Acoustic barriers which are positioned along traffic lanes are designed to protect the surroundings from excessive noise. Such structures are to reverberate, diffract and damp the propagating acoustic waves. However, this method of shielding has some disadvantages which include constraint visibility and structure-born noise. The interaction between traffic-caused movement of air mass and acoustic barriers may generate infra noise waves. That is undesirable and should be estimated. The authors undertook the research to diagnose the plausible side effect of structure-born noise of such barriers because it may influence human body (Kasprzak, 2014). As a mechanical structure, the acoustic barrier is characterized by mechanical parameters which, in the field of modal analysis, are made up of natural frequencies, damping factors and mode shapes. In this paper the authors investigated the acoustic pressure distribution in the neighborhood of a real acoustic barrier in the scope of infra noise propagation. The methods of modal analysis were used to identify natural frequencies of the barrier and dominating frequencies of propagating waves in the far field. The correlation between observed vibration and acoustic signals is presented.

In this work we present the design and the manufacturing processes, as well as the acoustics standardization tests, of an acoustic barrier formed by a set of multi-phenomena cylindrical scatterers. Periodic arrangements of acoustic scatterers embedded in a fluid medium with different physical properties are usually called Sonic Crystals. The multiple scattering of waves inside these structures leads to attenuation bands related to the periodicity of the structure by means of Bragg scattering. In order to design the acoustic barrier, two strategies have been used: First, the arrangement of scatterers is based on fractal geometries to maximize the Bragg scattering; second, multi-phenomena scatterers with several noise control mechanisms, as resonances or absorption, are designed and used to construct the periodic array. The acoustic barrier reported in this work provides a high technological solution in the field of noise control.