Test and analysis of window vibration for anti-laser-eavesdropping

Abstract

Windows are obvious targets for laser eavesdropping and can be easily eavesdropped. However, studies on the window vibration characteristics and associated anti-laser-eavesdropping measures are relatively scarce. To reduce the window vibration and decrease the eavesdropping risk, this study investigates the influence of the glass thickness, glass size, and number of window layers on glass vibration by carrying out theoretical analysis, full-scale testing, and finite element analysis. To begin, the effect of the window size and thickness on voice-induced vibration is investigated using elastic thin plate theory. It is found that the vibration is relatively low if the window’s natural frequency exceeded 500 Hz. Then, a full scale test is conducted to investigate the effect exerted by the number of window layers, and it is found that the glass vibration in the double-pane (Insulated Glass Unit) window is 74% less than that in the single-pane window. To further investigate the multi-layer window characteristics, a refined finite element model that considers acoustic-structural coupling is established in ABAQUS and validated by the test results. The analysis results reveal that only 1% of the glass vibration is transmitted by the window frames, and the two glasses in the Insulated Glass Unit(IGU) have similar vibration magnitude and characteristics when the total glass thickness is the same. Additionally, when the windows have the same glass thickness, the vibration of the IGU is 55% less than that of the single-pane window, and 40% less than that of the triple pane window. Hence, when the size and glass thickness are the same, IGU windows are the best option for reducing the glass vibration and prevent laser eavesdropping.