HBAR Phonon Eavesdropping — Brillouin Scattering as Covert Acoustic Intelligence: ETH Zürich Werner (2023) Thesis Applied to Building Materials
Based on Werner J. (2023) ETH Zürich HyQu Group Master Thesis. Every building is full of unintentional High-Overtone Bulk Acoustic Wave Resonators (HBARs): window glass (Brillouin freq 16.2 GHz, T₁=0.8µs, range 500m), quartz countertops (12.64 GHz, T₁=4.9µs — identical to Werner's experimental crystal), ceramic tiles (18.9 GHz), phone sapphire screens (57.8 GHz). A PDH-locked 1550 nm laser reads out phonon states via anti-Stokes Brillouin scattering. Victim's speech continuously writes phonons; attacker's balanced heterodyne detector (14 MHz IF, 100 MSPS) reconstructs room audio. Attack chain: OMIT mapping → PDH lock (Red Pitaya, 50 MHz BW) → phonon storage (T₁ up to 4.9 µs at 60 kHz detuning — Werner Fig 3.11) → anti-Stokes readout → DFT audio recovery. High-cooperativity (C=20) attack extracts 95% of phonons. Detection: IR viewer on windows, RTL-SDR 14 MHz IF monitoring, contact accelerometer, window opacification. Cross-references: S9 (photoacoustic), S26 (laser forensics), S36 (transparent home), S55 (seismic coupling).
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