Low Output Current Research Articles

Inhalation‐Driven Vertical Flutter Triboelectric Nanogenerator with Amplified Output as a Gas‐Mask‐Integrated Self‐Powered Multifunctional System

AbstractWith the widespread use of sensors and small electronics in the Internet of Things (IoT) era, triboelectric nanogenerators (TENGs) have emerged as sustainable and renewable energy sources owing to their high efficiency, compatibility with various materials, and low cost. However, the existing TENGs exhibit a low current output and require a large mechanical input to continuously generate an enhanced current output. In this study, an inhalation‐driven vertical flutter TENG (IVF‐TENG) with an amplified current output is developed. The IVF‐TENG exhibits two types of mechanical behaviors simultaneously, generating a high‐frequency continuous electrical voltage and closed‐circuit current (ICC) output of 17 V and 1.84 μA, respectively, during inhalation, and an electrostatic discharge voltage and ICC output of 456 V and 288 mA at the beginning and end of every inspiratory cycle, respectively. As a user‐position‐indicating light, the IVF‐TENG can power 130 LEDs in series and 140 LEDs in parallel for every inhalation. The IVF‐TENG can charge a capacitor of 660 μF, with a discharge process of a few seconds, to power a commercial Bluetooth tracker and wirelessly transfer the Bluetooth signal to a smartphone. Moreover, the IVF‐TENG can detect the user's respiration state or the presence of chemical warfare agents (GB, DMMP, etc.) via output waveforms.

Controllable Triboelectric Series Using Gradient Positive and Negative Charge-Confinement Layer with Different Particle Sizes of Mesoporous Carbon Materials.

As a method to maximize the energy efficiency of triboelectric nanogenerators (TENGs), high-voltage charge injection (HVCI) on the surface is a simple and effective method for increasing surface charge densities. In this study, positive and negative triboelectric series are controlled using a 3-layer gradient charge-confinement wherein the particle sizes of the mesoporous carbon spheres (mCSs) are sequentially arranged depending on the external surface area of the mCSs. In the gradient charge-confinement layers of this study, the mCS with different sizes perform charge transport from the surface to a deep position during HVCI while mitigating the charge loss through charge confinement to induce the high space charge densities. Through this process, the output voltage-which is initially 15.2 V-is measured to be 600 V after HVCI, thus representing an increase of about 40 times. Further, to amplify the low output current, which is a disadvantage of triboelectric energy, two types of electrical energy-triboelectric and electromagnetic energy-are produced in single mechanical motion. As a result, the output current produced by the cylindrical TENG and electromagnetic generator is recorded as being 1300 times higher, increasing from 12.8 µA to 17.5 mA.

Laryngeal Muscle-Evoked Potential Recording as an Indicator of Vagal Nerve Fiber Activation

BackgroundVagus nerve stimulation (VNS) is an adjunctive therapy for drug-resistant epilepsy. Noninvasive evoked potential recordings in laryngeal muscles (LMEPs) innervated by vagal branches may provide a marker to assess effective vagal nerve fiber activation. We investigated VNS-induced LMEPs in patients with epilepsy in acute and chronic settings. Materials and MethodsA total of 17 of 25 patients underwent LMEP recordings at initiation of therapy (acute group); 15 of 25 patients after one year of VNS (chronic group); and 7 of 25 patients were tested at both time points (acute + chronic group). VNS-induced LMEPs were recorded following different pulse widths and output currents using six surface laryngeal EMG electrodes to calculate input/output curves and estimate LMEP latency, threshold current for minimal (Ithreshold), half-maximal (I50), and 95% of maximal (I95) response induction and amplitude of maximal response (Vmax). These were compared with the acute + chronic group and between responders and nonresponders in the acute and chronic group. ResultsVNS-induced LMEPs were present in all patients. Ithreshold and I95 values ranged from 0.25 to 1.00 mA and from 0.42 to 1.77 mA, respectively. Estimated mean LMEP latencies were 10 ± 0.1 milliseconds. No significant differences between responders and nonresponders were observed. In the acute + chronic group, Ithreshold values remained stable over time. However, at the individual level in this group, Vmax was lower in all patients after one year compared with baseline. ConclusionsNoninvasive VNS-induced LMEP recording is feasible both at initiation of VNS therapy and after one year. Low output currents (0.25–1.00 mA) may be sufficient to activate vagal Aα-motor fibers. Maximal LMEP amplitudes seemed to decrease after chronic VNS therapy in patients.

Metal Oxides/Carbon Felt Pressure Sensors with Ultra‐Broad‐Range High Sensitivity

AbstractFlexible piezoresistive pressure sensors have been extensively used in the field of wearable sensors. However, it is difficult to achieve both ultrahigh sensitivity and pressure range, with traditional pressure sensors. Therefore, a new Co3O4/carbon felt pressure sensor is proposed here, where Co3O4 as nanospacer provides low initial current without loading. Carbon felt with a rough surface as a flexible substrate provides a high output current under loading and extends the measurement range of the pressure sensors. The high sensitivity of the pressure sensors can be achieved with a low initial current and high output current. The Co3O4/carbon felt pressure sensors exhibit high sensitivity (243 kPa−1), ultralow detection limit (1.3 Pa), fast response (14 ms), and broad range (up to 180 kPa) of measurements. These excellent performances indicate that the Co3O4/carbon felt pressure sensor has great potential for application in wearable, healthcare devices. Furthermore, this strategy can be extended to the fabrication of other metal oxides/carbon felt pressure sensors.

A Linear-Motor Type HTS Flux Pump With Pumped Current Exceeding 640 A

In this paper, we present the fabrication and performance of a linear-motor type flux pump with a pumped current larger than 640 A. This high-temperature superconducting (HTS) flux pump can be used for magnetic resonance imaging (MRI) magnets and HTS electric machines. We use the flux pump to charge 10 superconducting closed-loops, and show the tested results of pumping current under different applied frequencies and magnetic field amplitudes. This flux pump device can output direct current larger than 640 A at 77 K. The output of this flux pump equals to a DC power source with low output voltage and high output current. Comparing with the traditional power supply of the same rated current, the size of this HTS flux pump is much smaller, while it also eliminates the harmful metal current leads that cause heat leakage. We show that, by increasing the length of the travelling wave region of this flux pump, there is no limit to the output of the current output, which can reasonably reach the kilo-ampere level. The purpose of this paper is to test the reliability of the methodology for the large current HTS flux pump.

From Zero- to One-Dimensional, Opportunities and Caveats of Hybrid Iodobismuthates for Optoelectronic Applications.

The association of the electron acceptor 4,4'-amino-bipyridinium (AmV2+) dication and BiI3 in an acidic solution affords three organic-inorganic hybrid materials, (AmV)3(BiI6)2 (1), (AmV)2(Bi4I16) (2), and (AmV)BiI5 (3), whose structures are based on isolated BiI63- and Bi4I164- anion clusters in 1 and 2, respectively, and on a one-dimensional (1D) chain of trans-connected corner-sharing octahedra in 3. In contrast with known methylviologen-based hybrids, these compounds are more soluble in polar solvents, allowing thin film formation by spin-coating. (AmV)BiI5 exhibits a broad absorption band in the visible region leading to an optical bandgap of 1.54 eV and shows a PV effect as demonstrated by a significant open-circuit voltage close to 500 mV. The electronic structure of the three compounds has been investigated using first-principles calculations based on density functional theory (DFT). Unexpectedly, despite the trans-connected corner-shared octahedra, for (AmV)BiI5, the valence state shows no coupling along the wire direction, leading to a high effective mass for holes, while in contrast, the strong coupling between Bi 6px orbitals in the same direction at the conduction band minimum suggests excellent electron transport properties. This contributes to the low current output leading to the low efficiency of perovskite solar cells based on (AmV)BiI5. Further insight is provided for trans- and cis-MI5 1D model structures (M = Bi or Pb) based on DFT investigations.

Identification of Permanent Faults and Disturbance Induced by Deicing Based on Permutation Entropy for the Large-Scale Clean Energy Transmission in Winter

Ice shedding may induce isolated ground wires’ temporary grounding, which can cause electric quantities of direct current (DC) deicing devices to fluctuate. Hence, the disturbance of ice shedding is able to trigger the protective relay frequently and unnecessarily, which adversely affects the deicing process. Due to the randomness of ice shedding, the grounding resistance varies quickly; thus, the disturbance in poles of deicing devices can be detected multiple times in a short time. Moreover, the permanent fault requires steady arc plasma because of the low output voltage and current of deicing devices, which cannot bring out multiple-time disturbances in the poles. This paper proposes the identification of permanent faults and disturbance induced by deicing based on the permutation entropy, which is verified by a large number of simulations.

Ultrahigh current density and fatigue stability in flexible energy harvester by designing delivery paths

Flexible piezoelectric energy harvesters that efficiently convert mechanical energy into electrical energy have been extensively studied due to their great application potential in low-power wearable electronics and self-powered sensors. However, the low current output and poor thermal fatigue resistance severely restrict their practical applications. Here, we propose a new strategy to simultaneously improve the current density and thermal conductivity of the flexible piezocomposites (PCs) by designing delivery paths. High-quality (Ba0·85Ca0.15) (Ti0·90Zr0.10)O3/copper nanorods/polydimethylsiloxane (BCZT/Cu NRs/PDMS) PCs with a novel co-chained structure prepared using a well-suited technique of dielectrophoresis were reported for the first time. The BCZT particles and Cu NRs aligned in same chains throughout PDMS matrix results in an efficient delivery path both for induced charge transfer and heat dissipation, thus leading to ultrahigh current density (4.7 μA/cm2) and thermal conductivity (0.31 W/(m · K)). Further, a faster charging speed and a dramatically fatigue stability were realized in the co-chained PCs. Our work is expected to provide a potential solution for simultaneously enhancing current density and heat dissipation for a variety of composites in the field of flexible energy harvesting.

Reduction of the Circulating Current Among Parallel NPC Inverters

In medium/high power applications, including smart transformers, active power filters, and wind turbines, three-level neutral-point-clamped (NPC) inverters proved to be a reliable solution, providing high efficiency and low harmonic distortion. In practice, several NPCs are parallel connected and operated in interleaved manner to further increase the power handling and reduce the line filters size. However, if such configuration has a common dc-link, high-frequency zero-sequence circulating current (HF-ZSCC) arises among the inverters, increasing power losses of the switching devices and propagating the stress on the dc-capacitors. Moreover, the amplitude of the HF-ZSCC is inversely proportional to the filter inductance size, therefore in real applications, it can reach hundreds of amperes even with relatively low output currents. The research on the HF-ZSCC is mostly concentrated on two-level inverters for low voltage grids and traction applications, where the inductance size is relatively big and the HF-ZSCC does not affect the system efficiency. Differently, NPCs provide higher switching degree of freedom and more sophisticated methods can be applied to reduce the HF-ZSCC. This article investigates a double-reference pulsewidth modulation (DRPWM) as solution for diminishing the HF-ZSCC in paralleled NPCs. The performance of DRPWM method is confirmed by both simulation and experiments, performed on a 1.6-MVA system.

Long-term hybrid galvanic corrosion protection of reinforced-concrete structures

Hybrid corrosion protection (HCP) can be used to provide corrosion arrest and prevention in degrading reinforced-concrete structures to increase their service life. The proprietary technology is a relatively new electrochemical treatment for concrete structures, having been patented in 2005 (patent GB2426008B). Due to this fact, accurate and reliable empirical data over the life span of a structure protected by an HCP system does not yet exist. This paper is the first to present over 10 years of empirical data, from one of the very first installations of HCP, providing a rigorous and reliable assessment of the structure's long-term performance. Results demonstrate that hybrid galvanic anodes exhibit a responsive behaviour to maintain the concrete environment and respond to corrosion hazards. Even after prolonged periods of low current output, the anodes respond to changing environmental conditions, providing the higher current output required to afford the necessary polarisation to the reinforcement, and hence the protection to the structure. Steel potentials also continued to trend towards more positive values, a generally agreed indication of passive reinforcement. Overall, this study is unique, being the first to present continuous, long-term performance data on hybrid galvanic anodes for the corrosion protection of reinforced-concrete structures.

Influences of different barrier films on microstructures and electrical properties of Bi2Te3-based joints

Diffusion barrier film was strongly proposed to utilize in Bi2Te3-based thermoelectric (TE) module. However, effects of different barriers on microstructures of solder joints and electrical properties of TE modules were still unclear, which were vital in practical applications. In current work, Bi2Te3-based TE modules without barrier (TM), with Ni (TMNi) and with Ni/Au (TMNi/Au) were fabricated via reflow-soldering. Experimental results revealed that at the interface between SAC305 solder and P- or N- type Bi2Te3 sample, the Ni or Ni/Au barrier could efficiently inhibit severe growth of the intermetallic compound (IMC) phase. Remarkably, a thinner IMC layer was observed at the solder/Au/Ni/Bi2Te3 interface, which was attributed to effects of Au elements on suppressing the formation of IMCs. The results of power generation ability test revealed that TMNi exhibited higher value of output power (P) under the temperature difference (ΔT) due to its higher values of open circuit voltage (V) and output current (I). On the other hand, since the lowest electrical resistance (R) and relatively low output current of TMNi/Au were measured during the test, the TMNi/Au was suggested to generate less heat, meaning it consumed less energy, and hence be theoretically more efficient in improving the conversion efficiency.

Measuring the Output Voltage of a Linear-Motor Type Flux Pump With an Insulated HTS Coil

High-temperature superconducting (HTS) flux pump can supply DC current into the superconducting magnet coil in a contactless manner. The flux pump works similarly as a DC power supply, with low output voltage and high output current. In this paper, based on the linear-motor type flux pump previously introduced from our laboratory (W. Wang et al. 2018), we miniaturized it and measured its the output DC voltage. By using different peak values and frequencies of the applied AC travelling magnetic wave, we obtained the pumping characteristics of this linear-motor type flux pump. With the same applied magnetic strength, it was found that the pumped current is not directly proportional to the frequency, we interpret that the critical current of the HTS stator was likely deteriorated by the heat generated in the stator due to high magnetic field amplitude and frequency. From the pumping current curve, a voltage-current relationship of the HTS flux pump was obtained. This method mentioned in this paper can directly derive the output voltage of the HTS flux pump, and could also be applicable for all other types of flux pumps. The method helps further optimizing HTS flux pumps which will be applied in the dedicated MRI and the brushless superconducting motor under developing.

Integrated Magnetic Buck–Boost Converter With “Zero” Output Current Ripple

This article presents an integrated magnetic buck-boost converter (IMBBC) with a positive output voltage. The input inductor, two power transfer inductors, and an auxiliary inductor in the ripple cancellation network of this converter are integrated in one magnetic core, and an additional capacitor is included for output current ripple cancellation. The IMBBC inherently operates in the continuous conduction mode and exhibits a nonpulsating input current and a very low ripple output current, thereby not only decreasing the current stress on both the input and output capacitors but also reducing the output voltage ripple. Because the input of the IMBBC is connected to the output during the switch-on period (similar to the operation of buck converters), the proposed IMBBC overcomes the right-half-plane zero problem in the buck or boost mode, thus achieving a higher dynamic performance. The use of the magnetic integration technique not only helped realize the aforementioned performance, but can also help reduce the weight and volume of dc-dc converters. Finally, the feasibility and effectiveness of the proposed topology and design approaches are experimentally verified.

Voltage control of sediment microbial fuel cell to power the AC load

This paper presents an innovative method for green energy generation by sediment microbial fuel cell (SMFC). SMFC has low output voltage and current, which can be extended for applications in modern electronic devices. In this paper, the different connection of SMFC (four modules: module1, module2, module3 and module4) is used to increase the output voltage as well as current. All modules are tested to the required time for charging four super capacitors (5.5 V, 4 F). Module4 (7 Parallel × 5 series connected SMFCs) charges a super capacitor from 2.76 V to 4.5 V in 30 min which takes less charging time as compared to other modules. The boost converter steps up input voltage super capacitor connected module4 at a constant voltage of 13.5 V to charge a 12 V battery for the time of 6.5 min. Further, module4 is expanded in six similar SMFC modules which are connected to charge the battery continuously. After 100% charging the battery, astable multi-vibrator inverter circuit is used to convert the direct current (battery) into alternating current for LED bulb lighting (7 W, 230 V, 50 Hz). This technique is useful for SMFC application as a power source in the practical AC load.

Current Measurement Transducer Based on Current-to-Voltage-to-Frequency Converting Ring Oscillator with Cascade Bias Circuit.

We propose a ring oscillator (RO) based current-to-voltage-to-frequency (I–V–F) converting current transducer with a cascade bias circuit. The I–V–F converting scheme guarantees highly stable biasing against RO, with a rail-to-rail output operation. This device was fabricated using National NanoFab Center (NNFC) 180 nm complementary metal-oxide-semiconductor (CMOS) technology, which achieves a current resolution of 1 nA in a measurement range up to 200 nA. A noise floor of 11.8 pA/√Hz, maximum differential nonlinearity (DNL) of 0.15 in 1 nA steps, and rail-to-rail output with a 1.8 V power supply is achieved. The proposed transducer can be effectively applied to bio-sensing devices requiring a compact area and low power consumption with a low current output. The fabricated structure can be applied to monolithic-three-dimensional integration with a bio-sensing device.

Bi-Directional Grid-Connected Modular Multilevel Converters With Direct Digital Control and D-Σ Processes

This paper presents bidirectional grid-connected modular multilevel converters (MMC) with direct digital control and division-summation processes to achieve power-injection and rectification functions. A direct digital control is developed to track current references, regulate dc-bus voltage and cell voltage, and balance the upper and lower dc-bus voltages. It can accommodate wide filter-inductance variation and take care of source voltage harmonics to achieve tight current tracking and low distortion output current. Based on the power-balance principle, the commands of arm currents can be determined directly. In this paper, the MMC configuration is introduced first, and then the control laws for current tracking and voltage regulation are derived in detail. Experimental and simulated results obtained from two 50 kW MMCs operated in power-injection and rectification modes have verified the analysis and discussion.

Low Detection Limit and High Sensitivity Wind Speed Sensor Based on Triboelectrification-Induced Electroluminescence.

The rapid development of the Internet of Things (IoT) has tremendously increased the demands for wind speed sensors in various applications, such as weather forecasting and environmental monitoring. To date, many wind speed sensors are developed based on triboelectric nanogenerators (TENGs). However, the low output current leads to a poor sensing precision, which greatly limits their practical applications. Here, a wind speed sensor is proposed by integrating a wind‐driven triboelectrification‐induced electroluminescence (TIEL) component with a perovskite‐based photodetector (PD) for enlarged electric current output. Compared with mechanoluminescence (ML), TIEL displays significantly higher signal intensity even under gentle breezes. In addition, the emission peak of TIEL matches with the absorption band of perovskite materials. Thus, TIEL materials are promising candidates for generating distinct electrical signals in real‐time to facilitate the detection of wind speed. With a comparable detection limit (5 m s−1) to a conventional TENG‐based wind speed sensor, the sensitivity of this hybrid sensor is three magnitudes higher at low bias voltages and, the response time is extremely short (<0.3 s). Moreover, it shows a favorable correlation with a commercial sensor. This research provides important progress toward environmentally‐friendly light sources and TIEL‐related sensor systems.

New approaches for the determination of electrochemical parameters in the model of proton-conducting solid oxide fuel cell

Proton-conducting solid oxide fuel cell is an electrical energy generation device with great potentials in the industrial and civil applications. The values of empirical parameters adopted in the corresponding simulations significantly determines the quality and reliability of the modeling results. Two new and practicable approaches are proposed in this paper, in order to accurately evaluate several critical electrochemical parameters in the relevant simulations. According to our models, effective hole conductivity of the electrolyte under working conditions, along with cathode electrochemical reaction order, are directly derived from the experiment. To examine the proposed approaches, single cells with BaCe0.8Sm0.2O3-δ electrolyte and Sm0.5Sr0.5CoO3-δ–BaCe0.8Sm0.2O3-δ cathode are manufactured, further the related experiments are performed as case studies. To determine the cathode activation overpotentials for cells with different particle sizes, a transferable parameter named TPB-specific exchange current density is introduced, and an expression which is much more convenient for numerical simulation of the cathode activation overpotential than the previously reported one is put forward in our model. These proposed expressions and parameters possess desirable transferability, and accurate numerical predictions of the cell output performances are achieved for both our and reported experiments. Then the influences of the involved polarizations are explored. Emphasis is drawn on the electrolyte hole conductivity. Its impact on the cell performance is non-negligible particularly under relatively high temperature and low output current, and hence has to be considered seriously in the simulation.

Hole conductivity in the electrolyte of proton-conducting SOFC: Mathematical model and experimental investigation

Proton-conducting solid oxide fuel cell (SOFC) is promising for the intermediate and low temperature applications. The hole conductivity within the electrolyte has noticeable impact on the cell performance. In this article, a new model is proposed to evaluate the hole conductivity of the electrolyte directly. Single cells with different electrolyte thicknesses are fabricated to validate our model. The BaCe0.7Zr0.1Y0.2O3−δ electrolyte and Sm0.5Sr0.5CoO3−δ-Ce0.8Sm0.2O2−δ cathode is employed in our experiments. The predicted cell output capacities are in accord with both our experiments and the reported results, confirming that our proposed method is valid and effective. There are several distinct features of our model compared with previous reports: 1) Hole conductivity could be evaluated directly from the measured output voltages of the full cell, thus it simplifies the relevant experiment; 2) in order to make the cathode reaction model transferable among samples with diverse micro-structures, new parameters named TPB-specific exchange current density is proposed; and 3) for proton-conducting SOFC, an equivalent circuit model with the consideration of both electrolyte hole conductivity and various overpotentials is firstly proposed. Our model points out that the influence of the hole conductivity on the cell capacity could not be neglected in cases of relatively low output current, high temperature and thin membrane. Therefore the hole conductivity of the electrolyte must be taken into consideration in the related simulations.

Comparative Experimental Evaluation of Zero-Voltage-Switching Si Inverters and Hard-Switching Si and SiC Inverters

Several efforts have been put in the reduction of the power losses of dc–ac converters by investigating soft-switching topologies, which have been reported to boost efficiencies of silicon inverters up to 99%. However, the auxiliary circuits of the switches significantly impact on the circuit complexity. Conversely, the use of wide bandgap devices offers an alternative for the reduction of the losses, while keeping the simple structure of a traditional inverter. This paper aims to experimentally evaluate the performance of four prototypes in terms of efficiency and costs. Two zero-voltage switching inverters, differing only in the power switches, and two comparable hard-switching inverters, mounting both silicon and silicon carbide devices, have been built and compared. Overall, the soft-switching inverters allow improving the efficiency at high output current in comparison with hard-switching Si inverters, but their efficiency is comparable to that of silicon carbide (SiC) inverters or even lower at low output currents. The economic analysis has shown that the cost of the power stage of the soft-switching inverters and the hard-switching SiC inverter is about 2.5 and 1.5 times that of the hard-switching inverter based on Si insulated gate bipolar transistors, respectively.