Electric Field Contours Research Articles

Design of tunable photothermal porous thermal emitter based on nonreciprocal effect

Tunable thermal emitters have become a research hotspot for high-efficiency, low-loss novel thermal radiation devices. It has been found that the tunability of thermal radiation devices can be greatly strengthened and the efficiency of photothermal conversion enhanced through the tuning of the radiation temperature by magneto-optical microstructures. In this paper, a novel porous thermal emitter for the mid-infrared band is designed and the interconnection between nonreciprocal radiation and photothermal conversion is investigated for the first time. The three-hole column (THC) porous structure is optimized from the traditional one-hole column (OHC) porous structure. Through detailed analysis of the light incident angle, external magnetic field strength, and hole diameter, it is shown that the strong nonreciprocal radiation is due to the variation of the cavity structure parameters, which enhances the microcavity resonance effect, thereby enhancing the surface plasmon resonance (SPR) on the porous surface. The electric field contours at different positions also visualize the enhancement mechanism of SPR for nonreciprocal radiation. It has been investigated that different magnetic field strengths and porous structures have significant impact on nonreciprocal thermal tuning. The nonreciprocal system can be used to tune the local heat around the hole, and the temperature difference increase as nonreciprocal effects is greater as the magnetic field strength and input power increases. This work also provides new ideas for the application of thermal emitters and the design of energy conversion devices.

Improved breakdown voltage mechanism in AlGaN/GaN HEMT for RF/Microwave applications: Design and physical insights of dual field plate

This work investigated and proposed the source–gate dual field plate (SG-FP) AlGaN/GaN HEMT for different gate-to-drain drift distances with a fixed gate length of 0.25 μm using ATLAS-TCAD. The increment in the GaN buffer thickness and gate-to-drain drift distance with the variation in the field plate length improves the device performance and breakdown voltages by maintaining the impact ionization mechanism. The breakdown voltage behavior, physical insights of electric field contour, impact generation rate, and potential profile intricacies of source field plate (S-FP), gate field plate (G-FP), and dual field plate (SG-FP) are illustrated. The proposed source–gate dual field plate (SG-FP) with the SiN passivation interfacial layer, SiO2, thicker GaN buffer, and extended gate-to-source drift region is best suited for optimal performance in high breakdown voltage, with optimum cut-off frequency and low gate-leakage current. The proposed dual field plate AlGaN/GaN device with the source field plate (LS-FP = 4 μm), gate field plate (LG-FP = 2 μm), the AlGaN buffer thickness of 3.697 μm, and gate-to-drain drift distance of 8 μm show the highest breakdown voltage of 562 V with the optimum frequency of 8.861 GHz. Finally, the AC/DC characteristics of the optimized dual field plate (SG-FP) are demonstrated. We observed that the source–gate dual field plate (SG-FP) device shows a 6.70% and 4.09% improvement in breakdown voltage compared to individual source field plate (S-FP) and gate field plate (G-FP) designs, respectively. This work shows that the proposed dual field plate device is used in power switching, high-power, and RF/Microwave applications due to its superior breakdown voltage performance, reduction in parasitic capacitances, and optimal cut-off frequency.

Process investigation of nanofiber diameter based on linear needleless spinneret by response surface methodology

Needleless electrsopinning is of a great attention to researcher in industrial production of nanofibers for nearly ten years. Many innovative and different shapes needleless spinnerets are designed and then used to fabricate mass nanofibers. There are a lot of reports about spinning process parameters. In this study, we developed a novel linear flume needleless spinneret to fabricate nanofiber. The finite element analysis software was used to simulate electric field contour of different included angle spinneret. The curves of electric field intensity were drawn to evaluate the tip electric field intensity of spinneret. In addition, Response Surface Methodology (RSM) was adopted to investigate the effect of process parameters on nanofiber diameter. Two-dimensional and three-dimensional response surface contour were obtained to discuss the interaction of the different process parameters. This work provided a novel idea and approach for optimizing design of the needleless spinneret through numerical simulation method. Investigation of process parameter could guide the controllable production of desired nanofibers.

Nanoscale electric-field imaging based on a quantum sensor and its charge-state control under ambient condition

Nitrogen-vacancy (NV) centers in diamond can be used as quantum sensors to image the magnetic field with nanoscale resolution. However, nanoscale electric-field mapping has not been achieved so far because of the relatively weak coupling strength between NV and electric field. Here, using individual shallow NVs, we quantitatively image electric field contours from a sharp tip of a qPlus-based atomic force microscope (AFM), and achieve a spatial resolution of ~10 nm. Through such local electric fields, we demonstrated electric control of NV’s charge state with sub-5 nm precision. This work represents the first step towards nanoscale scanning electrometry based on a single quantum sensor and may open up the possibility of quantitatively mapping local charge, electric polarization, and dielectric response in a broad spectrum of functional materials at nanoscale.

Diffusion Law of Whole-Space Transient Electromagnetic Field Generated by the Underground Magnetic Source and Its Application

Mine water inrush stays as one of the major disasters in coalmine production and construction. As one of the principal methods for detecting hidden water-rich areas in coal mines, underground transient electromagnetic method (TEM) adopts the small loop of a magnetic source which generates a kind of whole-space transient electromagnetic field. To study the diffusion of whole-space transient electromagnetic field, a 3-D finite-difference time-domain (FDTD) is employed in simulating the diffusion pattern of whole-space transient electromagnetic field created by the magnetic source in any direction and the whole-space transient electromagnetic response of the 3-D low-resistance body. The simulation results indicate that the diffusion of whole-space transient electromagnetic field is different from ground half-space and that it does not conform to the “smoke ring effect” of half-space transient electromagnetic field, for the radius of the electric field's contour ring in whole space keeps expanding without moving upward or downward. The low-resistance body can significantly affect the diffusion of transient electromagnetic field. When the excitation direction is consistent with the bearing of the low-resistance body, the coupling between the transient electromagnetic field and the low-resistance body is optimal, and the abnormal response is most obvious. The bearing of the low-resistance body can be distinguished by comparing the response information of different excitation directions. Based on the results above, multi-directional sector detection technology is adapted to detect the water-rich areas, which can not only detect the target ahead of the roadway but also distinguish the bearing of the target. Both numerical simulation and practical application in underground indicate that the mining TEM can accurately reflect the location of water-rich areas.

Observation and analysis of kink effect during drain current inception of GaN HEMT

Drastic change of drain current has been measured with drain voltage at the inception when there is a transition from OFF to ON state for two-dimensional electron gas at the AlGaN/GaN heterojunction on sapphire substrate. Hysteresis in the drain current characteristics has also been observed when drain bias has been traced back to zero at certain gate bias during this transition. Both horizontal and vertical energy band diagrams have been incorporated along with electric field contour mapping of the device to explain the related electron and hole transport physics. These nanoscale phenomena are the combined effect of energy barrier modulation due to both the drain and gate bias in presence defect related fabrication anomalies. Therefore, different possible transport mechanisms such as electron punch through, Fowler-Nordheim tunneling, impact ionization, hot-electron effect, trap assisted tunneling, de-trapping are discussed in correlation with the band diagrams.

Mitigation of impedance changes due to electroporation therapy using bursts of high-frequency bipolar pulses.

BackgroundFor electroporation-based therapies, accurate modeling of the electric field distribution within the target tissue is important for predicting the treatment volume. In response to conventional, unipolar pulses, the electrical impedance of a tissue varies as a function of the local electric field, leading to a redistribution of the field. These dynamic impedance changes, which depend on the tissue type and the applied electric field, need to be quantified a priori, making mathematical modeling complicated. Here, it is shown that the impedance changes during high-frequency, bipolar electroporation therapy are reduced, and the electric field distribution can be approximated using the analytical solution to Laplace's equation that is valid for a homogeneous medium of constant conductivity.MethodsTwo methods were used to examine the agreement between the analytical solution to Laplace's equation and the electric fields generated by 100 µs unipolar pulses and bursts of 1 µs bipolar pulses. First, pulses were applied to potato tuber tissue while an infrared camera was used to monitor the temperature distribution in real-time as a corollary to the electric field distribution. The analytical solution was overlaid on the thermal images for a qualitative assessment of the electric fields. Second, potato ablations were performed and the lesion size was measured along the x- and y-axes. These values were compared to the analytical solution to quantify its ability to predict treatment outcomes. To analyze the dynamic impedance changes due to electroporation at different frequencies, electrical impedance measurements (1 Hz to 1 MHz) were made before and after the treatment of potato tissue.ResultsFor high-frequency bipolar burst treatment, the thermal images closely mirrored the constant electric field contours. The potato tissue lesions differed from the analytical solution by 39.7 ± 1.3 % (x-axis) and 6.87 ± 6.26 % (y-axis) for conventional unipolar pulses, and 15.46 ± 1.37 % (x-axis) and 3.63 ± 5.9 % (y-axis) for high- frequency bipolar pulses.ConclusionsThe electric field distributions due to high-frequency, bipolar electroporation pulses can be closely approximated with the homogeneous analytical solution. This paves way for modeling fields without prior characterization of non-linear tissue properties, and thereby simplifying electroporation procedures.

Investigation of Rapid-Prototyping Methods for 3D Printed Power Electronic Module Development

The recent research in wide-bandgap (WBG) power electronic semiconductors has produced a wide variety of device and combinational topologies, such as HFETS, MOSHFETS, and the Cascode Pair. Each variation needs to be tested with certain package criteria (e.g. high voltage SiC devices up to 15kV, high current GaN devices up to 300A, or unprecedented high frequencies). Having a common package is costly and cannot provide an investigation of optimized performance. Hence, use of a rapid prototyping method to print power electronic packages and modules is needed. Also, the continual move to higher frequencies will require greater integration of packaging into the end application, as is presently done with point-of-load converters. The future modules will take on more functional integration, including more mechanical features, which further supports use of printed fabrication technologies. It is not reasonable to assume that a complete module can be directly printed, though most would be; some assembly is required. This paper discusses partitioning of a module process, and identifying key elements that can be combined for optimum power package production. To select the best process, or combination, for rapid-prototype printing of power modules current, Additive Manufacturing (AM) methods are evaluated, such as Stereolithography (SLA), Selective Laser sintering (SLS), and Fused Deposition Manufacturing (FDM). Several modules were fabricated to demonstrate mechanical resolutions in the packaging. A thermoplastic printer, specifically the MakerBot, which is a high end consumer 3D printer, produces packages with 100 micron resolution. The Acrylonitrile butadiene styrene (ABS) build object can have surface texture enhancement with post chemical treatment, such as an acetone vapor bath. Today, this is finding a home and proving useful in low volume rapid prototyping in small electronics companies. The ABS plastics are typically rated for <105°C applications. Another printed module to be reported uses a high-end commercial machine with <20 microns in resolution (Stratasys Objet) using standard UV curable polymers. This provides a slightly higher temperature range with greater mechanical integrity. Materials for >250°C that use both UV and thermal sintering are available, but not evaluated in this paper. Functional integration can include electrical, mechanical, and thermal appendages and sub-systems. Electrical sub-systems, such as gate drivers and sensors, can impact process partitioning, by requiring “low power” circuit fabrication processes integrated with those for high power. This paper demonstrates a printed polymer substrate process for functional integration of a signal-circuit. Since nearly all AM processes were developed initially for mechanical systems, many processed materials have not been electrically characterized, though the basic material compositions may have suitable electrical characteristics. This paper categorizes several materials for their potential suitability for power packaging. The evaluation is based on the electrical, mechanical, and thermal parameters, along with precision, surface texture (affecting electric field contours) and process times. Cost and performance will be of main concern.

(Invited) Microstrucutural Characterizaton of Stressed AlGaN/GaN HEMT Devices

AlGaN/GaN high electron mobility transistors are used in high temperature, high power, and high frequency applications due to their superior combination of high breakdown voltage and high frequency performance. Unfortunately, their reliability in the field has warranted further investigation because of the stochastic nature of the variety of defects that arise during their operation. Many analytical techniques are not well suited to this analysis because they sample regions of the device which are either too small or too large for accurate observation. This talk will give a review of recent studies that employ structural, chemical, and electrical device characterization paired with simulation in order to develop structure-property relationships between defects and device performance. This includes the use of a new approach to chemical deprocessing combined with surface-sensitive analysis techniques such as scanning electron microscopy and scanning probe microscopy in the analysis of large-area defect formation. Wet etching of the passivation nitride and metal contacts was used to strip the transistor surface features and remove organic contaminants. This exposed the top surface of the AlGaN epilayer for analysis. This processing revealed and surface analysis revealed three different defects. One of these defects is a nanoscale crack which emanates from metal inclusions formed during alloying of the ohmic contacts of the device prior to use in the field, and could impact the yield of production-level manufacturing of these devices. This defect also appears to grow, in some cases, during electrostatic stressing. Another defect, a native oxide at the surface of the semiconductor under the gate, appears to react in the presence of an electric field, which could play a role in the degradation of the gate contact during high-field, off-mode electrostatic stressing. This defect could also facilitate the formation of the pitting of the AlGaN epilayer beneath the gate contact. The composition of the as-grown gate interfacial layers were characterized using atom probe tomography and are composed of two distinct oxide layers, NiOx and AlOx. Furthermore, using off-state reverse bias electrical stress, Ni-gate metal reactions with AlGaN epilayers emulate the shape and size of the electric field contours between 5 – 6 MV/cm; suggesting a critical field for defect formation. This talk will summarize these finding and place them in the overall context of failure mechanisms in AlGaN/GaN HEMT structures.

Plasma ionization by annularly bounded helicon waves

The general solution to the electrostatic and magnetic fields is derived with respect to the boundary conditions of a coaxial helicon plasma source. The electric field contours suggest that a simple antenna design can ionize the gas in a coaxial configuration. In addition, the power deposition as a function of excitation frequency is derived. The solution is validated by comparison with the standard cylindrical helicon plasma source. Further, a parametric study of source length, channel radius, channel width, and antenna excitation frequency are presented. This study suggests that it is possible to create a helicon plasma source with a coaxial configuration.

Multiple ion-focusing effects in plasma immersion ion implantation

In plasma immersion ion implantation, the sample is negatively biased and a plasma sheath forms. Ions are accelerated to the sample surface through this sheath. The electric field contours dictate the shape of the plasma sheath that wraps around corners and tends to be smoother and rounder than the surface topography, for instance, at a sharp corner. Our theoretical and experimental studies reveal ion flux focusing effects leading to lateral nonuniformity of the incident ion dose. Ion focusing occurs not only at the sample edge but also in the central region even for a planar sample (wafer). In this work, we numerically and experimentally investigate this ion focusing effect and ion dose nonuniformity. A simple geometric model is also presented in this letter to understand the mechanism. The results demonstrate that ion focusing originates from plasma sheath convergence that is time and space dependent. Consequently, multiple ion focusing may occur at different local sites when the target shape and processing parameters vary, and a small plasma sheath relative to the target is of paramount importance for uniform implantation.

When do sphenoidal electrodes yield additional data to that obtained with antero-temporal electrodes?

The advantage of using sphenoidal (SE) over antero-temporal electrodes (ATE) remains controversial among epileptologists. Yet, in a recently published study of 17 patients with seizures of antero-temporal origin (Kanner et al., 1995), we demonstrated that SE placed under fluoroscopic guidance (FPSE), in order to insure that their recording tips are positioned immediately below the foramen ovale (FO), yielded a significant advantage over SE placed with the standard blind method of insertion (BPSE), in both interictal and ictal recordings. This study was done to test the following hypothesis: FPSE advantage over BPSE and ATE resides in the recording of epileptiform activity with a restricted electric field. We compared spike voltages at FPSE, BPSE and ATE in sets of 5 randomly selected spikes per interictal focus, recorded in the course of separate monitoring studies with BPSE and FPSE. We represented the voltage differences as ratios, VATE/FPSE and VATE/BPSE and calculated a mean ratio for each spike set. The spikes' voltage was almost identical at BPSE and at ATE (mean VATE/BPSE = 0.94), while it was significantly higher at FPSE than at ATE (mean VATE/FPSE = 0.66; P < 0.001, t test). A significantly narrower electric field contour was found among interictal foci in which FPSE yielded additional data during interictal (P < 0.001) and ictal (P = 0.016) recordings. Conversely, VATE/FPSE did not differ from VATE/BPSE among interictal foci where FPSE failed to yield any advantage over BPSE in either interictal (P = 0.240), or ictal (P = 0.311) recordings. These findings prove that SE yield additional localizing data when recording epileptiform activity with a restricted field, provided that its recording tip is positioned below the FO. When distant from FO, SE can be expected to yield comparable data to that obtained with ATE.

Numerical Analysis of Bubble Growth under Electric Field.

Numerical analysis has been performed on bubble growth and deformation under an electric field in order to elucidate the mechanisms of boiling heat transfer enhancement by EHD (Electro- Hydrodynamic) effects. Transient Navier-Stokes and Maxwell's equations were solved simultaneously for liquid and vapor phases in a two-dimensional cylindrical co-ordinate system making use of the VOF (Volume of Fluid) method. Bubble growth in liquid R113 under atmospheric pressure has been simulated. First, elongation of a single bubble under uniform electric field is simulated and the final shapes of the bubble are found to be in good agreement with Garton's analytical and experimental results. Second, the bubble deformation process under non-uniform electric field was simulated. A bubble initially attached to the lower electrode starts to deform and finally detaches from the lower electrode. The shape of bubble depends on the intensity of the electric field. The behavior of bubbles, the velocity vectors, and the contours of electric field are also shown and compared with experiment.

An approximate image solution method for the electrostatic quadrupole lens

While no simple image method exists that yields an exact solution for the potential around the parallel conducting cylinders of a quadrupole electrostatic lens, we have found that using two line image charges in each cylinder makes an excellent approximation. Graphs are presented of the equipotentials and contours of electric field squared for different rod spacing.

Field-contour plots in parabolic cylinder by method of moments

Quantitative data on the field strength inside a parabolic cylinder when excited by a normally incident uniform plane wave are provided. The result is given in the form of contours of electric field within the cylinder and current distributions on the reflector, both for different focal-length/aperture (f/a) ratios.