Square-wave Current Research Articles

Thermal Impedance Measurement of Thick-Film Resistor in High-Frequency Range Using Single-Detector IR System

This paper presents an innovative and simple method of high-frequency thermal impedance measurement using infrared (IR) technique. The method is based on the Fourier transformation of the input power signal and the thermal response of the object after supplying the heat source with square-wave current of different frequencies. The experiment was carried out using a single-detector, low-cost infrared system equipped with a photovoltaic detector module to measure the thermal impedance of an SMD thick-film resistor. Both the simulation using a compact thermal model and the measurement results are discussed.

A comparison study of constant current and square wave current in the bidirectional electromigration rehabilitation on chloride-contaminated concrete

The objective of this study is to reduce the hydrogen embrittlement risk of rebar caused by the continuous constant current (CC) in the bidirectional electromigration rehabilitation (BIEM). Three types of square wave current (SWC) were applied in the BIEM treatment on a Cl--contaminated concrete, in the saturated calcium hydroxide containing 1 mol/L triethylenetetramine (TETA). The sample experienced the BIEM with a constant current density of 3 A/m2 was chosen as the control sample with the same electricity consumption. After 4 cycles of treatment, the concentration profiles of Cl- and TETA were measured in the protective layer. The corrosion current densities of the rebar were analyzed by various electrochemical tests. The stress-strain curve of the rehabilitated rebar was tested, and its hydrogen embrittlement risk was estimated. The results suggested that the SWC more effectively removed Cl- and migrated TETA than the CC did, with the same electricity consumption and treatment duration. The rebar experienced the former BIEM exhibited a higher fracture energy ratio and a lower corrosion rate than the one experienced the latter treatment. In general, the SWC was more effective and lower hydrogen embrittlement risk than CC in the BIEM rehabilitation treatment.

Low-frequency experimental method for measuring the electric double-layer capacitances of multi-cell electrolysis stacks based on equivalent circuit model

In recent years, the green hydrogen production via water electrolysis has acquired significant attention, and the dynamic operation of electrolysis stacks has become a crucial research area. The electric double-layer capacitance (EDLC) is the primary factor indicating the performance of the stack and affecting the dynamic behavior of the electrolysis stack. High-frequency testing methods are commonly used to measure the EDLCs of electrolysis cells in laboratory, but these methods are not suitable for cost-efficiency and a bottleneck of the engineering power electronic devices. This study proposes a novel square-wave pulse current (SPC) method for determining the EDLCs of multi-cell electrolysis stacks using industrial rectifiers. The response of the stack subjected to SPC is analyzed based on a semi-empirical equivalent circuit (SEEC) model. The feasibility of the proposed method is verified through experiments on a 2 Nm3/h alkaline water electrolysis stack, and an accuracy of 2.67% is obtained.

Smartphone-Based Electrochemical Immunoassay for Point-of-Care Detection of SARS-CoV-2 Nucleocapsid Protein.

Large-scale, rapid, and inexpensive serological diagnoses of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) are of great interest in reducing virus transmission at the population level; however, their development is greatly plagued by the lack of available point-of-care methods, leading to low detection efficiency. Herein, an ultrasensitive smartphone-based electrochemical immunoassay is reported for rapid (less than 5 min), low-cost, easy-to-implement detection of the SARS-CoV-2 nucleocapsid protein (SARS-CoV-2 N protein). Specifically, the electrochemical immunoassay was fabricated on a screen-printed carbon electrode coated with electrodeposited gold nanoparticles, followed by incubation of anti-N antibody (Ab) and bovine serum albumin as the working electrode. Accompanied by the antigen–antibody reaction between the SARS-CoV-2 N protein and the Ab, the electron transfer between the electroactive species [Fe(CN)6]3–/4– and the electrode surface is disturbed, resulting in reduced square-wave voltammetry currents at 0.075 V versus the Ag/AgCl reference electrode. The proposed immunoassay provided a good linear range with SARS-CoV-2 N protein concentrations within the scope of 0.01–1000 ng/mL (R2 = 0.9992) and the limit of detection down to 2.6 pg/mL. Moreover, the detection data are wirelessly transmitted to the interface of the smartphone, and the corresponding SARS-CoV-2 N protein concentration value is calculated and displayed. Therefore, the proposed portable detection mode offers great potential for self-differential diagnosis of residents, which will greatly facilitate the effective control and large-scale screening of virus transmission in resource-limited areas.

Multiple Sine-Wave Superposition Drive for the Doubly Salient Motor Based on Fourier Linearization Modeling

Doubly salient motor (DSM) is a new type of high-speed motor. For aeronautics applications, DSM has a nonsinusoidal nonlinear structure and is driven by the square-wave current. As a result, the driving of DSM is hard to be quantitatively designed and optimized. This article proposes a multiple sine-wave superposition (MSWS) driving method that generates current waveforms composed of fundamental component and harmonic components with specific amplitudes and initial phases. That is based on a new accurate DSM Fourier linearization modeling, completely different from present square-wave driving methods of DSMs. In this article, a simplified linear relation between the current and the torque harmonic component is established. Then, a tradeoff between torque-to-current ratio and torque ripple is made. As a result, the optimal current waveforms of maximum torque-per-ampere and torque ripple suppression are given, and the new driving method is proposed. The MSWS driving is simple, easy to use, and greatly improves torque characteristics and the dynamic performance of DSM compared with square-wave driving. It is proposed for DSMs, however, it could be extended to other nonsinusoidal motors. This driving method is verified on a 12/8 DSM by simulation and experiment.

Impact of the load angle on magnetic radial pressure and torque ripple of a low power PMSM with trapezoidal control

PurposeThis paper deals with the study of the influence of the phase shift between currents and back-electromotive forces (back-EMF) on torque ripple and radial magnetic forces for a low power synchronous machine supplied with 120 degrees square-wave currents. This paper aims to establish a good compromise between efficiency, harmonics of torque and harmonics of radial forces at the origin of the electromagnetic noise.Design/methodology/approachBased on a finite element approach, torque and magnetic pressure harmonics versus space and frequency are evaluated for different angle values. The evolutions of the different harmonics against the load angle are analyzed and compared to those of experimental measurements.FindingsDepending on the load torque, field-weakening or field-boosting can be used to reduce current harmonics contributing the most to the radial magnetic forces responsible for the noise. Besides, a compromise can be found to avoid deteriorating too much the performances of the machine, thus being suitable with an industrial application.Research limitations/implicationsThis study concerns low power permanent magnet synchronous machines with concentrated windings and driven with a trapezoidal control, while having sinusoidal back-EMF.Originality/valueThe use of a simple mean and suitable with a large-scale manufacturing industry to reduce the identified electromagnetic-borne noise of a specific electric drive makes the originality.

Control and Experimental Verification of a Bidirectional Nonisolated DC–DC Converter Based on Switched-Capacitor Converters

This article presents a bidirectional nonisolated dc-dc converter based on switched-capacitor converters intended for electric railway system applications. It consists of plural main converters with two power devices per converter, plural auxiliary converters each of which is formed by cascaded chopper cells, and small-sized inductors for current control. The dc-dc converter can achieve zero-current switching (ZCS) for all power devices used in the main converters under arbitrary load conditions and an arbitrary voltage ratio of high-voltage-side voltage and low-voltage-side voltage. Consequently, square-wave currents can be removed from both the high- and low-voltage sides of the converter. The validity of the operating principles as well as the control methods proposed in this article is verified by experiments using a 200-V, 2-kW downscaled model.

Multidomain Analysis and nth-Order Synchronous Reference Vector Adaptive Control of the Doubly Salient Motor

Due to the significant nonlinearity of the commutation of the square-wave current, the control of the doubly salient electromagnetic motor is hard to analyze quantitatively. This is because the present model is nonlinear and coupled. In this article, a linear decoupled model and symmetrical frequency shift cluster (SFSC) model are proposed based on a precise analysis of the time domain and complex-frequency domain. The results are extremely simple and mathematically computable. Moreover, these models focus on the average output torque, which is a key parameter at the same time. Furthermore, they explain well how torque ripple is generated. Based on the abovementioned results, a vector diagram of the harmonics of the phase current and inductance is proposed to precisely control the commutation in theory. Finally, n th-order synchronous reference vector adaptive control is proposed. The phase difference of each order is weighted to obtain the target function, which is proportional to the average output torque. The weighted phase difference is controlled adaptively to reach a maximum to realize the maximum torque per ampere. The theoretical results are verified by a 12/8 pole air-cooled prototype and related simulation and experimental results.

Synchronous Commutation Control of Doubly Salient Motor Drive With Adaptive Angle Optimization

Due to the strong nonlinearity of the commutation process of doubly salient motors fed by square-wave currents, it is difficult to establish accurate models and design an appropriate commutation control strategy to achieve satisfactory commutation performance. The synchronous commutation control method is proposed to improve commutation control. By introducing an additional angle loop to synchronize the zero crossings of the phase current and the alignment of the core poles, the commutation angle can be adaptively optimized without requiring the accurate model. Also presented is a vector control scheme during the commutation process to shape the trajectory of the current vector into a regular hexagon. Based on the linearized model of the commutation process, the digital control law to synchronize the zero crossings is designed with robustness considered. Finally, simulations and experiments were conducted. The results show less commutation torque loss with the method. Ultimately, the method provides a high torque-to-current ratio and low-torque ripple at a wide range of speeds.

Study on the Influence of Pulse Current Cathodic Protection Parameters of Oil Well Casing

Pulse current cathodic protection had obvious advantages over traditional DC cathodic protection, but when square-wave pulse current was used for cathodic protection of oil well casing, the influence of pulse protection parameters on potential distribution was not very clear. Therefore, according to the current situation of oil fields in China, the typical formation characteristic structure of oil wells was selected and the cathodic protection model of pulse current for oil well casing was established. Based on the established model, the effects of pulse current parameters (frequency and duty cycle) and anode distance on the cathodic protection effect of square-wave pulse current were studied. The results showed that better protection effect could be obtained by choosing appropriate anode distance, high frequency, and moderate duty cycle.

Inspiratory-Activated Airway Vagal Preganglionic Neurones Excited by Thyrotropin-Releasing Hormone via Multiple Mechanisms in Neonatal Rats.

The airway vagal preganglionic neurons (AVPNs) providing projections to intrinsic tracheobronchial ganglia are considered to be crucial to modulation of airway resistance in physiological and pathological states. AVPNs classified into inspiratory-activated AVPNs (IA-AVPNs) and inspiratory-inhibited AVPNs (II-AVPNs) are regulated by thyrotropin-releasing hormone (TRH)-containing terminals. TRH causes a direct excitatory current and attenuates the phasic inspiratory glycinergic inputs in II-AVPNs, however, whether and how TRH influences IA-AVPNs remains unknown. In current study, TRH regulation of IA-AVPNs and its mechanisms involved were investigated. Using retrogradely fluorescent labeling method and electrophysiology techniques to identify IA-AVPNs in brainstem slices with rhythmic inspiratory hypoglossal bursts recorded by a suction electrode, the modulation of TRH was observed with patch-clamp technique. The findings demonstrate that under voltage clamp configuration, TRH (100 nM) caused a slow excitatory inward current, augmented the excitatory synaptic inputs, progressively suppressed the inhibitory synaptic inputs and elicited a distinctive electrical oscillatory pattern (OP). Such a current and an OP was independent of presynaptic inputs. Carbenoxolone (100 μM), a widely used gap junction inhibitor, fully suppressed the OP with persistence of TRH-induced excitatory slow inward current and augment of the excitatory synaptic inputs. Both tetrodotoxin (1 μM) and riluzole (20 μM) functioned to block the majority of the slow excitatory inward current and prevent the OP, respectively. Under current clamp recording, TRH caused a slowly developing depolarization and continuously progressive oscillatory firing pattern sensitive to TTX. TRH increased the firing frequency in response to injection of a square-wave current. The results suggest that TRH excited IA-AVPNs via the following multiple mechanisms: (1) TRH enhances the excitatory and depresses the inhibitory inputs; (2) TRH induces an excitatory postsynaptic slow inward current; (3) TRH evokes a distinctive OP mediated by gap junction.

Fault-Tolerant Operation of a Novel Dual-Channel Switched Reluctance Motor Using Two 3-Phase Standard Inverters

This paper proposes a novel dual-channel switched reluctance motor (DCSRM) driven by two 3-phase standard inverters. The key of the proposed DCSRM is its two operational models. For the first operational model (Model I), it works like a 3-phase traditional SRM supplied by an H-bridge inverter, which is driven by square-wave currents. For the second operational model (Model II), it can be considered as two mutually coupled SRMs that are supplied by sine-wave currents. These operational models are used to overcome different faults, and the corresponding remedial current strategies are proposed to realize fault-tolerant operation. Then, Model I is adopted for power switch fault. Meanwhile, Model II is employed for open-circuit fault. Moreover, the performances of proposed DCSRM are calculated by a finite element, method and the fault-tolerant performances under different fault conditions are verified by cosimulation. Results show that the proposed DCSRM can be used for safety-critical applications by combining the advantages of traditional SRM and mutually coupled SRM.

Parabola‐trapezoid and staircase current supply methods for PMBLM with full inverter utility and reduced torque ripple

The permanent magnet brushless motors (PMBLM) are utilised extensively in many high-performance applications where smoothness of output torque is necessary. When driven with conventional square-wave current, the PMBLM is hard to make full use of inverter capacity because of short current supply time. Besides, it is hard to produce smooth output torque because the phase inductances slow down the desired step response of the phase current seriously. Although the sinusoidal-wave current changes continuously, there exists a fixed-frequency torque ripple for trapezoid back-electromotive force motor. To solve the problems, two novel current supply methods, called as staircase waveform and parabola-trapezoid waveform, are proposed in this study. With the same phase current magnitude as square waveform, the staircase waveform can output two times torque with low-resolution position sensors. The parabola-trapezoid supply method can further improve the smoothness of doubled output torque by unique parabolic rising and falling edge waveform design, while a high-resolution position sensor is needed. Simulation and experimental tests of four different current supply methods are given to corroborate the effectiveness of the proposed method in inverter utility and torque ripple reduction.

A remote-control datalogger for large-scale resistivity surveys and robust processing of its signals using a software lock-in approach

Abstract. We present a new versatile datalogger that can be used for a wide range of possible applications in geosciences. It is adjustable in signal strength and sampling frequency, battery saving and can remotely be controlled over a Global System for Mobile Communication (GSM) connection so that it saves running costs, particularly in monitoring experiments. The internet connection allows for checking functionality, controlling schedules and optimizing pre-amplification. We mainly use it for large-scale electrical resistivity tomography (ERT), where it independently registers voltage time series on three channels, while a square-wave current is injected. For the analysis of this time series we present a new approach that is based on the lock-in (LI) method, mainly known from electronic circuits. The method searches the working point (phase) using three different functions based on a mask signal, and determines the amplitude using a direct current (DC) correlation function. We use synthetic data with different types of noise to compare the new method with existing approaches, i.e. selective stacking and a modified fast Fourier transformation (FFT)-based approach that assumes a 1∕f noise characteristics. All methods give comparable results, but the LI is better than the well-established stacking method. The FFT approach can be even better but only if the noise strictly follows the assumed characteristics. If overshoots are present in the data, which is typical in the field, FFT performs worse even with good data, which is why we conclude that the new LI approach is the most robust solution. This is also proved by a field data set from a long 2-D ERT profile.

Understanding the molecular mechanism of pulse current charging for stable lithium-metal batteries.

High energy and safe electrochemical storage are critical components in multiple emerging fields of technologies. Rechargeable lithium-metal batteries are considered to be promising alternatives for current lithium-ion batteries, leading to as much as a 10-fold improvement in anode storage capacity (from 372 to 3860 mAh g-1). One of the major challenges for commercializing lithium-metal batteries is the reliability and safety issue, which is often associated with uneven lithium electrodeposition (lithium dendrites) during the charging stage of the battery cycling process. We report that stable lithium-metal batteries can be achieved by simply charging cells with square-wave pulse current. We investigated the effects of charging period and frequency as well as the mechanisms that govern this process at the molecular level. Molecular simulations were performed to study the diffusion and the solvation structure of lithium cations (Li+) in bulk electrolyte. The model predicts that loose association between cations and anions can enhance the transport of Li+ and eventually stabilize the lithium electrodeposition. We also performed galvanostatic measurements to evaluate the cycling behavior and cell lifetime under pulsed electric field and found that the cell lifetime can be more than doubled using certain pulse current waveforms. Both experimental and simulation results demonstrate that the effectiveness of pulse current charging on dendrite suppression can be optimized by choosing proper time- and frequency-dependent pulses. This work provides a molecular basis for understanding the mechanisms of pulse current charging to mitigating lithium dendrites and designing pulse current waveforms for stable lithium-metal batteries.

Variable-Focus Liquid Lens Integrated with a Planar Electromagnetic Actuator.

In this paper, we design, fabricate and characterize a new electromagnetically actuated variable-focus liquid lens which consists of two polymethyl methacrylate (PMMA) substrates, a SU-8 substrate, a polydimethylsiloxane (PDMS) membrane, a permanent magnet and a planar electromagnetic actuator. The performance of this liquid lens is tested from four aspects including surface profiling, optical observation, variation of focal length and dynamic response speed. The results shows that with increasing current, the optical chamber PDMS membrane bulges up into a shape with a smaller radius of curvature, and the picture recorded by a charge-coupled device (CCD) camera through the liquid lens also gradually becomes blurred. As the current changes from −1 to 1.2 A, the whole measured focal length of the proposed liquid lens ranges from −133 to −390 mm and from 389 to 61 mm. Then a 0.8 A square-wave current is applied to the electrode, and the actuation time and relaxation time are 340 and 460 ms, respectively. The liquid lens proposed in the paper is easily integrated with microfluidic chips and medical detecting instruments due to its planar structure.

Electrochemical behavior and analytical detection of Imidacloprid insecticide on a BDD electrode using square-wave voltammetric method

Abstract A sensitive square-wave voltammetric method for the determination of Imidacloprid (IMD) was developed using electrochemically pretreated boron-doped diamond (BDD) electrode. Aqueous solutions were prepared with Confidor 200 SL as the commercial formulation of IMD. Sodium sulfate (Na 2 SO 4 ) was used as supporting electrolyte. The influence of operating parameters, such as the pH of the medium, frequency, pulse amplitude, scan increment and the concentration of IMD was investigated. An irreversible cathodic peak, corresponding to the reduction of IMD is observed at −1.21 V ( vs. SCE) and the electrode reaction was controlled by adsorption. Under optimized conditions, the square-wave reduction peak current was linear over the concentration range of (30–200 μmol L −1 ) with a detection and quantification limits of 8.60 μmol L −1 and 28.67 μmol L −1 , respectively. The results were compared with spectrophotometry and HPLC methods under some conditions and found to be in good agreement. To investigate applicability to real samples, the proposed method was applied to the determination of IMD in plum juice.

Sinusoidal Versus Square-Wave Current Supply of PM Brushless DC Drives: A Convenience Analysis

Permanent-magnet (PM) brushless direct current (BLDC) drives are utilized in a variety of applications because of their inherent features and would be even more utilized if their torque performance could be improved. Indeed, when supplied with square-wave currents, the torque-speed characteristic undergoes a drop at high speeds, and a significant torque ripple arises at both low and high speeds due to the commutation phenomena. In this paper, the sinusoidal current supply of the PM BLDC motors is investigated in depth, and an analytical formulation of the torque-speed characteristic, the torque ripple, and the base speed for such a supply are found. Based on the resulting equations, a thorough convenience analysis of the sinusoidal current supply is carried out with respect to the square-wave current in the presence of the commutation phenomena, which is hereafter termed as the real square-wave current supply. Simulation and experimental tests for a study case are given to corroborate the theoretical results. Generation of the sinusoidal current references using Hall sensors is also discussed.

Polyurea spin-coated thin films: Pyro- and piezoelectric properties and application to infrared sensors

We have investigated the pyro- and piezoelectric properties of polyurea spin-coated films with thermal and chemical stability and their performance as infrared sensors. The piezoelectric coefficient d33 was measured by a laser Doppler vibrometer to be 23.5 pC/N. This coefficient increased with the poling electric field up to around 75 MV/m, suggesting that the polyurea dipole is aligned by applying an electric field greater than 75 MV/m. When a triangular thermal wave was applied, a square-wave pyroelectric current was observed and the pyroelectric coefficient measured to be 5.11 µC/(m2·K). The infrared sensor performance of the polyurea thin film was examined by measuring the voltage sensitivity to infrared irradiation. The obtained result of 70.4 V/W at 1 Hz is consistent with the results calculated from the measured pyroelectric coefficient. Our findings suggest that the performance of the sensor may be improved by increasing the pyroelectric coefficient of the polyurea films.

Sensitive electrochemical sensor using a graphene–polyaniline nanocomposite for simultaneous detection of Zn(II), Cd(II), and Pb(II)

This work describes the development of an electrochemical sensor for simultaneous detection of Zn(II), Cd(II), and Pb(II) using a graphene–polyaniline (G/PANI) nanocomposite electrode prepared by reverse-phase polymerization in the presence of polyvinylpyrrolidone (PVP). Two substrate materials (plastic film and filter paper) and two nanocomposite deposition methods (drop-casting and electrospraying) were investigated. Square-wave anodic stripping voltammetry currents were higher for plastic vs. paper substrates. Performance of the G/PANI nanocomposites was characterized by scanning electron microscopy (SEM) and cyclic voltammetry. The G/PANI-modified electrode exhibited high electrochemical conductivity, producing a three-fold increase in anodic peak current (vs. the unmodified electrode). The G/PANI-modified electrode also showed evidence of increased surface area under SEM. Square-wave anodic stripping voltammetry was used to measure Zn(II), Cd(II), and Pb(II) in the presence of Bi(III). A linear working range of 1–300μgL−1 was established between anodic current and metal ion concentration with detection limits (S/N=3) of 1.0μgL−1 for Zn(II), and 0.1μgL−1 for both Cd(II) and Pb(II). The G/PANI-modified electrode allowed selective determination of the target metals in the presence of common metal interferences including Mn(II), Cu(II), Fe(III), Fe(II), Co(III), and Ni(II). Repeat assays on the same device demonstrated good reproducibility (%RSD<11) over 10 serial runs. Finally, this system was utilized for determining Zn(II), Cd(II), and Pb(II) in human serum using the standard addition method.