Dynamically tunable ultralong photonic nanojet by a curved surface truncated dielectric microcylinder

As for micro-particles (microspheres or microcylinders) that form Photonic nanojet (PNJ) in near fied,a curved truncated dielectric microcylinder structure (CSTDM) is investigated by finite element method(FEM) which can form ultralong PNJ with the longest effective length:209.49λ. We found that changing parameter h of structure can realize long dynamic range tuning of the effective length of PNJ. The effective length varies quasi-periodically with h; the law of the variation of main indicators of microcylinder are further discussed, such as the effective length,the working distance, peak electric field intensity and full width half height

Transcranial direct current stimulation in patients after decompressive craniectomy: a finite element model to investigate factors affecting the cortical electric field

Objective To simulate the process of transcranial direct current stimulation (tDCS) on patients after decompressive craniectomy (DC), and to model cortical electric field distributions under different electrode montages, we constructed a finite element model that represented the human head at high resolution. Methods Using computed tomography images, we constructed a human head model with high geometrical similarity. The removed bone flap was simplified to be circular with a diameter of 12 cm. We then constructed finite element models according to bioelectrical parameters. Finally, we simulated tDCS on the finite element models under different electrode montages. Results Inward current had a linear relationship with peak electric field value, but almost no effect on electric field distribution. If the anode was not over the skull hole (configuration 2), there was almost no difference in electric field magnitude and focality between the circular and square electrodes. However, if the anode was right over the hole (configuration 1), the circular electrodes led to higher peak electric field values and worse focality. In addition, configuration 1 significantly decreased focality compared with configuration 2. Conclusion Our results might serve as guidelines for selecting current and electrode montage settings when performing tDCS on patients after DC.

Study on Surface Enhanced Raman Scattering of Au and Au@Al2O3 Spherical Dimers Based on 3D Finite Element Method

In this paper, the surface enhanced Raman scattering (SERS) characteristics of Au and Au@Al2O3 nanoparticle dimers were calculated and analyzed by using finite element method (3D-FEM). Firstly, the electric field enhancement factors of Au nanoparticles at the dimer gap were optimized from three aspects: the incident angle of the incident light, the radius of nanoparticle and the distance of the dimer. Then, aluminum oxide is wrapped on the Au dimer. What is different from the previous simulation is that Al2O3 shell and Au core are regarded as a whole and the total radius of Au@Al2O3 dimer is controlled to remain unchanged. By comparing the distance of Au nucleus between Au and Au@Al2O3 dimer, it is found that the electric field enhancement factor of Au@Al2O3 dimer is much greater than that of Au dimer with the increase of Al2O3 thickness. The peak electric field of Au@Al2O3 dimer moves towards the middle of the resonance peak of the two materials, but the peak electric field of Au dimer is more concentrated than that of Au dimer, so that the excitation wavelength has less influence on Raman enhancement. The maximum electric field enhancement factor 583 is reached at the shell thickness of 1 nm. Our results provide a theoretical reference for the design of SERS substrate and the extension of the research scope.

SiC Trenched Schottky Diode with Step-Shaped Junction Barrier for Superior Static Performance and Large Design Window

A novel silicon carbide (SiC) trenched schottky diode with step-shaped junction barrier is proposed for superior static performance and large design window. In the proposed diode, to improve tradeoff between specific on-resistance and surface peak electric field, the shape of the trenched-junction is modified to stair-step, without extra fabrication process. To investigate the performances of the SiC step-shaped trenched junction barrier schottky (SSTJBS) diode, numerical simulations are carried out through Silvaco TCAD. The results indicate that the proposed diode can accommodate highly doped drift region with no degradation of its reverse blocking characteristic. In comparison with the conventional SiC trenched junction barrier schottky (TJBS) diode, the proposed SiC SSTJBS diode shows a larger design window of drift region doping concentration from 7.9×1015cm-3 to 9.5×1015cm-3. In the design window, the specific on-resistance and surface peak electric field can be reduced by 12.9% and 11%, respectively.

Estimating the electric field response to the Halloween 2003 and September 2017 magnetic storms across Scotland using observed geomagnetic fields, magnetotelluric impedances and perturbation tensors

Geomagnetic storms generate heightened magnetovariational activity, which induces electric fields that drive hazardous currents known as geomagnetically induced currents (GICs) through man-made technological conductors including power transmission lines, railway networks and gas pipelines. We multiply magnetotelluric (MT) impedances from 23 sites in Scotland and northern England with measured geomagnetic field spectra from the Halloween 2003 and September 2017 storms to estimate maximum peak-to-peak, electric field magnitudes and directions for these storms, which we present as hazard maps. By sampling these electric fields in the direction of the longest (>50 km), high-voltage (275 and 400 kV) Scottish power transmission lines and integrating along their lengths, we estimate their associated transmission-line voltages. Lateral electrical conductivity variations in the Earth generate horizontal magnetic field gradients. We investigate the effect of these gradients on electric field estimates obtained using remote magnetic fields by applying a correction to the impedance tensor derived from the magnetic perturbation tensor between the local MT site and the remote magnetic field site. For the September 2017 storm, we also compare our estimated electric fields with a unique dataset comprising measured storm-time electric fields from 7 MT sites. We find that peak-to-peak, electric field magnitudes may have reached 13 V/km during the Halloween storm in some areas of the Scottish Highlands, with line-averaged electric fields >5 V/km sustained along a number of long-distance, high-voltage power transmission lines; line-averaged electric fields for the September 2017 storm are 1 V/km or less. Our surface electric fields show significant site-to-site variability that arises due to Earth’s internal 3D electrical conductivity structure, as characterised by the MT impedance tensors.

Improving Linearity and Robustness of RF LDMOS by Mitigating Quasi-Saturation Effect

This paper discusses linearity and robustness together for the first time, disclosing a way to improve them. It reveals that the nonlinear transconductance with device working at quasi-saturation region is significant factor of device linearity. The peak electric field is the root cause of electron velocity saturation. The high electric field at the drift region near the drain will cause more electron-hole pairs generated to trigger the parasitic NPN transistor turn-on, which may cause failure of device. Devices with different drift region doping are simulated with TCAD and measured. With LDD4 doping, the peak electric field in the drift region is reduced; the linear region of the transconductance is broadened. The adjacent channel power ratio is decreased by 2 dBc; 12% more power can be discharged before the NPN transistor turn-on, indicating a better linearity and robustness.

Design, Modeling & Simulation of Analysis of coupling to Cables due to Electromagnetic Pulse (EMP)

This paper is to analyze the EMP coupling to cables using 3D EM Modeling and Simulation Analysis. Bounded wave transmission line structure as per MIL-STD 461, RS105 EMP requirement in terms of peak electric field of 50KV/m with rise time-2.3ns and pulse width-25ns was developed. Single conductor cable, RF Coaxial cable were modeled. EMP Coupling to cables was carried out by placing the cable under generated EMP field in terms of induced voltage and currents due to EMP fields. EMP coupling to active line with matched termination also analyzed.