Electrochemical micromachining (ECMM) is a well-known advanced machining process for fabrication of micro components such as tools, nozzles, mixers, etc. on electrically conductive workpieces. In the present work, experiments are conducted for fabrication of micro tools and micro patterns on the in-house developed and fabricated electrochemical micromachining setup. Effect of various process parameters such as voltage, interelectrode gap, machining time, duty cycle, and electrolyte concentration are studied on micro tools and over potential (in case of fabrication of micro patterns). It is observed that the average change in diameter of the micro tool after the ECMM process increases almost linearly with increase in voltage and time, and increases quadratically with increase in pulse duty ratio and electrolyte concentration. Overpotential increases with increase in applied voltage, interelectrode gap, and duty cycle. Further, overpotential initially decreases quadratically with increase in electrolyte concentration and then increases.

We consider a multi-pair two-way amplify-andforward massive multi-input multi-output (MIMO) hybrid relay with MIMO user-pairs. A hybrid relay has lesser number of radio frequency (RF) chains than the antennas, which significantly reduces the implementation cost. We employ block-diagonalizationbased baseband processing at the hybrid relay to cancel the inter user-pair interference and equal-gain-combining-based RF processing to maximize the beamforming gain. We also use an algebraic norm maximizing relay transmit strategy to maximize the spectral efficiency (SE) of each user-pair. We numerically show that the proposed hybrid relay has only marginally inferior SE than a full RF-chain relay.

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