Papers by Author: Xiao Ping Li

Abstract: Currently, deep brain stimulation (DBS) is one of the most effective surgical treatments of treating serious stubborn resistance movement disorders (such as Parkinson's disease, essential tremor and dystonia, etc.). The nerve probe has been greatly favored by the authorities and scientists with the respect to the role it acted as the main brain stimulation tool. This article mainly introduces the materials of brain stimulated micro-electrode, the matched specifications and the evaluation on the compound functions in the developing course. The application prosperity and its development trendy will also be included with the intention to help people gain more systematic acknowledgement on the electrodes for deep brain stimulation.

Abstract: Deep brain stimulation (DBS) is increasingly used in clinical treatment for various neurological disorders, particularly for movement disorders such as Parkinsons disease. The more the accuracy of locating the cerebral target of these diseases is, the more cure effect is, the accuracy of locating the cerebral target depends on the all surgery system. Although there have many surgery systems, for more accuracy of those locating target based on CT images, it need to develop a new kind of robotic surgery system. Some requirements of this robotic system are present in this paper, such as the movement degrees of freedom and its dimension error. Each functional sub-system of this robotic surgery system with some constraint condition is also analyzed. When all of those sytem are implemented with more precise location, predictability, reliability, and robustness sufficient for trial evaluation in stereotactic biopsy of brain lesions, the robotic surgery system can be used in clinical application.

Abstract: Magnetic sensors are widely used in areas such as high-density magnetic recording, navigation, military and security, target detection and tracking, anti-theft systems, non-destructive testing, magnetic marking and labeling, geomagnetic measurements, space research, measurements of magnetic fields onboard spacecraft and biomagnetic measurements in the body ¹. For magnetic sensors used to detect weak magnetic fields, a highly sensitive sensing element, with extremely high permeability, is needed. Permalloy is useful due to its initial high permeability and near-zero magnetostriction. Current fabrication methods used to produce these sensing elements include sputtering, electroplating, cold drawing and wet etching. Laser ablation, however, has always not been seriously considered due to domain pinning effects induced by nanosecond lasers². Femtosecond laser machining, on the other hand, has shown great potential in processing such soft magnetic materials without affecting its permeability. In fact, Jia et al. had observed that when femtosecond laser micromachining was carried out on FINEMET, the amorphous phase was observed to remain in the damaged zone and few crystallization was found in the ablation zone³.

Abstract: Owing to its various distinct advantages over the other machining technologies, abrasive jet machining has become a promising machining technology for brittle and hard-to-machine materials. An experimental study is presented on the micro-grooving of quartz crystals using an abrasive airjet. The effect of the various process parameters on the major machining performance measures are analysed to provide a deep understanding of this micro-machining process. Predictive models are then developed for quantitatively estimating the machining performance. The models are finally verified by an experiment. It shows that the model predictions are in good agreement with the experimental results under the corresponding conditions.

Abstract: The mechanical properties of Potassium Dihydrogen Phosphate (KDP) crystal had been relatively well investigated, and it was reported that mechanical properties of KDP crystal are anisotropic corresponding to crystallography orientation. However, the affect of the crystallography orientation to the critical undeformed chip thickness and cutting force variation in ductile mode cutting of KDP crystal are still not clear, which are important in determining proper cutting parameters to get fine finished surface. This paper investigates the influence of crystallographic orientation to critical undeformed chip thickness by a kind of groove cutting on {001} plane, and the influence to cutting force is also researched by face turning. The experiment results demonstrate that the cutting forces and critical undeformed chip thickness for ductile mode cutting varies greatly according to KDP crystallographic orientation. This paper point out that two slipping plane, {110} and {1__,10}, account for the variation of cutting force and critical undeformed chip thickness in different orientation on {001} plane. A set of cutting parameters for ductile mode cutting are selected based on the derived critical undeformed chip thicknesses at different crystal orientations, and overall sooth surface has been achieved on face turned {001} surface, which the roughness is Ra 2.6nm measured by Veeco white-light interferometer.

Abstract: Microgroove processes are carried out on Potassium Dihydrogen Phosphate (KDP) crystals of different crystalline orientation using diamond tool, the speed of groove is very low in order to avoid the influence of temperature. The main process characteristics are examined including the groove geometry, cutting forces and critical underformed chip thickness at the onset of ductile-to-brittle cutting transition. Additionally, the cutting pressure is calculated from the cutting force and grooving geometry. The experimental results show that as the groove depth increase, the groove geometry clearly revealed that ductile-to-brittle cutting transition occurred, and the transition are well reflected by changing in the cutting pressure. Further, it is shown that the critical undeformed chip thickness varies greatly with the workpiece KDP crystalline orientation.

Abstract: Potassium Dihydrogen Phosphate (KDP) crystals are used for the key components in high power density solid-state laser for Inertial Confinement Fusion. KDP crystals are mainly machined in the dry cutting condition to avoid ‘Fogging’ of the crystals. The main difficulty identified in dry machining of KDP is chip removal from the machined surface. A vacuum sucking device based on venturi vacuum pump is used to suck the chips during cutting, and the relationship between level of vacuum in cutting zone and the comply air pressure was established. An empirical model for chip emission during turning processes is used to analyze the influence of cutting parameters on the chip emission. The influence of cutting parameters on the removal of chips is investigated. Finally, a face turning of KDP crystals is carried out with the turning parameters of feed rate 1um/rev, depth of cut of 0.8 um/rev and the cutting speed from 1.82m/s to 3.9m/s. A super-smooth surface with chips free in the whole sample is achieved, having the surface roughness of 2.994nm (Ra) measured by AFM. The surface quality achieved satisfies the requirements of KDP crystals implemented in high power lasers.

Abstract: In order to develop high sensitivity micro sensors for bio-magnetic field using NiFe electroplated composite sensing elements, it is important to study how different plating processes can affect the magnetic properties in terms of the chemical composition and magnetic structure of the plated layer. In this study, to study the effect of the magnetic field on the magnetic structure of the electroplated NiFe layers, magnetic controlled plating in which a longitudinal magnetic field ranging from 0 to 400 Oe is applied during nanocrystalline electroplating of permalloy Ni80Fe20 layer of 2 µm thick onto a 20 µm diameter Cu wire. The magnetic structure of the plated layers is studied by investigating the Giant magneto-impedance (GMI) effect of the plated layer. GMI has been measured from a frequency range of 100 kHz to 50 MHz. It is observed that under conventional electroplating without an external magnetic controlling field, the anisotropy of the plated layer is generally circumferential as indicted by the double peaks of the MI curves in testing at high frequency. When a longitudinal magnetic field is applied during electroplating, the plated layer shows single peak MI curves, suggesting that the anisotropy is changed from circumferential to longitudinal. The results also show that the sensitivity and resolution of a magnetic field sensor is improved greatly by changing the anisotropy of the plated layer from circumferential to longitudinal.

Abstract: For the purpose of developing a composite micro sensor for weak magnetic field, fabrication of high permeability ferromagnetic material is needed. The magnetic properties of the pulse-plated samples depend greatly on the chemical composition and nanocrystalline grain size of the ferromagnetic layer. In this study, the effect of the pulse plating parameter: duty cycle on the chemical composition and grain size of the deposited layer was investigated. A layer of soft ferromagnetic material Ni-Fe was deposited onto copper wires of 20µm diameter by means of pulse and dc plating and tested under XRD for grain size measurement. It was found that variations in duty cycle do not affect the thickness of the plated layer, but affect significantly the chemical composition. There is an optimum duty cycle for getting the minimum grain size of plated layer in pulse plating with saccharin. The results from the magnetic measurement showed that the permeability of the plated material increased greatly as the grain size decreased in the range of 10 – 55 nm.