Design of Half Impulse Radiating Antenna (HIRA) With Tapered Transverse Electromagnetic (TEM) Horn–Based Novel Feeding Mechanism for Intentional Electromagnetic Interference (IEMI) Applications

Body: Newly emerged wide bandgap semiconductor (WBG) β-Ga2O3 has been extensively researched for power electronics, RF electronics and optoelectronics due to its large bandgap of 4.7- 4.9 eV and high breakdown field of ~ 8 MV/cm. Due to the absence of p-type Ga2O3, most of demonstrated β-Ga2O3 devices are unipolar devices such as high electron mobility transistors (HEMTs) and Schottky barrier diodes. To overcome this limitation, other p-type materials, such as GaN and NiO, have been investigated to produce Ga2O3 based p-n heterojunctions. Among these p-type materials, p-GaN has attracted especial interests since GaN is also a WBG semiconductor and has a clear crystallographic relationship to β-Ga2O3 for epitaxial growth. In addition, both β-Ga2O3 and GaN can be produced in the industrial standard tools, i.e., the metalorganic chemical vapor deposition (MOCVD). The growth of high-quality GaN on Ga2O3 by MOCVD has been recently reported. β-Ga2O3/GaN p-n heterojunction via mechanically exfoliation also showed decent rectifying behaviors. However, the breakdown capability of the β-Ga2O3 based p-n heterojunctions is still far from expectations due to the lack of effective edge terminations. Here we design and simulate mesa based edge terminations for the vertical β-Ga2O3/GaN p-n heterojunctions using SILVACO TCAD simulator. The model was first calibrated by the experimental results, including the conduction and valance band offsets of the heterojunction and electrical properties. The device structure consisted of n+-Ga2O3 n-contact layer, 5 µm unintentionally doped (UID) β-Ga2O3 drift layer and 500 nm p-GaN layer. The ideal breakdown voltage (BV) of the heterojunction was 1.37 kV, while the BV of the reference device without effect mesa edge termination dropped dramatically to 300 V due to the electric field crowding at the device edge. Therefore, it is critical to design and optimize the mesa edge termination to improve the BV of the β-Ga2O3/GaN p-n heterojunctions. Three mesa edge termination structures were investigated in this work: beveled mesa, step mesa, and deeply-etched mesa. The beveled mesa angle θ is the key parameter in determining the device BV. When θ was varied from 15° to 90°, the highest BV of 1224 V was obtained for θ =15°. For the step mesa edge termination, the width (W), depth (D), and the number of steps define the mesa structure. It was found that the BV of the devices increased with increasing number of steps. The combination of (W, D) values of (0.5,0.5) and (0.5,1.0) and (1.0,1,0) was investigated, where all the values are in µm. The highest value was obtained for W = 0.5µm, D = 1.0µm and the number of steps = 5. Smaller W and larger D led to better BV. The electric field distributions of devices with different mesa edge terminations were compared at –300V. Without effect mesa edge termination, the peak electric field at the junction edge was ~ 4.2 MV/cm. By incorporating the mesa edge termination techniques, the electric field crowding at the device edge was mitigated, and the peak electric fields were reduced to 1.8 MV/cm and 2.4 MV/cm for the beveled and step mesa edge terminations, respectively. For the deeply-etched mesa structure, it was found that a more uniform electric field distribution was observed when the mesa depth was increased from 0.5,1.0, 2.0, to 3.0 µm, where the peak electric fields were decreased from 2.1, 1.8 ,1.5 to 1.2 MV/cm, respectively. In summary, this work presents a comprehensive design and optimization of mesa edge terminations for the wide bandgap vertical β-Ga2O3/GaN p-n heterojunctions, which is first of its kind. Three mesa structures were explored, including beveled mesa, step mesa and deeply-etched mesa. It was found that these mesa edge terminations can alleviate the electric field crowding at the junction edge and increase the device BV. This work can provide critical guidance for the development of high-performance β-Ga2O3 based bipolar high voltage and high power devices.

The bit error rate (BER) of ultra-wideband (UWB) impulse communication system may vary significantly with the reception direction due to the angle-dependent pulse distortion in UWB radiation. UWB system with aperture antenna of uniform tangent electric field distribution suffers more system degradation than those with linearly- tapered distribution or Gaussian distribution. For UWB impulse system with serious pulse distortion, proper design of the temperate pulse waveform improves effectively the system performance.

In this paper, experimental results are reported about the new Al0.25Ga0.75N/GaN high electron mobility transistor (HEMT) with a step AlGaN layer. The rule of 2DEG concentration variation with the thickness of AlGaN epitaxial layer has been applied to the new AlGaN/GaN HEMTs: The step AlGaN layer is formed at the gate edge by inductively coupled plasma etching, the 2DEG concentration in the etched region is much lower than the other parts of the device. A new electric field peak appears at the corner of the step AlGaN layer. The high electric field at the gate edge is decreased effectively due to the emergence of the new electric field peak, and this optimizes the surface electric field of the new AlGaN/GaN HEMTs. The new devices have the same threshold voltage and transconductance as the conventional structure, -1.5 V and 150 mS/mm. That means, the step AlGaN layer does not affect the forward characteristics of the AlGaN/GaN HEMTs. As the more uniform surface electric field distribution usually leads to a higher breakdown voltage (BV), with the same gate to drain length LGD=4 m, the BV can be improved by 58% for the proposed Al0.25Ga0.75N/GaN HEMTs as compared with the conventional structure. At VGS=1 V, the saturation currents (Isat) is 230 mA/mm for the conventional Al0.25Ga0.75N/GaN HEMT and 220 mA/mm for the partially etched Al0.25Ga0.75N/GaN HEMT (LEtch=4 m, LGD=4 m). The decrease of Isat is at most 10 mA/mm. However, as the BV has a significant enhancement of almost 40 V, these drawbacks are small enough to be acceptable. During the pulse I-V test, the current collapse quantity of the conventional structure is almost 40% of the maximum IDS(DC), but this quantity in the new devices is only about 10%, thus the current collapse effect in Al0.25Ga0.75N/GaN HEMTs has a significant remission for a step AlGaN layer. And as the high electric field peak at the gate edge is decreased, the effect of the gate electrode on electron injection caused by this electric field peak is also included. The injected electrons may increase the leakage current during the off-state, and these injected electrons would form the surface trapped charge as to decrease the 2DEG density at the gate. As a result, the output current and the transconductance would decrease due to the decreased electron density during the on-state. That means, with the region partially etched, the electron injection effect of the gate electrode would be remissed and the stability of Schottky gate electrode would be improved. In addition, due to the decrease of the high electric field at the gate edge, the degradation of the device, which is caused by the high electric field converse piezoelectric effect, will be restrained. The stability of the partially etched AlGaN/GaN HEMT will become better.

The breakdown performance of the AlGaN/GaN high electron mobility transistor (HEMT) is limited by the high electric field peaks in the device. To obtain a more uniform electric field distribution, the drift region width modulation (DWM) technique is proposed to reshape the charge distribution between the gate and drain electrodes. By applying the Gaussian box method, an effective designing guidance for the structure optimization of the AlGaN/GaN HEMT with adaptive-width drift region pillars (AWD-HEMT) is obtained. The fabricated AWD-HEMT demonstrated a significant improvement in breakdown performance. The Baliga’s figure of merit (BFOM) of AWD-HEMT improved 65.3% compared with the conventional HEMT, without introducing complicated processes. In addition, the mechanism of the AWD-HEMT is explored by numerical methods. The simulations indicate that a more uniform electric field distribution at AlGaN/GaN interfaces could be obtained, and the increased varying rate of the adaptive-width drift region (AWD) pillars results in a more obvious electric field modulation effect.

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The cell pitch of high voltage lateral power devices determines many important device performance specifications such as the area of the chip, on-state voltage drop and the maximum controllable current. Since the cell pitch of lateral power devices is determined by the long drift region lengths required to support high voltages in accordance with the RESURF principle, it is desirable to have a uniform lateral electric field distribution in the drift region to minimize the drift region length for a device with a given breakdown voltage. It is generally assumed that the breakdown voltage of DI RESURF devices scales up linearly with increasing drift region length till a limit associated with vertical breakdown is reached. However, 2D numerical simulations of the breakdown of DI PIN diodes indicate non-ideal electric field distribution in the drift region. Two techniques have been studied for achieving a more uniform electric field distribution in the drift region for DI lateral power devices. One technique involves the use of a SIPOS field plate over the drift region to spread the electric field uniformly. The other technique involves tailoring the drift region doping profile, so that the drift region charge increases linearly from the anode end to the cathode end.

Transverse electromagnetic (TEM) cells are usually used to perform electromagnetic interference (EMI) measurements of equipment inside the cell in a plane wave-field environment. A newly developed technique of generating predominantly high-impedance electric or low-impedance magnetic fields inside a TEM cell for EMI measurements of relatively small printed circuit boards (PCBs), electronic devices, etc., is described. The technique simulates environments similar to the near-field EMI environment for intrasystem EMI/EMC (electromagnetic compatibility) studies. Variations of electric and magnetic fields, as well as impedances along the length of the cell, are given. The results indicate that a test region of reasonable size exists in the cell over which the field amplitudes are uniform within +or-1 dB. >

Electromagnetic Environment Associated with Lightning Strikes to Tall Strike Objects

A balanced transverse electromagnetic (TEM) horn type antenna is designed and developed for a 120 kV, 66 Ω high power ultra wideband (UWB) radiator. This antenna consists of a coaxial to parallel plate unzipper BALUN followed by an exponentially tapered TEM horn structure. Analysis of this antenna in time and frequency domain is performed using CST Microwave Studio. This antenna is having a power handling capacity of 1000 MW, with percentage bandwidth of 167%. This antenna has a gain of ~10 dB at 1 GHz frequency. Return loss performance of better than −10 dB is observed in 150 MHz to 1 GHz frequency range. Effective radiation of short pulses (<5 ns) with very fast rise time (300–500 ps) has been demonstrated using this high‐power antenna. Practical results at 220 MW power are presented in this article. Directional performance of this antenna is practically established through peak power patterns in horizontal and vertical plane.

Uniform electric field distribution in electroporation is crucial for achieving the effective localized delivery of drug molecules. Currently, in vitro electroporation studies on adherent cells lack a standardized test setup for obtaining consistent and repeatable results, unlike in vitro electroporation studies on cell suspensions that use electroporation cuvettes, which provide uniform electric field distribution. Considering this, we designed, built, and tested a novel inset design for low-volume round well plates, such as the 24- and 96-well plates which are most commonly used in cell culture labs. The inset design was realized using 3D printing and experimentally tested using potato phantoms and HeLa cells. Finite element analysis (FEA) was used to compute the electric field distribution in the round well plates with and without the inset. The FEA indicated that the electric field contour map at the bottom of the well with the inset had a more uniform electric field distribution, with an average value close to the expected 1000 V/cm. In contrast, it was only 840 V/cm without the inset, indicating non-uniform electric field distribution. Uniform electric fields were also obtained using the inset for the potato phantoms and the HeLa cells, indicating the merit of the inset and its usability with low-volume cell culture well plates, which enable the transfer of cells for various assays without additional steps, as well as its cost-effectiveness.

The formation of avalanche charge domain in high-power GaAs device has been studied numerically. According to the numerical simulation results of the distribution of electric field in the bulk of the device, the variation rules of peak electric field within the domain and the domain width with the bias electric field, the carrier concentration, and the device length are obtained, respectively, and by the comparison of the variation rules with and without considering carrier impact ionization, the effect of the carrier impact ionization on the peak electric field and the domain width have been obtained. It shows that 1) the peak electric field is mainly determined by the bias electric field, the carrier concentration and the device length, and the domain width is mainly determined by the carrier concentration and the device length; 2) the carrier impact ionization and avalanche multiplication have a significant effect on the peak electric field and domain width; and 3) the value of the peak electric field and domain width are closely related to the position of domain in the direction of domain motion. Based on the variation of peak electric field and domain width, the formation of avalanche charge domain is discussed. Our results can deepen the understanding of breakover mechanism of GaAs devices and contribute to the optimization of GaAs devices performance.

Electric field plays a key role in producing required nanofibers in electrospinning. This study aims to achieve uniform electric field distribution in multijet electrospinning by designing the appropriate spinneret and collector geometry. Based on the three-dimensional electric field simulation, three kinds of spinneret and two kinds of collectors have been designed. The simulation results show that a flat spinneret creates a more uniform electric field distribution than the multineedle spinneret with an auxiliary plate. The two-step spinneret can intensify the electric field at the central area and create a rather uniform electric field. A smaller collector creates a more uniform electric field distribution, and a curved collector creates a more uniform surface electric field. The simulation results have been verified by experiments. The experiments show that thinner and more uniform fibers are collected when using the two-step spinneret and a smaller flat collector, and the thickness of fiber mat is mor...

Corona discharge at the tip of buildings in a thunderstorm environment is an important factor causing changes in the near-ground electric field, but the influence of a quadratic growth law and quantitative research on the parameters is still rare. Therefore, based on the three-dimensional corona discharge model, this paper studies the influence of positive and negative symmetrical triangular wave electric fields with different amplitudes on the corona discharge of an independent lightning rod. Studies have shown that the corona current is synchronized with the peak of the background electric field. Studies have shown that the corona current is synchronized with the peak of the background electric field. When the polarity of the electric field changes from positive to negative, the positive charge accumulated in the positive half-cycle promotes the subsequent negative corona, so the negative corona starts in advance when the polarity reverses. Compared with unipolar discharge, the amplitude of the negative current and the number of negative charges have significantly improved. However, due to the counteraction of neutralization between positive and negative charges, the total corona charge is at a low level, which shows a net negative polarity result. The corona current and the amount of charge increase nonlinearly with an increase in the background electric field amplitude. Under the symmetrical triangular wave electric field, the quantitative fitting relationship between the peak value of the negative corona current in the second half-cycle and the amount of charge is established for the 5 m high independent lightning rod, which is I− = −0.0532 − 0.153 E − 0.0682 E2, Q− = −3.18 × 10−3 + 7.762 × 10−4E − 4.671 × 10−5 E2, respectively. The increase in the background electric field amplitude will aggravate the disturbance of the corona discharge to the near-surface electric field. When the direction of the electric field has reverted to zero, the existence of the space charge will lead to a significant change in the strength and polarity of the ground electric field. When the thunderstorm background electric field changes from positive to negative, the corona effect reverses the polarity of the ground electric field in advance, and the larger the peak value of the background electric field, the larger the advance. The corona interference mechanism revealed by this study can provide an important reference for correcting the electric field monitoring data and improving the accuracy of lightning warnings.

Planar UWB integrated with multi narrowband cylindrical dielectric resonator antenna for cognitive radio application

We are conducting research in photoconductive switching for the purpose of generating a microwave pulse. This paper describes our experiments of ultra-wideband (UWB) pulse generation using a photoconductive switch in GaAs:Cr operating in the linear mode and radiation by an exponential flared section to the line. The pulse waveform radiated is measured by a UWB conical antenna and the peak electric field is about 1 kV/m in 3 m from the end of the flared line.