Low-Cost Specification Based Testing of RF Amplifier Circuits using Oscillation Principles

In this paper, we propose a low-cost approach for testing GHz RF amplifiers. It is demonstrated for the first time that GHz RF amplifiers can be tested for their specifications using oscillation principles. In the test mode, the RF test signal is “self generated” by the amplifier with the help of additional external circuitry which forces the amplifier to oscillate (Barkhausen criterion) around its characteristic frequency. The RF sinusoidal output from the oscillating RF amplifier is down-converted to a lower frequency enabling low frequency test response analysis as well as increased sensitivity to parametric deviations. In addition to the detection of catastrophic failures, it is shown that multiple RF specifications (Gain, P1dB, and Noise Figure) can be predicted via analysis of the frequency of the down-converted response. To account for RF parasitics on the production floor, a calibration technique is proposed in the test-setup. Thus, the proposed method reduces test cost significantly by reducing the cost of test setup (by as much as 80%) and significantly reducing test time. The viability of the proposed test method is demonstrated both by simulation experiments and measurement.     

Microfabricated Silicon High-Frequency Waveguide Couplers and Antennas

A method has been developed to fabricate waveguide-to-waveguide couplers and tapered dielectric rod antennas for the millimeter-wave regime from microetched silicon. A proof-of-concept study shows that the structures can be realized using relatively simple wet etching and robotic process control. Experimental measurements of the waveguide-waveguide couplers agree in key features with simulations. The results indicate that two-stepped tapers perform nearly as well as smooth linear tapers, but are much easier to fabricate. Coupling transmissivity of better than -1 dB, and peak antenna gain of 8-10 dB are indicated at W-band frequencies. Lateral dimension etch control of 5-mum precision was realized. To solve a challenge of controlling the length of the first step, either an improved masking method or a switch to dry etching processes is required.     

A repair operator for the preliminary design of a composite structure using genetic algorithms

This paper deals with the preliminary design of a composite structure where the design variables are the thicknesses and the percentages of fiber orientations in the zones of the structure. In this paper, we propose to include the design and manufacturing rules in the preliminary design. A stacking sequence generator is used to compute admissible stacking sequences with respect to these rules and which correspond to the design variables. Given that an admissible stacking sequence does not exist for every set of values of the design variables, a repair operator is proposed to cope with this problem. It aims at changing the values of the percentages of the fiber orientations in order to guarantee the existence of admissible stacking sequences with respect to the manufacturing rules. The repair operator is integrated into an optimization loop which uses a genetic algorithm to perform the preliminary design of a composite structure. Its efficiency is shown with a test case which involves a large number of fiber orientations and stacking sequences.     

Modeling of pH process using wavenet based Hammerstein model

This paper outlines an approach for developing a Hammerstein model for nonlinear dynamic systems. The nonlinearity is sought to be captured through functional approximation using wavelets cast in a wavenet structure. Nonlinear block of wavenet at input side is cascaded with a linear dynamic block described by a state space model. A sequential approach is used for development of static nonlinear and linear dynamic parts of the model. Configuration and parameters of the nonlinear wavenet structure are determined from near steady state data extracted from dynamic test data while the state space model parameters of the linear dynamic part are obtained using a subspace identification approach. This approach has been applied for modeling a strongly nonlinear pH process operated over a wide range of operating conditions.     

Combining scanning tunneling microscopy and synchrotron radiation for high-resolution imaging and spectroscopy with chemical, electronic, and magnetic contrast

The combination of high-brilliance synchrotron radiation with scanning tunneling microscopy opens the path to high-resolution imaging with chemical, electronic, and magnetic contrast. Here, the design and experimental results of an in-situ synchrotron enhanced x-ray scanning tunneling microscope (SXSTM) system are presented. The system is designed to allow monochromatic synchrotron radiation to enter the chamber, illuminating the sample with x-ray radiation, while an insulator-coated tip (metallic tip apex open for tunneling, electron collection) is scanned over the surface. A unique feature of the SXSTM is the STM mount assembly, designed with a two free-flex pivot, providing an angular degree of freedom for the alignment of the tip and sample with respect to the incoming x-ray beam. The system designed successfully demonstrates the ability to resolve atomic-scale corrugations. In addition, experiments with synchrotron x-ray radiation validate the SXSTM system as an accurate analysis technique for the study of local magnetic and chemical properties on sample surfaces. The SXSTM system's capabilities have the potential to broaden and deepen the general understanding of surface phenomena by adding elemental contrast to the high-resolution of STM.     

Peroxomonosulphate, an efficient oxidant for the photocatalysed degradation of a textile dye, acid red 88

Visible light-assisted degradation of a mono azo textile dye acid red 88 (AR88) was carried out in presence of titanium dioxide photocatalyst. Various operational parameters such as variation of the initial dye concentration, photocatalyst and pH on the photocatalytic degradation rate were studied. Effect of the amount of oxidants such as peroxomonosulphate (PMS) and peroxodisulphate (PDS) and the ratio of concentration of oxidant to the concentration of dye (C_oxidant/C_dye) on the photocatalysed degradation rate were also investigated. Though the rate of photodegradation of the dye decreased with increase in dye concentration, the rate increased with C_oxidant/C_dye ratio. Total organic carbon (TOC) analysis revealed a rapid mineralisation of AR88 in the presence of PMS. A suitable mechanism explaining the observed enhanced decolorisation and mineralisation rate of the dye with PMS is presented.     

Waveguide mode solution using a hybrid edge element approach

A hybrid edge element approach for the computation of waveguide modes is presented. The electric field is decomposed into its transverse and longitudinal components, which are modeled in terms of two-dimensional edge elements and scalar nodal elements, respectively, thereby satisfying the Dirichlet boundary condition at the perfect electric conductor boundaries and dielectric interfaces. Failure to do so results in the generation of spurious modes. This approach allows for the modeling of a three-dimensional field quantity over a two-dimensional boundary, namely the waveguide cross section. Another approach, the method of moments, serves as an excellent means of verifying the results obtained through use of hybrid edge elements. A comparison of the results obtained from both techniques are presented, along with the associated field plots obtained from the hybrid edge element approach for several geometries.     

Calibration of analyzing magnet for beam energy measurement using the recoil mass separator HIRA

Beam energy measurements have been carried out using the energy achromatic recoil mass separator HIRA at NSC. The energy was obtained from a measurement of the time-of-flight through HIRA which offers a flight distance of about 8.8 m. The method is quite useful for the calibration of the analyzer magnet over the entire operating range.     

Models and logics for true concurrency

A distributed computer system consists of different processes oragents that function largely autonomously and coordinate their actions by communicating with each other. In such a situation, actions may be performed by different agents of the system locally, in a concurrent manner. In this paper, we first discuss formal models of distributed systems in which concurrency is specifiedexplicitly, in contrast to more traditional approaches where concurrency is representedimplicitly as a nondeterministic choice between all possible sequentializations of concurrent actions. This naturally leads to models based on partially-ordered sets of actions rather than sequences of actions and is often called thetrue concurrency approach. The models we focus on are distributed transition systems, elementary net systems and event structures. In the second half of the paper, we develop a family of logics to specify and reason about the behavioural properties of the models we have described. The logics we define are extensions of temporal logic with new modalities to directly describe concurrency. This paper is essentially a survey of work done by the authors during the last few years on modelling distributed systems with true concurrency and using logic to reason about these models. The emphasis is on motivating definitions through examples and on presenting major results, without going into too many formal details. We provide pointers to the literature where these details can be found.