Shanghai group develops heatproof fiber microphone to monitor power networks

12 Feb 2026

Immune to heat and high voltage, optical sensor can spot problems inside transformers.

Researchers have fabricated a “hair-thin” microphone made entirely of silica fiber that can detect a large range of ultrasound, sound frequencies beyond the reach of the human ear. Able to withstand temperatures up to 1,000 °C, they say that the device could be used inside high-voltage transformers to detect early signs of failure before power outages occur.

“Conventional electronic sensors often fail under thermal stress or suffer from severe signal interference,” said Xiaobei Zhang, a member of the research team from Shanghai University. “Our all-fiber microphone can survive in hazardous environments and is completely immune to electromagnetic interference while remaining sensitive enough to hear the subtle early warning signals of equipment failure.”

Described in a paper in Optics Express, the researchers describe their new microphone, which is sensitive to frequencies from 40 kHz to 1.6 MHz. Unlike traditional microphones that rely on bulky housing, the new microphone is integrated within a fiber just 125 µm in diameter.

“Our all-fiber microphone can be placed directly inside voltage transformers to listen for tiny internal electrical sparks in real-time, preventing blackouts or explosions and keeping our power supply safe,” said Zhang. “The microphone’s incredible durability and wide hearing range make it ideal for everything from industrial testing and medical imaging to monitoring aerospace engines and providing early natural disaster alerts.”

Detecting sound with light

The researchers focused on detecting partial discharge inside high-voltage transformers, a type of small electrical fault that can signal equipment problems before wide power-grid failures occur. They say that detecting these signals directly inside the equipment is “difficult with current sensors due to extreme heat and strong electromagnetic interference, making reliable monitoring a major challenge for power systems”.

To solve this challenge, the researchers developed a fiber-based microphone based on the photoelastic effect. This effect can be used to detect mechanical changes — like vibrations — that alter a light’s refractive index.

They developed a unique sound-sensing design that uses a vibration-sensitive membrane and an internal glass micro-beam suspended inside a single-mode optical fiber. Together, these components form a Fabry-Pérot interferometer that can detect extremely small vibrations, including the sparks produced by electrical discharges.

To sculpt the suspended structure deep within the hair-thin fiber, the researchers used picosecond laser-induced chemical etching, an advanced technique that can be used to create highly precise micro- and nanostructures.

Performing across extremes

“The entire interferometric structure is integrated directly within a hair-thin fiber,” said Zhang. “This self-packaged monolithic design enables seamless deployment in high-temperature and space-constrained environments without needing any additional protection.”

The researchers tested the microphone in a 1000°C furnace for 100 minutes, reporting that it remained stable and continued to transmit clear signals during this time. They also demonstrated the sensor’s acoustic performance across an ultra-wide range of 40 kHz to 1.6 MHz, verifying its ability to detect sounds in both air and underwater environments.

Looking ahead, the researchers plan to integrate acoustic metamaterials into the device to push the boundaries of sensitivity even further. They also plan to use a multi-laser additive and subtractive manufacturing platform, combining silica 3D printing with ultrafast laser micromachining, to create ultra-robust, all-silica packaging that will significantly enhance both the sensing and mechanical performance of the microphone.