<p>Acoustic magnifying lenses are utilized in a diversity of applications, from biomedical imaging to leakage detection. metamaterial have allowed unparalleled dominate over acoustic waves, in which spiral conformation have been principally exploited and shown their exquisite wave manipulation capacity to convert the acoustic pressure field into desired spatial arrangement. The existing acoustic metalens are commonly associated with designing dispersive metamaterial or connect with local resonator, thus result in inevitable deformity of waveforms. we report a magnifying lens to reveal the microscopic signals, which is composed of a compact 3D metamaterial array with matched impedance to free space. Different from previous research, the metalens that is established by periodic spiral elements which exhibit a non-dispersive great transmission coefficient. We show, both theoretically and experimentally, the thin flat acoustic magnifier can turn normally incident signals focusing on the prescribed point. Depend on transformation acoustics, effective medium theory and finite element simulations, the metalens is capable of augmenting pressure amplitude about six times even at different calibrated focus point in numerical study. Moreover, in the experimental examination, the sensitivity of acoustic sensor can be greatly upgraded and the focus point can be modified by shifting the pitch of unit cells within metamaterial lens. In addition, the diameter of elements is only 10 mm, and the thickness of the metalens layer is 40mm。With this acoustic system, the weak impulse submerged by background noise can be disclosed much more easily. All the result expressed that the metalens of compact non-dispersive spiral metamaterial array embellished acoustic sensing apparatus to overcome the diagnosis limit of conservative acoustic systems. This work unlocked up brand new prospect for acoustic signal detections.</p>

Acoustic Magnifying Lens Based on Compact Non-Dispersive Spiral Metamaterial Array

Paper Proceedings: https://asmedigitalcollection.asme.org/qnde/QNDE2021/volume/85529

ASME 2021 48th Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE2021)

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