Electric Field Mapping Research Articles

Electromagnetic Stimulation of Two-Phase Transport in Water for Geoenvironmental Applications

Air sparging is a popular remediation technology for contaminated soils. However, the application is not efficient due to the limitations of airflow that result from the formation of random preferential air channels. Controlling the formation of these air channels and enhancing diffusion surrounding them can considerably improve the effectiveness of air sparging. This work is a study on how electromagnetic (EM) waves—without a measureable increase in temperature—enhance the transport of a nonreactive dye in water as a visible analogy of air sparging (i.e., airflow within groundwater). This paper explains the details of the experimental setup and procedures required to conduct the EM-stimulation experiment as well as electric-field mapping and digital imaging of dye transport for the purpose of digital visual analysis. Several antenna designs and the way they direct the transport mechanism are studied. The results of EM-stimulation tests with no measureable temperature increase show that EM waves enhance and direct the dye transport in accordance with the EM source (transmitting antenna) and its radiation pattern. The rate of transport of the dye is studied and compared for unstimulated and EM-stimulated tests. Because of the small size of the dye molecules and existence of an alternating electric field, dielectrophoresis is the most likely potential transport mechanism. However, the existence of other competing factors dominating dielectrophoresis interferes with this type of study. Future modifications in the experimental design seem to have the potential to improve the investigation of the transport phenomenon.

High frequency acceleration system of the DC-280 cyclotron

The radio-frequency (RF) accelerating system designed at the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research (FLNR JINR), for the DC-280 cyclotron is described. The cyclotron is intended to increase the capabilities and efficiency of experiments on the synthesis of superheavy elements and investigate their nuclear-physical and chemical properties. The DC-280 isochronous heavyion cyclotron will produce an accelerated beam of ions in the range from neon to uranium. The results of the preliminary and 3D numerical calculations of the main cavity of this system are reported. The preliminary calculations by the Coaxresonator software have allowed the geometry of the main cavity to be chosen. 3D numerical simulation has completely confirmed the correctness of the preliminary calculations. For example, the difference in frequency between the preliminary and 3D numerical calculations is no larger than 1%. The electric-field component maps obtained from the simulations are used to calculate the beam dynamics in the cyclotron.

Optimizing frequency and pulse shape for ultrasound current source density imaging.

Electric field mapping is commonly used to identify irregular conduction pathways in the heart (e.g., arrhythmia) and brain (e.g., epilepsy). Ultrasound current source density imaging (UCSDI), based on the acoustoelectric (AE) effect, is a promising new technique for mapping electrical current in four dimensions with enhanced resolution. The frequency and pulse shape of the ultrasound beam affect the sensitivity and spatial resolution of UCSDI. In this study, we explore the effects of ultrasound transducer frequency bandwidth and coded excitation pulses for UCSDI and the inherent tradeoff between sensitivity and spatial resolution. We used both simulations and bench-top experiments to image a time-varying electrical dipole in 0.9% NaCl solution. To study the effects of ultrasound bandwidth, we chose two ultrasound transducers with different center frequencies (1.0 and 2.25 MHz). For coded excitation, we measured the AE voltage signal with different chirp excitations. As expected, higher bandwidth correlated with improved spatial resolution at the cost of sensitivity. On the other hand, chirp excitation significantly improved sensitivity (3.5 μV/mA) compared with conventional square pulse excitation (1.6 μV/mA) at 1 MHz. Pulse compression achieved spatial resolution similar to that obtained using square pulse excitation, demonstrating enhanced detection sensitivity without loss of resolution. Optimization of the time duration of the chirp pulse and frequency sweep rate can be further used to improve the quality of UCSDI.

The spatial statistics formalism applied to mapping electromagnetic radiation in urban areas

Determining the electromagnetic radiation levels in urban areas is a complicated task. Various approaches have been taken, including numerical simulations using different models of propagation, sampling campaigns to measure field values with which to validate theoretical models, and the formalism of spatial statistics. In the work, we present here that this latter technique was used to construct maps of electric field and its associated uncertainty from experimental data. For this purpose, a field meter and a broadband probe sensitive in the 100-kHz-3-GHz frequency range were used to take 1,020 measurements around buildings and along the perimeter of the area. The distance between sampling points was 5 m. The results were stored in a geographic information system to facilitate data handling and analysis, in particular, the application of the formalism of spatial statistical to the analysis of the distribution of the field levels over the study area. The spatial structure was analyzed using the variographic technique, with the field levels at non-sampled points being interpolated by kriging. The results indicated that, in the urban area analyzed in the present work, the linear density of sampling points could be reduced to a distance which coincides with the length of the blocks of buildings without the statistical parameters varying significantly and with the field level maps being reproduced qualitatively and quantitatively.

Fabrication of an Inductively Coupled Plasma Antenna in Low Temperature Co‐Fired Ceramic

A miniature electrostatic thruster is being developed in Low Temperature Co‐fired Ceramic (LTCC) at Boise State University. The thruster is composed of an antenna to create the plasma, a cylinder to contain the plasma, and grids to extract the plasma beam at high velocity. In this work, the development of the inductively coupled plasma (ICP) antenna in LTCC will be presented. This antenna is fabricated using DuPont 951 LTCC tape. A Direct Write dispenser is used to apply silver paste for the spiral ICP antenna. Using LTCC allows for the antenna to be embedded in the device under a thin sheet of LTCC dielectric, which protects the antenna from ion back bombardment during operation. This thin sheet is the seventh layer of the total device, with the ICP antenna one layer below the top. The design of the antenna is based on the research done by J. Hopwood. This article discusses the fabrication and performance of the ICP antennas in LTCC. These ICP antennas are operated at pressures from 10 mTorr to 1 Torr with radio frequencies (RF) of 500 MHz to 1 GHz to inductively couple with low‐pressure argon to produce plasma. The performance of the antennas will be verified with data showing the start and stop power of the plasma at various pressures and an electric field map of the RF field above the antenna.

Portable Real-Time Microwave Camera at 24 GHz

This paper presents a microwave camera built upon a two-dimensional array of switchable slot antennas. The camera borrows from modulated scattering techniques to improve isolation among the array elements. The camera was designed to measure vector electric field distribution, be compact, portable, battery operated, possess high dynamic range, and be capable of producing real-time images at video frame-rate. This imaging system utilizes PIN diode-loaded resonant elliptical slot antennas as its array elements integrated in a simple and relatively low-loss waveguide network thus reducing the complexity, cost and size of the array. The sensitivity and dynamic range of this system is improved by utilizing a custom-designed heterodyne receiver and matched filter for demodulation. The performance of the multiplexing scheme, noise-floor and dynamic range of the receivers are presented as well. Sources of errors such as mutual-coupling and array response dispersion are also investigated. Finally, utilizing this imaging system for various applications such as 2-D electric field mapping, and nondestructive testing is demonstrated.

LOCAL ELECTRIC FIELD MEASUREMENTS BY OPTICAL TWEEZERS

We report a new technique to measure direction and amplitude of electric fields generated by microelectrodes embedded in polar liquid environment, as often used in microfluidic devices. The method is based on optical tweezers which act as sensitive force transducer while a trapped charged microsphere behaves as a probe. When an electric field is applied the particles moves from its equilibrium position and finishes in a new equilibrium position where electric and optical forces are balanced. A trapped bead is moved to explore the electric field in a wide region around the microelectrodes. In such way maps of electric fields with high spatial resolution can be reconstructed even for complex electrode geometries where numerical simulation approaches can fail. Experimental results are compared with calculations based on finite element analysis simulation.

Fabrication of an Inductively Coupled Plasma Antenna in LTCC

With the size reduction of satellites, the need for miniaturized propulsion systems is increasing. This has led to research funding for the miniaturization of chemical and electric propulsion by NASA and the Air Force Office of Scientific Research (AFOSR). Miniaturized electric propulsion research has been an active area of interest recently. Electric propulsion systems are interesting candidates for miniaturization due to efficiency and the reduction in onboard propellant and the ability to apply existing techniques in electronic fabrication. A miniature electrostatic thruster is being developed in LTCC at Boise State University. The thruster is composed of an antenna to create the plasma, a cylinder to contain the plasma and grids to extract the plasma beam at high velocity. In this work, the development of the inductively coupled plasma (ICP) antenna in LTCC will be presented. This antenna is fabricated using DuPont's 951 Low Temperature Co-fired Ceramic (LTCC). A Direct Write is used to apply silver paste for the spiral ICP antenna. Using LTCC allows for the antenna to be embedded in the device under a thin sheet of LTCC dielectric, which protects the antenna from ion back bombardment during operation. This thin sheet is the seventh layer of the total device, with the ICP antenna one layer below the top. The design of the antenna is based on the research done by J. Hopwood. This paper discusses the fabrication and performance of the ICP antennas in LTCC. These ICP antennas are operated at pressures from 10 mTorr to 1 Torr with radio frequencies (RF) of 500 MHz to 1 GHz to inductively couple with low pressure argon to produce plasma. The performance of the antennas will be verified with data showing the start and stop power of the plasma at various pressures and an electric field map of the RF field above the antenna.

The hydrostatic pressure and electric field effects on the normalized binding energy of hydrogenic impurity in a GaAs/AlAs spherical quantum dot

A theoretical study of combined effects of the hydrostatic pressure and the electric field on the subband ground state energy and on the normalized ground state binding energy of a hydrogenic donor impurity on center located in a GaAs/AlAs spherical quantum dot with fixed dot radius is presented. The study is performed in the framework of the effective mass and parabolic band approximations and using a variational procedure. As a key result, it may be possible to gather high resolution maps of electric field on the studied structure with described technique.

Design and realization of a two-dimensional spatial magnetic field mapping apparatus to measure magnetic fields of metamaterials

The two-dimensional (2D) spatial electric-field mapping apparatus [Opt. Express 14, 8694 (2006)] plays an important role in experiments involving metamaterials, such as the verification of free-space and ground-plane invisibility cloaks. However, such an apparatus is valid only for the transverse-electric (TE) mode and is invalid for the transverse-magnetic (TM) mode, as it requires perfectly magnetic conducting (PMC) planes, which do not exist in nature. In this paper, we propose a 2D spatial magnetic-field mapping apparatus based on artificial magnetic conductor (AMC) plates. The AMC structure is designed using periodically perfectly electrical conducting patches with a sub-wavelength size on a dielectric substrate backed with the ground plane, which can simulate a PMC plane. Using two parallel PMC plates to form a TM-wave planar waveguide, we realize the 2D spatial magnetic-field mapping apparatus in order to measure the external and internal magnetic fields of metamaterials. Two types of excitations, a plane-wave source and a magnetic dipole, are used to feed the system. In order to validate the performance of the magnetic-field mapper, two gradient-index metamaterial lenses are measured, and the experimental results are in good agreement with the full-wave simulations.

SU-E-I-177: Electric Field and Ionization Signal Simulation in Liquid Xenon Detectors for PET

Purpose: A liquid xenon (LXe) detector prototype was developed to assess the performance of LXe for use in positron emission tomography. In this prototype, the measurement of ionization signals was achieved by using a time projection chamber (TPC), and scintillation light was measured by large area avalanche photodiodes. This work is aimed to simulate the electric field and readout signals in the LXe TPC.Methods: The electric field inside a single sector of the prototype detector was calculated through the finite element method using the software of Opera‐3d, with focus given to determining the uniformity of the field. The simulation model consists of a cathode, an anode, and field cage strips, which were immersed in a liquid xenon volume. With the electric field map obtained by Opera‐3d, the signals simulation were implemented in the Garfield package. The detector responses, including the primary ionization, generation of electron clouds, electron drift, diffusion, induced current signals on induction wires, and collection signals on anodes, were simulated. Comparison of simulation signals and measurement signals was made.Results: Three‐dimensional simulation results for the prototype detector showed that the field was nearly uniform in the center, with electron drifts deviating by less than 1 mm between the cathode and anode. The region of dead space constitutes 2.9% of the total volume in this sector. The simulation signals were in a good agreement with measurements. Conclusions: The good uniformity inside the chamber guaranteed 3‐D sub‐millimeter position resolution across the entire field of view. Based on the 3D electric field map, we can assign correction factors to correct the non‐uniformity in the whole sector. We also correctly simulated the signals of the TPC.

Atomically Resolved Mapping of Polarization and Electric Fields Across Ferroelectric/Oxide Interfaces by Z‐contrast Imaging

Direct atomic displacement mapping at ferroelectric interfaces by aberration corrected scanning transmission electron microscopy(STEM) (a-STEM image, b-corresponding displacement profile) is combined with Landau-Ginsburg-Devonshire theory to obtain the complete interface electrostatics in real space, including separate estimates for the polarization and intrinsic interface charge contributions.

Modulated Elliptical Slot Antenna for Electric Field Mapping and Microwave Imaging

Microwave and millimeter wave imaging has shown significant potential in various applications. An imaging system commonly consists of a sensitive electric field mapping array devised to measure the spatial distribution of the scattered field from an object to be imaged. One of the most prominent methods used to realize a cost-effective real-time imaging system is the modulated scatterer technique (MST). Although the conventional MST, using small loaded dipole antennas, performs well at lower microwave frequencies, its utility at high microwave and millimeter wave frequencies is limited. To improve upon the conventional MST, a novel modulated elliptical slot antenna, loaded with a PIN diode, is introduced and analyzed in this paper. The modulation-depth (effectiveness in modulating the slot), current distribution around the slot, and the influence of PIN diode bias structure are discussed based on numerical simulation results and experiments. Finally, the efficacy of the proposed slot for electric field measurements at 24 GHz is demonstrated using a prototype slot.

Local SAR reduction in parallel excitation based on channel‐dependent Tikhonov parameters

To reduce the local specific absorption rate (SAR) obtained with tailored pulses using parallel transmission while obtaining homogenous flip angle distributions. Finite-element simulations on a human head model were performed to obtain the individual magnetic and electric field maps for each channel of a parallel transmit array. From those maps, SAR calculations were carried out for "spoke" pulses designed to homogenize the flip angle in an axial slice of a human brain at 7 T. Based on the assumption that the coil element nearest to the maximum local energy deposition is the dominant contributor to the corresponding hot spot, a set of channel-dependent Tikhonov parameters is optimized. Resulting SAR distributions are compared to the ones obtained when using standard pulse design approaches based on a single Tikhonov parameter. In both the small- and large-tip-angle domain, the simulations show local SAR reductions by over a factor of 2 (4) for a well-centered (off-centered) head model at the expense of roughly 1% increment in flip-angle spread over the slice. Significant SAR reductions can be obtained by optimizing channel-dependent Tikhonov parameters based on the relation between coil elements and SAR hot spot positions.

Turbulent times in the northern polar ionosphere?

A model is presented of the growth rate of turbulently generated irregularities in the electron concentration of northern polar cap plasma patches. The turbulence is generated by the short‐term fluctuations in the electric field imposed on the polar cap ionosphere by electric field mapping from the magnetosphere. The model uses an ionospheric imaging algorithm to specify the state of the ionosphere throughout. The growth rates are used to estimate mean amplitudes for the irregularities, and these mean amplitudes are compared with observations of the scintillation indices S4 and σϕ by calculating the linear correlation coefficients between them. The scintillation data are recorded by GPS L1 band receivers stationed at high northern latitudes. A total of 13 days are analyzed, covering four separate magnetic storm periods. These results are compared with those from a similar model of the gradient drift instability (GDI) growth rate. Overall, the results show better correlation between the GDI process and the scintillation indices than for the turbulence process and the scintillation indices. Two storms, however, show approximately equally good correlations for both processes, indicating that there might be times when the turbulence process of irregularity formation on plasma patches may be the controlling one.

Investigation of the internal electric field in cadmium zinc telluride detectors using the Pockels effect and the analysis of charge transients

The Pockels electro-optic effect can be used to investigate the internal electric field in cadmium zinc telluride (CZT) single crystals that are used to fabricate room temperature x and gamma radiation detectors. An agreement is found between the electric field mapping obtained from Pockels effect images and the measurements of charge transients generated by alpha particles. The Pockels effect images of a CZT detector along two mutually perpendicular directions are used to optimize the detector response in a dual anode configuration, a device in which the symmetry of the internal electric field with respect to the anode strips is of critical importance. The Pockels effect is also used to map the electric field in a CZT detector with dual anodes and an attempt is made to find a correlation with the simulated electric potential in such detectors. Finally, the stress-induced birefringence effects seen in the Pockels images are presented and discussed.

Non-contact electrical detection of intrinsic local charge and internal electric field atnanointerfaces

A nanoscale non-contact electrical measurement has been developed based on Augerelectron spectroscopy. This approach used the specialty of an Auger electron, which isself-generated and free from external influences, to overcome the technical limitations ofconventional measurements. The detection of the intrinsic local charge and internal electricfield for nanostructured materials was achieved with a resolution below 10 nm. Asan example, the electrical properties at the GaN/AlGaN/GaN nanointerfaceswere characterized. The concentration of the intrinsic polarization sheet chargesembedded in GaN/AlGaN nanointerfacial layers were accurately detected to be−4.4 e nm−2. The mapping of the internal electric field across the nanointerface revealed the actualenergy-band configuration at the early stage of the formation of a two-dimensional electrongas.

Two-dimensional nanosecond electric field mapping based on cell electropermeabilization

Nanosecond, megavolt-per-meter electric pulses cause permeabilization of cells to small molecules, programmed cell death (apoptosis) in tumor cells, and are under evaluation as a treatment for skin cancer. We use nanoelectroporation and fluorescence imaging to construct two-dimensional maps of the electric field associated with delivery of 15 ns, 10 kV pulses to monolayers of the human prostate cancer cell line PC3 from three different electrode configurations: single-needle, five-needle, and flat-cut coaxial cable. Influx of the normally impermeant fluorescent dye YO-PRO-1 serves as a sensitive indicator of membrane permeabilization. The level of fluorescence emission after pulse exposure is proportional to the applied electric field strength. Spatial electric field distributions were compared in a plane normal to the center axis and 15-20 μm from the tip of the center electrode. Measurement results agree well with models for the three electrode arrangements evaluated in this study. This live-cell method for measuring a nanosecond pulsed electric field distribution provides an operationally meaningful calibration of electrode designs for biological applications and permits visualization of the relative sensitivities of different cell types to nanoelectropulse stimulation. PACS Codes: 87.85.M-

Multi-passband tunneling effect in multilayered Epsilon-Near-Zero Metamaterials

Recently, several experimental results verified the tunneling effect theory of that the electromagnetic energy can be squeezed through an ultra-narrow channel filled with epsilon-near-zero (ENZ) medium. However, the energy squeezing can be only achieved in a narrow region. Here, we present a full-wave simulation of the tunneling effect in multilayered channels full of thin ENZ metamaterials with different plasma frequencies. Thin metallic wires arrays with different radiuses are employed to form these effective ENZ media, whose plasma frequencies are different. The appearance of several passbands in the transmission curve verifies that multi-passband energy tunneling effect can be implemented by multilayer ENZ channels. There are two possible reasons for these peaks, one is the ENZ tunneling effect, and the other is the Fabry-Pérot resonance. For each transmission peak corresponding two-spatial maps of electric field are given, in order to distinguish the causes.

In-situ Visualization and Two Dimensional Mapping of Local Electric Field at Probe Apex Using Scanning Electron Optical System

We demonstrate an in-situ visualization of electric field distribution and the two-dimensional (2D) mapping of a local field by using a conventional scanning electron microscopy (SEM) system combined with a grid detector. The deflection of the primary electron that obeys Rutherford scattering projects a cross grid shape to a shadow constructed by concentric rings and radial spokes that appear to superimpose immediately behind the conventional SEM image. The correlation of the beam scanning position with the deflection position gives the true local field intensity, and thus, the 2D electric field distribution is obtained. The resulting 2D field distribution agrees well with the field element method (FEM) simulation.