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US 4,829,729 AGranted
Anti-eavesdropping window structure
AssigneeFlachglas Aktiengesellschaft
InventorsPaul Derner, Peter Reichmann
Life of this patent
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Abstract
An anti-eavesdropping window structure in which the inner and outer panes, separated by a spacer frame have thickness d and D such that D/d is at least equal to 1.5. The space between the panes is filled with a gas mixture having a density in excess of that of air and a body-sound generator applied directly to the outer pane generates thermal noise over a frequency range of 200 to 3000 Hz to superimpose a level of such noise of at least 20 dB on transmitted sound.
Claims10
An anti-eavesdropping window structure comprising:
- an outer transparent pane having a thickness d;
- an inner transparent pane having a thickness D such that D/d is at least equal to 1.5, said inner transparent pane being a composite pane having two glass sheets sandwiching a vibration damping glass-sheet-bonding layer between them;
- a spacer frame engaging the peripheries of said panes and defining with said panes and between said panes a chamber;
- a filling of a sound-damping gas having a density greater than that of air in said chamber;
- and
- at least one body-sound generator of thermal noise in a frequency range of 200 to 3000 Hz acting through the inside of said chamber solely upon said outer pane,
- said panes, said frame and said filling having a sound-transmission attenuation of at least 40 dB, and
- said body-sound generator being so energized that thermal noise emitted to the exterior from said outer pane is superimposed with an amplitude of at least 10 dB on sound transmitted through said window over all of said frequency range, said panes and said gas limiting penetration of sound generated by said generator into a space bounded by said window.
5 more elements
Dependencies are inferred from the claim text.