Application and Optimization of Stiffness Abruption Structures for Pressure Sensors with High Sensitivity and Anti-Overload Ability.

The influence of diaphragm bending stiffness distribution on the stress concentration characteristics of a pressure sensing chip had been analyzed and discussed systematically. According to the analysis, a novel peninsula-island-based diaphragm structure was presented and applied to two differenet diaphragm shapes as sensing chips for pressure sensors. By well-designed bending stiffness distribution of the diaphragm, the elastic potential energy induced by diaphragm deformation was concentrated above the gap position, which remarkably increased the sensitivity of the sensing chip. An optimization method and the distribution pattern of the peninsula-island based diaphragm structure were also discussed. Two kinds of sensing chips combined with the peninsula-island structures distributing along the side edge and diagonal directions of rectangular diaphragm were fabricated and analyzed. By bonding the sensing chips with anti-overload glass bases, these two sensing chips were demonstrated by testing to achieve not only high sensitivity, but also good anti-overload ability. The experimental results showed that the proposed structures had the potential to measure ultra-low absolute pressures with high sensitivity and good anti-overload ability in an atmospheric environment.

A Novel Slope Method for Measurement of Fluid Density with a Micro-cantilever under Flexural and Torsional Vibrations.

A novel method, which was called a slope method, has been proposed to measure fluid density by the micro-cantilever sensing chip. The theoretical formulas of the slope method were discussed and established when the micro-cantilever sensing chip was under flexural and torsional vibrations. The slope was calculated based on the fitted curve between the excitation and output voltages of sensing chip under the nonresonant status. This measuring method need not sweep frequency to find the accurate resonant frequency. Therefore, the fluid density was measured easily based on the calculated slope. In addition, the micro-cantilver was drived by double sided excitation and free end excitation to oscillate under flexural and torsional vibrations, respectively. The corresponding experiments were carried out to measure the fluid density by the slope method. The measurement results were also analyzed when the sensing chip was under flexural and torsional nonresonant vibrations separately. The measurement accuracies under these vibrations were all better than 1.5%, and the density measuring sensitivity under torsional nonresonant vibration was about two times higher than that under flexural nonresonant vibration.

Equivalent Circuit Model for a Large Array of Coupled Piezoelectric Micromachined Ultrasonic Transducers With High Emission Performance.

In this article, an analytical equivalent circuit model is established for the piezoelectric micromachined ultrasonic transducer (PMUT) cell and array with a combination of the annular and circular diaphragms used for structural optimization and complex array design. Based on this model, a comprehensive analysis is conducted on the acoustic-structural coupling of an annular and circular diaphragm-coupled PMUT (AC-PMUT) with a new excitation method. The model-derived results are in good agreement with the simulation and experimental results. Then, an optimized design has been presented to achieve high-output pressure and a good array working performance. In summary, a comparison of the array working performance is conducted between the arrays that consist of AC-PMUTs and traditional circular diaphragm PMUTs (C-PMUTs). The results indicate that the AC-PMUT array has a much lower crosstalk effect than that of the traditional C-PMUT array. By this means, the AC-PMUT array can fully use the high vibration amplitude achieved by each AC-PMUT cell to improve its output ability. As a result, the highest ultrasonic output pressure generated by the AC-PMUT array in its resonant condition can achieve an increase of 155%, compared with that generated by the C-PMUT array.

Closed-Form Expressions on CMUTs With Layered Anisotropic Microplates Under Residual Stress and Pressure.

Capacitive micromachined ultrasonic transducers (CMUTs) are promising in the emerging fields of personalized ultrasonic diagnostics, therapy, and noninvasive 3-D biometric. However, previous theories describing their mechanical behavior rarely consider multilayer and anisotropic material properties, resulting in limited application and significant analysis errors. This article proposes closed-form expressions for the static deflection, collapse voltage, and resonant frequency of circular-microplate-based CMUTs, which consider both the aforementioned properties as well as the effects of residual stress and hydrostatic pressure. These expressions are established by combining the classical laminated thin plate (CLTP) theory, Galerkin method, a partial expansion approach for electrostatic force, and an energy equivalent method. A parametric study based on finite-element method simulations shows that considering the material anisotropy can significantly improve analysis accuracy (~25 times higher than the theories neglecting the material anisotropy). These expressions maintain accuracy across almost the whole working voltage range (up to 96% of collapse voltages) and a wide dimension range (diameter-to-thickness ratios of 20-80 with gap-to-thickness ratios of ≤2). Furthermore, their utility in practical applications is well verified using numerical results based on more realistic boundary conditions and experimental results of CMUT chips. Finally, we demonstrate that the high accuracy of these expressions at thickness-comparable deflection results from the extended applicable deflection range of the CLTP theory when it is used for electrostatically actuated microplates.

Equivalent Circuit Models of Cell and Array for Resonant Cavity-Based Piezoelectric Micromachined Ultrasonic Transducer.

This article presents a design of resonant cavity-based piezoelectric micromachined ultrasonic transducers (PMUTs), including impedance matching tube-integrated (T) and Helmholtz resonant (HR) cavity-integrated PMUTs. In addition, equivalent circuit models for single PMUT cell and PMUT array are developed for structural optimization and complex array design. The model-derived results agree well with the FEM results. On the basis of the proposed models, an optimized design is established to achieve high output pressure and a good array working performance. The working performance of arrays that consist of HR-PMUTs and traditional circular diaphragm PMUTs (C-PMUTs) is compared. Results indicate that the HR-PMUT array has a lower crosstalk effect than the traditional C-PMUT array. Furthermore, the highest ultrasonic output pressure of HR-PMUT array at the resonant frequency can be achieved with an increase of up to 163% compared with that of the C-PMUT array because of the liquid amplification effect. Also, the cavity-based design and its model can be used for further advanced PMUT cell structures in other arrays to improve their performance.

Array Design of Piezoelectric Micromachined Ultrasonic Transducers With Low-Crosstalk and High-Emission Performance.

This article presents a resonant cavity-based array design for piezoelectric micromachined ultrasonic transducers (PMUTs). The cavity depth is designed to ensure that its open end achieves a considerably smaller acoustic impedance than the surrounding PMUT cells. The interference acoustic wave generated between every two adjacent PMUT cells at the near surface of the array will take an easy path down to the cavity bottom. As such, the crosstalk effect among different adjacent cells in the array can be largely reduced. An equivalent circuit model of the proposed array is established for its design and optimization. In addition, the solutions for circuit parameters in the electromechanical domain are analytically derived and verified via FEM simulations. Given the low crosstalk effect achieved by the proposed array design, the output sensitivity of the proposed PMUTs can be improved by 259% compared with the traditional PMUTs with a high distribution density of the same size. The cavity-based array design and its model can be used for further advanced PMUT cell structures in other arrays to improve their performance.

An Analytical Equivalent Circuit Model for Optimization Design of a Broadband Piezoelectric Micromachined Ultrasonic Transducer With an Annular Diaphragm.

This paper presents an equivalent circuit model, a systematic design, and optimization method for developing a broadband annular diaphragm piezoelectric micromachined ultrasonic transducer (A-PMUT). By utilizing array analysis methods, an annular diaphragm is regarded as an array consisting of equally spaced sector diaphragms influencing each other by crosstalk effect. The model successfully explains the phenomenon of multi-resonance peaks in the frequency response curve, sharing the same vibration mode. The study finds that the analytical predictions of the model are in good agreement with the simulation and experimental results. Meanwhile, based on the phenomenon of multi-resonance peaks, a systematic design method is proposed to extend the bandwidth of the A-PMUT. In this method, the radiation impedance of the A-PMUT is separated into crosstalk-free and crosstalk contributed parts. This method enables the determination of the optimal structure counting for the influences on the frequency response of A-PMUTs for broadband applications. The model here can also be further generalized to be a guideline for the design and optimization of broadband PMUTs.