Broadband reflective metasurface for focusing underwater ultrasonic waves with linearly tunable focal length

Wu, Xiaoxiao; Xia, Xiangxiang; Tian, Jingxuan; Liu, Zhengyou; Wen, Weijia

doi:10.1063/1.4947437

Cited by 56 publications

(13 citation statements)

References 30 publications

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“…To break this limitation, some researchers have proposed a new concept of metasurface (MS) in sub-wavelength scale, which can achieve wavefront manipulation using ultrathin structures. Although various previous works have realized acoustic focusing by taking advantage of MS with phase modulation (PM) [9][10][11][12][13][14][15][16][17][18], there are relatively few studies on the manipulation of focusing intensity. Essentially, the realization of acoustic focusing with intensity modulation in sub-wavelength scale needs to design an acoustic MS that can achieve both amplitude modulation (AM) and PM simultaneously.…”

Section: Introductionmentioning

confidence: 99%

Acoustic Focusing with Intensity Modulation Based on Sub-Wavelength Waveguide Array

Zhang¹,

Gu²

2021

Crystals

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Acoustic focusing with intensity modulation plays an important role in biomedical and life sciences. In this work, we propose a new approach for simultaneous phase and amplitude manipulation in sub-wavelength coupled resonant units, which has not been reported so far. Based on the equivalent impedance and refractive index modulation induced by the change of geometry, arbitrary amplitude response from 0 to 1 and phase shift from 0 to 2π is realized. Thus, the acoustic focusing with intensity modulation can be achieved via waveguide array. Herein, the focal length can be adjusted by alternating the length of supercell, and the whole system can work in a broadband of 0.872f0–1.075f0. By introducing the coding method, the thermal viscosity loss is reduced, and the wavefront modulation can be more accurate. Compared with previous works, our approach has the advantages of simple design and broadband response, which may have promising applications in acoustic communication, non-destructive testing, and acoustic holography.

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Section: Introductionmentioning

confidence: 99%

Acoustic Focusing with Intensity Modulation Based on Sub-Wavelength Waveguide Array

Zhang¹,

Gu²

2021

Crystals

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“…Different from GRIN lenses, which rely on gradually varying refractive index to obtain phase delay, diffractive lenses are realized by controlling local phases of transmitted waves to generate interference and diffraction patterns. The concept of local phase is also used to achieve the focusing of reflected waves [23][24][25][26][27][28], such as reflected lenses using Fano resonance [26,27] and Helmholtz resonance [28]. Usually, the focal length also has dependence on frequency, and thus there are few works on acoustic achromatic focusing.…”

Section: Introductionmentioning

confidence: 99%

Achromatic reflected metalens for highly directional and long-distance acoustic probing

Wang

et al. 2020

New J. Phys.

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Simultaneous temporal and spatial focusing of a pulse is of significance for detection and imaging.Here, an achromatic reflected metalens is designed using hybrid resonance and anti-resonance. The theoretical result demonstrates that the anti-resonance provides an extra degree of freedom to control local phases of reflected waves, yielding an achromatic lens of thickness equal to one half of central wavelength. To overcome the shortcoming of traditional approach to design lenses (neglecting the intercell coupling), a boundary integral method is proposed to alleviate the focus deviation over a broadband. The achromatic feature of designed lens is then verified in the frequency range from 2800 to 5600 Hz by an experiment. Owing to a very weak frequency dependence of focal point and a high reflected focusing efficiency over a broadband, a highly directional and long-distance acoustic probing scheme (the mainlobe width about 8 0 ) is proposed with the aid of achromatic reflected metalens and being confirmed by another experiment, where a signal processing method using triple sensors separated by a subwavelength interval is adopted to eliminate the interferences between incident waves and reflected waves. Our result may find its application in a long-distance underwater acoustic probing.

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“…13 For reflective focusing, metasurfaces have been used to induce a dispersive phase interference, resulting in a frequency dependent focal length. 14 Unlike both fluidic lenses and phased array sources, metasurfaces and transfer function-based tuning are frequency modulated.…”

Section: Introductionmentioning

confidence: 99%

“…Variable focusing has also been accomplished with fluidic lenses that pneumatically change the shape of a fluid-filled membrane. , Pneumatically changing the filling volume of the lens results in a lens with a dynamic radius, and thus a variable focal length . For reflective focusing, metasurfaces have been used to induce a dispersive phase interference, resulting in a frequency dependent focal length . Unlike both fluidic lenses and phased array sources, metasurfaces and transfer function-based tuning are frequency modulated.…”

Section: Introductionmentioning

confidence: 99%

Tunable Hybrid Phononic Crystal Lens Using Thermo-Acoustic Polymers

Walker¹,

Reyes-Contreras

Jin

et al. 2019

ACS Omega

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Solid phononic crystal (PnC) lenses were made active on infiltration with thermosensitive polymers to produce a thermoactuated hybrid solid lens with variable focusing. Acoustic lenses, both solid state and PnCbased, are passive elements with a fixed focal length. Their focal characteristics are functions of the lens structure or the arrangement of the PnC unit cell. Dispersion effects, liquid-filled membranes, and phase delay in a multi-element emitter have been used for variable focusing. The high thermal, electric, and electromagnetic sensitivity of the elastic properties of poly(vinyl alcohol) (PVA) poly(N-isopropylacrylamide) (PNIPAm)-based hydrogels enable them to operate as tunable solids. However, these solids do not have strong enough contrast with water or well-controlled shape parameters to function as standalone lenses. Here, a tunable hybrid solid ultrasonic lens is realized by combining a PnC lens with PVA-PNIPAm thermoacoustic hydrogel to modify the transmission and dispersion properties of transient acoustic waves. Variable focusing is demonstrated from 40 to 50 mm using the anomalous thermosensitivity of the elasticity and speed of sound of the hydrogel.

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Broadband reflective metasurface for focusing underwater ultrasonic waves with linearly tunable focal length

Cited by 56 publications

References 30 publications

Acoustic Focusing with Intensity Modulation Based on Sub-Wavelength Waveguide Array

Acoustic Focusing with Intensity Modulation Based on Sub-Wavelength Waveguide Array

Achromatic reflected metalens for highly directional and long-distance acoustic probing

Tunable Hybrid Phononic Crystal Lens Using Thermo-Acoustic Polymers

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