arXiv subjects

Liuxian Zhao

Publications and source records attributed to Liuxian Zhao.

14 recordsLinked to original sources

arXiv2024

Ultra-low Frequency Acoustic Luneburg Lens

In this paper, a novel structural Luneburg lens with local resonators is proposed. This lens allows for the realization of subwavelength focusing in low frequency range. The lens is achieved by graded refractive index from the lens centre to the outer surface. Numerical simulations are conducted to obtain data on wave propagation waveform, maximum displacement amplitude, and full width at half maximum of the lens's focal region. The results show that a broadband frequency range can be achieved for subwavelength focusing. This provides a straightforward and adaptable method for designing the structural Luneburg lens for numerous applications.

physics.app-ph↗

arXiv2024

Elastic wave imaging with Maxwell's fish-eye lens

In this paper, a modified Maxwell's fish-eye lens is proposed in order to achieve super-resolution imaging. This lens possesses elevated refractive index profile compared with the traditional Maxwell's fish-eye lens. The refractive index profile is achieved with variable thickness configuration defined in a sheet plate structure, to realise desired changes in refractive indices. The wave propagation behaviours and the full width at half maximum (FWHM) are obtained from numerical simulations and experimental studies at the focal region of the lens. Super-resolution imaging is observed in a broadband frequency scope, with the FWHM around 0.2λ from 5 to 10 kHz. This work provides a straightforward and flexible approach to the engineering of the MFEL imaging characteristics and energy distributions for related applications.

physics.class-ph↗

arXiv2023

Active Encoding of Flexural Wave with Non-Diffractive Talbot Effect

This study employs the theory of conformal transformation to devise a Mikaelian lens for flexural waves manipulation. We investigate the propagation patterns of flexural waves in the lens under scenarios of plane wave and point source incidence. Additionally, the study explores the Talbot effect generated by interference patterns of multiple sources. Within the Mikaelian lens, the Talbot effect displays non diffractive characteristics, facilitating propagation over considerable distances. Leveraging the non-diffractive attributes of the Talbot effect in the Mikaelian lens, the paper discusses the feasibility of encoding flexural waves based on active interference sources. Simulation and experimental validation attest to the lens's effective active encoding. This research introduces novel perspectives on flexural wave encoding, showcasing potential applications in flexural wave communication, detection, and related fields.

physics.app-ph↗

arXiv2023

Acoustic Metamaterial Beam Splitter

This paper proposes an acoustic beam splitter based on acoustic Luneburg lens. A two-dimensional acoustic Luneburg lens with gradient refractive index is achieved to provide a practical realization for the acoustic beam splitter. The acoustic wave propagation through the beam splitter was explored theoretically, numerically and experimentally. Results show that three output channels can be achieved using a point source on the edge of the beam splitter in a broadband frequency range. Furthermore, the output channel directions can be tuned via changing the design parameter.

physics.app-ph↗

arXiv2022

Structural Lens Based on Variable Thickness Structures

In this article, we report a lens design based on a concentric circular structure with continuous changing of thickness defined in a thin plate structure for focusing a plane wave into three spots (triple focusing) and for splitting elastic waves emanating from a point source into three collimated beams of different directions (three-beam splitting). Inspired by the principle of optical graded index triple focusing lens, the governing equations of the gradient refractive index profiles necessary for achieving such structural lens were obtained. The refractive index profiles were realized by using a lens design with two concentric circular areas of different thickness variation profiles defined in a thin plate. Analytical, numerical, and experimental studies were conducted to investigate the functionalities of the variable thickness structural lens. The results showed that the lens developed in this study were able to perform triple focusing and three-beam splitting with broadband property. Furthermore, the locations of focal points and directions of collimated beams can be engineered by changing the lens thickness profiles according to the governing equations. In addition, the proposed lens is miniature and simple design, which overcome the limitations of previous triple focusing and beam splitters.

physics.app-ph↗

arXiv2022

Acoustic Lenses Design based on the Rays Inserting Method

The ability to control and manipulate elastic waves is important for applications such as structural health monitoring, signal processing, and vibration isolations. In this paper, we investigated the feasibility of using the Rays Inserting Method, an approach originally proposed for optical elements, to design structural components for flexural wave manipulation. The RIM entails a simple process that allows to design thickness variations in a thin plate with a desirable refractive index distribution for an intended wave path. Based on this method, a focusing and collimating lens and a waveguide that rotates the wavefront by 45 degree were designed and studied. Frequency domain simulations and time-based experimental characterizations were carried out. The results demonstrated that the effectiveness of the RIM for designing variable thickness structures for manipulation of flexural wave propagation along desired paths.

physics.app-ph↗

arXiv2022

Ultralong Wave Focusing via Generalized Luneburg Lens

In this paper, a novel gradient index (GRIN) structural lens based on the concept of generalized Luneburg lens (GLL) is proposed. This lens allows for the realization of double foci and localization of energy flow between the two focal spots, thereby achieving ultralong focusing. The double-foci GRIN lens consists of two concentric circular regions with varying thickness defined in a thin plate structure. The two concentric circular regions are designed to realize continuous change of refractive indices with different profiles. Numerical simulations and experimental studies are performed to obtain the maximum displacement amplitude, full length at half maximum (FLHM), and full width at half maximum (FWHM) of the focal region of the lens. The results demonstrate that ultralong subwavelength focusing can be achieved for a broadband frequency range. In addition, our results show that the FLHM and FWHM can be tailored through the design of the focal length of the GLL. This offers a simple and flexible approach of engineering the GLL focusing characteristics and energy distributions for many applications.

physics.app-ph↗

arXiv2022

Directional Acoustic Luneburg Lens Waveguide

This paper investigates the acoustic Luneburg Lens (ALL) as a design framework for guiding acoustic wave propagation. In this study, we propose to develop an acoustic waveguide based on the characteristics of both acoustic wave focusing and collimation of cascaded ALLs. The continuous variation of refractive index of the ALL is achieved by using lattice unit cells with a graded filling ratio. A cascaded ALL waveguide device is fabricated based on the additive manufacturing technique. The experimental results obtained with this device are consistent with the numerical simulations and theoretical calculations.

physics.app-ph↗

arXiv2021

Acoustic jet based on acoustic metamaterial

In this paper, a novel gradient index (GRIN) acoustic metamaterial is proposed based on the concept of optical modified generalized Luneburg lens (MGLL). With the MGLL, double-foci and high energy density between the two foci can be achieved, which enables the realization of an ultra-long acoustic jet between the two foci. Compared to the generalized Luneburg lens with a single focus, which can only achieve short acoustic jet in the near field or ultra-long acoustic jet in the far field, the proposed MGLL can achieve an acoustic jet extending from the near field to the far field. This capability of the MGLL is theoretically and numerically demonstrated. Furthermore, acoustic metamaterial based MGLL is designed with lattice unit cells having a variable filling ratio. Numerical simulation results show that ultra-long acoustic jets can be achieved with a jet length of up to 30λ , covering both the near field and the far field.

physics.app-ph↗

arXiv2020

Broadband Acoustic Collimation and Focusing using Reduced Aberration Acoustic Luneburg Lens

Acoustic Luneburg lens is a symmetric gradient-index lens with a refractive index decreasing radially from the centre to the outer surface. It can be used to manipulate acoustic wave propagation with collimation and focusing capabilities. However, previously studied acoustic Luneburg lens works only at audible frequency ranges from 1 kHz to 7 kHz, or at a single ultrasonic frequency of 40 kHz. In addition, the acoustic Luneburg lens at high frequency is not omnidirectional in the previous researches. Furthermore, there is no realization of simulation and experimental testing of 3D acoustic Luneburg lens until now. In this paper, a practical reduced aberration acoustic Luneburg lens (RAALL) are proposed for broadband and omnidirectional acoustic collimation and focusing with reduced aberrations. Ray tracing technique shows that RAALL can achieve a better acoustic focusing compared with traditional modified acoustic Luneburg lens. Following that, two models of RAALL are designed and fabricated through additive manufacturing technology: a 2D version and a 3D version. Collimation and focusing performances of the ultrasonic waves are theoretically, numerically and experimentally demonstrated for both 2D and 3D lenses, and their broadband and omnidirectional characteristics are verified.

physics.app-ph↗

arXiv2020

Realization of Flattened Structural Luneburg Lens Based on Quasi-Conformal Transformation

Conventional structural Luneburg lens is a symmetric circular gradient-index lens with refractive indices decreasing from the centre along the radial direction. In this paper, a flattened structural Luneburg lens (FSLL) based on structural thickness variations is designed by using the quasi-conformal transformation (QCT) technique. Through numerical simulations and experimental studies, the FSLL is demonstrated to have excellent beam steering performance for the manipulation of flexural wave propagation at desired angles.

physics.app-ph↗

arXiv2020

Bi-functional Structural Luneburg Lens for Broadband Structural Wave Cloaking and Waveguide

In this paper, we explore the concept of structural Luneburg Lens (SLL) as a design framework for performing dynamic structural tailoring to obtain a structural wave cloak and a structural waveguide. The SLL is a graded refractive index lens, which is realized by using a variable thickness structure defined in a thin plate. Due to the thickness variation of the plate, the refractive index decreases radially from the centre to the outer surface of the lens. By taking advantage of the unique capabilities of SLL for flexural wave focusing and collimation, we develop a structural wave cloak and waveguide based on cascaded SLLs. The cascaded SLL design enables the integration of functional devices into thin-walled structures while preserving the structural characteristics. Analytical, numerical, and experimental studies are carried out to characterize the performance of the SLL cloak and the SLL waveguide. The results demonstrate that that these cascaded SLL devices exhibit excellent performance for structural wave cloaking and waveguiding over a broadband operating frequency range.

physics.app-ph↗

arXiv2020

Multi-Functional Variable Thickness Structure for Broadband and Omnidirectional Focusing and Collimation

Luneburg lens is a symmetric gradient-index lens with a refractive index that increases from the outer surface to the center in a radial manner. It has the ability to focus and collimate waves, which makes it useful for energy harvesting, waveguiding and as a component in transducers. An ideal Luneburg lens should be easy to fabricate, has broadband and omnidirectional characteristics, as well as a focal length that can be easily tuned. However, existing structural Luneburg lenses based on phononic crystals can hardly achieve these requirements. Here, we propose an alternative structural Luneburg lens which has a refractive index that varies smoothly with its radial distance as a result of a changing thickness. Theoretical calculations, numerical simulations and experimental measurements of flexural wave propagation through the lens showed that flexural wave focusing can be obtained inside, at the edge and outside of the variable thickness lens for different frequencies and propagation directions. Flexural wave collimation was also demonstrated when a point source was placed at the respective focal points for each lens. Furthermore, it was shown that flexural waves that were focused onto a piezoelectric energy harvester by the Luneburg lens can lead to a significant increase in the harvested voltage compared to that obtained without focusing.

physics.app-ph↗

arXiv2019

Ultrasound Beam Steering with Flattened Acoustic Metamaterial Luneburg Lens

We report ultrasound beam steering based on 2D and 3D flattened acoustic metamaterial Luneburg lenses at 40 kHz. The effective properties of the lenses are obtained by using the quasi-conformal transformation (QCT) technique and solving the Laplace equation with Dirichlet and Neumann boundary conditions. A 2D lens and a 3D lens were designed and fabricated. The numerical and experimental results with these lenses demonstrate excellent beam steering performance of ultrasonic waves in both near field and far field.

physics.app-ph↗