Generation Of Electrical Pulses Research Articles

Facilitated permeation of methyl viologen into chloroplasts in situ during electric pulse generation in excitable plant cell membranes

Generation of action potential (AP) in plasma membranes of characean algae has a strong impact on photoreactions occurring in chloroplasts. Under physiological conditions, AP suppresses electron transport in alkaline and acidic regions, although to a different extent; these changes are transient and reversible. In the presence of the artificial electron acceptor, methyl viologen (MV2+), AP-induced changes in electron transport in photosystem II become irreversible. Incubation of Chara corallina internodal cells with MV2+ has no effect on the chlorophyll P700 photooxidation kinetics in photosystem I reaction centers, suggesting that MV2+ is inaccessible for interactions with photosystem I, because its permeation into chloroplasts of a resting cell is hindered by membrane barriers. At the same time, AP generation in the presence of MV2+ is accompanied by irreversible modification of P700 photooxidation kinetics, as can be evidenced from differences in absorption changes at 810 and 870 nm (ΔA810 signals). These findings suggest that MV2+ permeation into chloroplasts in situ is facilitated during or after the AP generation. Similar to the ΔA810 signals, light-induced changes in membrane potential do not depend on the presence of MV2+ in the external medium until the first excitatory stimulus is applied. Electric photoresponses of the cell are irreversibly modified by AP generated in the presence of MV2+ at the expense of non-cyclic photosynthetic electron transport redirected to the MV2+ reduction. It is concluded that AP effects on chloroplast photosynthesis in situ are complex and involve permeability changes for MV2+ in membrane barriers of the “plasmalemma-chloroplast envelope” system.

A 30-kHz Monocycle Generator Using Linear Photoconductive Switches and a Microchip Laser

We have demonstrated that diode-pumped microchip laser technology can be well adapted for the generation of electrical kilovolt pulses. An ultra-compact system is presented. It delivers a smooth bipolar pulse of 2 ns, a peak-to-peak voltage of 1.3 kV, and a repetition rate of 30 kHz. The required optical energy to achieve a complete switching is as low as 10 muJ. Because of the linear switching regime, this generator still works after half a billion shots. No limitation in terms of life time is currently expected. Nevertheless, heating problems start to occur at a high repetition rate.

Simulation Studies for Nonlinear-Transmission-Line Based Ultrafast Rise Times and Waveform Shaping for Pulsed-Power Applications

The generation of high-voltage electrical pulses with very fast rise times is important for several pulsed-power applications. Although several techniques and devices have been used to generate ultrashort rise-time pulses, most suffer from problems relating to reliability, lifetime, and power-handling capacity. Here, the concept of using nonlinear transmission lines is used for attaining ultrashort rise times and pulse sharpening. Numerical simulations are carried out using barium strontium titanate as the dielectric system. The concept is based on using the nonlinear voltage-dependent capacitance of the granular material. The presence of internal grains increases the breakdown strength and also provides for a nonlinear voltage-dependent capacitance that depends on the internal grain size. The output characteristics of transmission lines based on such nonlinear material are simulated. Our results clearly demonstrated rise-time shortening. The results were in agreement with some published experimental data.

Full-Wave Analysis of Quasi-Steady Propagation along Transmission Lines Periodically Loaded with Resonant Tunneling Diodes

The full-wave characterization of wave propagation on a transmission line periodically loaded with resonant tunneling diodes (RTDs) is discussed for the generation of ultrashort electrical pulses. Once the input pulse crosses the peak voltage of loaded RTDs, the exponential wave is developed at voltages smaller than the peak voltage, and the ordinary sinusoidal one is coupled to it at voltages larger than the peak voltage. The wave number of this exponential wave must be much larger than those of the waves forming the input pulse, so that significant compression of the pulse width is achieved. After discussing the model of RTDs in the framework of finite-difference time-domain (FDTD) method, we demonstrate the pulse compression through FDTD calculations.

Experimental characterization of short-pulse generation using switch lines

We report the experimental observation of the generation of short electrical pulses in a switch line, which is a transmission line periodically loaded with electronic switches. Pulse-width compression was experimentally demonstrated in the test switch line, using discrete Esaki diodes as the switches.

Analogue summation of electrical spike trains in semiconductor nerve fibres

We fabricate and investigate electrical pulse propagation in modulation-doped semiconductor nerve fibres made of sub-micron pn wires. We report the analogue summation of electrical impulses at the junction of three or more fibres. These wires model the longitudinal conductivities of potassium and sodium ions inside and outside a nerve capillary as well as the transverse capacitance of the nerve membrane and the non-linear conductance of its ion channels. We demonstrate the summation and annihilation of electrical impulses at both 300 and 77 K, which forms the basis for making spike-timing neural networks. A comparison of experimental and theoretical parameters of pulse propagation at these two temperatures is presented. The successful implementation of artificial nerve fibres promises parallel computation devices and spiking neural networks.

Examination of machining parameters on surface roughness in EDM of tool steel

Abstract Electrical discharge machining (EDM) is one of the important non-traditional machining processes and it is widely accepted as a standard machining process in the manufacture of forming tools to produce molds and dies. Since its introduction to manufacturing industry in late 1940s, EDM became a well-known machining method. The method is based on removing material from a workpiece by means of a series of repeated electrical discharges, produced by electric pulse generators at short intervals, between an electrode (tool) and a part being machined in dielectric fluid medium. This paper is devoted to a study of the influences of EDM parameters on surface roughness for machining of 40CrMnNiMo864 tool steel (AISI P20) which is widely used in the production of plastic mold and die. The selected EDM parameters were pulsed current (8, 16 and 24 A), pulse time (2, 3, 4, 6, 12, 24, 48 and 100 μs) and pulse pause time (2 and 3 μs). It was observed that surface roughness of workpiece and electrode were influenced by pulsed current and pulse time, higher values of these parameters increased surface roughness. Lower current, lower pulse time and relatively higher pulse pause time produced a better surface finish.

High-Voltage Rectifier Diodes Used as Photoconductive Device for Microwave Pulse Generation

Generation of unipolar and bipolar pulses by using high- and medium-voltage silicon rectifier diodes is achieved. These components are provided by the French Atomic Energy Commission (CEA). Furthermore, these devices work in the linear mode of photoconducting switches. Generation of electrical unipolar pulses with an amplitude of 10.7 kV and a full-width at half-maximum of 300 ps by using only 1.2 mJ of optical power is demonstrated. This energy value is 10-100 times less than usually published during the past decades. Furthermore, the linear mode running of these devices permits to synchronize several generators with a precision as low as 2 ps. This low timing jitter is useful for bipolar generators in order to control their spectrum with high precision, i.e., bipolar pulses of 3 kV peak-to-peak have been generated with a cycle duration of 400 ps and an optical energy of 1 mJ

Parthenogenetic development of rabbit oocytes after electrical stimulation

The aim of this study was to determine the effect of electric pulses on the structural and functional condition of rabbit oocytes. The New Zealand White female rabbits at 3–5 months of age and at 3–4 kg body weight served as oocyte donors. Oocytes after flushing from the oviducts were placed between two electrodes in an electroporation chamber which was filled with a dielectric solution. Following a short incubation in B2 medium, oocytes were subjected to an electric pulse released by an electrical pulse generator. Oocytes were then incubated in 500 µl of B2 medium supplemented with 20% foetal calf serum (FCS) at 38°C in an atmosphere of 5% CO<sub>2 </sub>in air. Oocytes were cultured until the morula/blastocyst stage (approx. 72 h). The experiment was conducted using 430 oocytes obtained post mortem. In vitro cultured oocytes not subjected to an electric pulse were the control. Each group was subdivided into replications according to electric current intensity. The analysis of experimental variants shows that in the first variant all embryos developed to the morula stage but only 10% of them continued to develop to the blastocyst stage. In the second variant we observed that 5–10% of oocytes developed to the blastocyst stage after treatment with 2.0 and 2.5 kV/cm pulse but in the group of 1.0 kV/cm pulse 35% of oocytes developed only to the 2–12 b stage. In the third variant only 1 oocyte (5%) continued to develop to the blastocyst stage, but in the fourth variant oocyte development stopped at the morula stage. In the fifth variant, called an “extreme” one, oocytes stopped to develop at the stage of 2–12 b (about 25%) and the percentage of degenerated oocytes dramatically increased (about 60%).  

Pulse Compression by Quasi-Steady Propagation along Switch Lines

The characterization of wave propagation on a switch line, which means a transmission line periodically loaded with electronic switches such as diodes, is discussed for the generation of ultrashort electrical pulses. Once the input pulse crosses the threshold voltage of loaded shunt switches, the exponential wave is developed at the voltage range where the switch is on, and the ordinary sinusoidal wave is coupled to it at the voltage range where the switch is off. The wave number of this exponential wave has to be much larger than those of the waves forming the input pulse, so we expect a significant compression of the input pulse after its propagation along a switch line.

Generation of short electrical pulses based on bipolar transistorsny

Abstract. A system for the generation of short electrical pulses based on the minority carrier charge storage and the step recovery effect of bipolar transistors is presented. Electrical pulses of about 90 ps up to 800 ps duration are generated with a maximum amplitude of approximately 7V at 50Ω. The bipolar transistor is driven into saturation and the base-collector and base-emitter junctions become forward biased. The resulting fast switch-off edge of the transistor’s output signal is the basis for the pulse generation. The fast switching of the transistor occurs as a result of the minority carriers that have been injected and stored across the base-collector junction under forward bias conditions. If the saturated transistor is suddenly reverse biased the pn-junction will appear as a low impedance until the stored charge is depleted. Then the impedance will suddenly increase to its normal high value and the flow of current through the junction will turn to zero, abruptly. A differentiation of the output signal of the transistor results in two short pulses with opposite polarities. The differentiating circuit is implemented by a transmission line network, which mainly acts as a high pass filter. Both the transistor technology (pnp or npn) and the phase of the transfer function of the differentating circuit influence the polarity of the output pulses. The pulse duration depends on the transistor parameters as well as on the transfer function of the pulse shaping network. This way of generating short electrical pulses is a new alternative for conventional comb generators based on steprecovery diodes (SRD). Due to the three-terminal structure of the transistor the isolation problem between the input and the output signal of the transistor network is drastically simplified. Furthermore the transistor is an active element in contrast to a SRD, so that its current gain can be used to minimize the power of the driving signal.

Realization of Broadband Matched Filter Structures Based on Dual Networks

Abstract. This paper deals with the basic electrical properties of dual networks and with their application in broadband matched filter structures. Starting with the main characteristics and different realization methods of dual networks, a filter structure is presented, which is based on a combination of dual networks and which provides a broadband matched input and two decoupled output ports. This filter synthesis focuses on the design of high pass filters, which are suitable to be used as differentiating stages in electrical pulse generators as a part of the so-called pulse shaping network. In order to achieve a proper pulse shape and for the prevention of multiple reflections between the switching circuit and the differentiating network, a broadband matched filter is a basic requirement.

Electrodynamic analogue of detonation waves in a ferroelectric transmission line

The formation of electrodynamic shock waves in non-linear transmission lines is an experimentally demonstrated phenomenon. Theoretical treatment of such phenomena has so far been limited to device-specific models. In this paper, a general hyperbolic conservation law formalism has been developed to describe non-linear propagation of electrical pulses in arbitrary transmission lines. This enables the use of powerful mathematical methods developed in the context of hyperbolic systems of partial differential equations.This formalism is used to examine the possibility of an electrodynamic analogue of detonation wave in a ferroelectric transmission line. A poled ferroelectric material forming the dielectric of a transmission line not only acts as a non-linear medium with a voltage-dependent dielectric constant but also as a charge and energy storage element. An electric pulse greater than the coercive field injected into this transmission line would steepen during its propagation because of the non-linear, voltage-dependent propagation velocity and also depolarize the ferroelectric material as it travels, adding charge and energy to the wave and sustaining it in the face of losses in a manner reminiscent of detonation waves in a reactive energetic material.

Implantable technology for pain management

The conventional management of chronic pain can be unsatisfactory. Implantable technology allows electronic and mechanical devices to be used for neuromodulation at any site in the CNS. Neurochemical transmission in the dorsal horn of the spinal cord can be modulated by electrical stimulation or direct drug delivery. Systems available for stimulation include single or dual multipolar electrodes that can be implanted extradurally via a percutaneous route. Tunnelled subcutaneous connections can be made to an implanted electrical pulse generator capable of multifunction stimulation with a transcutaneous reprogramming facility. Stimulation is useful for chronic mixed spinal and neuropathic pain, refractory angina and peripheral vascular disease. Using a similar technique, an intraspinal catheter can be sited to deliver a drug. It is connected to an implanted electromechanical pump that can be programmed transcutaneously to deliver combinations of drug and dose regimens, allowing reductions in dose requirements and more accurate neuromodulation. This system is particularly useful in palliative care.

High-power ultra-wideband electrical-pulse generation using a doped silicon photoconductive switch

By using photoconductive semiconductor switches in the linear mode, we achieve generation of electrical pulses of duration between 43 and 300 ps with a peak voltage between 150 and 10700 V. Moreover, these generators can be synchronised with a precision lower than 5 ps and they need only 1.2 mJ of optical energy. © 2005 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 121–125, 2006; Published online in Wiley InterScience www.interscience.wiley.com). DOI 10.1002/mop.21282

Feedback control of Hodgkin–Huxley nerve cell dynamics

Nerve cells communicate by generation and transmission of short electrical pulses (action potentials). A cascaded feedback control scheme consisting of an optimal controller (model predictive control, MPC) and a state feedback controller to control the time-courses of the biophysical state variables underlying action potential generation was developed and evaluated in simulations. The control scheme was shown to provide new means for action potential generation, suppression of oscillations and blockage of action potential transmission. These new theoretical developments could represent a starting point for the design of new closed-loop electrical stimulation systems for patients suffering from different nerve system dysfunctions.

Subpicosecond Faraday effect in Cd1−xMnxTe and its application in magneto-optical sampling

We present our studies on a subpicosecond Faraday effect in diluted magnetic semiconducting Cd1−xMnxTe single crystals and its application in a magneto-optical (MO) sampling system for time-resolved detection of ultrafast current pulses. The measurements were performed at 10 K. We used the Cd0.38Mn0.62Te crystal as the active MO medium and a low-temperature-grown free-standing GaAs photoconductive switch integrated into a coplanar transmission line as the picosecond electrical pulse generator. We observed subpicosecond MO transients that correspond to the intrinsic MO low-temperature response in the Cd1−xMnxTe system with the high Mn concentration. The current sensitivity of our MO system was found to be ∼0.1mA. We have demonstrated that the MO sampling technique using the Cd0.38Mn0.62Te transducer is as fast as the standard LiTaO3, electro-optical sampling technique and allows for a complementary (magnetic-field component) characterization of electrical picosecond transients in ultrafast switching devices. Observation of the subpicosecond Faraday effect in Cd1−xMnxTe crystals makes them very attractive for ultrafast optical modulators.

Generation of short electrical pulses and millimeter wave oscillations on a resonant tunnel diode nonlinear transmission line

Abstract Nonlinear wave propagation effects on a resonant tunnel diode nonlinear transmission line are considered. It is shown by computer experiments that this line can be used for short electrical pulses generation as pairs kink–antikink structures, as well as millimeter wave oscillator.

Project ‘Baikal’ – testing the scheme for electric pulse generation

The scheme of a multi-objective installation ‘Baikal’, a multi-megajoule source of X-ray emission with a temperature of 250–300 eV and a power of 500–1000 TW, is described in this article. The Project of the ‘Baikal’ installation is based on an inductive energy store, which in the process of step-by-step energy transmission with increasing power generates an electric pulse with parameters required for compression of liners. Electric parameters of the ‘Baikal’ installation are: current −50 MA, voltage 8–10 MV, pulse duration −150 ns, pulse energy 30 MJ. An installation ‘MOL’ is intended for testing the scheme of one of ‘Baikal’ modules. It consists of an inductive store IN-1 with accumulated energy of 12,5 MJ, capacitor banks, a magnetic amplifier, a magnetic compressor with a capacitor bank for generation of initial magnetic flow, a plasma opening switch (POS) and a load simulator.

Photoconductive generation of short electrical pulses of variable duration using a coplanar waveguide with capacitively coupled ground termination

Short electrical pulses with variable duration are generated by optically exciting a coplanar waveguide that is capacitively connected to a ground termination. The underlying concept is based on the superposition of the original pulse and the reflected one with an opposite sign and a variable round trip delay. By sliding the pump beam along the coplanar waveguide, generation of short electrical pulses with different peak voltages, widths, and signs are demonstrated in a laser-diode-based system.