Innovative Technique for Targeted Sound Delivery

The institution recognizes that “it sounds like science fiction.” A research team from Pennsylvania State University has developed a method to transmit sounds directly to a specific individual without others overhearing. Announced on March 17, the study involved using two separate beams of inaudible ultrasound that enveloped the recipient’s head from either side. When these beams intersect in front of the face, they combine to recreate the sound of Handel’s renowned chorus from Messiah: “Hallelujah! Hallelujah!” The researchers refer to these sound transmissions as “audible enclaves” or “whispering beams.”

Potential Applications in Public Spaces

Mechanical engineer Jiaxin Zhong discusses various potential uses of this technology, such as personalized audio experiences in public areas. He suggests that “museums, libraries, or exhibitions could provide tailored sound without requiring headphones.” Additionally, he envisions scenarios where drivers can receive navigation instructions while passengers enjoy music without interference. Zhong, a lead author of the study, indicates that these sound bubbles could also enhance confidential military communication, enrich virtual reality experiences, and even create noise-free areas in loud settings by selectively eliminating unwanted sounds. The findings were published in the PNAS journal of the U.S. National Academy of Sciences.

Challenges and Limitations

While the experiment shows promise, it also presents significant challenges, according to Yun Jing, a professor of acoustics and biomedical engineering at Penn State College of Engineering. He mentions that the chorus from Messiah resembles the sound of a poorly tuned radio. “For improved audio quality, we will need superior ultrasound emitters since those currently used were inexpensive and intended for proof of concept,” Jing explains. His team is also investigating artificial intelligence solutions to enhance results.

Distance Constraints

Distance poses another important challenge. The ultrasound source is an acoustic metasurface—a very thin material that can manipulate wave patterns. In their trial, the researchers placed a dummy just a few centimeters from the emitter, but Jing asserts that they could create a sound bubble for a person standing “a few meters” away. “Ultrasonic waves lose strength rapidly in air, so achieving a distance of 100 meters will be tough without very powerful emitters,” he elaborates. The ultrasound device’s compact design, measuring just 16 centimeters, is a favorable aspect for practical applications.

Expert Opinions and Perspectives

Telecommunications engineer Juan Miguel Navarro of the Catholic University of Murcia, who collaborated with Yun Jing on acoustic models for large venues, points out that sound focusing has been utilized for security purposes for more than two decades. He mentions that long-range acoustic devices are considered non-lethal weapons capable of emitting distressing sounds to incapacitate adversaries. He highlights that the novelty of this research lies in its ability to reproduce a sound spectrum suitable for transmitting low-fidelity vocal and musical signals.

Technological Hurdles Ahead

In 2017, Spanish sound engineer Marcos Simón founded Audioscenic in Southampton, where he works on devices that detect listeners’ ears and deliver focused sound. Although Simón was not involved in this latest research, he commends the innovative methodology presented. However, he warns of notable technological barriers that hinder practical implementation. “Ultrasonic speakers require considerable energy, leading to high power consumption. Additionally, generating audible sound from these speakers necessitates high acoustic pressure, raising concerns about its effects on human hearing, especially given that safe exposure limits to ultrasound remain undefined,” he cautions. Simón concludes that while the research contributes intriguing insights, it requires substantial development for practical applications.

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