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Description
In recent years, phase gradient metamaterials have attracted significant attention for their ability to steer incident waves in specific directions. This behavior follows the generalized Snell’s law, which relates the directions of reflected and transmitted waves to the phase gradient of their coefficients along the surface. By imposing a specific linear phase profile, these materials can convert reflected and transmitted waves into surface waves, which can then be completely suppressed by adding an absorbing layer, making them promising for high-performance absorbers. In practice, such metamaterials consist of periodic arrays of discrete cells incorporating structures like porous layers, space-coiling geometries, or locally resonant elements, each designed to produce a targeted phase response. Recent studies aim to combine strong absorption with high sound transmission loss, requiring control over both reflection and transmission phase gradients. However, achieving these profiles often leads to bulky and impractical designs. This study proposes a metamaterial based on high tortuous perforated foam considered normally for outdoor use, resembling a double-porosity material. Its tunable perforation parameters, along with excellent low-frequency absorption, make it a strong candidate for generating the required phase gradients within a subwavelength structure. The paper outlines the full design process, from initial phase-control analysis demonstrating sufficient flexibility through perforation tuning to the optimization of the metamaterial. This includes selecting suitable foam properties and geometries to obtain a thin structure with high absorption and transmission loss. A sensitivity analysis is also performed to evaluate the impact of variations in phase and amplitude due to discrepancies between theoretical and actual material properties.