Dynamic Control of the Shielding Effectiveness of Optically Transparent Screens

Abstract

This article presents the design, fabrication, and characterization of an active electromagnetic shield intended to dynamically protect optical and electromagnetic sensors against high intensity radiated fields. The shield exhibits high and constant optical transparency level over the entire visible light spectrum thanks to a micrometric mesh metal thin film printed on a glass substrate. The central micrometric mesh area is separated from the peripheral ground plane of the shield by a peripheral slot. This slot is fitted out with p-i-n diodes and resistors, connecting electrically the central micrometric mesh area and the ground plane. The aim of these components is to dynamically control the shielding effectiveness of the screen, by using the conducting (ON) or blocking (OFF) states of the p-i-n diodes. Accordingly, the shielding effectiveness can be set at high level to protect the system against high intensity radiated fields, and conversely at low level to both prevent system electromagnetic self-perturbation and increase the sensitivity of the internal electromagnetic sensors. Dynamic control of the shielding effectiveness of the fabricated screen, whose optical transparency is close to 85% over the entire visible light spectrum, is fully demonstrated. A shielding effectiveness contrast ranging from 5 dB to 24 dB between the ON and OFF diode states was measured in the 2-10.5 GHz frequency range in a reverberation chamber.

Auto-activated Electromagnetic Shield Upon High Intensity Radiated Field Illumination

“…Second, we observe that the SE variation is restricted to the lower part of the frequency range and is also limited in magnitude, compared with SE variation as measured in [9]. The effect was predictable and mainly due to the decrease of the effective area of the receiving antenna.…”

“…As far as this 132 p-i-n diodes prototype is concerned, a supply of 150 mA under a voltage of 1.4 V would be necessary to reach the complete forward bias. However, it was shown in [9] that 10 mA are enough to reach a significant SE contrast. The assembly would therefore be self-sufficient in energy, in addition to being self-adaptive.…”

“…Recently, the authors presented an important advance of this early proposal, using a set of p-i-n diodes to perform an automatic, controlled and reversible change of the contact impedance of each connecting ribbon. The bias of all pi-n diodes was controlled simultenaously from a DC voltage/current source [9]. We briefly recall its principle and properties.…”

“…The sample in [9] consisted of a 50 mm square sample of 0.7 mm-thick soda-lime glass (Fig. 1) partly covered (using radiofrequency sputtering technique followed by photolithography and wet etching processes) by a thin metal layer (2 μm-thick silver layer onto a 5-nm-thick titanium underlayer) arranged in four different parts:…”

“…This solution can indeed provide high SE over a very large frequency range up to dozens of GHz, while maintaining a high level of optical transparency (higher than 80%) over the entire visible or infrared range. In a recent contribution [9], the authors have presented a solution made of a micrometric mesh-metal film screen whose SE level is controlled through the adjustment of the contact impedance between the screen and its electrically conducting support. This impedance adjustment was ensured by the bias current variation of a set of peripheral p-i-n diodes.…”