To explore the simple low-loss operation of directional acoustic transmission technology, the propagation of acoustic waves in resonant phononic crystals was studied, and a transmission model based on acoustic metamaterials was constructed. Using the local resonance characteristics between acoustic waves and original cells, the multi-directional transmission of acoustic waves was modeled in the COMSOL software. It was found that acoustic waves generated by a point source are refocused into another point source after passing through the transmission model, and that the transmission loss is small. Under the control of this model, the effect of point-source propagation in various directions was achieved. The acoustic field characteristics of the model samples were also tested to verify the feasibility of the model structure, providing a new direction for applications such as underwater acoustic communication and detection.

To realize the multi-functional manipulation of the acoustic field with a simple artificial structure, a waveguide array based on resonant units was proposed in this work. Based on the transmission spectrum and zero-like refractive index of the waveguide unit, the amplitude of the transmitted wave can be manipulated. By changing the size of the waveguide unit flexibly, the phase of the transmitted wave can be manipulated. In addition, by extending the waveguide array to the sub-wavelength scale, an acoustic metasurface with both amplitude and phase modulation functions can be implemented, which provides new ways for the design of lightweight artificial periodic structures.

To achieve high-efficiency and high-resolution acoustic focusing, we used artificial periodic acoustic structures composed of cell arrays to manipulate the acoustic transmission wave front, and used finite element software to simulate the acoustic field characteristics. We found that when focuses generated by arc-shaped acoustic excitation sources are incident on one side of the model, the energy will be localized within the structure to reduce its transmission loss, and then the high-resolution emission focus will be generated on the other side of the model. The magnitude of the acoustic pressure at the focus point will change with the frequency of the incident acoustic wave and will reach an extreme value at the resonant frequency. In addition, we explored the acoustic transmission characteristics of structures at different widths and found that it is only necessary to increase the width of the model by an integer multiple of half a wavelength to achieve low loss focusing effects at various distances. The acoustic phenomena studied in this paper may provide new methods for the application of photoacoustic signal detection, ultrasound medical imaging and ultrasonic nondestructive testing.

Conventional acoustic systems exhibit a difficulty in sensing weak acoustic fault signals in complex mechanical vibration environments. Therefore, it is necessary to develop an acoustic sensing mode and a corresponding functional device with pressure amplification. This paper proposes a three-dimensional device, coupling gradient acoustic metamaterials (GAM) with phononic crystals (GAM–PC). The strong wave compression effect coupled with the phononic crystal equivalent medium mechanism is utilized to achieve the enhancement of weak acoustic signal perception at the target frequency. The superior amplification capability of the GAM–PC structure for the amplitude of loud signals is verified by numerical simulations and experiments. Moreover, the GAM–PC structure has a narrower bandwidth per slit, making it more frequency selective. Furthermore, the structure can separate different frequency components. This work is expected to be applied to signal monitoring in environments with strong noise.

To overcome the negative impact of diffraction effect on the transmission wave front at the bend and to improve the transmission efficiency of acoustic wave in the bend waveguide, the finite element method by COMSOL was used to simulate the propagation characteristics of acoustic wave in the structure of bending acoustic waveguide, based on local resonance acoustic metamaterials. Specifically, the vibration mechanism of three-dimensional (3D) component locally resonant phononic crystals was presented, and the acoustic metamaterial models of M-shaped, L-shaped and S-shaped bent waveguides were constructed on the basis of the protocells. The local resonance between the acoustic wave and the protocells in the waveguide model was investigated, in order to produce the nondestructive bending propagation effect of the acoustic wave. The results of finite element analysis show that the plane acoustic waves incident from the M-shaped, L-shaped and S-shaped bending waveguide model will propagate directionally along the model structure after being controlled at the resonance frequency. These results confirm the flexibility and feasibility of the bending acoustic waveguide model designed by the local resonance acoustic metamaterials. In addition, the acoustic waveguide model in long-distance special environment was designed and the low loss transmission of acoustic signal was implemented. This study provides a new solution for engineering applications, such as ultrasonic signal detection and underwater acoustic communication transmission.

Acoustic sensing systems play a critical role in identifying and determining weak sound sources in various fields. In many fault warning and environmental monitoring processes, sound-based sensing techniques are highly valued for their information-rich and non-contact advantages. However, noise signals from the environment reduce the signal-to-noise ratio (SNR) of conventional acoustic sensing systems. Therefore, we proposed novel nonlinear gradient-coiling metamaterials (NGCMs) to sense weak effective signals from complex environments using the strong wave compression effect coupled with the equivalent medium mechanism. Theoretical derivations and finite element simulations of NGCMs were executed to verify the properties of the designed metamaterials. Compared with nonlinear gradient acoustic metamaterials (Nonlinear-GAMs) without coiling structures, NGCMs exhibit far superior performance in terms of acoustic enhancement, and the structures capture lower frequencies and possess a wider angle acoustic response. Additionally, experiments were constructed and conducted using set Gaussian pulse and harmonic acoustic signals as emission sources to simulate real application scenarios. It is unanimously shown that NGCMs have unique advantages and broad application prospects in the application of weak acoustic signal sensing, enhancement and localization.