Integral And Fractional Over Sampling Techniques For Reduction Of Jitter Noise Power In High Speed Ofdm System

摘要

There are various techniques which can be used for the manufacture of microproducts, micro electromechanical systems (MEMS) based manufacturing .Broadly these techniques are photolithography, chemical etching, plating, laser fabrication. Micro machining may be seen as an ultra precision material removal process and by this process it is able to achieve micro form accuracy and nanometers finish. There are still some challenging issues to be addressed from precision machining to micro machining. To achieve3 D micro components mechanical micro machining is not the suitable technique. Electro physical and chemical micro machining processes play an important role in micromachining due to their special materials removal mechanisms. Electrical discharge machining (EDM) is especially suitable for manufacturing micro components due to its thermal material removal mechanisms. High precision micro EDM can process functional materials like hardened steel, cemented carbide and electrically conductive ceramics with sub micron precision. It applications are far beyond dies, moulds fabrication such as micro gears, micro fluidic devices medical implants. In this tool electrodes are miniaturized compared to conventional EDM. Discharge energy is also minimized and by this a very small material removal at one single discharge is made possible and hence extremely small gap width 1.5 to 5 μm holes are made possible. High surface roughness, relatively poor fatigue properties, difficult to make sharp corners etc will be the negative features during the micro manufacturing. For precision manufacturing a pulsed power of relatively short duration has to be used. Development of hybrid processes seem now another focus for micro/ nano manufacturing related research. Micro EDM and laser assembly were combined to fabricate 3 D metal micro structures. Combining ECM and EDM the so called hybrid ECM-EDM is another example of improving material processing efficiency, Electro photochemical machining is a hybrid of photo chemical machining and electro chemical machining. This technique has been attempted first time by the present authors is a unique one. It is essentially a non traditional machining in which the removal of metal is accomplished by electrochemical reactions. The desired pattern to be etched on the surface is formed by photo lithography technique. This includes cleaning of the sample, the preparation of the photographic mask, and application of the photo resist on the work piece and the generation of pattern to be etched on the piece on exposure to suitable UV radiations. This method is thus used to cover the work piece with the mask in such a way that only the portions to be etched remain exposed. The etching is done by electro polishing. This is an electrolytic method in which the metal removal is achieved by electrochemical dissolution of anodically polarized work piece. The principle is the reverse of electro plating. In addition to etching it is possible to get good surface finish. Thus this method is popular for the production of complex configurations in thin materials and for production of delicate parts that could be easily damaged by the forces of conventional cutting tools. This method is also applied for high strength and high resistant alloys and materials that are difficult to cut by the conventional methods. The details of the process are discussed in the paper