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A skyscraper as a huge diffraction grating

Amelia Carolina Sparavigna (Department of Applied Science and Technology, Politecnico di Torino)

Published in engi.philica.com

Abstract
The paper is showing how the surface of a building can become a huge diffraction grating, which can create diffracted beams of colored light. The case here discussed is that of the Intesa Sanpaolo Tower in Torino.

Article body

A skyscraper as a huge diffraction grating

Amelia Carolina Sparavigna

Politecnico di Torino

The paper is showing how the surface of a building can become a huge diffraction grating, which can create diffracted beams of colored light. The case here discussed is that of the Intesa Sanpaolo Tower in Torino.

The Torre Intesa Sanpaolo in Turin is the headquarters for the homonymous banking group. It is the second tallest building in the city, after the Mole Antonelliana. The tower was planned by Renzo Piano, who described it as a "bioclimatic building", because it is naturally ventilated and cooled. A substantial amount of its power requirement is generated by photovoltaic panels [1-4].

Figure 1: A façade of Intesa Sanpaolo Tower. Note the grid in front of it.

As we can see in the Figure 1, the surface of the building is made of windows which are covered by a fine grid. Therefore, we have a structure which is like a huge mirror covered by a grating, which actually becomes a diffraction grating. The light of the sun (white light) arrives on the face of the building and is reflected by it in several beams. One is composed of white light, the others are made of dispersed colored light. Let us remember that a  diffraction grating is an optical device used to disperse the white light into its constituent optical frequencies. The simplest possible grating is a glass substrate with a series of parallel, equally spaced lines on its front surface [5,6].

Let us consider the Figure 2. In the upper part it is represented the diffraction grating (in our case, the façade of the skyscraper with its windows and the grid in front of them). The sun hits the building and a beam of white light and colored beams are produced.

Figure 2:  The upper part  is representing the diffraction grating. The white light hits the grating and a beam of white light and colored beams are produced (see also https://www.quora.com/What-is-a-diffraction-grating).

To the author's best knowledge, the fact that the surface of a building can behave like a diffraction grating is not mentioned in literature or in the web. Here, in the Figures 3-6, we can see the effect as seen from the southern side of the tower. Only the central part of this façade is covered by the grid. The rest is covered by the photovoltaic panels. The direct view of the colors is much better than that shown by these images from a camera. The phenomenon is even better if it is observed for the façade shown in the Figure 1. Let us note that the observation of the diffraction of light depends on the direction of the incident light and on the position of the observer. The phenomenon is visible only for about ten minutes.

Figure 3: South side of the building (6 September 2016).

Figure 4: South side of the building (7 September 2016).

Figure 5: Diffracted colored beams from the part of the south façade which is acting like a diffraction grating. The direct view of the colors is much better than that shown by these images. The images had been recorded on 6 September 2016, between 15.55 and 16.05

Figure 6: Diffracted colored beams from the part of the south façade.  The sequence of images had been recorded on 7 September 2016, between 15.55 and 16.05.

References

[1]Barus, T., Tizzano, A., & Vulpio, D. (2008). Torino Vertical Towers (Doctoral dissertation, Politecnico di Torino).

[2] Di Stefano, L. (2009). Aspetti Tecnologici e Paesaggistici di un Edificio Alto in un Tessuto Urbano Consolidato (Doctoral dissertation, Politecnico di Torino).

[3] Carpinteri, A., Lacidogna, G., & Cammarano, S. (2013). Structural analysis of high-rise buildings under horizontal loads: A study on the Intesa Sanpaolo Tower in Turin. Engineering Structures, 56, 1362-1371.

[4] Corres-Peiretti, H., Dieste, S., León, J., Pérez, A., Sánchez, J., & Sanz, C. (2012). New Materials and Construction Techniques in Bridge and Building Design. In Innovative Materials and Techniques in Concrete Construction (pp. 17-41). Springer Netherlands.

[5] Born, M., & Wolf, E. (2000). Principles of optics: electromagnetic theory of propagation, interference and diffraction of light. CUP Archive.

[6] Loewen, E. G., & Popov, E. (1997). Diffraction gratings and applications. CRC Press

This Article was published on 7th September, 2016 at 17:25:33 and has been viewed 905 times.