Large Array Size Research Articles

Nonlinear dynamic behavior of a microbeam array subject to parametric actuation at low, medium and large DC-voltages

The dynamic response of parametrically excited microbeam arrays is governed by nonlinear effects which directly influence their performance. To date, most widely used theoretical approaches, although opposite extremes with respect to complexity, are nonlinear lumped-mass and finite-element models. While a lumped-mass approach is useful for a qualitative understanding of the system response it does not resolve the spatio-temporal interaction of the individual elements in the array. Finite-element simulations, on the other hand, are adequate for static analysis, but inadequate for dynamic simulations. A third approach is that of a reduced-order modeling which has gained significant attention for single-element micro-electromechanical systems (MEMS), yet leaves an open amount of fundamental questions when applied to MEMS arrays. In this work, we employ a nonlinear continuum-based model to investigate the dynamic behavior of an array of N nonlinearly coupled microbeams. Investigations focus on the array’s behavior in regions of its internal one-to-one, parametric, and several internal three-to-one and combination resonances, which correspond to low, medium and large DC-voltage inputs, respectively. The nonlinear equations of motion for a two-element system are solved using the asymptotic multiple-scales method for the weakly nonlinear system in the afore mentioned resonance regions, respectively. Analytically obtained results of a two-element system are verified numerically and complemented by a numerical analysis of a three-beam array. The dynamic behavior of the two- and three-beam systems reveal several in- and out-of-phase co-existing periodic and aperiodic solutions. Stability analysis of such co-existing solutions enables construction of a detailed bifurcation structure. This study of small-size microbeam arrays serves for design purposes and the understanding of nonlinear nearest-neighbor interactions of medium- and large-size arrays. Furthermore, the results of this present work motivate future experimental work and can serve as a guideline to investigate the feasibility of new MEMS array applications.

Performance improvement of quantum well infrared photodetectors through modeling

We study the performance of quantum well infrared photodetectors (QWIPs) in the case of infrared irradiation. This type of photodetector is interesting from the point of view that QWIPs have numerous advantages over photodetectors based on HgCdTe in terms of large array size, high uniformity, high yield, radiation hardness and lower cost of the systems. Therefore, it is important to evaluate their characteristics theoretically. We develop a simple modeling for this interesting type of photodetector. This model describes a nontrivial evaluation of the most important characteristics. The potential distribution of the developed model is obtained by self-consistently solving the Poisson equation. On the other hand, it is used to calculate the dark current, responsivity and detectivity as a function of the structural parameters. These parameters are the spacing between the wells, the number of quantum wells and the operating temperature. Also, the optimization of the characteristics of QWIPs is of primary concern. The effect of uniformity of the dopant density in the QWIP is studied theoretically. We find that the uniformity of the dopant distribution in the plane of QW decreases the dark current.

CHARACTERIZATION OF SECOND GENERATION ADVANCED DYNAMIC PYROELECTRIC FOCAL PLANE ARRAY

ABSTRACT The pyroelectric effect has been characterized for single-pixel elements consisting of strontium bismuth tantalate (SBT) ferroelectric material as the sensing element. The pixels include also a thermal insulating layer and an infrared (IR) absorber layer. These MEMS-less devices are operated in active mode, a technique that eliminates the need for a radiation chopper found in passive pyroelectric IR imagers. Test results of the SBT pixels of dimensions 7.5 μm × 7.5 μm to 200 μm × 200 μm have shown high endurance to polar cycling, high responsivity values, and very low noise-equivalent temperature difference for focal plane array applications. This paper describes and analyses the results of precursor 2 × 2 arrays using discrete sensing elements, the active detection mechanism, and its unique read-out electronics. A second-generation 32 × 32 pixels array being implemented to demonstrate the performance of a 1k-pixel array as precursor to larger size arrays is also described. The active mode detection, in addition to eliminating the use of a chopper, enables the dynamic partition of the array into pixel domains in which the pixel sensitivities in each domain can be adjusted independently. This unique feature in IR detection is not readily found in other types of IR imagers and can be applied to the simultaneous tracking of diverse contrast objects. By controlling the absorber material thickness, the arrays can be optimized for maximum response at specified wavelengths by means of quarter-wavelength interferometric technique.

INTERNAL RESONANCES AND BIFURCATIONS OF AN ARRAY BELOW THE FIRST PULL-IN INSTABILITY

A nonlinear continuum model is used to investigate the dynamic behavior of an array of N nonlinearly coupled microbeams. Investigations concentrate on the region below the array's first pull-in instability, which is shown to be governed by several internal three-to-one and combination resonances. The nonlinear equations of motion for a two-element system are solved using the asymptotic multiple-scales method for the weak nonlinear system. The analytically obtained periodic response of two coupled microbeams is numerically evaluated by a continuation technique and complemented by a numerical analysis of a three-element array which exhibits quasi-periodic responses and lengthy chaotic transients. This study of small-size microbeam arrays serves for design purposes and the understanding of nonlinear nearest-neighbor interactions of medium- and large-size arrays.

Design and Implementation of a Scalable Channel Emulator for Wideband MIMO Systems

Wireless channel emulation is becoming increasingly important, particularly with the advent of multiple-input-multiple-output (MIMO) systems, where system performance is highly dependent on the accurate representation of the channel condition. In this paper, we compare the conventional finite impulse response (FIR)-based emulator versus solely performing the emulation in the frequency domain. We show that for single-input-single-output (SISO) systems, FIR-based emulators are computationally efficient but that the complexity rapidly becomes impractical for larger array sizes. On the other hand, frequency-domain approaches exhibit a fixed initial complexity cost that grows at a reduced rate as a function of the array size, resulting in significant savings in complexity for higher order arrays. As an illustrative example of this approach, field-programmable gate array (FPGA) architecture implementing a sample 3 times 3 MIMO system exhibits resource savings of up to 67% over a similarly constrained FIR approach. The architecture is discussed in detail, and implementation results, as well as laboratory measurements, are presented.

Analyses of infrared focal plane array figure of merit and its impact on sensor system trades

The performance of infrared focal plane arrays (IRFPAs) is usually described by a set of figures of merit and operating parameters. They include FPA format, pixel pitch, operating temperature, cut-on and cutoff wavelengths, median detectivity, uniformity, and integration time. This article examines the promise of superlattice infrared materials and how the improved FPA figure of merit affects sensor system performance as measured by range, update rate, size, power, and cost. A simple analysis shows that for space-based surveillance, the system cost, as measured by the number of hosting satellites, may be decreased substantially by using detector arrays with large array size and longer detection range. It also shows that to make long-wavelength superlattice IRFPAs useful for future space applications, the residual nonuniformity must be improved.

Third-generation infrared photodetector arrays

Hitherto, two distinct families of multielement detector arrays have been used for infrared (IR) imaging system applications: linear arrays for scanning systems (first generation) and two-dimensional arrays for staring systems (second generation). Nowadays, third-generation IR systems are being developed which, in the common understanding, provide enhanced capabilities such as larger numbers of pixels, higher frame rates, better thermal resolution, multicolor functionality, and/or other on-chip signal-processing functions. In this paper, fundamental and technological issues associated with the development and exploitation of third-generation IR photon detectors are discussed. In this class of detectors the two main competitors, HgCdTe photodiodes and quantum-well photoconductors, are considered. This is followed by discussions focused on the most recently developed focal plane arrays based on type-II strained-layer superlattices and quantum dot IR photodetectors. The main challenges facing multicolor devices are concerned with complicated device structures, thicker and multilayer material growth, and more difficult device fabrication, especially for large array sizes and/or small pixel dimensions. This paper also presents and discusses the ongoing detector technology challenges that are being addressed in order to develop third-generation infrared photodetector arrays.

Extension of Coupled Mode Analysis to Infinite Photonic Superlattices

Coupled-mode theory (CMT) is extended to the case of infinite 2-D photonic arrays, made of periodically repeated identical groups of different waveguides (supercells). Born-Karman boundary conditions, applied to the CMT equations for this system, are used to compute the photonic band structure. This method was found to be more efficient and much less resource-consuming than the existing approaches, for the analysis of finite large-sized arrays.

Stochastic inhibitor release and binding from single-enzyme molecules

Inhibition kinetics of single-beta-galactosidase molecules with the slow-binding inhibitor d-galactal have been characterized by segregating individual enzyme molecules in an array of 50,000 ultra small reaction containers and observing substrate turnover changes with fluorescence microscopy. Inhibited and active states of beta-galactosidase could be clearly distinguished, and the large array size provided very good statistics. With a pre-steady-state experiment, we demonstrated the stochastic character of inhibitor release, which obeys first-order kinetics. Under steady-state conditions, the quantitative detection of substrate turnover changes over long time periods revealed repeated inhibitor binding and release events, which are accompanied by conformational changes of the enzyme's catalytic site. We proved that the rate constants of inhibitor release and binding derived from stochastic changes in the substrate turnover are consistent with bulk-reaction kinetics.

Optical implementation of a polarization-independent bidirectional 3 × 3 optical switch

Based on the important role of optical switching in all-optical communications, a novel 3 × 3 optical switch is proposed using Phase Spatial Light Modulators (PSLM), Polarizing Beam-Splitters (PBS), mirrors, and Quarter-Wave Plates (QWP). This new configuration of optical switch has the advantages of being compact in structure, efficient in performance, and insensitive to polarization of the signal beam. Moreover, the functions of the 3 × 3 optical switch have been implemented bidirectionally in free-space. According to the routing-state table of the polarization-independent 3 × 3 optical switch, its operational processes are analyzed, and the results show that the experimental module of the 3 × 3 optical switch can connect an arbitrary output port to any input port beams. Simultaneously, the module is scalable to large array sizes and has the capability of reconfiguration. Therefore, it should be helpful in the design of a large-scale switching matrix.

Optimal stimulus and noise distributions for information transmission via suprathreshold stochastic resonance

Suprathreshold stochastic resonance (SSR) is a form of noise-enhanced signal transmission that occurs in a parallel array of independently noisy identical threshold nonlinearities, including model neurons. Unlike most forms of stochastic resonance, the output response to suprathreshold random input signals of arbitrary magnitude is improved by the presence of even small amounts of noise. In this paper, the information transmission performance of SSR in the limit of a large array size is considered. Using a relationship between Shannon's mutual information and Fisher information, a sufficient condition for optimality, i.e., channel capacity, is derived. It is shown that capacity is achieved when the signal distribution is Jeffrey's prior, as formed from the noise distribution, or when the noise distribution depends on the signal distribution via a cosine relationship. These results provide theoretical verification and justification for previous work in both computational neuroscience and electronics.

Test Planning and Test Resource Optimization for Droplet-Based Microfluidic Systems

Recent years have seen the emergence of droplet-based microfluidic systems for safety-critical biomedical applications. In order to ensure reliability, microsystems incorporating microfluidic components must be tested adequately. In this paper, we investigate test planning and test resource optimization for droplet-based microfluidic arrays. We first formulate the test planning problem and prove that it is NP-hard. We then describe an optimization method based on integer linear programming (ILP) that yields optimal solutions. Due to the NP-hard nature of the problem, we develop heuristic approaches for optimization. Experimental results indicate that for large array sizes, the heuristic methods yield solutions that are close to provable lower bounds. These heuristics ensure scalability and low computation cost.

Uncooled thermo-mechanical detector array with optical readout

AbstractThis paper reports a novel uncooled infrared FPA whose performance is comparable to the cooled FPA’s in terms of noise parameters. FPA consists of bimaterial microcantilever structures that are designed to convert IR radiation energy into mechanical energy. Induced deflection by mechanical energy is detected by means of optical methods that measure sub nanometer thermally induced deflections. Analytical solutions are developed for calculating the figure of merits for the FPA. FEM simulations and the analytical solution agree well. Calculations show that for an FPA, NETD of < 5 mK is achievable in the 8–12 μm band. The design and optimization for the detectors are presented. The mechanical structure of pixels is designed such that it can be possible to form large array size FPA’s. Microfabrication of the devices to improve the performance further, employs low cost standard MEMS processes.

Tolerance of phase-locked VCSEL arrays to random and systematic parameter deviations among cavities

Cavity parameter deviations from their nominal values affect phase-locking in vertical-cavity surface-emitting lasers (VCSEL) arrays. The phase-locking tolerance is studied analytically and numerically for both random as well as systematic parameter variations. Parameter-induced deviations among the cavity eigenfrequencies cause the dominant effect. For small externally imposed variations, self-regulated nonlinear frequency pulling among cavities overcomes original detuning and permits phase-locking. The root mean square (rms) tolerance threshold is derived by solving a quasi-random matrix eigenvalue under simplifying assumptions. Tolerance increases with intercavity coupling strength and decreases with the array size M. Systematic variations, such as thermal drifts, exhibit a lower tolerance decreasing as /spl prop/1/M or faster, compared to random variations /spl prop/1//spl radic/M. Theory results qualitatively agree with large size array simulations employing actively coupled rate equations.

Design of surface shape control for large two-dimensional arrays

This paper develops control design technology for active shape control of reflective surfaces using large spatially distributed actuator arrays. The potential applications are in astronomy, adaptive optic, beam control, space-based imaging, and other optics and imaging applications. In a very large lightweight active reflector, surface shape (figure) might be controlled by an array of actuators and sensors that counts millions of cells. The control technology discussed in this paper is scalable to these large array dimensions. This paper develops a classically motivated design methodology for distributed localized control laws of very large actuator/sensor arrays. The methodology uses standard PI-compensation, plus lags and/or notch-filters, to deal with temporal dynamics in each actuator channel. It achieves scalability to very large array sizes by imposing spatially localized fixed-form constraints on the control law structure. In this setup, the entire spatial-temporal design model can be transformed, via Laplace transforms in time and two-dimensional (2-D) discrete Fourier transforms in space, to produce a family of dynamic systems whose closed-loop characteristics can be subjected to standard classical control-engineering specifications, including stability, performance, and robustness. These specifications can be satisfied for all members of the family by solving linear programs (LPs) to find parameters of the fixed-form structure. The veracity of this methodology is illustrated with a design example loosely resembling an actively controlled reflector whose local deformations are controlled by a hexagonal array of actuator/sensor cells.

Influence of semantic relatedness and array size on single-word reading comprehension in aphasia

Background: Previous research has shown that aphasic individuals' ability to select a pictured object from a group of pictures depends on (1) the number of pictures arrayed, (2) whether the pictures are situationally related to each other, and (3) whether they are displayed in a situational context versus a standard matrix. Aims: The present study expands on these results to include printed words and relationships based on semantic categories rather than common situational environments. Methods & Procedures: Ten aphasic participants were asked to match a spoken word to the printed word. The nature of the foils was systematically varied based on array size (two, four, six, and eight words) and whether the words were semantically related or not. Outcomes & Results: The result for array size was similar to previous results in that performance with larger arrays (eight words) was worse than with smaller arrays. However, the results for relatedness were different. Earlier results showed that performance with situationally related pictures was worse than with unrelated pictures only at larger array sizes (six and eight pictures). In contrast, performance with semantically related printed words was worse than for unrelated printed words at all array sizes. Conclusions: Whether similarity among stimuli is based on semantic or situational relatedness changes how relatedness interacts with array size to affect performance. The impact of this on diagnostic test results and treatment considerations is discussed.

Superconducting detectors and mixers for millimeter and submillimeter astrophysics

Superconducting detectors will play an increasingly significant role in astrophysics, especially at millimeter through far-IR wavelengths, where the scientific opportunities include key problems in astronomy and cosmology. Superconducting detectors offer many benefits: outstanding sensitivity, lithographic fabrication, and large array sizes, especially through the recent development of multiplexing techniques. This paper describes the scientific opportunities, the basic physics of these devices, the techniques for radiation coupling, and reviews the recent progress in direct detectors, such as transition-edge bolometers, and the work on tunnel junction (superconductor-insulator-superconductor) and hot-electron mixers.

Les nouvelles générations de détecteurs infrarouge à base de HgCdTe

The technology of very high performance cooled infrared detectors made with HgCdTe has progressed continuously for ten years and reached today an industrial maturity that allows the production of large size arrays at a more and more reasonable cost. At the same time, new prototypes of more complex sensors have appeared (megapixel arrays, multicolour arrays, high definition long linear arrays, … ) that show the strong potentialities of this very high performance technology. This paper presents the technology developed in France and gives the state of the art of products available in industry; it then focuses on some very recent realizations of advanced prototypes made at LETI (dualband arrays, megapixel arrays, … ). To cite this article: G. Destefanis, C. R. Physique 4 (2003).

Compact low-power calibration mini-DACs for neural arrays with programmable weights

This paper considers the viability of compact low-resolution low-power mini digital-to-analog converters (mini-DACs) for use in large arrays of neural type cells, where programmable weights are required. Transistors are biased in weak inversion in order to yield small currents and low power consumptions, a necessity when building large size arrays. One important drawback of weak inversion operation is poor matching between transistors. The resulting effective precision of a fabricated array of 50 DACs turned out to be 47% (1.1 bits), due to transistor mismatch. However, it is possible to combine them two by two in order to build calibrated DACs, thus compensating for inter-DAC mismatch. It is shown experimentally that the precision can be improved easily by a factor of 10 (4.8% or 4.4 bits), which makes these DACs viable for low-resolution applications such as massive arrays of neural processing circuits. A design methodology is provided, and illustrated through examples, to obtain calibrated mini-DACs of a given target precision. As an example application, we show simulation results of using this technique to calibrate an array of digitally controlled integrate-and-fire neurons.

The Effects of Event Rate and Array Size on a Cognitive Vigilance Task with Associated EEG Rhythms and a Derived Engagement Index

This study investigated the effects of event rate and stimulus array size during a vigilance task on performance and relative EEG power bandwidths (alpha, beta, theta) and a derived EEG engagement index, EI = (beta/(alpha+ theta)). Forty participants, ages 18 to 40, engaged in a visual search task. Participants were required to distinguish a green “K” from an array of stimuli (yellow-green, green, and blue-green factorially combined with K, X, N, R). Each participant searched for the signal in arrays of 2 or 5 stimuli presented at either 12 or 24 events per minute over forty minutes. The design was a 2×2 factorial with four groups. The results indicated poorer performance, higher false alarm rates in the first 10-minute period, and longer response times associated with the larger array size. There were no performance effects for event rate. The EI decreased over periods. Relative alpha and beta power in the midline sites (PZ, CZ, and FZ) were greater for the higher event rate, but were unrelated to array size. These EEG findings are discussed in the context of earlier vigilance studies using EEG measures.