Abstract: An apparatus for producing orthohydrogen and/or parahydrogen. The apparatus includes a container holding water and at least one pair of closely-spaced electrodes arranged within the container and submerged in the water. A first power supply provides a particular first pulsed signal to the electrodes. A coil may also be arranged within the container and submerged in the water if the production of parahydrogen is also required. A second power supply provides a second pulsed signal to the coil through a switch to apply energy to the water. When the second power supply is disconnected from the coil by the to switch and only the electrodes receive a pulsed signal, then orthohydrogen can be produced. When the second power supply is connected to the coil and both the electrodes and coil receive pulsed signals, then the first and second pulsed signals can be controlled to produce parahydrogen.

Abstract: Disclosed is a method of surface-roughening an aluminum support comprising the step of electrolytically surface-roughening an aluminum support in an electrolyte solution, supplying an alternating current with an alternating waveform having a positive polarity period and a negative polarity period in one cycle, and comprising arriving at the largest current value from a zero current value in the positive polarity period of one cycle and then falling, followed by rising to a current maximum in one cycle, wherein the time t.sub.1, which is required to arrive at the largest current value, has the following relationships:1 millisecond<t.sub.1 .ltoreq.10 milliseconds, and1 millisecond<t.sub.1 .ltoreq.one third of the positive polarity period time.

Abstract: A method of killing microorganisms which form a biofilm on surfaces, including the surfaces of medical articles or on tissue or implant surfaces in a living subject. Killing of biofilm microorganisms is accomplished by applying an electric field to an electrically conductive medium in which the biofilm is contained. The electrically conductive medium either includes a biocide or is capable of generating a biocide in situ upon application of an electric field. A means of utilizing the method in vivo and a sterilizer are disclosed.

Abstract: Method of electrochemically machining an electrically conductive workpiece (2) in an electrolyte by applying bipolar electric pulses between the workpiece (2) and an electrically conductive electrode (6), one or more current pulses of normal polarity alternating with voltage pulses of opposite polarity. The amplitude (Un) of the voltage pulses is adjusted between two predetermined values (Un1, Un2) derived from the occurrence of a given surface quality of the workpiece (2) and the occurrence of wear of the electrode (6). The derivation is effected by means of at least one test which precedes the machining of the workpiece (2). During the test the amplitude (Un) of the voltage pulses is increased gradually from an initial value to a final value. The two predetermined values (Un1, Un2) are determined upon the occurrence of a sign reversal in the difference between successive values of a parameter which is representative of a property of a gap (5) between the electrode (6) and the workpiece (2).

Abstract: A computer system for controlling the parameters used during molecule transfer operations. The computer system includes a processor coupled to a memory. The memory stores instructions that are executed by the processor. The computer system controls the value of parameters that affect the characteristics of pulses delivered by a pulse generating circuit to a solution. The pulse generating unit delivers individual pulses during cycles. The cumulative pulse delivered during a specified number of cycles is a pulse output. The magnitude of a pulse output is determined by the number of cycles corresponding to the pulse output and the characteristics of the individual pulses delivered during the cycles. A pulse group is a series of pulse outputs. The computer system controls a molecule transfer operation by causing the pulse generation circuit to deliver one or more pulse groups to the solution. A user selects the shape and number of pulse groups to be delivered for an operation.

Abstract: Electrolytic cell apparatus and methods for generating a useful energy product from a plurality of energy sources. In a preferred embodiment, hydrogen gas is produced at a cathode by transmission of electrons through a low voltage potential barrier to electron flow achieved by careful control of electrolyte constituent concentrations and surface materials on the cathode. A portion of the energy captured in the hydrogen gas is provided by heat transmitting activity of ions dissociated from water at an anode which catalytically dissociates the water and thereby transfers thermal energy from the anode to the ions and other constituents of the cell electrolyte. Thermal energy is replaced in the anode by absorption of heat from the surrounding environment.

Abstract: A method and apparatus for plating metals which delivers a voltage pulse with the possibility of a widely varying current magnitude characteristic to a plating electrode and an object having a large electrical reactance in terms of a parallel resistance and capacitance in order to raise the voltage potential between the electrode and an object to a programmed plating voltage overpotential and underpotential. The programmed plating voltage overpotential determines how fast the electrochemical reaction is allowed to proceed in the diffusion layer, and the programmed voltage underpotential determines how quickly the electrochemical reaction of the diffusion layer will slow down.

Abstract: The present invention relates to a method of etching aluminum foil for electrolytic capacitors that is improved in etching efficiency, wherein when the aluminum foil is etched by applying alternating current in an electrolytic solution containing chloride ions and the like, the alternating current contains, during the positive half period and the negative half period, two half waves having different waveforms, amplitudes, and applied times, and a rest period between the half waves with the amplitude being 0 or with microcurrent being applied on the positive side or the negative side at at most 1/15 of the maximum amplitude during a half period.

Abstract: A method of monitoring ion mobility in an electro-conductive fluid, such as an electrolyte in a lead-acid battery to determine the state of charge of the battery, includes the steps of immersing a pair of test electrodes in the electro-conductive fluid, and generating a test signal having a pulsed waveform. The pulsed waveform of the test signal has a voltage which remains constant over a predetermined portion of the signal's period, that portion being selected to ensure that ion mobility in the electro-conductive fluid has reached a steady state velocity. The method further includes the steps of applying the test signal to the pair of test electrodes to cause a current to flow through the test electrodes and the electro-conductive fluid, and sensing the current flow through the test electrodes and fluid. The sensed current is indicative of ion mobility in the electro-conductive fluid.

Abstract: A process and apparatus for the application of a control variable having a fractal structure to a body or process. The process of the present invention comprises the steps of generating a control variable having a fractal structure and applying the control variable to a body or process reacting in accordance with the control variable. The process is applicable to electroforming where first, second and successive pulsed-currents are applied to cause the deposition of material onto a substrate, such that the first pulsed-current, the second pulsed-current, and successive pulsed currents form a fractal pulsed-current waveform.

Abstract: A pump for exerting a pumping force on a fluid in an attached conduit, the pump being actuated by a voltage from a power supply, the pump comprising a liquid metal pool, a containment vessel for confining the pool, an inner tubular member in hydraulic contact with the attached conduit and with an open end disposed in the pool to divide a free upper surface of the pool into an actuation surface and a working surface, an electrolyte in contact with the actuation surface, an electrode in contact with the electrolyte, and an electrode in contact with the pool, such that application of a voltage to the electrodes causes a surface tension change in the actuation surface and a resulting height change in the working surface, whereby a pumping action is transferred to the fluid in the attached conduit.

Abstract: Aluminum sheet is electrochemically roughened for use as a lithographic printing plate support or as capacitor foil. The alternating current used for electrochemical roughening is initially biased in a first way, e.g. anodically, and then in a second way, e.g. cathodically. Each biased current is sufficient at least to initiate formation of a pitting structure on the surface of the sheet. The method allows improved control over the pitting structure and more rapid electrograining of the sheet.

Abstract: The photoelectro-chemical etching system of compound semi-conductor is disclosed. The system comprises a laser generator, a shutter to cut off laser beam, a laser beam chopper, a secondary high reflection mirror, a beam expander, a waveform generator, a chopper controller, a potentiostat to apply the reverse or forward voltage to the optical glass cell. Instead of applying the reverse-bias voltage to a semiconductor material, the reverse and/or forward voltage with a uniform pulse period is applied so that homogeneous and damage-free surface is obtained and etching process is made available in a more efficient manner.

Abstract: In electrochemical machining of workpieces a predetermined product of current quantity and machining time (amp. seconds) is necessary to remove a given quantity of material from a workpiece edge. In order to minimize machining time it is proposed to divide the machining process into at least two machining periods, a first short one during which a relatively small working current is applied and a longer second one during which a much higher working current is set. Between both periods a discontinuous momentary steep current rise in the region of 100 percent to 1000 percent is effected. Due to this new method not only the total machining time is reduced but the current feed control becomes easier and test runs in many cases are unnecessary.

Abstract: Method of predicting a short circuit in an electrolytic finishing system where a machining pulse is supplied between an electrode and a work disposed in electrolyte with a predetermined space is disclosed. An abnormal change of electrode-to-electrode voltage during the supply of the machining pulse is detected, and the supply of the machining pulse is stopped in accordance with the detection.

Abstract: A mechanically roughened substrate is conveyed through an electrolytic bath and is given a superposed electrochemical roughening, which is carried out by means of electrodes which are arranged in the electrolytic bath at a specific spacing from the substrate. The electrodes are connected to corresponding windings on the secondary side of a three-phase transformer. The corresponding windings on the primary side of the three-phase transformer are connected to a three-phase frequency converter, to which three-phase current is applied via leads. The three-phase frequency converter transforms the line frequency of the three-phase current supplied into a frequency range of about 50 to 300 Hz at a voltage of between about 1 and 380 V.

Abstract: A method of electrolytically graining aluminium, aluminium alloy or aluminium laminate, desirably in a substantially uniform manner, in particular for use as a lithographic printing plate substrate, is disclosed wherein the graining is effected using a square wave alternating current.

Abstract: The invention relates to a method of electrolytically machining the surface of a workpiece by applying positive and negative electric current pulses alternately and repeatedly across the workpiece and a tooling electrode located oppositely in a neutral electrolyte so as to keep a predetermined gap therebetween, wherein the time interval from a negative pulse to a positive pulse is shorter than that from the positive pulse to the next positive pulse.

Abstract: A method of preparing a support for a lithographic printing plate which comprises roughing electrochemically the surface of an aluminum plate which is rendered an anode in an aqueous neutral salt solution by supplying pulse-formed electric potential. According to this method uniform deep pits can be obtained easily.

Abstract: The invention relates to the electrochemical dissolution of semiconductors by alternating application of anodic and cathodic direct currents to an electrode formed by contacting a semiconductor material with an electrolyte.

Abstract: A method for making a battery electrode includes roughening the surface of a substrate (10) that constitutes a precursor to the electrode, using an electrolytic solution (12) with electrical potential perturbations applied thereto. The substrate (10) of porous sintered nickel powder is first formed. The electrolytic solution (12) prefereably contains the pure metal that forms the electrode. Then all gases in and around the substrate (10) are preferably removed. Next, the substrate (10) is placed in the solution (12) for a predetermined amount of time. Potential perturbations are then applied to the substrate (10) and the solution (12). The potential peturbations vary between the voltages necessary for electrodissolution and electrodepositon of the substrate (10), and thus, cause the surface of the substrate (10) to be roughened as portions of the substrate (10) are dissolved into the solution (12) and then redeposited onto the substrate's (10) surface.

Abstract: A diamond film of the vapor phase process is produced by a method which comprises a step of (1) electrolytically polishing the surface of a hard metal substrate with a pulse voltage or, after electrolytic polishing, further subjecting it to a scratching treatment with an abrasive powder or (2) electrolytically polishing the surface of a hard metal substrate with a constant voltage and thereafter subjecting it to a scratching treatment with an abrasive powder, thereby heightening the adhesive force of the surface of the substrate, and then effecting deposition of dense diamond of high adhesive strength by the vapor phase process on the substrate.

Abstract: An improved process for recovering tellurium from copper electrolysis slime. The process comprises leaching copper and tellurium from said slime with sulfuric acid and recovering tellurium from the solution after leaching (called "leach") by suspending at least one copper electrode plate in a bath of a leach, allowing tellurium to deposit on the surface thereof as copper telluride, agitating the bath as required so as to remove the copper telluride formed on the surface of the copper plates and allow it to settle, collecting the copper telluride precipitate and obtaining tellurium by means known per se. A high grade copper tellurium precipitate is obtained.

Abstract: A process for the production of a composition modulated alloy having a predetermined concentration is disclosed, in which alternating layers of at least two metals are successively deposited upon a substrate by electrodeposition, vacuum deposition, vapor deposition, or sputtering. The individual thicknesses of at least one metal's layers are varied in a predetermined manner. Pulsed galvanostatic electrodeposition using a tailored waveform is preferred. A copper-nickel concentration graded alloy is disclosed. Concentration graded alloys of predetermined concentration having at least one region of local homogeneity are also disclosed. The region of local homogeneity has a thickness corresponding to the thickness of two adjacent layers of different metals which have been diffusion annealed together. A pulsed electrodeposition/diffusion anneal process for production of such alloys is also disclosed.

Abstract: Cells are disclosed using doped electroconductive polymer electrodes and electrolytes of alkali metal cations and soft anions in polar organic solvents. The structure of the negative electrodes comprises layers of electroconductive polymers and ion exchange resin. Conditioning the negative electrodes is effected with AC current, the energy of the negative pulses exceeding that of the positive pulses.

Abstract: A method for electrochemical machining a work piece using an electrochemical machining device including a tool electrode opposing the workpiece across a predetermined machining gap and a device for supplying a pulse current to the machining gap via electrolyte provided in the machining gap includes the steps of determining a predetermined pulse current having a predetermined pulse width, selecting a plurality of partial pulse currents each having a predetermined partial pulse period, calculating a plurality of rest periods based on said partial pulse widths and applying the partial pulse currents, each of the partial pulse periods separated by at least one of the rest periods. According to the method of the present invention, the predetermined pulse width is in the range of about 10-50 msec.

Abstract: For the electrophoretic separation of a dispersed phase or contaminant (solid, liquid, or gaseous) from a continuous liquid phase under conditions of intrinsic ionic conductivity due to intrinsic bipolar ions in the continuous phase, especially for conductivities of the continuous liquid phase in excess of about 10.sup.-8 (.OMEGA..m).sup.-1 for which known electrofiltration processes are relatively ineffective or unworkable, a voltage is applied to the dispersed phase-containing liquid phase. The dispersed phase has a field-dependent mobility, and the applied voltage is such as to establish, within the liquid to be treated, a periodic asymmetric electric field E(t), conveniently comprising alternate positive and negative rectangular pulses, having the properties that the time-averaged amplitude of E(t) over one complete period, T, is zero but the average amplitude of each positive feature of the periodic waveform is unequal to that of each negative feature.

Abstract: A mechanically roughened substrate is conveyed through an electrolytic bath and is given a superposed electrochemical roughening, which is carried out by means of electrodes which are arranged in the electrolytic bath at a specific spacing from the substrate. The electrodes are connected to corresponding windings on the secondary side of a three-phase transformer. The corresponding windings on the primary side of the three-phase transformer are connected to a three-phase frequency converter, to which three-phase current is applied via leads. The three-phase frequency converter transforms the line frequency of the three-phase current supplied into a frequency range of about 50 to 300 Hz at a voltage of between about 1 and 380 V.

Abstract: A process for producing support for aluminum printing-plate in which an aluminum support is electrochemically surface-roughed uses an alternating current in an acid electrolyte containing nitric acid. The alternating current has a waveform in which the frequency is within a range of 60 to 140 Hz and the ratio of an anode time t.sub.F to a period T, that is, t.sub.F /T, is within a range of 0.33 to 0.15, and this current is used as an electrolytic power source.

Abstract: In order to perform the electrochemical roughening of the surface of preferably strip-like metal substrate for the production of printing plates or the like so that the surface is free of smuts and stripes with an even distribution of the roughness, there is a roughening station with three zones and in each zone the current density, the frequency, the temperature of the electrolyte, the type of electrolyte and the residence time may be individually set. Accordingly in the first zone it is possible to use a higher frequency and a higher current density than in the second zone in order to produce a large number of points of attack. In the second zone a longer residence time serves to enlarge the points of attack which have already been formed. In the third zone a particularly high frequency may be used to remove smuts.

Abstract: A method for electroplating a layer of a precious metal, copper or aluminum on a surface of a semiconductor device, an integrated circuit, or the like employs an electrolytic cell in which the cathode comprises a semiconductor device, an integrated circuit device, or the like, having a surface for receiving the precious metal layer. The surface is oriented in a position normal to a vector representing the acceleration of gravity and facing the anode of the cell. An electroplating direct current on the order of about 0.1 milliamp/cm.sup.2 is employed while superimposing a time varying electromagnetic field in the range of about 1 to about 100 megahertz on the direct current. The electroplating current and the electromagnetic field are employed in the absence of convection, i.e. stirring, in the electrolyte. The product produced by the described method comprises a smooth, evenly distributed layer of the precious metal having a microstructure that is characteristic of single crystals.

Abstract: A method of electropolishing and grinding the both surfaces of a circular workpiece comprises polishing and grinding the both surfaces of a circular workpiece with a pair of grindingstones which are so arranged as to oppose the polishing/grinding surfaces, the body material of the polishing/grinding surface of the grindingstones being composed of an electric conductive material wherein the grindingstones are connected to the positive pole of a power source and an electrode located in the vicinity of the grindingstones is connected to the negative pole, and a voltage is applied across the positive and negative poles, whereby a dressing operation to the polishing/grinding surfaces is conducted by the electrolysis of the pair of grindingstones during the polishing and grinding operation.

Abstract: The invention consists of a process for pulse electroplating electroactive polymer substrates at potentials sufficient to cause reduction of the substrates. The inventive process can be used to make polymer-metal composites having one or more metal films. More specifically, it can be used to electroplate polyimide substrates with gold, or to electroplate gold over a copper plated polyimide substrate. These inventive composites exhibit improved polymer-metal adhesion when they are exposed to elevated temperatures and humidities, i.e., 85.degree. C. and 85% R.H.

Abstract: A process and circuitry for the electrolytic coloring of an anodized article of aluminum or aluminum alloy in a coloring bath containing at least one metal salt for coloring the article. The process comprises applying to the coloring bath a controllable, asymmetrical and substantially sinusoidal a.c. voltage of substantially constant frequency. The sinusoidal a.c. voltage is obtained from a voltage source supplying a symmetrical sinusoidal a.c. voltage and at least one of the two current paths is divided into two parallel main lines and fed to electrical components whereby the amplitude level of the positive half wave and the amplitude level of the negative half wave and the ratio of the amplitude level of the positive half wave to the amplitude level of the negative half wave of the a.c.

Abstract: The production of uniformly blackened nickel deposits for decorative or functional purposes can be achieved by depositing nickel from an electroless nickel plate composition or electrolytically followed by forming a conversion coating on the electroless nickel deposit in a chromate bath which includes nitrate ions.

Abstract: A method and apparatus for electro-chemical machining involve: supplying a pulse having a predetermined current density between an electrode and an object to be worked while they face each other with a static electrolyte therebetween; detecting the current of the pulse supplied between the electrode and the object to be worked; comparing the detected current with a reference current set in accordance with factors such as properties of the object to be worked, and increasing the current density of the pulse on the basis of the result of the comparison; supplying pulses having the increased current density between the electrode and the object to be worked a predetermined number of times; and removing electrolytic products generated between the electrode and the object to be worked.

Abstract: A method of grinding includes the application to an abrasive wheel in a grinding zone of a pulse voltage, arranged out of the grinding zone is an electrode to which is applied a rectified voltage having an amplitude and a ripple factor ensuring formation of an oxide film on a surface of the wheel, and use is made of a coolant having a conductivity from 2.multidot.10.sup.-3 to 2.multidot.10.sup.-2 ohm.sup.-1 cm.sup.-1.

Abstract: A two-step process and apparatus for the electrolytic coloring of anodized aluminum using an electrode and the anodized aluminum immersed in an electrolyte. First the aluminum is anodized to form an oxidized film on its surface and then a coloring step is performed. In the coloring step a modified sinusoidal voltage waveform is applied to the anodized aluminum and the electrode to color the oxidized film. Suitably gated thyristors in the secondary of a power supply may be used to provide the desired voltage waveform. The voltage waveform is generated with a leading edge rise time in the negative portion substantially longer than in the positive portion. The average negative voltage is greater than the average positive voltage to provide good throwing power, coloring speed, color uniformity and electrode dissolution, with tha capability to subtract color. Excellent throwing power with fair coloring speed is obtained if the average negative voltage substantially equals the average positive voltage.

Abstract: The present invention relates to a roughened printing plate support of aluminum or an alloy thereof, which shows equally distributed tubular depressions. Furthermore, a process for the production of the printing plate-support is disclosed, in which roughening is performed in an acidic electrolyte by means of a pulsed direct current. The invention also relates to arrangements which are suitable for carrying out the process.

Abstract: A finishing method employing electro-chemical process includes the steps of: supplying identical pulses between an electrode and a workpiece disposed opposite to each other in a stationary electrolyte with a predetermined gap therebetween; reducing the gap after the pulses have been supplied; thereafter enlarging the gap; and injecting electrolyte into the gap during the step of enlarging the gap.

Abstract: An electro-chemical machine supplies pulses to a spaced workpiece and electrode in a working tank through an electrolyte in order to finish the workpiece, while eliminating electrolytic products produced in a gap between the workpiece and electrode by supplying clean electrolyte to the gap. This machine includes: an electrolyte filtering apparatus for removing dirty electrolyte containing electrolytic products from the working tank and filtering it; an electrolyte supplying apparatus for intermittently supplying the filtered electrolyte to the gap through a supply hole formed in the electrode; and a power supply apparatus for supplying the pulses to the workpiece and electrode when the flow of electrolyte to the gap stops. Clean electrolyte can be supplied to the gap almost simultaneously with the removal of dirty electrolyte, and then the finishing work is started. A glossy mirror surface on the workpiece can be automatically obtained by repeating those operations.

Abstract: An electrode is positioned to form a predetermined gap between the electrode and a surface of a work, and the electrode and the work are submerged in an electrolyte. Pulses are applied to the electrode to machine the work. The electric energy of the pulse is set in such a manner that the electric energy per unit area is reduced with increase of the area.

Abstract: In the continuous electrodeposition of chromium metal and chromium oxide on metal surfaces the codeposition of chromium and its oxide, inert and insoluble, is obtained from the same bath and at high current density, by using a number of cycles of impressed cathodic current and defined ranges of electrolyte velocities in the deposition cell. In this manner a product is obtained wherein a specific quantitative relationship between chromium metal and chromium oxide ensures corrosion resistance superior to that obtainable in known products.

Abstract: A power supply system for an electrolytic processing apparatus which uses a discharge of pulses between a work and electrode including a discharge section having plural capacitors, rectifiers connected the capacitors so as to prevent reversing of current to the power source side, a plurality of discharge switches having an on-off function and connected to said capacitors, and a control section for turning the discharge switches on and off so as to control the discharge of charges from the capacitors to the work and electrode. A power supply section supplies a predetermined electric power for the capacitors, and a charging section selectively transfers power from the power supply section so as to charge the capacitors in a desired manner.

Abstract: A power supply system is provided for an electrolytic processing apparatus of the type which has an electrode positioned to oppose a work within an electrolyte and which processes and finishes the work by discharge of at least two modes of pulses of different current densities between the work and the electrode. The power supply system includes a plurality of capacitors capable of discharging charges so as to supply discharge pulses across the work and the electrode, a plurality of discharge swithches connected between the capacitors and the work and adapted to selectively cause the charges from the capacitors to be discharged; and a control section arrangement for selectively turning the discharge switches on and off in accordance with the current densities.

Abstract: An electrode is positioned with a predetermined gap between the electrode and a surface of a work in an electrolyte tank. Pulses are applied to the electrode. Electrolyte including residual products is discharged from the tank. Clean electrolyte is supplied to the electrolyte tank for next machining. After predetermined time, pulses for the next machining are applied to the electrode.

Abstract: A process for the fusion of second conductive element into the matrix of a first conductive element is provided in which the second element as a dissociable solution is placed in contact with the first conductive element and subjected to an interrupted electrical signal of a predetermined frequency. Solutions for carrying out the process are disclosed and products produced by the process.

Abstract: A method and a device for finishing the cut surface of a work which is cut from a metal blank by a wire cut discharge process. The work and the waste piece of the metal blank are positioned in the same condition as just after the process. Electrolyte is fed through a clearance between the work and the waste piece and, at the same time, current is caused to flow from the work to the remainder. This subjects the cut surface of the work to electrolytic treatment to thereby make it smooth while removing oxide films and degenerated surface layers therefrom.

Abstract: An electrode is positioned with a predetermined gap between the electrode and a surface of a work in an electrolyte tank. Pulses are intermittently applied to the electrode. Electrolyte including residual products is discharged from the tank. The discharged electrolyte is cleaned by a filtering device to produce clean electrolyte. The clean electrolyte is supplied to the electrolyte tank for next machining.

Abstract: A power supply in a system utilizing as a source of fuel a generator for separating hydrogen and oxygen gasses from natural water and having the capabilities to control the production of gasses by varying the amplitude of the voltage and/or the pulse repetition rate of the voltage pulses applied to a pair of plate exciters in a vessel of natural water, comprising a sequence of circuitry operative to limit the current of a d.c. potential to a minimum value relative to the magnitude of the voltage applied to the plate exciters. The circuits each function up to a given magnitude of voltage to inhibit and curtail the flow of electrons from the plate exciter having the negative voltage potential applied thereto. The first circuit operative from a first magnitude of voltage comprises converting the voltage potential applied to the plate exciters to a unipolar pulse voltage d.c. of a repetitive frequency. The next circuit varies the duty cycle of the unipolar pulse voltage d.c.