WASHINGTON, Dec. 16, 2025 — Helium leaks are hard to detect. Helium is odorless, colorless, tasteless, and does not react with other chemical substances. Not only can we not see or smell it, but traditional gas sensors have trouble detecting the element because they rely on chemical reactions. Despite this, identifying a helium leak is still crucial, because excess helium can displace oxygen in a confined space, leaving less oxygen for people to breathe.
In Applied Physics Letters, by AIP Publishing, researchers from Nanjing University developed a device that utilizes sound waves to detect helium.
The researchers built a device inspired by a traditional Japanese bamboo weaving technique called "Kagome-biki." The resulting triangular Kagome structure consists of nine cylinders arranged in three sub-triangles that share their apexes. Microphones record the sound signal in the corner cylinders, and small tubes between each cylinder allow air to fill the device.
Speakers placed under the corner cylinders generate sound waves, which are localized at the structure's corner cylinders. Sound waves are vibrations that carry energy through a medium, such as air or water. The shape of a sound wave determines its pitch, loudness, and speed — also called its frequency — amplitude, and sound velocity. In their helium-detection device, the researchers took advantage of how sound velocity changes in different media.
Sound waves travel faster in denser media — they are fastest in a solid, slower through air, and cannot transmit in a vacuum. All objects have a resonant frequency, which is the natural speed at which they vibrate, and adding energy to something at that resonant frequency drastically increases its amplitude.
When helium fills the device, the density of the gas in the device changes. The sound waves traveling through the device suddenly change speed and no longer vibrate the cylinders at their special resonant frequency. This causes a drastic change in the amplitude that the microphones record, and this shift in frequency tells the researchers the concentration of helium in the room.
"Because the relative sensitivity of our sensor remains constant and is not related to working conditions, such as temperature and humidity, the sensor can be applied at an extremely low temperature, which remains challenging for traditional gas sensors working with sensitive materials," says author Li Fan.
The triangular device also allows the researchers to determine the location of helium leaks in a 2D space by measuring which corner experiences a frequency shift first.
The team hopes to expand the device to locate leakage points in 3D space and develop the system into a portable device.
