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Micro-mechanical resonators are widely used in modern sensing technology due to their high quality-factor (Q), enabling sensitive detection of various stimuli. However, the performance of these resonators in fluid environments is limited by significant viscous and acoustic radiation losses that reduce their Q. Here, we present a paradigm-shifting discovery that challenges the conventional wisdom of resonant sensing in fluids. We report an optimal volume of fluid over a 2D micro-resonator that increases the Q by up to 1000% compared to that in air. We have conducted precise experiments on piezoelectric, circular, membrane-type micro-resonators of 4 mm diameter fabricated using MEMS technology on silicon-on-insulator (SOI) wafers. The top side of the resonator was filled with different volumes of fluid and its Q was measured through resonance tracking by actuating the resonator with an appropriate voltage. We found the existence of an optimal volume of fluid that maximized the Q. We argue that this phenomenon is a result of a balance between the enhancement of kinetic energy of the resonator due to mass loading of the fluid and the energy dissipation through viscous and acoustic radiation losses in the fluid medium. This remarkable enhancement in Q substantially improves the sensitivity of the resonator, with important implications for diverse applications such as biosensing, chemical detection, and environmental monitoring. Our findings challenge the prevailing understanding of resonant sensing in fluids and open up new avenues for the development of highly sensitive and accurate sensors., Comment: 20 pages, 5 figures

This report introduces a novel optofluidic platform based on piezo-MEMS technology, capable of identifying subtle variations in the fluid concentration. The system utilizes piezoelectric micromachined ultrasound transducers (PMUTs) as receivers to capture sound waves produced by nanosecond photoacoustic (PA) pulses emanating from a fluid target housed in PDMS microchannels. Additionally, a dedicated low-noise single-channel amplifier has been developed to extract the minute analog voltage signals from the PMUTs, given the inherently weak ultrasound signals generated by fluid targets. The PMUTs' proficiency in detecting changes in fluid concentration under both static and time-varying conditions has been documented and verified, confirming the platform's efficacy in monitoring fluid concentrations., Comment: 9 pages, 10 figures

A concise review on the thin-film PMUTs, which has been one of the rather important research topics amongst microultrasound experts is being reported. It has been rigorously surveyed, scrutinized, and perceived that the work in this direction began nearly 44 years ago, with the primitive development of functional piezoelectric thin-film material, and now there are already three major companies commercializing them on a bulk scale. This fascinating fact illustrates the enormous contribution made by more than 70 different centers, research institutes, and agencies spread across 4 different continents to develop the vast know-how of these devices design, make, and function. This review covers such important contributions in a short but comprehensive fashion and in particular, intends to educate the readers about the global scenario of PMUTs, the principles governing their design, the ways following their make, all non-conventional useful PMUT designs, and lastly, category wise applications. Crucial comparison charts in terms of thin-film piezoelectric material used in PMUTs, and in terms of targeted applications are also depicted and discussed, which is believed to enlighten any MEMS designer planning to begin working with PMUTs. Moreover, each relevant section is provided with a crisp future forecast, from the authors past knowledge and expertise in this very field of research along with the elements of a careful literature survey. In short, this review can be considered a one-stop time-efficient guide for whoever is interested in knowing about these small devices., Comment: 17 pages, 6 figures, 2 tables

Photoacoustic image (PAI) quality improvement using a low frequency piezoelectric micromachined ultrasound transducer (PMUT) having the fundamental resonant frequency 1 MHz is being reported. Specifically, three different methods are implemented such as the frame averaging, mathematically improved algorithms, and a hardware position accurate arrangement in order to obtain unparallel PAI image quality. Validation study has been conducted in both agar phantom and ex-vivo tissue samples. Measurable image quantifiers in the form of full width at half maximum (FWHM), signal to noise ratio (SNR), and contrast ratio (CR) are used to evaluate the improvement in the image quality. It is found that the FWHM increases by 34%, SNR by 23% and CR by 25%, suggesting the efficacy of the methods to achieve better photoacoustic images employing PMUT-based detector. The study demonstrates that the suggested methods of improvement could play a key role in a promising cost-effective PMUT-PAI system in future., Comment: 7 pages, 5 figures, will be submitted to Applied Physics Letters

For the past two decades piezo MEMS technology are emerging for its low power consumption of ultrasonic sensing and actuation devices for biomedical applications. Still researchers are facing challenges in miniaturization of piezo-MEMS devices. But up-to-date there is no reports on achieving better sensitivity and actuation strength properties in the same piezoelectric material. As piezoelectric materials are anisotropic in nature, for that it is essential to grow different textured PZT thin film on a single silicon substrate. In the present investigation we have demonstrated the simple method of growing different textured PZT thin film with same process condition without introducing any buffer layer on a platinised silicon wafer by wet chemical method. For this two types of modified bottom electrode Ti/Pt stacks have been proposed i.e., mono- and bilayer Pt on a same silicon substrate using lithography techniques. The texture of the PZT thin film grown on these Pt layers shows (111) and (100) preferred orientations. The XPS surface analysis was carried out on both Pt surfaces to investigate the anomalous behaviour of different textured PZT on different Pt layers. The measured ferroelectric and piezoelectric properties has shown low remanent polarization and high piezocoefficient values for (100) oriented film as reported. The (100) oriented film shows piezocoefficient (d33,f) value twice than that of (111) oriented PZT thin films on a single silicon substrate., Comment: Major modification required

Piezoelectric micromachined ultrasound transducers (PMUTs) have gained popularity in the past decade as acoustic transmitters and receivers. As these devices usually operate at resonance, they can deliver large output sound pressures with very low power consumption. This paper explores the influence of the transmitter's packaging on the radiated acoustic field in air. We run simplified axisymmetric numerical models to observe the change in the acoustic field and directivity with respect to the device's package dimensions. The simulations demonstrate a notable change in the directivity of transmitter based on the size of the baffle. Experimental measurements are carried out to validate the simulations, which prove useful in designing packages for transmitters to meet application specific requirements., Comment: 6 pages, 10 figures

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., Comment: 8 pages, 16 figures