Acoustic Vector Sensor technology
The Microflown AVISA acoustic vector sensor (AVS) technology provides capabilities for detection, localization, tracking, and categorization of firing events (small arms fire, board cannons, mortars, artillery, rockets) and audible platforms (drones, heavy vehicles). The use of sound pressure transducer (microphone) technology is the traditional approach in the domain of battlefield acoustics, AVS technology is relatively new to this domain. AVS technology has unique characteristics that are particularly beneficial to military and security applications.
Sound pressure transducer versus acoustic vector sensor
Any sound field has two physical quantities, 1) sound pressure, and 2) acoustic particle velocity. Sound pressure is measured with a microphone, acoustic particle velocity is measured with an AVS, a so-called microflown. A microflown determines particle velocity through measurement of heat transfer between 2 heated parallel wires, providing directional sensitivity (illustrated in the figures). Compared with the electrical domain, sound pressure is the equivalent of the potential (voltage, the driving force), acoustic particle velocity is the equivalent of the current (amperes, the result). Whereas sound pressure is a scalar (only having a magnitude value), acoustic particle velocity is a vector (having a magnitude as well as a direction).
To be able to achieve directionality with microphones, usually three (or more) of these sensors are required. The spacing between the microphones determines the acoustic frequency range where the chosen configuration has an optimal signal-to-noise ratio. Consequently, directionality for systems using sound pressure transducers yields a narrow-banded solution. Microflown’s flown is acoustic broad-banded sensor, pointing in the direction of the sound source across the entire frequency spectrum, i.e. being able to sense simultaneously different types of threat.
AVS sensor hardware
The AVS technology is implemented to build two sensor nodes that are universal to all solutions. The ground capabilities are built around the Acoustic Multi Mission Sensor (AMMS).
The UAS sensor payloads are built around the Acoustic Pointer, essentially a miniturized AMMS repackaged in dagger-shape form factor.
4 AMMS, an Acoustic Master, a weather station and a geo-referencing device are combined in the so-called CASTLE sensor post. The AMMS’s generate 4 streams of acoustic data for coherent processing in the Acoustic Master. The CASTLE can be used as a non-networked sensor post (for localization of small arms fire and board cannons), but also in a network of sensor posts (for localization of mortars, artillery, rockets, drones etc.).
Software defined capabilities
A dedicated set of processing functions is configured for each user application to deliver optimal results. The dedicated software having these functions all run on the universal sensor and processing hardware; the capabilities of the solution are software-defined.
AVS signal processing
AVS sensor hardware detects acoustic events, both transients (muzzle blast, impact explosion, ...) and continuous events (shockwaves, tonal sound, …). In the AVS signal processing, these events need to be reliably detected, separated and categorized against background noise (wind, vehicle noise and other non-relevant acoustic events). Related acoustic events generated by a single occurrence (e.g. muzzle blast and shockwave for a shot of small arms fire) arrive at the sensor with time difference. Correlation of such events for a single occurrence is straightforward, though rapidly becomes challenging in complex scenarios with simultaneous shooting, multiple shooting and impact positions, and a variety of weapons.
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