Farfield coherent infrasound generation using an air-propane burner

Area of Science:

• Acoustics and Signal Processing
• Geophysics and Environmental Science

Background:

• Characterizing acoustic receivers, propagation paths, and detection systems requires a reliable signal source.
• Designing infrasound sources (0.25-4.0 Hz) presents significant engineering challenges due to long wavelengths and the inverse square relationship between frequency and volume displacement for constant pressure amplitude.

Purpose of the Study:

• To present the theoretical development and engineering design of a coherent infrasound source.
• To address the challenges of generating low-frequency, high-volume displacement acoustic signals.

Main Methods:

• Theoretical modeling based on the simple source equation for low-frequency acoustics.
• Engineering design utilizing gas combustion for controlled, periodic large-volume air displacement.
• Prototype testing in open atmosphere conditions.

Main Results:

• Successful generation of continuous infrasound signals at a fundamental frequency of 0.25 Hz.
• Demonstrated capability to produce frequency content across the 0.25-4.0 Hz band with a reasonable signal-to-noise ratio.
• Verified operation in far-field ranges where acoustic parameters are in-phase (wavenumber-range product near 4.7).

Conclusions:

• The developed coherent infrasound source is a viable tool for characterizing acoustic systems in the sub-hertz to several hertz band.
• Gas combustion provides a practical method for achieving the necessary large volume displacements for low-frequency sound generation.
• The prototype validates the design for producing repeatable, controlled infrasound signals.