Open-loop Configuration Research Articles

A micro-electro-mechanical memory based on the structural phase transition of VO2

The structural phase transition (SPT) in VO2 and its hysteretic behavior is used in the present work to program mechanical displacements of a micro-electro-mechanical memory through electro-thermal actuation (i.e., Joule heating). The memory element consists of a silicon dioxide cantilever with buried Ti/Pt heating electrodes and a nanocoating of VO2. The integrated heating electrode is used to actuate the structure, and its resistance is monitored to determine the phase transition of the material. A closed-loop system is implemented to ensure proper operation over a larger temperature window than previous work. The closed-loop control system is designed using the system parameters obtained from a static and transient response analysis. The advantages of the feedback configuration over an open-loop configuration are demonstrated by a larger difference between programmed states (i.e., higher noise margin). The micro-electro-mechanical memory shows no noticeable degradation after being operated for 12 000 cycles. Multiple mechanical states are programmed using oscillatory pulse sequences that produced bi-directional displacements.

A Fully Integrated Hall Sensor Microsystem for Contactless Current Measurement

Contactless current measurement based on Hall-effect sensors can be performed in either closed- or open-loop configuration. In this paper an open-loop sensor system with a current-mode output is described. The system measures the magnetic field induced around the current path targeting high linearity, accuracy, and speed. As the accuracy of the Hall sensor microsystem is affected by temperature-dependent offset and sensitivity of the sensing element, system-level solutions are developed to minimize these effects. The full system integration represents a design challenge as both voltage and current references are directly involved in the sensitivity calibration and both contribute to the system sensitivity drift. The measurements show a sensitivity drift lower than 80 ${\rm ppm}/^{\circ}{\rm C}$ , the offset drifts less than 300 ${\rm nT}/^{\circ}{\rm C}$ and the nonlinearity is less than ${\pm}{0.08\%}$ . The effects of the varying external field on the calibration loop are analyzed and the theoretical prediction is validated by measurement.

Causal inversion of non-minimum-phase systems for hardware-in-the-loop transmission testing

Hardware-in-the-loop transmission testing requires precise speed and torque tracking of the actuators that emulate the engine and vehicle dynamics. System-inversion-based feedforward controllers offer a solution, but they do not work for non-minimum-phase systems. Preview filters can provide stable approximate inversion of non-minimum-phase systems, but they require future values, which are not available in hardware-in-the-loop tests. This article develops a simple but effective controller to enable preview filters to provide causal inversion within the frequency range of interest. Causality is achieved by adding manual delays to the measured response signal either in a closed-loop or open-loop configuration, followed by system identification in the frequency domain. The proposed controller was initially validated experimentally for precise speed and torque tracking of uncoupled actuators. Then additional compensators were designed to deal with two dynamometers, which are coupled through a transmission system. The effectiveness of the proposed coupled controllers is demonstrated experimentally by using the dual actuator hardware-in-the-loop transmission test facility and commercially supplied models for the engine, driver and vehicle.

Evaluation of a readout circuit with ASIC oscillator for acoustic-wave sensor application

This article is concerned with the study of readout electronics for new-generation acoustic-wave sensors with high sensitivity. An integrated circuit programmable- frequency square wave oscillator is used in open-loop configuration and resonant frequency shift is detected using an undersampling analogue-to-digital converter. Simulated and measured results are reported which show that a simple setup with a low resolution frequency sweep provides sufficient accuracy to detect a frequency difference of less than 1 kHz (0.06% deviation from the nominal frequency), suitable for binary screening applications.

Closed-loop micromachined accelerometer based on thermal convection

A significant improvement of thermal accelerometer bandwidth κ demonstrated. In a classic open-loop configuration, a micromachined thermal accelerometer having a width of 1500 µm has a sensitivity of 0.045°C/g and a bandwidth up to 66 Hz limited by gas thermal response. A new sensor architecture is proposed to improve bandwidth with no sensitivity decrease: a closed-loop configuration with the addition of two resistors placed close to detectors to rebalance their temperature. They directly act on the thermal response of the fluid. Thus, sensor bandwidth is increased up to 1 kHz with a similar sensitivity of 0.034°C/g.

Experimental Study to Characterize the Performance of Combined Photovoltaic/Thermal Air Collectors

Combined photovoltaic/thermal (PV/T) collectors show great potential for reaching the objective of net-zero energy consumption in buildings, but the number of products on the market is still very limited. One of the reasons for the slow market uptake of PV/T collectors is the absence of standardized methods to characterize their performance. Performance characterization is a challenge for PV/T collectors because of the interaction between the thermal and electrical yield. This study addresses this particular issue for PV/T air collectors used in either closed-loop or open-loop configurations. In particular, it presents the potential of the equivalent cell temperature method to determine the temperature of the PV cells in a PV/T air collector and validates models to predict the thermal performance and cell temperature for this particular type of solar collector. Indoor and outdoor experimental tests were performed on two c-Si unglazed PV/T modules. The indoor part of this procedure provided the thermal diode voltage factor and the open-circuit voltage temperature coefficient, two parameters that are essential in the calculation of the equivalent cell temperature. The outdoor procedure consisted of acquiring simultaneous electrical and thermal measurements at various inlet temperatures and flowrates. For the collector used in a closed-loop configuration, thermal efficiency models using the fluid inlet, outlet, or average temperature in the calculation of the reduced temperature provided similar results. For an open-loop configuration, a thermal efficiency model as a function of the fluid outlet flowrate was found to be more appropriate. Using selection of variable methods, it was found that a multiple linear regression model using the fluid inlet temperature, the irradiance, and the fluid outlet temperature as predictive variables could be used to estimate both the PV module back surface average temperature and the equivalent cell temperature. When using the PV temperature predicted by these models in the electrical efficiency model, both PV temperatures showed similar performance. In collectors where the PV back surface temperature is not accessible for temperature sensors mounting, the equivalent cell temperature provides a valuable alternative to be used as the PV temperature. The PV/T collector thermal and electrical performance in either closed-loop or open-loop configurations was found to be encapsulated with a series of five-plots.

Analysis of the indoor GPS system as feedback for the robotic alignment of fuselages using laser radar measurements as comparison

The alignment of aircraft fuselages in the aerospace sector is currently done either manually or by complex, expensive automated systems. The manual process introduces a significant production delay and the automated systems are purpose-built and have limited flexibility, apart from its financial drawback. This work proposes a low-cost, high-flexibility system and, as part of it, evaluates the performance of a Rotary-Laser Automatic Theodolite (R-LAT) as a feedback source for the adaptive robot control of an anthropomorphic manipulator. In the proposed solution the robot carries a fuselage barrel and aligns it with respect to a second barrel. A high accuracy, frequency-modulated laser equipment is used to generate the reference system for the procedure. The measurements of the R-LAT are then verified with the frequency-modulated laser equipment in order to determine the linear and angular alignment tolerances achieved by the robot/R-LAT closed loop in a predefined work envelope. A throughout, step-by-step analysis of the measuring procedure is carried out to allow the recognition of error sources and thus the determination of an optimized method. These results identify the operation boundaries of the R-LAT within the process and yield its best configuration for the intended purpose. Using the EN ISO 9283 robot evaluation standard, the closed loop system was found to attain the nominal position with an average accuracy of 0.38mm and 0.01^o, contrasting with an average accuracy of 4.53mm and 0.21^o when the robot was operating in an open loop configuration.

Dispersion compensation in an open-loop all-optical chaotic communication system

The optical chaotic communication system using open-loop fiber transmission is studied under strong injection conditions. The optical chaotic communication system with open-loop configuration is studied using fiber transmission under strong injection conditions. The performances of fiber links composed of two types of fiber segments in different dispersion compensation maps are compared by testing the quality of the recovered message with different bit rates and encrypted by chaotic modulation (CM) or chaotic shift keying (CSK). The result indicates that the performance of the pre-compensation map is always worst. Two types of symmetrical maps are identical whatever the encryption method and bit-rate of message are. For the transmitting and the recovering of message of lower bit rate (1 Gb/s), the post-compensation map is the best scheme. However, for the message of higher bit rate (2.5 Gb/s), the parameters in communication system need to be modified properly in order to adapt to the high-speed application. Meanwhile, two types of symmetrical maps are the best scheme. In addition, the CM method is superior to the CSK method for high-speed applications. It is in accordance with the result in a back-to-back configuration system.

On dynamical behaviour of two-dimensional biological reactors

The dynamical behaviour for a generic two-dimensional model of a continuous bioreactor is studied in this article. The state variables for the bio-reacting system are restricted to concentrations of substrate and biomass, where the specific growth rate is a smooth function of the substrate concentration, which can be a kinetic function, monotone or non-monotone (as Monod, Haldane, Teissier, etc.). The effect of input (dilution rate) on multiplicity and bifurcation of equilibrium is shown in open-loop configuration. The absence of limit cycles on open-loop configuration and through state-feedback on the dilution rate are demonstrated. The aim of analysing oscillations under state feedback control is related to the possible improvement of reactor yields under this operation regime. An example for a cell-producing bioreactor illustrates the analytical results.

WORM GEAR ANALYSIS IN TERMS OF NUMERICAL MODELLING

A worm gear mechanism, widely used in numerous mechanical applications, is the essential component in energy ef­ficiency considerations. Compared to traditional gearboxes, worm gear is characterized by lower value of efficiency, provided by the manufacturers as 70-90%. However, the efficiency level can differ depending on the specific conditions of operation such as output torque, input rotational velocity, ambient temperature and type of lubrication. In order to analyse and simulate the worm gear mechanism in mechanical systems, it is essential to establish the actual efficiency value for specific conditions. The following article contains the description of efficiency test performed for the worm gear as a part of tram pantograph system studied in frame of ESTOMAD project. The aim of the experiment was to deter­mine the actual efficiency value of the transmission tested. The worm gear has been tested in an open loop configuration, therefore the efficiency has been determined basing on input and output torque and rotational velocity measurements. The tests have been performed for various output torques and input velocities to obtain view on losses in worm gear under different operational conditions, paying special attention to the velocity that drives the pantograph mechanism. The efficiency changes with the output torque variation, while the impact of rotational velocity level on the mentioned value is minimal. The results of measurements are used in modelling phase of worm gear component in 1D simulation environment, particularly creating new model and its correlation and validation.

A Formulation Case Study Comparing the Dynamic Gastric Model with Conventional Dissolution Methods

Even in the 21st century, conventional compendial dissolution testing remains a key cornerstone of the drug development process and quality control testing. However, opportunities exist with respect to in vitro technology developments that provide the potential for formulation and analytical scientists to exceed the capabilities of the conventional dissolution test toward a more biorelevant testing regime. This work presents a product development case study in which bioequivalence was observed between an immediate-release (IR) innovator product and a comparative singlelayer reference product. Despite this, when the constituent granule of the comparative single-layer reference product was formulated in a bilayer formulation with a nondisintegrating second layer, bioequivalence versus the innovator was not achieved. The use of USP Apparatus 2 dissolution testing failed to predict the bioequivalence failure, and hence an investigation was undertaken to develop a mechanistic understanding of in vivo behavior. Using both USP Apparatus 4 dissolution in the open-loop configuration and the dynamic gastric model (a novel in vitro model designed to mimic the human stomach), an understanding of the dissolution and disintegration properties of the reference product was established. The insights gained using novel technology facilitated the redesign and subsequent improvement in pharmacokinetic parameters of a complex pharmaceutical dosage form. INTRODUCTION The correlation of in vitro performance to in vivo behavior is a critically important and cost-effective objective for the drug development process within the pharmaceutical industry (1). It is imperative to work toward the development of a mechanistic understanding of the conditions of the gastrointestinal environment and its influence on drug liberation phenomena from the various oral pharmaceutical dosage forms (2). While fully characterizing the complexity of the gastrointestinal tract may remain an elusive goal (3), understanding the key parameters that can facilitate the prediction of dosage form behavior in vivo may be achieved. A key contributor to developing an understanding is the development of dissolution technologies that are designed to mimic the in vivo environment more closely. The noncompendial dissolution methods have been detailed in an excellent recent review (4). These include multicompartmental models such as the artificial stomach duodenal model (ASD), which has been used to evaluate the effect of gastric emptying on drug dissolution, solubilization, and precipitation in separate duodenal compartment in several studies (5–8). In addition, models exist that are designed to simulate GI physical stress forces such as the novel stress dissolution tester (9, 10) or the modified Apparatus 2 by Burke et al. (11). Systems that mimic absorption have been described, from the simple partitioning approach using USP apparatus with organic solvents (12–14) to the more complex models like the FloVitro Dissolution Testing system provided by Rohm and Haas (15). In addition, the human gastric simulator (HGS) is a recent technological advance that has been used to study the gastric digestion of foods (16), although this has yet to be applied in the pharmaceutical development space. The next evolutionary stage of dissolution technology comprises complex systems that are multicompartmental, not only mimicking the hydrodynamics and composition of media but also incorporating mechanical processing, digestion of real food, and gastric emptying. Examples of these systems are the TNO TIM–1 system (17) and the dynamic gastric model (DGM). The DGM, developed by the Institute of Food Research in Norwich, UK, is designed to simulate the human gastric compartment of the fundus and antrum (18, 19). It is the first “dynamic” in vitro model that replicates both the complex biochemical conditions and the array of gastric hydrodynamics, critical for the prediction of digestive processes and the bioperformance of pharmaceutical agents and dosage forms. The DGM is gaining increasing utility not only as a general biopharmaceutics tool for the evaluation of dosage form disposition and drug release characteristics, but also for the evaluation of (1) food effect potential, (2) dosage form integrity (especially the propensity for dose dumping), and (3) bespoke drug–alcohol interactions. This work reports a formulation development case study that utilized noncompendial in combination with traditional in vitro tools. The study has proved useful in gaining insight into the in vivo mechanisms of success and failure of the pharmaceutical product development of a complex multilayer pharmaceutical dosage form. *Corresponding author. e-mail: james_mann@merck.com dx.doi.org/10.14227/DT190412P14

Calculation of Frequency Response Envelope for Dynamic Systems With Uncertain Parameters

Frequency response finds a wide range of applications in many engineering sectors. When variations and uncertainties exist during the operation and lifetime of an engineering system, the calculation of frequency response for an uncertain dynamic system is required in order to assess the worst cases in terms of various criteria, for example gain and phase margins in control engineering, or peak magnitude at different modes in the finite element analysis of structures. This paper describes an analytical approach toward the identification of critical interior lines that possibly contribute to the boundary of the frequency response. It is allowed that uncertain parameters perturb transfer function coefficients in a nonlinear form. Conditions for critical interior lines contributing to the boundary of the frequency response are presented. An invariant property of these critical lines under open-loop and closed-loop configurations augmented by control systems or compensators is established, which greatly simplifies the analysis, design, and verification process when using frequency domain techniques. A procedure for computing frequency response and identifying the worst cases is then developed based on the combination of symbolic and numerical computation.

OPTIMAL DESIGN OF SOLVENT GRADIENT SIMULATED MOVING BED CHROMATOGRAPHY FOR AMINO ACID SEPARATION

A solvent gradient mode was applied to the simulated moving bed (SMB) chromatography for the separation of two amino acids, phenylalanine and tryptophan, for the first time. The optimal design of such a solvent gradient SMB (SG-SMB) system was performed under a four-zone open loop configuration, in which zone IV is disconnected from zone I. One of the prerequisites for such an optimal design is to obtain the adsorption isotherm and mass-transfer parameters (i.e., intrinsic parameters) of ethanol that functions as a mobile phase modifier. For this task, a multiple frontal experiment was carried out, which showed that ethanol followed a Langmuir-type adsorption behavior. Based on the resultant parameters of ethanol, the SG-SMB for amino acid separation was optimized to maximize the productivity under the constraints of pump capacities and product purities. The inlet and outlet flow rates, the switching time, and a local distribution of ethanol along the chromatographic bed were optimized using non-dominated sorting genetic algorithm with elitism and jumping genes (NSGA-II-JG) and rate-model simulations. The optimal SG-SMB for amino acid separation was found to have 110% higher productivity, 53% lower desorbent consumption, and 71% higher product concentration, compared to the corresponding isocratic SMB.

Optimal measurement allocation for parametric model identification of electrical networks

In this paper we develop optimal sensor siting methods along the edges of a large network of electrical oscillators to identify a parametric model for the network using dynamic measurements of electrical signals corrupted with Gaussian noise. We pose the identification problem as estimation of four essential parameters for each edge in the network, namely the real and imaginary components of the edge-weight, or equivalently, the resistance and reactance of the tie-line connecting any two oscillators, and the inertias of the oscillators connected by this edge. We then formulate the Cramer-Rao bounds for the estimates of these four unknown parameters using three fundamental outputs - namely, the magnitude, the phase angle and the frequency of the voltage phasor along each edge, and show that the bounds are functions of the sensor locations on the edges as well as of the contribution of each variable in the combined output. We finally state the condition for finding the optimal sensor location and the optimal signal combination to achieve the tightest Cramer-Rao bound. The problem is first addressed for open-loop networks and, thereafter, for networks where outputs measured at desired locations on the edges are fed back to the nodes to improve transient performance. We show that unlike the first case where the open-loop configuration allows us to optimize the bounds in a distributed fashion for each individual edge, for the latter situation the problem no longer has a decoupled structure under the influence of feedback, and must be carried out in a centralized fashion.

Optimal design and experimental validation of a modified four-zone SMB process for the separation of a ternary amino acid mixture

For a standard four-zone simulated moving bed (SMB) chromatography, several process modifications have been made in previous studies such that its application scope could be extended to a ternary separation. One of the effective modifications reported was to (1) replace its closed-loop configuration with an open-loop configuration and (2) utilize the extract port for collecting both the intermediate-affinity and the highest-affinity components in regular sequence in every switching period. Most of previous researches on such a modified four-zone SMB (MF-SMB) have been limited to process simulation and optimization. The experimental validation of the MF-SMB process with linear isotherms was attempted in this article for the first time using a ternary amino acid mixture as a model system. First, the intrinsic parameters of three amino acids were estimated from a series of multiple-frontal experiments. The estimated parameter values were then used in the stage of the MF-SMB optimization, which was assisted by an up-to-date genetic algorithm. Based on the optimized conditions, the MF-SMB experiment was conducted and the assay results for product samples verified the attainment of a ternary separation. The experimental purities and concentrations were also found to agree closely with the model predictions.

Model development and simulation for predicting risk of foaming in anaerobic digestion systems

Although there is not a complete agreement on the causes of foaming in anaerobic digestion, experts and operators do have valuable empirical knowledge of key factors. Based on this knowledge, a model for calculating the risk of foaming in anaerobic digestion systems due to microbiological causes has been developed. Organic loading rate, variation in organic loading rate, and the presence of filamentous microorganisms in the activated sludge system, used as a feed source for the digester, have been selected as the inputs of a knowledge-based model designed to provide as output the risk of foaming in an anaerobic digester. The performance of the model is demonstrated by means of a case study using the IWA Benchmark Simulation Model No. 2 as a framework, where risk of foaming is used as a new evaluation criterion. The simulated results of an open-loop configuration and two closed-loop control strategies illustrate the usefulness of this knowledge-based approach as a means of estimating the risk of foaming in anaerobic digestion.

Evolving refractory major depressive disorder diagnostic and treatment paradigms: toward closed-loop therapeutics.

Current antidepressant therapies do not effectively control or cure depressive symptoms. Pharmaceutical therapies altogether fail to address an estimated 4 million Americans who suffer from a recurrent and severe treatment-resistant form of depression known as refractory major depressive disorder. Subjective diagnostic schemes, differing manifestations of the disorder, and antidepressant treatments with limited theoretical bases each contribute to the general lack of therapeutic efficacy and differing levels of treatment resistance in the refractory population. Stimulation-based therapies, such as vagus nerve stimulation, transcranial magnetic stimulation, and deep brain stimulation, are promising treatment alternatives for this treatment-resistant subset of patients, but are plagued with inconsistent reports of efficacy and variable side effects. Many of these problems stem from the unknown mechanisms of depressive disorder pathogenesis, which prevents the development of treatments that target the specific underlying causes of the disorder. Other problems likely arise due to the non-specific stimulation of various limbic and paralimbic structures in an open-loop configuration. This review critically assesses current literature on depressive disorder diagnostic methodologies, treatment schemes, and pathogenesis in order to emphasize the need for more stringent depressive disorder classifications, quantifiable biological markers that are suitable for objective diagnoses, and alternative closed-loop treatment options tailored to well-defined forms of the disorder. A closed-loop neurostimulation device design framework is proposed, utilizing symptom-linked biomarker abnormalities as control points for initiating and terminating a corrective electrical stimulus which is autonomously optimized for correcting the magnitude and direction of observed biomarker abnormality.

Real-time hybrid predictive modeling of the Teniente Converter

The Teniente Converter (TC) is an important technology for smelting and converting copper concentrates. Due to the complexities of its autogenous operation, which combines continuous input flows with intermittent product extraction, efforts to model and control this dynamic have only been partially successful. This work presents a model of TC operation that combines phenomenological equations with empirical expressions and includes both continuous and discrete variables. Six different operating modes are described. To improve predictive capabilities, an adaptive compensation technique takes account of changes in concentrate mix characteristics. The model predicts five important variables: white metal copper concentration, slag magnetite concentration, white metal temperature, and white metal and slag levels. It is calibrated and validated with real operating data from Codelco’s Potrerillos smelter. Once the model is implemented, it delivers online estimates of process variables that are measured intermittently. Based on the model, a hybrid predictive controller is developed to control the quantities and characteristics of the TC products as a function of the number of dependent units such as Peirce-Smith converters and slag-cleaning furnaces. The controller’s performance is evaluated via simulation under a variety of operating conditions. It is currently employed in an open-loop configuration to provide suggestions on set points for the local flow controllers and on the product extraction sequences.

In Vitro Dissolution Testing with Flow-Through Method: A Technical Note

In vitro dissolution testing is important for providing process control and quality assurance, determination of stability release characteristics of the product over time, and facilitating certain regulatory determinations (e.g., absence of effect of minor formulation changes or of change in manufacturing site on performance). In the past two decades, the dissolution test has also been widely discussed to serve as an indicator of how the formulation will perform in vivo (1–3). Although basket and paddle methods are currently the most popular methods for many drug products, both methods are operated under closed finite sink condition and cannot mimic the conditions present in the digestive system. A flow-through method using the official USP 4 apparatus operated in open-loop mode is capable of maintaining a continuous flow of fresh dissolution medium, thus, maintaining infinite sink conditions (3–6). This operational mode provides an environment potentially closer to that of the digestive tract. Thus, this technique may offer advantages for establishing in vitro and in vivo correlations (IVIVCs). To compare dissolution testing under finite and infinite sink conditions, this study applied both paddle and flow-through methods for dissolution testing with disintegrating prednisone and nondisintegrating salicylic acid tablets. The closed- and open-loop configurations of the flow-through method were used to provide comparisons with the paddle method. In addition to studies based on the official USP dissolution apparatus, several authors have reported development of novel, multicompartment dissolution apparatus in their efforts to develop good IVIVCs (7–9; Hughes et al., private communication). The reported novel systems have potential to simulate in vivo condition such as gastric volume and pH, gastric emptying to the intestine, and intestinal volume and pH etc., which may give a good in vivo and in vitro correlation. However, these novel apparatus require special configurations or parts, which may be difficult to duplicate in other labs. This study applies the idea of a multicompartment dissolution apparatus but attempts to minimize modifications to the current official USP apparatus so as to facilitate adoption by other labs for application to their specific studies. In this study, the flow-through apparatus with open-loop configuration has been modified by adding a flow-through reservoir after the flow-through cell. This reservoir is maintained at intestinal pH. Disintegrating prednisone and nondisintegrating salicylic acid were used as test drugs.

A Micropower $\Delta\Sigma$-Based Interface ASIC for a Capacitive 3-Axis Micro-Accelerometer

In this paper, a micropower interface IC for a capacitive 3-axis micro-accelerometer is presented. The IC is implemented in a 0.25-mum CMOS process. The fully-integrated sensor interface is based on a DeltaSigma sensor front-end that operates mechanically in an open-loop configuration and converts the acceleration signals directly into the digital domain, thus avoiding the use of separate analog-to-digital converters. A detailed analysis with transfer functions is presented for the front-end circuit. Furthermore, the interface IC includes a decimator, a frequency reference, a clock generator for the front-end, a voltage and current reference, the required reference buffers, and low-dropout regulators (LDOs) needed for system-on-chip power management. The interface IC provides operating modes with 12-bit resolution for 1 and 25 Hz signal bandwidths. The former is optimized for very low power dissipation at the cost of reduced bandwidth, and is intended for example for activity monitoring in otherwise powered-off devices. The chip, with a 1.73 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> active area, draws typically 21.2 muA in the 1 Hz mode, and 97.6 muA in the 25 Hz mode, from a 1.2-2.75 V supply. In the 1 and 25 Hz modes with a plusmn 4-g capacitive 3-axis accelerometer, the measured noise floors in the x-, y-, and z-directions are 1080, 1100 and 930 mug/radic{Hz}, and 360, 320 and 275 mug/radic{Hz} , respectively. The implemented prototype achieves competitive figures of merit (FOMs) compared to the other published or commercially available, low-g, low-power accelerometers.