The paper reports the design, fabrication and experimental results of a liquid crystal polymer (LCP) membrane-based pressure sensor for flow rate and flow direction sensing applications. Elaborate experimental testing results demonstrating the sensors' performance as an airflow sensor have been illustrated and validated with theory. MEMS sensors using LCP as a membrane structural material show higher sensitivity and reliability over silicon counterparts. The developed device is highly robust for harsh environment applications such as atmospheric wind flow monitoring and underwater flow sensing. A simple, low-cost and repeatable fabrication scheme has been developed employing low temperatures. The main features of the sensor developed in this work are a LCP membrane with integrated thin film gold piezoresistors deposited on it. The sensor developed demonstrates a good sensitivity of 3.695 mV (ms−1)−1, large operating range (0.1 to >10 ms−1) and good accuracy in measuring airflow with an average error of only 3.6% full-scale in comparison with theory. Various feasible applications of the developed sensor have been demonstrated with experimental results. The sensor was tested for two other applications—in clinical diagnosis for breath rate, breath velocity monitoring, and in underwater applications for object detection by sensing near-field spatial flow pressure.

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Medium damping influences on the resonant frequency and quality factor of piezoelectric circular microdiaphragm sensors (PCMSs) are investigated theoretically and experimentally in this paper. The acoustic radiation and viscosity damping as the two main sources of energy dissipation in a medium virtually added the mass of the diaphragm and therefore decrease the frequency and Q-factor of the diaphragm. The magnitude of medium damping inversely depends on the radius-to-thickness ratio. An increase in this ratio is the trend in the fabrication of thin microdiaphragms by MEMS fabrication processes, which implies the higher influence of medium damping on the dynamic behavior of microdiaphragms. The fabricated PCMSs were tested in vacuum, air, and ethanol. The Q-factor and the resonant frequency of the device increase by almost seven times, 4.7% from air to 0.05 atmpressure, respectively. The Q-value drops from 111.195 in air to 23.908 in ethanol. Throughout this work, theoretical and experimental values were compared and a fairly good correlation was observed.

In this study, residual stress influences on the vibrational behavior of piezoelectric circular microdiaphragm-based biosensors are investigated theoretically and experimentally. The piezoelectric microdiaphragm was first fabricated by combining sol-gel PZT thin film and MEMS technology. The stress measurements by the wafer curvature method and the micro-Raman technique demonstrate that high tensile stresses are generated in the upper films (Pt/PZT/Pt), while the silicon oxide layer experiences a compressive stress. After backside etching of the microdiaphragm, the suspended membrane method was used to measure the average stress and equivalent Young's modulus of the diaphragm, which were 96 MPa and 106.4 GPa, respectively. The dynamic behavior of the fabricated sensor under this stress was then investigated. A comprehensive mechanics model based on vibration modes is presented and the natural frequencies of the diaphragm are obtained. A nondimensional tension parameter is defined, and effects of this parameter on the resonant frequency of the diaphragm are presented. It was concluded that both flexural rigidity and tension contribute to the resonant frequency of the diaphragm sensor. Finally, the resonant frequencies of the fabricated sensor were measured by impedance analysis and laser vibrometry techniques. These frequencies were compared with their theoretical counterparts and a good agreement was observed.

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