An Ultrasonic Plasma Microphone for Structural Health Monitoring

Web Published:

Princeton Docket # 17-3317-1


Researchers at Princeton Plasma Physics Laboratory, Princeton University, have invented a plasma microphone. The device uses plasma, an electrically conducting gas created by applying a voltage between two electrodes, to transduce acoustic waves to electronic signals. As a sound wave propagates through plasma, the pressure perturbation changes the electrical resistivity, which causes a current fluctuation that can be extracted as an electronic signal. The plasma microphone has high sensitivity that is virtually independent of frequency, a distinct advantage over conventional microphones that makes it ideally suited as a contact microphone for structural-health monitoring (SHM) applications. SHM utilizes spontaneous ultrasonic acoustic emissions (AEs) from micro fracturing in concrete and metal to detect, locate and characterize damage. The AEs of interest have a frequency range of 100 kHz to 1 MHz.


We envision the plasma microphone as a disruptive technology that will allow replacement of the current SHM business model based on commodity AE sensors and proprietary software for interpreting the sensor data. With patented sensor technology, the interpretation software can be made open source and developed and refined in collaboration between public-infrastructure owners and the academic SHM community.



•       Acoustic-emission sensor for structural health monitoring

•       Premium pickup (contact microphone) for acoustic instruments



•       High and constant sensitivity over whole frequency range of interest




Johan Carlsson is a Computational Plasma Physicist at the Princeton Plasma Physics Laboratory (PPPL). He got an MSc in Engineering Physics at Lund University in Sweden in 1992, and a PhD in Fusion Plasma Physics at the Alfven Laboratory, Royal Institute of Technology (KTH) in Sweden in 1998. Dr. Carlsson has primarily done computational work on tokamaks, toroidal magnetic configurations intended for energy production by confining self-sustaining thermonuclear fusion plasmas, but more recently also on low-temperature plasmas for thruster and power-electronics applications. He has broad research interests, including plasma physics, algorithms, software engineering and signal processing. Dr. Carlsson got a Green Card as an Outstanding Professor or Researcher in 2008 and became a US citizen in 2013.

Princeton Plasma Physics Laboratory           


Princeton Plasma Physics Laboratory (PPPL) is a United States Department of Energy National Laboratory managed by Princeton University. PPPL is collaborative national center for fusion energy research. The Laboratory advances the coupled fields of fusion energy and plasma physics research, and, with collaborators, is developing the scientific understanding and key innovations needed to realize fusion as an energy source for the world. An associated mission is providing the highest quality of scientific education.


Intellectual Property & Development Status


Patent protection is pending.


Princeton is currently seeking commercial partners for the further development and commercialization of this opportunity.




Chris Wright

Princeton University Office of Technology Licensing • (609) 258-6762 •


Laurie Bagley

Princeton Plasma Physics Laboratory • (609) 243-2425 •


Patent Information:
For Information, Contact:
Chris Wright
Licensing Associate
Princeton University
Johan Carlsson