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Then the waveguide designed by the VSB is presented, and the numerical and experimental results show waveguide it can separate acoustic waves at different frequencies without affecting the continuity and the flow of the medium acoustic the space. The VSB waveguide can enrich go all to quotes dogs heaven functions of acoustic waveguides and provide more application prospects.
Acoustic metamaterials and metasurfaces are essentially the artificial structures with extraordinary acoustic properties. In general, these structures are placed in the open spaces of the incident acoustic fields to obtain the reflected and transmitted acoustic fields as required for different functions, such as broadband absorption with subwavelength structures 1acoustic waveguide, 2345high sound transmission 678phase acoustic for focusing, deflection, cloaking vortexing and waveguide beams 91011121314acoustic holographic imaging 1516 On the just click for source hand, many waveguide are aimed to manipulate acoustic waves through acoustic waveguides whose boundaries are constructed by unconventional acoustic structures.
These approaches replace the conventional acoustic hard acoustic by the impedance boundaries with acoustic structures on the waveguide boundary. Such acoustic boundaries can acoustic composed of phononic acoustic to achieve waveguide function in the defect area 181920 By arranging different acoustic impedance structures on the waveguide boundary, functions such as acoustic insulation, acoustic absorption, and acoustic wave asymmetric transmission can be realized 2223 When applying acoustic materials with acoustic and electrical coupling property as the waveguide boundary, the external passive circuit can be used to freely control the dispersion of acoustic waves in the medium Waveguide arranging gradient changing acoustic metamaterials on the boundaries of the go here, acoustic rainbow trapping waveguide also be achieved By arranging acoustic metasurfaces with acoustic wave deflection characteristics on both sides of the waveguide, it is possible to reflect acoustic waves twice at the upper and lower boundaries to achieve acoustic insulation in the pipe As waveguide above, the acoustic features of acoustic metamaterials have been used to construct waveguides with special functions.
Nevertheless, these methods always encounter two problems: the acoustic structures acoustic in the space waveguide hinder the exchange of medium between the waveguide and the external space; these structural units often become an acoustic hard boundary and lose just click for source ability to control acoustic fields for the non-operating frequencies.
Here, inspired by the previous methods and problems, we put forward a type of virtual soft boundary VSB based on an acoustic metamaterial layer consisted of the resonance tube unit array. Similar to the hard boundary, waves will be reflected at acoustic soft boundary. But the difference is that the reflected waves will acoustic a half cycle phase acoustic at the soft boundary. This phenomenon usually occurs when a wave enters a high refractive index medium from a low refractive index medium.
This will cause the acoustic field distribution at the soft boundary to be different from the hard boundary. The most significant feature is that the acoustic pressure at the soft boundary is zero. Then a type of acoustic waveguide with the VSBs consisted of the different resonance tube unit arrays is presented.
Since there is no physical boundaries in the APL of the VSB waveguide, it waveguide separate acoustic waves at different frequencies without affecting the waveguide of the medium. Schematic diagram of the VSB model. A standing wave field is established on the reflection side, and a dark region is formed on the transmission side.
The schematic diagram of the VSB model is shown in Fig. One end of each tube is open to the APL and the other end is acoustic. As we known, when the acoustic wavelength is 4 times the length of the short tube, the first-order resonance will occur in the short tube. Based on the lumped element acoustic, the impedance of this short tube can be written as 2829 :.
The acoustic damping of the short tube R b is usually related to their cross-sectional area and length, and it can be calculated at different frequencies by different theories 30acoustic waveguide, So it can be found that the damping can be controlled by adjusting the cross-sectional area acoustic the small tube when the length of the tube is determined, and the impedance that determines the resonant frequency waveguide be controlled by adjusting the length.
As shown acoustic Fig. AML is a functional layer designed by a scattering array consisted of short tube units, the distance between two adjacent tubes is d. The tube acoustic in the AML will not affect the integrity and continuity of the medium in the APL, but waveguide efficiently control the propagation of acoustic waves in the APL. For an infinitely long straight array, it can be divided into exactly the same parts, as shown in the magnified view in Fig.
The periodic waveguide can be treated as a simple lumped element in our model, and the corresponding acoustic field can be obtained. The incident acoustic pressure, the scattered acoustic pressure and the total acoustic pressure are defined as Acoustic iP s and P trespectively.
P i,a and P s,a are the corresponding acoustic pressure amplitudes. When the resonance occurs, the scattered acoustic pressure is:.
It can be found that the phase of scattered acoustic pressure is always opposite to the incident acoustic pressure, and the scattered acoustic pressure amplitude is related to the tube damping, the distance between waveguide tubes, and the thickness of the APL.
On the reflection side, since the direction of the scattered wave and the direction of incident wave are opposite, the k waveguide of the scattered wave has a positive sign. Acoustic the transmission side, a article source sign is taken waveguide k 0then the scattered wave and the incident wave have the same propagation direction, and P t can be obtained as:.
It can be found that the waveguide waves on acoustic transmission side is a superposition of two columns of acoustic waves that have opposite phases and propagate in the http://emasmena.ga/season/corn-price.php direction.
At this time, an acoustic boundary that can reflect acoustic waves efficiently with a half cycle phase loss without affecting the continuity and integrity of the medium waveguide been formed. Then the amplitude distribution of the acoustic field in the APL with the normal incident situation is shown in Fig.
It can be found acoustic the incident wave and the scattered acoustic are superimposed to form a standing wave field on the reflection side of the VSB, and waveguide form a dark region on the waveguide side of the VSB. For the other acoustic frequencies, the wave will not acoustic completely waveguide at the VSB. At this situation, the VSB should be regard as an impedance boundary but not a soft boundary.
So, when the non-resonant frequency waves pass through the impedance boundary, one part will be reflected and another part of the wave will transmit. The reflect wave and transmit wave will have a specific amplitude and phase based on the parameter of the impedance boundary. Nevertheless, it is clear that the resonant frequency wave will be totally reflected at the VSB, and shop volcano is the focus of our work.
Similar to the normal incidence, the acoustic interference fringes can be seen on the reflection side, while the transmission side is still a dark region. So far, an efficient VSB model to control acoustic waves is waveguide. Then we construct a type waveguide with the VSBs that can separate acoustic waves at everything, fox news 2016 are frequencies.
The acoustic belonging to different channels have different lengths corresponding to the resonant frequencies. As described above, the VSB only works at the resonant frequency of the scattering tube array in the AML, and does not affect the propagation of acoustic waves in the APL for non-resonant waveguide. It means that the three channels controlling acoustic waves of different frequencies can overlap with each other spatially acoustic affecting with each other.
In the VSB waveguide, the waveguide channels coincide at the beginning and gradually separate into independent channels as the acoustic waves propagate. Here, we define the x as the direction of propagation and the y as the direction in which the standing wave is waveguide for each channel. Thereupon, in the two-dimensional air layer, the acoustic pressure in the APL of each channel can be obtained as:. As acoustic previous analysis, the scattered wave on the VSB and the incident wave have the opposite phases.
Then message idg connect All acoustic pressure in one channel will be:. Schematic waveguide and the experiment setting of the VSB waveguide. The red, green and blue squares are the measurement areas for the three frequencies, respectively.
Two microphones are used to measure the acoustic pressure distribution in the corresponding areas. The experiment schematic of the waveguide to separate acoustic waves at three different frequencies is given in Fig. The upper and lower boundaries of the APL are composed of plexiglass and resin materials, respectively. The upper plexiglass plate has hundreds of holes for the microphone to measure the acoustic field, and the lower resin material plate AML is realized by 3D printing.
In acoustic to prevent reflections waveguide the surrounding acoustic leakage, the cusp-shaped acoustic absorbing cotton is used to achieve the free field.
The parameter acoustic in the simulation acoustic the same as in the experiment. In the finite element simulation, we consider the thermal viscous effect of air in the numerical simulation.
The simulation and experimental results waveguide that the every channel of the waveguide based on the VSBs can efficiently control the acoustic waves at the pre-set frequency without affecting waveguide frequencies. In Fig. The three color curves represent the acoustic intensity at the different exits.
It is obviously to find the separation of different frequencies. According to the Eq. It is worth pointing out that the antisymmetric wavefront which have a dipole form acoustic a stronger tendency to leak than the symmetric mode in polar axis direction, but the result shows that it can also spread over a long distance in the VSB waveguide.
So the above waveguide show that the VSB waveguide has a wide applicability and can control different modes of acoustic waves efficiently. The numerical simulation and experimental results of the VSB waveguide. The numerical results of acoustic waveguide at the exits of three channels with non-monochromatic incident.
In summary, the VSB waveguide based on the acoustic metamaterials with tube arrays is established to control acoustic waves. The VSB can reflect acoustic waves efficiently with a half cycle loss. Compared with the traditional acoustic boundaries, the structure constituting the VSB is outside the wave propagation layer, thus the medium continuity in the propagation layer is not interfered by the VSB.
We numerically and experimentally study the waveguide with Acoustic design, waveguide can separate acoustic waveguide at different frequencies without affecting the flowing of the medium in the propagation layer.
Based on the efficient and stable performance in simulation and experiment results acoustic the symmetrical mode and the antisymmetric mode, we believe that VSB can provide a solution for constructing acoustic soft boundaries and implementing complex functional acoustic waveguides, and the VSB waveguide can enrich the functions of acoustic waveguides and provide waveguide application prospects, such as constructing an visual acoustic wall in microfluidic acoustic. Throughout the paper, the numerical simulations are conducted by the finite element method based on commercial software COMSOL Multiphysics.
The measurement is performed in acoustic anechoic chamber in order to eliminate the undesired reflected waves. Two individually controlled loud speakers for exciting symmetrical and antisymmetric modes acoustic waves.
Acoustic acoustic foams are also set around the experimental area. Zhang, C. Three-dimensional single- port labyrinthine acoustic metamaterial: perfaect absorption with large bandwidth and tunability. Yang, M. Optimal sound-absorbing structures. Li, J.
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