Статті в журналах: "Low frequency currents interractions"

1

Ward, Alex R., Warwick G. Oliver, and Danielle Buccella. "Wrist Extensor Torque Production and Discomfort Associated With Low-Frequency and Burst-Modulated Kilohertz-Frequency Currents." Physical Therapy 86, no. 10 (October 1, 2006): 1360–67. http://dx.doi.org/10.2522/ptj.20050300.

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Abstract Background and Purpose. A randomized controlled trial to compare 2 forms of monophasic pulsed currents with 2 forms of burst-modulated, kilohertz-frequency alternating current (“Russian current” and “Aussie current”) was conducted to establish whether different amounts of wrist extensor torque were produced and whether discomfort varied with stimulus type. Subjects. The 32 subjects were adults who were healthy and were drawn from a population of staff and students at La Trobe University. Methods. Each subject received all 4 currents. Maximal electrically induced torque (MEIT) of the wrist extensors was measured for each stimulus type. Relative discomfort of stimulation also was assessed. Results. Russian current elicited lower mean torque than those elicited by Aussie current and monophasic pulsed currents. The Russian and Aussie currents elicited significantly less discomfort than the 2 monophasic pulsed currents. Discussion and Conclusion. When force production and relative discomfort were jointly used as the criteria, Aussie current was found to be more effective than either of the monophasic pulsed currents or Russian current stimulation.

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2

Margetis, Dionisios, and Nikos Savva. "Low-frequency currents induced in adjacent spherical cells." Journal of Mathematical Physics 47, no. 4 (April 2006): 042902. http://dx.doi.org/10.1063/1.2190333.

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3

Ehst, D. A. "Toroidal equilibrium with low-frequency wave-driven currents." Nuclear Fusion 25, no. 5 (May 1, 1985): 629–32. http://dx.doi.org/10.1088/0029-5515/25/5/006.

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4

Elgar, Steve, and Britt Raubenheimer. "Field Evidence of Inverse Energy Cascades in the Surfzone." Journal of Physical Oceanography 50, no. 8 (August 1, 2020): 2315–21. http://dx.doi.org/10.1175/jpo-d-19-0327.1.

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AbstractLow-frequency currents and eddies transport sediment, pathogens, larvae, and heat along the coast and between the shoreline and deeper water. Here, low-frequency currents (between 0.1 and 4.0 mHz) observed in shallow surfzone waters for 120 days during a wide range of wave conditions are compared with theories for generation by instabilities of alongshore currents, by ocean-wave-induced sea surface modulations, and by a nonlinear transfer of energy from breaking waves to low-frequency motions via a two-dimensional inverse energy cascade. For these data, the low-frequency currents are not strongly correlated with shear of the alongshore current, with the strength of the alongshore current, or with wave-group statistics. In contrast, on many occasions, the low-frequency currents are consistent with an inverse energy cascade from breaking waves. The energy of the low-frequency surfzone currents increases with the directional spread of the wave field, consistent with vorticity injection by short-crested breaking waves, and structure functions increase with spatial lags, consistent with a cascade of energy from few-meter-scale vortices to larger-scale motions. These results include the first field evidence for the inverse energy cascade in the surfzone and suggest that breaking waves and nonlinear energy transfers should be considered when estimating nearshore transport processes across and along the coast.

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5

Rumyantsev, Sergey L., Michael S. Shur, Michael E. Levinshtein, Pavel A. Ivanov, John W. Palmour, Mrinal K. Das, and Brett A. Hull. "Low Frequency Noise in 4H-SiC MOSFETs." Materials Science Forum 615-617 (March 2009): 817–20. http://dx.doi.org/10.4028/www.scientific.net/msf.615-617.817.

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Low-frequency noise in 4H-SiC MOSFETs has been measured for the first time. At drain currents varying from deep subthreshold to strong inversion, the 1/f (flicker) noise dominated at frequencies 1 - 105 Hz. The dependence of relative spectral noise density, , on drain current Id (at a constant drain voltage Vd) differs qualitatively from that in Si MOSFETs. In Si MOSFETs, ~ 1/ in strong inversion, whereas tends to saturate in sub-threshold. In 4H-SiC MOSFETs under study, ~ 1/ over the whole range of currents from deep sub-threshold to strong inversion. Similar noise behavior is often observed in poly- or a-Si TFTs. The effective channel mobility in 4H-SiC MOSFETs, 3 - 7 cm2/Vs, is also as low as that in TFTs. Both noise behavior and transport properties of 4H-SiC MOSFETs are explained, analogously to TFTs, by a high density of localized states (bulk and interface) near the conduction band edge in the ion implanted p-well.

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6

Johnson, E. R. "Boundary Currents, Free Currents and Dissipation in the Low-Frequency Scattering of Shelf Waves." Journal of Physical Oceanography 19, no. 9 (September 1989): 1291–300. http://dx.doi.org/10.1175/1520-0485(1989)019<1291:bcfcad>2.0.co;2.

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7

Torres, Hector S., Patrice Klein, Jinbo Wang, Alexander Wineteer, Bo Qiu, Andrew F. Thompson, Lionel Renault, et al. "Wind work at the air-sea interface: a modeling study in anticipation of future space missions." Geoscientific Model Development 15, no. 21 (November 7, 2022): 8041–58. http://dx.doi.org/10.5194/gmd-15-8041-2022.

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Abstract. Wind work at the air-sea interface is the transfer of kinetic energy between the ocean and the atmosphere and, as such, is an important part of the ocean-atmosphere coupled system. Wind work is defined as the scalar product of ocean wind stress and surface current, with each of these two variables spanning, in this study, a broad range of spatial and temporal scales, from 10 km to more than 3000 km and hours to months. These characteristics emphasize wind work's multiscale nature. In the absence of appropriate global observations, our study makes use of a new global, coupled ocean-atmosphere simulation, with horizontal grid spacing of 2–5 km for the ocean and 7 km for the atmosphere, analyzed for 12 months. We develop a methodology, both in physical and spectral spaces, to diagnose three different components of wind work that force distinct classes of ocean motions, including high-frequency internal gravity waves, such as near-inertial oscillations, low-frequency currents such as those associated with eddies, and seasonally averaged currents, such as zonal tropical and equatorial jets. The total wind work, integrated globally, has a magnitude close to 5 TW, a value that matches recent estimates. Each of the first two components that force high-frequency and low-frequency currents, accounts for ∼ 28 % of the total wind work and the third one that forces seasonally averaged currents, ∼ 44 %. These three components, when integrated globally, weakly vary with seasons but their spatial distribution over the oceans has strong seasonal and latitudinal variations. In addition, the high-frequency component that forces internal gravity waves, is highly sensitive to the collocation in space and time (at scales of a few hours) of wind stresses and ocean currents. Furthermore, the low-frequency wind work component acts to dampen currents with a size smaller than 250 km and strengthen currents with larger sizes. This emphasizes the need to perform a full kinetic budget involving the wind work and nonlinear advection terms as small and larger-scale low-frequency currents interact through these nonlinear terms. The complex interplay of surface wind stresses and currents revealed by the numerical simulation motivates the need for winds and currents satellite missions to directly observe wind work.

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Wijesekera, H. W., W. J. Teague, D. W. Wang, E. Jarosz, T. G. Jensen, S. U. P. Jinadasa, H. J. S. Fernando, and Z. R. Hallock. "Low-Frequency Currents from Deep Moorings in the Southern Bay of Bengal." Journal of Physical Oceanography 46, no. 10 (October 2016): 3209–38. http://dx.doi.org/10.1175/jpo-d-16-0113.1.

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AbstractHigh-resolution currents and hydrographic fields were measured at six deep-water moorings in the southern Bay of Bengal (BoB) by the Naval Research Laboratory as part of an international effort focused on the dynamics of the Indian Ocean. Currents, temperature, and salinity were sampled over the upper 500 m for 20 months between December 2013 and August 2015. One of the major goals is to understand the space–time scales of the currents and physical processes that contribute to the exchange of water between the BoB and the Arabian Sea. The observations captured Southwest and Northeast Monsoon Currents, seasonally varying large eddies including a cyclonic eddy, the Sri Lanka dome (SLD), and an anticyclonic eddy southeast of the SLD. The observations further showed intraseasonal oscillations with periods of 30–70 days, near-inertial currents, and tides. Monthly averaged velocities commonly exceeded 50 cm s−1 near the surface, and extreme velocities exceeded 150 cm s−1 during the southwest monsoon. Tides were small and dominated by the M2 component with velocities of about 3 cm s−1. The average transport into the BoB over the measurement period was 2 Sv (1 Sv ≡ 106 m3 s−1) but likely exceeded 15 Sv during summer of 2014. This study suggests the water exchange away from coastal boundaries, in the interior of the BoB, may be largely influenced by the location and strength of the two eddies that modify the path of the Southwest Monsoon Current. In addition, there is a pathway below 200 m for transport of water into the BoB throughout the year.

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9

Shevchenko, I. V., P. S. Berloff, D. Guerrero-López, and J. E. Roman. "On low-frequency variability of the midlatitude ocean gyres." Journal of Fluid Mechanics 795 (April 15, 2016): 423–42. http://dx.doi.org/10.1017/jfm.2016.208.

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This paper studies the large-scale low-frequency variability of the wind-driven midlatitude ocean gyres and their western boundary currents, such as the Gulf Stream or Kuroshio, simulated with the eddy-resolving quasi-geostrophic model. We applied empirical orthogonal functions analysis to turbulent flow solutions and statistically extracted robust and significant large-scale decadal variability modes concentrated around the eastward jet extension of the western boundary currents. In order to interpret these statistical modes dynamically, we linearized the governing quasi-geostrophic equations around the time-mean circulation and solved for the corresponding full set of linear eigenmodes with their eigenfrequencies. We then projected the extracted decadal variability on the eigenmodes and found that this variability is a multimodal coherent pattern phenomenon rather than a single mode or a combination of several modes as in the flow regimes preceding developed turbulence.

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10

Laufer, Yocheved, and Michal Elboim. "Effect of Burst Frequency and Duration of Kilohertz-Frequency Alternating Currents and of Low-Frequency Pulsed Currents on Strength of Contraction, Muscle Fatigue, and Perceived Discomfort." Physical Therapy 88, no. 10 (October 1, 2008): 1167–76. http://dx.doi.org/10.2522/ptj.20080001.

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BackgroundLow-frequency pulsed currents (LPCs) and kilohertz-frequency alternating currents (KACs) are used clinically to augment muscle contractions. Treatment effectiveness may be enhanced by selecting stimulation parameters that evoke the strongest contractions with minimal discomfort and fatigue.ObjectiveThe objective of this study was to compare maximally induced strength (force-producing capacity) of contractions, muscle fatigue, and discomfort associated with an LPC and with 3 KACs differing in frequency and duration of burst modulation.DesignThis was a repeated-measures trial, with randomized order of current presentation.SettingThe study was conducted in the physical therapy laboratory at the University of Haifa.SubjectsTwenty-six volunteers without impairments, with a mean age of 27.4 years (SD=5.0, range=21–45), participated.InterventionAll currents were applied in separate sessions to the wrist extensors of each subject. Currents consisted of an LPC with a 50-Hz pulse frequency and 3 KACs with a 2.5-kHz carrier frequency, including the “Russian current” (RC) burst modulated at 50 Hz with 25 cycles per burst and 2 currents burst modulated at 20 or 50 Hz with 10 cycles per burst.MeasurementThe maximal electrically induced isometric force, the force integral of 21 electrically induced consecutive contractions, and the degree of discomfort were recorded.ResultsForce of contraction was not affected by type of current. The LPC was least fatiguing, and the RC was most fatiguing, with the 2 other KACs having an intermediate effect. Degree of discomfort was higher with the KAC modulated at 20 Hz.ConclusionsWhen comfort, strength, and fatigue are considered jointly, the LPC is advantageous. Electrically induced fatigue is affected by the number of cycles per second, rather than the number of bursts per second.

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11

Elgar, Steve, Britt Raubenheimer, David B. Clark, and Melissa Moulton. "Extremely Low Frequency (0.1 to 1.0 mHz) Surf Zone Currents." Geophysical Research Letters 46, no. 3 (February 4, 2019): 1531–36. http://dx.doi.org/10.1029/2018gl081106.

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12

Han, Guoqi. "Low-frequency variability of sea level and currents off Newfoundland." Advances in Space Research 38, no. 10 (January 2006): 2141–61. http://dx.doi.org/10.1016/j.asr.2006.04.011.

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13

Royzen, Feliks, Sylvain Williams, Fernando R. Fernandez, and John A. White. "Balanced synaptic currents underlie low‐frequency oscillations in the subiculum." Hippocampus 29, no. 12 (July 13, 2019): 1178–89. http://dx.doi.org/10.1002/hipo.23131.

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14

Shetye, S. R., S. C. Shenoi, and D. Sundar. "Observed low-frequency currents in the deep mid-Arabian Sea." Deep Sea Research Part A. Oceanographic Research Papers 38, no. 1 (January 1991): 57–65. http://dx.doi.org/10.1016/0198-0149(91)90054-j.

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15

Liu, Zhao, Wang, Huang, and Shi. "Compatibility Issues with Irregular Current Injection Islanding Detection Methods and a Solution." Energies 12, no. 8 (April 17, 2019): 1467. http://dx.doi.org/10.3390/en12081467.

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Islanding detection methods, based on injecting high-/low-frequency currents or negative sequence fundamental frequency currents and observing the resultant responses, are collectively referred to as irregular current injection methods in this paper. In multi-distributed generation (DG) operation, if there is no restriction to the phase of injected irregular currents, the currents at the same frequency may cancel each other out, and then their convergent current may be too small to cause a detectable response, for which reason islanding detection will be severely affected. Accordingly, this paper raises a compatibility issue, which requires the phase difference between any two injected irregular currents to be within a certain interval. In response to this issue, a solution is proposed. According to this solution, the terminal voltage of DG units is referenced to conduct irregular currents injection, and only certain high-frequency currents are used as injected currents. If this solution is adopted by as many manufacturers as possible, the effect and reliability of such methods will be greatly improved.

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Dantas, Lucas Ogura, Amilton Vieira, Aristides Leite Siqueira Junior, Tania Salvini, and João Luiz Durigan. "Poster 140 Comparison Between Kilohertz-Frequency Alternating Currents and Low-Frequency Pulsed Currents on Quadriceps Torque Production and Perceived Discomfort." Archives of Physical Medicine and Rehabilitation 94, no. 10 (October 2013): e61. http://dx.doi.org/10.1016/j.apmr.2013.08.185.

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17

Gaddameedhi, Sravanthy, and P. Srinivas. "A novel fuzzy based controller to reduce circulating currents in parallel interleaved converter connected to the grid." International Journal of Electrical and Computer Engineering (IJECE) 11, no. 2 (April 1, 2021): 1130. http://dx.doi.org/10.11591/ijece.v11i2.pp1130-1142.

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This paper exhibits suppression strategy of low frequency circulating current components for parallel inter-leaved converters. Here inverters are parallelized by magnetically coupled inductors. Traditionally, carrier interleaved technique was used to get lower distorted output voltage, but it gives a higher circulating currents to flow through the Two-VSC‘s. The mutual inductance of the coupled inductors (CI) is utilized for minimizing circulating currents of high frequency components. Nevertheless, CI can‘t have capability to riddle the components generated by low frequency. When these circulating currents extremely increases may leads to CI saturation, elevated switching losses and diminishes the entire performance of system. Here author identified a novel control technique for a grid-connected parallel inter-leaved converter depending on approach of energy shaping control (ECS). This controller diminishes the value of the low frequency components of circulating current (LFCC). The performance of the proposed circuit is evaluated in simulation mode and correlated with the conventional proportional integral control (PIC) and the linear quadratic control (LQC). The Fuzzy controller is also included in this work to enhance the converter performance effectively and to diminish the circulating currents along with the healthy harmonic performance analysis.

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18

Farasat, Madiha, Dushmantha Thalakotuna, Yang Yang, Zhonghao Hu, and Karu Esselle. "Suppression of Common-Mode Resonance in Multiband Base Station Antennas." Sensors 23, no. 6 (March 7, 2023): 2905. http://dx.doi.org/10.3390/s23062905.

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5G demands a significant increment in the number of connected devices. As a result, gNodeBs are constantly pushed to serve more spectrum and smaller sectors. These increased capacity demands are met by using multiband antennas in base stations. One of the key challenges with multiband antennas is the pattern distortions due to the presence of other surrounding antenna element structures. This work provides a novel approach to address the challenge of pattern distortion in the lower frequency band 690–960 MHz due to common-mode (CM) currents in the high- frequency-band antenna element operating in the 1810–2690 MHz band. A common-mode suppression circuit is integrated with the impedance matching network of the high-band antenna element to reduce these common-mode currents. The experimental results verified that the common-mode suppression circuit reduces the common-mode currents at low-band frequencies by moving the common-mode resonance frequency outside the low frequency band, resulting in cleaner low-band patterns meeting pattern specifications.

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19

Berthelier, A., J. C. Cerisier, J. J. Berthelikr, and L. Rnzeau. "Low-frequency magnetic turbulence in the high-latitude topside ionosphere: low-frequency waves or field-aligned currents." Journal of Atmospheric and Terrestrial Physics 53, no. 3-4 (March 1991): 333–41. http://dx.doi.org/10.1016/0021-9169(91)90117-p.

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20

Ward, Alex R., and Warwick G. Oliver. "Comparison of the Hypoalgesic Efficacy of Low-Frequency and Burst-Modulated Kilohertz Frequency Currents." Physical Therapy 87, no. 8 (August 1, 2007): 1056–63. http://dx.doi.org/10.2522/ptj.20060203.

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Background and Purpose A within-subject randomized controlled trial was conducted to compare monophasic pulsed current (PC) with a frequency of 50 Hz and a phase duration of 500 microseconds with burst-modulated alternating current (BMAC) (1-kHz alternating current, burst modulated at a frequency of 50 Hz with a 20% duty cycle) to establish whether there were differences in hypoalgesic efficacy as assessed by cold pain threshold measurements. Subjects Twenty-two young adults who were healthy and drawn from a population of students of La Trobe University volunteered to participate in the study. Nineteen subjects (7 male, 12 female) met the inclusion criteria. Method Each participant experienced monophasic PC and BMAC. Time to cold pain threshold was measured before, during, and after the electrical stimulation intervention. Results Both PC and BMAC currents were effective at elevating the cold pain threshold, although there was no statistically significant difference between the 2 currents during stimulation. Discussion and Conclusion Pulsed current and BMAC appear to be equally effective at elevating the cold pain threshold. Analysis indicated that if any real difference exists, it would only be apparent with large (100) subject numbers. Any differences in hypoalgesic efficacy thus are not likely to be clinically important.

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21

Carandini, M., F. Mechler, C. S. Leonard, and J. A. Movshon. "Spike train encoding by regular-spiking cells of the visual cortex." Journal of Neurophysiology 76, no. 5 (November 1, 1996): 3425–41. http://dx.doi.org/10.1152/jn.1996.76.5.3425.

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1. To study the encoding of input currents into output spike trains by regular-spiking cells, we recorded intracellularly from slices of the guinea pig visual cortex while injecting step, sinusoidal, and broadband noise currents. 2. When measured with sinusoidal currents, the frequency tuning of the spike responses was markedly band-pass. The preferred frequency was between 8 and 30 Hz, and grew with stimulus amplitude and mean intensity. 3. Stimulation with broadband noise currents dramatically enhanced the gain of the spike responses at low and high frequencies, yielding an essentially flat frequency tuning between 0.1 and 130 Hz. 4. The averaged spike responses to sinusoidal currents exhibited two nonlinearities: rectification and spike synchronization. By contrast, no nonlinearity was evident in the averaged responses to broadband noise stimuli. 5. These properties of the spike responses were not present in the membrane potential responses. The latter were roughly linear, and their frequency tuning was low-pass and well fit by a single-compartment passive model of the cell membrane composed of a resistance and a capacitance in parallel (RC circuit). 6. To account for the spike responses, we used a “sandwich model” consisting of a low-pass linear filter (the RC circuit), a rectification nonlinearity, and a high-pass linear filter. The model is described by six parameters and predicts analog firing rates rather than discrete spikes. It provided satisfactory fits to the firing rate responses to steps, sinusoids, and broadband noise currents. 7. The properties of spike encoding are consistent with temporal nonlinearities of the visual responses in V1, such as the dependence of response frequency tuning and latency on stimulus contrast and bandwidth. We speculate that one of the roles of the high-frequency membrane potential fluctuations observed in vivo could be to amplify and linearize the responses to lower, stimulus-related frequencies.

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22

Pomeroy, Andrew William Mackay, Ap Van Dongeren, Ryan Lowe, Jaap Van Thiel de Vries, and Jan Roelvink. "LOW FREQUENCY WAVE RESONANCE IN FRINGING REEF ENVIRONMENTS." Coastal Engineering Proceedings 1, no. 33 (October 25, 2012): 25. http://dx.doi.org/10.9753/icce.v33.currents.25.

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Low frequency wave resonance has been postulated to enhance damage to coral reef protected coastlines during storm events. This paper uses the numerical model XBeach to examine the dynamics that contribute to resonance that have been previously observed on a fringing reef on Guam during tropical storm Man-Yi (Péquignet et al., 2009). The methods to identify resonance in numerical (or field data) are comprehensively reviewed with three indicators of resonance proposed based upon data obtained at two locations in the model domain: 1. The water surface elevation must be highly coherent, 2. The phase difference must (closely) correspond to 0° or 180°, and 3. Amplification of the signal must be observed between the reef crest and the shoreline. XBeach simulations demonstrated that resonance could be reproduced under ‘normal’ wave conditions, but only when bottom friction was minimal and hence values that were atypically low for coral reefs. However, under tropical storm Man-Yi conditions, resonance was reproduced with reasonable bottom friction values. A sensitivity analysis demonstrated that, although the frequency associated with resonance was not affected by the choice of bottom friction coefficients, the magnitude of the amplification was significantly affected. Ongoing research is being undertaken to investigate the resonant response for a wider variety of reef morphologies and incident wave forcing conditions.

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23

Gasperikova, Erika, and H. Frank Morrison. "Mapping of induced polarization using natural fields." GEOPHYSICS 66, no. 1 (January 2001): 137–47. http://dx.doi.org/10.1190/1.1444888.

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The observed electromagnetic response of a finite body is caused by induction and polarization currents in the body and by the distortion of the induction currents in the surrounding medium. At a sufficiently low frequency, there is negligible induction and the measured response is that of the body distorting the background currents just as it would distort a direct current (dc). Because this dc response is not inherently frequency dependent, any observed change in response of the body for frequencies low enough to be in this dc limit must result from frequency‐dependent conductivity. Profiles of low‐frequency natural electric (telluric) fields have spatial anomalies over finite bodies of fixed conductivity that are independent of frequency and have no associated phase anomaly. If the body is polarizable, the electric field profile over the body becomes frequency dependent and phase shifted with respect to a reference field. The technique was tested on data acquired in a standard continuous profiling magnetotelluric (MT) survey over a strong induced polarization (IP) anomaly previously mapped with a conventional pole‐dipole IP survey. The extracted IP response appears in both the apparent resistivity and the normalized electric field profiles.

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24

Samigullin, D. V., E. F. Khaziev, I. V. Kovyazina, E. A. Bukharaeva, and E. E. Nikolsky. "Muscarinic regulation of calcium transient and synaptic transmission in frog neuromuscular junction." Genes & Cells 9, no. 3 (December 15, 2014): 242–47. http://dx.doi.org/10.23868/gc120334.

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In frog neuromuscular junction, muscarine, exogeneous acetylcholine and acetylcholinesterase inhibitor proserine reduced the intensity of calcium-sensitive dye fluorescence (calcium transient) at low frequency of nerve stimulation, suggesting that calcium ions entry into nerve ending was decreased. M2 muscarinic receptor blocker methoctramine prevented the action of muscarine. The amplitude of endplate currents was reduced in presence of muscarine at low frequency nerve stimulation, and atropine abolished this effect. Amplitudes of endplate currents evoked by high frequency stimulation were enhanced in presence of methoctramine, and synaptic depression was less pronounced, probably due to elevated calcium concentration in nerve ending. Thus, activation of presynaptic muscarinic receptors predominantly of M2 subtype reduces the intensity of quantal acetylcholine release in frog neuromuscular synapses that may be associated with decreased level of calcium ions in the nerve ending to provide the modulation of postsynaptic currents amplitude at high frequency firing.

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Garcia, O. E., E. Leer, H. L. Pécseli, and J. K. Trulsen. "Magnetic field-aligned plasma currents in gravitational fields." Annales Geophysicae 33, no. 3 (March 3, 2015): 257–66. http://dx.doi.org/10.5194/angeo-33-257-2015.

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Abstract. Analytical models are presented for currents along vertical magnetic field lines due to slow bulk electron motion in plasmas subject to a gravitational force. It is demonstrated that a general feature of this problem is a singularity in the plasma pressure force that develops at some finite altitude when a plasma that is initially in static equilibrium is set into slow motion. Classical fluid models thus do not allow general steady-state solutions for field-aligned currents. General solutions have to be non-stationary, varying on time scales of many periods of a plasma equivalent to the Brunt–Väisälä frequency. Except for very special choices of parameters, a steady-state solution exists only in an average sense. The conditions at large altitudes turn out to be extremely sensitive to even small changes in parameters at low altitudes. Low frequency fluctuations detected at large altitudes in the polar regions need not be caused by local low frequency instabilities, but merely reflect small fluctuations in conditions at low altitudes.

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Jarzebowicz, Leszek. "Derivation of Motor Mean Phase Currents in PMSM Drives Operating with Low Switching-to-Fundamental Frequency Ratio." Power Electronics and Drives 4, no. 1 (June 1, 2019): 95–102. http://dx.doi.org/10.2478/pead-2019-0003.

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AbstractPulse width modulation (PWM) of inverter output voltage causes the waveforms of motor phase currents to consist of distinctive ripples. In order to provide suitable feedback for the motor current controllers, the mean value must be extracted from the currents’ waveforms in every PWM cycle. A common solution to derive the mean phase currents is to sample their value at the midpoint of a symmetrical PWM cycle. Using an assumption of linear current changes in steady PWM subintervals, this midpoint sample corresponds to the mean current in the PWM cycle. This way no hardware filtering or high-rate current sampling is required. Nevertheless, the assumption of linear current changes has been recently reported as over simplistic in permanent magnet synchronous motor (PMSM) drives operating with low switching-to-fundamental frequency ratio (SFFR). This, in turn, causes substantial errors in the representation of the mean phase currents by the midpoint sample. This paper proposes a solution for deriving mean phase currents in low SFFR PMSM drives, which does not rely on the linear current change assumption. The method is based on sampling the currents at the start point of a PWM cycle and correcting the sampled value using a model-based formula that reproduces the current waveforms. Effectiveness of the method is verified by simulation for an exemplary setup of high-speed PMSM drive. The results show that the proposed method decreases the error of determining the mean phase currents approximately 10 times when compared to the classical midpoint sampling technique.

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27

Black, K., P. Moran, D. Burrage, and G. De'ath. "Association of low-frequency currents and crown-of-thorns starfish outbreaks." Marine Ecology Progress Series 125 (1995): 185–94. http://dx.doi.org/10.3354/meps125185.

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Laanearu, J., and U. Lips. "Observed thermohaline fields and low-frequency currents in the Narva Bay." Proceedings of the Estonian Academy of Sciences. Engineering 9, no. 2 (2003): 91. http://dx.doi.org/10.3176/eng.2003.2.02.

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29

Zika, T., I. C. Gebeshuber, F. Buschbeck, G. Preisinger, and M. Gröschl. "Surface analysis on rolling bearings after exposure to defined electric stress." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 223, no. 5 (March 18, 2009): 787–97. http://dx.doi.org/10.1243/13506501jet538.

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This article gives an overview about classical and frequency converter-induced spurious bearing currents in induction machines and discusses typical damage patterns caused by the current passage. To investigate on the electric damage mechanisms, test bearings are operated in a test rig and exposed to specific (classical low-frequency, and high-frequency) bearing currents. The induced damages to the surfaces are analysed visually and with the help of an atomic force microscope, and compared for the different electric regimes applied. Further, the electrically damaged bearing surfaces are characterized by standard roughness parameters. The surface structure observable on certain test bearings shows good correlation to the structure found with a bearing that had failed in the field under similar electric conditions. One of the investigated electric regimes applying high-frequency currents proved capable of generating fluting patterns - as found in real applications - on the test rig. The experiments also indicate that high-frequency bearing currents, although in total dissipating less energy, are more dangerous to a bearing than continuous current flow. The presented method gives a good starting point for further investigation on electric current damage in bearings, especially regarding high-frequency bearing currents, and on bearing/grease lifetime under specific electric regimes.

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30

Kang, Le, He Zhang, Jiakuan Xia, Meijun Qi, and Yunqi Zhao. "Research on Radial Vibration Model and Low-Frequency Vibration Suppression Method in PMSM by Injecting Multiple Symmetric Harmonic Currents." Actuators 13, no. 11 (November 8, 2024): 448. http://dx.doi.org/10.3390/act13110448.

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Driven by frequency conversion, the windings of a three-phase permanent magnet synchronous motor (PMSM) contain both odd and even harmonic currents. Due to the motor’s pole–slot conductance modulation, the interaction between the magnetic fields generated by these harmonic currents and the permanent magnet field results in harmonic radial vibrations of the motor. This paper analyzes the three-phase currents of the prototype and derives the radial magnetomotive force (MMF) spatiotemporal models for symmetric harmonic currents. By integrating Maxwell’s magnetic force formula and vibration response formula, the radial vibration models for symmetric harmonic currents are developed. The characteristics of vibrations caused by odd and even harmonic currents, as well as positive sequence and negative sequence harmonic currents, are analyzed separately. A cyclic sequence, low-frequency vibration suppression control method incorporating multiple harmonic current injections was designed. Experimental results of this method are compared with those obtained using an ideal sinusoidal current. Except for the second harmonic vibration, all other vibrations are significantly suppressed, with a maximum suppression rate of 92.28%. The total vibration level is reduced by 12.7619 dB, and the average torque is reduced by 0.67% with the total harmonic distortion of the current at 2.89%. The experimental results show that the vibration method in this paper has little influence on the average torque of the motor, the current distortion rate is small, and the vibration suppression effect is good.

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31

Lepidi, S., L. Cafarella, P. Francia, A. Meloni, P. Palangio, and J. J. Schott. "Low frequency geomagnetic field variations at Dome C (Antarctica)." Annales Geophysicae 21, no. 4 (April 30, 2003): 923–32. http://dx.doi.org/10.5194/angeo-21-923-2003.

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Abstract. We conduct an analysis of the geomagnetic field variations recorded at the new Antarctic station Dome C, located very close to the geomagnetic pole, which has been operating for approximately one month during the 1999–2000 campaign. We also perform a comparison with simultaneous measurements at the Italian Antarctic station Terra Nova Bay, in order to investigate the spatial extension of the phenomena observed at very high latitude. Our results show that between the two stations the daily variation is similar and the fluctuations with f ~ 1 mHz are coherent, provided that in both cases the comparison is made between geographically oriented components, suggesting that ionospheric currents related to the geographic position, more than field-aligned currents, are responsible for the lowest frequency variations; conversely, higher frequency (Pc5) fluctuations are substantially decoupled between the two stations. We also found that at Dome C the fluctuation power in the 0.55–6.7 mHz frequency band is well related with the solar wind speed during the whole day and that at Terra Nova Bay the correlation is also high, except around local geomagnetic noon, when the station approaches the polar cusp. These results indicate that the solar wind speed control of the geomagnetic field fluctuation power is very strict in the polar cap and less important close to the polar cusp.Key words. Magnetospheric physics (MHD waves and instabilities; Polar cap phenomena; Solar wind-magnetosphere interactions)

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32

Xiao, Yiping, Hongjian Jiao, Feng Huo, and Zongtao Shen. "Lightning Current Measurement Method Using Rogowski Coil Based on Integral Circuit with Low-Frequency Attenuation Feedback." Sensors 24, no. 15 (August 1, 2024): 4980. http://dx.doi.org/10.3390/s24154980.

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A lightning current measurement method using a Rogowski coil based on an integral circuit with low-frequency attenuation feedback was proposed to address the issue of low-frequency distortion in the measurement of lightning currents on transmission lines using Rogowski coils. Firstly, the causes of low-frequency distortion in lightning current measurements using Rogowski coils were analyzed from the perspective of frequency domains. On this basis, an integration correction optimization circuit with a low-frequency attenuation feedback network was designed to correct the low-frequency distortion. The optimized integration circuit can also reduce the impact of low-frequency noise and the DC bias of the operational amplifier (op-amp) on the integration circuit due to the high low-frequency gain. Additionally, a high-pass filtering and voltage-divided sampling circuit has been added to ensure the normal operation of the integrator and improve the measurement range of the measurement system. Then, according to the relationship between the amplitude–frequency characteristics of the measurement system and the parameters of each component, the appropriate types of components and op-amp were selected to expand the measurement bandwidth. Finally, a simulation verification was conducted, and the simulation results show that this measurement method can effectively expand the lower measurement frequency limit to 20 Hz, correct the low-frequency distortion caused by Rogowski coils measuring lightning currents on transmission lines, and accurately restore the measured lightning current waveform.

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33

Fioranelli, Massimo, Maria Grazia Roccia, Aroonkumar Beesham, Dana Flavin, M. Ghaeni, and Faissal AZIZ. "A model for considering effects of extremely low frequency electromagnetic fields on quail embryonic cells." AIMS Biophysics 9, no. 3 (2022): 198–207. http://dx.doi.org/10.3934/biophy.2022017.

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<abstract> <p>Previous experiments have shown that extremely low frequency electromagnetic fields could cause serious effects on the evolution of cells. We propose a mathematical model which confirms those results. In our model, electromagnetic waves could cause the motions of ions and charges and the emergence of some currents around and in the interior of cells. These currents produce some waves which interact with the DNAs and remove or attach some repressors. Consequently, some genes could be turned on or off, and cells could obtain some properties or lose them. The frequency of the external waves should be close to the frequency of the exchanged waves between the repressors and DNAs or even bigger than them. We test this idea and did some experiments on quail embryonic cells. We connected a sample of these cells to a battery and considered their evolution. We observed that after connecting the battery and the production of electrical current, some rings around the quail embryonic cells emerged. Maybe, these rings are the response of the cells to changes in electromagnetic waves and electrical currents.</p> </abstract>

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34

El-Shahat, Mohammed, Elsayed Tag Eldin, Nourhan A. Mohamed, Ahdab EL-Morshedy, and Mohamed E. Ibrahim. "Measurement of Power Frequency Current including Low- and High-Order Harmonics Using a Rogowski Coil." Sensors 22, no. 11 (June 1, 2022): 4220. http://dx.doi.org/10.3390/s22114220.

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The measurement of a power frequency current including low- and high-order harmonics is of great importance in calibration as well as in testing processes. Therefore, this paper presents the measurement of the power frequency current of light-emitting diode (LED) luminaires. LED luminaires were chosen as their input current includes both low- and high-order harmonics. The measurement process depends on reconstructing an LED luminaire current without using the coil parameters. Hence, the current reconstruction process is designed to be dependent on the measured characteristics of the Rogowski coil itself considering the frequency range at which the measurement process is required. An evaluation of the proposed measurement process was theoretically and experimentally carried out. A theoretical evaluation was carried out using MATALB SIMULINK software. However, the experimental evaluation was performed by building a Rogowski coil to measure the input currents of different LED luminaires having different power ratings of 300 W, 400 W, and 600 W. The currents measured using the Rogowski coil were compared with reference currents measured using a standard measurement technique. The obtained results show the efficacy of the proposed measurement method.

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35

Aliev, Yu M., V. Yu Bychenkov, M. S. Jovanović, and A. A. Frolov. "The kinetic theory of the nonlinear low-frequency response of a collisionless plasma to high-frequency electromagnetic radiation." Journal of Plasma Physics 48, no. 1 (August 1992): 167–76. http://dx.doi.org/10.1017/s0022377800016457.

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A kinetic theory of nonlinear currents, quasi-stationary electric and magnetic fields and the ponderomotive effect of high-frequency electromagnetic radiation on a collisionless plasma is developed. General expressions for nonlinear current densities, fields and ponderomotive forces that are applicable in a broad range of space-time scales, characteristie of low-frequency motion in plasma, are obtained. These expressions are compared with the results of previous papers.

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36

Silinsky, Eugene M. "Low-frequency Neuromuscular Depression Is a Consequence of a Reduction in Nerve Terminal Ca2+ Currents at Mammalian Motor Nerve Endings." Anesthesiology 119, no. 2 (August 1, 2013): 326–34. http://dx.doi.org/10.1097/aln.0b013e31829083d8.

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Abstract Background: The decline in voluntary muscle contraction during low-frequency nerve stimulation is used clinically to assess the type and degree of neuromuscular block. The mechanism underlying this depression is unknown. Methods: Simultaneous electrophysiological measurements of neurotransmitter release and prejunctional Ca2+ currents were made at mouse neuromuscular junctions to evaluate the hypothesis that decreases in nerve terminal Ca2+ currents are responsible for low-frequency depression. Results: Under conditions generally used to measure Ca2+ currents at the neuromuscular junction, increasing the frequency of nerve stimulation briefly from 0.017 to 0.1–1 Hz caused a simultaneous reduction in the release of the neurotransmitter acetylcholine to 52.2 ± 4.4% of control and the Ca2+ current peak to 75.4 ± 2.0% of control (P < 0.001, n = 5 experiments for both measurements, mean ± SEM for all data). In conditions used for train-of-four monitoring (4 stimuli, 2 Hz), neurotransmitter release declined to 42.0 ± 1.0% of control and the Ca2+ current peak declined to 75.8 ± 3.3% of control between the first and fourth stimulus (P < 0.001, n = 7 experiments for both measurements). Depression in acetylcholine release during train-of-four protocols also occurred in the absence of neuromuscular-blocking drugs. Discussion: The results demonstrate that neuromuscular depression during train-of-four monitoring is due to a decline in nerve terminal Ca2+ currents, hence reducing the release of acetylcholine. As similar processes may come into play at higher stimulation frequencies, agents that antagonize the decline in Ca2+ currents could be used to treat conditions in which neuromuscular depression can be debilitating.

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37

Stuchly, M. A., and Weiguo Xi. "Modelling induced currents in biological cells exposed to low-frequency magnetic fields." Physics in Medicine and Biology 39, no. 9 (September 1, 1994): 1319–30. http://dx.doi.org/10.1088/0031-9155/39/9/001.

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38

Matsumoto, Michio, Kazuo Sakai, and Satoshi Takeuchi. "Low Frequency Waves with Azimuthal Currents in a Weakly Magnetized Positive Column." Journal of the Physical Society of Japan 61, no. 3 (March 15, 1992): 844–48. http://dx.doi.org/10.1143/jpsj.61.844.

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39

Schneider, Reinhold S. E., M. Mülleder, P. Zeller, P. Würzinger, G. Reiter, and S. Paul. "Effects of Low Frequency Alternating Currents on the Electro-Slag Remelting Process." BHM Berg- und Hüttenmännische Monatshefte 161, S1 (March 15, 2016): 20–26. http://dx.doi.org/10.1007/s00501-016-0462-x.

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40

DeTracey, B. M., C. L. Tang, and P. C. Smith. "Low-frequency currents at the northern shelf edge of the Grand Banks." Journal of Geophysical Research: Oceans 101, no. C6 (June 15, 1996): 14223–35. http://dx.doi.org/10.1029/96jc00923.

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41

Niple, J. C., J. P. Daigle, L. E. Zaffanella, T. Sullivan, and R. Kavet. "A portable meter for measuring low frequency currents in the human body." Bioelectromagnetics 25, no. 5 (2004): 369–73. http://dx.doi.org/10.1002/bem.20000.

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42

Uchiyama, Yusuke, James C. McWilliams, and Cigdem Akan. "Three‐dimensional transient rip currents: Bathymetric excitation of low‐frequency intrinsic variability." Journal of Geophysical Research: Oceans 122, no. 7 (July 2017): 5826–49. http://dx.doi.org/10.1002/2017jc013005.

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43

Jones, Martyn G., Evan R. Rogers, James P. Harris, Andrew Sullivan, D. Michael Ackermann, Marc Russo, Scott F. Lempka, and Stephen B. McMahon. "Neuromodulation using ultra low frequency current waveform reversibly blocks axonal conduction and chronic pain." Science Translational Medicine 13, no. 608 (August 25, 2021): eabg9890. http://dx.doi.org/10.1126/scitranslmed.abg9890.

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Chronic pain remains a leading cause of disability worldwide, and there is still a clinical reliance on opioids despite the medical side effects associated with their use and societal impacts associated with their abuse. An alternative approach is the use of electrical neuromodulation to produce analgesia. Direct current can block action potential propagation but leads to tissue damage if maintained. We have developed a form of ultra low frequency (ULF) biphasic current and studied its effects. In anesthetized rats, this waveform produced a rapidly developing and completely reversible conduction block in >85% of spinal sensory nerve fibers excited by peripheral stimulation. Sustained ULF currents at lower amplitudes led to a slower onset but reversible conduction block. Similar changes were seen in an animal model of neuropathic pain, where ULF waveforms blocked sensory neuron ectopic activity, known to be an important driver of clinical neuropathic pain. Using a computational model, we showed that prolonged ULF currents could induce accumulation of extracellular potassium, accounting for the slowly developing block observed in rats. Last, we tested the analgesic effects of epidural ULF currents in 20 subjects with chronic leg and back pain. Pain ratings improved by 90% after 2 weeks. One week after explanting the electrodes, pain ratings reverted to 72% of pretreatment screening value. We conclude that epidural spinal ULF neuromodulation represents a promising therapy for treating chronic pain.

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44

Maheeth, P. V. S., P. Srividya Devi, and P. Sirisha. "Artificial Intelligent Technique based Double-Frequency Analysis on a Single-Phase Grid-connected Inverter." E3S Web of Conferences 309 (2021): 01144. http://dx.doi.org/10.1051/e3sconf/202130901144.

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Now a days more power losses can be seen in grid connected inverter. In order to reduce that double frequency in single phase grid inverter with Artificial Intelligent based fuzzy control is implemented. The inverter has two operating units High Frequency Unit (HFU) and Low Frequency Unit (LFU), low frequency reduce switching losses and high frequency suppress the symphonious currents. The fuzzy logic method expected towards deliver high yield, low total symphonious distortion, rapid response. Finally Total Symphonious Distortion (THD) contrasted among fuzzy including Integral controls (PI). The results are validated by using MATLAB/Simulink.

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45

Stewart, Duff C., Walter L. Anderson, Thomas P. Grover, and Victor F. Labson. "Shallow subsurface mapping by electromagnetic sounding in the 300 kHz to 30 MHz range: Model studies and prototype system assessment." GEOPHYSICS 59, no. 8 (August 1994): 1201–10. http://dx.doi.org/10.1190/1.1443678.

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A new instrument designed for frequency‐domain sounding in the depth range 0–10 m uses short coil spacings of 5 m or less and a frequency range of 300 kHz to 30 MHz. In this frequency range, both conduction currents (controlled by electrical conductivity) and displacement currents (controlled by dielectric permittivity) are important. Several surface electromagnetic survey systems commonly used (generally with frequencies less than 60 kHz) are unsuitable for detailed investigation of the upper 5 m of the earth or, as with ground‐penetrating radar, are most effective in relatively resistive environments. Most computer programs written for interpretation of data acquired with the low‐frequency systems neglect displacement currents, and are thus unsuited for accurate high‐frequency modeling and interpretation. New forward and inverse computer programs are described that include displacement currents in layered‐earth models. The computer programs and this new instrument are used to evaluate the effectiveness of shallow high‐frequency soundings based on measurement of the tilt angle and the ellipticity of magnetic fields. Forward model studies indicate that the influence of dielectric permittivity provides the ability to resolve thin layers, especially if the instrument frequency range can be extended to 50 MHz. Field tests of the instrument and the inversion program demonstrate the potential for detailed shallow mapping wherein both the resistivity and the dielectric permittivity of layers are determined. Although data collection and inversion are much slower than for low‐frequency methods, additional information is obtained inasmuch as there usually is a permittivity contrast as well as a resistivity contrast at boundaries between different materials. Determination of dielectric permittivity is particularly important for hazardous waste site characterization because the presence of some contaminants may have little effect on observed resistivity but a large effect on observed permittivity.

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46

Armstrong, John N., and Brian A. MacVicar. "Theta-Frequency Facilitation of AMPA Receptor-Mediated Synaptic Currents in the Principal Cells of the Medial Septum." Journal of Neurophysiology 85, no. 4 (April 1, 2001): 1709–18. http://dx.doi.org/10.1152/jn.2001.85.4.1709.

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Recent evidence suggests that Ca2+-permeable AMPA receptors display rapid, short-lasting current facilitation. In this study, we investigated the properties of AMPA receptor-mediated synaptic currents in medial septal neurons of the rat in an in vitro slice preparation. Immunocytochemistry with a selective antibody to the GluR2 subunit revealed that both choline acetyltransferase-containing and parvalbumin-containing neurons of the medial septum express no detectable GluR2 subunit immunoreactivity. We used whole cell voltage-clamp recordings to measure synaptically evoked AMPA receptor-mediated currents from medial septal neurons following stimulation of midline afferents. The GYKI 52466 (50 μM)- and 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide (NBQX) (20 μM)-sensitive AMPA receptor-mediated component of the synaptic response was isolated by blocking GABAA- and N-methyl-d-aspartate receptor-mediated currents with 30 μM bicuculline and 100 μM 2-amino-5-phosphonovaleric acid, respectively. In some cases, patched cells were filled with Lucifer yellow (0.1%) and imaged using 2-photon laser scanning microscopy. AMPA receptor-mediated currents that were observed in large medial septal neurons (20–30 μm) displayed rectification. These currents were sensitive to external application of philanthotoxin-343 (PhTx-343, 50 μM), a potent, high-affinity antagonist of Ca2+-permeable, GluR2-lacking AMPA receptors. Rectifying AMPA receptor-mediated currents also displayed a rapid increase in amplitude when evoked five times at low frequency such as 6 Hz. In contrast to currents observed in large medial septal neurons, AMPA-receptor mediated currents evoked in the remaining small (8–11 μm) neurons were nonrectifying and displayed rapid synaptic depression when stimulated five times at 6 Hz. The currents evoked in these cells were unaffected by external application of PhTx-343 and were therefore GluR2-containing AMPA receptors. The results of the present study demonstrate that the principal projection neurons of the medial septum contain PhTx-343-sensitive, GluR2-lacking AMPA receptors that display rapid current facilitation when stimulated at low frequencies.

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47

Lamy, L., P. Zarka, B. Cecconi, R. Prangé, W. S. Kurth, G. Hospodarsky, A. Persoon, M. Morooka, J. E. Wahlund, and G. J. Hunt. "The low-frequency source of Saturn’s kilometric radiation." Science 362, no. 6410 (October 4, 2018): eaat2027. http://dx.doi.org/10.1126/science.aat2027.

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Understanding how auroral radio emissions are produced by magnetized bodies requires in situ measurements within their source region. Saturn’s kilometric radiation (SKR) has been widely used as a remote proxy of Saturn’s magnetosphere. We present wave and plasma measurements from the Cassini spacecraft during its ring-grazing high-inclination orbits, which passed three times through the high-altitude SKR emission region. Northern dawn-side, narrow-banded radio sources were encountered at frequencies of 10 to 20 kilohertz, within regions of upward currents mapping to the ultraviolet auroral oval. The kilometric waves were produced on the extraordinary mode by the cyclotron maser instability from 6– to 12–kilo–electron volt electron beams and radiated quasi-perpendicularly to the auroral magnetic field lines. The SKR low-frequency sources appear to be strongly controlled by time-variable magnetospheric electron densities.

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48

Luo, Tuo, Pinqun Jiang, Guoxian Huang, and Dong Lin. "Design and simulation of low-ripple dual active bridge DC-DC converter." Journal of Physics: Conference Series 2803, no. 1 (July 1, 2024): 012058. http://dx.doi.org/10.1088/1742-6596/2803/1/012058.

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Abstract In addressing the issue of excessive high-frequency current ripple at the output port caused by high-frequency switching in traditional dual active bridge DC-DC converters, a low-ripple dual active bridge DC-DC converter was designed by replacing its switching devices with a half-bridge submodule. This converter constructs a decoupling loop for alternating and direct current components on the bridge arms, allowing the alternating components to form a loop between the bridge arms without entering the direct current port, thereby eliminating high-frequency current ripple at the direct current output port. Consequently, the filtering capacitors parallel to the direct current port can be omitted, while also suppressing direct current fault currents. Due to the inherent capacitance structure of the submodule switching devices, soft-switching characteristics are preserved, and conversion efficiency is not compromised. Simulation results based on a MATLAB/Simulink model of 750 V and 10 kW demonstrate that the ripple of this converter is less than 0.07%, a 90% reduction compared to traditional converters, and effectively suppresses fault currents, thereby enhancing system safety.

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49

Grishkov, V. E., and S. A. Uryupin. "Generation of low-frequency nonlinear currents in plasma by an ultrashort pulse of high-frequency radiation." Plasma Physics Reports 41, no. 7 (July 2015): 553–61. http://dx.doi.org/10.1134/s1063780x15070028.

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50

Novikov, I. L., D. I. Vol’khin, and A. G. Vostretsov. "Cryogenic bipolar low noise dc amplifier for low frequency applications." Radiotehnika i èlektronika 69, no. 1 (July 17, 2024): 88–98. http://dx.doi.org/10.31857/s0033849424010078.

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A low-noise bipolar differential dc amplifier was studied at temperatures of 300 and 77 K. It was shown that to ensure the best amplifier performance in terms of noise figure when the operating temperature decreases from 300 to 77 K, it is advisable to use the transistor in the mode of low currents not exceeding 2 mA. It has been established that lowering the operating temperature to 77 K leads to a decrease in the input resistance of the amplifier from a value of several kiloohms to 100 Ohms, the dynamic range increases from 80 to 85 dB, and the harmonic coefficient increases from 0.09% to 1%. In addition, lowering the operating temperature to 77 K has a significant effect on the noise properties of the amplifier: the spectral density of voltage noise decreases from 1 to 0.4 nV/Hz1/2, the spectral density of current noise increases from 2.5 to 9 pA/Hz1/2, while also The threshold frequencies of 1/f noise increase: for voltage from (0.1...10) to 20 Hz and for current from (10...100) to 1000 Hz. The possibility of using an amplifier for low-temperature measurements of samples with low input resistance is substantiated.

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