Description of Acoustic Experimental Facilities

A team of physicists arrived at ISTerre in 2005, in order to develop innovative imaging strategies and procedures at the laboratory scale. This team has broad interests, ranging from underwater acoustics (oceanography), non-destructive testing and evaluation, medical imaging and, of course, seismic imaging. The facility includes two large experimental rooms for a total surface of 200 m2.

The Mega-Hertz room is equipped since 2006 with two powerful multi-channel ultrafast ultrasonic acquisition equipments from Lecoeur Electronics. One is a 64-channel acquisition devoted to small-scale ocean experiments, and the other is an 8-channels acquisition with specific source amplification and reception pre-amplification, and is fully devoted to ultrasound probing in concrete.

A newer version of this multi-channel electronics was purchased in July 2014 from Verasonics. This equipment consists in 128-channel electronics with programmable emission that permits ultrafast acquisitions (more than 1000 images per second) with ultrasonic signals in the MHz regime. The pulser amplitude is adjustable between 3 and 190 V peak-to-peak. The signals are received with 14-bit A/D converters with programmable sample rate up to 62.5 MHz. The local buffer memory is 64 Mb/channel which allows long acquisitions to be performed in a burst sequence mode. Digital averaging, filtering and decimation may be performed on data prior to transfer to host computer to improve signal to noise. The data transfer to host computer operates at 6.6 GB/s. Individual channel acquisition data and complex reconstruction data are made available in Matlab workspace for storage and advanced processing.

These multi-channel ultrasonic systems are coupled with a large set of ultrasonic arrays. At present, we have pairs of 64-element arrays (allowing to work in emission / transmission with different source-receiver arrays) centered at 0.5 MHz, 1 MHz, 3 MHz, 5 MHz and 7 MHz. These arrays have a 70 % bandwidth that make them very useful for broadband acquisitions.

The Kilo-Hertz room deals with wave propagation at lower frequencies with :
–  A network of 32 mini-accelerometers from Bruel & Kjaer with an excellent sensitivity (>90 dB) in the frequency range from 1 Hz to 20 kHz.
–  Two laser vibrometers associated with mirrors and step motors to scan the field normal to a surface with mm accuracy. The frequency range of the vibrometers is 10 Hz-10 kHz.
–  A large collection of piezoelectric transducers that can emit and receive the field between 100 Hz and 12 kHz.
–  Four 16-channel NI acquisitions card (16 input + 2 output) that can be chained together and connected to a PC through USB port. This NI acquisition device is driven by Matlab.
–  Two high-speed synchronized cameras that allow the measurement of the normal displacement (at a maximum speed of 10 images per second) on large surfaces (1 m x 1 m) through a stereo-correlation algorithm.

Kilo-Hertz room
3D view of the Kilo_Hertz room- click on image to start the video -
Mega-Hertz room
3D view of the Mega-Hertz room- click on image to start the video -