Material Optimization and Mechanism Study of a Phononic Crystal Metastructure for Broadband Mid-Low Frequency Sound Insulation

In the mid-low frequency noise range, designing phononic crystals with both broadband characteristics and high sound transmission loss (STL) remains challenging. This paper focuses on studying STL, an indicator with direct application value that is not often emphasized, but of great importance and potential. This study proposes a phononic crystal metastructure (PCM) and verifies its effectiveness through cross-validation of phononic band gaps. This PCM achieves broadband characteristics covering the common 0–3 kHz noise range, with a maximum STL exceeding 120 dB. While exploring the optimal material combination, this paper investigates the relationship between STL and the dimensional variation of PCM. This study uses liquid crystal as the filling material and innovatively proposes an improved equivalent model for in-depth mechanism explanation. The proposed PCM has unique advantages due to its simple structure together with small size and can be used as the main component of sound insulation equipments in promising fields such as mechanical noise reduction and traffic sound insulation.