The influence of thermo-hygrometric conditions on metamaterials' acoustic performance: an investigation on a 3D printed coiled-up resonator

Abstract

In the last decades, coiled-up resonators have become popular within the metamaterial research community for narrow band, low frequency resonances combined to subwavelength thickness. Such structures are particularly suited to one of the most widespread manufacturing processes, i.e. PET-based 3D printing. Acoustic performance of coiled-up resonators depends on the geometrical parameters' variation, which is influenced by thermo-hygrometric conditions; however, the deformation itself needs to be further investigated. For this reason, the present paper evaluates the correlation between temperature, relative humidity, and the geometrical parameters' (spiral length and hole diameter) deformations and, consequently, the acoustic performance of a 3D printed coiled-up resonator. A combined approach through analytical, numerical, and experimental measurements quantified the frequency shift of the resonance peaks (within 300 Hz - 5000 Hz) in terms of sound absorption coefficient increasing the temperature (T=10-50° C), and the relative humidity (RH=20-80 %) of the samples. Relative humidity variations turned neglectable discrepancies on sound absorption's peaks. On the other hand, the increase in temperature caused a frequency peaks' shift following an exponential trend: this behavior is straight related to the exponential relationship between the temperature and specific volume function of polyethylene resins.