Wei Hu

Experimental study of laser dicing sapphire substrate by green DPSS laser

Sapphire is an important material for fabricating photonic devices such as light emitting diode (LED). The matter is strongly resistant to wet and dry chemical etching because of its unique physical property. Moreover, there also exist some problems like chipping and edge crack by diamond dicing. Thereby, lots of emerging laser-based techniques have been invented, including various lasers at different wavelength and different technologies, which have gradually become the alternative powerful and efficient methods to dicing this material. Most of investigations on laser dicing sapphire are conducted by UV and ultra-short pulse laser, few by green laser with wavelength of 532nm. So a green laser with wavelength of 532nm and high repetition frequency is employed to dice sapphire substrate. The effects of machining parameters as laser power, repetition frequency, scanning velocity and number of scans on kerf width, kerf depth and aspect ratio are analyzed. Kerf width and depth are measured by optical microscope (OM) and micro-morphology of sapphire is observed by scanning electron microscopy (SEM). Results indicate that narrower kerf, higher aspect ratio and better surface quality can be obtained under the combined processing parameters of medium laser power, lower repetition frequency, medium scanning velocity and multiple scans, which proves green laser to be an effective tool to dice sapphire substrate.

Ablation Threshold of Sapphire by Pulsed Green Laser in Nanosecond Regime

To establish the green laser ablation process more accurately, a detailed knowledge of the exact value of ablation threshold is of great importance. Therefore, the presented paper has investigated the single pulse ablation threshold using four different methods, namely, fitting method via diameter square, fitting method via depth, micro-topography method and the one-dimensional heat conduction model. Through this research, the well-defined threshold in term of laser fluence (J/cm2) is obtained, and the comparison among different methods casts a light on the effective way to determine the ablation threshold. Also, the underlying laser-material interaction mechanism is analyzed.

Development of MEMS component library with Modelica

For rapid modeling and simulation of MEMS, a MEMS component library consisting of beam, anchor, plate and gap is developed with Modelica. The hierarchy structure of this library are proposed. In order to show micro components structure, pin definitions, parameters and behaviors of mechanical beam are analyzed and then the lumped parameter beam is modeled based on object-oriented method with Modelica. Simulation results of a cantilever beam show accordance with FEA simulations, which indicates that this model can achieve precision, efficiency, reusability and extensibility.

Modeling and Simulation of Micro Hydraulic Transducer Based on Component Library

For MHT is an integrated system for different domains, namely fluids, structures, piezoelectrics and circuitry, a component library consisting of inlets, outlets, chambers and piezoelectric blocks is developed with Modelica. The governing equations of inlet and outlet channels, chamber and piezoelectric block are proposed and parameter models are created based on object-oriented method with Modelica. Then the model of MHT is established by connecting different components’ pins of equivalent type. Simulation results on Dymola show accordance with that on Simulink, which indicates that this method can achieve high efficiency and precision.

Study on the Modal Analysis of the Cleaning Mechanical Drive Axle Housing

A finite element method (FEM) is used to make the modal analysis of the drive axle housing, the first ten natural frequencies and modal shapes are obtained. The parameter identification method is applied to obtain the experimental modes. There is a great agreement with the calculating modes and the experimental ones, which proves that the finite element method is rational. According to the theoretical analysis, the main deformations are bending and torsion at both ends of the drive axle housing and the deformation of the middle part is relatively high. The natural frequencies are at middle and high frequencies which are close to the mesh frequencies of the drive axle gears. Therefore increasing the thickness and redesigning of stiffened palates are applied to avoid the resonance region effectively.

Influence of Beam Polarizations on Evaporative Laser Cutting Nonmetallic Materials within High Absorptance

The three dimensional (3D) coupling model is set up for analyzing the energy reflection and absorption on the kerf using ray tracing method after the laser beam cutting nonmetallic materials with high absorptance through multiple reflections. The laser beam characterized by focused gauss beam and fresnel absorption on the kerf are taken into account. The influences of the polarization on the absorbed intensity both in the front and the two walls are also discussed. Results indicate the differences of absorptive intensity among the three polarized lights are relatively small compared to metal. Thus, the polarization has little effects on the kerf of nonmetallic materials with high absorptance. The experimental results also agree well with the theoretical analysis.