The metascreen-based acoustic passive phased array provides anew degree of freedom formanipu-latingacoustic waves due to their fascinating properties, such as afully shifting phase, keeping impedance matching, and holding subwavelength spatial resolution. We develop acoustic theories to analyze the transmission/reflection spectra and the refracted pressure fields of a metascreen composed of elements with four Helmholtz resonators (HRs) in series and a straight pipe. We find that these propertiesare also valid under oblique incidence with large angles, with the underlying physics stemming from the hybrid resonances between the HRs and the straight pipe. By imposing thedesired phase profiles, the refracted fields can be tailored in ananomalous yet controllable manner. In particular, two typesof negative refractionare exhibited,based on two distinct mechanisms: one is formed fromclassical diffraction theory and the other is dominated by the periodicity of the metascreen. Positive (normal) and negative refractions can be converted by simply changing the incident angle, with the coexistence of two typesof refractionin a certain range of incident angles. 1 2 . The symbols p i , p r , and p t represent the obliquely incident, reflected and transmitted sound waves, respectively. (b) A single HR is illustrated for the purpose of the corrected acoustic impedance of the cavity. (c) A single HR is located in front of a hard boundary (dashed line) to obtain the corrected acoustic radiation impedance at the junction between the neck and the straight pipe.New J. Phys. 18 (2016) 043024 Y Li et al

International audienceWe report theoretically and numerically on the sound transmission loss performance through a thick plate-type acoustic metamaterial made of spring-mass resonators attached to the surface of a homogeneous elastic plate. Two general analytical approaches based on plane wave expansion were developed to calculate both the sound transmission loss through the metamaterial plate (thick and thin) and its band structure. The first one can be applied to thick plate systems to study the sound transmission for any normal or oblique incident sound pressure. The second approach gives the metamaterial dispersion behavior to describe the vibrational motions of the plate, which helps to understand the physics behind sound radiation through air by the structure. Computed results show that high sound transmission loss up to 72 dB at 2 kHz is reached with a thick metamaterial plate while only 23 dB can be obtained for a simple homogeneous plate with the same thickness. Such plate-type acoustic metamaterial can be a very effective solution for high performance sound insulation and structural vibration shielding in the very low-frequency range