In-situ Acoustic Emission sensor
Because pendulum-based seismometers like geophones or accelerometers are not capable to record seismic waves above 25 kHz, the Bedretto Reservoir Project is monitored in addition by piezoelectric In-situ Acoustic Emission (AE) sensors. These sensors are about ten times more sensitive in the kHz range than other seismic sensors and are capable to record frequencies up to several hundred kHz.
For this project a new sensor was developed by GMuG GmbH that is custom made for the Bedretto project in terms of frequency range, sensitivity and reduced resonances. It is optimized for the monitoring of the frequency range 1 kHz to 80 kHz, which allows us to monitor the formation of small cracks of centimeter size within the reservoir, an important observation in order to understand the damage evolution. The sensor is made for installation via cementation and able to withstand high pressures > 100 bar. Eight to sixteen AE sensors are placed per borehole. Data is digitized with a 200 kHz sampling frequency.