ECE Faculty Publications

A reconfigurable MEMS-less CMOS tuner for software defined radio

Laleh Rabieirad et al. — Fri, 01 Jul 2011 10:45:23 PDT

Design, simulation and measurement of a reconfigurable CMOS RF tuner that can be utilized in the RF front-end of a software defined radio are presented. 0.13m high Q CMOS varactors controlled by a 22bit shift register are placed periodically on a low loss Coplanar Waveguide (CPW) transmission line to form a 4-11GHz reconfigurable tuner. The monolithic tuner does not use any MEMS devices to achieve the reconfigurability.

A planar parasitic array antenna for tunable radiation pattern

Jeong Seongheon et al. — Fri, 01 Jul 2011 10:45:20 PDT

In this paper, a cross-type parasitic array antenna is designed to tune the radiation pattern which attenuates incoming interference and improve packet reception. Using only a 5-element planar array allows full 2-dimensional beam steering. The measurement shows that approximately 30 degrees of beam steering can be achieved by terminating parasitic elements with commercial Si-based varactors allowing rapid and automatic adjustment of antenna patterns.

A physical 3-D analytical model for the threshold voltage considering RDF

Georgios Panagopoulos et al. — Fri, 01 Jul 2011 10:45:17 PDT

Scaling of technology leads to both a countable number and random position of dopants in the channel region (Fig. 1), known as random dopants fluctuations (RDF), which affects vital device and circuit performance parameters (delay, transconductunce, etc). RDF causes large variations of performance between similar transistors on the same die. The variations of the threshold voltage have been ruminated and examined not only experimentally but also numerically, through the use of 3D atomistic level simulators [1]-[2]. However, existing simulation methods and analytical models for RDF fail to meet the requirements for small computational time and accuracy simultaneously. In this paper we propose a fast and accurate analytical model and a corresponding simulator which captures the 3-D effects.

A pH-tunable hydrogel microlens array with temperature-actuated light-switching capability

Ding Zhenwen et al. — Fri, 01 Jul 2011 10:45:14 PDT

In this letter, we demonstrate a two step casting process to fabricate a bifunctional hydrogel-based microlens array, which responds to both temperature (becomes opaque above certain temperature) and pH (changes its focal length at different pH levels), and can be operated in air for an extended period of time. Each lens in the array is 1 mm in diameter and its focal length changes from 4.5 to 55 mm when the environmental pH is varied between 2.0 and 5.0. The light-switching capability is measured to be ~92% when temperature increases from 25 to 35C.

A phenomenological discrete brittle damage-mechanics model for fatigue of MEMS devices with application to LIGA Ni

T. S. Slack et al. — Fri, 01 Jul 2011 10:45:10 PDT

Fatigue initiation and failure of various microelectromechanical systems (MEMS) is of significant importance as they gain widespread acceptance in sensors and electronics. This paper presents an approach for utilizing available experimental fatigue data to evaluate the fatigue lives of MEMS components. The approach is based on a phenomenological discrete material representation in which a domain is represented by a collection of rigid elements that interacts via springs along their boundaries. The principles of continuum damage mechanics are used to degrade the spring stiffnesses as brittle damage occurs when the domain is subjected to fatigue loading. The model utilizes experimental stress-life data for LIGA Ni to identify the material properties used in the model. The proposed model captures the statistical distribution of material properties and geometrical randomness of the microstructure commonly observed in a wide variety of MEMS. Consequently, simulations that account for the variability in fatigue life can be readily performed. The model is applied to a dog-bone-shaped specimen to evaluate the influence of material heterogeneity and material flaws on fatigue crack initiation life and scatter. The ability of the model to predict the fatigue life of different types of MEMS devices and loading conditions is also demonstrated by simulating the fatigue stress-life behavior of a MEMS resonator support beam.

A parallel Levenberg-Marquardt algorithm

Jun Cao et al. — Fri, 01 Jul 2011 10:45:06 PDT

This paper describes a parallel Levenberg-Marquardt algorithm that has been implemented as part of a larger system to support the kinetic modeling of polymer chemistry. The Levenberg-Marquardt algorithm finds a local minimum of a function by varying parameters of the function. The modeling system uses the algorithm to optimize the values of constants that describe the rate at which reactions proceed in a model of the chemical reaction. We present a detailed description of the Levenberg-Marquardt algorithm, and describe three levels of parallelization enabled by our algorithm. The performance and precision of our algorithm is compared to that of the IMSL package's implementation of the algorithm, using two models developed by the polymer chemistry research group at Purdue. Our experimental results show increased precision of the final result relative to the IMSL implementation. We also show good scaling with increased numbers of processors, compared to both a sequential version of our algorithm and against the IMSL implementation.

A Parallel Direct Solver for the Simulation of Large-Scale Power/Ground Networks

S. Cauley et al. — Fri, 01 Jul 2011 10:45:02 PDT

An algorithm is presented for the fast and accurate simulation of power/ground mesh structures. Our method is a direct (non-iterative) approach for simulation based upon a parallel matrix inversion algorithm. The new dimension of flexibility provided by our algorithm allows for a more accurate analysis of power/ground mesh structures using resistance, inductance, capacitance, interconnect models. Specifically, we offer a method that employs a sparse approximate inverse technique to consider more reluctance coupling terms for increased accuracy of simulation. Our algorithm shows substantial computational improvement over the best known direct and iterative numerical techniques that are applicable to these large-scale simulation problems.

A parallel color-based particle filter for object tracking

Henry Medeiros et al. — Fri, 01 Jul 2011 10:44:58 PDT

Porting well known computer vision algorithms to low power, high performance computing devices such as SIMD linear processor arrays can be a challenging task. One especially useful such algorithm is the color-based particle filter, which has been applied successfully by many research groups to the problem of tracking nonrigid objects. In this paper, we propose an implementation of the color-based particle filter suitable for SIMD processors. The main focus of our work is on the parallel computation of the particle weights. This step is the major bottleneck of standard implementations of the color-based particle filter since it requires the knowledge of the histograms of the regions surrounding each hypothesized target position. We expect this approach to perform faster in an SIMD processor than an implementation in a standard desktop computer even running at much lower clock speeds.

A numerical fatigue damage model for life scatter of MEMS devices

B. Jalalahmadi et al. — Fri, 01 Jul 2011 10:44:55 PDT

This paper presents a fatigue damage model to estimate fatigue lives of microelectromechanical systems (MEMS) devices and account for the effects of topological randomness of material microstructure. For this purpose, the damage mechanics modeling approach is incorporated into a new Voronoi finite-element model (VFEM). The VFEM developed for this investigation is able to consider both intergranular crack initiation (debonding) and propagation stages. The model relates the fatigue life to a damage parameter "D" which is a measure of the gradual material degradation under cyclic loading. The fatigue damage model is then used to investigate the effects of microstructure randomness on the fatigue of MEMS. In this paper, three different types of randomness are considered: (1) randomness in the microstructure due to random shapes and sizes of the material grains; (2) the randomness in the material properties considering a normally (Gaussian) distributed elastic modulus; and (3) the randomness in the material properties considering a normally distributed resistance stress, which is the experimentally determined material property controlling the ability of a material to resist the damage accumulation. Thirty-one numerical models of MEMS specimens are considered under cyclic axial and bending loading conditions. It is observed that the stress-life results obtained are in good agreement with the experimental study. The effects of material inhomogeneity and internal voids are numerically investigated.

A Novel Model for (percolating) Nanonet Chemical Sensors for Microarray-based E-Nose Applications

J. Go et al. — Fri, 01 Jul 2011 10:44:52 PDT

Our numerical simulations for percolating multi-nanowire (NW) chemical sensors demonstrate the fundamental role of potential barriers at NW-to-NW junctions in dictating sensor response and how the sensor response changes with NW density. Based on this model, we explain the counterintuitive enhancement of detection limit at a high-density NW network sensor.

A novel low overhead fault tolerant Kogge-Stone adder using adaptive clocking

Swaroop Ghosh et al. — Fri, 01 Jul 2011 10:44:49 PDT

As the feature size of transistors gets smaller, fabricating them becomes challenging. Manufacturing process follows various corrective design-for-manufacturing (DFM) steps to avoid shorts/opens/bridges. However, it is not possible to completely eliminate the possibility of such defects. If spare units are not present to replace the defective parts, then such failures cause yield loss. In this paper, we present a fault tolerant technique to leverage the redundancy present in high speed regular circuits such as Kogge-Stone adder (KSA). Due to its regularity and speed, KSA is widely used in ALU design. In KSA, the carries are computed fast by computing them in parallel. Our technique is based on the fact that even and odd carries are mutually exclusive. Therefore, defect in even bit can only corrupt the even Sum outputs whereas the odd Sums are computed correctly (and vice versa). To efficiently utilize the above property of KSA in presence of defects, we perform addition in two- clock cycles. In cycle-1, one of the correct set of bits (even or odd) are computed and stored at output registers. In cycle-2, the operands are shifted by one bit and the remaining sets of bits (odd or even) are computed and stored. This allows us to tolerate the defect at the cost of throughput degradation while maintaining high frequency and yield. The proposed technique can tolerate any number of faults as long as they are confined to either even or odd bits (but not in both). Further, this technique is applicable for any type of fault model (stuck-at, bridging, complete opens/shorts). We performed simulations on 64-bit KSA using 180nm devices. The results indicate that the proposed technique incur less that 1% area overhead. Note that there is very little throughput degradation (0.3%) for the fault-free adders. The proposed technique utilizes the existing scan flip-flops for storage and shifting operation to minimize the area/performance overhead. Finally, the proposed technique is used in a superscalar processor, whereby the faulty adder is assigned lower priority than fault-free adders to reduce the overall throughput degradation. Experiments performed using Simplescalar for a superscalar pipeline (with four integer adders) show throughput degradation of 0.5% in the presence of a single defective adder.

A novel image analysis method based on bayesian segmentation for event-related functional MRI

Lejian Huang et al. — Fri, 01 Jul 2011 10:44:45 PDT

This paper presents the application of the expectation-maximization/ maximization of the posterior marginals (EM/MPM) algorithm to signal detection for functional MRI (fMRI). On basis of assumptions for fMRI 3-D image data, a novel analysis method is proposed and applied to synthetic data and human brain data. Synthetic data analysis is conducted using two statistical noise models (white and autoregressive of order 1) and, for low contrast-to-noise ratio (CNR) data, reveals better sensitivity and specificity for the new method than for the traditional General Linear Model (GLM) approach. When applied to human brain data, functional activation regions are found to be consistent with those obtained using the GLM approach.

A novel evidence accumulation framework for Robust multi-camera person detection

Hidekazu Iwaki et al. — Fri, 01 Jul 2011 10:44:42 PDT

We propose a novel evidence accumulation framework that accurately estimates the positions of humans in a 3D environment. The framework consists of a network of distributed agents having different functionalities. The modular structure of the network allows scalability to large surveillance areas and robust operation. The framework does not assume reliable measurements in single cameras (referred to as 'sensing agents' in our framework) or reliable communication between different agents. There is a position uncertainty associated with single camera measurements and it is reduced through an uncertainty reducing transform that performs evidence accumulation using multiple camera measurements. Our framework has the advantage that single camera measurements do not need to be temporally synchronized to perform evidence accumulation. The system has been tested for detecting single and multiple humans in the environment. We conducted experiments to evaluate the localization accuracy of the position estimates obtained from the system by comparing them with the ground truth. Also, two different configurations of the agents were tested to compare their detection performance.

A new Kalman-filter-based framework for fast and accurate visual tracking of rigid objects

Yoon Youngrock et al. — Fri, 01 Jul 2011 10:44:39 PDT

The best of Kalman-filter-based frameworks reported in the literature for rigid object tracking work well only if the object motions are smooth (which allows for tight uncertainty bounds to be used for where to look for the object features to be tracked). In this contribution, we present a new Kalman-filter-based framework that carries out fast and accurate rigid object tracking even when the object motions are large and jerky. The new framework has several novel features, the most significant of which is as follows: the traditional backtracking consists of undoing one-at-a-time the model-to-scene matchings as the pose-acceptance criterion is violated. In our new framework, once a violation of the pose-acceptance criterion is detected, we seek the best largest subset of the candidate scene features that fulfill the criterion, and then continue the search until all the model features have been paired up with their scene correspondents (while, of course, allowing for nil-mapping for some of the model features). With the new backtracking framework, our Kalman filter is able to update on a real-time basis the pose of a typical industrial 3-D object moving at the rate of approximately 5 cm/s (typical for automobile assembly lines) using off-the-shelf PC hardware. Pose updating occurs at the rate of 7 frames per second and is immune to large jerks introduced manually as the object is in motion. The objects are tracked with an average translational accuracy of 4.8 mm and the average rotational accuracy of 0.27.

A new field reconstruction method for permanent magnet synchronous machines

A. Khoobroo et al. — Fri, 01 Jul 2011 10:44:35 PDT

The performance of the permanent magnet synchronous machines depends on the torque ripple and radial forces acting on its shaft and stator frame. There are two major ways to treat the undesirable torque ripples. In the first group of the methods machine design issues is considered. The second group considers optimal excitation of the machine so that the resulting performance is acceptable. In this paper a voltage formulation of the field reconstruction method is derived to predict the machine performance. The voltage source waveforms are used to find the associated 3 phase currents. The currents are used to calculate magnetic field distribution in the middle of the air gap. These quantities are used to predict the performance of the targeted PMSM.

A nanofluidic channel with embedded transverse nanoelectrodes

T. Maleki et al. — Fri, 01 Jul 2011 10:44:32 PDT

In this paper, we demonstrate fabrication and characterization of a nanofluidic channel with embedded transverse nanoelectrodes using a combination of conventional photolithography and focused ion beam technologies. Glass-capped silicon dioxide nanochannels having 20 nm depth, 50 nm width, and 2 m length with embedded platinum nanoelectrodes were fabricated. Channel patency was verified through measurements of the resistivity in phosphate buffered saline and electrostatic action on charged fluorescent nanospheres. Platinum nanoelectrode functionality was also tested using transverse resistance measurements in nanochannels filled with air, deionized water, and saline solution.

A multirate field construction technique for efficient modeling of the fields and forces within inverter-fed induction machines

Wu Dezheng et al. — Fri, 01 Jul 2011 10:44:29 PDT

In recent research, a field construction technique (FCT) was derived to enable more efficient evaluation of the magnetic fields and forces within induction machines. Using the FCT, the results of two finite-element (FE) solutions are used to establish basis functions for the flux densities in the airgap of the machine. The basis functions are then used to predict the magnetic fields and forces under arbitrary stator excitation. In this paper, a multirate FCT (MRFCT) is proposed to enable efficient FCT modeling of machines that are connected to power electronic converters. Within the MRFCT, the low- and high-frequency components of the stator current are partitioned. The partitioned currents are then used to calculate the flux density and forces at time steps commensurate with the respective low- and high-frequency dynamics. It is shown that applying the MRFCT, the forces and fields of a machine connected to a power electronic circuit can be obtained at a small fraction of the time required for a coupled FE/circuit model.

A multiaxial stretchable interconnect using liquid-alloy-filled elastomeric microchannels

Kim Hyun-Joong et al. — Fri, 01 Jul 2011 10:44:26 PDT

We report on the fabrication and characterizations of a multiaxial stretchable interconnect using room-temperature liquid-alloy-filled elastomeric microchannels. Polydimethylsiloxane (PDMS) microchannels coated at the bottom with a gold wetting layer were used as the reservoirs which were subsequently filled by room-temperature liquid alloy using microfluidic injection technique. Using a diamond-shaped geometry to provide biaxial performance, a maximum stretchability of 100% was achieved (R=0.24 ). Less than 0.02 resistance variation was measured for 180 bending. Active electronics, light emitting diode, was also integrated onto the PDMS substrate with stretchable interconnects to demonstrate stable electrical connection during stretching, bending, and twisting.

A MIMO-OFDM channel estimation scheme utilizing complementary sequences

T. R. Qureshi et al. — Fri, 01 Jul 2011 10:44:22 PDT

We present a pilot-assisted method for estimating the frequency selective channel in a MIMO-OFDM system. The pilot sequence is designed using the DFT of the Golay complementary sequences. Novel exploitation of the perfect autocorrelation property of Golay complementary sequences, in conjunction with OSTBC based pilot waveform scheduling across multiple OFDM frames, facilitates simple separation of the channel mixtures at the receive antennas. The DFT length used to transform the complementary sequence into the frequency domain is shown to be a key critical parameter for correctly estimating the channel. This channel estimation scheme is then extended to antenna arrays of arbitrary sizes.

A method for recognizing the shape of a Gaussian mixture from a sparse sample set

H. J. Santos-Villalobos et al. — Fri, 01 Jul 2011 10:44:19 PDT

The motivating application for this research is the problem of recognizing a planar object consisting of points from a noisy observation of that object. Given is a planar Gaussian mixture model T (x) representing an object along with a noise model for the observation process (the template). Also given are points representing the observation of the object (the query). We propose a method to determine if these points were drawn from a Gaussian mixture Q(x) with the same shape as the template. The method consists in comparing samples from the distribution of distances of T (x) and Q(x), respectively. The distribution of distances is a faithful representation of the shape of generic Gaussian mixtures. Since it is invariant under rotations and translations of the Gaussian mixture, it provides a workaround to the problem of aligning objects before recognizing their shape without sacrificing accuracy. Experiments using synthetic data show a robust performance against type I errors, and few type II errors when the given template Gaussian mixtures are well distinguished.