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Acoustic intensity distributions of Airy-like beams generated by the CAMs with the tilted angles of (a) À5 , (b) 5 , and (c) 10 at frequencies of 6, 7, 8, and 9 kHz.
Source publication
We propose a coded acoustic metasurface (CAM) to generate Airy-like beams (ALBs) in air. A space-folding structure is designed to act as the bit “1” unit of the CAM, and an air unit with the same size is used as the bit “0”. Finite-element simulations demonstrate that the ALBs generated by this simple CAM have excellent self-accelerating, self-heal...
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Citations
... As an important non-diffraction beam, the Airy-like beam has the interesting features of self-acceleration, self-healing and shapepreserving accelerating. Thus, it has promising applications in particle manipulation, medical ultrasound, ultrasonic imaging, and super-resolution focusing [48][49][50][51][52][53]. To generate an acoustic Airy-like beam, a planar acoustic source function can be described as ...
A customized transmission-type metasurface design is developed for high-efficiency wavefront modulation by employing a level set-based topology optimization approach. The metasurface consists of periodically arranged supercells made of discrete unit cells aiming to form a precisely linear phase gradient of the transmitted wave ranging from 0 to $2\pi$ with high transmittances. The configuration of each unit is optimized to generate a desired phase and amplitude response of the transmitted wave at the interface. The transmitted wavefront steering realized by the phase-gradient metasurface is numerically and experimentally verified according to the diffraction theory, demonstrating that the level set-based topology optimization approach is a viable and effective technique for developing a transmitted phase-gradient metasurface. Afterwards, the designed optimal unit cells are elaborately arranged to form desired phase shift distributions for realizing fascinating acoustic functionalities, including acoustic energy focusing and acoustic Airy-like beam generation, further demonstrating the ability of the optimal units to achieve unprecedented transmitted wavefront control. This study presents a promising approach for customized transmission-type metasurface design based on the level set-based topology optimization, which is expected to be significantly valuable for acoustic device development.
... Such unusual yet spectacular bent routes for waves have particularly capitalized on the use of metamaterials and metasurfaces, which enable the necessary phase and amplitude textures for the desired outcome [39][40][41] . ...
Self-imaging phenomena for nonperiodic waves along a parabolic trajectory encompass both the Talbot effect and the accelerating Airy beams. Beyond the ability to guide waves along a bent trajectory, the self-imaging component offers invaluable advantages to lensless imaging comprising periodic repetition of planar field distributions. In order to circumvent thermoviscous and diffraction effects, we structure subwavelength resonators in an acoustically impenetrable surface supporting spoof surface acoustic waves (SSAWs) to provide highly confined Airy-Talbot effect, extending Talbot distances along the propagation path and compressing subwavelength lobes in the perpendicular direction. From a linear array of loudspeakers, we judiciously control the amplitude and phase of the SSAWs above the structured surface and quantitatively evaluate the self-healing performance of the Airy-Talbot effect by demonstrating how the distinctive scattering patterns remain largely unaffected against superwavelength obstacles. Furthermore, we introduce a new mechanism utilizing subwavelength Airy beam as a coding/decoding degree of freedom for acoustic communication with high information density comprising robust transport of encoded signals.
... In general, we consider a metasurface consisting of only two kinds of units with opposite phases 0 and π as a 1-bit coding metasurface, one containing four phase configurations 0, π/2, π, 3π/2 as a 2-bit coding metasurface, and so on. By arranging these units according to a certain coding sequence based on Huygens-Fresnel principle [37], wavefront modulation of acoustic waves can be achieved, such as beam splitting [38][39][40], acoustic focusing [41][42][43], airy beams [44][45][46], acoustic diffuser [47][48][49], etc. ...
... Metasurface is an expansion of the metamaterial, with well-designed units in subwavelength scale to control the reflection, transmission, and direction of an acoustic wave, for example, the ultrathin Schroeder diffuser, 9 subwavelength acoustic absorber, [10][11][12][13] acoustic metalens, [14][15][16] and coding metasurface. [17][18][19][20][21][22] Among them, the appliance of gain-loss acoustic metamaterials has been a new approach to manipulate the wave; the elaborately modulated balanced gain-loss acoustic materials are a research focus of parity-time (PT) symmetric acoustics. 23 Although the concept of PT-symmetry was originally introduced from quantum mechanics, 24 several interesting physical properties have been deeply studied in PT-symmetric acoustics. ...
The realization of multifunction by simply combining acoustic devices together is always attractive, but it is never an easy task due to the complexity of most acoustic metamaterials. In this paper, a kind of unbalanced gain–loss acoustic metasurface is designed, which can work as an energy amplifier, suggesting that it may be applied to an acoustic signal detector or a sensor. In addition, an acoustic negative refraction system is established by simply putting two of these metasurfaces together, which can produce negative refraction for the acoustic waves from different directions and different incident angles, even focusing and imaging with precisely selected parameters. These functions are quite rare for materials without the double-negative-parameter. This work provides a new route to use the gain/loss materials and achieve multifunctions without complex design.
... [1] During the past decade, acoustic meta-surface (AMS) has been proposed and realized successfully, providing us a new path in acoustic device design [2]. Many peculiar phenomena like negative refraction [3][4][5], acoustic planar focusing [6,7], and acoustic one-way device [8,9] have been observed by carefully designing and arranging the sub-units of the metasurface. The loss of the sub-units is considered as an adverse factor for phase gradient metasurface, while the nearly perfect sound absorption can be achieved by adjusting the inherent loss appropriately in the further studies [10,11]. ...
Low-frequency sound-absorbing meta-surface is an eye-catching topic in scientific and engineering community. Numerous studies of low-frequency sound-absorbing meta-surface have been explored. However, an acoustic meta-surface with simultaneous low-frequency sound absorption and reversible shape changing property remains absent up till now. In this paper, we propose an acoustic meta-surface by coupling 15 sub-units to realize a desired low-frequency sound absorption. The measured energy attenuation of acoustic meta-surface is average up to 90% from 300 to 1000 Hz, well agreed with stimulated results. The sound absorption band of the designed structure can be customized through flexibly adjusting the sub-units. More surprisingly, the proposed acoustic meta-surface is capable of withstanding large loads and possesses a reversible shape changing property. The unique low-frequency sound absorption and the mechanical properties open interesting perspectives for the use of acoustic meta-surface in low-frequency noise control applications.
... For example, sub-diffraction focusing and enhanced far-field focusing greatly improve the efficiency of energy concentration. 10,14,15 Furthermore, focusing with advanced features, such as sharp focusing, [16][17][18][19][20][21] needle focusing, 22,23 and long depth-of-focus, 13,24 has been demonstrated. With the advanced acoustic holographic technology, more sophisticated patterns have also been shown. ...
A single acoustic metamaterial with multifunctional use is highly needed for various applications. Herein, a bifunctional acoustic metamaterial for beam switching between the focusing beam and bottle beam is demonstrated, which consists of a groove structure for binary phases and a partitioned piezoelectric transducer (p-PZT) for incident wavefront modulation. The p-PZT is divided into inner and outer regions for selective excitation, and the focusing beam and bottle beam can be switched in real-time by applying different exciting signals on the p-PZT. Theoretical calculation, numerical simulation, and experimental measurement are conducted to verify the effectiveness of the proposed bifunctional acoustic metamaterial for beam switching. Furthermore, the focal plane of both the focusing beam and bottle beam can be linearly tuned by the operating frequency. This work may find potential applications in medical ultrasonic therapy, sound printing, and biological particle manipulation.
... Furthermore, Tian et al. [158] designed and fabricated programmable acoustic metasurfaces to generate various types of acoustic beams based on an array of tunable subwavelength unit cells by pumping in (or out) water to the cavities of the resonators (Fig. 9(e)). Other coding acoustic metasurfaces based on resonator [163], space-folding structure [164,165], and helical structure with three spiral channel [166] have been developed for acoustic lens design. ...
... Additionally, by taking advantage of the acoustic gradient metasurface, ultrathin and easily integrated metalens can be realized as well. [15][16][17][18][19][20][21][22][23][24][25][26][27] However, as a major issue hindering the development and application of metalens, the wavelength-dependent response inevitably brings chromatic aberration, which affects the imaging quality of acoustic imaging systems. Zhu et al. 28) have achieved dispersionless wavefront modulation via reflected metasurfaces, while the thickness of the device was on the order of wavelength. ...
By utilizing array of cascaded Helmholtz resonators with high transmittance and linear phase response, a broadband achromatic acoustic lens (AAL) is realized and verified in numerical simulations as well as experimental measurements. The focal length is independent of the incident frequencies from 2000 to 4500 Hz owing to the phase compensation provided by Helmholtz resonator (HR) arrays. The FWHM of the focal point could remain approximately half of the wavelength within the operating band, showing an excellent performance of the lens. This work enriches the design of AAL, which may have potential applications in biomedical imaging and acoustic detection.
... [10][11][12][13] Various fascinating acoustic phenomena, for instance, negative refraction/reflection, zero refraction, and perfect absorption, have been realized by utilizing coiling-up cavities, helical resonators, and labyrinth configurations. [14][15][16][17][18][19][20][21][22][23][24][25][26] Note that the manipulation of transmitted acoustic wavefront needs a precondition of impedance matching; otherwise, the transmission efficiency will be low. The generation of hybrid resonance is an effective way to modulate the transmitted wavefront under a high transmittance, but the working band is limited by the resonance frequency. ...
In this work, a Helmholtz resonator (HR) with a subwavelength scale is proposed to modulate the acoustic wavefront in multiple manners. The phase response of the reflection wave can be continuously adjusted by altering the height of the cavity. Several HR arrays with gradient phase shifts are constructed to achieve various beam shaping phenomena, including beam deflection and beam focusing. Both the reflection angle and the focal length can be controlled by changing the phase gradients along the structure. Meanwhile, the binary design with only two kinds of HR is utilized to achieve multifunctional acoustic wavefront modulations, which extremely simplify the design philosophy. Moreover, by taking advantage of the resonance mechanism of the HR, an integrated structure composed of two HRs with different cavity volumes is adopted to achieve bifunctional acoustic wavefront modulations, making it convenient to customize the switchable device on demand. Our work offers a solution for multifunctional reflected acoustic wavefront modulations, which may have potential applications in acoustic communication, detection, and holography.
... As a kind of artificial layered structure, the emergency of acoustic metasurface provides an alternative to achieve acoustic field modulation in a passive device. [1][2][3][4][5] Numerous fascinating acoustic phenomena including acoustic focusing, [6][7][8] beam splitting, 9,10) vortex beam 11) and Airy beam 12) have been realized by taking advantage of various well-designed acoustic units with subwavelength scales, such as Helmholtz resonators (HRs), 13,14) coiling-up cavities, 15) and helical particles. 16) Generally speaking, multiple discrete units with different phase responses are needed to meet the requirement of phase profile during the design process, which increases the preparation complexities. ...
In this work, the acoustic coding waveguide array of a bilayer configuration is proposed to realize asymmetric acoustic field modulation. The designed device is composed of two types of meta-atom, Helmholtz resonator and air cavity, with high transmittance and opposite phase responses, through which the plane wave is shaped into focusing beam or splitting beam when input from one side but hardly transmitted when input from the other side. More uniquely, the device can be switched from unidirectional to bidirectional transmission relying on the tunable gap between two composing layers, showing potential applications in acoustic communication, isolation, and stealth.
