It is theoretically conceivable for sound to pass through a perfect vacuum under the appropriate conditions. These conditions have now been determined by two physicists.
The University of Jyväskylä in Finland’s Zhuoran Geng and Ilari Maasilta claim that their research is the first thorough demonstration of complete acoustic tunneling in a vacuum.
Two piezoelectric materials—materials that can convert motion into voltages and vice versa—are required to do it. The distance between the items must be lower than the sound’s wavelength in order for it to entirely leap — or “tunnel” — across that distance.
Although acoustic wave tunneling has been known about since the 1960s, scientists have only lately started to look into the phenomena, thus we still don’t fully understand how it operates.
In order to address this, Geng and Maasilta initially described a formalism for the study of acoustic tunneling and are currently putting it to use.
Sound requires a medium to travel through in order to spread. Atoms and molecules in the medium vibrate when sound is produced, and this vibration is transferred to nearby particles. A sensitive membrane in our ears allows us to feel these vibrations.
A complete lack of a medium is a perfect vacuum. Sound shouldn’t be able to travel because there aren’t any particles to vibrate.
However, there are gaps. For the study of sound propagation through otherwise empty spaces, piezoelectric crystals are an attractive material because even a vacuum can still buzz with electrical fields.
These are substances that change mechanical energy into electrical energy as well as the other way around. In other words, the crystal will generate an electric field if mechanical stress is applied to it. Additionally, the crystal will distort when exposed to an electrical field. The inverse piezoelectric effect is what causes that.
Okay, this is where the fun begins. The vibration of sound causes mechanical tension. Geng and Maasilta discovered that a crystal may transform this stress into an electrical field under specific circumstances using zinc oxide as their piezoelectric crystals.
The sound wave can travel across the vacuum if there is a second crystal close by that can change the electrical energy back into mechanical energy. This requires a distance between the two crystals that is no larger than the initial acoustic wave’s wavelength.
Additionally, the impact grows with frequency. Even ultrasound and hypersound frequencies can tunnel through the vacuum between the two crystals if the vacuum gap is sized appropriately.
The findings of the study may aid in the study of quantum information science as well as other branches of physics because the phenomena is comparable to the quantum mechanical effect of tunneling.
The effect is typically negligible, but Maasilta notes that in some instances, the wave’s entire energy can jump across the vacuum with 100% efficiency and no reflections.
As a result, the phenomena may have uses in the management of heat and microelectromechanical systems (MEMS, smartphone technology).
The research has been published in Communications Physics.
