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The Effect of Rotational Disorder on the Microwave Transmission of Checkerboard Metal Square Arrays.

Tremain B, Durrant CJ, Carter IE, Hibbins AP, Sambles JR - Sci Rep (2015)

Bottom Line: By applying rotational disorder to the elements comprising the arrays, with the lattice constant and element size unchanged, the electrical connectivity of the structure can be controlled whilst maintaining periodicity.When approximately half of the connections are broken, the resonant features are suppressed, with scattering loss shown to dramatically increase to as much as 40% of the incident power over a broad frequency range.The result is a thin, highly effective scatterer of microwaves.

View Article: PubMed Central - PubMed

Affiliation: School of Physics and Astronomy, University of Exeter, Exeter EX4 4QL.

ABSTRACT
The effect of rotational disorder on the microwave transmission through thin metallic checkerboard arrays has been experimentally studied. Broad resonant features below the onset of diffraction, attributed to electromagnetic radiation coupling through the structure via the evanescent fields of bound surface waves, are found to be strongly dependent on the electrical connectivity of the surface. By applying rotational disorder to the elements comprising the arrays, with the lattice constant and element size unchanged, the electrical connectivity of the structure can be controlled whilst maintaining periodicity. The results show that rotational disorder can significantly affect transmission only when it changes the structure's connectivity. When the initial structure is just above the connectivity threshold (where the metallic occupancy is 50%), increasing disorder causes the resonant features in transmission to invert as the structure switches from a predominantly connected array to a disconnected array. When approximately half of the connections are broken, the resonant features are suppressed, with scattering loss shown to dramatically increase to as much as 40% of the incident power over a broad frequency range. The result is a thin, highly effective scatterer of microwaves.

No MeSH data available.


Related in: MedlinePlus

Percentage of squares that are connected to at least one neighbouring square as a function of standard deviation of the rotation for both 51% and 60% patch arrays, based on a 20 × 20 array.There is a limiting standard deviation of approximately 26.5°, which corresponds to the standard deviation of the uniformly distributed sample (here defined as ‘random’).
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f4: Percentage of squares that are connected to at least one neighbouring square as a function of standard deviation of the rotation for both 51% and 60% patch arrays, based on a 20 × 20 array.There is a limiting standard deviation of approximately 26.5°, which corresponds to the standard deviation of the uniformly distributed sample (here defined as ‘random’).

Mentions: The most interesting behaviour is observed just above the connectivity threshold in the 50% occupancy arrays. In this region the connectivity of the arrays is at its most sensitive to rotation. Figure 3c,d demonstrates strong transmission dependence on rotational disorder. For 0 ≤ σ ≤ 2° the majority of squares remain connected and so the strong resonant transmission associated with connected arrays is observed. Above this level of disorder the transmission inverts suggesting a critical change in the connectivity of the array. Figure 4 shows the percentage of square elements which are connected to at least one neighbour as a function of standard deviation. This plot was produced by analyzing 53 20 × 20 arrays each with a different standard deviation. The resonant feature is centred at 40 GHz which corresponds to a free space wavelength of approximately two connected patches. Therefore, whilst connected squares can form chains and clusters with a variety of lengths, the number of chains of at least two patches is significant for understanding the transmission inversion in Fig. 3c. For X = 51%, between σ = 2° and σ = 6°, Fig. 4 shows that the array promptly changes from a connected to a primarily disconnected array. This change in connectivity inverts the transmission shape as the large clusters of connected metal patches have become disconnected and so propagating currents no longer support transverse magnetic surface modes. Regions of metal patches are now linked by displacement currents, supporting a transverse electric mode and the overall transmission behaviour is that of a disconnected array. (For the 51% hole arrays which are initially disconnected, Fig. 3d, the opposite of this argument is then true as metallic regions surrounding the holes begin to connect with the introduction of disorder.) The rate of decrease of the peak transmission value with standard deviation qualitatively corresponds to the gradient of the red points within Fig. 4. The large change in peak intensity between σ = 2° and σ = 6° in Fig. 3c coincides with a large number of squares becoming isolated from their neighbours, as shown by the steep gradient in Fig. 4. The large difference in connectivity between these two arrays is demonstrated more clearly in Fig. 5. Connections between squares are shown by lines connecting the lattice points of the array with isolated squares shown as dots.


The Effect of Rotational Disorder on the Microwave Transmission of Checkerboard Metal Square Arrays.

Tremain B, Durrant CJ, Carter IE, Hibbins AP, Sambles JR - Sci Rep (2015)

Percentage of squares that are connected to at least one neighbouring square as a function of standard deviation of the rotation for both 51% and 60% patch arrays, based on a 20 × 20 array.There is a limiting standard deviation of approximately 26.5°, which corresponds to the standard deviation of the uniformly distributed sample (here defined as ‘random’).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4645165&req=5

f4: Percentage of squares that are connected to at least one neighbouring square as a function of standard deviation of the rotation for both 51% and 60% patch arrays, based on a 20 × 20 array.There is a limiting standard deviation of approximately 26.5°, which corresponds to the standard deviation of the uniformly distributed sample (here defined as ‘random’).
Mentions: The most interesting behaviour is observed just above the connectivity threshold in the 50% occupancy arrays. In this region the connectivity of the arrays is at its most sensitive to rotation. Figure 3c,d demonstrates strong transmission dependence on rotational disorder. For 0 ≤ σ ≤ 2° the majority of squares remain connected and so the strong resonant transmission associated with connected arrays is observed. Above this level of disorder the transmission inverts suggesting a critical change in the connectivity of the array. Figure 4 shows the percentage of square elements which are connected to at least one neighbour as a function of standard deviation. This plot was produced by analyzing 53 20 × 20 arrays each with a different standard deviation. The resonant feature is centred at 40 GHz which corresponds to a free space wavelength of approximately two connected patches. Therefore, whilst connected squares can form chains and clusters with a variety of lengths, the number of chains of at least two patches is significant for understanding the transmission inversion in Fig. 3c. For X = 51%, between σ = 2° and σ = 6°, Fig. 4 shows that the array promptly changes from a connected to a primarily disconnected array. This change in connectivity inverts the transmission shape as the large clusters of connected metal patches have become disconnected and so propagating currents no longer support transverse magnetic surface modes. Regions of metal patches are now linked by displacement currents, supporting a transverse electric mode and the overall transmission behaviour is that of a disconnected array. (For the 51% hole arrays which are initially disconnected, Fig. 3d, the opposite of this argument is then true as metallic regions surrounding the holes begin to connect with the introduction of disorder.) The rate of decrease of the peak transmission value with standard deviation qualitatively corresponds to the gradient of the red points within Fig. 4. The large change in peak intensity between σ = 2° and σ = 6° in Fig. 3c coincides with a large number of squares becoming isolated from their neighbours, as shown by the steep gradient in Fig. 4. The large difference in connectivity between these two arrays is demonstrated more clearly in Fig. 5. Connections between squares are shown by lines connecting the lattice points of the array with isolated squares shown as dots.

Bottom Line: By applying rotational disorder to the elements comprising the arrays, with the lattice constant and element size unchanged, the electrical connectivity of the structure can be controlled whilst maintaining periodicity.When approximately half of the connections are broken, the resonant features are suppressed, with scattering loss shown to dramatically increase to as much as 40% of the incident power over a broad frequency range.The result is a thin, highly effective scatterer of microwaves.

View Article: PubMed Central - PubMed

Affiliation: School of Physics and Astronomy, University of Exeter, Exeter EX4 4QL.

ABSTRACT
The effect of rotational disorder on the microwave transmission through thin metallic checkerboard arrays has been experimentally studied. Broad resonant features below the onset of diffraction, attributed to electromagnetic radiation coupling through the structure via the evanescent fields of bound surface waves, are found to be strongly dependent on the electrical connectivity of the surface. By applying rotational disorder to the elements comprising the arrays, with the lattice constant and element size unchanged, the electrical connectivity of the structure can be controlled whilst maintaining periodicity. The results show that rotational disorder can significantly affect transmission only when it changes the structure's connectivity. When the initial structure is just above the connectivity threshold (where the metallic occupancy is 50%), increasing disorder causes the resonant features in transmission to invert as the structure switches from a predominantly connected array to a disconnected array. When approximately half of the connections are broken, the resonant features are suppressed, with scattering loss shown to dramatically increase to as much as 40% of the incident power over a broad frequency range. The result is a thin, highly effective scatterer of microwaves.

No MeSH data available.


Related in: MedlinePlus