An acoustic diode (AD) is proposed and designed based on a mechanism different from the previous designs by using two structured impedance-matched acoustic metasurfaces. This AD can realize unidirectional acoustic transmission within a broad band with high transmission efficiency due to the impedance-matching condition while allowing other entities such as objects or fluids to pass freely. What is more, the backtracking waves that come from the incoming waves can be efficiently prevented and cannot disturb the source. The acoustic pressure field distribution, intensity distribution, and transmission efficiency are calculated by using the finite element method. The simulation results agree well with the theoretical predictions. Our proposed mechanism can experimentally provide a simple approach to design an AD and have potential applications in various fields such as medical ultrasound and noise insulation.
In this paper, the tuning characteristics of band gaps and waveguides in a locally resonant phononic crystal structure, consisting of multiple square stubs deposited on a thin homogeneous plate, are investigated. Using the finite element method and supercell technique, the dispersion relationships and power transmission spectra of those structures are calculated. In contrast to a system of one square stub, systems of multiple square stubs show wide band gaps at lower frequencies and an increased quantity of band gaps at higher frequencies. The vibration modes of the band gap edges are analyzed to clarify the mechanism of the generation of the lowest band gap. Additionally, the influence of the stubs arrangement on the band gaps in multi-stub systems is investigated. The arrangements of the stubs were found to influence the band gaps; this is critical to understand for practical applications. Based on this finding, a novel method to form defect scatterers by changing the arrangement of square stubs in a multi-stub perfect phononic crystal plate was developed. Defect bands can be induced by creating defects inside the original complete band gaps. The frequency can then be tuned by changing the defect scatterers’ stub arrangement. These results will help in fabricating devices such as acoustic filters and waveguides whose band frequency can be modulated.
In this letter, we propose a theoretical description of double nonuniform cross-section (DNUCS) channels, which can achieve the designed absorption coefficient with a shorter channel overall. Introducing channels with a nonuniform cross section changes the period of the surface acoustic impedance, which has a significant impact on the dominant operating frequencies. In this paper, we give the relation between the absorption peak position and the geometric parameters, which can be used to design DNUCS channels with a specific operating frequency. Furthermore, multiple nonuniform cross-section channels can be studied in the same way. Based on the above theory, we reduce the operating absorption frequency range of a new type of Fabry–Pérot absorbers to a lower regime in a constant volume. Our theoretical framework may be important in designing absorption metasurfaces and for further research.
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