Fluid Density Sensing Using Piezoelectric Micromachined Ultrasound Transducers

We report on the suitability of a PiezoelectricMicromachined Ultrasound Transducer (PMUT) based systemfor fluid density measurement in both static and dynamicconditions. We exploit the well-known phenomenon of thevirtual added mass induced changes in the resonant fre-quency of a structure vibrating in a fluid medium to design,fabricate and test a unique PMUT-fluid-PMUT (PFP) system asa fluid density sensor. The proposed system uses through-transmission of ultrasound waves from one PMUT transducerto another identical transducer with the test fluid in betweenand records the shift in the resonant peak of the receiverPMUT. We also study the sensitivity of the system usingdifferent sized PMUTs with resonant frequencies ranging from140 kHz to 1.8 MHz and show how the system can be designed for a desired sensitivity. Further, we carry out experimentswith dynamic density changes by mixing fluids to study how the system could be used to track changes in the densityof a flowing liquid in real-time. We also study the effect of the distance separating the transmitter and the receiver toestablish the utility of the system in both micro and macro scales in static as well as dynamic condition