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.
European Physical SocietyCastiñeira Ibáñez, S.; Romero García, V.; Sánchez Pérez, JV.; García-Raffi, LM. (2010 Abstract. -Acoustic Band Gap materials are suitable materials to construct devices for controlling the propagation of sonic waves by means of the multiple scattering phenomenon. One of their applications is the control of outdoor noise, acting as acoustic filters. Thus, a great effort to increase the non-transmission properties has been done. To do that, a design of acoustic scatterers with added acoustic properties, as absorption or resonance behaviour, has been developed. But to obtain a high acoustical performance in the control of noise, it seems necessary to improve to the maximum level the different involved mechanisms. In this work we present a new arrangement of scatterers based on fractal geometries to increase the multiple scattering phenomenon.
The focusing capabilities of a pinhole zone plate lens are presented and compared with those of a conventional Fresnel zone plate lens. The focusing properties are examined both experimentally and numerically. The results confirm that a pinhole zone plate lens can be an alternative to a Fresnel lens. A smooth filtering effect is created in pinhole zone plate lenses, giving rise to a reduction of the side lobes around the principal focus associated with the conventional Fresnel zone plate lens. The manufacturing technique of the pinhole zone plate lens allows the designing and constructing of lenses for different focal lengths quickly and economically and without the need to drill new plates.
The focusing properties of Fresnel Zone Plates (FZPs) against frequency are analyzed in this work. It is shown that the FZP focal length depends almost linearly on the operating frequency. Focal depth and focal distortion are also considered, establishing a limit on the frequency span at which the operating frequency can be shifted. An underwater FZP ultrasound focusing system is demonstrated, and experimental results agree with the theoretical analysis and simulations.
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