Johan Carlsson: Plasma microphone for structural health monitoring

Thursday, Nov 8, 2018

A microphone that picks up the faint creaks and groans of bridges and other structures could provide early warning signs that maintenance is needed. Johan Carlsson, a computational plasma physicist formerly at the U.S. Department of Energy's Princeton Plasma Physics Laboratory (PPPL) and now at RadiaSoft, has developed a new ultrasensitive microphone that uses charged clouds of gas known as plasmas to measure structural health.

The new plasma microphone is highly sensitive to the ultrasonic frequencies emitted by the microfracturing of concrete and metal. Each microphone consists of a glass tube filled with plasma, which conducts electricity. As a sound wave propagates through the plasma, the change in pressure causes perturbations in electrical resistivity that can be detected as an electronic signal.

These microphones are far more sensitive than existing technologies for measuring bridge health. A network of them could potentially detect, locate and characterize flaws before major damage occurs.

“These microphones are relatively inexpensive to manufacture and could have great value in terms of preventing structural failures.” - Johan Carlsson, Principal Research Scientist, RadiaSoft

Development status: Patent protection is pending. Princeton is seeking outside interest for further development of this technology.
Funding: U.S. Department of Energy

Contact: Laurie Bagley, Head of Technology Transfer at PPPL, at or 609-243-2425