851 resultados para Radio frequency identification


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"17 February 1961."

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Mode of access: Internet.

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The manufacture of a radio frequency filter box using high pressure die casting (HPDC) is compared to the traditional high speed machining route. This paper describes an industrial exercise that concluded HPDC to be an economical and appropriate method to produce larger volumes of thin-walled telecommunications components. Modifications to the component design were made to make the component suitable for the HPDC process. Development of the die design through simulation modelling is described. The wrought alloy was replaced by near-eutectic Al-Si die casting alloy that was found to give better temperature stability performance. Apart from the economic benefits, HPDC was found to give lower filter efficiency losses through better surface finish. The effects of HPDC process variables, such as intensification pressure and injection piston velocity, on component quality, particularly porosity levels, were investigated. The pressure was analysed in terms of HPDC machine set pressure and the pressure measured in the die cavity by pressure sensors. Porosity was found to decrease with increased pressure and slightly increase with higher casting velocities.

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The following thesis describes the computer modelling of radio frequency capacitively coupled methane/hydrogen plasmas and the consequences for the reactive ion etching of (100) GaAs surfaces. In addition a range of etching experiments was undertaken over a matrix of pressure, power and methane concentration. The resulting surfaces were investigated using X-ray photoelectron spectroscopy and the results were discussed in terms of physical and chemical models of particle/surface interactions in addition to the predictions for energies, angles and relative fluxes to the substrate of the various plasma species. The model consisted of a Monte Carlo code which followed electrons and ions through the plasma and sheath potentials whilst taking account of collisions with background neutral gas molecules. The ionisation profile output from the electron module was used as input for the ionic module. Momentum scattering interactions of ions with gas molecules were investigated via different models and compared against results given by quantum mechanical code. The interactions were treated as central potential scattering events and the resulting neutral cascades were followed. The resulting predictions for ion energies at the cathode compared well to experimental ion energy distributions and this verified the particular form of the electrical potentials used and their applicability in the particular geometry plasma cell used in the etching experiments. The final code was used to investigate the effect of external plasma parameters on the mass distribution, energy and angles of all species impingent on the electrodes. Comparisons of electron energies in the plasma also agreed favourably with measurements made using a Langmuir electric probe. The surface analysis showed the surfaces all to be depleted in arsenic due to its preferential removal and the resultant Ga:As ratio in the surface was found to be directly linked to the etch rate. The etch rate was determined by the methane flux which was predicted by the code.

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We propose a new approach to the generation of an alphabet for secret key exchange relying on small variations in the cavity length of an ultra-long fiber laser. This new concept is supported by experimental results showing how the radio-frequency spectrum of the laser can be exploited as a carrier to exchange information. The test bench for our proof of principle is a 50 km-long fiber laser linking two users, Alice and Bob, where each user can randomly add an extra 1 km-long segment of fiber. The choice of laser length is driven by two independent random binary values, which makes such length become itself a random variable. The security of key exchange is ensured whenever the two independent random choices lead to the same laser length and, hence, to the same free spectral range.