Characterizing the pressure field in a modified microbubble flow cytometer: Using a laser Doppler vibrometer to validate the internal pressure

Previously, a flow cytometer was modified with a PZT transducer in order to study the radial oscillations of statistically significant numbers of microbubbles (J. Acoust. Soc. Am. 126, 2954–2962, (2009)). We reported the results of pressure calibration for transient sonication in a recent symposium (ASA, Indianapolis, 2013). Here, we report the results of pressure calibration for steady-state sonication. Because the flow channel width (<200 μm) is too narrow to insert our hydrophones, we rely on finite element analysis (FEA) to predict the acoustic pressure field. In this study the simulation results were compared to Laser Doppler Vibrometer in-situ measurements of the velocities of the surface of the flow chamber. The OFV-534 sensor head with OFV-5000 controller (Polytec, Irvine CA) was mounted so that the laser reflected off the proximal outer surface of the flow chamber. The FEA model coupled structural vibration and linear acoustic physics to calculate the steady state pressure. The FEA model compared favorably with the LDV measurements. The FEA simulations were used to predict the pressure field, leaving only the shell elasticity and viscosity χ and κ as unknown variables in the bubble dynamics model. Excellent fits to Optison bubble oscillations were obtained.