Performance Optimization of μDMFC with Foamed Stainless Steel Cathode Current Collector

The micro direct methanol fuel cell (μDMFC) has attracted more and more attention in the field of new energy due to its simple structure, easy operation, and eco-friendly byproducts. In a μDMFC’s structure, the current collector plays an essential role in collecting the conduction current, and the rational distribution of gas and water. The choice of its material and flow fields would significantly impact the μDMFC’s performance. To this end, four different types of cathode current collector were prepared in this study. The materials selected were stainless steel (SS) and foam stainless steel (FSS), with the flow fields of hole-type and grid-type. The performance of the μDMFC with different types of cathode current collector was investigated by using polarization curves, electrochemical impedance spectroscopy (EIS), and discharging. The experimental results show that the maximum power density of μDMFC of the hole-type FSS cathode current collector is 49.53 mW/cm2 at 70 °C in the methanol solution of 1 mol/L, which is 115.72% higher than that of the SS collector. The maximum power density of the μDMFC with the grid-type FSS collector is 22.60 mW/cm2, which is 27.39% higher than that of the SS collector. The total impedance of the μDMFC of the FSS collector is significantly lower than that of the μDMFC of the SS collector, and the total impedance of the μDMFC with the hole-type flow field collector is lower than that of the grid-type flow field. The discharging of μDMFC with the hole-type FSS collector reaches its optimal value at 70 °C in the methanol solution of 1 mol/L.

Reduction of Reactive Power Waste of Inductive Electrical Appliances using Power Factor Correction

Electricity is the primary source of power in most countries including Sri Lanka, and saving or minimising the waste of it has become crucial in facing the world power crisis. Electrical power is wasted in various ways including reactive power waste due to induction and capacitance of appliances, and standby power loss. These two contribute most to the waste. This paper focuses on reducing the reactive power waste of inductive electrical appliances commonly used in home and office by increasing the power factor. An attempt was made to reduce the power waste of inductive electrical appliances by connecting a capacitor bank with a variable capacitance in parallel with the appliance. Optimal capacitance and the power factor are determined using the capacitor bank. Results indicate about 30 percent of power saving could be achieved for fluorescent tube lamps using a power factor correction. A maximum power factor of 0.93 is achieved at the capacitance value of 2.99 F. It is not possible, by this method, to increase the power factor of more capacitive equipment such as CFL bulbs and ceiling fans. In this case, power minimisation could be tried connecting inductors in parallel with the equipment. Power factor and power consumption of home electrical appliances were measured for advising the general public of high power consuming equipment, especially in stand-by mode. To attain a further reduction of power waste it is proposed to measure inductance, capacitance and resistance of appliances using Hendry, Farad and Ohm meter. Total impedance can then be calculated and the power waste could be minimised using appropriate capacitors and/or inductors. Keywords: reactive power, power factor, power waste, reactive power waste, power minimisation

Design and Optimise a GARField MRI Resonator

The design of a Nuclear Magnetic Resonance (NMR) sensor coil for a GARField NMR system was examined. The target design has a diameter about mm and length mm tuned to frequency of MHz at 50 Ω total impedance. Nine different sets of coils were built with different numbers of turns (3, 5, and 7) and different thickness of wire to vary the wire resistance. The report was to examine based on the design parameters the best resonant circuit for a GARField MRI system. The acquired tuning characteristics from these resonant circuits were interpreted using MATLAB scripts and Excel spreadsheet to compare each coil with already existing theory of resonators. This was achieved by matching each resonant circuit using a match and tuning capacitor to the required frequency (22-23.4 MHz) and to 50 Ω total impedance at resonance. It was found that there is no easy method to estimate the inductance of the coil of wire. The result for the experimental inductance was found to be 0.5 µF and resistance of 0.4 Ω for a medium coil of wire with 5 numbers of turns, diameter of 0.45 and length of 0.7 mm. The initial attempt to fit the experimental data to that of the theory failed due to the absence of stray capacitance in the theory. However, when stray capacitor with value ranging between pF was incorporated in parallel with the tank circuit, it was found that both the experiment and theory fit as expected. Three coils were tested in the NMR laboratory using a GARField spectrometer to examine the best coil that will be suitable for NMR experiment. Coils were compared on the basis of signal to noise ratio (SNR) and P90 pulse length. It was found that medium coil of wire with 3 number of turns has the biggest SNR of 177 which is good for NMR procedures. On the other hand, coil with 5 numbers of turns has the shortest P90 pulse length of 2.0 µs which is good for spatial resolution. At all rate, this research have shown how theories are verified through experiment.

Design and Investigation of Modern UWB-MIMO Antenna with Optimized Isolation

This paper proposes a compact, semi-circular shaped multiple input multiple output (MIMO) antenna design with high isolation and enhanced bandwidth for ultrawide band (UWB) applications. A decoupling stub is used for high isolation reaching up to −55 dB over the entire bandwidth. The proposed antenna is used for UWB as well as super wide band (SWB) applications. The overall size of the proposed antenna is 18 × 36 × 1.6 mm3. The | S 11 | and voltage standing wave ratio (VSWR) of the proposed antenna are less than −10 dB and 2, respectively, in the range of 3–40 GHz. The total impedance bandwidth of the proposed design is 37 GHz. The VSWR, | S 11 | , | S 22 | , | S 21 | , | S 12 | , gain, envelope correlation coefficient (ECC), radiation pattern, and various other characteristic parameters are discussed in detail. The proposed antenna is optimized and simulated in a computer simulation technology (CST) studio, and printed on a FR4 substrate.

Multiwalled Carbon Nanotubes and the Electrocatalytic Activity of Gluconobacter oxydans as the Basis of a Biosensor

This paper considers the effect of multiwalled carbon nanotubes (MWCNTs) on the parameters of Gluconobacter oxydans microbial biosensors. MWCNTs were shown not to affect the structural integrity of microbial cells and their respiratory activity. The positive results from using MWCNTs were due to a decrease in the impedance of the electrode. The total impedance of the system decreased significantly, from 9000 kOhm (G. oxydans/chitosan composite) to 600 kOhm (G. oxydans/MWCNTs/chitosan). Modification of the amperometric biosensor with nanotubes led to an increase in the maximal signal from 65 to 869 nA for glucose and from 181 to 1048 nA for ethanol. The biosensor sensitivity also increased 4- and 5-fold, respectively, for each of the substrates. However, the addition of MWCNTs reduced the affinity of respiratory chain enzymes to their substrates (both sugars and alcohols). Moreover, the minimal detection limits were not reduced despite a sensitivity increase. The use of MWCNTs thus improved only some microbial biosensor parameters.

Magnetoimpedance Effect in the Ribbon-Based Patterned Soft Ferromagnetic Meander-Shaped Elements for Sensor Application

Amorphous and nanocrystalline soft magnetic materials have attracted much attention in the area of sensor applications. In this work, the magnetoimpedance (MI) effect of patterned soft ferromagnetic meander-shaped sensor elements has been investigated. They were fabricated starting from the cobalt-based amorphous ribbon using the lithography technique and chemical etching. Three-turn (S1: spacing s = 50 μm, width w = 300 μm, length l = 5 mm; S2: spacing s = 50 μm, width w = 400 μm, length l = 5 mm) and six-turn (S3: s = 40 μm, w = 250 μm, length l = 5 mm; S4: s = 40 μm, w = 250 μm and l = 8 mm) meanders were designed. The ‘n’ shaped meander part was denominated as “one turn”. The S4 meander possesses a maximum MI ratio calculated for the total impedance ΔZ/Z ≈ 250% with a sensitivity of about 36%/Oe (for the frequency of about 45 MHz), and an MI ratio calculated for the real part of the total impedance ΔR/R ≈ 250% with the sensitivity of about 32%/Oe (for the frequency of 50 MHz). Chemical etching and the length of the samples had a strong impact on the surface magnetic properties and the magnetoimpedance. A comparative analysis of the surface magnetic properties obtained by the magneto-optical Kerr technique and MI data shows that the designed ferromagnetic meander-shaped sensor elements can be recommended for high frequency sensor applications focused on the large drop analysis. Here we understand a single large drop as the water-based sample to analyze, placed onto the surface of the MI sensor element either by microsyringe (volue range 0.5–500 μL) or automatic dispenser (volume range 0.1–50 mL).

Barium Strontium Titanate Humidity Sensor: Impact of Doping on the Structural and Electrical Properties

The influence of Mg2+ doping (3 mol %) on structural and humidity sensing properties of (Ba0.5,Sr0.5)TiO3 (BST) perovskite nanocomposite were studied in details. Microstructural properties revealed the particle size, surface area, and average pore volume diminished for doped sample. For the MgO doped BST sensor, the film resistance and total impedance are changed more than four orders of magnitude in the 20–95% RH range, while BST sensor shows three orders change. The 3 mol % MgO doped sample with maximum hysteresis of 6.1 RH% and response/recovery time of about 30/80 s exhibits faster characteristics compare to pure BST sample with 6.8 RH% hysteresis and response/recovery of 41 s and 98 s, respectively. Transduction mechanism was found based on the proton transfer and further confirmed by a Bode plot and Nyquist complex impedance plane plot.

Power quality enrichment using enhanced adaptive control-detuned-LC proposal in voltage source control conquered distributed generation with hardware implementation

This paper presents the collective operation and comparative assessment of artificial neural network (ANN)-based adaptive controller with detuned-inductor capacitor (LC) filter facility in grid-tied voltage source control (VSC) system. In order to facilitate proper shaping of VSC outputs and to avoid voltage surge or current surge issues that may occur during the synchronization, the controlling action should reflect importance of total impedance (Zt) effect for: (i) accurate online weight updating, (ii) generation of correct references for proper shaping of VSC outputs, (iii) accurate assessment and exclusion of current harmonics and (iv) robust in defending any system perturbation. This impedance is taken into consideration during the run-time weight updation process through extended control steps in order to pass over various losses that certainly occurs in transformers, filters, line parameters and so forth. Performance of the system is well improved with an inclusion of total impedance (Zt) measured between the VSC and point of common coupling (PCC). A detuned-LC filter is predominantly intended for reactive power compensation, power factor correction, prompt and accurate alleviation of the harmonics. A comparative assessment in between enhanced and conventional adaptive controllers that are designed in MATLAB/Simulink clarifies the robust performances of the proposed control design under sundry system turbulences. The verification of the proposed enhanced controller is approved with the hardware results obtained using dSPACE RTI 1202 kit.

Analytical Approach to Circulating Current Mitigation in Hexagram Converter-Based Grid-Connected Photovoltaic Systems Using Multiwinding Coupled Inductors

The hexagram multilevel converter (HMC) is composed of six conventional two-level voltage source converters (VSCs), where each VSC module is connected to a string of PV arrays. The VSC modules are connected through inductors, which are essential to minimize the circulating current. Selecting inductors with suitable inductance is no simple process, where the inductance value should be large to minimize the circulating current as well as small to reduce an extra voltage drop. This paper analyzes the utilization of a multiwinding (e.g., two, three, and six windings) coupled inductor to interconnect the six VSC modules instead of six single inductors, to minimize the circulating current inside the HMC. Then, a theoretical relationship between the total impedance to the circulating current, the number of coupled inductor windings, and the magnetizing inductance is derived. Owing to the coupled inductors, the impedance on the circulating current path is a multiple of six times the magnetizing inductance, whereas the terminal voltage is slightly affected by the leakage inductance. The HMC is controlled to work under variable solar radiation, providing active power to the grid. Additional functions such as DSTATCOM, during daytime, are also demonstrated. The controller performance is found to be satisfactory for both active and reactive power supplies.