Direct Measurement Of Electric Field Research Articles

Abstract B032: Designing arrays for the mouse head to facilitate in vivo studies of Tumor Treating Fields (TTFields) treatment of glioblastoma

Abstract Background: Tumor Treating Fields (TTFields) therapy is a noninvasive, anticancer treatment delivered by two pairs of arrays placed on the skin surrounding the tumor location. Based on efficacy and safety data from phase 3 global clinical studies, TTFields therapy is FDA-approved and CE marked for treatment of glioblastoma (GBM), the most common malignant brain tumor. In vivo studies of TTFields in GBM models, which are mostly based on mice, are complicated by the relatively small size of the mouse head and corresponding limited surface area to apply the arrays. This challenge has thus far limited in vivo research on TTFields treatment in GBM. Materials and Methods: To identify a method for efficient delivery of TTFields to the mouse brain, we examined the ability of different array layouts to accommodate the geometries of the mouse head while minimally impacting head movement, taking into account that it may not be feasible to place two pairs of arrays on the head. The properties of different adhesive tapes, specifically their ability to attach to the skin, was also investigated. Finally, the ability of array layouts to deliver therapeutic intensities to the desired region was validated using simulations and direct electric field measurements. Results: Assessments showed an optimal layout consisted of arrays such that one of the pair was on the mouse head, and the other on the mouse torso; and the arrays for placement on the head divided into two smaller disks, A thin, transparent adhesive tape was identified that allowed the arrays to be securely attached to the skin, but was easily removed without leaving residues. Validation studies using simulations demonstrated that the array layout met the minimum treatment requirements (field intensity ≥1 V/cm RMS; current ≥50 mA), and facilitated TTFields usage for ≥75% of each day. Conclusions: These data show that TTFields treatment can be effectively delivered to the heads of mice by utilizing carefully designed arrays. Our newly developed mouse head arrays are a flexible construct, that adheres strongly to the skin, and enables efficient electric field delivery to the mouse brain. These improvements in the delivery of TTFields treatment to mice will facilitate research of TTFields as a therapy for GBM. Citation Format: Sewar Zbidat, Roni Blatt, Mariell Sellevoll, Martin Gabay, Inbar Schlachet, Shay Cahal, Shiri Davidi, Itai Tzchori, Amal El-Mabhouh, Adi Haber, Moshe Giladi, Yoram Palti. Designing arrays for the mouse head to facilitate in vivo studies of Tumor Treating Fields (TTFields) treatment of glioblastoma [abstract]. In: Proceedings of the AACR Special Conference on Brain Cancer; 2023 Oct 19-22; Minneapolis, Minnesota. Philadelphia (PA): AACR; Cancer Res 2024;84(5 Suppl_1):Abstract nr B032.

Electric field temporal interference stimulation of neurons in vitro.

Electrical stimulation (ES) techniques, such as deep brain and transcranial electrical stimulation, have shown promise in alleviating the symptoms of depression and other neurological disorders in vivo. A new noninvasive ES method called temporal interference stimulation (TIS), possesses great potential as it can be used to steer the stimulation and possibly selectively modulate different brain regions. To study TIS in a controlled environment, we successfully established an in vitro 'TIS on a chip' setup using rat cortical neurons on microelectrode arrays (MEAs) in combination with a current stimulator. We validated the developed TIS system and demonstrated the spatial steerability of the stimulation by direct electric field measurements in the chip setup. We stimulated cultures of rat cortical neurons at 28 days in vitro (DIV) by two-channel stimulation delivering 1) TIS at 653 Hz and 643 Hz, resulting in a 10 Hz frequency envelope, 2) low-frequency stimulation (LFS) at 10 Hz and 3) high-frequency stimulation (HFS) at 653 Hz. Unstimulated cultures were used as control/sham. We observed the differences in the electric field strengths during TIS, HFS, and LFS. Moreover, HFS and LFS had the smallest effects on neuronal activity. Instead, TIS elicited neuronal electrophysiological responses, especially 24 hours after stimulation. Our 'TIS on a chip' approach eludicates the applicability of TIS as a method to modulate neuronal electrophysiological activity. The TIS on a chip approach provides spatially steerable stimuli while mitigating the effects of high stimulus fields near the stimulation electrodes. Thus, the approach opens new avenues for stimulation on a chip applications, allowing the study of neuronal responses to gain insights into the potential clinical applications of TIS in treating various brain disorders.

Direct Measurement of the Electric Field Induced by a Transcranial Magnetic Stimulator

This work proposes a simple method to carry out in lab a direct measurement of the primary solenoidal electric field that transcranial magnetic stimulation coils generate in the brain. This method avoids indirect estimation of this electric field from measurements of magnetic fields, and at the same time, overcomes the difficulty posed by the presence of a dominant conservative electric field, also produced by the coil. This conservative electric field, which is removed in practice by human tissue, is eliminated in the proposed measurement method by using a simple setup that does not require the introduction of the measurement probe inside a conducting solution resembling the human tissue. The proposed measurement method allows for measuring the primary solenoidal electric field in front of the coil in the air. This method has been validated by comparing the results of electromagnetic simulation with the measurement of the magnetic field and the non-conservative electric field produced by a commercial transcranial magnetic stimulation coil.

A Novel Method for Lightning Prediction by Direct Electric Field Measurements at the Ground Using Recurrent Neural Network

A Novel Method for Lightning Prediction by Direct Electric Field Measurements at the Ground Using Recurrent Neural Network

Edge termination in vertical GaN diodes: Electric field distribution probed by second harmonic generation

We characterized the electric field distribution of GaN-on-GaN p–n diodes with partially compensated ion-implanted edge termination (ET) using an electric field induced second harmonic generation technique (EFISHG). The distributed electric field from the anode to the outer edge of the ET demonstrates the effectiveness of the ET structure. However, EFISHG also shows that its effectiveness is strongly dependent on the acceptor charge distribution in the ET's partially compensated layer (PC). A generally lower amount of acceptor charge can be inferred from the measured electric field distribution resulting from excessive ion implantation energy or dose during ET fabrication and causing lower than optimal breakdown voltage. Localized field crowding can be observed when the remaining acceptors uncompensated by the implant in the PC layer are nonuniformly distributed around the periphery of the devices. Important information can be obtained from these direct electric field measurements and used for optimizing the device design and fabrication process.

Shorting Factor In-Flight Calibration for the Van Allen Probes DC Electric Field Measurements in the Earth's Plasmasphere.

Satellite-based direct electric field measurements deliver crucial information for space science studies. Yet, they require meticulous design and calibration. In-flight calibration of double-probe instruments is usually presented in the most common case of tenuous plasmas, where the presence of an electrostatic structure surrounding the charged spacecraft alters the geophysical electric field measurements. To account for this effect and the uncertainty in the boom length, the measured electric field is multiplied by a parameter called the shorting factor (sf ). In the plasmasphere, the Debye length is very small in comparison with spacecraft dimension and there is no shorting of the electric field measurements (sf = 1). However, the electric field induced by spacecraft motion greatly exceeds any geophysical electric field of interest in the plasmasphere. Thus, the highest level of accuracy in calibration is required. The objective of this work is to discuss the accuracy of the setting Sf =1 and therefore to examine the accuracy of Van Allen Probes electric field measurements below L = 2. We introduce a method to determine the shorting factor near perigee. It relies on the idea that the value of the geophysical electric field measured in the Earth's rotating frame of reference is independent of whether the spacecraft is approaching perigee or past perigee, i.e. it is independent of spacecraft velocity. We obtain that Sf =0.994 ± 0.001. The resulting margins of errors in individual electric drift measurements are of the order of ± 0.1% of spacecraft velocity (a few meters per second).

Measuring Electric Fields in Biological Matter Using the Vibrational Stark Effect of Nitrile Probes.

Measurement of the electrostatic interactions that give rise to biological functions has been a longstanding challenge in biophysics. Advances in spectroscopic techniques over the past two decades have allowed for the direct measurement of electric fields in a wide variety of biological molecules and systems via the vibrational Stark effect (VSE). The frequency of the nitrile stretching oscillation has received much attention as an electric field reporter because of its sensitivity to electric fields and its occurrence in a relatively transparent region of the infrared spectrum. Despite these advantages and its wide use as a VSE probe, the nitrile stretching frequency is sensitive to hydrogen bonding in a way that complicates the straightforward relationship between measured frequency and environmental electric field. Here we highlight recent applications of nitrile VSE probes with an emphasis on experiments that have helped shape our understanding of the determinants of nitrile frequencies in both hydrogen bonding and nonhydrogen bonding environments.

P097 Direct measurement of electric fields in human and monkeys during transcranial electric stimulation

Introduction Transcranial electric stimulation (TES) is an emerging technique to non-invasively modulate brain function. However, the spatiotemporal distribution of electric fields during TES remains poorly understood. Objectives In this study we perform direct intracranial measurements of the electric field generated by transcranial alternating current (tACS) in epilepsy patients and cebus monkeys and evaluate the capacity of finite element method (FEM) models to predict the spatial distribution of measured electric fields. Methods Two presurgical epilepsy patients, with ca. 100 intracranially implanted electrodes participated in a single TES session. Two sponge electrodes (25 cm2) were attached over the left and right temporal cortex and a current of 1 mA with a frequency of 1 Hz was applied for 2 min. In two cebus monkeys three electrodes, with a total of 32 contacts were permanently implanted with posterior-anterior orientation. In multiple sessions intracranial EEG was recorded during TES. We varied the frequency of stimulation from 1–150 Hz and computed amplitude and phase relationships of recorded voltages. We constructed FEM models with increasing anatomical complexity for one epilepsy patient and compared the measured and simulated electric fields. Results Voltage magnitude slightly decreased with stimulation frequency up to 10% and small phase differences between electrode contacts up to a few degrees were observed. Electric field strengths were strongest in superficial brain regions with maximum values of 0.5 mV/mm ( Download : Download high-res image (1MB) Download : Download full-size image Fig. 1). Comparison of measured and simulated potentials and electric fields showed very high correlation values for the potentials (r = 0.95) and correlations of r = 0.7 for the electric fields. Evaluating the predictive value of increasingly complex FEM models highlighted the importance of accurate skull modeling especially in the vicinity of skull defects ( Download : Download high-res image (746KB) Download : Download full-size image Fig. 2). Conclusion We conducted a comprehensive evaluation of intracranial electric field during TES in both human patients and monkeys. Our results indicate that TES currents spread in a linear ohmic manner and capacitive effects are small indicating that the quasi-static approximation is well justified in the low frequency range. The spatial variation of the electric fields can be captured using realistic FEM models.

Geomagnetic disturbances on ground associated with particle precipitation during SC

Abstract. We have examined several cases of magnetosphere compression by solar wind pressure pulses using a set of instruments located in the noon sector of auroral zone. We have found that the increase in riometric absorption (sudden commencement absorption, SCA) occurred simultaneously with the beginning of negative or positive magnetic variations and broadband enhancement of magnetic activity in the frequency range above 0.1 Hz. Since magnetic variations were observed before the step-like increase of magnetic field at equatorial station (main impulse, MI), the negative declinations resembled the so-called preliminary impulse, PI. In this paper a mechanism for the generation of PI is introduced whereby PI's generation is linked to SCA – associated precipitation and the local enhancement of ionospheric conductivity leading to the reconstruction of the ionospheric current system prior to MI. Calculation showed that PI polarity depends on orientation of the background electric field and location of the observation point relative to ionospheric irregularity. For one case of direct measurements of electric field in the place where the ionospheric irregularity was present, the sign of calculated disturbance corresponded to the observed one. High-resolution measurements on IRIS facility and meridional chain of the induction magnetometers are utilized for the accurate timing of the impact of solar wind irregularity on the magnetopause.

Modeling and Direct Electric-Field Measurements of Passively Mode-Locked Quantum-Dot Lasers

A delay differential equation model of a passively mode-locked two-section quantum-dot laser reveals pulse asymmetry that is experimentally confirmed through direct electric-field measurements using frequency-resolved optical gating. This finding indicates that conventional autocorrelators, which obscure the underlying pulse structure due to the symmetry inherent in autocorrelation, are of limited utility in the characterization of these lasers.

Quench detection in YBa2Cu3O7−δ coated conductors using interferometric techniques

Digital speckle pattern interferometry has been used to detect inhomogeneous heating in YBa2Cu3O7−δ coated conductors. The analysis was performed in a sample with a controlled defect, which causes a significant local reduction in the critical current value, Ic. The experiments, which were performed with the sample surrounded by nitrogen vapor, have shown that the location of the initial hot spot leading to the complete transition to the normal state of the conductor (quench) is strongly dependent on the sample cooling configuration. When the sample is mainly cooled by gas convection, the quench always starts in the low-Ic region, while for improved cooling configurations the initial hot spot does not always coincide with this region. The results have been compared with those obtained by direct electric field measurements along the sample in nitrogen vapor and liquid.

Development of Supersonic Metastable Helium Pulsed Beam Source for Plasma Diagnostics

A supersonic metastable helium (2 1S) pulsed beam source, which consists of an electromagnetic valve, a collimation skimmer, and discharge electrodes for production of a plasma, has been constructed, which is essential for the direct measurement of electric fields in plasmas by means of polarization laser-induced fluorescence spectroscopy. A supersonic helium atomic beam with a short pulselength (∼300 µs), narrow divergence (∼1.1°), and high density of ∼1.4×1014 cm-3 has been achieved. In order to generate metastable atoms in this beam source, a Penning-type discharge was employed, which is suitable for producing stable plasma with high temperature, even at low gas densities, due to the particular configuration of electrodes together with a magnetic field. Spectroscopic observations indicated that the temporal behaviors of neutral atom and ion emissions were almost the same as that of the helium atom profile, and on increasing the discharge voltage applied between electrodes, the spectral intensity increased approximately linearly. Moreover, the fact that the ion emission can also be observed showed that it was probable that a high-temperature plasma was generated by the Penning discharge.

Localized picosecond resolution with a near-field microwave/scanning-force microscope

We modify a scanning-force microscope tip/cantilever with a coaxial metal shield for use as an ultra-small field probe, observing 30 ps waveforms on an integrated circuit at a spatial resolution set by the tip radius, the first direct measurements of electric field at these levels of temporal and spatial resolution. This new ability to acquire topography while maintaining constant tip–sample distance for calibrated measurement or excitation of near-zone picosecond time-resolved electric fields is useful not only for probing advanced circuits but also for localized broadband spectroscopy of condensed matter and biological samples.

Electric fields in the magnetosphere— a review

The satellites S3-3, GEOS-1, GEOS-2, ISEE-1 and Viking have extended direct measurements of electric fields to include the outer regions of the magnetosphere. The measurements confirm some of the theoretically expected properties of the electric fields. More importantly, they also reveal unexpected features and a high degree of complexity and variability. The existence of a magnetospheric dawn-dusk electric field has been confirmed in an average sense. However, the actual field exhibits large spatial and temporal variations, including strong fields of inductive origin. At the magnetopause the average (dawn-dusk directed) tangential electric field component is typlcally obscured by irregular fluctuations of larger amplitude. The magnetic field-aligned component of the electric field, which is of particular importance for ionosphere-magnetosphere coupling and for auroral acceleration is even now very difficult to measure directly. However, the data from electric field measurements provide further support for the conclusion, based on a variety of evidence, that a non-vanishing magnetic field-aligned electric field exists in the auroral acceleration region.

Mapping electrodynamic features of the high‐latitude ionosphere from localized observations: Combined incoherent‐scatter radar and magnetometer measurements for January 18–19, 1984

The large‐scale electric potential patterns, describing ionospheric convection, are estimated for northern high latitudes during January 18‐19, 1984, from combined incoherent‐scatter radar and ground magnetometer observations, using the technique of Richmond and Kamide (this issue). The patterns usually have a dominant two‐cell characteristic, although the intensities, orientations and shapes of the cells undergo considerable changes with time. Often evident during substorm expansive phases is a “tongue” of low electric potential extending toward the east along the low‐latitude edge of the high potential cell at night. Time‐series plots of the maximum and minimum electric potentials show that they can respond rapidly to changes in the interplanetary magnetic field Bz component. Total estimated potential drops for this 2‐day period range from about 15 kV up to 108 kV. The influence of the different types of data on the resultant estimated electric potential patterns is analyzed. Where available, the direct electric field observations by the radars primarily control the characteristics of the estimated potential patterns, while the magnetometer data have their greatest influence in regions where direct electric field measurements are unavailable. We also employ the statistical electric potential model of Foster et al. (1986) to help fill in the patterns in datasparse regions. For the present study, data coverage is often good enough that the statistical model plays only a secondary role in determining the estimated convection patterns. The ionospheric electrical conductance observations from the Sondrestrom and EISCAT radars are very important in helping modify the statistical conductance model of Fuller‐Rowell and Evans (1987) to yield modified conductance distributions suitable for interrelating the electric fields, currents, and magnetic perturbations. Analysis of the statistical uncertainty in the estimated large‐scale electric field patterns shows the uncertainty to exceed 50% in the polar cap and sub auroral regions and to be less than 20% only in the vicinity of the radar electric field observations.

Direct measurement of electric field at line conductors during a.c. corona

An electrostatic-fluxmeter probe has been used to obtain a direct measurement of the electric field at a cylindrical conductor during a.c. corona. For conductor diameters of 1.59, 2 and 2.75 cm, the resultant electric field falls below the onset level for both positive and negative corona. For the positive discharge, the field becomes independent of the applied voltage, a maximum fall of 9%, being observed. In contrast, the average field in the negative corona discharge decreases with increasing applied voltage, the effective field being reduced by up to 15% of the onset value. The assumption in many theoretical analyses of the discharge that the surface field remains at the onset value is thus invalid. It is suggested that increased secondary ionisation processes account for the maintenance of corona at reduced field strength. The measurements also fail to support the hypothesis that field enhancement occurs during positive corona owing to a negative-ion sheath. Field enhancement is observed to occur in a.c. corona prior to onset, because of remnant space charge from the preceding half cycle, but the effect is small. The field immediately following negative corona extinction is reduced, but, after positive corona, is enhanced because of electron attachment near the anode surface. The method, suitably modified, would appear to offer a useful means of study of bundle-conductor corona and precipitator assemblies of parallel line conductors.