Design, analysis, and feedback control of a nonlinear micro-piezoelectric–electrostatic energy harvester

A nonlinear micro-piezoelectric–electrostatic energy harvester is designed and studied using mathematical and computational methods. The system consists of a cantilever beam substrate, a bimorph piezoelectric transducer, a pair of tuning parallel-plate capacitors, and a tip–mass. The governing nonlinear mathematical model of the electro-mechanical system including nonlinear material and quadratic air-damping is derived for the series connection of the piezoelectric layers. The static and modal frequency curves are computed to optimize the operating point, and a parametric study is performed using numerical methods. A bias DC voltage is used to adapt the system to resonate with respect to the frequency of external vibration. Furthermore, to improve the bandwidth and performance of the harvester (and achieve a high level of harvested power without sacrificing the bandwidth), a nonlinear feedback loop is integrated into the design

Multiscale Elasticity of 3D Boron Carbonitride Foam for Tunable Mechanical Resisting Devices

Boron carbonitride (BCN) foam is a three-dimensional material with a hierarchical structure, which has promising potential due to its semiconducting properties and high surface area. However, the lack of understanding of its elastic properties impedes its large-scale integration into advanced applications. We grew BCN foam samples with different atomic compositions and studied their microscopic- and macroscopic-scale mechanics, which revealed that samples with high concentrations of carbon have lower elastic resistance across different scales (i.e., lower Young’s moduli). While the microscopic elasticity is dominated by interlayer interactions, the macroscopic elasticity is also strongly influenced by the buckling and fracturing of the three-dimensional structure of the BCN foam, and thus, the macroscopic Young’s moduli are lower than the microscopic ones. Our findings shed light on the mechanism that underlies the multiscale mechanics of BCN foam and pave the path toward its integration into tunable mechanical resisting devices such as flexible electronic devices and resonators

Highly sensitive MEMS frequency modulated accelerometer with small footprint

A single-axis resonant MEMS accelerometer is presented here. The goal is to achieve the maximum sensitivity on a set of predefined constraints: small footprint of 500 μm × 500 μm, vacuum operation under 150 Pa (requirement for a single-chip IMU) and fabrication using a Bosch silicon surface micromachining process. The sensor is composed by double-ended tuning fork resonators in differential architecture and a force amplification mechanism to increase its sensitivity. A complete characterization of the device was performed including closed-loop operation. A proportional-integral-derivative closed-loop controller architecture updates in real-time the excitation frequency to half the resonance frequency of the resonators. A scale-factor of 170 Hz/g and a non-linearity of 0.63 %FS (operation range of ±1 g) were experimentally measured. The relative sensitivities of 0.08 %Hz/g/nkg and 0.48 %Hz/g are among the highest reported for DETF-based devices. Long-term (700 μg/√Hz noise floor measured), dynamic and thermal drift measurements are also reported. The differential operation improved the thermal performance by 77 %.The authors would like to offer special thanks to the author Luis A. Rocha, who, although no longer with us, continues to inspire by his example and dedication to the students and collaborators he served over the course of his career. The first author is supported by FCT– Fundação para a Ciência e Tecnologia through the grant PDE/BDE/114564/2016. This work is supported by FCT with the reference project UID/EEA/04436/2019