Experiments on Nonlocal Fluid‐Flow Metamaterials

Metamaterials for controlling fluid flow have recently attracted considerable attention as an emerging new direction in the field of metamaterials. Herein, nonlocal metamaterials composed of one-dimensionally periodic networks of standard microfluidic tubes and connectors are designed, comprising nearest-neighbor (local) and beyond-nearest-neighbor (nonlocal) connections of order N = 2,3,4. The relative importance of laminar water flow through the nonlocal and local tubes is controlled by introducing tailored constrictions into the local tubes that serve as water-flow resistors. Unusual alternating backward/forward laminar flows of water that depend on the metamaterial parameters and on the boundary conditions are observed. Qualitatively, the backward/forward flows can be seen with the naked human eye by following microparticles introduced into the water. Quantitatively, the backward/forward flows are characterized and mapped by digital image analysis of movies taken with a camera. The experimental findings agree well with finite-element calculations of the network’s fluid streamlines that exhibit loop-like behavior as well with calculations of the evanescent zero-frequency Bloch eigenmodes of a simplified discrete periodic model, providing an intuitive understanding.