Researchers have created a microphone so thin it looks like a human hair, yet tough enough to survive temperatures as high as 1,000°C.
Made entirely from silica glass, this tiny device can detect ultrasonic sounds far beyond the range of human hearing—and it could one day help prevent power outages by listening for early warning signs inside high-voltage equipment.
The new microphone was developed by a research team at Shanghai University and described in the journal Optics Express.
Unlike conventional microphones that use electronic parts, this one is built directly into an optical fiber just 125 microns wide.
Because it contains no electronics, it is immune to electromagnetic interference and does not break down under extreme heat, two problems that often cripple traditional sensors in harsh industrial environments.
“This kind of environment is extremely challenging for normal sensors,” explained team member Xiaobei Zhang. “Electronic devices can fail under high temperatures or produce unreliable signals because of strong electromagnetic fields. Our fiber-based microphone avoids both problems.”
The microphone can detect ultrasound frequencies ranging from 40 kilohertz to 1.6 megahertz. That wide range is important because many early signs of equipment failure—such as tiny electrical sparks known as partial discharges—produce ultrasonic vibrations.
These sparks often appear inside high-voltage transformers long before a serious fault, explosion, or blackout occurs. Hearing them early could allow engineers to fix problems before they become disasters.
Instead of detecting sound electrically, the device uses light. When sound waves hit the microphone, they cause extremely small vibrations inside the glass fiber.
These vibrations slightly change how light travels through the fiber, a phenomenon known as the photoelastic effect.
By carefully analyzing those light changes, the system can detect even the faintest ultrasonic signals.
To make this possible, the researchers sculpted an intricate structure inside the fiber itself.
Using ultra-fast picosecond laser pulses followed by chemical etching, they carved a tiny vibrating membrane and a suspended glass beam inside the fiber. Together, these form an optical cavity that acts like a highly sensitive listening chamber for sound.
The team tested the microphone in a furnace at 1,000°C for more than an hour and found that it continued to work reliably throughout the test. They also showed that it can detect ultrasound in both air and water, opening the door to applications beyond power systems. Possible future uses include industrial inspections, medical imaging, monitoring aircraft engines, and even early warning systems for natural disasters.
Looking ahead, the researchers plan to further boost the microphone’s sensitivity and durability.
Their goal is to make the device robust enough for long-term use inside operating industrial equipment. If successful, this glass microphone could quietly listen in places no ordinary sensor could survive—and help keep critical systems running safely.
