Helium is often associated with balloons and squeaky voices, but in modern technology it is a strategic and irreplaceable resource. It is critical for MRI machines, semiconductor manufacturing, space exploration, and advanced scientific research. Despite its importance, helium is scarce, expensive, and difficult to store. Even small leaks can lead to significant losses. Detecting those leaks quickly, however, has remained a technical challenge because helium is chemically inert. A recent study by researchers at Nanjing University points to a promising solution by replacing chemistry with sound.
Why helium evades conventional sensors
Most gas sensors work by exploiting chemical reactivity. They absorb gas molecules or trigger chemical reactions that alter an electrical signal. This approach functions well for reactive gases such as ammonia or nitrogen dioxide. Helium, however, is a noble gas. It does not readily form chemical bonds, which means it fails to interact with the sensitive coatings used in standard sensors. As a result, detection becomes unreliable or impossible.
Highly accurate techniques like mass spectrometry can identify helium, but they are large, costly, and unsuitable for continuous industrial monitoring. This gap between accuracy and practicality has long constrained helium leak detection.
Listening to gas instead of reacting with it
The new study, published in the December 2025 issue of Applied Physics Letters, takes a fundamentally different route. Instead of relying on chemical reactions, the researchers use acoustics. Sound travels at different speeds in different gases. When helium mixes with air, it changes the speed at which sound propagates. This physical property offers a way to detect helium without requiring any chemical interaction.
By converting a chemical detection problem into a physical one, the researchers bypass helium’s inert nature altogether.
The role of acoustic topological materials
At the core of the sensor is an acoustic topological material built using a Kagome lattice — a geometric arrangement of interlaced triangles and hexagons. The structure consists of rigid cylinders connected by narrow tubes. This specific geometry produces what are known as topological corner states, where sound waves become trapped at the corners of the structure instead of spreading throughout it.
Once sound enters the system, it localises at the three corners of the triangular design. Importantly, this trapping is extremely stable and does not depend on precise manufacturing or delicate components.
How helium alters trapped sound
When helium leaks into the sensor and mixes with the air inside the tubes, the speed of sound changes. This alters the frequency, or pitch, of the sound trapped at the corners. By measuring this frequency shift, the sensor can calculate the concentration of helium present almost instantly.
Because the design has three corners, the sensor can do more than confirm the presence of helium. By comparing which corner registers a frequency change first, the device can infer the direction from which the gas is leaking, allowing for faster localisation of the problem.
Durability and operational advantages
Unlike chemical sensors, the acoustic device does not rely on fragile coatings that degrade over time. It functions reliably across a wide temperature range, from about 26°C down to –34°C, and remains unaffected by changes in humidity. This eliminates the need for frequent recalibration, a major drawback of conventional gas sensors.
The topological nature of the design also makes it robust. Even when large holes were drilled into the structure to allow gas to enter more quickly, the sound trapping effect remained intact. This enables rapid leak detection without sacrificing accuracy.
Why this matters for industry and research
Helium shortages can disrupt critical services, from hospital imaging to high-tech manufacturing and space missions. A rugged, low-maintenance, and relatively inexpensive sensor could significantly reduce losses and improve safety. More broadly, the study highlights how principles from physics — such as topology and acoustics — can offer solutions where chemistry falls short.
What to note for Prelims?
- Helium is chemically inert, making it difficult to detect using conventional gas sensors.
- Acoustic sensing relies on changes in the speed of sound in different gases.
- The Kagome lattice consists of interlaced triangles and hexagons.
- Topological corner states trap sound in stable locations.
What to note for Mains?
- Explain why helium leak detection is technologically challenging.
- Discuss how acoustic methods overcome the limits of chemical gas sensors.
- Analyse the importance of topological design in creating robust sensing technologies.
- Evaluate the relevance of such innovations for strategic resources and advanced industries.
