RF Current Research Articles

Excitation of the Gyrotropic Mode in a Magnetic Vortex by Time-Varying Strain.

We demonstrate the excitation of the gyrotropic mode in a magnetostrictive vortex by time-varying strain. The vortex dynamics is driven by a time-varying voltage applied to the piezoelectric substrate and detected electrically by spin rectification at subthreshold values of rf current. When the frequency of the time-varying strain matches the gyrotropic frequency at a given in-plane magnetic field, the strain-induced in-plane magnetic anisotropy leads to a resonant excitation of the gyration dynamics in the magnetic vortex. We show that nonlinear gyrotropic dynamics can be excited already for moderate amplitudes of the time-varying strain.

Contact and bulk rectification effects in ferromagnetic resonance experiments

We present an experimental study of the spin rectification effects produced by ferromagnetic resonance in a NiFe wire. A system of four independent nonmagnetic contact probes was used to supply both rf and dc currents to the wire and to measure dc voltages at different locations in the wire. The rf current drives the ferromagnet’s magnetization into resonance and produces a dc photovoltage which results from the rectification of rf current in the ferromagnet with oscillating magnetization. Our 4-probe system provided a means to detect the photovoltage and separate contributions from the ferromagnet/nonmagnet contacts and the bulk of the ferromagnet. The contact photovoltage was found to increase approximately linearly with the dc bias applied to the wire. In contrast, the bulk contribution was found to be almost independent of the dc bias. By tuning properties of individual contact probes we were able to change the magnitude of the contact photovoltage and even reverse its sign. Our results highlight the different contributions to photovoltage and the importance of contact properties/nonlinearities for rectification effects in spintronic devices.

Effects of RF Electric Currents on Hair Follicle Growth and Differentiation: A Possible Treatment for Alopecia.

Androgenic alopecia (AGA) is the most common type of alopecia and its treatments involve drugs that have various adverse effects and are not completely effective. Radiofrequency-based therapies (RF) are an alternative for AGA treatment. Although there is increasing clinical evidence of the effectiveness of RF for alopecia, its effects at the tissue and cellular level have not been studied in detail. The objective of this study was to analyze ex vivo the potential effect of RF currents used in capacitive resistive electrical transfer (CRET) therapy on AGA. Hair follicles (HFs) were donated by patients with AGA and treated with CRET. AGA-HFs were exposed in vitro to intermittent 448 kHz electric current in subthermal conditions. Cell proliferation (Ki67), apoptosis (TUNEL assay), differentiation (β-catenin), integrity (collagen and MMP9), thickness of the epidermis surrounding HF, proportion of bulge cells and melanoblasts in AGA-HF were analyzed by immunohistochemistry. CRET increased proliferation and decreased death of different populations of AGA-HF cells. In addition, the melanoblasts increased in bulge and the epidermis surrounding the hair follicle thickened. These results support the effectiveness of RF-based therapies for the treatment of alopecia. However, clinical trials are necessary to know the true effectiveness of CRET therapy and other RF therapies for AGA treatment.

Flexible multi-purpose integrated RF/shim coil array for MRI and localized B0 shimming.

To develop a flexible, lightweight, and multi-purpose integrated parallel reception, excitation, and shimming (iPRES) coil array that can conform to the subject's anatomy and perform MR imaging and localized B0 shimming in different anatomical regions with a high SNR, shimming performance, ease of positioning, and subject comfort. A four-channel flexible iPRES coil array was constructed by enabling RF and direct currents to flow on the same flexible coil elements for imaging and shimming, respectively. Shimming experiments were performed with the coil array wrapped around the knee or neck of healthy subjects to demonstrate its high shimming performance and versatility. Additionally, its SNR and shimming performance in the knee were compared to those obtained with the coil array wrapped around a larger rigid tube designed to fit most knee sizes. Shimming with the coil array wrapped around the knee or neck resulted in an average reduction in B0 RMSE of 50.1% and 40.5% relative to first-order and second-order spherical harmonic shimming, respectively, and substantially reduced distortions in DWI images. In contrast, shimming the knee with the coil array wrapped around the rigid tube only provided a 29.6% reduction in B0 RMSE, whereas the SNR was reduced by 58.7%. The flexible iPRES coil array can conform to different anatomical regions and perform imaging and localized B0 shimming with a higher SNR, shimming performance, ease of positioning, and comfort compared to a rigid iPRES coil array, which should be valuable for many applications throughout the human body.

Implant-friendly MRI of deep brain stimulation electrodes at 7 T.

The purpose of this study is to present a strategy to calculate the implant-friendly (IF) excitation modes-which mitigate the RF heating at the contacts of deep brain stimulation (DBS) electrodes-of multichannel RF coils at 7 T. An induced RF current on an implantable electrode generates a scattered magnetic field whose left-handed circularly polarizing component ( ) is approximated using a -mapping technique and subsequently used as a gauge for the electrode's induced current. Using this approach, the relative induced currents resulting from each channel of a multichannel RF coil on the DBS electrode were calculated. The IF modes of the corresponding multichannel coil were determined by calculating the null space of the relative induced currents. The proposed strategy was tested and validated for unilateral and bilateral commercial DBS electrodes (directional lead; Infinity DBS system, Abbott Laboratories) placed inside a uniform phantom by performing heating and imaging studies on a 7T MRI scanner using a 16-channel transceive RF coil. Neither individual IF modes nor shim solutions obtained from IF modes induced significant temperature increase when used for a high-power turbo spin-echo sequence. In contrast, shimming with the scanner's toolbox (i.e., based on per-channel fields) resulted in a more than 2°C temperature increase for the same amount of input power. A strategy for calculating the IF modes of a multichannel RF coil is presented. This strategy was validated using a 16-channel RF coil at 7 T for unilateral and bilateral commercial DBS electrodes inside a uniform phantom.

A Broadband Multifunctional Reconfigurable Polarization Conversion Metasurface

In this work, a reflective polarization conversion metasurface (PCM) with symmetrical L-shaped patches is proposed which enables to switch between different polarization modes by PIN diodes, i.e., linear-to-linear (LTL) cross-polarization and linear-to-circular (LTC) polarization. Because of multimodes activated in the structure, the PCM shows an ultrawide bandwidth both for LTL and LTC polarization conversion. A microstrip line-based DC biasing network composed of radial stubs is introduced to isolate RF currents, which can resolve problems raised by RF lumped choke inductors in the ultrawide bandwidth. A prototype with 15 × 15 units is fabricated. The simulated and measured results show that when the PIN diodes are forward biased, the PCM achieves LTC polarization conversion in the range of 5.96–15.34 GHz (relative bandwidth of 88.4%) with the axial ratio (AR) less than 3 dB; when the PIN diodes are reverse biased, the PCM achieves LTL polarization conversion in the range of 6.05–14.76 GHz (relative bandwidth of 83.75%) with the polarization conversion ratio (PCR) higher than 90%. The proposed PCM is expected to be potentially applied to a broad scanning range array, intelligent reflecting surfaces (IRS), and remote sensing.

Local impedance changes are a suitable real time surrogate for lesion formation in RF-ablation

Abstract Funding Acknowledgements Type of funding sources: None. Background Radiofrequency current remains one of the most important techniques for catheter ablation. Creating durable lesions is key for sufficient and safe procedures. Several possibilities were tested for estimating the progress of lesion formation. For instance, force-time-integral, ablation index and lesion size index are used to assess quality of RF-application and, therefore, lesion size and durability. Nevertheless, recovered conduction after acute conduction block remains an issue in RF-ablation. The aim of this study was to evaluate local impedance (LI) changes as real time surrogate for lesion formation. Methods RF-lesions were created using an ex vivo porcine cardiac model and a force and local impedance sensing catheter. The experimental setup consisted of a saline-filled container, a dispersive electrode, a heated thermostat and a circulation pump to imitate in vivo conditions. Global impedance was kept at 120 Ohm as well as the temperature at 37°C. RF-lesions were created using identic values of RF duration and contact force. RF power (20W, 30W, 40W, 50W) and level of electrode-tissue-coupling were also systematically varied between minor and full coupling. In minor ETC-level, only the distal end of the catheter is in contact with the tissue. In full ETC-level, the whole catheter tip is in contact with the tissue. All parameters (power, temperature, global and local impedance, contact force, ETC, lesion size) were measured constantly during application of RF-current, enabling real-time correlation of RF parameters and lesion size. In case of an audible steam pop, RF application was stopped. Results Including a total of 8654 measurements into the analysis, maximum diameter and depth were 9.51 ± 1.91 mm and 7.29 ± 2.50 mm in average. Local impedance correlated well with lesion depth (r= 0,78, p<0,001), as well as lesion diameter (r=0,652, p<0,001, Figure 1). After significant declines of LI at the beginning of RF-application, it slowly approximates a minimum. Lesion size on the other hand, rises exponentially in first seconds and gets closer to a maximum after more than 25 seconds. This relationship is illustrated in Figure 2. With decreasing lesion growth at the end of RF-application, LI changes decrease to low level (Figure 3). Conclusion Lesion formation in RF-ablation is not linear during application of RF current. Local impedance changes seem to be a suitable real-time surrogate for assessing changes in lesion size during ablation.

PO-02-076 AN INVESTIGATION OF LESION EFFICACY AND SAFETY WITH THE TACTIFLEX™ SE ABLATION CATHETER

Treatment of cardiac arrhythmias by the creation of myocardial lesions utilizing RF current is well established as an effective mode of therapy in the clinical electrophysiology laboratory. Efficacy, however, should be evaluated in concert with safety considerations, as passive resistance in the cardiac tissue creates heating that can lead to adverse events (e.g., steam pops). A bench top bovine tissue model allows for comparative testing of RF ablation with the TactiFlex™ SE Ablation Catheter (test device) and a commercially available solid-tip RF ablation catheter with uniform irrigation profile (control device), analyzed with respect to both efficacy and safety. To generate comparative statistics for lesion dimension (maximum width and depth) and steam pop likelihood for the TactiFlex™ SE and control RF catheter designs. In this bench ablation model, recently harvested bovine ventricles were sectioned and placed in a body-temperature saline solution (∼37oC). A catheter in a holding fixture was placed in contact with the tissue at a predefined contact force using an independent force gauge. RF energy was applied to the tissue; lesions (N=288 trials) were created at three different power levels (30W at 30s or 50s, 40W at 12s or 20s, 50W at 6s and 10s), steam pop occurrences were noted. Applied contact force levels were fixed at either 5g or 20g. After ablation, the tissue was stained with 1% Triphenyltetrazolium chloride (TTC). Lesions were measured with respect to maximum width and depth. A linear regression model was applied for lesion width and depth vs. catheter design, power, duration, contact force and orientation. The trials did not result in significantly different widths between catheter designs (p = 0.137); refer to Figure 1 for dimensions vs. RF power and duration. Trials with the TactiFlex™ SE yielded shallower lesions (p=0.018) compared to the control device, but with a regression bias of only 0.2mm. Logistic regression demonstrated that steam pops were significantly less likely with the TactiFlex™ SE (p=0.002). Steam pops occurred in only 1.4% of trials with the TactiFlex™ SE Ablation Catheter (2/144 trials) versus 9.7% of trials with the control catheter design (14/144 trials). RF lesions can be created with the TactiFlex™ SE Ablation Catheter that are clinically similar in size to those created with the control device, with a significant reduction in steam pop likelihood.

PO-03-066 LOCAL IMPEDANCE CHANGES ARE A SUITABLE REAL TIME SURROGATE FOR LESION FORMATION IN RF-ABLATION

Radiofrequency current remains one of the most important techniques for catheter ablation. Creating durable lesions is key for sufficient and safe procedures. Several possibilities were tested for estimating the progress of lesion formation. For instance, force-time-integral, ablation index and lesion size index are used to assess quality of RF-application and, therefore, lesion size and durability. Nevertheless, recovered conduction after acute conduction block remains an issue in RF-ablation. The aim of this study was to evaluate local impedance (LI) changes as real time surrogate for lesion formation. RF-lesions were created using an ex vivo porcine cardiac model and a contact force and LI sensing catheter. The experimental setup consisted of a saline-filled container, a dispersive electrode, a heated thermostat and a circulation pump to imitate in vivo conditions. Global impedance was kept at 120 Ohm as well as the temperature at 37°C. RF-lesions were created using identic values of RF duration and contact force. RF power (20W, 30W, 40W, 50W) and level of electrode-tissue-coupling were also systematically varied between minor and full coupling. All parameters (power, temperature, global and local impedance, contact force, ETC, lesion size) were measured constantly during 60 seconds of RF-application, enabling real-time correlation of RF parameters and lesion size. In case of an audible steam pop, RF application was stopped. Including a total of 8654 measurements into the analysis, maximum diameter and depth were 9.51 ± 1.91 mm and 7.29 ± 2.50 mm in average. LI correlated well with lesion depth (r= 0,78, p<0,001), as well as lesion diameter (r=0,652, p<0,001). After significant declines of LI at the beginning of RF-application, it slowly approximates a minimum. Lesion size on the other hand, rises exponentially in first seconds and gets closer to a maximum after more than 25 seconds. With decreasing lesion growth at the end of RF-application, LI changes decrease to low level (Figure 1). Lesion formation in RF-ablation is not linear during application of RF current. Local impedance changes seem to be a suitable real-time surrogate for assessing changes in lesion size during ablation.

Improvement of the magnon-magnon coupling strength in Y3Fe5O12/Py heterostructures

Magnon-quasiparticle couplings perform magnon information transferences and transports, thus controlling the coupling strengths is significant for novel information function devices. Here, we report the modulation of the magnon-magnon (M−M) coupling strength in Y3Fe5O12/permalloy (YIG/Py) heterostructures via ferromagnetic resonance (FMR) technique. The anti-crossing gap gc enhances 80 Hz by changing the radio frequency (rf) microwave power, which could be ascribed to the enhancement of the dipolar interaction and spin pumping effect. Furthermore, the gc decreases with the increasing angle θ between external magnetic field and rf current due to the increase of magnon relaxation. Moreover, the FMR linewidths change with increasing angle θ due to the magnetic anisotropy parameters and the two-magnon relaxation mechanism induced by the more oblique external field.

2D simulations of inductive RF heating in the drivers of the SPIDER device

This paper presents the basic physical and numerical principles of a fluid model of the negative ions source. The model gives self-consistent two-dimensional description of the source, including the neutral gas flow, plasma chemistry, RF coupling in the source driver and plasma transport through the magnetic filter. The different particle species (electrons, the three types of the positive ions: H+, H2+, H3+, negative ions H− and the neutral species: hydrogen atoms H and molecules H2) are described by separate continuity equations and the electron temperature is governed by the electron energy balance equation. The particle fluxes are found from momentum equations neglecting the inertia terms (drift-diffusion approximation). The electrostatic coupling between electrons and ions is described by the Poisson equation. The paper focuses on details of the RF model and on the initial code developments to simulate the currents in the source induced by the RF currents flowing in the feeding coils. In our approach, the RF electrical field is split in a plasma part plus another one in vacuum, E = Ep + EV, which simplifies the boundary conditions for Ep while EV is obtained from a theoretical formulation for the field generated by a current loop, which results in a fast and flexible numerical algorithm providing converged solution for the RF field after a few iterations, even for the cases with high conductivity of the plasma. The numerical method is based on finite volume approximation and 9-point discretization is used to account on anisotropy due to magnetic field. The semi implicit numerical solver allows for large time steps (>1000× explicit time step) producing steady-state solution in a reasonable time (few hours for a typical mesh). The RF model has been successfully coupled to the fluid equations of the source and self-consistent solutions are analyzed in order to see the influence of the driver parameters and RF model assumptions (e.g. stochastic conductivity, induced magnetic field) on the heating efficiency and the plasma dynamics. It has been found that without magnetic field the plasma dynamics in the SPIDER source is almost independent on the details of the RF coupling model.

On the Effectiveness of SPIDER RF System Improvements

Source for the production of ions of deuterium extracted from a radio frequency plasma (SPIDER), the full-scale prototype of the ion source of the ITER heating neutral beam (HNB) injector, started the operation in June 2018. During the first experimental phase, some issues concerned its novel and complex power supply system. Dedicated analyses and studies, carried out to understand and address them, resulted in beam source and plant modifications to be implemented during the SPIDER major shutdown, started in late 2021. To assess the validity of the conceived countermeasures, reducing the risks of introducing additional issues, partial modifications, or mitigating actions were adopted in SPIDER in 2020, as an intermediate step to confirm each intervention with experimental evidence. This article deals mainly with two problems: the stray RF currents, flowing on plant components not intended for that purpose and the mutual interaction of the oscillators supplying the RF driven plasma source. A modification of the output stage of the oscillators allowed the reduction of the stray currents to at least 25% of the original value, while the RF circuits layout improvement resulted in the reduction of the mutual inductance of the nearby circuits to 25% of the original value. The introduced improvements and the obtained experimental results are presented and discussed.

Injection locking of spin torque nano oscillators using surface acoustic waves

Conventional methods use RF currents or magnetic fields for injection locking the Spin Torque Nano Oscillators (STNO) devices. In this paper, we demonstrate the injection locking of STNO devices using the Surface Acoustic Waves (SAW). The SAW interacts with the free layer of the STNO devices through magneto elastic coupling. This interaction produces some effective magnetic field, which we show, can be used for injection locking of the STNO device. We have studied the dynamics of the injection locking process and how it depends upon the characteristics of the driving SAW signal in great details. This is done through macrospin as well as micromagnetic simulations. Our results suggest that SAW can be very good candidates for injection locking of the STNO devices with a locking range of 50 MHz and locking time of 10 ns for a strain of 100 ppm. This roughly corresponds to the requirement of RF current of amplitude 0.05 mA or field of amplitude 5 Oe, if we use the conventional methods. To explain our simulation results, we use the universal auto oscillator model. The amplitude of the locking signal depends strongly upon the power of the oscillations in case of SAW. We have extended the universal auto oscillator model to consider this effect and explain our results.

Limitations of Baseline Impedance, Impedance Drop and Current for Radiofrequency Catheter Ablation Monitoring: Insights from In silico Modeling.

Background: Baseline impedance, radiofrequency current, and impedance drop during radiofrequency catheter ablation are thought to predict effective lesion formation. However, quantifying the contributions of local versus remote impedances provides insights into the limitations of indices using those parameters. Methods: An in silico model of left atrial radiofrequency catheter ablation was used based on human thoracic measurements and solved for (1) initial impedance (Z), (2) percentage of radiofrequency power delivered to the myocardium and blood (3) total radiofrequency current, (4) impedance drop during heating, and (5) lesion size after a 25 W–30 s ablation. Remote impedance was modeled by varying the mixing ratio between skeletal muscle and fat. Local impedance was modeled by varying insertion depth of the electrode (ID). Results: Increasing the remote impedance led to increased baseline impedance, lower system current delivery, and reduced lesion size. For ID = 0.5 mm, Z ranged from 115 to 132 Ω when fat percentage varied from 20 to 80%, resulting in a decrease in the RF current from 472 to 347 mA and a slight decrease in lesion size from 5.6 to 5.1 mm in depth, and from 9.2 to 8.0 mm in maximum width. In contrast, increasing the local impedance led to lower system current but larger lesions. For a 50% fat–muscle mixture, Z ranged from 118 to 138 Ω when ID varied from 0.3 to 1.9 mm, resulting in a decrease in the RF current from 463 to 443 mA and an increase in lesion size, from 5.2 up to 7.5 mm in depth, and from 8.4 up to 11.6 mm in maximum width. In cases of nearly identical Z but different contributions of local and remote impedance, markedly different lesions sizes were observed despite only small differences in RF current. Impedance drop better predicted lesion size (R2 > 0.93) than RF current (R2 < 0.1). Conclusions: Identical baseline impedances and observed RF currents can lead to markedly different lesion sizes with different relative contributions of local and remote impedances to the electrical circuit. These results provide mechanistic insights into the advantage of measuring local impedance and identifies potential limitations of indices incorporating baseline impedance or current to predict lesion quality.

The PSR effect of matching network in 8/100 MHz geometrically symmetrical capacitively coupled Ar plasma

The high-order harmonics caused by the self-excitation of nonlinear plasma series resonance (PSR) in a geometrically symmetric (8 + 100) MHz capacitively coupled argon plasma are studied by using a nonlinear global model. The voltage waveforms and current waveforms measured by oscilloscope between the two electrodes are used to observe the harmonics. The voltage waveforms are used as input parameters for the nonlinear global model to simulate harmonics of the sheath charges of low-frequency electrode, bias voltage, and plasma RF current. These discharged parameters considering coupling effect between these two frequencies and without considering coupling effect are compared in (8 + 100) MHz capacitively coupled plasma with the increasing low-frequency powers at a pressure of 30 mTorr. These results indicate that the theoretical discharge behavior without considering the coupling effect has big difference from the real experiment. The PSR effect of the matching network plays an important role in modulating the plasma homogeneity. Therefore, how to design a suitable matching network to enhance the PSR effect is more meaningful for the nonlinear dynamics of plasma.

Langmuir probe without RF compensation

Langmuir probes with RF compensation are used for measurements of electron concentration, electron temperature and the DC value of plasma potential in RF discharges. In order to obtain all the RF components of plasma potential, simple probes without RF compensation are used. However, it has been believed that these uncompensated probes can not be used for determination of the DC value of plasma potential and of electron concentration and temperature, since their VA characteristics is distorted by the RF current. Consequently, the evaluation of data measured with uncompensated probes was not possible without additional measurement with a RF compensated Langmuir probe. This contribution analyzes the possibility to use uncompensated probes not only for measurement of RF components of plasma potential, but also for measurement of the DC component of plasma potential, electron concentration and electron temperature.

An iPRES-W Coil Array for Simultaneous Imaging and Wireless Localized B0 Shimming of the Cervical Spinal Cord.

To develop a wireless integrated parallel reception, excitation, and shimming (iPRES-W) coil array for simultaneous imaging and wireless localized B0 shimming, and to demonstrate its ability to correct for distortions in DTI of the spinal cord in vivo. A 4-channel coil array was modified to allow an RF current at the Larmor frequency and a direct current to flow on each coil element, enabling imaging and localized B0 shimming, respectively. One coil element was further modified to allow additional RF currents within a wireless communication band to flow on it to wirelessly control the direct currents for shimming, which were supplied from a battery pack within the scanner bore. The RF signals for imaging were transferred via conventional wired connections. Experiments were conducted to evaluate the RF, B0 shimming, and wireless performance of this coil design. The coil modifications did not degrade the SNR. Wireless localized B0 shimming with the iPRES-W coil array substantially reduced the B0 RMSE (-57.5% on average) and DTI distortions in the spinal cord. The antenna radiation efficiency, antenna gain pattern, and battery power consumption of an iPRES-W coil measured in an anechoic chamber were minimally impacted by the introduction of a saline phantom representing tissue. The iPRES-W coil array can perform imaging and wireless localized B0 shimming of the spinal cord with no SNR degradation, with minimal change in wireless performance and without any scanner modifications or additional antenna systems within the scanner bore.

Optically detected spin–orbit torque ferromagnetic resonance in an in-plane magnetized ellipse

Time-resolved scanning Kerr microscopy has been used to perform optically detected, phase-resolved spin–orbit torque ferromagnetic resonance (SOT-FMR) measurements on a microscale CoFeB ellipse at the center of a Pt Hall cross subject to RF and DC current. Time-resolved polar Kerr images revealed localized dynamics with large amplitude at the center and weaker amplitude at the edges. Therefore, field swept SOT-FMR spectra were acquired from the so-called center mode to probe the SOTs active at the center of the ellipse, thus minimizing non-uniform edge contributions. When the magnetic field was applied at 30° from the hard axis of the ellipse and a DC current was applied, a marked asymmetry was observed in the amplitude and linewidth of the FMR peaks as the applied field was reversed. Both absorptive and dispersive parts of the spectra were in good agreement with a macrospin calculation. The damping parameter (α) and the Slonczewski torque parameter were determined to be 0.025 and (6.75 ± 0.75) × 10−7 Oe A−1 cm2, respectively. The hard axis SOT-FMR linewidth was found to be almost independent of the DC current value, suggesting that the SOT has a minimal influence in the hard axis configuration and that thermal effects were insignificant. This study paves the way for spatially resolved measurements of SOT probed using localized modes of microscale devices that go beyond the spatially averaged capability of electrical measurement techniques.

Suppression of nonlinear standing wave excitation via the electrical asymmetry effect

The electrical asymmetry effect (EAE) enables separate control of the ion flux and the mean ion energy in capacitively coupled plasmas (CCP). While a variety of plasma processing applications benefit from this, large-area, very-high-frequency CCPs still suffer from lateral nonuniformities caused by electromagnetic standing wave effects (SWE). Many of such plasma sources are geometrically asymmetric and are operated at low pressure so that high frequency nonlinear plasma series resonance (PSR) oscillations of the RF current are self-excited. These PSR oscillations lead to the presence of short wavelength electromagnetic waves and a more pronounced SWE. In this work, we investigate the influence of the EAE on the nonlinear standing wave excitation in a geometrically asymmetric, low pressure capacitively coupled argon plasma driven by two consecutive harmonics (30 MHz and 60 MHz) with an adjustable phase shift, θ. We use a hairpin probe to determine the radial distribution of the electron density in combination with a high-frequency B-dot probe to measure the radial distribution of the harmonic magnetic field, which in turn is used to calculate the harmonic current density based on Ampere’s law. Our experimental results show that the asymmetry of the discharge can be reduced electrically via the EAE. In this way the self-excitation of high frequency PSR oscillations can be attenuated. By tuning θ, it is, therefore, possible to switch on and off the nonlinear standing wave excitation caused by the PSR and, accordingly, the plasma uniformity can be optimized.

Effects of the signal modulation on the response of human fibroblasts to in vitro stimulation with subthermal RF currents

ABSTRACT Capacitive-Resistive Electric Transfer (CRET) thermotherapies aim at tissue repair and regeneration through non-invasive application of RF currents. We have reported that the cellular response to subthermal CRET currents is non-linearly dependent on the signal frequency, and that in vitro exposure to a 448-kHz CRET signal promotes ADSC proliferation, as well as collagen and glycosaminoglycan synthesis in prechondrocytic cells. The present work investigates the response of neonatal fibroblasts to subthermal exposure (100 µA/mm2) to two CRET signals: a 448-kHz, non-modulated sinusoidal wave vs. a 20-kHz amplitude-modulation of the 448-kHz carrier. To that end, cell proliferation and expression of the biomarkers Hsp47, Hsp27 and decorin were assessed by cell count, PCNA and Western blotting. The results revealed that while both signals significantly and equivalently increased early (4 h) expression of Hsp47, the modulated signal was more efficient in inducing Hsp27 and decorin overexpression and promoting cell proliferation. These data indicate that the cellular response is dependent on the RF signal modulation and suggest that the therapeutic effects of CRET could be mediated by promotion of fibroblastic proliferation and overexpression of biomarkers that are essential in skin regeneration.