The Waves and Imaging Laboratory at the University of Minnesota is devoted to the development and implementation of experimental techniques for wave-based imaging, characterization, and diagnostics of complex material and structural systems.
Laser Doppler Vibrometer
The centerpiece of the lab is the Polytec PSV-400-3D-M Scanning Laser Doppler Vibrometer (LDV). A laser vibrometer is a sensing device that provides accurate non-contact measurements of the velocities of points belonging to the surface of vibrating solid objects. Non-contact measurement techniques are non invasive and allow superior measurement accuracy (compared to standard transducer-based methods). 3D scanning vibrometers, in particular, are capable of scanning the surface of a vibrating body, thus allowing full reconstruction of the three-dimensional velocity fields associated with the wave or vibration state of the medium. Scanning lasers are agile sensing devices as a result of their ability to quickly reconfigure the spatial location and density of the scanning grid points.
- PSV-400-3D-M vibrometer can detect displacements of the order of nanometers (10-9m)
- The spatial resolution is ± 0.1 mm. This translates in the possibility to make O(104) measurements in a 1in x 1in region, which translates in the possibility to resolve small-scale features in the reconstructed wavefields
- The frequency range is DC-1MHz, spanning across applications, from modal analysis of structures to ultrasonic-based NDE.
- B&K Vibration Exciter Type 4809: electromechanical shaker with a frequency range from 10 Hz – 20 kHz.
- Olympus V101 RB Piezoceramic Transducer: P-wave ultrasonic contact transducer with resonance frequency at 0.5 MHz.
- Olympus V1548 Piezoceramic Transducer: S-wave ultrasonic contact transducer with resonance frequency at 0.1 MHz.
- E&I 1140LA 1000 Watt Class AB amplifier: capable of providing a nominal gain of 55dB in the frequency range 9 kHz – 250 kHz.
- E&I 1020L 200 Watt Class AB amplifier: capable of providing a nominal gain of 53 dB in the frequency range 10 kHz – 5 MHz.
- B&K 2718 Power Amplifier: characterized by continuous variable output current from 1A to 5A.
- Nicollet Sigma60 8-channel Digital Oscilloscope Workstation.
- Spectral Dynamics Siglab portable dynamic signal analyzer.
Gallery of experimental setups and applications
Scan of a nuclear graphite block experiencing bulk and surface wave propagation. The wavefield captured form the block surface is subsequently fed to an inverse-elasticity algorithm to reconstruct the position, size and shape of defects (e.g. internal damage due to thermal gradients) that may have developed in the interior of the block. PI: Bojan B. Guzina – Student: Roman Tokmashev.
20kHz ultrasonic waves propagating across an arrested fracture in a granite slab (3-point bending configuration): in-plane (ux,uy) displacement waveforms captured by LDV. The experiment aims to better understand the fracture’s (linearized) interfacial condition, quantified in terms of the shear and normal specific stiffness distributions (kn,kt).