Ultrasonic reflection mode imaging of the nonlinear parameter B/A. II: Signal processing

Area of Science:

• Nonlinear Acoustics
• Acoustic Wave Propagation
• Materials Science

Background:

• Nonlinear acoustic interactions can reveal material properties.
• The nonlinear parameter B/A is a key indicator of material nonlinearity.
• Previous methods for B/A mapping have limitations in spatial resolution.

Purpose of the Study:

• To develop a new method for spatially mapping the nonlinear acoustic parameter B/A.
• To utilize nonlinear acoustic interactions between counter-propagating waves for B/A imaging.
• To explore advanced waveform design for improved spatial frequency resolution of B/A.

Main Methods:

• Generating phase changes in a probe wave via nonlinear interaction with a broadband pump wave.
• Expressing phase change as a convolution of the pump waveform and the spatial B/A distribution.
• Employing Fourier transformation for space-to-frequency mapping with impulsive pumps.
• Utilizing matched filtering to restore spatial coherence with swept-frequency pumps.

Main Results:

• Phase changes in the probe are directly proportional to the nonlinear parameter B/A.
• An "A-mode" representation of B/A can be achieved through phase detection and deconvolution.
• Fourier transformation enables extraction of spatial B/A information from phase modulation.
• Matched filtering effectively processes signals with swept-frequency pumps.

Conclusions:

• The proposed method offers a viable approach for spatial B/A mapping.
• The technique allows for the design of pump waveforms to resolve a wide range of spatial frequencies in B/A.
• This advancement has implications for nonlinear acoustic imaging and material characterization.