Imaging Vibrations inside Acoustofluidic Devices

This application note illustrates how SmarAct’s PICOSCALE Vibrometer enables the selective imaging of vibrations on internal surfaces of acoustofluidic devices. Its infrared confocal measurement principle allows precise focus through transparent materials like glass, even in the presence of fluid. The system reveals how different channel surfaces respond differently to acoustic excitation—critical insight for optimizing particle manipulation in microfluidic applications.

Problem

Acoustofluidic devices use ultrasonic waves to manipulate particles in microfluidic channels, but standard vibrometry techniques struggle to differentiate vibrations on individual internal surfaces—especially in glass or fluid-filled systems. Without surface-selective measurement, accurate evaluation is not possible.

Solution

The PICOSCALE Vibrometer, equipped with confocal infrared optics, enables vibration measurements on specific surfaces within transparent microfluidic devices—both with and without fluid. This allows full modal analysis of critical areas involved in particle manipulation.

Implementation

• A microfluidic chip was scanned to detect reflections from multiple internal surfaces, resolving layer positions via a confocal focusing curve.

• Surfaces b and c were individually excited using a linear chirp (500 kHz–1 MHz) and their vibration spectra recorded.

• Modal imaging at 820 kHz revealed different bending modes for each surface.

• Tests were repeated after filling the channel with water, confirming mass-loading effects on resonance frequencies.

Results

• Surface-selective measurements revealed distinct resonance peaks for each glass interface.

• Fluid-filled tests showed a downshift of vibration peaks by ~6 kHz, confirming the added mass effect.

• The device’s behavior varied significantly depending on which surface and medium was being analyzed.

Conclusion

The PICOSCALE Vibrometer offers unique surface selectivity and MHz-range bandwidth, enabling advanced vibration analysis in acoustofluidic devices. This makes it a powerful tool for optimizing particle control in lab-on-a-chip systems.