Small Signal Variations Research Articles

Operando Spectroelectrochemical Imaging of Concentration Fields and Tafel Kinetics in Microfluidic Electrochemical Devices.

With the development of microtechnologies for energy conversion and storage, mass transfer and micromolar concentration variations need to be measured at the microscale. These advances need to be accompanied by novel imaging techniques with the capability of achieving high spatial resolution while detecting very small signal variations (less than 0.1%). Thus, in this study, a new microscopy technique is proposed based on a combination of electrochemical impedance spectroscopy (EIS) and visible imaging spectroscopy to measure the concentration fields at the micromolar scale in operando microfluidic fuel cells (MFCs). This technique exploits EIS modulation and Fourier analysis to reduce the noise during concentration field imaging. A mass transfer model in the periodic regime is derived to validate the measurements and to estimate the Tafel kinetics and mass diffusivities during potassium permanganate reduction from only one potential measurement. The proposed imaging method and mathematical framework presented in this study can be used to study binary electrochemical reactions without gas production.

Analysis of Pre-Driver and Last-Stage Power-Ground-Induced Jitter at Different PVT Corners.

This paper presents the study of power/ground (P/G) supply-induced jitter (PGSIJ) on a cascaded inverter output buffer. The PGSIJ analysis covers the IO buffer transient simulation under P/G supply voltage variation at three process, voltage, and temperature (PVT) corners defined at different working temperatures and distinct DC supply voltages at the pre-driver (i.e., /) and last stage (i.e., ). Firstly, the induced jitter contributions by the pre-driver, as well as the last, stage are compared and studied. Secondly, the shared and decoupled P/G supply topologies are investigated. The outcomes of these simulation analyses with respect to worst case jitter corners are determined, while highlighting the importance of modeling the pre-driver circuit behavior to include the induced jitter in the input–output buffer information specification (IBIS)-like model. Accordingly, the measured PGSIJ depends on the corners to be analyzed and, therefore, the designer needs to explore the worst-case corner for the driver’s technology node and the most supply voltage noise affecting the jitter output for signal and power integrity (SiPI) simulations. Finally, the jitter transfer function sensitivity to the amplitude and frequency/phase variations of the separate and combined impacts of the pre-driver and last stage are explored, while discussing the superposition of the power supply induced jitter (PSIJ) induced by both the driver’s IO stages under small signal and large signal supply voltage variations. The linear superposition of the separate PSIJ effects by the pre-driver and last stage depends on the amplitude of the variation of the supply voltage that can drive the transistor to their nonlinear working regions.

Sulphide geochemistry of the superlarge Tiegelongnan Cu (Au) deposit in Tibet, China: Implication for the mineralization process

The Tiegelongnan deposit in central Tibet presents a typical high‐sulfidation porphyry Cu (Au) mineralization system. Optical microscopy, scanning electron microscopy–energy dispersive spectrometry (SEM–EDS), and laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS) were used to understand the mineralization processes. The advanced argillic alteration zone directly contacts the phyllic alteration zone, which is linked to the Early Cretaceous porphyritic intrusions. In this study, the spatial distributions of chief copper sulphides with variable gangue minerals are illustrated. The deep inner phyllic zone typically produced an end‐member assemblage of chalcopyrite–sericite (±dolomite), which trended upwards to produce more bornite–sericite (±siderite ± magnesite), and subsequently, the advanced argillic alteration yielded the representative end‐member assemblage of tennantite–alunite ± (aluminium‐phosphate‐sulphate, namely, APS, ±kaolinite). In the phyllic–advanced argillic transition zone, intensive covellite precipitation with the widespread occurrence of sericite–kaolinite (±APS) assemblage is proposed as an important feature in this study, which is mainly produced on the southwest side of the ore‐body centre. The typical co‐occurrence of chalcopyrite with dolomite at great depths indicates that it was related to a gently acidic fluid containing CO2; however, the pervasive tennantite–alunite association present at shallower levels suggests that fluids with SO2 were mainly involved and produced stronger acidic conditions. Acidic fluids are demonstrated to highly accelerate water‐rock alteration. Trace element analyses of the copper sulphides reflect that Au concentrations of bornite and tennantite are higher than chalcopyrite and covellite and present small signal variations. Moreover, comparing the presence of micron‐sized Au‐telluride in tennantite under advanced argillic alteration with the nano‐sized native gold in bornite resulting from phyllic alteration suggests that to a certain extent, Au enrichment is affected by the shift of more Te contents in fluid towards shallower levels, which could promote Au precipitation. Additionally, the Se contents of the selected samples were typically concentrated in chalcopyrite, bornite, and covellite, which yielded contents an order of magnitude greater than those in tennantite, indicating the intimate hydrothermal origin of the first three sulphides. Overall, the sulphide–gangue mineral associations and their copper sulphide geochemistry indicate that the hypogene–chalcopyrite of low Au contents from the phyllic zone closely corresponds to the action of gentle acidic fluids with CO2, while more acidic fluids with SO2 are involved in the formation of supergene tennantite with relatively high values of Au and Te in the advanced argillic alteration.

Quantitative measurement of solid fraction in a silo using SPRITE

The purpose of this study is to develop MRI methods to measure the solid fraction in granular flows quantitatively. It is increasingly recognised that solid fraction plays a key role in granular rheology, but experimental characterisation of it during flow is challenging. Here centric sectoral-SPRITE imaging is applied to image mustard seeds discharging from a 3D-printed hopper. Quantitative images are obtained after considering and correcting artefacts that may arise from flow and relaxation. The image intensity is then further corrected for spatial variations in the B1 field. Various maps of nominally homogeneous samples were tested to correct for variations in the B1 field. The B1 field was found to be sensitive to the geometry of the sample and the material in the sample. Hence, here static images of the seeds in the hopper were used to correct for B1 field variations. Moreover, small signal variations were observed from measurements performed on different days owing to subtle differences in the spectrometer operation. Here an internal standard was used to scale the signal intensity and correct for these variations. Following these corrections, a linear correlation (R2 = 0.999) was observed between the scaled image intensities and the known solid fractions of packed samples with solid fractions between 0.55 and 0.64. This correlation was used as a calibration of the 3D image of the hopper to extract quantitative time-averaged spatial maps of solid fraction during steady flow. The measurements were confirmed to be quantitative by also measuring the velocity of the particles. Together these measurements were used to calculate a mass flow rate in the hopper, which was consistent with the mass flow measured gravimetrically.

Digital System Performance Enhancement of a Tent Map-Based ADC for Monitoring Photovoltaic Systems

Efficient photovoltaic installations require control systems that detect small signal variations over large measurement ranges. High measurement accuracy requires data acquisition systems with high-resolution analogue-to-digital converters; however, high resolutions and operational speeds generally increase costs. Research has proven low-cost prototyping of non-linear chaotic Tent Map-based analogue-to-digital converters (which fold and amplify the input signal, emphasizing small signal variations) is feasible, but inherent non-ideal Tent Map gains reduce the output accuracy and restrict adoption within data acquisition systems. This paper demonstrates a novel compensation algorithm, developed as a digital electronic system, for non-ideal Tent Map gain, enabling high accuracy estimation of the analogue-to-digital converter analogue input signal. Approximation of the gain difference compensation values (reducing digital hardware requirements, enabling efficient real-time compensation), were also investigated via simulation. The algorithm improved the effective resolution of a 16, 20 and 24 Tent Map-stage analogue-to-digital converter model from an average of 5 to 15.5, 19.2, and 23 bits, respectively, over the Tent Map gain range of 1.9 to 1.99. The simulated digital compensation system for a seven Tent Map-stage analogue-to-digital converter enhanced the accuracy from 4 to 7 bits, confirming real-time compensation for non-ideal gain in Tent Map-based analogue-to-digital converters was achievable.

Lightweight Lossless Compression for $N$ -Dimensional Data in Multi-Sensor Systems

During the last years, multi-sensor acquisition systems have experienced a great diffusion. One of the main limiting factors is related to the huge amount of data generated within these systems and that must be carefully addressed to guarantee a certain efficiency. A solution consists in compressing data before transmission or storage. Furthermore, a lossless compression is required in monitoring applications, such as biomedical applications, where even very small signal variations can convey important information about the physical process under analysis. In this paper, we propose the lossless compression algorithm for multi-sensor systems characterized by low computational capabilities. The proposed method is based on a modified Golomb code that takes an advantage of the definition of union sets to reduce the redundancy associated to the prefix of codewords. The experimental results show that a compression gain up to 50%–60% can be achieved in different contexts.

Change of snow and ice melting time in High Mountain Asia

High Mountain Asia (HMA) is very sensitive to climate changes. In HMA, air temperature and precipitation shifts or increases are reflected in the timing of snowmelt onset. In this study, a long-term series (1979–2018) of snow melt onset time is first derived using spaceborne microwave radiometer data, following which the long-term trend of snow and ice-melt time of Tienshan, Altay, Karakorom, Hindu Kush, and Pamir is analyzed. Previous studies proposed many algorithms for detecting snowmelt onset and freeze-up using microwave remote sensing. The previously proposed algorithms were extensively applied to polar regions (including the Antarctic, Siberia, Greenland, and sea ice surface), where the impact of topography or mixed pixel problem is relatively small. However, for high mountain regions, complex topography and a potential mixed pixel issue would result in a very complicated and noisy satellite-observed active and passive microwave remote sensing signal. This study thus proposes a recently developed snow and ice-melt detection algorithm in which, for passive microwave data, a median filter is first applied to the original signal (brightness temperature) to suppress random, small, or short-duration signal variations. The differential average derivative of a particular date is then calculated using the time series first-order derivative as the average first-order derivative of a specific count of observations after this particular date. Generally, the differential average derivative is an indicator of sudden changes in time series brightness temperature. Results show that the melt onset time in the majority of HMA occurs earlier, except in the case of the Karakorom Mountains and a part of the West Kunlun Mountains. Moreover, the melt onset time derived from satellite morning (6:00 local time) pass data shows that the melt onset time of Karakorom, the West Kulun Mountains, and southeast Tibet remains stable, or even occurs later. The trend of southeast Tibet is unique, with its earlier melt based on afternoon (18:00 local time) pass data and its later melt based on morning pass data. This suggests that the melt–refreeze period of southeast Tibet is increasing together with the increasing diurnal temperature difference. Then, a 2-m air temperature in ERA5 reanalysis data is used for comparison with melt onset time for validation and analysis. ERA5 is the latest climate reanalysis produced by ECMWF, providing hourly data on many atmospheric, land-surface, and sea-state parameters. A strong correlation exists between monthly average air temperatures and melt onset time, with the maximum linear fit R 2 of 0.76. This strong correlation indicates the good data quality of ERA5 reanalysis and melt onset time. The unique trend of southeast Tibet can also be explained using ERA5 reanalysis data, which show that the monthly mean daily maximum air temperature is increasing, but the monthly mean daily minimum air temperature is decreasing. This renders a slope of the linear fit of melt onset data in the period of 1988–2018 in the whole HMA region. Because the satellite overpasses time difference, data from only 1988 to 2018 is used for trend analysis. The analysis of the relationship between the melt onset time change rate and elevation shows that the areas with an earlier melt are almost all located in low-elevation regions, and the rate of melt time change is positively correlated with elevation. This suggests that low-elevation regions are more affected by climate changes. This study provides objective evidence of the impact of climate change on the cryospheric system in HMA.

A simplified control scheme for electric vehicle-power grid circuit with DC distribution and battery storage systems

The direct current (DC) system is becoming the major trend for future internal power grid of electric vehicles (EVs). Since DC power grid system has a different nature to conventional alternating current (AC) grid system, appropriate design of the controller for EV-grid circuit is mandatory. In this paper, an EV employing a pure DC grid circuit with battery storage system (BSS) is considered as a study case. To enable a more efficient use of BSS, a flyback DC-DC converter for batteries charger/or discharger strategy is selected, which satisfies the power flows requirements. The dynamic and control performances of the combined system, i.e. ‘BSS-flyback DC-DC converter connected to a DC motor’, is investigated in terms of voltage/current signal fluctuations. The small-signal based control method is used, which limits the small-signal variations to about zero. To verify the effectiveness of the control strategy, several simulations are done using Matlab. The simulation results illustrate the performances obtained.

Seat Occupancy Detection Based on a Low-Power Microcontroller and a Single FSR.

This paper proposes a microcontroller-based measurement system to detect and confirm the presence of a subject in a chair. The system relies on a single Force Sensing Resistor (FSR), which is arranged in the seat of the chair, that undergoes a sudden resistance change when a subject/object is seated/placed over the chair. In order to distinguish between a subject and an inanimate object, the system also monitors small-signal variations of the FSR resistance caused by respiration. These resistance variations are then directly measured by a low-cost general-purpose microcontroller unit (MCU) without using either an analogue processing stage or an analogue-to-digital converter. Two versions of such a MCU-based circuit are presented: one to prove the concept of the measurement, and another with a smart wake-up (generated by the sudden resistance change) intended to reduce the energy consumption. The feasibility of the proposed measurement system is experimentally demonstrated with subjects of different weight sitting at different postures, and also with objects of different weight. The MCU-based circuit with a smart wake-up shows a standby current consumption of 800 nA, and requires an energy of 125 µJ to carry out the measurement after the wake-up.

Digital Signal Analysis of Electrochemical Signals of Graphene Oxides for Display Devices

ABSTRACTBy using electrochemical tests, small signal variations were study by digital signal processing techniques. Electrochemical noise and electrochemical polarization curves were very useful to obtained electrochemical behavior of alloys, but the low signal levels of measurements obtained showed that some of the information was not likely to be measured and, therefore, not being able to identify. Graphene oxides (GO) samples were prepared by ball milling procedure adding Lithium. SIGVIEW software was used for Digital Signal studies. Comparing, the signals obtained by electrochemical techniques and the research by computational tools; it was possible to find out a behavior path of samples. Display devices made by graphene were observed to provide new information about the structure of samples and how nanotechnology area can be improved. The current investigation aimed at maintaining electrochemical stability, since different deformations, as twisting and bending are quite relevant in portable electronics devices.

Monolithic quasi-sliding-mode controller for SIDO buck converter with a self-adaptive free-wheeling current level

An analog implementation of a novel fixed-frequency quasi-sliding-mode controller for single-inductor dual-output (SIDO) buck converter in pseudo-continuous conduction mode (PCCM) with a self-adaptive freewheeling current level (SFCL) is presented. Both small and large signal variations around the operation point are considered to achieve better transient response so as to reduce the cross-regulation of this SIDO buck converter. Moreover, an internal integral loop is added to suppress the steady-state regulation error introduced by conventional PWM-based sliding mode controllers. Instead of keeping it as a constant value, the free-wheeling current level varies according to the load condition to maintain high power efficiency and less cross-regulation at the same time. To verify the feasibility of the proposed controller, an SIDO buck converter with two regulated output voltages, 1.8 V and 3.3 V, is designed and fabricated in HEJIAN 0.35 μm CMOS process. Simulation and experiment results show that the transient time of this SIDO buck converter drops to 10 μs while the cross-regulation is reduced to 0.057 mV/mA, when its first load changes from 50 to 100 mA.

Design of the PIXIE adiabatic demagnetization refrigerators

The Primordial Inflation Explorer (PIXIE) is a proposed mission to densely map the polarization of the cosmic microwave background. It will operate in a scanning mode from a sun-synchronous orbit, using low temperature detectors (at 0.1K) and located inside a telescope that is cooled to approximately 2.73K – to match the background temperature. A mechanical cryocooler operating at 4.5K establishes a low base temperature from which two adiabatic demagnetization refrigerator (ADR) assemblies will cool the telescope and detectors. To achieve continuous scanning capability, the ADRs must operate continuously. Complicating the design are two factors: (1) the need to systematically vary the temperature of various telescope components in order to separate the small polarization signal variations from those that may arise from temperature drifts and changing gradients within the telescope, and (2) the orbital and monthly variations in lunar irradiance into the telescope barrels. These factors require the telescope ADR to reject quasi-continuous heat loads of 2–3mW, while maintaining a peak heat reject rate of less than 12mW. The detector heat load at 0.1K is comparatively small at 1–2μW. This paper will describe the 3-stage and 2-stage continuous ADRs that will be used to meet the cooling power and temperature stability requirements of the PIXIE detectors and telescope.

Characteristics of Highly Sensitive pH Sensors with Charge Accumulation Operation

A charge-transfer-type pH sensor operated by charge accumulation was demonstrated, and it was confirmed that its pH sensitivity was 1130 mV/pH with five signal integration cycles. The most familiar pH sensor using a semiconductor is the ion-sensitive field effect transistor (ISFET). The sensitivity of our pH sensor was 20 times higher than that of the ISFET. The sensitivity of the ISFET, which is similar in structure to a metal–insulator–semiconductor (MIS) structure, is restricted by the Nernst equation (59 mV/pH at room temperature). The output signal from an ISFET disappears into its noise as pH variation becomes small. The charge-transfer-type pH sensor increases the pH output signal to integrate signals in the time domain that are noise-free. It is expected that with this sensor it is possible to measure small pH signal variations.

Robust multi-scale clustering of large DNA microarray datasets with the consensus algorithm

Hierarchical and relocation clustering (e.g. K-means and self-organizing maps) have been successful tools in the display and analysis of whole genome DNA microarray expression data. However, the results of hierarchical clustering are sensitive to outliers, and most relocation methods give results which are dependent on the initialization of the algorithm. Therefore, it is difficult to assess the significance of the results. We have developed a consensus clustering algorithm, where the final result is averaged over multiple clustering runs, giving a robust and reproducible clustering, capable of capturing small signal variations. The algorithm preserves valuable properties of hierarchical clustering, which is useful for visualization and interpretation of the results. We show for the first time that one can take advantage of multiple clustering runs in DNA microarray analysis by collecting re-occurring clustering patterns in a co-occurrence matrix. The results show that consensus clustering obtained from clustering multiple times with Variational Bayes Mixtures of Gaussians or K-means significantly reduces the classification error rate for a simulated dataset. The method is flexible and it is possible to find consensus clusters from different clustering algorithms. Thus, the algorithm can be used as a framework to test in a quantitative manner the homogeneity of different clustering algorithms. We compare the method with a number of state-of-the-art clustering methods. It is shown that the method is robust and gives low classification error rates for a realistic, simulated dataset. The algorithm is also demonstrated for real datasets. It is shown that more biological meaningful transcriptional patterns can be found without conservative statistical or fold-change exclusion of data. Matlab source code for the clustering algorithm ClusterLustre, and the simulated dataset for testing are available upon request from T.G. and O.W.

Focus on Photonics and Imaging

Focus on Photonics and Imaging

Cluster trending analysis for control loop assessment and diagnosis

Highly reliable automated systems require health monitoring capable of detecting any equipment faults as they occur and identifying the faulty components. Loop re-tuning can improve the performance when the operating environment has changed. However, if some equipment in the loop is malfunctioning, the simple control loop re-tuning will be less effective in improving the loop performance. Therefore, it is important to design a loop performance monitoring system with the capability of monitoring both the loop performance and the faults of equipment in-loop. This paper presents a new mechanism for control loop performance monitoring and equipment fault detection, based on cluster trending analysis. This mechanism is very sensitive to small signal variations and capable of detecting the abnormal signals embedded in the normal signals.

Half-cycle control of the parallel resonant converter operated as a high power factor rectifier

A half-cycle control technique for the parallel resonant power converter operated as a high power factor rectifier is introduced in this paper. Switching of the bridge power transistors is determined such that the bridge input current averaged over a half switching cycle exactly follows the reference proportional to the input voltage. Zero current switching and below-resonance operation are guaranteed, while control of the input current is the fastest possible, regardless of the operating point. In contrast to conventional regulators, the performance is preserved under both small and large signal variations, and also for large variations of the power-stage parameter values. Fast response, stability and robustness are experimentally verified on a 1.4 kW prototype.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

900 MHz Land Mobile Radio Improved Using Circular Polarization

Land mobile systems currently use vertically polarized antennas while trying to solve the problem of small sector signal variations, which are greater for vertical polarization than for either horizontal or circular polarization; This difference in small sector variations is shown from results of tests at 430 MHz. The variations at 900 MHz should be more rapid and have amplitudes at least as great as those shown for 450 MHz. At 900 MHz antennas can be made small for mobile service and the improvements noted here may spur developments in circularly polarized antennas.

900 MHz land mobile radio improved using circular polarization

Land mobile systems currently use vertically polarized antennas while trying to solve the problem of small sector signal variations, which are greater for vertical polarization than for either horizontal or circular polarization. This difference in small sector variations is shown from results of tests at 430 MHz. The variations at 900 MHz should be more rapid and have amplitudes at least as great as those shown for 450 MHz. At 900 MHz antennas can be made small for mobile service and the improvements noted here may spur developments in circularly polarized antennas.

Evaluation of feedback-control systems subjected to large signals

IN THIS PAPER methods are presented for determining design modifications to improve the large-step response of a feedback-control system. This may be the response to a command or to a disturbance. The methods are applicable to systems of higher order as well as second order, and to systems with one or more important nonlinear effects. It is shown that the results obtained by application of the methods may be used to investigate questions not ordinarily answered by studies on a system subjected to small signal variations, such as: 1. Should a controller which has a dual mode of operation be instrumented for the system? 2. Should the saturation level for the cascaded components of the system be increased, thus usually mcreasing the linear range; or decreased, thus usually saving weight, bulk, and cost. 3. For an over-all required power gain in several cascaded components from the error to output, how should this power gain be distributed among the several cascaded components?