This paper presents an electret-based MEMS energy harvester synergizing the advantages of multi-modal structure and impact mechanism for broad operating bandwidth. The device with a volume of 295 mm³ comprises an electret-based primary subsystem for power generation and an electrode-free auxiliary subsystem for frequency tuning. The tiny auxiliary subsystem helps to induce close resonances with comparable outputs at low excitations, as well as introduces impact-based nonlinearity to drive the first resonant peak upward and further approach the second one at elevated excitations. The experimental results demonstrate that at an excitation of 12.8 m/s², the 3-dB bandwidth of the first peak is increased from 20.4 to 60.4 Hz and a low frequency ratio of 1.15 between the two peaks is achieved. The two degree-of-freedom resonant structure with impact-based nonlinearity is systematically investigated through an equivalent circuit representation. An electrical equivalent circuit model of the proposed device with impact mechanism is derived. The circuit simulation confirms the nonlinear behavior of the system, and reveals the mechanism of peak shifting and bandwidth enhancing dynamics. [2017-0207]

Dielectric particles in a non-uniform electric field are subject to a force caused by a phenomenon called dielectrophoresis (DEP). DEP is a commonly used technique in microfluidics for particle or cell separation. In comparison with other separation methods, DEP has the unique advantage of being label-free, fast, and accurate. It has been widely applied in microfluidics for bio-molecular diagnostics and medical and polymer research. This review introduces the basic theory of DEP, its advantages compared with other separation methods, and its applications in recent years, in particular, focusing on the different electrode types integrated into microfluidic chips, fabrication techniques, and operation principles.

This paper reports an acceleration sensing method based on two weakly coupled resonators (WCRs) using the phenomenon of mode localization. When acceleration acts on the proof masses, differential electrostatic stiffness perturbations will be applied to the WCRs, leading to mode localization, and thus, mode shape changes. Therefore, acceleration can be sensed by measuring the amplitude ratio shift. The proposed mode localization with the differential perturbation method leads to a sensitivity enhancement of a factor of 2 than the common single perturbation method. The theoretical model of the sensitivity, bandwidth, and linearity of the accelerometer is established and verified. The measured relative shift in amplitude ratio (~312162 ppm/g) is 302 times higher than the shift in resonance frequency (~1035 ppm/g) within the measurement range of ±1 g. The measured resolution based on the amplitude ratio is 0.619 mg and the nonlinearity is ~3.5% in the open-loop measurement operation.

This paper reports a high-sensitivity resonant electrometer based on the mode localization of two degree-of-freedom weakly coupled resonators (WCRs). When charges are applied to the input electrodes, the effective stiffness of a specific resonator of the WCRs will be perturbed, leading to a drastic change in mode shape owing to the mode localization phenomenon. By measuring the shift of the amplitude ratio, the small charge fluctuation can be accurately sensed. The theoretical mode of the electrometer is established based on the transfer functions of the WCRs. In particular, we establish the design rules of the coupling factor according to the -3-dB bandwidth, amplitude ratio measurement errors, and frequency misalignment between the resonators. The experimental results show that the amplitude ratio-based sensitivity is ~2151 times higher than the frequency-based sensitivity. The amplitude ratio-based resolution of the electrometer is approximately 1.269 fC.