The Microflown AVISA

Microflown AVISA develops acoustic intelligence, surveillance and reconnaissance (ISR) systems, based on its worldwide unique and patented in-house Acoustic Vector Sensor (AVS) technology.

Based in the Netherlands, Microflown AVISA is an internationally staffed SME spending 70% of efforts on R&D. Next to offering both commercial off the shelf products as well as customized solutions for a global range of customers in defense and security, Microflown AVISA also advises governmental agencies and NATO industry groups in the field of acoustic situational awareness.

Microflown AVISA develops and markets highly innovative and complete battlefield acoustic solutions, providing 3D situational awareness by detecting, localizing and classifying the full range of audible battlefield threats, such as small arms fires, rockets, artillery and mortars and engine driven platforms (heavy ground vehicles, helicopters and UAV's).

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

Microflown AVISA as the leader of the WP6 together with its Greek partner company, CERTH, provides Acoustic Detection System (ADS) for the TeamAware project in which the following objectives will be followed:

• Design of a compact and lightweight georeferenced array of acoustic vector sensor to be installed on a UAV

• Detection and localization of gunshots and explosions

• Detection and localization of people whistling or asking for help (human speech)

The main objective of the ADS of WP6 is to detect and determine the location of explosions or gunshots near first responders. ADS will detect and locate explosions, gunshots, and snipers as well as human voices (e.g., screams asking for help) and whistling in the operations. This is done through an array of acoustic vector sensor and required acoustic signal processing algorithms for rescue purposes. The ADS system can be drone mounted or portable depending on the situation and requirements of end users.

The ADS system will be able to detect and locate the above-mentioned acoustic sources in emergency events (i.e., terrorist attack, search and rescue, natural disasters). An initial implementation of the ADS system will be conducted using commercial equipment by CERTH to prepare and test the relevant algorithms. Then the developed algorithms will be evaluated and modified using a recorded data from an acoustic vector sensor array similar to what it is supposed to be designed and developed for the ADS system. While CERTH will be working on evaluating and developing the algorithms with the recorded data, a prototype of the acoustic vector sensor array with a recording capability will be developed by AVISA to be tested and used on a drone for the system’s tests and demonstrations at the end of the project. Figure 1 illustrates a detailed view of the ADS architecture, regarding its software components.

Acoustic vector sensor

Acoustic vector sensor (AVS), also called particle velocity sensor is a MEMS based sensor enabling measurements of acoustic particle velocity. The very small sized elements are created on silicon wafers using clean room technology. The sensing element consists of two ultra-thin wires. These wires are platinum resistors that act as temperature sensors. They are powered by an electrical current which causes them to heat up. Local temperature variations cause changes in the wires’ resistance. When the sound propagates across the wires, it asymmetrically alters the temperature distribution around the resistors (wires). The resulting resistance difference provides a broad band (20 Hz up to at least 10 kHz) signal with a figure of directivity that is proportional to the acoustic particle velocity. Directivity of a particle velocity sensor (produced by Microflown AVISA) versus a microphone is shown in Figure 2. The Microflown particle velocity sensor provides broad banded directionality, over the entire audio range in the human’s hearing range.

Acoustic Multi Mission Sensor

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 (AMMS) is created. There are two versions of AMMS, with a 30 cm and 23 cm outer diameters. Reducing the diameter implies an increase in the sensitivity to wind, which is important especially for moving platforms. Each AMMS provides directional information. A figure of an AMMS with wind-cap is demonstrated in Figure 4.

For the TeamAware project, AVISA will design a light weight AMMS with a 23 cm diameter footprint that can be installed on a multicopter. This array will equip with a memory and the capability of recording data on it. This will be an important feature for doing tests and algorithm developments especially for the UAV during the flight. The recorded data during the flight can be extracted and used later for analysis, debugging and algorithm development part of the ADS.

The goal is to have the array and related electronic parts fit in the size of an AMMS. The exact size and weight of the array and related electronics cannot be determined at this stage, but we estimate that the unit will have a size of 23-30 cm (outer diameter) and a weight of 4-5 kg.