In this paper, we study the snapping action of a micromachined bistable mechanism harmonically driven with an ultra-small actuation stroke, which is realized through the mode amplification in a ...two-degrees-of-freedom (2-DOF) vibration system using an on-chip electrostatic actuator. The micromachined bistable mechanism is based on a curved beam configuration. The dynamic response of the device is theoretically predicted with the harmonic balance method. Further, to demonstrate this proposed study, a microelectromechanical systems (MEMS) prototype device is designed, fabricated, and tested. In experiments, the forward and backward state switching actions of the prototype device are realized with actuation stroke smaller than <inline-formula> <tex-math notation="LaTeX">0.4~\mu \text{m} </tex-math></inline-formula>, while the traveling distance between the two states is about <inline-formula> <tex-math notation="LaTeX">18~\mu \text{m} </tex-math></inline-formula>. To the best of our knowledge, we demonstrate for the first time the state switching of a cured beam bistable mechanism using harmonic driving in a 2-DOF vibration system. This paper has potential in applications including MEMS switches and MEMS filters. 2017-0221
A silicon chip integrated microelectromechanical (MEMS) wind energy harvester, based on the vortex-induced vibration (VIV) concept, has been designed, fabricated, and tested as a proof-of-concept ...demonstration. The harvester comprises of a cylindrical oscillator attached to a piezoelectric MEMS device. Wind tunnel experiments are conducted to measure the power output of the energy harvester. Additionally, the energy harvester is placed within a formation of up to 25 cylinders to test whether the vortex interactions of multiple cylinders in formation can enhance the power output. Experiments show power output in the nanowatt range, and the energy harvester within a formation of cylinders yield noticeably higher power output compared to the energy harvester in isolation. A more detailed investigation conducted using computational fluid dynamics simulations indicates that vortices shed from upstream cylinders introduce large periodic transverse velocity component on the incoming flow encountered by the downstream cylinders, hence increasing VIV response. For the first time, the use of formation effect to enhance the wind energy harvesting at microscale has been demonstrated. This proof-of-concept demonstrates a potential means of powering small off-grid sensors in a cost-effective manner due to the easy integration of the energy harvester and sensor on the same silicon chip.
A novel microtribometer is developed to characterize microelectromechanical systems (MEMS) sidewall friction with high resolution. The design is based on a rotational grating displacement sensing ...mechanism, with which 1.2-nm sensing sensitivity can be achieved. Employing it, the adhesion force (1.85 μN) and the coefficients of static (0.801) and kinetic (0.363) frictions on the sidewall of an as-fabricated MEMS device have been measured. Besides these, the whole process of stick-slip associated with the movement under friction, including the transition between static and kinetic frictional states, has also been clearly revealed. To reduce friction, a localized lubrication method is developed, with which liquid lubricant can be applied directly onto the desired region without affecting other components on the same device. From the experimental results, reduced values in adhesion force (1.23 μN ) and coefficients of friction (0.262 for static and 0.183 for kinetic) are obtained in the same MEMS device after lubrication treatment, demonstrating improved frictional performance.
In this paper, a modified soft lithography based on-demand microchannel fabrication technology is presented. Different from the widely adopted solid mold, a concept of deformable mold made of ...poly(dimethylsiloxane) (PDMS) is developed, in which the mold contour can be changed due to the excellent elasticity associated with PDMS (can withstand strain higher than 100%). Through combining with the special curing property associated with PDMS, several types of processes have been developed, based on which not only can 2D microchannels with various rounded cross sectional contours be fabricated using the same deformable mold, but also microchannels with multi-depth can be obtained simultaneously with only one replication step. In addition, more complicated microchannel than the most common 2D planar configuration, such as vertically arranged 3D self-aligning dual-channel, can also be achieved with the proposed strategy.
A novel microelectromechanical systems (MEMS)-based microscanner is developed with the ultimate goal of integrating it into an endoscopic probe for use in clinical investigations. Microassembly ...technology is utilized to construct this device, which consists of an electrostatic-based microactuator and a pyramidal polygonal microreflector. A two-stage double T-shaped spring beam system is introduced to the actuator for displacement amplification as well as for motion transfer from the translational movement of the in-plane comb drives to the rotation of the central ring-shaped holder. In the meantime, an eight-slanted-facet-highly-reflective pyramidal polygonal microreflector is developed using high-precision diamond turning and soft lithography technologies. This reflector design requires only a small mechanical rotational angle to achieve full circumferential scanning. This MEMS device is developed with the goal of integrating it into an optical coherence tomography probe that could provide an alternative for endoscopic optical coherence tomography applications that would have the advantages of circumferential imaging capability, fast scanning speed, and low operational power consumption.
We report an open-loop digitally driven precision positioning mechanism, termed micromechanical digital-to-analog converter (MDAC), and its pioneering application in a grating light modulator. A ...prototype grating light modulator driven by a 6-bit MDAC has been fabricated using the polysilicon multiuser microelectromechanical systems processes, achieving a total stroke of 296 nm (full-scale output) and step size least significant bit (LSB) of 4.7 nm in a highly repeatable and stable manner. The grating light modulator demonstrated about 13-dB contrast ratio between maximum and minimum intensity of the zeroth diffraction order. The proposed mechanism can be configured for many promising applications including digital variable optical attenuators for optical fiber communications.
On-chip nanophotonic waveguide sensor is a promising solution for miniaturization and label-free detection of gas mixtures utilizing the absorption fingerprints in the mid-infrared (MIR) region. ...However, the quantitative detection and analysis of organic gas mixtures is still challenging and less reported due to the overlapping of the absorption spectrum. Here,an Artificial-Intelligence (AI) assisted waveguide "Photonic nose" is presented as an augmented sensing platform for gas mixture analysis in MIR. With the subwavelength grating cladding supported waveguide design and the help of machine learning algorithms, the MIR absorption spectrum of the binary organic gas mixture is distinguished from arbitrary mixing ratio and decomposed to the single-component spectra for concentration prediction. As a result, the classification of 93.57% for 19 mixing ratios is realized. In addition, the gas mixture spectrum decomposition and concentration prediction show an average root-mean-square error of 2.44 vol%. The work proves the potential for broader sensing and analytical capabilities of the MIR waveguide platform for multiple organic gas components toward MIR on-chip spectroscopy.
This paper presents an effective method to achieve multiwavelength collinear laser scanning using micromachined vibratory grating scanners, which have the potential to scan at high frequencies ...without the optical performance degradation resulting from dynamic nonrigid-body deformation. An optical simulation model has been developed to predict the scanning patterns of the vibratory grating scanners. The proposed multiwavelength collinear scanning method was studied both analytically with the optical simulation model and experimentally with a prototype device fabricated by the MUMPS polysilicon surface micromachining process. The experimental results agree very well with the simulation data. The prototype scanner demonstrated collinear scanning of 532 nm (green) and 632.8 nm (red) wavelengths laser beams and achieved an optical scan angle of 12.7 degrees with virtually bow-free scan-line at a resonant frequency of 9.9 kHz when driven by electrostatic comb-drive resonators with 60 V dc bias and 32 V pp ac voltages
In this paper, we present a design method for bi-layered composite gratings to achieve high diffraction efficiency. These composite gratings feature strong near-field coupling between their ...constituent dielectric subwavelength gratings, thus enabling high-efficiency first-order diffraction in the far-field. An intuitive explanation based on a wavevector matching condition for such high diffraction efficiency composite gratings is provided. According to theoretical analysis, a design strategy for the proposed composite gratings is developed and verified by numerical simulations with gratings working in both TE and TM modes. The proposed strategy could open door to develop bi-layered composite gratings for manipulating diffracted waves with high efficiency, thus may potentially enable new applications in photonic systems.
Edible vegetable oil is a necessity in people's daily diet, and its safety has attracted the attention of the government and consumers. In recent years, the safety incidents of edible vegetable oil ...are reported, and the safety problems of edible vegetable oil caused by chemical hazards such as benzopyrene, heavy metal and aflatoxin B1 are more serious. In this research, a risk assessment model through dietary exposure assessment and margin of exposure (MOE) were built to assess the health risks of benzopyrene, aflatoxin B1, and heavy metals in edible vegetable oils. And then an early warning model of food oil safety risk was established by using analytic hierarchy process (AHP) and back propagation (BP) neural network. According to the national standards and sampling data, the risk early warning model determined eight evaluation indexes of vegetable oil quality and safety, and calculated the risk value of chemical pollution in vegetable oil by Entropy Weight-Analytic Hierarchy Process(EW-AHP). The data of eight evaluation indexes were taken as the input of the model, and the comprehensive risk value was taken as the output of the model. The model learning process was carried out, and four algorithms, namely Support Vector Machine (SVM), Random Forest (RF), Radial Basis Function Neural Network (RBF) and Neural Network (BP), were selected for construction and comparison of model. The daily sampling data of chemical hazard factors in edible vegetable oil were quantified into specific chemical hazard risk levels. Thus the goal of predicting chemical hazard levels was achieved in edible vegetable oil. This study provides targeted reference suggestions for the safety supervision of edible vegetable oil, so as to improve the efficiency of supervision and ensure the consumption safety of edible vegetable oil.
•Quantitative risk assessment models for benzopyrene, aflatoxin-B1 and heavy metals in edible vegetable oils (EVO) in China.•Early warning model based on machine learning for EVO.•Analyses of exposure and health risk for EVO.
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