2/12/2024 0 Comments Sound diffraction around a barrier![]() ![]() ![]() Here a negative angle indicates that the reflected ray propagates downward (i.e., toward the ground). A simple consequence of such a gradient surface is that if sound impinges normally onto the surface, the reflected angle will be −30°. Figure 1(b) shows the relation of the incident and the reflected angles for an inhomogeneous surface with a negative gradient β = −1/2 (solid curve), while that for specular reflection is given by the dotted curve for comparison. Therefore, d ϕ / d y represents the phase shift gradient along the surfaces, and β is regarded as the gradient index of the surface. Where k 0 is the wave number of sound in air, θ i and θ r denote the angles of incidence and reflection, respectively, and is the phase shift due to sound reflection at the barrier surface, which varies with the position y along the surface. Such barriers are called sound dredging barriers (SDBs). Here, instead of trapping the sound energy, the designed barriers work by “dredging” the energy flux outward in an engineered direction deviated enough from the noise sensitive region. 6 In this paper, a distinct solution is proposed in a contrary way. ![]() Immediately, a theoretical model combining the wave diffraction theory 4 and ray-tracing method 5 has been proposed to predict the performance of these sound trapping barriers (STBs). Consequently, less energy can “escape” and hence a better noise shielding effect can be expected in the surroundings. Such barriers work by trapping sound energy in between the opposite barrier walls. In the previous work, 3 an alternative solution-barriers having negative-phase-gradient surfaces-has been proposed. 2 In practice, however, using existing absorptive materials leads not only to impractically thick barriers for low frequency absorption, but also causes environmental problems such as the accumulation of dust and bacteria, as well as the irritation of a human respiration system due to fibers from porous materials. One way to eliminate such a degradation is applying absorption layers. 1,2 This deterioration in performance is caused by multiple reflections between the inner walls of the parallel barriers. However, it is found that the noise shielding effect of a single barrier is significantly reduced when another barrier is built on the other side of the source. Behind the barrier lies a shadow zone in which the acoustic field is dominated by diffracted sound, while the direct sound is negligible. A sound barrier is usually constructed to provide protection against noise. ![]()
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