http://hdl.handle.net/10197/2018 2013-05-19T18:06:08Z 2013-05-19T18:06:08Z Blokhina, Elena Galayko, Dimitri Harte, Peter Basset, Philippe Feely, Orla http://hdl.handle.net/10197/4277 2013-04-24T15:31:14Z 2012-10-24T00:00:00Z

Limit on Converted Power in Resonant Electrostatic Vibration Energy Harvesters Blokhina, Elena; Galayko, Dimitri; Harte, Peter; Basset, Philippe; Feely, Orla Based on the formal analysis of a resonant electrostatic vibration energy harvester operating in constant-charge mode with a gap-closing transducer, we show that the system displays universal behaviour patterns. In this paper, we treat the harvester as a nonlinear forced oscillator and bound the area of control parameters where the system displays regular harmonic oscillations allowing the conditioning circuit to operate in the most effective mode. Before the system exhibits irregular behaviour, there exists a universal optimal value of normalised converted power regardless of the system design and control parameters.

2012-10-24T00:00:00Z Ela, Erik O'Malley, Mark http://hdl.handle.net/10197/4191 2013-03-14T17:35:13Z 2012-08-01T00:00:00Z

Studying the variability and uncertainty impacts of variable generation at multiple timescales Ela, Erik; O'Malley, Mark With increasing levels of variable renewable energy, there is a growing need to study its impacts on power system operation. Variable generation (VG) is variable and uncertain at multiple timescales, and it is important that system operators understand how each of these characteristics impact their systems since each may have different mitigation strategies. To date, many of the studies of VG integration are limited to studying at one time resolution and therefore cannot analyze the variability and uncertainty impacts across multiple timescales. Here we study the variability and uncertainty impacts across multiple operational timescales. A model is used which integrates multiple scheduling sub-models with different update frequencies, time resolutions, and decision horizons. Using metrics that describe reliability and costs with a methodology that describes the sensitivities and tradeoffs of variability and uncertainty impacts separately with respect to the conditions that cause those impacts, case studies are performed which display greater information on expectations of these impacts on future systems with high penetrations of VG.

2012-08-01T00:00:00Z Sheridan, John T. Gleeson, M. R. Close, Ciara E. http://hdl.handle.net/10197/3937 2012-11-29T14:56:47Z 2012-03-01T00:00:00Z

Monomer diffusion rates in photopolymer material: Part I. Low spatial frequency holographic gratings: reply Sheridan, John T.; Gleeson, M. R.; Close, Ciara E. In [1,2] an error (by a factor of 1000) in the diffusion rate of monomer in a photopolymer material used by the authors of [3], is presented. In [3] no errors are identified in our analysis and our physical evidence is not addressed. It is implied that our model and our results are disproven by the results in the papers referenced in [3]. In fact these papers do not provide any such quantitative evidence. The observations made regarding the significance of the authors’ contributions, in particular the validity of their model and the practical importance of their material are also discussed.

2012-03-01T00:00:00Z Li, Dayan Kelly, Damien P. Kirner, Raoul Sheridan, John T. http://hdl.handle.net/10197/3902 2012-11-08T17:11:33Z 2012-02-01T00:00:00Z

Speckle orientation in paraxial optical systems Li, Dayan; Kelly, Damien P.; Kirner, Raoul; Sheridan, John T. The statistical properties of speckles in paraxial optical systems depend on the system parameters. In particular, the speckle orientation and the lateral dependence (x and y) of the longitudinal speckle size can vary significantly. For example, the off-axis longitudinal correlation length remains equal to the on-axis size for speckles in a Fourier transform system, while it decreases dramatically as the observation position moves off axis in a Fresnel system. In this paper, we review the speckle correlation function in general linear canonical transform (LCT) systems, clearly demonstrating that speckle properties can be controlled by introducing different optical components, i.e., lenses and sections of free space. Using a series of numerical simulations, we examine how the correlation function changes for some typical LCT systems. The integrating effect of the camera pixel and the impact this has on the measured first- and second-order statistics of the speckle intensities is also examined theoretically. A series of experimental results are then presented to confirm several of these predictions. First, the effect the pixel size has on the measured first-order speckle statistics is demonstrated, and second, the orientation of speckles in a Fourier transform system is measured, showing that the speckles lie parallel to the optical axis.

2012-02-01T00:00:00Z Fernandez, D. Jimenez, V. Madrenas, J. Gorreta, Sergi Blokhina, Elena Pons Nin, Joan O'Connell, Diarmuid Feely, Orla Dominguez, Manuel http://hdl.handle.net/10197/3875 2012-10-16T15:44:55Z 2012-07-25T00:00:00Z

Pulsed Digital Oscillators for Electrostatic MEMS Fernandez, D.; Jimenez, V.; Madrenas, J.; Gorreta, Sergi; Blokhina, Elena; Pons Nin, Joan; O'Connell, Diarmuid; Feely, Orla; Dominguez, Manuel This paper introduces a new actuation scheme for implementing Pulsed Digital Oscillators (PDOs) for electrostatic MEMS resonators. In this scheme, the capacitance of the device is biased with a voltage and it is periodically sampled. Short pulses of zero voltage are applied depending on the decisions taken by the oscillator loop. The paper discusses in detail the implementation of such electrostatic PDO (e-PDO) through a prototype and links the e-PDO to the conventional PDO theory. As an example, it is shown that with this actuation scheme it is possible to excite different resonances of the mechanical structure simply by changing the parameters of the feedback filter of the oscillator.

2012-07-25T00:00:00Z Blokhina, Elena Galayko, Dimitri Basset, Philippe Feely, Orla http://hdl.handle.net/10197/3867 2012-10-15T16:33:41Z 2012-01-01T00:00:00Z

Steady-State Oscillations in Resonant Electrostatic Vibration Energy Harvesters Blokhina, Elena; Galayko, Dimitri; Basset, Philippe; Feely, Orla In this paper, we present a formal analysis and description of the steady-state behavior of an electrostatic vibration energy harvester operating in constant-charge mode and using different types of electromechanical transducers. The method predicts parameter values required to start oscillations, allows a study of the dynamics of the transient process, and provides a rigorous description of the system, necessary for further investigation of the related nonlinear phenomena and for the optimisation of converted power. We show how the system can be presented as a nonlinear oscillator and be analysed by the multiple scales method, a type of perturbation technique. We analyse two the most common cases of the transducer geometry and find the amplitude and the phase of steady-state oscillations as functions of parameters. The analytical predictions are shown to be in good agreement with the results obtained by behavioural modeling.

2012-01-01T00:00:00Z O'Riordan, Eoghan Harte, Peter Blokhina, Elena Galayko, Dimitri Feely, Orla http://hdl.handle.net/10197/3866 2012-10-15T16:23:43Z 2012-07-01T00:00:00Z

Bifurcation Scenarios in Electrostatic Vibration Energy Harvesters O'Riordan, Eoghan; Harte, Peter; Blokhina, Elena; Galayko, Dimitri; Feely, Orla In this paper, we present numerical bifurcation analysis of an electrostatic vibration energy harvester operating in constant-charge mode and using the in-plane gap closing transducer. We show how the system can be represented as a nonlinear oscillator and analysed using methods of nonlinear dynamics. We verify previous analytical theories and explain the behaviour of these energy harvesters, particularly in the regime between the first period doubling bifurcation and chaos. Nonlinear Dynamics of Electronic Systems 2012 (NDES 2012), July 11-13, 2012, Wolfenbüttel, Germany

2012-07-01T00:00:00Z Bradley, Mark Alarcon, E. Feely, Orla http://hdl.handle.net/10197/3863 2012-10-15T15:45:33Z 2012-05-20T00:00:00Z

Analysis of Limit Cycles in a PI Digitally Controlled Buck Converter Bradley, Mark; Alarcon, E.; Feely, Orla Digital control of power converters has been an area of considerable research interest in recent times. One of the problems which arises in these systems is that of the limit cycle oscillations that occur due to quantization in the feedback loop. This paper investigates the limit cycle oscillations that occur in the digitally controlled version of the buck converter with a proportional-integral controller. The amplitude and frequency of the oscillations that may occur on two duty cycle levels are investigated and related to the controller gain parameters. The analysis shows that it is not possible to guarantee that limit cycle oscillations on two levels will not occur simply by adjusting the gain parameters, and yields a condition which will prevent oscillations on two levels from occurring. IEEE International Symposium on Circuits and Systems, May 20-23, 2012, Seoul, Korea

2012-05-20T00:00:00Z Grant, Peadar F. Lowery, Madeleine M. http://hdl.handle.net/10197/3847 2012-10-09T15:21:12Z 2012-06-08T00:00:00Z

Simulation of cortico-basal ganglia oscillations and their suppression by closed loop deep brain stimulation Grant, Peadar F.; Lowery, Madeleine M. A new model of deep brain stimulation is presented that integrates volume conduction effects with a neural model of pathological beta-band oscillations in the cortico-basal ganglia network. The model is used to test the clinical hypothesis that closed-loop control of the amplitude of DBS may be possible, based on the average rectified value of beta-band oscillations in the local field potential. Simulation of closed-loop high-frequency Deep Brain Stimulation was shown to yield energy savings, with the magnitude of the energy saved dependent on the strength of coupling between the subthalamic nucleus and the remainder of the cortico-basal ganglia network. When closed-loop DBS was applied to a strongly coupled cortico-basal ganglia network, the stimulation energy delivered over a 480 s period was reduced by up to 42 %. Greater energy reductions were observed for weakly coupled networks, as the stimulation amplitude reduced to zero once the initial desynchronization had occurred. The results provide support for the application of closed-loop highfrequency DBS based on electrophysiological biomarkers.

2012-06-08T00:00:00Z Grant, Peadar F. Lowery, Madeleine M. http://hdl.handle.net/10197/3846 2012-10-09T15:11:15Z 2010-10-01T00:00:00Z

Effect of dispersive conductivity and permittivity in volume conductor models of deep brain stimulation Grant, Peadar F.; Lowery, Madeleine M. The aim of this study was to examine the effect of dispersive tissue properties on the volume-conducted voltage waveforms and volume of tissue activated during deep brain stimulation. Inhomogeneous finite-element models were developed, incorporating a distributed dispersive electrode–tissue interface and encapsulation tissue of high and low conductivity, under both current controlled and voltage-controlled stimulation. The models were used to assess the accuracy of capacitive models, where material properties were estimated at a single frequency, with respect to the full dispersive models. The effect of incorporating dispersion in the electrical conductivity and relative permittivity was found to depend on both the applied stimulus and the encapsulation tissue surrounding the electrode. Under current-controlled stimulation, and during voltage-controlled stimulation when the electrode was surrounded by high-resistivity encapsulation tissue, the dispersive material properties of the tissue were found to influence the voltage waveform in the tissue, indicated by RMS errors between the capacitive and dispersive models of 20%–38% at short pulse durations. When the dispersive model was approximated by a capacitive model, the accuracy of estimates of the volume of tissue activated was very sensitive to the frequency at which material properties were estimated.When material properties at 1 kHz were used, the error in the volume of tissue activated by capacitive approximations was reduced to −4.33% and 11.10%, respectively, for current controlled and voltage-controlled stimulations, with higher errors observed when higher or lower frequencies were used.

2010-10-01T00:00:00Z Grant, Peadar F. Lowery, Madeleine M. http://hdl.handle.net/10197/3834 2012-10-02T15:47:18Z 2009-11-01T00:00:00Z

Electric field distribution in a finite-volume head model of deep brain stimulation Grant, Peadar F.; Lowery, Madeleine M. This study presents a whole-head finite element model of deep brain stimulation to examine the effect of electrical grounding, the finite conducting volume of the head, and scalp, skull and cerebrospinal fluid layers. The impedance between the stimulating and reference electrodes in the whole-head model was found to lie within clinically reported values when the reference electrode was incorporated on a localized surface in the model. Incorporation of the finite volume of the head and inclusion of surrounding outer tissue layers reduced the magnitude of the electric field and activating function by approximately 20% in the region surrounding the electrode. Localized distortions of the electric field were also observed when the electrode was placed close to the skull. Under bipolar conditions the effect of the finite conducting volume was shown to be negligible. The results indicate that, for monopolar stimulation, incorporation of the finite volume and outer tissue layers can alter the magnitude of the electric field and activating function when the electrode is deep within the brain, and may further affect the shape if the electrode is close to the skull.

2009-11-01T00:00:00Z De La Cruz Blas, Carlos A. Feely, Orla http://hdl.handle.net/10197/3741 2012-08-13T09:39:09Z 2011-08-01T00:00:00Z

Limit Cycle Behavior in a Class-AB Second-Order Square Root Domain Filter De La Cruz Blas, Carlos A.; Feely, Orla This paper shows how an unwanted limit cycle can be exhibited by a second-order CMOS companding filter. The filter employs the quasi-quadratic law of the MOS transistor in strong inversion and saturation to achieve compression together with a Class-AB topology to extend the dynamic range. In the zero-input case, the filter operates in the manner expected of an externally-linear circuit. However, when a standard linear IC design technique is applied to it, unwanted zero-input sustained oscillations may be observed. Simulations from PSpice and measurement results from a semi-custom realization in a 0.8μm CMOS process are used to explore this behavior. This work highlights an aspect of the behavior of such filters that must be taken into account by analog designers.

2011-08-01T00:00:00Z Bi, Chuang Feely, Orla http://hdl.handle.net/10197/3727 2012-07-26T15:33:30Z 2009-08-23T00:00:00Z

Nonlinear dynamics of alias-locked loop Bi, Chuang; Feely, Orla This paper examines the nonlinear dynamics of an alias-locked loop (ALL) which uses an aliasing divider instead of a traditional frequency divider in the feedback loop of a phaselocked loop. A nonlinear model of the ALL is developed and used to study the global and local nonlinear dynamics of the system. In the global dynamics, we see disconnected regions of stability, which arise as a direct result of the aliasing operation. In the local dynamics, we see how the orbits observed have a particular dependence on the ratio of sample and reference frequencies. European Conference on Circuit Theory and Design (ECCTD 2009), Antalya, Turkey, August 23-27, 2009

2009-08-23T00:00:00Z Feely, Orla http://hdl.handle.net/10197/3726 2012-07-26T15:19:29Z 2011-01-01T00:00:00Z

Discontinuous piecewise-linear discrete-time dynamics - maps with gaps in electronic sysems Feely, Orla Many important electronic systems are modelled by discrete-time equations with nonlinearities that are discontinuous and piecewise-linear, often arising as a result of quantization. Approximations based on linearization – the standard engineering response to nonlinearity – are often quite unhelpful in these systems, because of the form of the nonlinearity. Certain methods and results have been developed over a number of years for the analysis of discontinuous piecewise-linear discrete-time dynamics. The aim of this tutorial paper is to review that body of knowledge, and to show how it can be applied to representative electronic systems.

2011-01-01T00:00:00Z Moni, Aishwarya Bean, Christopher J. Lokmer, Ivan Rickard, Scott http://hdl.handle.net/10197/3698 2012-06-26T13:47:49Z 2012-05-01T00:00:00Z

Source separation on seismic data : application in a geophysical setting Moni, Aishwarya; Bean, Christopher J.; Lokmer, Ivan; Rickard, Scott This article gives a brief description of the Degenerate Unmixing Estimation Technique (DUET) and applies it in a geophysical setting. Source separation has not been fully addressed by geophysicists and is a crucial first step to locating simultaneous sources, which in turn helps with understanding the dynamics of the sources and their source mechanisms. DUET is applied to synthetic seismic signals. The source separation method works successfully to separate two contemporary explosive sources, and two simultaneous oblique tensile cracks in a 3D structural model of Mt Etna. The method is also applied to field recordings on Mt Etna from 2008. The method separates Long Period events from tremor, Long Period events from Volcano Tectonic events and different sources of tremor from each other.

2012-05-01T00:00:00Z Gopinathan, Unnikrishnan Monaghan, David S. Naughton, Thomas J. Sheridan, John T. http://hdl.handle.net/10197/3666 2012-06-14T16:22:01Z 2005-10-16T00:00:00Z

An optical encryption scheme that uses polarization of coherent light Gopinathan, Unnikrishnan; Monaghan, David S.; Naughton, Thomas J.; Sheridan, John T. We demonstrate an optical system that encodes two dimensional data as different polarization states. The encrypted image is recorded using a digital holographic setup and the decryption is done numerically. Image Information, Restoration and Encryption (FTuT, Frontiers in Optics (FiO), Tucson, Arizona, October 16, 2005

2005-10-16T00:00:00Z O'Neill, Feidhlim T. Lawrence, Justin R. Sheridan, John T. http://hdl.handle.net/10197/3665 2012-06-14T16:45:03Z 2002-02-01T00:00:00Z

Comparison of holographic photopolymer materials by use of analytic nonlocal diffusion models O'Neill, Feidhlim T.; Lawrence, Justin R.; Sheridan, John T. The one-dimensional diffusion equation governing holographic grating formation in photopolymers, which includes both nonlocal material response and generalized dependence of the rate of polymerization on the illuminating intensity, has been previously solved under the two-harmonic expansion assumption. The resulting analytic expressions for the monomer and polymer concentrations have been derived and their ranges of validity tested in comparison with the more accurate numerical four-harmonic case. We used these analytic expressions to carry out a study of experimental results presented in the literature over a 30-year period. Automatic fitting of the data with these formulas allows material parameters, including the nonlocal chain-length variance σ, to be estimated. In this way, (i) a quantitative comparison of different materials can be made, and (ii) a standard form of experimental result presentation is proposed to facilitate such a procedure.

2002-02-01T00:00:00Z Kelly, John V. Gleeson, M. R. Close, Ciara E. O'Neill, Feidhlim T. Sheridan, John T. http://hdl.handle.net/10197/3664 2012-06-14T16:10:45Z 2006-10-10T00:00:00Z

Generalized model of photopolymer behavior for use in optimized holographic data storage scheduling algorithms Kelly, John V.; Gleeson, M. R.; Close, Ciara E.; O'Neill, Feidhlim T.; Sheridan, John T. A generalized model of photo-polymerization in free radical chainforming polymers has been developed. Applying this model to data storage, optimized scheduling algorithms are developed for the multiplexing of multiple data pages of uniform diffraction efficiency. OLED Circuits, Solar Cells and Organic Memory (OPTuC) at Organic Photonics and Electronics (OPE) Rochester, New York, October 10, 2006

2006-10-10T00:00:00Z Bradley, Mark Feely, Orla Teplinsky, Alexey http://hdl.handle.net/10197/3622 2012-05-22T15:18:47Z 2011-08-29T00:00:00Z

Limit cycles in a digitally controlled buck converter Bradley, Mark; Feely, Orla; Teplinsky, Alexey We describe the mathematical model of a digitally controlled buck converter. This model is an autonomous discrete-time discontinuous piecewise-linear dynamical system in three dimensions. Investigating this system, we find its equilibrium points, describe the shape and size of possible limit cycles (i.e. stable periodic motions), and derive conditions for their existence and non-existence. European Conference on Circuit Theory and Design (ECCTD), Linkoping, Sweden, 29-31 Aug. 2011

2011-08-29T00:00:00Z Blokhina, Elena Lopez, David Gorreta, Sergi Molinero, David Feely, Orla Pons Nin, Joan Dominguez, Manuel http://hdl.handle.net/10197/3615 2012-05-15T16:15:03Z 2012-02-06T00:00:00Z

Dielectric charge control in electrostatic MEMS positioners / varactors Blokhina, Elena; Lopez, David; Gorreta, Sergi; Molinero, David; Feely, Orla; Pons Nin, Joan; Dominguez, Manuel A new dynamical closed-loop method is proposed to control dielectric charging in capacitive MEMS positioners/ varactors for enhanced reliability and robustness. Instead of adjusting the magnitude of the control voltage to compensate the drift caused by the dielectric charge, the method uses a feedback loop to maintain it at a desired level: the device capacitance is periodically sampled and bipolar pulses of constant magnitude are applied. Specific models describing the dynamics of charge and a control map are introduced. Validation of the proposed method is accomplished both through discrete-time simulations and with experiments using MEMS devices that suffer from dielectric charging.

2012-02-06T00:00:00Z Bi, Chuang Curran, Paul F. Feely, Orla http://hdl.handle.net/10197/3595 2012-05-01T11:44:50Z 2011-08-29T00:00:00Z

Linearized discrete-time model of higher order charge-pump PLLs Bi, Chuang; Curran, Paul F.; Feely, Orla In this paper, we derive linearized discrete-time models of higher order Charge-Pump Phase-Locked Loops (CPPLLs). The behaviour of CP-PLLs in the steady state is analysed and an important feature is developed. The nonlinear state equations of CP-PLLs are linearized around the equilibrium point. The linearized discrete-time model is finally verified using behavioral simulations in Matlab and PSpice. European Conference on Circuit Theory and Design (ECCTD), Linkoping, Sweden, 29-31 August, 2011

2011-08-29T00:00:00Z Tertinek, Stefan Feely, Orla http://hdl.handle.net/10197/3594 2012-05-01T11:34:14Z 2011-06-01T00:00:00Z

Output-jitter performance of second-order digital bang-bang phase-locked loops with nonaccumulative reference clock jitter Tertinek, Stefan; Feely, Orla Bang-bang phase-locked loops (BBPLLs) are inherently nonlinear systems due to the binary phase detector (BPD). While they are typically used for clock and data recovery, the ongoing trend toward digital loop implementations has resulted in several digital BBPLLs (DBBPLLs) suitable for frequency synthesis. This brief investigates the effect of nonaccumulative reference clock jitter (due to white phase noise) in second-order DBBPLLs, comparing the output jitter with that of first-order DBBPLLs. For small clock jitter, the nonlinear loop behavior is modeled as a two-dimensional Markov chain, and the output jitter is smaller than but close to that of a first order loop. For large clock jitter, the BPD nonlinearity is linearized, and the output jitter is larger than that of a first order loop; it is proportional to clock jitter and inversely proportional to the square root of the stability factor—the ratio of the proportional path gain to the integral-path gain of the digital loop filter.

2011-06-01T00:00:00Z Tertinek, Stefan Teplinsky, Alexey Feely, Orla http://hdl.handle.net/10197/3593 2012-05-01T11:24:54Z 2008-05-18T00:00:00Z

Phase jitter dynamics of first-order digital phase-locked loops with frequency-modulated input Tertinek, Stefan; Teplinsky, Alexey; Feely, Orla Inherent to digital phase-locked loops is frequency quantization in the number-controlled oscillator which prevents the loop from locking exactly onto its reference signal and introduces unwanted phase jitter. This paper investigates the effect of frequency quantization in a first-order loop with a frequency-modulated input signal. Using tools of nonlinear dynamics, we show that, depending on the modulation amplitude, trajectories in the phase space eventually fall into either an invariant region or a trapping region, the boundaries of which give useful bounds on the steady-state phase jitter excursion. We also derive a sufficient condition for the maximum modulation amplitude to prevent loop cycle slipping. IEEE International Symposium on Circuits and Systems (ISCAS), Seattle, USA, 18-21 May 2008

2008-05-18T00:00:00Z Tertinek, Stefan Gleeson, James Feely, Orla http://hdl.handle.net/10197/3592 2012-05-01T11:18:31Z 2010-09-01T00:00:00Z

Statistical analysis of first-order bang-bang phase-locked loops using sign-dependent random-walk theory Tertinek, Stefan; Gleeson, James; Feely, Orla Bang-bang phase-locked loops (BBPLLs) are inherently nonlinear due to the hard nonlinearity introduced by the binary phase detector (BPD). This paper provides an exact statistical analysis of the steady-state timing jitter in a first order BBPLL when the reference clock is subject to accumulative jitter. By elaborating on the analogy of viewing a first-order BBPLL as a single-integration delta modulator (DM) in the phase domain, we are able to relate hunting jitter and slew-rate limiting in a BBPLL to granular noise and slope overload in a DM. The stochastic timing-jitter behavior is modeled as a sign-dependent random walk, for which we obtain the asymptotic characteristic function and analytical expressions for the first four cumulants. These expressions are applied to the BBPLL to statistically analyze the static timing offset and the RMS timing jitter, including the effect of a frequency offset. The analysis shows that the RMS timing jitter is constant for small RMS clock jitter and grows quadratically with large RMS clock jitter, and that there exists an optimal bang-bang phase step for minimum RMS timing jitter. Computing the kurtosis reveals the effect of the BPD nonlinearity: the timing jitter is largely non-Gaussian.

2010-09-01T00:00:00Z Blokhina, Elena Feely, Orla http://hdl.handle.net/10197/3591 2012-05-01T11:13:27Z 2009-01-01T00:00:00Z

A kicked oscillator as a model of a pulsed MEMS system Blokhina, Elena; Feely, Orla In this paper, we study the behaviour of a MEMS oscillator by applying methods of nonlinear dynamics. We model the system as a kicked damped oscillator and obtain the iterative maps that describe the MEMS system. The dynamics of the maps are studied numerically: we present a study of limit cycles and their rotation numbers and show how the control parameters and initial conditions may affect the output frequencies.

2009-01-01T00:00:00Z Tertinek, Stefan Teplinsky, Alexey Feely, Orla http://hdl.handle.net/10197/3590 2012-05-01T11:05:28Z 2007-12-01T00:00:00Z

Frequency quantization in first-order digital phase-locked loops with frequency-modulated input Tertinek, Stefan; Teplinsky, Alexey; Feely, Orla Frequency granularity in a digital phase-locked loop arises from quantization in the number-controlled oscillator which prevents the loop from locking exactly onto its reference signal and introduces unwanted phase jitter. Based on a nonlinear analysis of trajectories in the phase space, we have recently investigated the effect of frequency quantization in a first-order loop with a frequency-modulated input signal and have derived useful bounds on the steady-state phase jitter excursion. In this paper, we continue that work and derive the maximum modulation amplitude such that loop cycle slipping is avoided. We also examine in detail the loop behavior in acquiring phase-lock. Presented at the International Workshop on Nonlinear Maps and their Applications (NOMA '07), INSA, Toulouse, December 13-14, 2007

2007-12-01T00:00:00Z Tertinek, Stefan Feely, Orla http://hdl.handle.net/10197/3585 2012-04-24T14:55:13Z 2009-05-24T00:00:00Z

Combined effect of loop delay and reference clock jitter in first-order digital bang-bang phase-locked loops Tertinek, Stefan; Feely, Orla Recently, several digital phase-locked loops (DPLLs) have been demonstrated to achieve the jitter performance of traditional charge-pump-based analog PLLs. This paper is concerned with a class of DPLLs employing a binary-quantized phase detector, referred to as bangbang PLLs (BBPLLs). They are widely used in clock and data recovery circuits and have recently been implemented as digital BBPLLs for high-bandwidth synthesis. Given that a DPLL implementation typically suffers from (excess) loop delay, this paper investigates the combined effect of loop delay and reference clock jitter in a first-order digital BBPLL. To statistically characterize the loop’s timing jitter we formulate it as a discrete-time vector Markov process and numerically solve the associated Chapman-Kolmogorov equation. This allows us to compute the timing jitter probability density function in steady-state and to evaluate the jitter performance (timing offset and RMS timing jitter) for varying loop detuning, RMS reference clock jitter and loop delay. Paper presented at the IEEE International Symposium on Circuits and Systems (ISCAS), Taipei, Taiwan, 24-27 May 2009

2009-05-24T00:00:00Z Tertinek, Stefan Feely, Orla http://hdl.handle.net/10197/3581 2012-04-19T15:05:19Z 2008-10-16T00:00:00Z

Investigation of first-order digital bang-bang phase-locked loops with reference clock jitter Tertinek, Stefan; Feely, Orla Bang-bang phase-locked loops (BBPLLs) are a class of PLLs with a binary-quantized phase detector (BPD). They are widely used in clock and data recovery circuits and have recently been implemented as digital BBPLLs for high-bandwidth synthesis. This paper investigates a first-order digital BBPLL with reference clock jitter. We derive the Chapman-Kolmogorov equation which statistically characterizes the timing jitter process. The numerical solution of this equation allows us to compute the timing jitter probability density function (PDF) in steadystate and to examine the effect of varying loop detuning and RMS reference clock jitter on the timing offset, the RMS timing jitter and the mean number of steps to slip a cycle. The analysis shows that the steady-state PDF is Gaussian-like only for a small range of RMS clock jitter values, which leads to a new curve for the BPD gain as a function of jitter. Paper presented at the Nordic microelectronics conference (NORCHIP), Tallinn, Estonia, 17-18 November, 2008

2008-10-16T00:00:00Z Tertinek, Stefan Gleeson, James Feely, Orla http://hdl.handle.net/10197/3580 2012-04-19T14:51:48Z 2010-12-10T00:00:00Z

Binary phase detector gain in bang-bang phase-locked loops with DCO jitter Tertinek, Stefan; Gleeson, James; Feely, Orla Bang-bang phase-locked loops (BBPLLs) are hard nonlinear systems due to the nonlinearity introduced by the binary phase detector (BPD). In the presence of jitter, the nonlinear loop is typically analyzed by linearizing the BPD and applying linear transfer functions in the analysis. In contrast to a linear PD, the linearized gain of a BPD depends on the rms jitter and the type of jitter (either non-accumulative or accumulative). Previous works considered the case of nonaccumulative reference clock jitter and showed that the BPD gain is inversely proportional to the rms jitter when the latter is small or large. In this brief we consider the case of accumulative DCO jitter and derive an asymptotic closed-form expression for the BPD gain which becomes exact in the limit of small and large jitter. Contrary to the reference clock jitter case, the BPD gain is constant for small DCO jitter and is inversely proportional to the square of jitter for large DCO jitter; in the latter case, the timing jitter has a normal-Laplace distribution.

2010-12-10T00:00:00Z Pladys, Mathieu Blokhina, Elena http://hdl.handle.net/10197/3551 2012-04-03T11:41:26Z 2011-05-15T00:00:00Z

MEMS with sigma-delta type of feedback loop control as an iterative map Pladys, Mathieu; Blokhina, Elena In this work, we consider a system that consists of a microresonator and a ΣΔ type feedback loop control which is typically a part of inertial sensors. We describe this architecture as a dynamical system (an iterative difference equation) in the time domain in order to study possible periodic solutions in the output. Paper presented at the IEEE International Symposium on Circuit and Systems 2011 (ISCAS 2011), Rio de Janeiro, Brazil, 15-18 May 2011

2011-05-15T00:00:00Z Blokhina, Elena Galayko, Dimitri Wade, Rhona Basset, Philippe Feely, Orla http://hdl.handle.net/10197/3550 2013-02-26T11:25:35Z 2012-05-01T00:00:00Z

Bifurcations and chaos in electrostatic vibration energy harvesters Blokhina, Elena; Galayko, Dimitri; Wade, Rhona; Basset, Philippe; Feely, Orla In this paper, we present an analysis of an electrostatic vibration harvester operating in the constant-charge mode. The goal of the study is to bound regions of control parameters where the system displays steady-state harmonic oscillations as required for practical use. We show how the system can be presented as a nonlinear oscillator and analysed employing the multiple scales method, Floquet theory and Lyapunov exponents. We determine the conditions for the onset of steady-state oscillations, the period doubling bifurcation and transition to chaos. This allows us to bound regions of control parameters where the system displays desired regular oscillations and, therefore, to identify maximal harvestable power for a particular architecture. Paper presented at the IEEE International Symposium on Circuits and Systems 2012 (ISCAS 2012), Seoul, Korea, 20-23 May 2012

2012-05-01T00:00:00Z Ricart, Jordi Pons Nin, Joan Blokhina, Elena Gorreta, Sergi Hernando, Jorge Manzaneque, Tomas Sánchez-Rojas, José Luis‏ Feely, Orla Dominguez, Manuel http://hdl.handle.net/10197/3549 2012-04-03T11:18:00Z 2010-08-01T00:00:00Z

Control of MEMS vibration modes with pulsed digital oscillators : part II — simulation and experimental results Ricart, Jordi; Pons Nin, Joan; Blokhina, Elena; Gorreta, Sergi; Hernando, Jorge; Manzaneque, Tomas; Sánchez-Rojas, José Luis‏; Feely, Orla; Dominguez, Manuel This paper extends our previous work on the selective excitation of mechanical vibration modes in MEMS devices using Pulsed Digital Oscillators. It begins by presenting extensive simulation results using the set of iterative maps that model the system and showing that it is possible to activate two or three spatial modes (resonances) of the mechanical structure with a Pulsed Digital Oscillator (PDO). The second part of this paper presents experimental results corroborating the theory and simulation results. It is shown that it is possible to separately excite vibration modes of the device by setting a few parameters of the PDO structure such as the sampling frequency and the sign of the feedback loop.

2010-08-01T00:00:00Z Hennelly, Bryan M. Sheridan, John T. http://hdl.handle.net/10197/3523 2012-02-22T14:38:53Z 2003-02-15T00:00:00Z

Optical image encryption by random shifting in fractional Fourier domains Hennelly, Bryan M.; Sheridan, John T. A number of methods have recently been proposed in the literature for the encryption of two-dimensional information by use of optical systems based on the fractional Fourier transform. Typically, these methods require random phase screen keys for decrypting the data, which must be stored at the receiver and must be carefully aligned with the received encrypted data. A new technique based on a random shifting, or jigsaw, algorithm is proposed. This method does not require the use of phase keys. The image is encrypted by juxtaposition of sections of the image in fractional Fourier domains. The new method has been compared with existing methods and shows comparable or superior robustness to blind decryption. Optical implementation is discussed, and the sensitivity of the various encryption keys to blind decryption is examined.

2003-02-15T00:00:00Z Gleeson, M. R. Kelly, John V. Close, Ciara E. Sabol, Dušan Sheridan, John T. http://hdl.handle.net/10197/3522 2012-02-22T14:33:39Z 2007-05-20T00:00:00Z

Holographic grating evolution in photopolymer materials Gleeson, M. R.; Kelly, John V.; Close, Ciara E.; Sabol, Dušan; Sheridan, John T. A generalized non-local polymerization driven diffusion (NPDD) model is presented, including the effects of absorption and inhibition. Experimentally obtained growth curves are fit using a four-harmonic numerical fitting algorithm and key material parameters are extracted. Poster presented at Optical Data Storage (ODS) Portland, Oregon, May 20, 2007

2007-05-20T00:00:00Z Ryle, James P. Al-Kalbani, Mohammed Collins, Niamh Gopinathan, Unnikrishnan Boyle, Gerard Coakley, Davis Sheridan, John T. http://hdl.handle.net/10197/3521 2012-02-22T14:27:42Z 2008-10-19T00:00:00Z

Speckle interferometric system for measuring ocular microtremor Ryle, James P.; Al-Kalbani, Mohammed; Collins, Niamh; Gopinathan, Unnikrishnan; Boyle, Gerard; Coakley, Davis; Sheridan, John T. A compact optical system has been developed capable of measuring minute movements of the eye. Eye movement is simulated through the application an electrical signal to a piezoelectric material which acts as the eye’s surface. Using this device, both the amplitude and frequency components of this movement can be accurately measured. Poster presented at Frontiers in Optics (FiO) Rochester, New York, October 19, 2008

2008-10-19T00:00:00Z Blokhina, Elena Feely, Orla Dominguez, Manuel http://hdl.handle.net/10197/3498 2012-02-07T16:29:02Z 2009-05-01T00:00:00Z

Dynamics of the MEMS pulsed digital oscillator with multiple delays in the feedback loop Blokhina, Elena; Feely, Orla; Dominguez, Manuel In this paper we apply methods of nonlinear dynamics to examine the behavior of the pulsed digital oscillator for microelectromechanical systems (MEMS). We study the regions of existence of oscillations and demonstrate the effect on these of including additional delays into the feedback loop. Paper presented at the IEEE International Symposium on Circuits and Systems 2009 (ISCAS 2009), May 24 -27, 2009, Taipei, Taiwan

2009-05-01T00:00:00Z Blokhina, Elena Feely, Orla Dominguez, Manuel http://hdl.handle.net/10197/3497 2012-02-07T15:26:52Z 2009-08-01T00:00:00Z

Excitation of multiple spatial modes of a MEMS cantilever in the pulsed digital oscillator Blokhina, Elena; Feely, Orla; Dominguez, Manuel The aim of this paper is to apply an approach that will allow us to consider different mechanical modes of a MEMS cantilever in the form of separate mass-spring-damper equations with the appropriate form of an external driving. In the paper, we focus on a specific MEMS cantilever and use a Pulsed Digital Oscillator (PDO) to keep self-sustained oscillations of the mechanical structure. By applying the order-reduction procedure to a partial differential equation that describes the transversal deflections, we obtain a system of coupled ordinary differential equations that describes the excitation of multiple spatial modes. On the basis of these ordinary differential equations, we formulate a set of iterative maps to describe the evolution of the modes between two sampling events. The numerical simulations we present are focused on the most common case when the first two mechanical modes are taken into consideration Paper presented at the European Conference on Circuit Theory and Design 2009 (ECCTD 2009), Antalya, Turkey, 23-27 August 2009

2009-08-01T00:00:00Z Blokhina, Elena Feely, Orla Ricart, Jordi Dominguez, Manuel http://hdl.handle.net/10197/3496 2012-02-07T15:18:56Z 2010-05-01T00:00:00Z

On some properties of the output of a pulsed digital oscillator working with multiple resonances Blokhina, Elena; Feely, Orla; Ricart, Jordi; Dominguez, Manuel In this paper, we study the possible output of the pulsed digital oscillator (PDO) with multiple resonant modes of the mechanical resonator in the feedback loop. PDOs are simple circuits that allow linear resonators to maintain self-sustained oscillations and can work as mass-change resonant sensors. For a resonant sensor, activation of higher vibration modes of a mechanical resonator can be a way to improve its performance. We show that the location of the sensing/actuation system affects the output and can enhance higher mechanical modes. Paper presented at the IEEE International Symposium on Circuits and Systems 2010 (ISCAS 2010), Paris, France, 30 May - 2 June, 2010.

2010-05-01T00:00:00Z Gallego, Sergi Ortuño, M. Neipp, Cristian Márquez, A. Beléndez, A. Pascual, I. Kelly, John V. Sheridan, John T. http://hdl.handle.net/10197/3476 2012-02-02T16:58:09Z 2005-03-21T00:00:00Z

Physical and effective optical thickness of holographic diffraction gratings recorded in photopolymers Gallego, Sergi; Ortuño, M.; Neipp, Cristian; Márquez, A.; Beléndez, A.; Pascual, I.; Kelly, John V.; Sheridan, John T. In recent years the interest in thick holographic recording materials for storage applications has increased. In particular, photopolymers are interesting materials for obtaining inexpensive thick dry layers with low noise and high diffraction efficiencies. Nonetheless, as will be demonstrated in this work, the attenuation in depth of light during the recording limits dramatically the effective optical thickness of the material. This effect must be taken into account whenever thick diffraction gratings are recorded in photopolymer materials. In this work the differences between optical and physical thickness are analyzed, applying a method based on the Rigorous Coupled Wave Theory and taking into account the attenuation in depth of the refractive index profile. By doing this the maximum optical thickness that can be achieved can be calculated. When the effective thickness is known, then the real storage capacity of the material can be obtained.

2005-03-21T00:00:00Z Rhodes, William T. Sheridan, John T. Hennelly, Bryan M. http://hdl.handle.net/10197/3475 2012-02-02T16:53:09Z 2005-10-16T00:00:00Z

Optical wave propagation simulation, Wigner phase-space diagrams, and wave energy confinement Rhodes, William T.; Sheridan, John T.; Hennelly, Bryan M. The number of samples required for efficient numerical simulation of wave propagation can be determined by a combination of Wigner phase-space techniques, wave energy confinement arguments, and a theorem relating energy confinement to accuracy. Paper presented at Frontiers in Optics (FiO), Tucson, Arizona, October 16, 2005

2005-10-16T00:00:00Z Close, Ciara E. Kelly, John V. Gleeson, M. R. O'Neill, Feidhlim T. Sheridan, John T. http://hdl.handle.net/10197/3474 2012-02-02T16:43:42Z 2005-10-16T00:00:00Z

Material kinetics during fabrication of holographic gratings in acrylamide-based photopolymer Close, Ciara E.; Kelly, John V.; Gleeson, M. R.; O'Neill, Feidhlim T.; Sheridan, John T. We describe holographic grating formation in Acrylamide-based photopolymer material using the NonLocal Diffusion Driven model & discuss radical suppression leading to an inhibition period before grating growth. Diffusion effects of monomer & polymer are discussed. Paper presented at Frontiers in Optics (FiO), Tucson, Arizona, October 16, 2005

2005-10-16T00:00:00Z Sheridan, John T. Hennelly, Bryan M. Kelly, Damien P. http://hdl.handle.net/10197/3473 2012-02-02T16:38:52Z 2003-06-01T00:00:00Z

Motion detection, the Wigner distribution function, and the optical fractional Fourier transform Sheridan, John T.; Hennelly, Bryan M.; Kelly, Damien P. It is shown that both surface tilting and translational motion can be independently estimated by use of the speckle photographic technique by capturing consecutive images in two different fractional Fourier domains. A geometric interpretation, based on use of the Wigner distribution function, is presented to describe this application of the optical fractional Fourier transform when little prior information is known about the motion.

2003-06-01T00:00:00Z Sheridan, John T. http://hdl.handle.net/10197/3462 2012-01-30T15:21:01Z 1994-02-01T00:00:00Z

Generalization of the boundary diffraction method for volume gratings Sheridan, John T. The boundary diffraction method (BDM) is an approximate method that permits the derivation of analytic solutions for the output beams, both forward and backward propagating, that arise from the fundamental nature of holographic gratings. The method is based on the assumption that the volume scatter inside the grating can be supplemented by boundary diffraction coefficients. The boundary diffraction method is used for analysis of thick transmission geometry gratings in a unified way that deals with both the slanted and the unslanted cases. During the analysis, evidence emerges for the superiority of the first-order two-wave beta-value method over the Kogelnik k-vector closure method. The BDM is then further generalized to the case of a volume transmission grating, index matched to its surroundings, and replayed normally on-Bragg, i.e., satisfying the Bragg condition for normal incidence. The analytic equations derived are compared with results calculated with the rigorous coupled-wave method.

1994-02-01T00:00:00Z Dovolnov, Eugene A. Sharangovich, Sergey N. Sheridan, John T. http://hdl.handle.net/10197/3461 2012-01-30T15:13:31Z 2005-10-16T00:00:00Z

Inharmonic theoretical models for photopolymers gratings formation Dovolnov, Eugene A.; Sharangovich, Sergey N.; Sheridan, John T. We present an analytical model of the dynamics of spatial harmonics of holographic grating profiles, taking into consideration record mechanisms (polymerization and components diffusion), absorption, interference pattern contrast and optional photopolymerization nonlinearity. On the basis of numerical simulation we compare the model presented with the non-local polymerization driven diffusion model. The results of fitting experimental data with the model results are also presented.

2005-10-16T00:00:00Z Rhodes, William T. Healy, John J. Sheridan, John T. http://hdl.handle.net/10197/3460 2012-01-30T15:04:57Z 2009-10-11T00:00:00Z

Wigner cross-terms in sampled and other periodic signals Rhodes, William T.; Healy, John J.; Sheridan, John T. If we sample a scalar wave field, it becomes periodic in frequency. We examine the cross-terms which occur between these periodic replicas in the Wigner-Ville distribution function of such a signal. We present analytic results for Gaussian signals. The results also have implications for physical systems which contain periodic gratings. Paper presented at Frontiers in Optics (FiO) San Jose, California, October 11, 2009

2009-10-11T00:00:00Z Lawrence, Justin R. O'Neill, Feidhlim T. Sheridan, John T. http://hdl.handle.net/10197/3459 2012-03-29T13:26:40Z 2002-04-01T00:00:00Z

Adjusted intensity nonlocal diffusion model of photopolymer grating formation Lawrence, Justin R.; O'Neill, Feidhlim T.; Sheridan, John T. Diffusion-based models of grating formation in photopolymers have been proposed in which the rate of monomer polymerization (removal) is directly proportional to the illuminating intensity inside the medium. However, based on photochemical considerations, the rate of polymerization is proportional in the steady state to the square root of the interference intensity. Recently it was shown that, by introducing a nonlocal response function into the one-dimensional diffusion equation that governs holographic grating formation in photopolymers, one can deduce both high-frequency and low-frequency cutoffs in the spatial-frequency response of photopolymer materials. Here the first-order nonlocal coupled diffusion equations are derived for the case of a general relationship between the rate of polymerization and the exposing intensity. Assuming a twoharmonic monomer expansion, the resultant analytic solutions are then used to fit experimental growth curves for gratings fabricated with different spatial frequencies. Various material parameters, including monomer diffusion constant D and nonlocal variance s, are estimated.

2002-04-01T00:00:00Z Blokhina, Elena Pons Nin, Joan Ricart, Jordi Feely, Orla Dominguez, Manuel http://hdl.handle.net/10197/3445 2012-04-03T11:10:14Z 2010-08-01T00:00:00Z

Control of MEMS vibration modes with Pulsed Digital Oscillators : Part I — theory Blokhina, Elena; Pons Nin, Joan; Ricart, Jordi; Feely, Orla; Dominguez, Manuel The aim of this paper is to show that it is possible to excite selectively different mechanical resonant modes of a MEMS structure using Pulsed Digital Oscillators (PDOs). This can be done by simply changing the working parameters of the oscillator, namely its sampling frequency or its feedback filter. A set of iterative maps is formulated to describe the evolution of the spatial modes between two sampling events in PDOs. With this lumped model, it is established that under some circumstances PDO bitstreams related to only one of the resonances can be obtained, and that in the antioscillation regions of the PDO the mechanical energy is absorbed into the electrical domain on average. The possibility of selecting for a given resonant frequency the oscillation and antioscillation behaviour allows one to obtain oscillations at any given resonant mode of the MEMS structure.

2010-08-01T00:00:00Z Gleeson, M. R. Kelly, John V. Sabol, Dušan Close, Ciara E. Liu, Shui Sheridan, John T. http://hdl.handle.net/10197/3440 2012-01-18T17:19:31Z 2007-07-26T00:00:00Z

Modeling the photochemical effects present during holographic grating formation in photopolymer materials Gleeson, M. R.; Kelly, John V.; Sabol, Dušan; Close, Ciara E.; Liu, Shui; Sheridan, John T. The development of a theoretical model of the processes present during the formation of a holographic grating in photopolymer materials is crucial in enabling further development of holographic applications. To achieve this, it is necessary to understand the photochemical and photophysical processes involved and to isolate their effects, enabling each to be modeled accurately. While photopolymer materials are practical materials for use as holographic recording media, understanding the recording mechanisms will allow their limitations for certain processes to be overcome. In this paper we report generalizations of the nonlocal polymer driven diffusion (NPDD) model to include the effects of photosensitive dye absorption and the inhibition effects.

2007-07-26T00:00:00Z Li, Dayan Kelly, Damien P. Sheridan, John T. http://hdl.handle.net/10197/3439 2012-01-18T17:12:35Z 2011-08-25T00:00:00Z

Three-dimensional static speckle fields: Part II Experimental investigation Li, Dayan; Kelly, Damien P.; Sheridan, John T. In Part I [J. Opt. Soc. Am. A 28, 1896 (2011) of this paper, the physical model for fully developed speckle is examined based on two critical assumptions. (i) It is assumed that in the object plane, the speckle field is delta correlated, and (ii) it is assumed that the speckle field in the observation plane can be described as a Gaussian random process. A satisfactory simulation technique, based on the assumption that spatial averaging can be used to replace ensemble averaging, is also presented. In this part a detailed experimental investigation of the threedimensional speckle properties is performed using spatial averaging. The results provide solid verification for the predictions presented in Part I. The results are not only of theoretical interest but have practical implications. Techniques for locating and aligning the optical system axis with the camera center, and for measuring out-ofplane displacement, are demonstrated

2011-08-25T00:00:00Z Abe, Sumiyoshi Sheridan, John T. http://hdl.handle.net/10197/3425 2012-01-05T17:16:52Z 1999-08-01T00:00:00Z

Random fractional Fourier transform : stochastic perturbations along the axis of propagation Abe, Sumiyoshi; Sheridan, John T. The fractional Fourier transform (FRT) is known to be optically implementable with use of a medium with a perfect radial quadratic-index profile. Using the quantum-mechanical operator formalism, we examine the effects on the FRT action of such a medium that are due to small random inhomogeneities in the longitudinal direction, the direction of propagation, and we formulate the random fractional Fourier transform (RFRT). Applying the RFRT to a self-fractional Fourier function, a Gaussian function, we discuss both the total power and the variance. The random Fourier transform is examined as a special limiting case.

1999-08-01T00:00:00Z