Two Finnish physicists have found the conditions under which sound can be transmitted in a perfect vacuum. The effect is similar to quantum tunneling, but ordinary physics and some equipment come into play. The discovery could aid the development of MEMS electronics and heat dissipation systems.

Zhuoran Geng and Ilari Maasilta of the University of Jyväskylä in Finland say their work represents the first definitive evidence of full acoustic tunneling in space. All that is needed for the experiment are two piezoelectric sensors, each of which can convert sound waves into electrical voltage and vice versa. At the same time, the piezo elements must be separated by a smaller gap than the wavelength of the transmitted sound. As a result, the sound will “switch” from one element to the next at full strength if the necessary conditions are met.

As we know, sound needs a medium to propagate. Sound is transmitted due to the sequential transmission of vibrations of atoms and molecules in the medium to neighboring particles. People hear (feel) air vibrations directly through the sensitive membrane in their ears. Such conditions obviously do not exist in a pure vacuum – there is nothing to oscillate and therefore nothing to propagate sound waves. But there is a gap – electromagnetic fields can propagate in space, and this is a chance for piezoelectric crystals that generate electricity in the process of deformation (under the influence of acoustic waves). And where there is electricity, there are fields.

Scientists used zinc oxide as piezoelectric elements. The sound vibration created a mechanical tension in the material, which in turn created an electrical tension in the material and under certain conditions led to the appearance of an electromagnetic field. If a second crystal was within the radius of action of the first crystal’s field, then it converted the field into electrical energy and back into mechanical energy – indeed, such a simple (or subtly) output acoustic signal. The road has passed pure vacuum. The width of the gap should not exceed the length of the transmitted sound wave.

Schematic of a system consisting of two piezoelectric bodies separated by a gap in vacuum. (Geng and Maasilta, commune. physical2023)

Scientists have also shown that the effect depends on the frequency of the sound. It works for both ultrasound and supersonic frequencies if the required range is observed. The discovered phenomenon can be used for both practical solutions and simulations of quantum tunneling, for example to help improve quantum communication.

“In most cases the effect is small, but we have also found cases where all the energy of the wave passes through space with 100% efficiency, without any reflection, – said Maasylta. “Thus, this phenomenon may find application in microelectromechanical components (MEMS, smartphone technology) and thermal management.”

In the latter case, the scientist clearly means removing heat from devices located in a vacuum, which can be used in space technology and beyond. The scientists mentioned the study itself in an article in the journal Communication Physics. Source