Plate-type acoustic metamaterials with strip masses

Plate-type acoustic metamaterials (PAM) consist of a thin plate with periodically added masses. Similar to membrane-type acoustic metamaterials, PAM exhibit anti-resonances at low frequencies at which the transmission loss can be much higher than the mass-law without requiring a pretension. Most PAM designs previously investigated in literature require the addition of up to thousands of masses per square meter. This makes manufacturing of such PAM prohibitively expensive for most applications. In this contribution, a much simpler PAM design with strip masses is investigated. An analytical model is derived which can be used to estimate the modal properties, effective mass, and oblique incidence sound transmission loss of PAM with strip masses. For high strip masses (compared to the baseplate), this analytical model can be simplified to yield explicit expressions to directly calculate the resonance and anti-resonance frequencies of such PAM. The analytical model is verified using numerical simulations and laboratory measurement results are presented to demonstrate the performance of PAM with strip masses under diffuse field excitation and finite sample size conditions.