Sensing a buried resonant object by single-channel time reversal

Area of Science:

• Acoustics
• Ultrasonics
• Signal Processing

Background:

• Monostatic sonar systems often face challenges with weak target echoes, especially for buried objects.
• Resonant scattering from spherical targets can be complex and difficult to isolate.
• Enhancing signal-to-noise ratio is crucial for accurate target detection and characterization.

Purpose of the Study:

• To evaluate the effectiveness of iterative, single-channel time reversal for improving monostatic ultrasonic returns.
• To assess the technique's performance for both free-field and sediment-buried resonant spheres.
• To demonstrate the application of time reversal for target imaging and discrimination.

Main Methods:

• Scaled laboratory experiments were conducted in a water tank using a broadband piston transducer (0.4–1.5 MHz).
• Metallic spheres (6.35 mm diameter) were used as targets, either in free field or buried in a glass bead sediment phantom.
• The iterative time reversal process involved broadband pulse excitation, signal sampling, time-domain reversal, and re-transmission.

Main Results:

• The spectral response of target echoes rapidly converged to the dominant backscattering mode.
• Significant signal-to-noise enhancement of target echoes was achieved for buried spheres at multiple depths.
• Imaging demonstrated the technique's capability to differentiate between target types and enhance specific scattering modes.

Conclusions:

• Iterative, single-channel time reversal is an effective method for enhancing monostatic ultrasonic returns from resonant spheres.
• The technique improves target detection and discrimination capabilities, particularly for buried objects in complex environments.
• Time reversal processing offers a valuable tool for advanced sonar imaging and target characterization.