Resonant coupling of Rayleigh waves through a narrow fluid channel causing extraordinary low acoustic transmission
(Color online) Experimental setup showing the geometrical parameters of the aperture (d) and length (h) of the slit.
(Color online) Transmission spectra obtained for several apertures of the slit separating two water-immersed unidentical (brass and aluminum) metal plates for a channel length mm. The maxima in the transmission are Fabry–Perot resonances. The minima are the frequencies where extraordinary absorption of sound occurs, corresponding to the frequencies of resonant excitation of coupled Rayleigh waves. Two resonances with and fall within the shown range of sound frequencies.
(Color online) Plots of the functions and [see Eq. (13) vs dimensionless parameter ]. Normalized phase velocity for uncoupled Rayleigh wave in the absence of fluid in the channel () for brass (aluminum) is given by the root of the dispersion equation . The roots obtained from the graph are and , respectively. The phase velocity of uncoupled Rayleigh wave for brass is km/s ( km/s) and for aluminum is km/s ( km/s).
(Color online) A typical plot showing the roots of the dispersion equations for slow and fast modes for , channel length mm, and aperture mm. are related to the slow and fast modes. Theplot is obtained for a metal combination of brass ( km/s, km/s, ) and aluminum ( km/s, km/s, ). The compressional velocity of sound in fluid (water) in the channel is taken as km/s.
(Color online) Dimensionless parameter plotted as a function of the aspect ratio for slow and fast modes at different resonances (a) and (b).
(Color online) Frequency versus aperture of the water channel for slow (solid line) and fast (dashed line) modes obtained using Eq. (15). While the slow mode does not have a critical minimum aperture, the fast mode has a critical minimum aperture at mm. For the case of a water channel clad between identical metal plates, the fast and slow modes become symmetric and antisymmetric modes, respectively, see Ref. 17.
(Color online) Measured resonant frequencies of the minima of transmission at different apertures of the water channel. It is clear from the above figure that the fast mode has a critical minimum aperture at around mm. On the contrary, the slow mode does not have a critical minimum aperture.
(Color online) Numerical (comsol) simulations for the longitudinal (, ) (a) and transverse (, ) (b) displacements of the both metal plates induced by propagating plane wave with kHz in water channel with mm and mm. This frequency corresponds to the first minimum in the transmission spectra in Fig. 2. The ratios of longitudinal to transverse displacements plotted using comsol and the theory are in a good agreement.
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