A study of low frequency sound insulation mechanism of a perforated plate-type acoustic metamaterial

This paper presents a new design of a perforated plate-type acoustic metamaterial (PAM) to evade the influence of membrane pre-tension on the acoustic performance of metamaterials and to enable air ventilation while achieving the designated sound insulation. The study embarks on the analysis of sound insulation mechanism of a typical perforated membrane-type acoustic metamaterial (MAM) from the acoustic context, and discloses that sound transmission loss (STL) peaks of a perforated MAM are due to the strong wave interference between sound sources transmitted through the orifice(s) and the membrane(s). The sound insulation mechanism is explored further in the study by an acoustic impedance analysis of a perforated metamaterial using an electro-acoustic analogy in the latter part of the paper, and the result confirms that the STL peaks of a perforated PAM (or MAM) are indeed the outcome of a strong sound interference. The study also compares an experiment test and a finite element simulation on the sound transmission of a perforated PAM based on the new design. The result confirms that the new perforated PAM can yield a good broadband STL at relatively low frequencies. A practical application using the perforated PAM design is applied to reduce the noise propagation from the compressor compartment of a commercial refrigerator. The test result verifies the effectiveness of the design in terms of both sound reduction and air ventilation.