Applications include thin acoustic metasurface lenses.. Ranges of constitutive parameters exhibited by their bulk forms have been extended to beyond classically available ranges in both electromagnetism and acoustics: single and double negativity as well as a wide range of double-positive parameters have brought many remarkable phenomena into reality, including negative refraction, reverse Doppler effect, superlensing, and cloaking define a metasurface as any array of metamaterial unit-cells (meta-atoms) on a surface for which the thickness and periodicity are small compared to the wavelength in the surrounding media.
For the simplest case of one-dimensional (1D) waves propagating in a waveguide, a metasurface is represented by a dot, or single meta-atom.
(c) Measured space-time diagrams of the normalized pressure amplitude for positive and negative group delay. However, for full control of the waves, additional measures may be needed because the span of the phase shift δ in our system is not optimal for redirecting beams.
Resonator B consists of a cavity of tunable length ~200 ± 50 mm and diameter 32.7 mm, and a mass-loaded membrane of the same type as in A.
Tunable metasurfaces mimicking EIT-like effects have only previously been demonstrated for electromagnetic systems, appropriate here since the characteristic geometrical parameters are small compared with our acoustic wavelengths (λ~0.68 m).
Using acoustic waves, we observe the process of wavepackets traversing a meta-atom with abrupt displacements, which appear as path discontinuities on a space-time diagram.
We construct a tunable meta-atom from two coupled resonators at ~500 Hz, map the spatiotemporal trajectories of individual sonic pulses, and reveal discontinuities at the meta-atom where the pulses exit at a time ~50 ms ahead or behind their arrivals.