized whether the line segments in the Cantor bar would represent either a-Si or SiO2. After evolving a population of 32 members for 1000 generations, the GA converged to the multi-generator Cantor superlattice shown in figure 7a with a total thickness of 27.9 µm and generator gap sizes g0 = 0.495 and g1 = 0.189. In the optimized superlattice, the Cantor bar line segments are replaced by a-Si, and the gaps are replaced by SiO2. The minimum layer thickness in the structure is 220 nm, which is well above the minimum for fabrication. The simulated transmission and reflection for this design show a high reflectivity over the entire optimized band with all transmission peaks suppressed under −25 dB. Although the optimization was conducted at normal incidence, the simulated scattering curves at 30° off-normal incidence in figure 7c also show high reflectivity over the entire 3–5 µm band for both transverse electric (TE) and transverse magnetic (TM) polarizations, indicating that these broadband reflectors could be useful for applications requiring moderate angular insensitivity.Figure 7.


Evolving random fractal Cantor superlattices for the infrared using a genetic algorithm.

Bossard JA, Lin L, Werner DH - J R Soc Interface (2016)

Random fractal Cantor superlattice comprised alternating a-Si and SiO2 layers on a glass substrate optimized by a GA to have broadband mid-IR reflectivity from 3 to 5 µm. (a) Fractal growth and superlattice structure. (b) Simulated scattering magnitudes at normal incidence. (c) Simulated scattering magnitudes at 30° off-normal incidence. (Online version in colour.)
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4759801&req=5

RSIF20150975F7: Random fractal Cantor superlattice comprised alternating a-Si and SiO2 layers on a glass substrate optimized by a GA to have broadband mid-IR reflectivity from 3 to 5 µm. (a) Fractal growth and superlattice structure. (b) Simulated scattering magnitudes at normal incidence. (c) Simulated scattering magnitudes at 30° off-normal incidence. (Online version in colour.)
Mentions: For the first a-Si and SiO2 design, the same cost function was used as for the theoretical superlattice. However, the total thickness range was limited to between 5 and 40 µm, and instead of optimizing the permittivity for the two dielectric materials, the GA optimized whether the line segments in the Cantor bar would represent either a-Si or SiO2. After evolving a population of 32 members for 1000 generations, the GA converged to the multi-generator Cantor superlattice shown in figure 7a with a total thickness of 27.9 µm and generator gap sizes g0 = 0.495 and g1 = 0.189. In the optimized superlattice, the Cantor bar line segments are replaced by a-Si, and the gaps are replaced by SiO2. The minimum layer thickness in the structure is 220 nm, which is well above the minimum for fabrication. The simulated transmission and reflection for this design show a high reflectivity over the entire optimized band with all transmission peaks suppressed under −25 dB. Although the optimization was conducted at normal incidence, the simulated scattering curves at 30° off-normal incidence in figure 7c also show high reflectivity over the entire 3–5 µm band for both transverse electric (TE) and transverse magnetic (TM) polarizations, indicating that these broadband reflectors could be useful for applications requiring moderate angular insensitivity.Figure 7.

Bottom Line: Fractal geometry, often described as the geometry of Nature, can be used to mimic structures found in Nature, but deterministic fractals produce structures that are too 'perfect' to appear natural.Furthermore, we introduce fractal random Cantor bars as a candidate for generating both ordered and 'chaotic' superlattices, such as the ones found in silvery fish.We present optimized superlattices demonstrating broadband reflection as well as single and multiple pass bands in the near-infrared regime.

View Article: PubMed Central - PubMed

Affiliation: Department of Electrical Engineering, The Pennsylvania State University, 211A Electrical Engineering East, University Park, PA 16802, USA jab678@psu.edu.

No MeSH data available.


Related in: MedlinePlus