We report on the development of a novel piezo-MEMS-based optofluidic platform to detect the concentration of various species dissolved in a fluid. This platform employs piezoelectric micromachined ultrasound transducers (PMUTs) to work as a photoacoustic receiver, receiving ultrasound from fluid targets present in microfluidic channels while illuminated with a nanosecond pulsed laser. We fabricate both the PMUTs and the microfluidic channels and subsequently use them for the experiment. We also show the capability of PMUTs as a general photoacoustic receiver and demonstrate its signal-to-noise characteristics (~31) and its wide fractional bandwidth (~73%).
In this work, we demonstrate the use of parylene C to reduce the ring down time and enhance the fractional bandwidth of a piezoelectric micromachined ultrasound transducer (PMUT). We further study the effect of increase in thickness of parylene C on the vibration response of a PMUT such as the fundamental resonant frequency and the maximum static deflection. It is found that the increase in the thickness of the deposited parylene C film, decreases the quality factor of a PMUT, following a linear trend, with negligible effect on its fundamental resonant frequency. This can be considered to be an important finding as far as the field of ultrasound imaging is concerned, since this technique paves the way to control the axial resolution of the B-mode ultrasound scan by simply tuning a PMUT’s quality factor.
We report the development of an opto-acousto-fluidic platform by combining an illumination source in the form of a pulsed laser, a microfluidic channel, and an ultrasound transducer to detect photoacoustic signals generated from the fluid sample inside the channel. We study the effect of the channel dimensions on the emitted acoustic signals using methylene blue solution, a dye of immense interest in processing industry, as a target fluid and select an appropriate channel for further studies. We vary the concentration of the methylene blue dye and collect the corresponding photoacoustic signals. We find that the measured acoustic signal strength varies linearly with the increasing dye concentration, thus making this measurement scheme a potential dye concentration detector. This is a significant finding as it paves the way for developing a miniaturized photoacoustic detector for onsite sensing of dye concentration and perhaps even an online monitoring system which will be radical departure for current analysis methods using bench top bulky and expensive analytical tools.
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