DISTRAN Acoustic Images Systems
Sound and Vibration
Both 2D and 3D systems are proposed for the localization of sound sources in space, both based on the latest digital technology to deliver maximum performance at very low cost.
How to localize sound sources?
One method to localize sound sources is to use many microphones. Since sound
waves propagate at a finite speed, the different microphones (black squares in the figure below) will perceive a given sound event at different times depending on the relative position of the source (S) and the microphone. Knowing the position of the microphones and this time delay, one can find the position of the source.
Sound source emitting and microphone array signal reception
Additionally to the time delay, the amplitude of the perceived sound wave will decrease as the distance between the source and the microphone increases.
Distran acoustic cameras exploit exactly these phenomena. They reconstruct an image where each pixel value corresponds to the intensity of a sound source emitting from that direction.
Proprietary technology and know-how have been developed at ETH, a world leading university located in Zurich, Switzerland. Whereas traditional methods used in acoustic imaging require seconds even minutes to compute a single image, Distran technology enables you to compute high-quality acoustic images in milliseconds.
Why does the microphone placement on Distran acoustic cameras looks irregular?
People regularly asks about the placement of the microphones on our acoustic camera. First of all, the placement is the result of sophisticated computation.
To optimize the performance of their microphone arrays, Distran’s engineers test billions of array configurations using highly parallelized algorithms and supercomputers (HPC). Thanks to their knowledge, their are able to improve the performance, the dynamic range, and the reliability of the arrays compared to regular patterns.
DISTRAN: make it simple
Simplicity is the cornerstone of Distran’s products. Acoustic cameras are one of the most sophisticated acoustic signal processing device that exists. But we believe it is our duty to keep the things simple. We deliver easy-to-use solutions to our customers so that they can concentrate on their application and not to waste their time on setting dozens of parameters to have meaningful results.
With simplicity comes robustness: our products are designed and produced in Switzerland. We use high-quality material and low tolerance machining to ensure robust products that withstand time and deliver dependable performance.
The spatial resolution Dx is in this case given by the ratio between the wavelength diameter D of the matrix (array) multiplied by the distance R between the antenna plane and source.
Examples:
If R = 1 m, D = 0.8m, at 800Hz: Dx = 0.5m
If R = 1 m, D = 0.8m, to 2500Hz: Dx = 0.17m
Distran Antenna and Specifications
- Real Time Images at 60Hz
- Frequency range between 215 Hz and 6 kHz for Antenna Omni 360 and Universal, and between 3kHz and 50 kHz for Antenna Ultra
- Proprietary Algoritmms for optimized performance and extended Dynamic Range
- Antenna optimized from 64 to 120 High Sensitivity microphones
- No DAQ external board and PC connection via USB
- Absolutely extra-light and portable (weight of 1kg)
- MATLAB interface in Real Time
- Each system includes optimized Notebook (Linux – Windows)
ALGORITHM – Acoustics Holography and Beamforming
The technique for Acoustic Holography assumes that the distribution 2-d of the sound pressure (amplitude and phase) on a plane (plane of measurement) satisfies the wave equation in an area external to the source (propagation) and is based on the use of algorithms of spatial transformation of acoustic fields; by simplifying the concept it can be said that a Fourier transform is applied in the spatial domain.
The acoustic holography has always been associated primarily with the analysis of the acoustic field near the source (near field) from measurements of sound pressure and / or particle velocity (intensity) carried on a plane (plane of measurement) at a certain distance from the source.
In the common bibliography the terminology established are abbreviations such NAH and SONAH, which respectively mean Near-Field Acoustic Holography and Statistically Optimized Near-Field Acoustic Holography.
The technique of Beamforming is quite similar to the principle used by a radar to identify objects in space 3d: the radar works on GHz, the Beamforming on the Hz / kHz. It is therefore to consider the Beamforming as a system capable of focusing to a source, however, instead of moving the antenna (as does the radar) to find the maximum signal, the antenna “planar” is fixed and artificial delays are introduced among the the microphones in the array that simulate virtually the focus.
ANTENNAS – Acoustic Holography
A planar antenna extent on the plane and is normally oriented towards the source, in doing so the measurement plane can be moved in the space closer to or far from the plane of the source (parallel to measurement plane). There are no particular restrictions in translating the measuring plane with the acoustic holography, the limits are defined by the antenna maximum width in regard to the minimum frequency and the minimum distance between microphones for the maximum frequency, while the spatial resolution for separation “visual source discrimination” of 2 adjacent sources is given by the distance R between the measurement plane and the source: the lower the value of R and the better the resolution.
The value of R shall not be less than the distance between the microphones, for which the order of magnitude is between 10 and 30 cm.
