Title: Terahertz Waves for Sensing Acoustic Vibrations
Withawat Withayachumnankul
Terahertz Engineering Laboratory, The University of Adelaide

Terahertz waves are capable of penetrating non-metallic materials with reasonably low levels of attenuation. The wavelength is in the order of sub-millimeter, translating to the same magnitude of spatial resolutions based on the diffraction limit. The usable absolute bandwidth is 100 GHz or more, yielding sub-millimeter depth resolutions. These attractive attributes in see-through high-resolution sensing have led to unorthodox applications. One group of applications is related to vibrometry, non-contact sensing of vibration, that will find their ultimate use in industries and healthcare. The tool is seen as complementary to conventional laser doppler vibrometry that cannot penetrate visually opaque blockage. Here, we demonstrate another application of terahertz vibrometry for acoustic eavesdropping. With a terahertz continuous-wave transceiver along with a quasi-optic setup, we corroborate that it is possible to sense minute vibration from individual speakers behind blockage such as a thin wall and an acoustic absorber. An ultimate goal for this study is to understand the capabilities and limitations of this technology to avert malicious use by bad actors.