High Direct Current Research Articles

High performance DC-TENG based on coupling of mismatched number of triboelectric units and electrodes with mechanical switches for metal surface anti-corrosion

Triboelectric nanogenerator (TENG) have proven to be a promising technology for harvesting dispersed mechanical energy. However, traditional TENGs based on triboelectrification and electrostatic induction generate electricity in alternating current (AC) mode, which needs to be converted into direct current (DC) for most applications. Here, we propose a DC-TENG based on the coupling of mismatched number of triboelectric units and electrodes with a mechanical switch design. This design not only simplifies the structure compared with previous multi-phase TENG and minimizes power loss, but enables a stable DC generation without post-management, which can be used directly to metal surface anti-corrosion. The experimental results show that the output current of this TENG with the mismatched number of triboelectric units (T) and electrodes (E) in 2T3E, 4T5E and 6T7E increases from 16.96 μA to 32.46 μA, achieving maximum power density of 33.20 mW with an external resistance of 80 MΩ. This enhancement in performance illustrates the effectiveness of the proposed design for harvesting and converting energy efficiently. Furthermore, the application of the mismatched MTE-TENG as a power source for metal surface anti-corrosion is explored. Through immersion experiments and electrochemical tests, the corrosion current decreases from 29.59 μA to 3.15 μA compared with bare carbon steel, which significant decreases in both anodic and cathodic branch currents, indicating the achievement of the anti-corrosion effect. This work provides a new way to achieve high DC output for metal surface anti-corrosion and realizes a green electrochemical anticorrosion process.

Compact Ion Beam System for Fusion Demonstration

We demonstrate a compact ion beam device capable of accelerating H+ and D+ ions up to 75 keV energy, onto a solid target, with sufficient beam current to study fusion reactions. The ion beam system uses a microwave driven plasma source to generate ions that are accelerated to high energy with a direct current (DC) acceleration structure. The plasma source is driven by pulsed microwaves from a solid-state radiofrequency (RF) amplifier, which is impedance matched to the plasma source chamber at the S-band frequency in the range of 2.4–2.5 GHz. The plasma chamber is held at high positive DC potential and is isolated from the impedance matching structure (at ground potential) by a dielectric-filled gap. To facilitate the use of high-energy-particle detectors near the target, the plasma chamber is biased to a high positive voltage, while the target remains grounded. A target loaded with deuterium is used to study D-D fusion and a B4C or LaB6 target is used to study p-11B fusion. Detectors include solid-state charged particle detector and a scintillation fast neutron detector. The complete ion beam system can fit on a laboratory table and is a useful tool for teaching undergraduate and graduate students about the physics of fusion.

Effects of current control modes on the morphological and biological properties of graded FeCrNi metal-matrix coatings containing Al2O3 nanoparticles for cardiovascular applications

Implant coatings represent the most effective strategy to address multiple issues, ultimately increasing implant longevity and improving implant compatibility. In this study, we investigated the electrodeposition of a novel graded FeCrNi/Al₂O₃ coating on a 316L substrate for cardiovascular implants using direct current (DC) and pulsed current (PC). The effects of a current density range of 3–11 A dm⁻² and decreasing the duty cycle from 90 % to 50 % and subsequently to 10 % on the concentration of Al₂O₃ nanoparticles in the FeCrNi matrix, as well as on the microstructure and morphological properties, were studied using scanning electron microscopy (SEM). Additionally, structural characterization of the FeCrNi/Al₂O₃ films was performed using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). To assess the cytocompatibility of the samples, human coronary artery endothelial cells (HCAEC) were used. The results indicate that the PC provides a uniform microstructure and a smoother surface compared to the direct current DC. The study also reveals that the PC results in fewer defects and microcracks in the coating due to reduced formation of chromium hydrides in the layer and a significant reduction in stress during the deposition process. When using PC, an increase in particle incorporation in the coating was achieved, but no effect of changing the duty cycle was found. The highest deposition rate of Al₂O₃ was achieved at a current density of 11 A dm⁻² with an electrolyte containing 10 g L⁻¹ Al₂O₃. The FeCrNi/Al₂O₃ coatings exhibit low cytotoxicity when deposited using a high alumina content and DC, showing cell viability of over 90 %. However, only a few samples demonstrated cell viability higher than 80 % on day three. The proposed composite coating may represent an initial step towards improving implant coatings for cardiovascular stent materials.

Mitigation Strategy of Neutral-Point DC for Transformer Caused by Metro Stray Currents

Metro stray currents flowing into neutral-point-grounded transformers can cause serious direct current (DC) bias. Affected by both metro train and urban power grid operations, transformer neutral-point DC caused by metro stray current is complex, dynamic, and time-varying, which changes the DC bias risk level of transformers. Thus, just installing blocking devices (BDs) at transformer neutral points with high instantaneous DC may make it difficult to comprehensively mitigate DC bias and lead to increased BD installation. To solve this, through optimizing BD installation placements, a mitigation method for transformer DC bias is proposed. In the proposed method, the DC bias risk level and BD installation number are included in the constraint and objective functions. To evaluate the risk level of transformer DC bias, four indicators are proposed considering the distribution characteristics of neutral DC. To optimize the BD installation placements, the effects of both the metro train dynamic operation and the operation topology of the urban power grid on neutral DCs are considered. The Monte Carlo method is used to sample the train operation conditions and a relation matrix among transformers is established. Applying the method to a certain power system, the result of BD installation placements shows that the transformers supplying the metro system must have BDs installed at their neutral points.

Low core loss and high DC bias performance of FeSiAl soft magnetic composites cores with hybrid insulating layers of MgO/SiO2

Soft magnetic composites (SMCs) play an indispensable role in electromagnetic conversion, transmission, and storage. However, in order to achieve miniaturization, energy conservation, and meet the application requirements of premagnetisation in direct-current (DC) components, SMCs are required to have low core loss and high DC bias performance. In this work, FeSiAl SMCs with hybrid insulating layers of MgO/SiO2 have been successfully prepared by the decomposition of magnesium acetate tetrahydrate and silicone resin. The presence of MgO and SiO2 insulating layers can effectively compensate for each other's coating defects, thereby forming complete insulating layers on the surface of FeSiAl powders to reduce the core loss. Finally, the FeSiAl@MgO/SiO2 SMC gets remarkable comprehensive magnetic properties with a low core loss (Pcv) of 163.7 mW/cm3 at 50 mT/100 kHz, a high DC bias performance of 53.7 % at 100 Oe, and an effective permeability (μe) of 46, which is promising for high-frequency and high-power applications.

Hysteresis measurement and generic modeling of magnetostrictive materials under high-frequency excitation and high-intensity bias field

The applied DC (direct-current) bias fields can cause the changes of hysteresis and loss properties of magnetostrictive alloys materials, which further affect the output characteristics of electromagnetic devices. This study investigates the impact of high-frequency AC (alternating-current) excitation and high intensity DC bias magnetic field on hysteresis characterization for different magnetostrictive materials. To obtain the hysteresis properties of materials, a generic dynamic magnetic measured system is established, which can test the low-permeability magnetic materials with a DC bias strength range of 0–20000 A/m at AC excitation frequency range of 1–9 kHz. The tested results show that the Terfenol-D, Fe83Ga17, and Fe30Co70 exhibit different DC bias sensitivities, which cause the largest deviation (31.68 %) of losses compared with unapplied DC bias field. To better predict these changes, a generic high-frequency dynamic Jiles-Atherton (J-A) model with the coupling AC excitation and DC bias field is proposed. The AC excitation and DC bias related terms are introduced to characterize distortion and ellipticity phenomenon for these hysteresis loops. A combined method of Simulated Annealing Particle Swarm Optimization-Linear Decreasing Inertia Weight (SA-PSO-LDIW) algorithm and Neural Network (NN) are proposed to identify the introduced relevant parameters. This paper solves the problem of high-frequency hysteresis measurement and loss calculation for low permeability and high electrical impedance magnetostrictive rods-shaped material which can help guide the high frequency application for magnetostrictive materials.

Multiscale evolution observation of the pore structures of porous media under an electrokinetic treatment

Direct current (DC) stimulation is a promising electrokinetic method for enhancing oil recovery in porous media, especially in tight sandstones, due to the more remarkable effect of electroosmosis in materials with narrower pore throats. However, an interesting reversal of enhanced oil recovery (EOR) occurs in which oil recovery begins to decrease with DC voltages; this phenomenon hinders the application of this electrokinetic technology in petroleum industry. To date, the reason for this phenomenon remains unclear. Thus, in this study, we applied nuclear magnetic resonance (NMR) and in-situ scanning electron microscope (SEM) methods to investigate the underlying mechanisms. We classified and inspected the evolution of pore structures in tight sandstones at multiple scales ranging from the nanoscale to micron scale as the strength of DC voltage increases. The effects of both low DC and high DC voltages were analyzed in detail. Results show that the size and number of nanopores increased as the DC voltage increases. A low DC voltage can transform submicropores to micropores, and a high DC voltage can fasten this transformation. Furthermore, a low DC voltage increased the number and size of micropores, but a high voltage decreased the number and size of micropores. This study provides insights into changes in the pore structures of reservoir rocks under the treatment of the DC voltage, helping develop DC voltage-related technologies to recover hydrocarbons from porous media.

Design high voltage gain DC converter based on maximum power point resistance for photovoltaic applications

Due to the nonlinear properties of photovoltaic (PV) modules, the design of the high-gain direct current (DC) converter for maximum power point tracking (MPPT) is complicated. In this paper, the design of a new step-up DC converter for MPPT applications is proposed. The proposed converter is structured of two symmetrical reverse-parallel DC-DC boost converters. This structure is supported by voltage multiplier cells equipped to increase output voltage and decrease voltage stress on semiconductor switches. To simplify the high-gain DC converter design, the PV module's maximum power point is treated as resistance by using the incremental conductance (INC) method. The MPPT boost converter's inductance, input capacitance, and output capacitance are calculated using the derived equations using nine parameters. The results showed that the proposed DC converter simulation meets the necessary requirements. The size of the input capacitor, inductor, and output capacitor have been decreased. When the proposed converter is compared to a traditional converter, there is less voltage stress, low current ripple, and an increase in voltage gain. This has led to an improvement in the overall converter efficiency.

Design high voltage gain DC converter based on maximum power point resistance for photovoltaic applications

Due to the nonlinear properties of photovoltaic (PV) modules, the design of the high-gain direct current (DC) converter for maximum power point tracking (MPPT) is complicated. In this paper, the design of a new step-up DC converter for MPPT applications is proposed. The proposed converter is structured of two symmetrical reverse-parallel DC-DC boost converters. This structure is supported by voltage multiplier cells equipped to increase output voltage and decrease voltage stress on semiconductor switches. To simplify the high-gain DC converter design, the PV module's maximum power point is treated as resistance by using the incremental conductance (INC) method. The MPPT boost converter's inductance, input capacitance, and output capacitance are calculated using the derived equations using nine parameters. The results showed that the proposed DC converter simulation meets the necessary requirements. The size of the input capacitor, inductor, and output capacitor have been decreased. When the proposed converter is compared to a traditional converter, there is less voltage stress, low current ripple, and an increase in voltage gain. This has led to an improvement in the overall converter efficiency.

The Time, Electric Field, and Temperature Dependence of Charging and Discharging Currents in Polypropylene Films.

The insulating properties of polypropylene (PP) film play a very important role in the operating status of direct current (DC) support capacitors. Charging and discharging currents in PP film under high DC electric fields and temperatures correspond to charge transportation and accumulation, which significantly influence the electrical insulating properties of PP. In this paper, we have comprehensively studied the dependence of charging/discharging currents in PP film on time, electric field (150-670 kV/mm), and temperature (40-120 °C). The results showed that the charging current increased by almost an order of magnitude from 150 kV/mm to 670 kV/mm and exhibits a steep increase with temperature above 80 °C. The discharging currents are about 10 times less than the corresponding charging currents. Carrier mobility varies little with the electric field and becomes slightly larger with an increase in temperature. The quantity of the accumulated charges was calculated by the integral of the charging and discharging current differentials and showed a significant increase with the electric field and temperature. The corresponding electric field distortion becomes larger above 80 °C compared to 20-60 °C. Both electric field and temperature have an important effect on PP film and capacitors based on charge transport and accumulation and their electric field distortion. This study is innovative in that it combines the operating status of DC support capacitors with traditional methods to research synthetically charged transport mechanisms of PP film. The findings are meaningful for understanding the insulation failure mechanisms of PP film and capacitors under complex stresses.

Characteristics stability assessment of silica/alumina trihydrate based silicone elastomer composites subjected to long-term weathering under bipolar direct current for industrial electrical insulation

Room temperature vulcanized silicone rubber (RTV-SiR) coatings co-filled with silica (SiO2) and alumina trihydrate (ATH) fillers were subjected to long-term accelerated weathering under bipolar direct current (DC). Experimentations were conducted on fabricated samples of RTV-SiR with 5% nano-silica and RTV-SiR with 20% ATH in a specially designed weathering chamber. An extended aging (10,000 h) was conducted on samples energized equally under both polarity voltages to evaluate the effect of positive and negative voltages on the performance of RTV coating under bipolar high voltage DC. The electrical stability of specimens was assessed using online leakage current measurement, hydrophobicity, volume, and surface resistivity analysis. For mechanical characteristics of test samples hardness shore-A, tensile strength, weight loss, and elongation-at-break were measured and analyzed. Variations in chemical, morphological, and thermal degradation of the samples with aging were assessed using characterization tools like Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Thermal Gravimetric Analyzer (TGA), respectively. Findings explicated that samples with nano SiO2, offer better hydrophobic recovery and hence better leakage current suppression while ATH-filled composites exhibited enhanced thermal stability and better resistance to mechanical alterations. Furthermore, the comparative analysis of voltage polarity elucidates that the impact of positive DC was more profound in aging.

The Improved DC Breakdown Strength Induced by Enhanced Interaction between SiO2 Nanoparticles and LLDPE Matrix.

Direct current (DC) power transmission systems have received great attention because it can easily integrate many types of renewable energies and have low energy loss in long-distance and large-capacity power transmission for electricity global sharing. Nanoparticles (NPs) have a positive effect on the insulation properties of polymers, but weak interaction between NPs and polymer matrix greatly decreases the effort of NPs on the enhancement of insulation properties, and thereby limits its engineering application. In this work, grafting strategy was used to link the modified NPs and polymer matrix to improve their interactions. Silica NPs (SiO2-NPs) were modified by 3-(methacrylyloxy) propyl-trimethoxysilane (MPS) to introduce highly active groups on the SiO2-NPs surface, followed by the pre-irradiated linear low-density polyethylene (LLDPE) being easily grafted onto the MPS modified SiO2-NPs (MPS-SiO2-NPs) in the melt blending process to obtain LLDPE-g-MPS-SiO2-NPs nanocomposites. Fourier-transform infrared (FT-IR) spectrum and X-ray photoelectron spectroscopy (XPS) confirm the successful incorporation of MPS into SiO2-NPs. Transmission electron microscopy (TEM) verifies that the modified SiO2-NPs exhibits more uniform distribution. The rheology result shows that the interaction between MPS-SiO2-NPs and LLDPE significantly improves. More importantly, the LLDPE-g-MPS-SiO2-NPs nanocomposites displays superior DC breakdown strength to that fabricated by conventional modification methods. When the addition of MPS-SiO2-NPs is 0.1 wt%, the highest DC breakdown strength values of 525 kV/mm and 372 kV/mm are obtained at 30 °C and 70 °C, respectively, and high DC breakdown strength can be well maintained in a wide loading range of NPs.

All‐Fabric Direct‐Current Triboelectric Nanogenerators Based on the Tribovoltaic Effect as Power Textiles

AbstractThe tribovoltaic effect is the direct‐current (DC) output that results from sliding a p‐type semiconductor on top of an n‐type semiconductor, and it is caused by the electron–hole pairs generated However, the rigid structure of traditional semiconductor limits its potential application in wearable fields. Here, p–type and n–type fabric with semiconductor properties are prepared by doping small organic molecules of cetyltrimethylammonium bromide and sodium dodecylbenzene sulfonate on the carbon atoms of single–wall carbon nanotubes (SWCNTs), and three all‐fabric direct‐current triboelectric nanogenerators based on the tribovoltaic effect (AFDC‐TENG) are developed , which exhibit high flexibility, satisfactory comfort, and stable DC output. In addition, the effects of structural parameters and environmental factors on the electrical output of AFDC‐TENG are systematically discussed. The output voltage, current, and power density of p‐type AFDC‐TENG can reach 0.2 V, 0.29 µA, and 45.5 mV m−2 at a maximum speed of 0.2 m s−1 and a sliding frequency of 1 Hz, respectively. This work proposes a simple and scalable design form for all‐fabric DC power supply devices, which has potential applications in the future micro/nano energy or self‐powered flexible sensors.

Parametric resonance of multi-frequency excited MEMS based on homotopy analysis method

The nonlinear dynamics and control of micro electromechanical systems (MEMS) is an important topic at present and homotopy analysis method (HAM) is an effective semi-numerical and semi-analytical method for solving strongly nonlinear problems. In this paper, the parametric resonance of MEMS with multi-frequency excitation is studied by HAM. Firstly, the differential equation of electrostatically driven microbeam is processed by Taylor expansion, and it is transformed into the parametric motion model with multi-frequency excitation. Then, the approximate solution and amplitude–frequency response equation of the system are obtained by HAM, and compared with the numerical solution. Finally, the influence of direct current (DC) and alternating current (AC) on principal parametric resonance and superharmonic resonance is discussed. The results show that HAM is an effective method to analyze the parametric vibration of multi-frequency excitation system, and the amplitude–frequency response curve of microbeam about parametric motion depends on the time scale in high DC and high AC state. This study effectively extends the application of HAM in parametric resonance, which is of great significance to the study of nonlinear vibration of MEMS.

A quantitative model of the cerebral windkessel and its relevance to disorders of intracranial dynamics.

Traditional models of intracranial dynamics fail to capture several important features of the intracranial pressure (ICP) pulse. Experiments show that, at a local amplitude minimum, the ICP pulse normally precedes the arterial blood pressure (ABP) pulse, and the cranium is a band-stop filter centered at the heart rate for the ICP pulse with respect to the ABP pulse, which is the cerebral windkessel mechanism. These observations are inconsistent with existing pressure-volume models. To explore these issues, the authors modeled the ABP and ICP pulses by using a simple electrical tank circuit, and they compared the dynamics of the circuit to physiological data from dogs by using autoregressive with exogenous inputs (ARX) modeling. The authors' ARX analysis showed close agreement between the circuit and pulse suppression in the canine cranium, and they used the analogy between the circuit and the cranium to examine the dynamics that underlie this pulse suppression. This correspondence between physiological data and circuit dynamics suggests that the cerebral windkessel consists of the rhythmic motion of the brain parenchyma and CSF that continuously opposes systolic and diastolic blood flow. Such motion has been documented with flow-sensitive MRI. In thermodynamic terms, the direct current (DC) power of cerebral arterial perfusion drives smooth capillary flow and alternating current (AC) power shunts pulsatile energy through the CSF to the veins. This suggests that hydrocephalus and related disorders are disorders of CSF path impedance. Obstructive hydrocephalus is the consequence of high CSF path impedance due to high resistance. Normal pressure hydrocephalus (NPH) is the consequence of high CSF path impedance due to low inertance and high compliance. Low-pressure hydrocephalus is the consequence of high CSF path impedance due to high resistance and high compliance. Ventriculomegaly is an adaptive physiological response that increases CSF path volume and thereby reduces CSF path resistance and impedance. Pseudotumor cerebri is the consequence of high DC power with normal CSF path impedance. CSF diversion by shunting is an accessory windkessel-it drains energy (and thereby lowers ICP) and lowers CSF path resistance and impedance. Cushing's reflex is an accessory windkessel in extremis-it maintains DC power (arterial hypertension) and reduces AC power (bradycardia). The windkessel theory is a thermodynamic approach to the study of energy flow through the cranium, and it points to a new understanding of hydrocephalus and related disorders.

Nonlinear current response and electric quantum oscillations in the Dirac semimetal Cd3As2

Chiral anomaly is a distinct quantum anomaly associated with chiral fermions in Dirac or Weyl semimetals. The use of negative magnetoresistance (negative MR) as a signature for this anomaly remains contentious, as trivial mechanisms such as current jetting and weak localization can also induce negative MR. In this study, we report a novel nonlinear behavior of the chiral anomaly in the longitudinal direction, which we observed by applying parallel current and magnetic field to the Dirac semimetal Cd3As2. This nonlinear characteristic peaks at an intermediate magnetic field of approximately 5 T, displaying a resistance-increasing property concomitant with strengthening of the current source. Through angle-dependence experiments, we were able to rule out trivial factors, such as thermal effects, geometric artifacts, and anisotropy. Furthermore, additional electric quantum oscillations were observed when the direct current (DC) was applied as high as 300 μA. Such an unusual phenomenon is ascribed to the formation of quantized levels due to Bloch oscillation in the high DC regime, suggesting that an oscillatory density distribution may arise as the electric field increases. The non-Ohmic electric quantum oscillations open a new avenue for exploring chiral anomaly and other nontrivial topological properties, which is also one of the salient features of nonequilibrium steady states in condensed matter physics.

Cascaded SiC JFET Topology for High-Voltage Solid-State Circuit Breaker Applications

With evolving landscape of direct current (DC) power transmission and distribution, a reliable and fast protection against faults is critical. High performance DC solid-state circuit breakers (SSCBs) can be designed using silicon carbide (SiC) junction field-effect transistors (JFETs), which utilize the device's intrinsic normally-ON characteristic and low ON-resistance. However, for SSCB that require high-voltage (HV) blocking capability, a proper number of JFETs need to be connected in series to achieve the desired voltage blocking rating. It has been conventional to add a controlling normally-OFF transistor, such a metal-oxide-semiconductor field-effect transistor (MOSFET), resulting in a circuit with normally-OFF behavior. However, disparities both in the voltage rating and in the ON-resistance between MOSFETs and JFETs tend to complicate the circuit design, and physically, they may lead to serious localized thermal stresses. A significant challenge remains with ensuring equal voltage balancing across the JFETs during the switching transitions as well as the blocking stage as it is crucial to prevent permanent damages from over-voltage stresses. Therefore, this article presents a new switch topology, in which a cascaded JFET configuration is operated without using a control MOSFET or other added control device. The dynamic voltage balancing network to synchronize both the JFETs' turn ON and OFF intervals is described analytically. Moreover, a novel static voltage balancing network is proposed to establish equal sharing of the total blocking voltage across the series connection of JFETs while maintaining low power loss.

Infrared Thermoelectric Nanoantenna with Maximum Output Voltage Using Grounded and Open‐Ended SiO2

AbstractThe potential of a nanoantenna‐coupled thermocouple to convert untapped infrared (IR) energy from low‐temperature heat sources into direct current (DC) energy has recently gained attention. In a typical nanoantenna with a thermocouple, heat spread at the antenna center leads to a limited temperature difference and lowers the open‐circuit voltage (Voc). Therefore, a membrane or air gap under the antenna has recently been used, but when a massive array is constructed for high DC voltage output, stability and fabrication issues can arise. To solve this, this work utilizes the constructively coupled fields at the antenna center in both vertical and horizontal directions via a grounded and open‐ended substrate and maximizes Voc of the thermoelectric nanoantenna. In the antenna structure, a titanium (Ti)‐based bowtie nanoantenna and nickel (Ni)‐Ti bimetal nano‐thermocouple are used for high Seebeck effect. The thermoelectric bowtie nanoantenna is designed and fabricated on a metal‐backed and open‐ended silicon dioxide (SiO2) substrate with optimum dimensions, demonstrating the maximum Voc of 2.03 µV at λ0 = 10.6 µm which is five times the maximum Voc of 0.4 µV from the state‐of‐the‐art substrate‐mounted thermoelectric nanoantennas. It is expected that the fabricated SiO2‐mounted thermoelectric nanoantenna with the maximum Voc can be used for a high DC output IR‐harvesting massive nanoantenna array.

A novel period–based method for the measurement direct current motor velocity using low-resolver encoder

Direct current (DC) motors—which have widespread usage areas such as industrial devices, automobiles, and household appliances—are also widely used in robotic systems that have developed rapidly in recent years and need precise control. Since the DC motors with encoder on its shaft used in robots have low resolution, accurate speed measurement cannot be made and this makes robot control difficult. In this study, a novel period–based measurement approach is presented to more accuracy and precision determine DC motor velocity at high speed with signals obtained from a low-resolver incremental encoder. First, the signals of the dual channel encoder are applied to the exclusive or gate to produce a single output signal with twice the frequency in order to reduce the number of interrupt pins used in the microcontroller and optimize the program cycle time. Based on the sample count calculated with the entered by user reference speed and microcontroller loop time, the mean filter is then applied to the half-wave period of the signal received through the Arduino board interrupt pin. In order to demonstrate the effectiveness of the method, measurement made with three different methods as follows: traditional period–based method, half-wave period method with only one channel, and exclusive or output signal half-wave period method. The results show the high-speed measurements through the presented method outperform other methods at high DC motor speeds. Especially in robots using more than one motor, the processing load of microcontroller has reduced and enabled the use of other peripheral interfaces by reducing the number of microcontroller pins used for the encoder. In addition, utilizing the results obtained with this method, the proportional–integral–derivative (PID) control of the motors in a four-wheel drive mobile robot is carried out for different speeds.

Optimising electrofishing settings for shrimp and fish in shallow tropical streams

Electrofishing is widely used to survey fish communities in freshwater, but uncertainties remain about electrotaxis (i.e. swimming toward the electrode) and the efficiency with which it catches decapod species. This three-part study was performed to define effective electrofishing settings for mixed communities of freshwater decapods and fish species. First, we studied the behaviour of five species of swimming decapods (Caridae) when exposed to four waveforms (direct current (DC) or pulsed direct current (PDC) at 2, 5 or 40 Hz) and two power density settings (low (30 µW.cm−3) or high (80 µW.cm−3)) in the laboratory. DC at low power density and PDC-2 Hz at high power density induced significantly more electrotaxis than the other settings. We then tested three electrofishing settings (low power DC (DClp), high power DC (DChp) and high power 40 Hz PDC (PDC40hp)) under natural conditions using the depletion method (with three passes) in enclosed sections of a shallow stream, followed by complete removal of bottom substrate and aquatic vegetation to catch the remaining individuals. DClp consistently detected all shrimp (nine species) and fish (seven species) after two electrofishing passes, but the two other settings did not. DC performed better than PDC for estimating the abundance of shrimp (80% vs. 70% of individuals caught, respectively) and fish (90% vs. 70%, respectively) after three electrofishing passes. Using depletion models, DClp gave the most accurate estimates of abundance for shrimp and fish species. Finally, we assessed the ability of three-pass DClp electrofishing to estimate abundances in nine shallow and coarse-substrate Caribbean streams. More than 10,000 shrimp from 10 species and 1600 fish from 8 species were caught and examined. We observed a correlation between estimated and total abundances after complete removal of bottom substrate and aquatic vegetation in the enclosed stream sections, except for small (≤ 20 mm long) shrimp. The fish mortality rate due to electrofishing was 0.22%, and only one species (Eleotris perniger) showed evidence of spinal damage (4.4% of individuals) based on ultrasound analysis of the spinal column. Thus, we recommend using DClp (30 µW.cm−3) to survey sympatric communities of shrimp and fish species in shallow, coarse-substrate tropical streams.