Kilohertz Frequency Research Articles

Combined KHFAC + DC nerve block without onset or reduced nerve conductivity after block

Objective. Kilohertz frequency alternating current (KHFAC) waveforms have been shown to provide peripheral nerve conductivity block in many acute and chronic animal models. KHFAC nerve block could be used to address multiple disorders caused by neural over-activity, including blocking pain and spasticity. However, one drawback of KHFAC block is a transient activation of nerve fibers during the initiation of the nerve block, called the onset response. The objective of this study is to evaluate the feasibility of using charge balanced direct current (CBDC) waveforms to temporarily block motor nerve conductivity distally to the KHFAC electrodes to mitigate the block onset-response. Approach. A total of eight animals were used in this study. A set of four animals were used to assess feasibility and reproducibility of a combined KHFAC + CBDC block. A following randomized study, conducted on a second set of four animals, compared the onset response resulting from KHFAC alone and combined KHFAC + CBDC waveforms. To quantify the onset, peak forces and the force-time integral were measured during KHFAC block initiation. Nerve conductivity was monitored throughout the study by comparing muscle twitch forces evoked by supra-maximal stimulation proximal and distal to the block electrodes. Each animal of the randomized study received at least 300 s (range: 318–1563 s) of cumulative dc to investigate the impact of combined KHFAC + CBDC on nerve viability. Main results. The peak onset force was reduced significantly from 20.73 N (range: 18.6–26.5 N) with KHFAC alone to 0.45 N (range: 0.2–0.7 N) with the combined CBDC and KHFAC block waveform (p < 0.001). The area under the force curve was reduced from 6.8 Ns (range: 3.5–21.9 Ns) to 0.54 Ns (range: 0.18–0.86 Ns) (p < 0.01). No change in nerve conductivity was observed after application of the combined KHFAC + CBDC block relative to KHFAC waveforms. Significance. The distal application of CBDC can significantly reduce or even completely prevent the KHFAC onset response without a change in nerve conductivity.

Alternating current and infrared produce an onset-free reversible nerve block.

Nerve block can eliminate spasms and chronic pain. Kilohertz frequency alternating current (KHFAC) produces a safe and reversible nerve block. However, KHFAC-induced nerve block is associated with an undesirable onset response. Optical inhibition using infrared (IR) laser light can produce nerve block without an onset response, but heats nerves. Combining KHFAC with IR inhibition [alternating current and infrared (ACIR)] produces a rapidly reversible nerve block without an onset response. ACIR can be used to rapidly and reversibly provide onset-free nerve block in the unmyelinated nerves of the marine mollusk Aplysia californica and may have significant advantages over either modality alone. ACIR may be of great clinical utility in the future.

Phenomena in the High-Latitude Ionospheric F Region Induced by a HF Heater Wave at Frequencies Near the Fourth Electron Gyroharmonic

We present the results of multi-instrument studies of the phenomena in the high-latitude ionospheric F region stimulated by high-power HF O-mode radio waves injected towards the magnetic zenith when the ratio of the heater frequency to the cutoff frequency of the F2 layer is near the fourth electron gyroharmonic. Based on the stimulated electromagnetic emission (SEE), spectral observations in the kilohertz and hertz frequency bands of detunings relative to the heater wave frequency, the behaviors of different parameters of the ionospheric plasma and small-scale artificial field-aligned irregularities are compared and analyzed. The coexistence of the thermal (resonance) parametric instability (TPI) and parametric decay (striction) instability (PDI) was found in the vicinity of the fourth gyroresonance harmonic.

Direct current contamination of kilohertz frequency alternating current waveforms.

Kilohertz frequency alternating current (KHFAC) waveforms are being evaluated in a variety of physiological settings because of their potential to modulate neural activity uniquely when compared to frequencies in the sub-kilohertz range. However, the use of waveforms in this frequency range presents some unique challenges regarding the generator output. In this study we explored the possibility of undesirable contamination of the KHFAC waveforms by direct current (DC). We evaluated current- and voltage-controlled KHFAC waveform generators in configurations that included a capacitive coupling between generator and electrode, a resistive coupling and combinations of capacitive with inductive coupling. Our results demonstrate that both voltage- and current-controlled signal generators can unintentionally add DC-contamination to a KHFAC signal, and that capacitive coupling is not always sufficient to eliminate this contamination. We furthermore demonstrated that high value inductors, placed in parallel with the electrode, can be effective in eliminating DC-contamination irrespective of the type of stimulator, reducing the DC contamination to less than 1 μA. This study highlights the importance of carefully designing the electronic setup used in KHFAC studies and suggests specific testing that should be performed and reported in all studies that assess the neural response to KHFAC waveforms.

Admittance of multiterminal quantum Hall conductors at kilohertz frequencies

We present an experimental study of the low frequency admittance of quantum Hall conductors in the [100 Hz, 1 MHz] frequency range. We show that the frequency dependence of the admittance of the sample strongly depends on the topology of the contacts connections. Our experimental results are well explained within the Christen and Büttiker approach for finite frequency transport in quantum Hall edge channels taking into account the influence of the coaxial cables capacitance. In the Hall bar geometry, we demonstrate that there exists a configuration in which the cable capacitance does not influence the admittance measurement of the sample. In this case, we measure the electrochemical capacitance of the sample and observe its dependence on the filling factor.

Homogenization Methods in Simulations of Transcutaneous Energy Transmitters

Transcutaneous Energy Transmitters (TETs) transfer wireless energy through an inductive link established between two pancake coils placed, respectively, outside and inside the body of a patient. The simulation of the misalignment between the coils must be performed in 3-D, e.g., with a Finite Element (FE) method. This paper introduces a homogenization method to minimize the cost of the expensive 3-D FE computation in the frequency domain. Its originality lies in the non-homogeneous TET geometry during the meshing process. The results of this technique are compared with those obtained by considering regular stranded TET coils. They showed improvements mainly at kilohertz frequencies, the typical TET operating frequency range.

Kilohertz ultrafast electrochemical supercapacitors based on perpendicularly-oriented graphene grown inside of nickel foam

Ultrafast electrochemical supercapacitors (EC) that can work at or above kilohertz (kHz) frequency, 3–4 orders higher than traditional EC, call for a structure with extremely low equivalent serial resistance (ESR) and a reasonably large surface area. Three-dimensional perpendicularly-oriented graphene (POG) network, grown inside of Ni foam (NF) by microwave plasma chemical vapor deposition, is reported as electrode to fabricate such ultrafast EC. The folded POG inside NF provides a large surface area, while the straight-forward and wide-open porous structure of POG ensures fast ion migration. In conjunction with the intrinsic high electronic conductivity of graphene and Ni, POG/NF electrode based ultrafast EC was demonstrated with a specific cell capacitance of 0.32mF/cm2 at 1kHz, a relaxation time constant of 0.248ms, and an ESR of 70mΩ. A charge–discharge rate as high as 500V/s was also measured, at which the cyclic voltammogram maintained a rectangular shape, corresponding to a single electrode capacitance of 0.83mF/cm2.

Laboratory measurement of seismic velocity dispersion in cracked quartzite

Reversible fluid flow within low aspect ratio cracks is expected to cause seismic velocities in hard rock to be strongly frequency dependent. Experimental measurements are necessary to constrain theoretical velocity dispersion models in order to allow comparisons between laboratory measurements at megahertz frequencies, sonic logging at kilohertz frequencies and in-situ exploration seismic at typically 10-300 Hz frequencies, but are rare due to the complexity of low frequency measurements on core samples. Quartzite samples from Cape Sorell, Australia and Alberta, Canada are thermally cracked to induce ~2% crack porosity with aspect ratio <0.01. The shear and Young's moduli of the samples are measured at frequencies of 0.01-1 Hz and 1 MHz while the samples are dry, saturated with argon and saturated with water over effective pressures of 10-150 MPa. As anticipated, no dispersion is exhibited while the samples are dry. Similarly, no dispersion is observed while the samples are argon saturated as a result of the low viscosity and high compressibility of argon. Water saturation, however, causes significant dispersion in both the shear and Young's moduli of the samples between the low and high frequency measurements.

A Novel Waveform for No-Onset Nerve Block Combining Direct Current and Kilohertz Frequency Alternating Current.

Kilohertz frequency alternating current (KHFAC) has been shown to produce a fast acting, reversible nerve block. The principal drawback to this technique is a short, but intense burst of firing at the initiation of the KHFAC which is referred to as the "onset response". The "onset response" can be eliminated by the use of a second electrode which delivers direct current (DC) briefly during the onset duration. However, the DC cannot be delivered for a sufficiently long time to suppress the onset without causing damage to the nerve. High surface area electrodes have been developed which can be used to deliver DC for long enough to eliminate the onset without causing damage. Furthermore, instead of using multiple electrodes to create a no onset block, the DC and KHFAC are combined in novel waveform which can be output on a single monopolar electrode. This novel waveform has been demonstrated to prevent onset in both simulation and in an in vivo rat sciatic nerve model.

Radiated sound from a scale-model pile submerged in a two-layer medium

Underwater noise due to both marine pile driving and offshore wind farm operation is not only radiated directly from the pile into the water, but also from the seabed surrounding the pile. While there is much interest in mitigating the noise from these activities, a better understanding of the source mechanisms and propagation is needed to determine optimal strategies for noise abatement. A recent analytical model of the acoustic field radiated by submerged piles includes radiation from the pile directly into the water and into a stratified viscoelastic sediment as well as propagation into a shallow water waveguide from both the direct and sediment radiation paths [Hay et al., Proceedings of Meetings on Acoustics 19, 070038 (2013)]. As a step towards validating this model, scale-model experiments were conducted in the high kilohertz frequency range with a model pile consisting of a mechanically excited metallic tube inserted into a laboratory tank filled with two stratified layers to simulate the water/sediment interface. Measurements of the acoustic field in the experiment are compared with the model predictions, and the relevance of these results to implementing noise abatement strategies will be discussed. [Work supported by ARL:UT IR&amp;D.]

Model for underwater noise radiated by submerged piles

There is concern that underwater noise generated by marine construction activities and radiated by towers supporting offshore wind turbines may disturb marine mammals, or interfere with passive sensors and communication equipment. In order to understand these effects a semi-analytic frequency-domain model was developed previously for the sound radiated in the water column by a pulsating cylindrical structure embedded in horizontally stratified layers of viscoelastic sediment. This model was in turn coupled to a parabolic equation code for long-range propagation over range-dependent environments [Hay et al., J. Acoust. Soc. Am. 133, 3396 (2013)]. A time-domain version of this model is now presented which enables simulation of impulsive sound sources such as those due to underwater pile driving, and pulsed tonal sources appropriate for use in a finite-sized laboratory tank. In order to validate the model a scaled physical model, consisting of a laboratory tank and metallic cylindrical tube driven in the high kilohertz frequency range, was constructed. Simulations will be presented for a variety of sound sources, and preliminary comparisons with measurements from the scaled model experiments will be made.

Numerical experiment and analysis of the differential acoustic resonance spectroscopy for elastic property measurements

Differential acoustic resonance spectroscopy (DARS) was recently developed to estimate the elastic parameters of rock samples with a resonant frequency perturbation caused by a test sample at kilohertz frequency. In the derivation of the DARS theory, the wave inside the cavity is assumed to be a harmonic acoustic plane wave, which may be a source of measurement errors. A simulation program may help researchers to understand the mechanism of this device and to find out whether the assumption in the theory derivation is correct. In this paper, we develop a simulation program based on the elastic wave equation in cylindrical coordinates, and model the DARS system. The modeled power spectrum agrees well with that obtained by the laboratory measurement. An analysis of the wave field snapshots and the pressure distribution curves shows that the standing wave inside the cavity along its long axis is asymmetrical. This study also investigates the relationships between the resonant frequencies and the density, the compressibility and the P-wave and S-wave velocities of the samples. By numerical experiments, this paper finds that only the compressibility can be estimated with the resonant frequency, when the sample is located at the velocity node. But when the sample is located at other positions, the P-wave and S-wave velocities can alter the shape of the vibration curve, though they have no impact on the resonant power spectrum. This implies that it may be possible to estimate the P-wave and S-wave velocities by using the full waveform of the vibration curve.

Reversible Nerve Conduction Block Using Kilohertz Frequency Alternating Current

The features and clinical applications of balanced-charge kilohertz frequency alternating currents (KHFAC) are reviewed. Preclinical studies of KHFAC block have demonstrated that it can produce an extremely rapid and reversible block of nerve conduction. Recent systematic analysis and experimentation utilizing KHFAC block have resulted in a significant increase in interest in KHFAC block, both scientifically and clinically. We review the history and characteristics of KHFAC block, the methods used to investigate this type of block, the experimental evaluation of block, and the electrical parameters and electrode designs needed to achieve successful block. We then analyze the existing clinical applications of high-frequency currents, comparing the early results with the known features of KHFAC block. Although many features of KHFAC block have been characterized, there is still much that is unknown regarding the response of neural structures to rapidly fluctuating electrical fields. The clinical reports to date do not provide sufficient information to properly evaluate the mechanisms that result in successful or unsuccessful treatment. KHFAC nerve block has significant potential as a means of controlling nerve activity for the purpose of treating disease. However, early clinical studies in the use of high-frequency currents for the treatment of pain have not been designed to elucidate mechanisms or allow direct comparisons to preclinical data. We strongly encourage the careful reporting of the parameters utilized in these clinical studies, as well as the development of outcome measures that could illuminate the mechanisms of this modality.

High-frequency viscoelastic measurements of fluids based on microcantilever sensing: New modeling and experimental issues

In general, microrheology is carried out using active or passive particle-tracking techniques. In the present paper, a novel technique based on the out-of-plane bending vibrations of a microcantilever beam immersed into a liquid is proposed for microrheological property measurement. We propose to analytically link the damped beam motion with the rheological properties of the fluid in order to establish a dynamic rheogram which spans at least one decade of the kiloHertz frequency domain. The latest improvements in terms of both analytical modeling and experimental set-up are detailed, along with a complete explanation of the calculation method. Four rheograms of Newtonian and non-Newtonian liquids obtained from the frequency response of three immersed cantilevers of different geometries are presented.

Compounds with low relaxation frequency and dual frequency mixtures useful for active matrix addressing

Dozens of three- and four-ring liquid crystal derivatives of alkylcyclohexyltolanes, alkylbicyclohexyltolanes and alkylbicyclohexylbiphenyls with a terminal polar group F or trifluoromethoxy (OCF3), cyano (CN), isothiocyanato (NCS) have been synthesised. Their dielectric properties upon temperature and electric field frequency f have been investigated. Compounds dissolved in a negative dielectric medium exhibit strong dispersion of the parallel permittivity ϵ||(f) falling on the kilohertz frequencies with practically constant value of the perpendicular permittivity ϵ⊥ in this frequency range. This causes a change of sign of the dielectric anisotropy from positive at low frequencies to negative at high frequencies. Many so-called dual frequency mixtures, convenient for active matrix addressing, with the fco values in the range of 1–10 kHz at 20°C, have been prepared and investigated. The cross-over frequency fco is close to the relaxation frequency fr. The discussion refers to relations among the relaxation frequency, compound structure and viscosity of a liquid crystal medium.

A Digitally Assisted Current Comparator Bridge for Impedance Scaling at Audio Frequencies

A current comparator impedance bridge, suitable for the comparison of four-terminal-pair impedance standards having similar phase angles (e.g., resistors or capacitors) in the audio frequency range at 1 : 1 and 10 : 1 nominal ratios, is here presented. The bridge is digitally assisted: Its accuracy is granted by an electromagnetic device, a high-permeability core current comparator, but the voltages and currents needed to achieve both principal and auxiliary equilibria are generated by programming a polyphase direct-digital-synthesis generator. The resulting implementation is neat and simple and does not include variable components such as decade dividers. The measurement is semiautomated: After an initial setting, the equilibrium can be achieved in a few minutes. Measurements performed on calculable resistors give a base accuracy of a few parts in $10^{7}$ at kilohertz frequency, sufficient for calibration purposes, with the potential for further improvement.

Dynamically Adaptive Control System for Bioanodes in Serially Stacked Bioelectrochemical Systems

Microbial bioelectrochemical systems (BESs) use microorganisms as catalysts for electrode reactions. They have emerging applications in bioenergy, bioproduction, and bioremediation. BESs can be scaled up as a linked series of units or cells; however, this may lead to so-called cell reversal. Here, we demonstrate a cell balance system (CBS) that controls individual BES cells connected electrically in series by dynamically adapting the applied potential in the kilohertz frequency range relative to the performance of the bioanode. The CBS maintains the cell voltage of individual BES cells at or below a maximum set point by bypassing a portion of applied current with a high-frequency metal oxide semiconductor field-effect transistor switch control system. We demonstrate (i) multiple serially connected BES cells started simultaneously and rapidly from a single power source, as the CBS imparts no current limitation, (ii) continuous, stable, and independent performance of each stacked BES cell, and (iii) stable BES cell and stack performance under excessive applied currents. This control system has applications for not only serially stacked BESs in scaled-up stacks but also rapidly starting individual- and/or lab-scale BESs.

Solution conformation of 2-aminopurine dinucleotide determined by ultraviolet two-dimensional fluorescence spectroscopy

We have observed the conformation-dependent electronic coupling between the monomeric subunits of a dinucleotide of 2-aminopurine (2-AP), a fluorescent analogue of the nucleic acid base adenine. This was accomplished by extending two-dimensional fluorescence spectroscopy (2D FS)—a fluorescence-detected variation of 2D electronic spectroscopy—to excite molecular transitions in the ultraviolet (UV) regime. A collinear sequence of four ultrafast laser pulses centered at 323 nm was used to resonantly excite the coupled transitions of 2-AP dinucleotide. The phases of the optical pulses were continuously swept at kilohertz frequencies, and the ensuing nonlinear fluorescence was phase-synchronously detected at 370 nm. Upon optimization of a point–dipole coupling model to our data, we found that in aqueous buffer the 2-AP dinucleotide adopts an average conformation in which the purine bases are non-helically stacked (center-to-center distance R12 = 3.5 ± 0.5 Å , twist angle θ12 = 5° ± 5° ), which differs from the conformation of such adjacent bases in duplex DNA. These experiments establish UV–2D FS as a method for examining the local conformations of an adjacent pair of fluorescent nucleotides substituted into specific DNA or RNA constructs, which will serve as a powerful probe to interpret, in structural terms, biologically significant local conformational changes within the nucleic acid framework of protein–nucleic acid complexes.

A comparison of two methods for phase response calibration of hydrophones in the frequency range 10–400 kHz

A comparison is made of two methods for determining the phase response of hydrophones in the kilohertz frequency range: The three-transducer spherical-wave reciprocity method and the method of optical interferometry. The implementation of the methods and the corresponding experimental systems are described. To facilitate a comparison, the methods are used to determine the phase response of three commercially available measuring hydrophones over the frequency range from 10 to 400 kHz. The results are compared, showing agreement within the estimated uncertainties of the methods. An investigation is conducted into the sources of uncertainties in the methods which increase with frequency. The major sources of uncertainty are residual positioning errors giving rise to phase uncertainties; a significant problem for the reciprocity method is that it requires one hydrophone to be rotated during the measurement procedure. An additional source of uncertainty at higher frequencies may be present if the position of the sensing element is not central within the outer hydrophone boot.

Dielectric analysis of TiO2-based electrorheological suspensions

Dielectric behaviors of titanium dioxide (TiO2)-based electrorheological (ER) suspensions with different particle concentrations and TiO2 polymorphs were investigated in the frequency range of 40 Hz to 110 MHz. Two relaxations in kilohertz and megahertz frequency range were attributed to interface polarization between TiO2 and silicone oil and ion pair polarization between dissociated counterions and fixed charges on TiO2 surfaces, respectively. Dipolar coefficient D, which is related to the construction or structure of the colloid, changes after critical volume fraction $\phi _{\rm c} \approx $ 0.05, indicating that chain-like or network structures are formed by particles. Based on percolation model, the values of critical exponent suggest that particles may form two-dimensional percolation network. Furthermore, the effective dielectric mismatch parameter, $\beta _{\rm eff}$ , was calculated based on the obtained phase parameters. We found that rutile should have better ER activity than anatase. The main reason for weak ER activity of pure TiO2 ER suspensions may due to poor conductivity properties of TiO2 crystals.