Long-Term Degradation Evaluation of the Mismatch of Sensitive Capacitance in MEMS Accelerometers.

During long-term use, MEMS accelerometers will experience degradation, such as bias and scale factor changes. Bias of MEMS capacitive accelerometers usually comes from the mismatch of parasitic capacitance and sensitive capacitance. This paper focuses on the mismatch of sensitive capacitance and analyzes the mechanism of long-term degradation of MEMS accelerometers. Firstly, the effect of sensitive capacitance mismatch on the performance of a MEMS accelerometer was investigated. Secondly, a method of measuring the mismatch of sensitive capacitance was proposed, and the validation experiment shows that the accuracy of this measurement can be less than 1.10×10−5 of the sensitive capacitance. For the samples in this experiment, the measurement error of this method can be less than 0.36 fF. Finally, a high-temperature acceleration experiment was performed. The mismatch of the sensitive capacitance during the experiment was monitored based on the proposed method, and the experimental results are analyzed. The experimental result demonstrates that the mismatch of sensitive capacitance varies linearly with time. The change rates of sensitive capacitance mismatch for the two samples are 2.95×10−7 C0/h and 2.66×10−7 C0/h in the high-temperature acceleration experiment at 145 °C, respectively. The change in sensitive capacitance mismatch seems small, but it is not to be ignored during long-term use. The rate of change is similar for the same batch of samples. This could imply that the adverse effects due to the mismatch of sensitive capacitance changes can be reduced by compensating for this variation.

Fabrication and Sensing Application of Phase Shifted Bragg Grating Sensors.

As a special kind of Bragg grating, phase-shifted fiber Bragg grating (PS-FBG) has attracted extensive attention because of its extremely narrow transmission window and excellent sensing performance. The main purpose of this manuscript is to discuss the PS-FBG with special sensing characteristics and explore the influence of different inscription technologies on the sensing characteristics of PS-FBG by comparing the existing inscription methods. The sensing characteristics, advantages and disadvantages of PS-FBG with different structures are analyzed.

Flexible and Precise Droplet Manipulation by a Laser-Induced Shape Temperature Field on a Lubricant-Infused Surface.

Light actuation on a lubricant-infused surface (LIS) has attracted great attention because of its flexibility and remote control of droplet motion. However, to actuate a droplet on a LIS flexibly and precisely by light, the key issue is to control two degrees of freedom of the droplet motion in real time. In this paper, we propose a C-shape temperature field (CSTF) induced by rapid and selective laser irradiation on a LIS. The CSTF could not only manipulate a single droplet precisely and flexibly but also process multiple droplets automatically and orderly in real time. The mechanism showed that the droplet was confined by the Marangoni force in two orthogonal directions. For single droplet manipulation, the CSTF had the capability of correcting the off-track droplet motion. Moreover, the droplet motion, including rectilinear motion and curvilinear motion, could be precisely and flexibly controlled by the motion of the CSTF. For manipulation of multiple droplets, coalescence of multiple droplets was successfully achieved by triple rotating CSTFs. Such a method was applied in the detection of 5 µL of bovine serum albumin (BSA) by triggering chromogenic reactions automatically and orderly, which improved the efficiency of the whole process. We believe that this method is a significant candidate for intelligent droplet manipulation.

Study on ablation threshold of fused silica by liquid-assisted femtosecond laser processing.

The femtosecond laser machining of fused silica in air and liquids is studied. The ablation threshold of fused silica is reduced from 2.22 to ${1.02}\;{{\rm J/cm}^2}$1.02J/cm2. In order to explore the ablation mechanism fabricated in a liquid medium, the absorption characteristics of water and alcohol are studied. It is found that alcohol could absorb more laser energy than water. By analyzing the variation trend of laser-induced electron density based on an ionization model, we find that alcohol requires lower laser energy to reach the electron density standard and form plasma than water and fused silica. Besides, we observe that a laser will induce bubbles in liquids after the formation of plasma, and the bubbles in alcohol will cause stronger impact pressure to the surface of fused silica than those in water. Therefore, the mechanism of threshold reduction should be owed to the assistance of liquids with different characteristics.

Substrate-independent, switchable bubble wettability surfaces induced by ultrasonic treatment.

Surfaces with switchable bubble wettability have attracted increasing interest due to their wide applications in the field of underwater drag reduction, gas collection and site water treatment. In this paper, a fast, simple and substrate-independent method that achieved reversible switching between underwater superaerophilicity and superaerophobicity on femtosecond laser induced superhydrophobic surfaces by alternative ultrasonic treatment in water and drying in air was reported. After laser processing, the as-prepared superhydrophobic surface showed underwater superaerophilicity due to the trapped air layer. In contrast, after ultrasonic treatment, the trapped air layer was removed and after being dipped into water again, the surfaces showed underwater superaerophobicity. The underwater superaerophobic surface easily recovered its superaerophilicity by drying the sample in air. Therefore, the as-prepared superhydrophobic surfaces could capture or repel air bubbles in water by selectively switching between underwater superaerophilicity and superaerophobicity. Furthermore, by combining hole processing and double side treatment, the sample allowed bubbles to pass through when the surface had underwater superaerophilicity and the sample intercepted the bubbles when the surface had underwater superaerophobicity. This switchable bubble wettability may provide an efficient route for gas bubble and water separation.

Enhancement of the Conductivity and Uniformity of Silver Nanowire Flexible Transparent Conductive Films by Femtosecond Laser-Induced Nanowelding.

In order to improve the performance of silver nanowire (AgNW) flexible transparent conductive films (FTCFs), including the conductivity, uniformity, and reliability, the welding of high repetition rate femtosecond (fs) laser is applied in this work. Fs laser irradiation can produce local enhancement of electric field, which induce melting at the gap of the AgNWs and enhance electrical conductivity of nanowire networks. The overall resistivity of the laser-welded AgNW FTCFs reduced significantly and the transparency changed slightly. Meanwhile, PET substrates were not damaged during the laser welding procedure in particular parameters. The AgNW FTCFs can achieve a nonuniformity factor of the sheet resistance as 4.6% at an average sheet resistance of 16.1 Ω/sq and transmittance of 91%. The laser-welded AgNW FTCFs also exhibited excellent reliability against mechanical bending over 10,000 cycles. The welding process may open up a new approach for improvement of FTCFs photoelectric property and can be applied in the fabrication of silver nanostructures for flexible optoelectronic and integration of functional devices.

Investigation on Eigenfrequency of a Cylindrical Shell Resonator under Resonator-Top Trimming Methods.

The eigenfrequency of a resonator plays a significant role in the operation of a cylindrical shell vibrating gyroscope, and trimming is aimed at eliminating the frequency split that is the difference of eigenfrequency between two work modes. In this paper, the effects on eigenfrequency under resonator-top trimming methods that trim the top of the resonator wall are investigated by simulation and experiments. Simulation results show that the eigenfrequency of the trimmed mode increases in the holes-trimming method, whereas it decreases in the grooves-trimming method. At the same time, the untrimmed modes decrease in both holes-trimming and grooves-trimming methods. Moreover, grooves-trimming is more efficient than holes-trimming, which indicates that grooves-trimming can be a primary trimming method, and holes-trimming can be a precision trimming method. The rigidity condition after grooves-trimming is also studied to explain the variation of eigenfrequency. A femtosecond laser is employed in the resonator trimming experiment by the precise ablation of the material. Experimental results are in agreement with the simulation results.