Low-frequency vibroacoustic behavior of thin plate coupled with membrane-type metamaterials for floor impact sound attenuation

This paper investigates the low-frequency vibroacoustic attenuation behavior of a thin plate coupled with membrane-type metamaterials (MTMs), with particular emphasis on their full-scale implementation in a reinforced concrete (RC) floor system. The vibroacoustic performance of the MTM-coupled plate is experimentally evaluated in an actual building through simultaneous measurements of slab flexural vibration and receiving-room sound pressure level (SPL). To provide the physical basis for interpreting the full-scale behavior, the established analytical framework is used to describe the locally resonant bandgap (LRBG) mechanism, while the resonance and effective dynamic mass behaviors of the MTM unit are further examined through numerical analysis and unit-level experiments. The unit-level characterization identifies a low-frequency bandgap of approximately 32.50–70 Hz (approximately 40 Hz bandwidth). In the full-scale RC slab, 100 MTM units, corresponding to a mass ratio of 1.03 %, produce significant vibroacoustic attenuation within this range. The slab flexural vibration was reduced by 24.28 % on average, with a maximum reduction of 63.40 % at its structural mode frequency. For the acoustic response, the energy-averaged receiving-room SPL reductions were 4.59, 2.78, and 1.90 dB in the 40, 50, and 63 Hz 1/6 octave bands, respectively, while a maximum reduction of 23.41 dB was observed at the first slab bending mode frequency. The observed attenuation is concentrated within the identified LRBG, supporting the effective-dynamic-mass-based attenuation mechanism. These results demonstrate the practical applicability of the compact MTM configuration for low-frequency structural vibration and floor impact sound attenuation in full-scale floor systems.