The iconic tagline from the movie “Alien,” “In space, no one can hear you scream,” has long ingrained the notion of sound’s absence in a vacuum. However, groundbreaking research from physicists at the University of Jyväskylä reveals a surprising twist: sound can travel through a vacuum, under specific circumstances. This article delves into this fascinating discovery, explaining how acoustic waves can, in fact, tunnel through empty space.
In a study published in Communications Physics, researchers Zhuoran Geng and Ilari Maasilta demonstrated that sound waves can traverse a vacuum gap separating two solid materials, provided these materials are piezoelectric. This phenomenon, seemingly counterintuitive, relies on the unique properties of piezoelectric substances.
The secret to this phenomenon lies in piezoelectric materials. These unique substances possess the ability to convert mechanical vibrations—sound waves—into electrical energy, and conversely, electrical energy back into mechanical vibrations. When sound waves encounter a piezoelectric material, they generate an electric field. Crucially, unlike sound waves themselves, electric fields can propagate through a vacuum. This electric field acts as a bridge, traversing the vacuum gap and then reconverting into sound waves when it reaches another piezoelectric material on the other side. For this acoustic tunneling to occur, the width of the vacuum gap must be smaller than the wavelength of the sound wave.
This intriguing effect is not limited to the audible range; it extends to ultrasound and even hypersound frequencies. The only requirement is adjusting the vacuum gap to be smaller than the sound wavelength as frequencies increase. While often subtle, the effect can become remarkably efficient, with up to 100% energy transfer observed in specific scenarios. Professor Ilari Maasilta highlights potential applications in microelectromechanical systems (MEMS), crucial components in smartphone technology, and even in advanced heat management technologies.
In conclusion, the seemingly impossible – sound traveling through a vacuum – becomes a reality through the fascinating phenomenon of acoustic tunneling. Leveraging piezoelectric materials and the intermediary role of electric fields, sound waves can effectively bridge vacuum gaps, opening up exciting possibilities for technological advancements in diverse fields from microelectronics to thermal management.
Source:
Geng, Z., & Maasilta, I. J. (2023). Complete tunneling of acoustic waves between piezoelectric crystals. Communications Physics, 6(1). https://doi.org/10.1038/s42005-023-01293-y
