Infrasound Detection and Sensor Development
Miltec Research and Technology
Figure 1. Miltec’s infrasound sensor
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Infrasound is defined as a wave phenomenon sharing the physical nature of sound
but with a range of frequencies below that of human hearing. Because infrasound
travels greater distances in the atmosphere than audible sound, it can be very useful
in monitoring activity on the battlefield and in other threatening situations. However,
low intensity infrasound sources are difficult to detect because of the masking
effect of wind noise. The conventional way to filter out this wind noise is to use
pipe arrays that average the pressure variations over an extended area. Such arrays
give a single signal that represents the average pressure over the sensed area.
Miltec has developed distributed arrays that sense the pressure at multiple points
over an extended area. Given that the multiple sensors are far enough apart so that
the signals are incoherent; averaging them will reduce the wind noise power proportional
to the number of sensors. It is also possible to locate the direction of the sound
source through the phase difference of the individually sensed infrasound signals.
Miltec has developed rugged inexpensive infrasound sensors proven to be very effective.
These sensors are shown in Figure 1. Using these sensors, Miltec has designed, built,
and tested multiple infrasound arrays that has been deployed for several test events
of interest. Figure 2 shows and infrasound signal in the 1-4Hz range that was only
detected after averaging 25 of the sensors data.
Figure 2. Results of wind noise reduction by averaging
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Miltec’s infrasound sensors are of an original design, have a sensitivity of approximately
2.5 mV/Pa, individually calibrated, and have a flat frequency response from 0.02
Hz to 100Hz. Miltec also offers a custom signal conditioning circuit board with
these sensors to provide filtering, adjustable gain, and low output impedance.
Contact Miltec for any of your infrasound sensing needs. With our expertise we are
capable of offering you a complete system from the sensing elements with all the
necessary data acquisition hardware to a custom tailored software application with
GUI to meet your requirements. We also offer services to collect and analyze your
infrasound data for you.
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