A classic movie was once promoted with the punchline: ”In space, no one can hear you scream”. Physicists Zhuoran Geng and Ilari Maasilta from the Nanoscience Center at the University of Jyväskylä, Finland, have demonstrated, on the contrary, that in certain situations sound can be transmitted strongly across a vacuum region!
In a recent publication they show that in some cases a sound wave can jump or “ tunnel ” fully across a vacuum gap between two solids if the materials in question are piezoelectric. In such materials, vibrations (sound waves) produce an electrical response, as well, and since an electric field can exist in vacuum, it can transmit the sound waves across. The requirement is that the size of the gap is smaller than the wavelength of the sound wave. This effect works not only in audio range of frequencies (Hz-kHz), but also in ultrasound (MHz) and hypersound (GHz) frequencies, as long as the vacuum gap is made smaller as the frequencies increase.
- In most cases the effect is small, but we also found situations, where the full energy of the wave jumps across the vacuum with 100 % efficiency, without any reflections. As such, the phenomenon could find applications in microelectromechanical components (MEMS, smartphone technology) and in the control of heat, says professor Ilari Maasilta from the Nanoscience Center at the University of Jyväskylä.
The study was funded by the Academy of Finland and European Union’s Horizon 2020 program, and was published in the journal Communications Physics, on 15th July 2023 .
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Complete tunneling of acoustic waves between piezoelectric crystals
15-Jul-2023