Smart Microfluidic Channels

Micro-fluidic systems involve moving fluids in micro-channels whose dimensions range from 30 um to 300 um. While moving the fluidic a variety of techniques is used to sense particles, measure density, flow rate, viscosity and observe chemical reactions inside the channels. These techniques include optical methods, fluorescence microscopy, capacitance measurements and so on. Surprisingly, ultrasound has been used very limitedly in micro channels in contrast to their successful applications for measurement of flow, physical properties and pressure in large scale devices. We proposed to integrate ultrasonic sensors in micro-fluidic channels. We developed a fluidic channel with integrated ZnO transducer. A ten-micron of ZnO film is deposited on a glass substrate. The transducer is sandwiched between top and bottom electrodes. The channel that is cast into PDMS using a silicon master is aligned on top of the transducer forming a narrow path for fluid flow. The transducer resonates at 400 MHz in thickness mode. A special electronics has been built to generate high voltage pulses with very short widths. Pulse/echo experiments have been performed using the setup. In addition to sensing, the transducers can be also used for actuation in the channels such as mixing, sorting, switching.

 

 

 

FIGURE 1. Microfluidic channels and associated electronic circuits.

 

 

 

FIGURE 2. Acoustic reflections in microfluidic channels.

 

 

 

FIGURE 3. Microfluidic mixer with integrated transducers.

 

 

 

FIGURE 4. Mixing in a microfluidic channel by ultrasound excitation.