Visualization of Fluid Mixing Using GHz Ultrasonic Imaging

This work demonstrates the first direct visualization of fluid mixing by measuring fluids' 2D ultrasonic impedance map in a fluid chamber using a novel CMOS-integrated GHz frequency imager array. A 128 x 128-pixel array of Aluminum Nitride (AlN) transducers stacked on a CMOS layer and silicon substrate allows visualizing fluid mixing on-chip based on acoustic impedance differences between the liquids. This compact portable imaging system allows real-time visualization of fluids mixing at a frame rate of up to 20 fps. Using ultrasound instead of light enables fluid monitoring of photo-sensitive liquid in microfluidic channels constructed using opaque materials. Furthermore, the measurement of mixing based on the changes in ultrasonic impedance allows potential measurement of the change of fluid density, compressibility, and viscosity.