Leonardo R. A. X. de Menezes

Probabilistic finite element analysis of radiofrequency liver ablation using the unscented transform.

The main limitation of radiofrequency (RF) ablation numerical simulations reported in the literature is their failure to provide statistical results based on the statistical variability of tissue thermal-electrical parameters. This work developed an efficient probabilistic approach to hepatic RF ablation in order to statistically evaluate the effect of four thermal-electrical properties of liver tissue on the uncertainty of the ablation zone dimensions: thermal conductivity, specific heat, blood perfusion and electrical conductivity. A deterministic thermal-electrical finite element model of a monopolar electrode inserted in the liver was coupled with the unscented transform method in order to obtain coagulation zone confidence intervals, probability and cumulative density functions. The coagulation zone volume, diameter and length were 10.96 cm(3), 2.17 cm and 4.08 cm, respectively (P < 0.01). Furthermore, a probabilistic sensitivity analysis showed that perfusion and thermal conductivity account for >95% of the variability in coagulation zone volume, diameter and length.

Probabilistic load flow for distribution systems with wind production using Unscented Transform method

In this paper, an approximate scheme called the Unscented Transforms (UT) method is proposed for probabilistic load flow studies. The proposed method involves carefully choosing a few selected points to approximate the probability distribution function of random variables within the system so as to significantly reduce the computation time. Since a power grid with embedded wind production is considered, the wind speed random variation is represented using a 3-parameter Weibull distribution. The wind power generated by the variable speed turbine is approximated as a composite distribution made up of the truncated Weibull-degenerate distributions. The Cumulative Distribution Function of the output variables are plotted using the Cornish-Fisher expansion technique. The effectiveness of the proposed method is proven by comparing the results obtained from it with those from the Monte Carlo simulation method using a simple 3-bus test system.

Modeling device manufacturing uncertainty in Electromagnetic Simulations

This work presents a technique for modeling of the effects of manufacturing uncertainty into Electromagnetic Simulations of microwave devices. The procedure combines the Unscented Transform (UT) with EM Simulations. The use of the UT allows efficient use of computational resources for the characterization of the random variables modeling the uncertainty. The technique is validated with the modeling of tolerance errors of an assembled microstrip pseudo-elliptic filter into the response of the electromagnetic simulation.

Unscented Transformation based array interpolation

It is impossible to enforce exact responses for each sensor involved in an antenna array. Important signal processing techniques such as Estimation of Signal Parameters via Rotational Invariance (ESPRIT), Forward Backward Average (FBA) and Spatial Smoothing (SPS) rely on sensor arrays with Vandermonde or centro-hermitian responses. To achieve such responses array interpolation is often necessary. In this work a novel way of performing array interpolation while minimizing the transformation error using the Unscented Transformation (UT) is presented. The UT provides a different method for mapping interpolated regions and also exhibits a new insight into array interpolation and its current limitations. A set of numerical simulations presents promising results for array interpolation employing the UT.

Design of low-pass microstrip filters based on defected ground structure

An improved periodic defected ground structure (DGS) is investigated for low-pass filter (LPF) applications. The realization in microstrip configuration consists in making the equivalence between the geometry of a DGS structure and a parallel LC resonator circuit. Initially, one filter is designed using identical DGS, equally spaced. Varying empirically the dimensions of the DGS, we obtain an improvement of frequency responses. In order to verify the performances of the proposed changes in the filter, simulations were done between the uniform periodic DGS circuit and the improved non uniform periodic DGS. The results show that the latter exhibits better stopband performance, with suppressing ripples and enlarging the bandwidth. One modified DGS filter was designed and fabricated. The measurements show good consistency with the simulated results.

Smart Antennas as an Approach to Instantaneous Air Interface with Software-Defined Radios

This work presents a new technique, called the instantaneous air interface (IAI). This method is useful for future convergent systems based on software-defined radio (SDR) with smart antennas. IAI modifies the traditional methods of obtaining the DFOA. This is the joint frequency and direction of arrival, which is an improvement to the direction of arrival (DOA). This is an approach that allows an interface estimation. DFOA is compared to the MUSIC, SPRIT, and CAPON algorithms. The numerical performance is evaluated.

Estimation of the probability distributions for cable coupling using unscented transforms

This work presents the use of unscented transforms (UT) for the description of statistical uncertainty in electromagnetic coupling between cables. UT greatly reduce the computational burden for the statistical analysis of nonlinear problems compared with more traditional approaches such as the Monte Carlo technique. Coupling between cables has a nonlinear parameter dependence and has a high variability due to the variability in the cable braid manufacture and the highly variable nature of cable layout. Therefore, cable coupling can only be defined within statistical limits. First, it is shown that by analyzing the resonances the important features of maximum coupling and the point of maximum coupling can be characterized. It is then demonstrated how UT can be used to efficiently identify the parameters which contribute significantly to the uncertainty in cable coupling and then to provide a measure of the probability distribution for the multivariate problem.

Modeling and characterization for microstrip filters in the manufacturing process through the unscented transform and use of electromagnetic simulators

This paper presents the unscented transform (UT) applied to uncertainty modeling of manufacturing tolerances at the design stage of microwave passive devices. The process combines the UT with electromagnetic simulations and assumes that the numerical sources of error are negligible in comparison to the imperfections due to the manufacturing process. The technique was validated with the simulation, construction, and test of several sets of identical microstrip filters with very good results. Although the combination of UT and electromagnetic simulators was presented for microstrip filters, it can also be used for different types of microwave devices.

Recent Advances in the Combination of the Unscented Transform (UT) with the Transmission Line Modeling Method (TLM)

This work presents some of the latest improvements in the combination of the Unscented Transform (UT) with Transmission Line Modeling Method (TLM) for the description of statistical uncertainty in electromagnetic simulations. These advances include: the correct approximation of different distributions, an effective general approach to the UT-TLM combination and their use in time and frequency domains. The work concludes with examples which are compared to Monte Carlo simulations and closed form solutions. Our results are in very good agreement, and were obtained at a fraction of computational cost.

Using Unscented Transform in Interference Studies [EM Programmer's Notebook]

When a new telecommunication system is deployed, an interference analysis is usually necessary. This is frequently achieved using the Monte Carlo (MC) method, which simulates the same problem (with different inputs) tens or hundreds of thousands of times to get the final result. In recent years, the unscented transform (UT) has been used as an alternative to the MC method in several engineering problems. This article shows how to analyze the interference between telecommunications systems using the UT. We illustrate this approach using the interference caused by an long-term evolution (LTE)-advanced small cell in the receiver of a television receive-only (TVRO) system. Results show that simulating with only 192 events using the UT produces similar results to simulations with 10,000, or even 100,000, events using the MC method.