Temporal and spatial apodization in defocused acoustic transmission microscopy.

Area of Science:

• Acoustic microscopy
• Wave physics
• Materials characterization

Background:

• Acoustic microscopy utilizes ultrasound waves for imaging and material property measurements.
• A line-shaped point spread function (PSF) is desirable for specific applications like acoustic transmission line tomography.
• Achieving a precise PSF is crucial for accurate spatially resolved velocity measurements in solids.

Purpose of the Study:

• To investigate the feasibility of implementing an acoustic microscope with a line-shaped PSF using two non-confocally adjusted spherical transducers.
• To analyze the factors affecting the achievable PSF, particularly the influence of edge waves and signal acquisition.
• To determine the constraints on obtaining a line-shaped PSF in acoustic transmission microscopy.

Main Methods:

• Employing two non-confocally adjusted spherical transducers in a transmission acoustic microscope setup.
• Utilizing time-selective signal acquisition to restrict ultrasound wave paths.
• Investigating the impact of exciting toneburst length and time gate position on the PSF.

Main Results:

• The dominant signal contribution originates from edge waves from the transducer rim, not the direct wave.
• Achieving a purely line-shaped PSF is constrained by these edge waves.
• A line-shaped PSF is impossible with long exciting tonebursts due to strong edge wave contributions.

Conclusions:

• Edge waves significantly limit the ability to achieve a line-shaped PSF in defocused acoustic transmission microscopy.
• The length of the exciting pulse and the placement of the time gate are critical parameters influencing the PSF.
• Further optimization is needed to overcome edge wave effects for applications requiring a line-shaped PSF.