  We demonstrate the design, fabrication and use of a dual electrode PMUT
(Piezoelectric Micromachined Ultrasound Transducer) integrated with a
microfluidic channel as a fluid density sensor in both static and dynamic
density-change conditions. The dual electrode configuration makes the PMUT
resonator a self-contained resonant peak-shift sensor and the microfluidic
integration makes this system a versatile fluid density sensing platform that
can be used with extremely low volumes of fluids in various industrial and
healthcare applications. The density measurements carried out here under
flowing fluid conditions demonstrate the potential of this system as a
real-time fluid density monitoring system. We include results of density
measurements in the range of 1020 - 1090 kg/m3 that corresponds to the human
blood density variation generally due to the change in its hemoglobin content.
The sensitivity of the sensor-26.3 Hz/(kg/m3)-is good enough to reliably detect
even 1% change in the hemoglobin content of the human blood. Thus, this system
could potentially be used also as a hemoglobin measurement sensor in healthcare
applications.
