Compact low-power time-based conversion with noise immunity similar to digital conversion

An analog signal representation based on the inter-pulse-interval (IPI) time is presented. Voltage-to-IPI and IPI-to-voltage conversion circuits based on the representation are described. The circuits have been fabricated using a 0.35 μm mixed-signal CMOS process. Simulation and test results agree with the theory. Voltage-to-IPI conversion needs significantly less area and power than ADC and is significantly more immune to noise and other problems than using analog voltage/current signals.     

Passivity-based control of saturated induction motors

A passivity-based controller, which takes into account saturation of the magnetic material in the main flux path of the induction motor, is developed to provide close tracking of time-varying speed and flux trajectories in the high magnetic saturation regions. The proposed passivity based controller is experimentally verified. Also, a comparison between the controllers based on the saturated and nonsaturated magnetics is presented to demonstrate the benefit of the controller based on the saturated magnetics     

New approach to gas pressure profile prediction for high temperature AA5083 sheet forming

A new theoretical approach to the prediction of gas pressure profiles that vary smoothly with time in high temperature forming of fine-grained AA5083 sheet is presented. The required pressure-flow stress relationship, which couples the gas pressure profile and the material constitutive model, was implemented in ABAQUS implicit. Forming of a rectangular pan in a die with variable entry radii was simulated with a single creep mechanism model that accounts for hardening/softening in AA5083. Predicted sheet thickness and thinning in a die entry radius region at the end of forming are examined in detail. Results are compared with those from two additional gas pressure schemes. One of these is taken directly from experiments and the other is based upon an algorithm that is internal to ABAQUS. The effect of friction on forming time is explored in the absence of a stability criterion for necking.     

Magnetic alignment of cellulose nanowhiskers in an all-cellulose composite

Unidirectional reinforced nanocomposite paper was fabricated from cellulose nanowhiskers and wood pulp under an externally applied magnetic field. A 1.2 Tesla magnetic field was applied in order to align the nanowhiskers in the pulp as it was being formed into a sheet of paper. The magnetic alignment was driven by the characteristic negative diamagnetic anisotropy of the cellulose nanowhiskers. ESEM micrographs demonstrated unidirectional alignment of the nanowhiskers in the all-cellulose composite paper. Comparing with control paper sheets made from wood pulp only, the storage modulus in the all-cellulose nanocomposites increased dramatically. The storage modulus along the direction perpendicular to the magnetic field was much stronger than that parallel to the magnetic field. This new nanocomposite, which contains preferentially oriented microstructures and has improved mechanical properties, demonstrates the possibility of expanding the functionality of paper products and constitutes a promising alternative to hydrocarbon based materials and fibers.     

An Initial Model for Control of a Tandem Hot Metal Strip Rolling Process

The tandem rolling of hot metal strip presents a significant control challenge because of nonlinearities and process complexities. The challenge is heightened by an extremely hostile environment that precludes the location of sensors to measure process variables that are important for control. In addition, it is essential that the controller structure allows for a high degree of physical intuition in the design process and provides for simplicity of tuning during commissioning. Based on our previous work using a state-dependent Riccati equation (SDRE) technique for control of the tandem cold rolling process, it is considered that a similar method might also be useful as a basis for the development of a control technique for tandem hot strip rolling. For the hot rolling process, the development of a process model in a form that is suitable for use with a SDRE-based method is a significant and challenging task. This paper describes our work to develop an initial model for this process. Based on simulation results, it is determined that this initial model has the potential to be the basis for the development of the complete nonlinear model that can be used for development of a viable control method which offers the likelihood for improvement in the control of the hot metal rolling process.      

On the gas pressure forming of aluminium foam sandwich panels: Experiments and numerical simulations

Forming of light-weight highly stiff aluminium foam sandwich (AFS) panels into complex 3D components would mark a development in the manufacturing of these materials. In this work, gas pressure forming of AFS panels is investigated experimentally and using numerical simulations. Deformation behaviour of AFS panels is studied during high-temperature uniaxial tension and compression, and constitutive models are developed and incorporated into FE simulations of the gas pressure forming process. Simulation results and experimental observations show reasonable agreement and demonstrate the possibility of forming AFS panels to significant deformations while maintaining considerable core porosity.     

A model for improved solar irradiation measurement at low flux

Accurate measurement of solar radiation heat flux is important in characterizing the performance of CSP plants. Thermopile type Heat Flux Sensors (HFSs) are usually used for this purpose. These sensors are typically reasonably accurate at high heat fluxes. However measurement accuracy drops significantly as the measured radiation is below 1 kW/m², this often leads to underestimation of the actual flux. At the Masdar Institute Beam Down Solar Thermal Concentrator (BDSTC), measurement of fluxes ranging from 0 kW/m² to more than 100 kW/m² is required. To improve the accuracy of the sensors in the lower range around 1 kW/m², we have performed a test under ambient (not-concentrated) sunlight. Such low irradiation levels are experienced in characterizing the concentration quality of individual heliostats. It was found during the test that the measurement at this low range is significantly affected by ambient conditions and transients in the HFS cooling water temperature. A Root Mean Square Error (RMSE) of more than 100 W/m² was observed even though we kept the transients in water temperature to a minimum. Hence we devised a model to account for this measurement error at this flux range. Using the proposed model decreased the RMSE to less than 10 W/m². The application of the model on existing heat flux measurement installations is facilitated by the fact that it only employs easily measurable variables. This model was checked by using a test data set and the results were in good agreement with the training data set.     

MAC Protocol for Opportunistic Cognitive Radio Networks with Soft Guarantees

Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closed-form expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CR network (CRN).