The paper from Huanming Xia and colleagues at the Singapore Institute of Manufacturing Technology reports the development of a microfluidic oscillator that converts otherwise steady laminar flow to oscillatory flow to enhance mixing in microfluidic devices. The key is an elastic diaphragm embedded inside a stepped cavity, perpendicular to the fluid channel. When fluid flows over the membrane it depresses and then bounces back due to the elasticity of the silicone membrane, creating oscillatory flow.
Read about how the membrane can also act as a valve in this Communication article:
Converting steady laminar flow to oscillatory flow through a hydroelasticity approach at microscales
H. M. Xia , Z. P. Wang , W. Fan , A. Wijaya , W. Wang and Z. F. Wang