Acoustic camera
What is acoustic camera?
Acoustic camera is camera with an array of microphones. Array of microphones is basically a group of microphones. Acoustic illustrates the source and intensity of the sounds.
Image 1. Acoustic camera with 32 microphones.
How it works?
General
Each microphone in the array records audio stream of their own from specific position on the camera. This creates the microphones amount of streams. The position difference is stored in memory so that other microphones audio data is filtered from other microphones in the array.
Beamforming
Because of the position of the microphone in the array, there is delays in the receiving sounds. It's dependent on the distance of the sound source and the microphone. Delays are adjusted to focus one single point in space. This is called beamforming. Area that is recorded is token as an image. The focusing process is repeated for every point in area which is recorded.
Problems/Challenges
Signal processing in acoustic camera is very hardware heavy and memory heavy. Due to this usually the digital signal processing is done after the recording.
Applications?
Acoustic camera is used to search sound sources and noise reduction. It is used for instance for cars, airplanes, helicopters, trains and structures.
Companies selling acoustic cameras
- http://www.distran.ch/
- http://www.gfaitech.de/en/products/acoustic-camera
- http://www.norsonic.com/en/products/acoustic_camera/Acoustic+Camera+Nor848A.b7C_wtnQYO.ips
- http://www.acoustic-camera.com/
Sources
http://www.metsystem.hu/Companies/Fellner/Acoustic-camera/Image17.jpg (1. Image)
http://blog.kaistale.com/?p=246
http://en.wikipedia.org/wiki/Beamforming
http://en.wikipedia.org/wiki/Acoustic_camera
Electret microphone
Material and manufacturing
Main reason to use electret microphone is low cost of manufacturing. Material choice is based on usage and low cost.
...
Manufacturing electret microphone is simply attaching pieces together. It can be homemade.
Sources for material and manufacturing
http://doc.utwente.nl/70403/1/Sprenkels89development.pdf
http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=00679385
http://scitation.aip.org/content/asa/journal/poma/9/1/10.1121/1.3466951
