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3D acoustic situational awareness


Acoustic Particle Velocity

The MEMS technology based Microflown transducer is the world’s first and only dedicated acoustic particle velocity sensor.
Any sound field can be described by two physical quantities:

  • Sound pressure
  • Acoustic particle velocity

If sound pressure were the equivalent of voltage, particle velocity is the equivalent of amperes.
Traditionally, in acoustics, directionality is obtained by putting two sound pressure transducers at a certain distance, combining their signals just a human hearing does.

However, the optimal frequency sensitivity for such a constellation depends upon the distance between both transducers.
It provides narrow banded directionality.

The Microflown transducer provides broad banded directionality, over the entire audio range as it can be heard by human beings.
This feature is referred to as a “figure of eight”.


By combining two orthogonally placed Microflown transducers and a microphone into a single wind and weather proof unit, a so called Acoustic Multi Mission Sensor is created.
Two versions exist, both with a 30 cm and a 23 cm outer diameter.
Reducing the diameter implies an increase in the sensitivity for wind, which is for instance importance for moving platforms.

Each AMMS in itself provides directional information, as can be seen in the time frequency plot where colors indicate direction and color intensity the level of the acoustic event.


Four Acoustic Multi Mission Sensors are connected in a hard wired acoustic subarray called the CASTLE. Both vehicle and ground based versions of the CASTLE do exist.

By default, 4 AMMS, an Acoustic Master and a weather station are part of the vehicle mounted sensor post.
The Acoustic Master is the intelligent computing device processing all the signals obtained in each AMMS.

For a ground based solution, also a geo referencing device providing both position and heading information is needed.
In general, for networked operations, a software defined radio is needed.

Software defined capabilities

Because of the intrinsic acoustic broadbandedness of the CASTLE, the entire frequency spectrum of audible firing events and noise making platforms can be processed, using algorithms based upon both Time Of Arrival (TOA) and Direction Of Arrival (DOA).

In itself, the AMMS already replaces several other kinds of acoustic arrays, all designed for a certain capability such as the localization of incoming small arms fire or indirect firing positions.
The CASTLE is the supercharger, bringing better acoustic performance, taking into account acoustic shadows and acoustic reflections on a vehicle deck for instance

Key benefits of AVS

The benefits to the user of the acoustic vector sensing technology are:

  • Low power consumption; persistent operations
  • Passive; undetectable, flown sensor cannot be jammed
  • Acoustic; day & night operations, line-of-sight not required, all-weather (temperature, dust, fog, rain, smoke)
  • Inherent directional; small form factor allows miniaturized sensor packaging
  • Inherent broadband; simultaneously sensing various threat types having an acoustic signature in low and high frequencies
3D acoustic situational awareness