Æmission is a fast digitizer/recorder (1.25MSps@18bit or 5MSps@16bit) specifically designed for the acoustic emission surveys.
Thanks to our collaboration with the Polytechnic University of Turin, patented algorithms have been implemented in the internal FPGA.
Æmission can process the aemission waves locally, extracting the desired information (βt, b-value, cumulative count)
Æmission is working in a large experimental project funded by Regione Toscana named MONFRON
Acoustic Emission (AE) is the phenomenon of radiation of acoustic (elastic) waves in solids as result of damage or irreversible change in the internal structure of the material. Although the name itself suggests an audible signal, this is misleading, because the range of the involved frequencies is between 50Khz up to 1Mhz, practically ultrasonic frequencies.
Typically the release of elastic energy and so the AE occours as result of cracks due to external forces (mechanical loading) or conditions (aging, temperatures).
Acoustic Emission is a very powerful method of survey applied to structural health monitoring.
Major application of AE technique are:
- Localization of cracks inside the material
- Crack evolution (stable or dangerous)
- State of Health monitoring (predictive alarms)
Æmission is supplied with 8 piezoceramic sensors, the sensing elements were selected and characterized with the help of the Polithecnic University of Turin so as to suit civil structure monitoring and to get the most accurate signals.
Sensors are placed around the area that is to be monitored and connected to the Æmission via 10 meter cables.
Æmission BLOCK DIAGRAM
Analog signals, coming from the piezoceramic sensors are first electronically conditioned and level adapted by a cascade of analog filters before they can be converted into digital.
Eight high speed ADCs (1.25MSps@18bit or 5MSpsp@16bit) continuously convert the analog signal into digital, synchronized to the same clock source.
Digital signals are then parallelly acquired and processed by the FPGA and, according to the defined parametrization, only the events that satisfy the setting parameters are transferred to the Linux CPU.
Inside the Linux CPU events are stored locally and can be shared remotely by WiFi or 3.5G connection.
The integrated GNSS receiver can synchronize more Æmission units; a virtually limitless number of acoustic sensors can be acquired.
4-channel Æmission board
After a reasonable period of monitoring, the plots of the parameters are available and are useful in understand the nature of the cracking pattern and to give an analysis to the monitored structure.
The following graph represents an ongoing survey in a marble quarry.
In order are represented:
- AE cumulative count
- Frequency of events
- Amplitude of events
A 3D graph of the emission sources is represented in the graph below
Blue squares are the AE sensors, red dots reppresent the localization of the sources of emissions.