Control of Shielding Effectiveness of Optically Transparent Films by Modification of the Edge Termination Geometry

Abstract

This article deals with the design, fabrication, and characterization of optically transparent electromagnetic screens to protect optical sensors against high-intensity radiated fields. To ensure the best tradeoff between high optical transparency over the entire visible light spectrum and high shielding effectiveness at microwaves, micrometric mesh metal films printed on glass substrates were selected. Changing the micrometric mesh pattern allows reaching various shielding effectiveness values required for different applications, but implies important adjustments of the design and fabrication processes. The variation of the number of contact ribbons between the mesh screen and its direct peripheral area consists of an alternative solution to modify the screen shielding effectiveness, while keeping the meshed part of the screen identical. An analytical model, which predicts the shielding effectiveness variation measured under statistically uniform illumination in a reverberation chamber as a function of the number of metal ribbons and the aperture sizes between them was specifically developed. Experimental results follow the trend predicted by the analytical model. As a result, adjusting the number of peripheral contact ribbons enables the shielding effectiveness to be fitted to specified requirements at constant optical transparency.

Dynamic Control of the Shielding Effectiveness of Optically Transparent Screens

“…It is worth noting that both performance depends on the selected mesh geometrical parameters. A previous work also demonstrated the possibility to decorrelate the SE response of the shield and its optical transparency by modifying the edge termination geometry of the mesh [13]. The measured results were in full accordance with the analytical transmission line model developed in the article.…”

“…Fig. 1) was measured in [13]. It displayed more than 80% of optical transparency over the entire visible light spectrum and a SE higher than 20 dB in the 2-18 GHz frequency range.…”

“…In a previous article [13], the SE of a micrometric mesh metal screen was statically adapted by modifying the contact impedance between the micrometric mesh and the peripheral metal strip, and thus the RF ground. On the one hand, when the number of metal ribbons connecting the central micrometric mesh area and the peripheral strip is low or null, the resulting SE is low, as the contact impedance between the mesh and the RF ground is high.…”

“…1) was fabricated using conventional photolithography and wet etching processes. Further details are reported elsewhere [13], [25].…”

“…Accordingly, the shields must exhibit high optical transparency over the entire visible light spectrum to enable sensors to get optical information. Multiple technical solutions fulfilling these requirements have been published over the years [5], such as the use of ultrathin silver film [6], silver nanowires in a transparent matrix [7]- [9], conducting graphene-based hybrid films [10], indium tin oxide thin films [11], [12], or mesh metal films [13]- [15] deposited on glass, polyethylene terephthalate, or freestanding. The last solution provides high shielding effectiveness (SE) over the 2-50 GHz frequency range, coupled with high level of optical transparency (higher than 80%) over the entire visible range.…”