Target strength analysis using reflection coefficient of a submarine with low-frequency anechoic coatings

As the technological development of modern weapons systems progresses, attack and defense against the weapons systems of the past can become useless. In the case of underwater weapon systems, improvements in sonar and torpedo technology necessitate enhancements in submarine stealth performance. The stealth performance of a submarine is analyzed through the acoustic target strength (TS), which is indicated by the degree of sound wave reflection in the sonar equation. Various methods have been researched to analyze the TS of submarines, but methods considering the Anechoic coating attached to submarines are rare. Coating-related research has mainly focused on the absorption characteristics of coatings attached to flat surfaces. Therefore, there is an increasing need for research to analyze the sound absorption performance of anechoic coatings considering the curved surface of a submarine. In this study, we propose a method to verify the stealth performance of a submarine by analyzing the TS according to the azimuth angle by applying periodic inclusion of anechoic coating (PIAC) to the submarine. The PIAC based on the meta-structure is designed to form a bandgap in the low-frequency region by considering the resonance of the cylindrical Inclusion and the air cavity, applying the Bloch Theorem and the Brillouin zone, as well as the periodic arrangement characteristics. The PIAC was attached to the submarine model and modeled, and the absorption and reflection coefficients according to the azimuth angle were calculated using the finite element equation. The TS analysis included the process of determining the effective area by combining Geometrical Optics (GO) based on ray tracing and Physical Optics (PO) using the Kirchhoff approximation. The stealth performance was verified by comparing the TS analysis results according to the azimuth angle of the submarine equipped with the existing Alberich coating and the submarine equipped with PIAC at the same frequency.