Direct Current Block Research Articles

A 0.01–50 GHz power detector with temperature compensation and wideband DC‐blocking capacitor

AbstractThis letter presents a 0.01–50‐GHz resistive matching power detector implemented in a commercial 0.15‐ GaAs pseudomorphic high electron mobility transistor technology. An analytical expression is derived for the voltage responsivity of the detector as a function of temperature. To compensate for the temperature dependence of the detector, bias diode topology and mesa resistor load are employed. For an input power of −20 dBm at 1 GHz, the maximum variation of the detector output voltage is less than 0.5 dB over the temperature from C to C. The detector's S11 is less than −8 dB, the dynamic range (DR) is 55 dB, and the maximum voltage responsivity is 700 V/W. An on‐chip wideband capacitor with a bent‐strip shape is designed for direct current blocking. The detector can be used for wideband power monitoring and power amplifier control loop for its high DR and temperature stability.

Detection of ion cyclotron emission by using an ion cyclotron range of frequency antennas-based diagnostic system in experimental advanced superconducting tokamak

In the experimental advanced superconducting tokamak (EAST), a novel ion cyclotron range of frequency (ICRF) antenna-based diagnostic system is designed to measure ion cyclotron emission (ICE) driven by high-energy ions. The diagnostic system includes ICRF antenna straps, a three-tune impedance matching system, a coaxial switching system, a direct current block, and a data acquisition and storage system. Using the coaxial switching system, the ICRF antenna can be switched from the heating mode to the coupling mode between two discharges. In the 2023 EAST experiment campaign, core ICE was observed using the ICRF antenna-based diagnostic system during neutron beam injection heating, and the obtained results agreed well with the signal detected by the previous high-frequency B-dot probe-based diagnostic system.

Model Analysis of Post-Stimulation Block of a Myelinated Axon by Direct Current.

To determine the role of ion concentrations and ion pump activity in conduction block of myelinated axon induced by a long-duration direct current (DC). A new axonal conduction model for myelinated axons based on the classical Frankenhaeuser-Huxley (FH) equations is developed that includes ion pump activity and allows the intracellular and extracellular Na+ and K+ concentrations to change with axonal activity. Action potential generation, propagation, and acute DC block occurring within a short period (milliseconds) that do not significantly change the ion concentrations or trigger ion pump activity are successfully simulated by the new model in a similar way as the classical FH model. Different from the classical model, the new model also successfully simulates the post-stimulation block phenomenon, i.e., the axonal conduction block occurring after terminating a long-duration (30 seconds) DC stimulation as observed recently in animal studies. The model reveals a significant K+ accumulation outside the axonal node as the possible mechanism underlying the post-DC block that is slowly reversed by ion pump activity during the post-stimulation period. Changes in ion concentrations and ion pump activity play an important role in post-stimulation block induced by long-duration DC stimulation. Long-duration stimulation is used clinically for many neuromodulation therapies, but the effects on axonal conduction/block are poorly understood. This new model will be useful for better understanding of the mechanisms underlying long-duration stimulation that changes ion concentrations and triggers ion pump activity.

Effects on heart rate from direct current block of the stimulated rat vagus nerve

Objective. Although electrical vagus nerve stimulation has been shown to augment parasympathetic control of the heart, the effects of electrical conduction block have been less rigorously characterized. Previous experiments have demonstrated that direct current (DC) nerve block can be applied safely and effectively in the autonomic system, but additional information about the system dynamics need to be characterized to successfully deploy DC nerve block to clinical practice. Approach. The dynamics of the heart rate (HR) from DC nerve block of the vagus nerve were measured by stimulating the vagus nerve to lower the HR, and then applying DC block to restore normal rate. DC block achieved rapid, complete block, as well as partial block at lower amplitudes. Main Results. Complete block was also achieved using lower amplitudes, but with a slower induction time. The time for DC to induce complete block was significantly predicted by the amplitude; specifically, the amplitude expressed as a percentage of the current required for a rapid, 60 s induction time. Recovery times after the cessation of DC block could occur both instantly, and after a significant delay. Both blocking duration and injected charge were significant in predicting the delay in recovery to normal conduction. Significance. While these data show that broad features such as induction and recovery can be described well by the DC parameters, more precise features of the HR, such as the exact path of the induction and recoveries, are still undefined. These findings show promise for control of the cardiac autonomic nervous system, with potential to expand to the sympathetic inputs as well.

Combining direct current and kilohertz frequency alternating current to mitigate onset activity during electrical nerve block

Objective. Electrical nerve block offers the ability to immediately and reversibly block peripheral nerve conduction and would have applications in the emerging field of bioelectronics. Two modalities of electrical nerve block have been investigated—kilohertz frequency alternating current (KHFAC) and direct current (DC). KHFAC can be safely delivered with conventional electrodes, but has the disadvantage of having an onset response, which is a period of increased neural activation before block is established and currently limits clinical translation. DC has long been known to block neural conduction without an onset response but creates damaging reactive species. Typical electrodes can safely deliver DC for less than one second, but advances in high capacitance electrodes allow DC delivery up to 10 s without damage. The present work aimed to combine DC and KHFAC into a single waveform, named the combined reduced onset waveform (CROW), which can initiate block without an onset response while also maintaining safe block for long durations. This waveform consists of a short, DC pre-pulse before initiating KHFAC. Approach. Simulations of this novel waveform were carried out in the axonal simulation environment NEURON to test feasibility and gain insight into the mechanisms of action. Two sets of acute experiments were then conducted in adult Sprague–Dawley rats to determine the effectiveness of the waveform in mitigating the onset response. Main results. The CROW reduced the onset response both in silico and in vivo. The onset area was reduced by over 90% with the tested parameters in the acute experiments. The amplitude of the DC pulse was shown to be particularly important for effective onset mitigation, requiring amplitudes 6–8 times the DC block threshold. Significance. This waveform can reliably reduce the onset response due to KHFAC and could allow for wider clinical implementation of electrical nerve block.

Non-monotonic kilohertz frequency neural block thresholds arise from amplitude- and frequency-dependent charge imbalance

Reversible block of nerve conduction using kilohertz frequency electrical signals has substantial potential for treatment of disease. However, the ability to block nerve fibers selectively is limited by poor understanding of the relationship between waveform parameters and the nerve fibers that are blocked. Previous in vivo studies reported non-monotonic relationships between block signal frequency and block threshold, suggesting the potential for fiber-selective block. However, the mechanisms of non-monotonic block thresholds were unclear, and these findings were not replicated in a subsequent in vivo study. We used high-fidelity computational models and in vivo experiments in anesthetized rats to show that non-monotonic threshold-frequency relationships do occur, that they result from amplitude- and frequency-dependent charge imbalances that cause a shift between kilohertz frequency and direct current block regimes, and that these relationships can differ across fiber diameters such that smaller fibers can be blocked at lower thresholds than larger fibers. These results reconcile previous contradictory studies, clarify the mechanisms of interaction between kilohertz frequency and direct current block, and demonstrate the potential for selective block of small fiber diameters.

High Voltage Ride through Strategy of Wind Farm Considering Generator Terminal Voltage Distribution

When wind power is transmitted via high-voltage direct current (HVDC), the problem of high-voltage ride-through (HVRT), caused by direct-current (DC) blocking must be seriously taken into account. All the wind turbines in a wind farm are usually equivalent to a single turbine in the existing research on HVRT, which ignores the generator terminal voltage distribution in a wind farm. In view of the fact that the severity of fault voltage felt by each wind turbine in the field is different, an improved HVRT strategy considering voltage distribution is proposed in this article. First, this article analyzes the mechanism of voltage swell failure caused by DC blocking, and the characteristics of the generator terminal voltage distribution in wind farms. Second, the reactive power characteristic equations of the synchronous condenser and the doubly-fed induction generator (DFIG) are derived. Third, based on the extraction of the key node voltage, this article takes the key node voltage as the compensation target, and put forwards a HVRT strategy combining the synchronous condenser and wind turbine. Finally, the simulation is carried out to demonstrate the effectiveness of the proposed strategy in improving the HVRT capability of all wind turbines.

SSBI-Free Direct-Detection System Employing Phase Modulation for Analog Optical Links

Analog optical transmission techniques such as radio-over-fiber (RoF) and multiple intermediate-frequency-over-fiber (multi-IFoF) have attracted a great deal of attention for use in 5G mobile fronthaul links. Recently, an IFoF transmission with a record CPRI-equivalent capacity of 1.53 Tb/s has been demonstrated by using the Kramers-Kronig (KK) receiver. However, one major issue associated with the KK receiver is its computational complexity. Also, since the minimum phase condition must be satisfied, the optimal carrier-to-signal power ratio (CSPR) should be large enough; however, this results in a low receiver sensitivity. To address these issues, we have recently proposed and demonstrated a signal-to-signal beat interference (SSBI)-free direct-detection (DD) system employing phase modulation (PM). Since a PM signal has a constant amplitude, its SSBI term becomes just a direct-current (DC) component. Therefore, the SSBI can be perfectly removed using a DC block without resorting to complicated digital-signal-processing (DSP)-based schemes such as the KK algorithm. In this article, we describe the principles of operation of the SSBI-free PM system in detail. We present a numerical study of performance comparisons between the SSBI-free and KK systems. The result reveals that the optimal CSPR is always 0 dB in the SSBI-free system, while it depends on optical-signal-to-noise-ratio (OSNR) levels in the KK system. The dispersion tolerance of the SSBI-free system is also investigated, showing that the SSBI-free system can support a 2-GHz 1024QAM-signal delivery in a typical deployment scenario of mobile fronthaul links. Finally, we present an experimental demonstration of a 2-GHz 1024QAM OFDM transmission with the SSBI-free system. To the best of our knowledge, this is the first demonstration of 1024QAM DD-based transmission for analog mobile fronthaul links.

Performance of grey‐coded IQM‐based optical modulation formats on high‐speed long‐haul optical communication link

In this article the performance of grey-coded advanced optical modulation formats is evaluated on a single-channel high-speed long-haul optical communication link and are compared to the respective differential-coded modulation formats. Polarisation division multiplexed optical in-phase quadrature modulator (IQM) structure and homodyne detection scheme are used to realise 100 Gbps quadrature phase-shift keying (QPSK), 120 Gbps 16-ary quadrature amplitude modulation (16-QAM), 360 Gbps 32-QAM and 480 Gbps 64-QAM modulation formats. Advanced digital signal processing unit with various pre-processing and recovery stages such as direct current blocking, normalisation, low-pass Bessel filter, resampling, quadrature imbalance compensation, chromatic dispersion compensation, non-linear compensation, timing recovery, adaptive equalisation, down-sampling, frequency offset estimation, and carrier phase estimation is used at the receiving end to compensate for signal impairments during propagation. Maximum transmission distances of 7200, 1050, 560, and 360 km have been achieved at an acceptable bit error rate for QPSK, 16-QAM, 32-QAM, and 64-QAM, respectively. The grey-coded systems outperformed the differential-coded systems regarding optical signal-to-noise ratio requirement, receiver sensitivity, and transmission distance.

A Carbon Slurry Separated Interface Nerve Electrode for Electrical Block of Nerve Conduction.

Direct current (DC) nerve block has been shown to provide a complete block of nerve conduction without unwanted neural firing. Previous work shows that high capacitance electrodes can be used to safely deliver a DC block. Another way of delivering DC safely is through a separated interface nerve electrode (SINE), such that any reactive species that are generated by the passage of DC are contained in a vessel away from the nerve. This design has been enhanced by using a high capacitance carbon "slurry" as the electrode in the external vessel to extend the capacity of the electrode (CSINE). With this new design, it was possible to provide 50 min of continuous nerve block without recharge while still maintaining complete recovery of neural signals. Up to 46 C of charge delivery was applied for a total of 4 h of nerve block with complete recovery. Because of the extended delivery time, it was possible to explore several properties of DC block that would not be revealed without the capability of a long-duration continuous block. It was possible to achieve complete block at lower values of DC if the block was applied for a longer period of time. Depending on the amount of charge applied during the block, the recovery was delayed for a period of time before complete force recovery was restored. These new properties provide novel techniques for device development to optimize charge delivery time and device powering concerns.

Accelerated Recovery of DC Blocking Using Repolarization.

Direct current (DC) can be applied to a nerve to generate a complete nerve block. However, using conventional platinum electrodes, reactions occur at the nerve interface causing damage to the nerve. The electrode can be separated from the nerve using a biocompatible, ionically conducting medium, which isolates the damaging reactions in a vessel away from the nerve. This electrode has previously been referred to as the Separated Interface Nerve Electrode (SINE). Recent experiments have shown that when a complete block is applied, for a prolonged period of time, there is a delay in the recovery of the response. For many applications it would be advantageous to have instantaneous recovery. To achieve this, the SINE electrode was used to provide a complete, instantaneous nerve block at the block threshold for 10 minutes and then the current was reversed for selected time periods to determine if instantaneous recovery could be achieved. Depending on the length of time of the repolarization, the amount of time for recovery can be reduced by as much as 50%.

Block of motor nerve conduction via transcutaneous application of direct current.

Nerve conduction block using implanted electrodes is being used increasingly for clinical applications. Alternatively, non-invasive electrical nerve block would be beneficial for applications including pain block and muscle spasticity. Here we developed a novel means of non-invasive electrical nerve conduction blockade - transcutaneous direct current block (tDCB) - that produces direct block of nerve conduction. In an in vivo rodent model, tDCB produced stable neuromotor blockade of sciatic nerve branches, dependent on stimulus parameters and electrode geometry. Partial-to-complete neuromotor block was achieved in all subjects using tDCB amplitudes at or below 20 mA, and complete block was achieved at amplitudes as low as 6 mA. Our results reveal that neuromotor activity can be rapidly, reliably and reversibly blocked using tDCB.

Differential expression of voltage-gated sodium channels in afferent neurons renders selective neural block by ionic direct current.

The assertion that large-diameter nerve fibers have low thresholds and small-diameter fibers have high thresholds in response to electrical stimulation has been held in a nearly axiomatic regard in the field of neuromodulation and neuroprosthetics. In contrast to the short pulses used to evoke action potentials, long-duration ionic direct current has been shown to block neural activity. We propose that the main determinant of the neural sensitivity to direct current block is not the size of the axon but the types of voltage-gated sodium channels prevalent in its neural membrane. On the basis of the variants of voltage-gated sodium channels expressed in different types of neurons in the peripheral nerves, we hypothesized that the small-diameter nociceptive fibers could be preferentially blocked. We show the results of a computational model and in vivo neurophysiology experiments that offer experimental validation of this novel phenomenon.

Characterization of high capacitance electrodes for the application of direct current electrical nerve block.

Direct current (DC) can briefly produce a reversible nerve conduction block in acute experiments. However, irreversible reactions at the electrode-tissue interface have prevented its use in both acute and chronic settings. A high capacitance material (platinum black) using a charge-balanced waveform was evaluated to determine whether brief DC block (13 s) could be achieved repeatedly (>100 cycles) without causing acute irreversible reduction in nerve conduction. Electrochemical techniques were used to characterize the electrodes to determine appropriate waveform parameters. In vivo experiments on DC motor conduction block of the rat sciatic nerve were performed to characterize the acute neural response to this novel nerve block system. Complete nerve motor conduction block of the rat sciatic nerve was possible in all experiments, with the block threshold ranging from -0.15 to -3.0 mA. DC pulses were applied for 100 cycles with no nerve conduction reduction in four of the six platinum black electrodes tested. However, two of the six electrodes exhibited irreversible conduction degradation despite charge delivery that was within the initial Q (capacitance) value of the electrode. Degradation of material properties occurred in all experiments, pointing to a possible cause of the reduction in nerve conduction in some platinum black experiments .

A 4 : 1 Transmission-Line Impedance Transformer for Broadband Superconducting Circuits

We present a 4 : 1 superconducting transmission-line impedance transformer for cryogenic applications. The device transforms 25 Ω in the coplanar waveguide to 6.25 Ω in the microstrip and is designed to operate at 20 mK. Calibrated measurements in a dilution refrigerator demonstrate a -3 dB bandwidth from 1.6 to 13 GHz. In a modified Ruthroff design, a small capacitor is integrated at the input as a direct-current block, making it suitable for biasing and matching to low-impedance active circuits, such as superconducting quantum interference device (SQUID) amplifiers.

Analysis of nerve conduction block induced by direct current

The mechanisms of nerve conduction block induced by direct current (DC) were investigated using a lumped circuit model of the myelinated axon based on Frankenhaeuser-Huxley (FH) model. Four types of nerve conduction block were observed including anodal DC block, cathodal DC block, virtual anodal DC block, and virtual cathodal DC block. The concept of activating function was used to explain the blocking locations and relation between these different types of nerve block. Anodal/cathodal DC blocks occurred at the axonal nodes under the block electrode, while virtual anodal/cathodal DC blocks occurred at the nodes several millimeters away from the block electrode. Anodal or virtual anodal DC block was caused by hyperpolarization of the axon membrane resulting in the failure of activating sodium channels by the arriving action potential. Cathodal or virtual cathodal DC block was caused by depolarization of the axon membrane resulting in inactivation of the sodium channel. The threshold of cathodal DC block was lower than anodal DC block in most conditions. The threshold of virtual anodal/cathodal blocks was about three to five times higher than the threshold of anodal/cathodal blocks. The blocking threshold was decreased with an increase of axonal diameter, a decrease of electrode distance to axon, or an increase of temperature. This simulation study, which revealed four possible mechanisms of nerve conduction block in myelinated axons induced by DC current, can guide future animal experiments as well as optimize the design of electrodes to block nerve conduction in neuroprosthetic applications.

Effects of thresholding in joint-transform correlation

The joint-transform power spectrum of two identical objects can be represented as a one-dimensional sinusoidal grating modulated by a Fourier transform, and the correlation peaks can be regarded as the first-order diffraction of the grating. The peak intensity and the width are then determined by the aperture and the modulation of the grating. Based on this analysis, it is shown that dc blocking, hard clipping, or binarization of the power spectrum results in higher correlation peak intensity and a narrower peak width. Direct-current blocking is also found to be preferable if the input pattern to the correlator is corrupted by noise.

Bilateral convergence of pulmonary stretch receptor inputs on I beta-neurons in the cat

Extracellular recordings were made from inspiratory beta- (I beta) neurons in the nucleus of the tractus solitarius in decerebrate cats. A reversible direct current block of myelinated fibers in the ipsilateral vagus nerve was used to evaluate the input from pulmonary stretch receptor afferents (PSR) of the contralateral vagus to individual I beta-neurons. This block served to remove all ipsilateral (which includes all monosynaptic) inputs from PSR to I beta-cells. The effect of withholding inflation on the firing rate and the time of onset of firing of I beta-neurons was determined before, during and after application of the direct current block. There was considerable variation in the strengths of the inputs from the ipsilateral and contralateral nerves; some cells received PSR inputs from only the ipsilateral vagus, but the majority were excited with varying magnitude from both vagi. Several neurons had powerful excitatory inputs from PSR of the contralateral vagus, with the ipsilateral (monosynaptic) contribution being of minor importance.