Nonlinear Imaging

Why use the Vantage system for nonlinear ultrasound?

  • The Vantage platform provides excellent system linearity. The nonlinear diffuse energy imaging example demonstrates the upper limit of the system nonlinearity (the difference in output energy between full aperture and single element transmission), which is less than 0.5%. For methods using larger sub-apertures, such as the checkerboard approach, which use a half-array sub-aperture, the transmit nonlinearity is even smaller.
  • The Vantage system’s programmable tri-state pulser allows precise transmit bandwidth control, pulse inversion and multi-frequency pulse transmission for modulation methods. Pulse inversion can be used with two sequential transmissions to cancel linear terms by summation of the received data sets, directly producing a nonlinear residual.
  • Every Vantage system includes programmable analog and digital filters to optimize the receive bandwidth. Programmable multi-stage gains optimize the receive dynamic range for the small signal amplitudes common in nonlinear measurements.
  • The Vantage system supports amplitude modulation and sub-aperture transmission methods including parallel-sequential field subtraction techniques.

Nonlinear Ultrasound for NDT

A recent research trend has been the development of methods utilizing phased arrays to allow imaging of elastic nonlinearity. Elastic nonlinearity is a modality of interest in NDE for its sensitivity to macroscopic defects such as closed cracks and also the micro-structural material changes associated with damage precursors. Cutting-edge developments in nonlinear imaging necessitate high performance hardware, placing Vantage as an ideal platform for such research.

An example of cutting-edge nonlinear imaging development on the Vantage system is nonlinear diffuse energy imaging.  This method measures elasticity nonlinearly through evaluation of later-time statistical diffuse energy rather than waves scattered coherently from the measurement point, providing complete separation of linear and nonlinear modalities.  The precise control of the waveform provided by the tri-state transmitter increases achievable nonlinear measurement sensitivity, making Vantage the ideal system for application and development of this technique.

Linear Imaging: TFM
Nonlinear Imaging: Diffuse Energy
Shown above is an example demonstrating the benefits of nonlinear ultrasonic imaging using the Vantage system.  Linear TFM and nonlinear diffuse energy images of a high-cycle fatigue crack within an aluminum compression test specimen acquired using a 5 MHz 64-element array (Imasonic).  The nonlinear image is seen to eliminate the linear back-wall and coherent noise features and more precisely resolve the size of the closed crack tip.
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NDE/NDT Applications & Techniques
NDE/NDT with vantage