Cathodal Current Pulses Research Articles

Stationary and pulsed electrodeposition of silicon in LiCl–KCl–CsCl–K2SiF6 melt

Silicon and its materials are widely used in metallurgy, micro- and nano-electronics, solar energy, and are also promising materials for anodes of lithium-ion power sources with increased specific capacity. The expansion of application areas of silicon with controlled morphology necessitates the development of new energy–efficient methods of its production. In the present work, the influence of the mode as well as parameters of electrolysis of the LiCl–KCl–CsCl–K2SiF6 melt with a temperature of 545 оC on the morphology of electrolytic precipitation of silicon on glassy carbon has been studied. The galvanostatic mode of electrodeposition, widely used in industry, as well as the pulsed mode, which is actively investigated at present, were used for the electrolysis. Silicon electrodeposition was carried out by varying such parameters as cathodic current density (from 3 to 50 mA/cm2) and electrolysis duration (from 30 to 180 min) in the galvanostatic mode, as well as by varying the density and duration of the cathodic current pulse, the duration of current pauses and the total duration of electrolysis in the pulsed mode. It is shown that electrodeposition of silicon on glassy carbon is accompanied by the formation of a continuous sediments of hemispherical nuclei with a diameter of about 1 micron on the electrode surface. An increase in the cathodic current density and an increase in the cathodic current pulse pause frequency contribute to the disruption of the sediment continuity and the growth of dendrites of ordered or arbitrary shape. At the same time, the pulsed mode allows to increase the cathode current density at silicon electrodeposition (from 25–30 to 250–500 mA/cm2) and stabilize the value of the cathode potential during electrolysis.

A 14-Bit, 12 V-to-100 V Voltage Compliance Electrical Stimulator with Redundant Digital Calibration.

Electrical stimulation is an important technique for modulating the functions of the nervous system through electrical stimulus. To implement a more competitive prototype that can tackle the domain-specific difficulties of existing electrical stimulators, three key techniques are proposed in this work. Firstly, a load-adaptive power saving technique called over-voltage detection is implemented to automatically adjust the supply voltage. Secondly, redundant digital calibration (RDC) is proposed to improve current accuracy and ensure safety during long-term electrical stimulation without costing too much circuit area and power. Thirdly, a flexible waveform generator is designed to provide arbitrary stimulus waveforms for particular applications. Measurement results show the stimulator can adjust the supply voltage from 12 V to 100 V automatically, and the measured effective resolution of the stimulation current reaches 14 bits in a full range of 6.5 mA. Without applying charge balancing techniques, the average mismatch between the cathodic and anodic current pulses in biphasic stimulus is 0.0427%. The proposed electrical stimulator can generate arbitrary stimulus waveforms, including sine, triangle, rectangle, etc., and it is supposed to be competitive for implantable and wearable devices.

Anodically‐Generated Alkyl Radicals Derived from Carboxylic Acids as Reactive Intermediates for Addition to Alkenes

AbstractElectrochemically driven C−C coupling has the potential to reduce the cost and environmental impact of some organic syntheses currently accomplished through thermochemical methods. Here, we use electrochemical oxidation of carboxylic acids as a source of reactive carbon‐centered radicals that enable radical addition to alkenes in the anode boundary layer. We demonstrate an optimization of reaction conditions to suppress the thermodynamically favored, but synthetically undesirable radical self‐coupling in favor of radical addition to styrene. In methanol solvent, 88 % selectivity and 72 % Faradaic efficiency for targeted functionalized benzenes are achieved. For low current densities, iridium anodes outperform platinum, gold, palladium, and glassy carbon anodes. With constant potential or constant current electrolyses, the deposition of organic by‐products on the catalyst surface leads to anode passivation. We show that periodic cathodic current pulses effectively regenerate the catalyst. Lastly, we confirm the role of free radicals in the reaction mechanism with a radical trap.

Исследование защитных свойств покрытий, полученных методом микродугового оксидирования в щелочных растворах электролитов

The article presents the results of a study of the corrosion properties of oxide coatings compacted with polymers and without compaction. Oxide coatings were obtained on VT1-0 and VT5 titanium alloys under the influence of fast pulsed actions of the micro-arc oxidation (MAO) process. To form MAO coatings, a pulsed mode of the process was used with an anodic current pulse duration of 250 ± 25 μs; the cathodic current pulse duration of 5 ± 0.5 ms; pause between anodic and cathodic current pulses 250 ± 25 μs; repetition rate of anodic and cathodic pulses 50 ± 0.5 Hz. Alkaline solutions were used as electrolytes. Fluoroplastic and epoxy resin solutions were used to seal the oxide coatings. The obtained MAO coatings have 4.4 – 7.5 % porosity on the VT1-0 alloy and 5.4 – 12.1 % on the VT5 alloy. The average diameter of oxide coating pores varies from 0.1 to 0,5 µm. X-ray phase analysis showed titanium dioxide in anatase and rutile modification in the oxide coatings composition. Tests performed in a 24 % solution of sulfuric acid at 40 and 75°C showed that the coatings on the VT1-0 alloy, both oxide and oxide-polymer, are more corrosion resistant than similar coatings on the VT5 alloy. All types of coatings produced on VT1-0 alloy are corrosion-resistant at a test temperature of 40 °C. Consolidation of MAO coatings with polymeric materials improves corrosion properties.

Charge injection characteristics of sputtered ruthenium oxide electrodes for neural stimulation and recording.

We have studied the charge-injection characteristics and electrochemical impedance of sputtered ruthenium oxide (RuOx ) films as electrode coatings for neural stimulation and recording electrodes. RuOx films were deposited by reactive DC magnetron sputtering, using a combination of water vapor and oxygen gas as reactive plasma constituents. The cathodal charge storage capacity of planar RuOx electrodes was found to be 54.6 ± 9.5mC/cm2 (mean ± SD, n=12), and the charge-injection capacity in a 0.2-ms cathodal current pulse was found to be 7.1 ± 0.3mC/cm2 (mean ± SD, n=15) at 0.6V positive bias versus Ag|AgCl, in phosphate buffer saline at room temperature for ~250 nm thick films. In general, the RuOx films exhibited high charge-injection capacities, with or without a positive interpulse bias, comparable to sputtered iridium oxide (SIROF) coatings. The charge-injection capacity increased monotonically with film thickness from 120 to 630 nm, and reached 11.30 ± 0.34 mC/cm2 (mean ± SD, n=5) at 0.6V bias versus Ag|AgCl at 630 nm film thickness. In addition, RuOx films showed minimal changes in electrochemical characteristics over 1.5 billion cycles of constant current pulsing at a charge density of 408 μC/cm2 (8nC/phase, 200 μs pulse width). The findings of low-impedance, high charge-injection capacity, and long-term pulsing stability suggest the suitability of RuOx as a comparatively inexpensive and favorable choice of electrode material for neural stimulation and recording.

Experimental investigation of single microdischarges in a barrier corona arrangement with a cathodic metal pin

Microdischarges (MDs) in a sinusoidally driven barrier corona discharge, operated in dry air at atmospheric pressure, are investigated using time-correlated single photon counting (TC-SPC) technique, electrical measurements (applied voltage and current pulses) and ICCD images. In the current contribution, results of the cathodic pin half-cycle are presented. Results of the anodic pin half-cycle were presented in a previous study (Jahanbakhsh et al 2018 Plasma Sources Sci. Technol. 27 115011). In the cathodic pin half-cycle appearance phase and current pulse amplitude of the MDs have an erratic behavior. Hence, a statistical study of the current pulse amplitudes is conducted, and it is correlated to the phase-resolved spatio-temporal development of the MDs, obtained from TC-SPC recordings. This study indicates that the breakdown and development of the MDs is dependent on their inception phase, which is related to the discharge activity in preceding (anodic pin) half-cycles. It is shown that the MDs appearing at lower applied voltages are ignited with a positive streamer starting near the anode (dielectric), similar to single dielectric barrier discharge MDs. On the other hand, the inception of the MDs appearing at higher applied voltages takes place with a double-streamer mechanism starting near the tip of the cathode (pin). These MDs have similarities to transient sparks, in particular much higher current pulse amplitudes compared to single DBDs.

A 0.034% Charge-Imbalanced Neural Stimulation Front-End (SFE) IC With on-Chip Voltage Compliance Monitoring Circuit and Analysis on Resting Potential by Utilizing the SFE IC

The proposed SFE IC adopts an eight-channel H-bridge structure with an integrated voltage compliance monitoring circuit. It has stimulation current ranged from 0.78mA to 6.2mA selected by 3b control and the stimulation current level can be controlled with 7b resolution within a selected current range. The current range can be expanded by using a high current option ranged from 2.71mA to 21.7mA under 3b control. The worst DNL and INL of the stimulation current source are 0.32 LSB and 0.3 LSB, respectively, from all the current ranges. The average mismatch between the cathodic and anodic current pulses in a biphasic stimulus is measured as 0.034% without using charge balancing techniques. The voltage compliance monitoring circuit is based on triode detection of a sensing MOSFET and it shows the detection accuracy of 45mV from its measurement results. The maximum steady-state voltage across the electrodes/ solution interface (resting potential) is also rigorously analyzed and verified through bench-top and saline experiments by utilizing the proposed stimulator. The SFE IC was fabricated in $0.18~\mu \text{m}$ 24 V CMOS process.

Optimal Electric Stimulus Amplitude Improves the Selectivity Between Responses of ON Versus OFF Types of Retinal Ganglion Cells.

Outer retinal degenerative diseases destroy photoreceptors primarily in the retina, resulting in a profound vision loss. Fortunately, surviving retinal neurons can be electrically stimulated using retinal prostheses to re-transmit visual information. Although retinal prostheses are promising for sight restoration, the best performance is still sub-optimal. For the enhanced performance, it is critical to optimize stimulation parameters. This study explored how stimulus charge and current amplitude alters responses of retinal ganglion cells (RGCs). From the isolated mouse retina, spiking activities of alpha ON, OFF sustained, and OFF transient RGCs were recorded in response to epiretinally-delivered cathodal current pulses ranging from -10 to [Formula: see text]. We have found that intermediate current amplitudes (-30 and [Formula: see text]) maximize the response ratio of ON over OFF types. Also, the ON/OFF response ratio was always bigger for 10-ms-long than 5-ms-long stimuli. It was because, by the longer pulses, ON RGC responses were always significantly enhanced ( ) while OFF RGC responses were minimally changed ( ). Given the earlier work reporting electrically-elicited responses are more natural in ON than OFF RGCs, the present study suggests effect strategies of more selective activation of ON RGCs for improved efficacy of retinal implant.

Non-rectangular waveforms are more charge-efficient than rectangular one in eliciting network-mediated responses of ON type retinal ganglion cells

Objective. For individuals blinded by outer retinal degenerative diseases, retinal prostheses would be a promising option to restore sight. Unfortunately, however, the best performance of existing devices is still far removed from normal vision. One possible reason for the shortcoming is thought to be suboptimal stimulation conditions such as the waveform shape of electric stimulus. In this study, we explored the effects of varying waveforms on network-mediated responses arising in retinal ganglion cells (RGCs). Approach. We used a cell-attached patch clamp technique to record RGC spiking activities in the isolated mouse retina. ON alpha RGCs were targeted by soma size and their light responses to stationary spot flashes. Spiking in targeted RGCs was measured in response to an epiretinally-delivered cathodal current pulse in four waveforms: rectangular, center triangular, increasing and decreasing ramp shapes. Each waveform was tested at three durations (20, 10, and 5 ms) with adjusted amplitude for a range of total charges (50–400 nC). Main results. ON alpha RGCs always generated two bursts of spikes in responses to all stimuli conditions we tested. However, at a given charge, effects of differing waveforms were distinct in the two bursts. For the first burst, the increasing ramp was most effective among the four waveforms (p < 0.05 for all pairwise comparisons with other waveforms). For example, in responses arising from 20 ms-long stimuli, the increasing ramp evoked ~44% more spikes on average than the rectangular shape which is the typical choice of neural stimulation. Also, the rectangular stimulus evoked the weakest response in the delayed burst arising from pulses of every duration. For instance, 20 ms-long stimuli in the three non-rectangular waveforms showed ~23% or more increment in spike counts compared to response arising from the rectangular one; but there was no statistical difference in response magnitudes across the non-rectangular waveforms. Significance. Although the rectangular waveform has been primarily used in retinal prostheses our results indicate that rectangular stimulus is not optimal for network-mediated responses of ON alpha RGCs. Instead, non-rectangular waveforms evoke stronger responses at a given charge, indicating higher charge-efficiency. Therefore, non-rectangular waveforms are expected to enhance clinical efficacy of retinal prostheses.

Silver Electrodeposition on Nanocrystalline Graphite: Galvanostatic Control As a Tool in the Study Electrodes with High Resistance

Carbon based materials, such as glassy carbon or highly oriented pyrolytic carbon (HOPG), have been used extensively as working electrodes for electrodeposition. Due to their chemical inertness and electrochemical stability they are commonly used as substrates for electrodeposition studies. HOPG in particular has attracted great deal of attention due to its close relation to carbon nanotubes and graphene [1]. Miranda-Hernández et al. [2] investigated silver electrodeposition on HOPG, mechanically polished glassy carbon and fractured glassy carbon. Their results showed that the surface conditions, including morphology of the carbon substrate, have an effect on the overpotential required to start a 3D silver electrocrystallization. Additionally, their results led to the conclusion that the active sites do not depend on physical features on the electrode's surface and thus their nature must be electronic. In carbon materials, the shape and magnitude of the density of electronic states (DOS) distribution vary according to their structure [3]. Since the rate of heterogeneous electron transfer depends on the electrode’s DOS [4], it is expected that different carbon materials would exhibit different electrodeposition behaviors. Furthermore, simple electrodeposition systems could be used to characterize the properties of novel carbon materials. Recently, Cholula-Díaz et al. [5] used aerosol assisted chemical vapor deposition to synthesize nanocrystalline graphite (NCG) thin films. The low nanoscale roughness of this material may lead to some insight into the electrodeposition process. Additionally, their complex electronic behavior may lead to the observation of new phenomena. These samples were used as working electrodes for silver electrodeposition. A single compartment electrochemical cell was used, with Hg|HgSO4 and a Pt wire as reference and counter electrodes, respectively. The composition of the platting bath was: 10 mM AgNO3, 1 M KNO3 and 1.6 M NH4OH [2]. Cyclic voltammetry experiments resulted in tilted voltammograms, which are typical of a high ohmic resistance. Since the platting bath had a high ionic concentration, this behavior is adscribed to the resistance of the NCG sample. The cell voltage U is equal to the sum of the double-layer potential φDL and the ohmnic drop. U= φDL + iR Hence, under potentistatic control, current changes result in variations of the ohmic term, to which the system responds by adjusting the double-layer potential to comply with the applied voltage value. This feedback loop between the double-layer potential and the current makes it difficult to establish a clear relationship between the experimental conditions and the characteristics of the deposited material. In contrast, galvanostatic control offers a far simpler scenario; since the current is fixed in the experiment, it is easier to determine the double-layer potential. Figure 1a shows the time evolution of the double-layer potential during controlled current experiments. The time scale on which the potential stabilizes is larger for the one observed for similar experiments on glassy carbon. This shows the importance of galvanostatic control as means to study electrodeposition samples with high resistivity. Figure 1b shows an SEM image in which submicrometric silver particles can be identified. We explore the dependence between the current pulses applied and the resulting particle size distributions. References R. Unwin, Faraday Discuss., 172, 521 (2014)Miranda-Hernández, I. González, and N. Batina, J. Phys. Chem. B, 105, 4214 (2001).Richard L. McCreery, Chem. Rev., 108, 2646 (2008)J. Royea, T. W. Hamann, B. S. Brunschwig, N. S. J. Lewis, Phys. Chem. B, 110, 19433 (2006).L. Cholula-Díaz, J. Barzola-Quiquia, H. Krautscheid, U. Teschner, P. Esquinazi, Carbon, 67, 10 (2014). Figure 1. a) Time dependence of nanocrystalline graphite electrode potential after applying cathodic current pulses from −50 to −325 µA in 10 mM AgNO3 + 1 M KNO3 + 1.6 M NH4OH electrolyte. b) SEM image (BS detector) of the surface of the nanocrystalline graphite showing particles of silver deposit. Figure 1

Current pulse based ion-selective electrodes for chronopotentiometric determination of calcium in seawater

Calcium is closely related to the oceanic biosphere and carbonate system. Potentiometry based on a calcium-selective electrode (Ca-ISE) represents a promising tool for detection of calcium ion activities in seawater. This technique, however, generally is limited by the low sensitivity for the inherent Nernstian response (i.e. ca 30 mV/dec). A current pulse based ion-selective electrode with enhanced sensitivity for chronopotentiometric measurements of calcium in seawater is proposed. The Ca2+-selective membrane containing lipophilic salt ETH 500 instead of traditional ion-exchanger is galvanostatically controlled. An applied constant cathodic current pulse can leads to the extraction of the calcium ions into the membrane to produce a chronopotential response, which shows a stable and reproducible super-Nernstian response in a narrow calcium activity range. The super-Nernstian region of the electrode depends on not only the the magnitude and duration of the applied current pulse but also the interfering ions. Under optimal conditions, the proposed Ca-ISE exhibits a super-Nernstian response between the calcium concentrations of 10−2.5–10−1.5 M with a slope of ca 80 mV/dec. The current pulse based Ca-ISE has been applied to determination of calcium in seawater with satisfactory results.

Experimental Research on Electroforming Nano-ZrO2 Reinforced Cu-Matrix Composite Aided by Pulse Power

Prepared the nanoZrO2 reinforced Cu-matrix composite by pulse electroforming. The effects of the content of nanoZrO2 particle in the casting solution, average cathodic current density, duty cycle, pulse frequency and ultrasonic power on the content of nanoZrO2 in the electroforming Cu-matrix composite have been studied. The microhardness and surface morphology of Cu-ZrO2 composite were analyzed. The experimental results demonstrate that the maximum content of nanoZrO2 in the electroforming Cu-ZrO2 composite is 2.94%, microhardness is 492 HV, which is significantly improved compared with pulse pure copper’s 337 HV, when the content of nanoZrO2 is 40 g/L, average cathodic current density is 4A/dm2, duty cycle is 0.2 , pulse frequency is 1100 Hz and ultrasonic power is 20w .The surface of composite prepared by pulse electroforming is more smooth, organization is denser, grain is finer and agglomeration of nanoZrO2 particles is fewer compared with Direct-current electroforming nanoZrO2 reinforced Cu-ZrO2 composite.

Redox fusion of metal particles using deep eutectic solvents.

Alternating anodic and cathodic current pulses have been applied to a metal powder on an electrode surface to fuse the particles together. It is shown that homogeneous films can be electroformed with different morphologies depending on the size of the powder and the experimental conditions.

The advantage of topographic prominence-adopted filter for the detection of short-latency spikes of retinal ganglion cells.

Electrical stimulation through retinal prosthesis elicits both short and long-latency retinal ganglion cell (RGC) spikes. Because the short-latency RGC spike is usually obscured by electrical stimulus artifact, it is very important to isolate spike from stimulus artifact. Previously, we showed that topographic prominence (TP) discriminator based algorithm is valid and useful for artifact subtraction. In this study, we compared the performance of forward backward (FB) filter only vs. TP-adopted FB filter for artifact subtraction. From the extracted retinae of rd1 mice, we recorded RGC spikes with 8×8 multielectrode array (MEA). The recorded signals were classified into four groups by distances between the stimulation and recording electrodes on MEA (200-400, 400-600, 600-800, 800-1000 µm). Fifty cathodic phase-1st biphasic current pulses (duration 500 µs, intensity 5, 10, 20, 30, 40, 50, 60 µA) were applied at every 1 sec. We compared false positive error and false negative error in FB filter and TP-adopted FB filter. By implementing TP-adopted FB filter, short-latency spike can be detected better regarding sensitivity and specificity for detecting spikes regardless of the strength of stimulus and the distance between stimulus and recording electrodes.

Processing-Microstructure Relationships in the Plasma Electrolytic Oxidation (PEO) Coating of a Magnesium Alloy

In the plasma electrolytic oxidation (PEO) coating of light metal alloys, changing the electrical parameters and electrolytic composition can change the discharge behaviour and, ultimately, the thickness, surface morphology and porosity of the coating. In the present study a combination of cathodic and anodic current pulses with suitable Ton and Toff periods were used to control the porosity and other structural defects of PEO coatings of an AM60B magnesium alloy. In order to investigate the effect of a current mode on the plasma discharge behaviour and coating microstructure during the PEO treatment of magnesium alloy, the emission intensities of six different spectral lines from the plasma species were recorded simultaneously as a function of both time and current mode using optical emission spectroscopy (OES) system. The fluctuations in signal intensities and temperature during the coating process reflect differences in location of both the discharge initiation, and discharge type. The coating surface morphology and microstructure that are obtained can be linked to the plasma discharge behavior. These results are discussed in relation to the discharge behaviour, and how such changes in discharge behaviour relate to the coating mechanisms.

Effects of prior cathodic polarization on crystallographic pit initiation on aluminum

The growth behavior of crystallographic pits on aluminum is examined during galvanostatic anodic etching with consideration of the effect of prior cathodic polarization. Pit density and size distribution are measured by using scanning electron microscope. The results show that prior cathodic polarization enhances pit nucleation greatly and the pit number density can be increased by 11 times with a cathodic current pulse of 100mAcm−2, 200ms. Cathodic polarization leads to passivation of a substantial number of small pits, which alters the pit size distribution. The amount of cathodic charge is a main determinant of the effects.

Development and evaluation of thin-film flexible microelectrode arrays for retinal stimulation and recording

We have described the development of a flexible microelectrode array with potential applications in the large scale recording of neural signals and in focal electrical stimulation for use as a prosthetic implant in degenerative retinal diseases. The array under test consisted of 61 platinum electrodes of 5 µm diameter with 60 µm spacing connected by 8 µm wide gold tracks encased in a flexible polyimide substrate of 15 µm thickness from which recordings were taken from 16 electrodes. The device was tested on an exposed frog eyecup preparation which is characterized by small retinal ganglion cells of similar dimensions to those present in the human retina. The responses of these cells evoked by photic stimulation consisted of trains of action potentials of high signal-to noise ratio at each of the recording sites. Delivery of cathodal constant voltage pulses and constant current pulses to specific electrodes in the array led to the generation of action potentials in adjacent electrodes, implying that retinal ganglion cells in the proximity had been stimulated. Since prolonged stimulation with supra-threshold voltages impaired neither electrode structure nor retinal function, these results provide a sound basis for scaling up the number of array electrodes to deliver focal electrical pulses to the retina, as would be required by a viable epiretinal prosthesis.

Electrical stimulation of retinal neurons in epiretinal and subretinal configuration using a multicapacitor array

Electrical stimulation of retinal neurons offers the possibility of partial restoration of visual function. Challenges in neuroprosthetic applications are the long-term stability of the metal-based devices and the physiological activation of retinal circuitry. In this study, we demonstrate electrical stimulation of different classes of retinal neurons with a multicapacitor array. The array--insulated by an inert oxide--allows for safe stimulation with monophasic anodal or cathodal current pulses of low amplitude. Ex vivo rabbit retinas were interfaced in either epiretinal or subretinal configuration to the multicapacitor array. The evoked activity was recorded from ganglion cells that respond to light increments by an extracellular tungsten electrode. First, a monophasic epiretinal cathodal or a subretinal anodal current pulse evokes a complex burst of action potentials in ganglion cells. The first action potential occurs within 1 ms and is attributed to direct stimulation. Within the next milliseconds additional spikes are evoked through bipolar cell or photoreceptor depolarization, as confirmed by pharmacological blockers. Second, monophasic epiretinal anodal or subretinal cathodal currents elicit spikes in ganglion cells by hyperpolarization of photoreceptor terminals. These stimuli mimic the photoreceptor response to light increments. Third, the stimulation symmetry between current polarities (anodal/cathodal) and retina-array configuration (epi/sub) is confirmed in an experiment in which stimuli presented at different positions reveal the center-surround organization of the ganglion cell. A simple biophysical model that relies on voltage changes of cell terminals in the transretinal electric field above the stimulation capacitor explains our results. This study provides a comprehensive guide for efficient stimulation of different retinal neuronal classes with low-amplitude capacitive currents.

Frequency dependent effect of selective biphasic left vagus nerve stimulation on heart rate and arterial pressure

Activation of the parasympathetic pathway leads to negative chronotropic, dromotropic, and inotropic changes of heart function. The ability to selectively stimulate certain superficial compartments of peripheral nerves has been demonstrated previously. The aim of the present study was to find a clinically acceptable selective biphasic vagus nerve stimulation technique, which could allow gradual regulation of heart rate and systemic arterial pressure. In two patients, the left vagus nerve was stimulated with a combination of quasi-trapezoidal cathodic and rectangular anodic current pulses with different stimulation frequencies (10Hz, 20Hz, 30Hz) and increasing current. The heart rate and systemic arterial pressure decreased with increasing current at all different stimulation frequencies (p<0.05). The heart rate and arterial pressure response was more gradual with 10Hz compared to 20Hz/30Hz vagus nerve stimulation (p<0.05). In conclusion, selective vagus nerve stimulation, with a combination of quasi-trapezoidal cathodic and rectangular anodic current pulses at 10Hz, offers gradual heart rate and systolic arterial pressure control.

Metamaterials based on polymer dispersions of nanoparticles and particles of copper obtained by cathodic current pulse electrolysis

In the present paper a novel group of electromagnetic metamaterials as well as the method of their fabrication is presented. The studied metamaterials are polymer composites and nanocomposites made of polymer matrix/host (ethylene-vinyl acetate (EVA), polyethylene, polypropylene etc.) filled with copper flakes, of micrometer and/or nanometer size, as the conducting inclusions. The copper filler flakes were obtained by cathodic current pulse electrolysis from copper sulfate electrolytes at the stainless steel electrodes. SEM analysis showed that the morphology and structure of the copper deposit can be precisely controlled by applying different kind of current pulse and reversed current pulsed electrolysis. The polymer composite metamaterials formed by extrusion of small beads of polymer mixed with the copper flakes consisted of polymer matrix and copper flakes, ranging in length from 1 to 500 micrometers, and ranging in thickness from 80 nm to 2000 nm. The concentration of the copper flakes ranged from 0.5 wt% to 40 wt%, depending on the applications and required electromagnetic and mechanical properties. The studied materials were found to exhibit effective magnetic permeability that was smaller than unity, which is indicative of the typical properties of metamaterials. Present development solves technological and economical problems related to modern microelectronics methods which are currently mainly used for metamaterial fabrication.