Three-dimensional Ultrathin Planar Lenses by Acoustic Metamaterials

Abstract

Acoustic lenses find applications in various areas ranging from ultrasound imaging to nondestructive testing. A compact-size and high-efficient planar acoustic lens is crucial to achieving miniaturization and integration, and should have deep implication for the acoustic field. However its realization remains challenging due to the trade-off between high refractive-index and impedance-mismatch. Here we have designed and experimentally realized the first ultrathin planar acoustic lens capable of steering the convergence of acoustic waves in three-dimensional space. A theoretical approach is developed to analytically describe the proposed metamaterial with hybrid labyrinthine units, which reveals the mechanism of coexistence of high refractive index and well-matched impedance. A hyperbolic gradient-index lens design is fabricated and characterized, which can enhance the acoustic energy by 15 dB at the focal point with very high transmission efficiency. Remarkably, the thickness of the lens is only approximately 1/6 of the operating wavelength. The lens can work within a certain frequency band for which the ratio between the bandwidth and the center frequency reaches 0.74. By tailoring the structure of the metamaterials, one can further reduce the thickness of the lens or even realize other acoustic functionalities, opening new opportunity for manipulation of low-frequency sounds with versatile potential.

Fingerprint‐to‐CH stretch continuously tunable high spectral resolution stimulated Raman scattering microscope

“…The broadband operation of our SRS microscope allows also to perform experiments with isotope‐labeled molecules, which have recently shown great potential to study the dynamics of metabolic processes in live cells . For example, culturing cells with deuterated glucose (glucose‐d 7 ) allows direct observation of de novo lipogenesis , for example, the process by which glucose is used as a substrate to synthesize new lipid molecules, which can be subsequently stored in cellular LDs as esterified fatty acids. In this regard, the possibility to simultaneously collect the signal in the silent region, typical of the isotope‐labeled molecules, and in the fingerprint and/or CH‐stretch region can add significant information on the biomolecular processes under investigation in the cells.…”

Theory of metascreen-based acoustic passive phased array

“…The excellent agreement between the theoretical/simulated results and the predicted ones demonstratesthe abilities of metascreen even for the cylinder wave from the line source. Due to the fully controllable phase pattern, acoustic lenses can be designed to focus energy effectively at an arbitrary position [26,49,50].…”

Modulation of water surface waves with a coiling-up-space metasurface

“…As a result, for the transmitted WSWs, the coupling of waves from two paths contributes to a relatively high energy transmission while a slightly decrease for the phase delay, as demonstrated in the acoustic metamaterial counterparts. 18 For a long-wavelength condition, due to the trade-off between a high refractive index and a good impedance matching, the coiling-up-space metasurface can be treated as an effective medium with a high relative effective refractive index n r and a good impedance matching. In this work, the frequency of WSWs is set to be 1.435 Hz, which corresponds to the WSW wavelength of 0.757 m, i.e., just 14 times larger than the unit width (0.05 m).…”