Rehan Ahmed

ABSTRACT Tribomechanical properties of nanostructured coatings deposited by suspension high velocity oxy-fuel (S-HVOF) and conventional HVOF (Jet Kote) spraying were evaluated. Nanostructured S-HVOF coatings were obtained via ball milling of the agglomerated and sintered WC-12Co feedstock powder, which were deposited via an aqueous-based suspension using modified HVOF (TopGun) process. Microstructural evaluations of these hardmetal coatings included transmission electron microscopy, x-ray diffraction, and scanning electron microscopy equipped with energy dispersive x-ray spectroscopy. The nanohardness and modulus of the coated specimens were investigated using a diamond Berkovich nanoindenter. Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that low porosity coatings with nanostructured features were obtained. High carbon loss was observed, but coatings showed a high hardness up to 1000 HV2.9N. S-HVOF coatings also showed improved sliding wear and friction behavior, which were attributed to nanosized particles reducing ball wear in three-body abrasion and support of metal matrix due to uniform distribution of nanoparticles in the coating microstructure.

ABSTRACT Recent research trend of passive RFID based sensors has posed stringent low power requirement for energy efficient communication, which can be addressed by sub/near-Vt operation with standard CMOS process. This paper discusses new design challenges under scaled voltages and presents critical building blocks for low power protocol processing. Two supply viltages -0.45V and 0.7V are selected for powering digital and analog circuits which process EPC Gen-2 physical layer data. The design was fabricated in 180nm CMOS process and probe station measurement are reported.

ABSTRACT An antenna has been designed for use with a UHF band (902–928 MHz) RFID tag for implantation in live human brain tissue as the front end for a smart RFID. The COMSOL computational electromagnetic package was used for the design process. The COMSOL model was validated against the measurement of several test antennas when radiating into a bulk homogenous medium simulating human tissue. The proposed antenna is a 22 mm by 3.5 mm planar folded dipole consisting of a thin gold conductor (1 µm thick) placed on a dielectric substrate and coated with acrylic, giving a bio-compatible structure. The folded dipole dimensions are chosen to give an inductive input impedance that provides a good match to the capacitive load of the RFID tag when operating within brain tissue to maintain near optimal harvest efficiency.

Rolling contact fatigue performance of thermal spray coatings has been investigated using an experimental approach. A modified four ball machine which simulates a rolling element bearing was used to examine the coating performance and failure modes in a conventional steel ...

ABSTRACT Maintaining optimum circulation rates is important in aerated mud drilling operations. However, reliable predictions of the optimum rates require accurate modeling of the frictional pressure loss at bottom-hole conditions. This paper presents a mechanistic model for underbalanced drilling with aerated muds. Extensive experiments in a unique field-scale high pressure and high temperature flow loop were performed to verify the predictions of the model. This flow loop has a 150x89 mm(2) (6(')x3.5(')) horizontal annular geometry and is 22 m long. In the experiments, cuttings were introduced at a rate of 7.5 kg/min, representing a penetration rate of 15 m/h in the annular test section. The liquid phase flow rates were in the range of 0.30-0.57 m(3)/min, representing superficial liquid velocities in the range of 0.47-0.90 m/s. The gas liquid ratio (gas volume fraction under in situ condition) was varied from 0.0 to 0.38. Test pressures and temperatures ranged from 1.28 to 3.45 MPa, and 27 degrees C to 80 degrees C, respectively. Gas liquid ratios were chosen to simulate practical gas liquid ratios under downhole conditions. For all the test runs, pressure drop and cuttings bed height over the entire annular section were measured. Flow patterns were identified by visual observations through a view port. The hydraulic model determines the flow pattern and predicts frictional pressure losses in a horizontal concentric annulus. The influences of the gas liquid ratio and other flow parameters on the frictional pressure loss are analyzed using this model. Comparisons between the model predictions and experimental measurements show a satisfactory agreement. The present model is useful for the design of underbalanced drilling applications in a horizontal wellbore.

ABSTRACT Tribomechanical properties of nanostructured coatings deposited by suspension high velocity oxy-fuel (S-HVOF) and conventional HVOF (Jet Kote) spraying were evaluated. Nanostructured S-HVOF coatings were obtained via ball milling of the agglomerated and sintered WC-12Co feedstock powder, which were deposited via an aqueous-based suspension using modified HVOF (TopGun) process. Microstructural evaluations of these hardmetal coatings included transmission electron microscopy, x-ray diffraction, and scanning electron microscopy equipped with energy dispersive x-ray spectroscopy. The nanohardness and modulus of the coated specimens were investigated using a diamond Berkovich nanoindenter. Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that low porosity coatings with nanostructured features were obtained. High carbon loss was observed, but coatings showed a high hardness up to 1000 HV2.9N. S-HVOF coatings also showed improved sliding wear and friction behavior, which were attributed to nanosized particles reducing ball wear in three-body abrasion and support of metal matrix due to uniform distribution of nanoparticles in the coating microstructure.