Influence of Thermal Annealing on Mechanical and Optical Property of SiO2 Film Produced by ALD.

The application range of fused silica optical components can be expanded and the cost of fused silica components can be reduced by depositing the same material film on fused silica substrate. However, due to the different manufacturing process, the performance of ALD SiO2 film is lower than that of fused silica substrate, which also limits the use of this process. In this paper, ALD SiO2 film with different thicknesses were deposited, and then the structure and properties were tested. Finally, the ALD SiO2 film was treated via the annealing process. Transmission electron microscopy (TEM) showed that the ALD SiO2 film had good compactness and substrate adhesion. The Raman spectra showed that the ALD SiO2 film and substrate had the same structure, with only slight differences. The XRD pattern showed that ALD-fused silica did not crystallize before or after annealing. The infrared spectra showed that there was an obvious Si-OH defect in the ALD SiO2 film. The laser damage showed that the ALD SiO2 film had a much lower damage threshold than the fused silica substrate. The nanoindentation showed that the mechanical properties of the ALD SiO2 film were much lower than those of the fused silica substrate. After a low-temperature annealing treatment, the ALD SiO2 film Si-OH defect was reduced, the ALD SiO2 film four-member ring content was increased, the elastic modulus of the ALD SiO2 film was increased from 45.025 GPa to 68.025 GPa, the hardness was increased from 5.240 GPa to 9.528 GPa, and the ALD SiO2 film damage threshold was decreased from 5.5 J/cm2 to 1.3 J/cm2.

Towards understanding the cutting temperature in ultrasonic vibration-assisted drilling based on the dynamic contact characteristics between the cutting edge and workpiece.

Compared with conventional drilling (CD), ultrasonic vibration-assisted drilling(UVAD) is experimentally proven a promising method to reduce the cutting temperature. But sometimes cutting temperature also becomes higher in UVAD than in CD. To further make clear the cutting temperature mechanisms in UVAD, this study aims to study the effect of tool's ultrasonic vibration on the cutting heat generation and heat dissipation at a relatively micro level. Firstly, drilling experiments are designed to explore the variations of cutting heat under different ultrasonic vibrations. Then, to analyze the influence of ultrasonic vibration on the cutting heat theoretically, a kinematic model is developed to describe the dynamic contact between the cutting edge and workpiece in UVAD. Besides, a cutting heat analysis model based on the contact characteristics in UVAD is proposed to study and compare the variations of cutting heat generation. The effect of ultrasonic vibration on the cutting heat generation, heat dispassion, and the resultant cutting temperature under different machining in UVAD conditions are discussed. It is indicated from the theoretical analysis that more cutting heat tends to be produced due to the significantly increased sliding velocity on the cutting edge-workpiece interface when the ultrasonic vibration is applied. The analysis agrees with the experimental results that the cutting temperature in dry UVAD is higher than in dry CD. But on the other hand, ultrasonic vibration can also improve the lubrication and cooling effect under appropriate machining conditions, which is beneficial to the reduction in cutting temperature. The investigation shows the multifaceted influences of ultrasonic vibration on the cutting temperature in the drilling process in detail, which provides a reference for UVAD parameter optimization.

Regulation of Bacterial Biofilm Formation by Ultrasound: Role of Autoinducer-2 and Finite-Element Analysis of Acoustic Streaming.

OBJECTIVE: The formation of bacterial biofilm regulated by quorum sensing (QS) is a critical factor that contributes to infections of indwelling medical devices. Autoinducer-2 (AI-2), as a signal molecule in QS, plays a crucial role in mediating bacterial signaling and regulating their biological behavior. This study investigated the impact of ultrasonic vibration at varying frequencies on biofilm formation in a mixture of Staphylococcus aureus and Escherichia coli. METHODS: By exciting ultrasound at different frequencies (20, 100 and 200 kHz), a vibration with an amplitude of 100 nm was generated on the material surface located at the bottom of the petri dish containing mixed bacteria. We measured the content of AI-2 and bacteria in the mixed bacterial solution and bioburden on material surfaces at different time points during culture. In addition, the relationships among AI-2 content, bacterial concentration and distribution were assessed through finite-element analysis of acoustic streaming under ultrasonic vibration. RESULTS: The AI-2 gradient is influenced by the diversity of acoustic streaming patterns on the material surface and in the mixed bacterial solution caused by ultrasonic vibration at different frequencies, thereby regulating biofilm formation. The experimental results showed that the optimal inhibition effect on AI-2 and minimal bacterial adhesion degree was achieved when applying an ultrasonic frequency of 100 kHz with a power intensity of 46.1 mW/cm2 under an amplitude of 100 nm. CONCLUSION: Ultrasound can affect the QS system of bacteria, leading to alterations in their biological behavior. Different species of bacteria exhibit varying degrees of chemotaxis toward different frequencies.

The Design and Evaluation of a High-Speed Jet Dispenser Driven by Single Piezoelectric Stack.

Droplet injection methods are widely used in the applications of microelectronic manufacturing, biological engineering, and 3-D printing. This work presents a new jet dispenser driven by a single piezoelectric stack that enables the capability of drop-on-demand patterning under a high working frequency (500 Hz). Due to the special designs of the jet dispenser, a broad range of liquids, whose viscosities span more than four orders of magnitude (21-665 320 cps), can be jetted. Moreover, a coupled Coulomb damping physical model is proposed, which includes an electromechanical and a dynamic model. Both the Coulomb and the fluid-solid damping are considered in the dynamic model. In order to validate the results obtained by using MATLAB/Simulink, the experiments were carried out. The injection performance of this jet dispenser has been tested by employing a self-made jetting platform. The minimum volume of a jetting droplet is about 14.4 nL with liquid wax. The error of volume uniformity among droplets does not exceed 8%, and the error of angle trajectory is about 0.17°. Furthermore, the versatility of the jet dispenser is demonstrated by printing liquid lubricant, food, glue, silver past, and a ceramic slurry in predefined patterns.

Ultrasonic micro-motor with multilayer piezoelectric ceramic and chamfered driving tips.

In this study, an oblate-type ultrasonic micro-motor with multilayer piezoelectric ceramic and chamfered driving tips was proposed and experimentally researched. The micro-motor works based on the standing-wave principle and has a higher rotary speed than the traditional standing-wave one in principle, reaching a rotary speed of 2100 r/min in this study at the voltage of 20 Vp-p. When the micro-motor rotates, single phase alternating current is required, namely, V=Asinωt, and exchanging the signal wire and ground wire will not change the rotary direction of the motor, which reinforces the safety and the compaction of this motor. The ratio of the maximum displacement value of the speed feeding direction and the preload direction is approximately 4, showing a characteristic of high speed and low ability to load.

Development of an ultrasonic linear motor with ultra-positioning capability and four driving feet.

This paper presents a novel linear piezoelectric motor which is suitable for rapid ultra-precision positioning. The finite element analysis (FEA) was applied for optimal design and further analysis, then experiments were conducted to investigate its performance. By changing the input signal, the proposed motor was found capable of working in the fast driving mode as well as in the precision positioning mode. When working in the fast driving mode, the motor acts as an ultrasonic motor with maximum no-load speed up to 181.2mm/s and maximum thrust of 1.7N at 200Vp-p. Also, when working in precision positioning mode, the motor can be regarded as a flexible hinge piezoelectric actuator with arbitrary motion in the range of 8µm. The measurable minimum output displacement was found to be 0.08µm, but theoretically, can be even smaller. More importantly, the motor can be quickly and accurately positioned in a large stroke.

A screw-thread-type ultrasonic actuator based on a Langevin piezoelectric vibrator.

A novel screw-thread-type ultrasonic actuator based on a Langevin piezoelectric vibrator, with an assembly comprised a threaded shaft, is presented. The bolt-clamped Langevin vibrator consists of 4 chips of PZT ceramics and generates more energy with a certain input power. The threads of the stator multiply the linear force and position resolution, and the threaded rod is rotated directly to achieve linear movement without additional mechanical conversion. The actuator was designed and optimized using the Finite Element Method (FEM), and a prototype was fabricated. At 300 Vp-p, the maximum thrust force, velocity, and efficiency were approximately 4.2 N, 9.5 mm s(-1), and 5.6%, respectively.