Theoretical considerations of tissue electroporation with high-frequency bipolar pulses

This study introduces the use of high-frequency pulsed electric fields for tissue electroporation. Through the development of finite element models and the use of analytical techniques, electroporation with rectangular, bipolar pulses is investigated. The electric field and temperature distribution along with the associated transmembrane potential development are considered in a heterogeneous skin fold geometry. Results indicate that switching polarity on the nanosecond scale near the charging time of plasma membranes can greatly improve treatment outcomes in heterogeneous tissues. Specifically, high-frequency fields ranging from 500 kHz to 1 MHz are best suited to penetrate epithelial layers without inducing significant Joule heating, and cause electroporation in underlying cells.     

Electric current and electric field induced in the human body whenexposed to an incident electric field near the resonant frequency

The electric field and current density induced in the human body when this is exposed to electric fields near the resonant frequency, 53 MHz, are determined analytically. Since this frequency range includes an important amateur radio band of 50-60 MHz and exposure to electric fields at this frequency has been shown to be hazardous, the study has a specific motivation. A cylindrical model of the body is used to derive formulas for the total axial current and current density induced in the body subject to skin effect. Tabulations and graphical representations illuminate the results     

Subnanosecond electric pulses cause membrane permeabilization and cell death

Subnanosecond electric pulses (200 ps) at electric field intensities on the order of 20 kV/cm cause the death of B16.F10 murine melanoma cells when applied for minutes with a pulse repetition rate of 10 kHz. The lethal effect of the ultrashort pulses is found to be caused by a combination of thermal effects and electrical effects. Studies on the cellular level show increased transport across the membrane at much lower exposure times or number of pulses. Exposed to 2000 pulses, NG108 cells exhibit an increase in membrane conductance, but only allow transmembrane currents to flow, if the medium is positively biased with respect to the cell interior. This means that the cell membrane behaves like a rectifying diode. This increase in membrane conductance is a nonthermal process, since the temperature rise due to the pulsing is negligible.     

Effect of a bichromatic electric field on the current-voltage characteristic of a graphene-based superlattice

The longitudinal current-voltage characteristic of a graphene-based superlattice in high-frequency electric fields, such that the strength of one of the fields oscillates along the superlattice axis and the strength of the other perpendicularly to this axis, is calculated. It is shown that, if there is a transverse high-frequency field only, there exists a possibility for sharply increasing the current density in the negative-differential-conductivity region of the static current-voltage characteristic of the superlattice. The current density exhibits a jump, if the oscillation frequency of the field strength approaches the Bloch oscillation frequency. It is shown that, in such a situation, absorption of an electromagnetic wave in the graphene-based superlattice gives way to amplification.     

Equivalent dipole moment method to characterize magnetic fields generated by electric appliances: extension to intermediate frequencies of up to 100 kHz

A previously proposed simple method to characterize magnetic fields near electric appliances was extended to intermediate frequencies of up to 100 kHz. The method consists of identification of the magnetic dipole moment that is equivalent to a magnetic field source of an electric appliance and simple estimation of the magnetic field distribution around the appliance. In addition, frequency characteristics of the magnetic field were taken into account by considering the harmonic components in the magnetic-field waveform for both power frequency and intermediate frequency ranges. For the application of the method, a wide-frequency range (from power frequency to 100 kHz) magnetic-field measuring instrument was developed and applied to appliances that generate intermediate frequency magnetic fields, i.e., an induction heating cooker, a TV set, and a metal detector. The results revealed that the method is adequate to quantify the magnetic field near the electric appliances at frequencies of up to 100 kHz.     

应用于EMC测量的集成光学电场传感器性能分析

依据集成光学电场传感器的工作原理,研制了可用于电磁兼容性测量的分段电极结构与锥形天线结构的电场传感器.测试结果表明:分段电极传感器频响范围为10 MHz～6 GHz,最小可测电场强度达到30 mV/m,在频率为200 MHz时,线性动态范围可达90 dB;锥形天线传感器频响范围为10 kHz～10 GHz,最小可测电场强度达到20 mV/m,在频率为1 GHz时,线性动态范围可达100 dB.     

Evaluation of interactions of electric fields due to electrostatic discharge with human tissue

Electrostatic discharges (ESDs) produce in the human tissue very strong electric fields of short duration. Possible biophysical interactions are evaluated by comparing the fields in subcutaneous fat/skin to the thresholds for peripheral nerve stimulation, and by computations of membrane potential and electric fields in cytoplasm of a typical cell in bone marrow. It is found that a 4-A peak ESD event is capable of stimulation of nerves located in subcutaneous fat of the lower arm of the hand eliciting a spark, with tens of kV/m and pulse duration of approximately 80 ns. For the same ESD event, the transmembrane potential (TMP) reaches 32 mV with a pulse duration of approximately 200 ns (half-width duration). The electric field in the cytoplasm of a bone marrow cell changes from about 8.8 kV/m to--2 kV/m in about 200 ns.     

Pacemaker interference and low-frequency electric induction in humans by external fields and electrodes

The possibility of interference by low-frequency external electric fields with cardiac pacemakers is a matter of practical concern. For pragmatic reasons, experimental investigations into such interference have used contact electrode current sources. However, the applicability to the external electric field problem remains unclear. The recent development of anatomically based electromagnetic models of the human body, together with progress in computational electromagnetics, enable the use of numerical modeling to quantify the relationship between external field and contact electrode excitation. This paper presents a comparison between the computed fields induced in a 3.6-mm-resolution conductivity model of the human body by an external electric field and by several electrode source configurations involving the feet and either the head or shoulders. The application to cardiac pacemaker interference is also indicated.     

Induced foot-currents in humans exposed to VHF radio-frequency EMfields

In order to limit the specific absorption rate (SAR) in the ankles of a person exposed to an electric field at frequencies below 100 MHz, induced current limits are prescribed in the 1992 ANSI/IEEE safety standard. The authors have measured the induced currents passing through the feet of nine subjects exposed to vertically polarized electric fields from nearby antennas, transmitting at frequencies between 90 and 104 MHz (in the FM broadcast band). The experimental results are in excellent agreement with the results obtained analytically for frequencies up to 110 MHz. The analytical results were obtained by applying the finite difference time domain (FDTD) method to an anatomically-based model of an average height male (1.75 m) and to a model of the tallest subject in the study (1.91 m). For the mean height of the nine subjects (1.75 m), the measured induced foot current for a unit strength vertically polarized electric field varied with frequency from 4.46 to 3.45 mA/(V/m) for frequencies between 90-104 MHz. For the tallest subject (1.91 m), the corresponding values ranged from 5.42 to 4.45 mA/(V/m), Foot currents in excess of the induced current limits in RF safety guidelines for both the controlled and uncontrolled environments could result even when the vertical component of the incident electric fields comply with the corresponding field limits. It is important, therefore, to not only measure the E- and H-fields, but also the induced currents up to the recommended maximum frequency of 100 MHz, and perhaps up to the upper frequency of the FM broadcast band (108 MHz)     

Electromagnetic fields induced in a person due to devices radiatingin the 10 Hz to 100 kHz range

Using dipole and image theory with prolate spheroid models, a qualitative evaluation is made of the electric, E, and magnetic, H¯, fields induced at selected points inside a person due to external electric, E¯₀, and magnetic, H¯₀, fields within the 10 Hz to 100 kHz range. Amplitude measurements of the E¯₀ and H¯₀ vectors are made at selected points in the region with the person absent. The evaluation is valid for any field radiating device if the amplitude and phase angles of the external fields are measured in accordance with the stated protocol     

Theoretical and experimental analysis of electroporated membrane conductance in cell suspension

An intense electric field can be applied to increase the membrane conductance G(m) and consequently, the conductivity of cell suspension. This phenomenon is called electroporation. This mechanism is used in a wide range of medical applications, genetic engineering, and therapies. Conductivity measurements of cell suspensions were carried out during application of electric fields from 40 to 165 kV/m. Experimental results were analyzed with two electroporation models: the asymptotic electroporation model was used to estimate G(m) at the beginning and at the end of electric field pulse, and the extended Kinosita electroporation model to increase G(m) linearly in time. The maximum G(m) was 1-7 × 10(4) S/m(2), and the critical angle (when the G(m) is insignificant) was 50°-65°. In addition, the sensitivity of electroporated membrane conductance to extracellular and cytoplasmatic conductivity and cell radius has been studied. This study showed that external conductivity and cell radius are important parameters affecting the pore-opening phenomenon. However, if the cell radius is larger than 7 μm in low conductivity medium, the cell dimensions are not so important.     

Progress in the United States on Electromagnetic Standards and Measurements at 30 kHz to 1 GHz 1963 - 1965

A digest of highlights is presented on the most significant U.S. contributions to the measurement of attenuation, impedance, phase, field strength, thermal noise, current, and voltage at 30 kHz to 1 GHz. A total of approximately 30 contributions are digested. The following accomplishments are among them: a supersensitive detector for a complex-insertion-ratio measurement system having accuracies of about 0.0005 dB/10 dB at 30 MHz; exact equations for mutual and self-inductance of various combinations of filaments, tapes, and bars; a modified Twin-T-Bridge for measuring resistances of 100 to 10 000 ohms to 15 MHz; a set of Q-factor standards for frequencies to 45 MHz based on data and experience accumulated over five years; a unique adjustable characteristic-impedance coaxial line; measurement of Q's greater than 100 000 of cryogenic circuits at frequencies to 300 MHz; a novel Tee-junction to enable calibrations of voltmeters of any practicable input impedances with VSWR's ranging fiom 1 to 200, to 1 GHz and higher; a miniaturized dipole-antenna field strength meter, employing a semiconducting plastic transmission line, to measure complex near-zone fields of 0.1 to 1000 V/m, from 150 kHz to 30 MHz; and a prototype 3-MHz model of precision thermal noise-power comparators for an equivalent noise-temperature range of 75 to 30 000° K at accuracies of 0.2 to 1 percent.     

Effects of Potassium Currents upon Action Potential of Cardiac Cells Exposed to External Electric fields

Previous studies show that exposure to high-voltage electric fields would influence the electro-cardiogram both in experimental animals and human beings.The effects of the external electric fields upon action potential of cardiac cells are studied in this paper based on the dynamical model,LR91.Fourth-order Runger-Kuta is used to analyze the change of potassium ion channels exposed to external electric fields in detail.Results indicate that external electric fields could influence the current of potassium ion by adding an induced component voltage on membrane.This phenomenon might be one of the reasons of heart rate anomaly under the high-voltage electric fields.     

Finite element implementation of Maxwell's equations for image reconstruction in electrical impedance tomography

Traditionally, image reconstruction in electrical impedance tomography (EIT) has been based on Laplace's equation. However, at high frequencies the coupling between electric and magnetic fields requires solution of the full Maxwell equations. In this paper, a formulation is presented in terms of the Maxwell equations expressed in scalar and vector potentials. The approach leads to boundary conditions that naturally align with the quantities measured by EIT instrumentation. A two-dimensional implementation for image reconstruction from EIT data is realized. The effect of frequency on the field distribution is illustrated using the high-frequency model and is compared with Laplace solutions. Numerical simulations and experimental results are also presented to illustrate image reconstruction over a range of frequencies using the new implementation. The results show that scalar/vector potential reconstruction produces images which are essentially indistinguishable from a Laplace algorithm for frequencies below 1 MHz but superior at frequencies reaching 10 MHz.     

Implantable Electric-Field Probes?Some Performance Characteristics

Performance characteristics of three implantable triaxial field probes for measuring intensities of the internal electric fields in biological tissues at radio frequencies are given. The sensitivity in air between 100 MHz and 3 GHz, and in phantom materials at 350, 915, and 2450 MHz, are given for the Holaday model IME-01, EIT model 979, and Narda model 2608 implantable probes, as well as their noise and modulation characteristics.     

Electromagnetic field of a horizontal electric dipole buried in a medium covering one-dimensionally anisotropic medium

The electromagnetic fields of a horizontal electric dipole buried in a medium covering one-dimensionally anisotropic medium are studied. There are three media, one-dimensionally anisotropic medium covered with a dielectric under the air. The electromagnetic field components are complex because of the multiple reflections from the up and down boundaries. The electromagnetic field components between air and one-dimensionally anisotropic medium are given, the trapped surface waves and lateral waves along the dielectric-anisotropic medium boundary are computed. The results have some practical applications in the communication in sea or lake above one-dimensionally anisotropic earth or sediments.     

Testing the immunity of active implantable medical devices to CW magnetic fields up to 1 MHz by an immersion method

This paper presents a magnetic-field system and the method developed for testing the immunity of the active implantable medical devices to continuous-wave magnetic fields in the frequency range up to 1 MHz. The system is able to produce magnetic fields of 150 A/m for frequencies up to 100 kHz and strengths decreasing as 1/f between 100 kHz and 1 MHz, with uniformity of the field within +/-2.5% in the volume for tests. To simulate human tissue, the medical device, together with its leads, is placed on a plastic grid in a saline tank that is introduced in the magnetic field of the induction coil. This paper offers an alternative for the injection voltage methods provided in the actual standards for assessing the protection of the implantable medical devices from the effects of the magnetic fields up to 1 MHz. This paper presents the equipment and signals used, the test procedure, and results from the preliminary tests performed at the Food and Drug Administration-Center for Devices and Radiological Health on implantable pacemakers and neurostimulators. The new system and test method are useful for the EMC research on the implantable medical devices.     

Electrical environmental characteristics for automotive electric systems

The electrical environment is one of the most important factors in the design of high reliability electronic systems mounted on automobiles. Studies were made of the generation mechanisms and characteristics of both transients and high-frequency conducted noise generated in automotive electrical components. The high-frequency conducted noise data were obtained in terms of amplitude-frequency through real-time statistical treatment of the acquired data. The most important transient for automotive electronic systems has been found to be the alternator load dump transient caused by battery disconnection, and the most influential high-frequency conducted noise is caused by contact breaking. The high-frequency conducted noise characteristics can be expressed in the amplitude-frequency relation in the frequency range of 100 kHz-80 MHz.     

Mixing and detection of RF signals in fibre-optic magnetostrictive sensor

The author report the first demonstration of the detection of magnetic fields at frequencies above 50 kHz in a fibre-optic magnetometer using a technique which employs mixing of the signal with the field from a local oscillator. A flat response from 0.1 Hz to near 1.0 MHz is shown.<>     

Electric Field Controlled Self‐Assembly of Hierarchically Ordered Membranes

Self‐assembly in the presence of external forces is an adaptive, directed organization of molecular components under nonequilibrium conditions. While forces may be generated as a result of spontaneous interactions among components of a system, intervention with external forces can significantly alter the final outcome of self‐assembly. Superimposing these intrinsic and extrinsic forces provides greater degrees of freedom to control the structure and function of self‐assembling materials. In this work we investigate the role of electric fields during the dynamic self‐assembly of a negatively charged polyelectrolyte and a positively charged peptide amphiphile in water leading to the formation of an ordered membrane. In the absence of electric fields, contact between the two solutions of oppositely charged molecules triggers the growth of closed membranes with vertically oriented fibrils that encapsulate the polyelectrolyte solution. This process of self‐assembly is intrinsically driven by excess osmotic pressure of counterions and the electric field is found to modify the kinetics of membrane formation as well as membrane morphology and properties. Depending on the strength and orientation of the field we observe a significant increase or decrease of up to nearly 100% in membrane thickness, or the controlled rotation of nanofiber growth direction by 90 degrees which leads to a significant increase in mechanical stiffness. These results suggest the possibility of using electric fields to control structure in self‐assembly processes that involve the diffusion of oppositely charged molecules.