Acousic Signature and Transparency of Composite Structures at High Frequencies

Modern active sonar imaging systems have achieved very high resolution, enabling detailed imaging of seabed and the detection of nearby objects. Operational frequencies now extend up to 100–500 kHz, and state-of-the-art reconstruc8on algorithms can resolve fine structural details and even analyze shadows cast by stationary objects on the seafloor. In the future, reducing the acoustic signature of man-made objects either resting on the seafloor or in motion in open water will require not only conventional anechoic treatments but also the suppression of shadow cones, meaning the mitigation of forward scabering.
Simultaneously, active and passive sonar systems embedded in vessels or autonomous underwater vehicles are increasingly integrated into highly anisotropic composite structures. This anisotropy can significantly affect acoustic performance at high frequencies. Optimizing both mechanical robustness and acoustic neutrality (e.g., transparency of acoustic windows) is therefore critical for the efficiency of detection and imaging systems.
These two interrelated challenges — acoustic transparency and signature — require precise manipulation of acoustic fields via abenuation, redirection, or guidance using specialized composite materials (e.g., anisotropic or inclusion-based). While the high-frequency context echoes some of the challenges found in ultrasonic acous8cs, it involves much larger structures (meter or sub-meter scale), leading to very large size- to-wavelength ratios. This severely complicates predictive modeling and structural design, making traditional tools such as full 3D finite element modeling increasingly impractical. Whether in terms of modeling and prediction or materials and structural engineering, the high-frequency acoustic context represents a major
challenge in this field.

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