Modal response-based technical countersurveillance measure against laser microphones

• Published in: Journal of Vibroengineering Vol. 18; no. 5; pp. 3369 - 3382
• Main Authors: Takács, Gergely, Otčenáš, Jakub, Vachálek, Ján, Rohal’-Ilkiv, Boris
• Format: Journal Article
• Language: English
• Published: 15.08.2016
• ISSN: 1392-8716; 2538-8460
• DOI: 10.21595/jve.2016.16943

This paper proposes a semi-active mechanical blocking method against reflected light-intensity instrument based surreptitious signal gathering via vibrating window surfaces. The technical countersurveillance method is based on driving a piezoceramic transducer mounted on the window pane with a sinusoidal input coincident with the first resonant mode of the surface. The article evaluates the simulated surveillance data gathered experimentally on a simplified laboratory model when supplying the proposed blocking system with different types of disturbance signals. It has been found that, while the use of a high amplitude random signal does block surveillance attempts effectively, the resulting acoustic noise can be bothersome to the occupants of the protected room. However, the analysis presented here also suggests that the use of a sinusoidal signal with a frequency equal to the first resonant frequency of the windowpane disrupts surveillance signals – depending on the properties of the target – without generating significant acoustic by-products. Results are applicable only to reflected light-intensity systems, as the efficacy of the method cannot be confirmed without classified surveillance equipment with broader dynamic range.