Capacitive micromachined ultrasonic transducers (CMUT) are MEMS-based transducers with advantages over conventional ultrasonic transducers, such as their small size, the ease of integration with semiconductor electronics, and batch fabrication. In this study, the effect of different membrane topologies on the displacement, resonant frequency, and output pressure of the CMUT membrane is investigated in the transmission mode in an air environment. A novel structural-support feature, the rocker stem, is introduced, where the membrane is weakly held to the substrate in order to minimize mechanical constraints. Four different CMUT topologies are designed and assessed to analyze the impacts of topological variations. A new CMUT array configuration is also designed to provide an approach for maximizing CMUT density. This study aims to contribute to efficient CMUT design and the determination of optimum structural parameters for portable applications in air.

Energy harvesting has become a fascinating topic of research. As the world moves towards reducing its dependency on fossil fuels, new and innovative techniques of energy harvesting have been tested and developed. The use of piezoelectric materials to harvest the ambient vibrations from the surroundings is one method that has seen a dramatic rise in use for power harvesting. Remote sensors can be powered by these piezoelectric materials and could potentially act as a continuous source of energy. In space vehicles, energy is generated using solar panels which are bulky, heavy and expensive. Instead piezoelectric harvesters can be used to generate power and are much lighter, compact and relatively cheap when produced in bulk. This paper presents a theoretical study on energy harvesting from structural vibration caused by combustion instability of a solid rocket motor through the motor burnout. Vibration data of tested solid rocket motor was taken as a reference and was inputted as the boundary condition. The 3-D model of the harvester system was designed on Fusion360 and the simulation was performed on COMSOL. Finally, improvements needed in the system to enhance practicality were discussed.

This letter presents a novel capacitive micromachined ultrasonic transducer (CMUT) fabricated with the MEMSCAP PolyMUMPs process and incorporating two new design elements: spring arms and rocker stems. The structure enables low $Q$-factor, broadband operation in a commercial surface micromachining technology, making it suitable for air-coupled applications. The device operates at a bias voltage as low as $26 \,\mathrm{V}$, which is advantageous for portable systems. Electrical characterization demonstrates a $6.5\times$ reduction in bias voltage compared with traditional designs. Four CMUTs were fabricated to isolate and assess the influence of each design element. The frequency spectra showed that the device with the novel design features had the broadest bandwidth (a $Q$-factor of approximately 1.2 compared to approximately 34 for the traditional design). These results highlight the potential of the proposed CMUT architecture for high axial resolution pulse–echo systems.