Showing papers in "IEEE Transactions on Electromagnetic Compatibility in 2021"

Assessment of Human Exposure to Electromagnetic Fields: Review and Future Directions

Abstract: This article reviews recent standardization activities and scientific studies related to the assessment of human exposure to electromagnetic fields (EMF). The differences of human exposure standards and assessment of consumer products and medical applications are summarized. First, we reviewed human body modeling and tissue dielectric properties. Then, we explain the rationale of current exposure standards from the viewpoint of EMF and the standardization process for product compliance based on these exposure standards. The assessment of wireless power transfer, as an example of emerging wireless devices, and environmental EMFs in our daily lives are reviewed. Safety in magnetic resonance systems, where the EMF exposure is much larger than from typical consumer devices, is also reviewed. Finally, we summarize future research directions and research needs for EMF safety.

A Novel Miniaturized Strong-Coupled FSS Structure With Excellent Angular Stability

Abstract: In this article, a novel miniaturized concept named strong-coupled frequency selective surface (SC-FSS) with excellent angular stability is presented. First, a conceptual design of SC-FSS is introduced, where the resonant frequencies are insensitive to almost all incident angles. A corresponding equivalent circuit model is developed to interpret the operating principle and formulate relevant design equations with an error of 0.2%. Furthermore, an ultraminiaturized and ultrathin band-stop structure with a unit cell size of λ 0/35 and thickness of 0.26 mm ( λ0 /578) is designed and fabricated to verify this concept. Analysis and experiment show that the proposed band-stop SC-FSS structure can work stably at 2 GHz for both TE and TM modes, even when the incident angle varies from 0° to 84°. The measurement results are consistent with those obtained by full-wave simulations and the equivalent circuit model, which fully demonstrates that the concept of SC-FSS can be widely used in designing antenna reflectors, electromagnetic interference shielding, and angle-insensitive absorbers.

Impact of Frequency-Dependent Soil Models on Grounding System Performance for Direct and Indirect Lightning Strikes

Abstract: The goal of this article is to investigate the effect of frequency-dependent soil models on the performance of grounding electrodes subjected to lightning strikes. Several soil models are examined while accounting for the variation of soil resistivity and permittivity as a function of the lightning current frequency spectrum. The analysis is performed for a homogeneous soil and a two-layer horizontally stratified soil. The impact of the frequency-dependent soil parameters on the ground potential rise (GPR) of simple grounding electrodes subjected to lightning is analyzed and discussed. The analysis is performed in the frequency domain and in the time domain. A wind turbine and its grounding system are also considered in this article. Special attention is given to the case of indirect lightning, rarely mentioned in the literature. The GPR of the grounding electrodes is examined when the frequency dependence of the soil is taken into account and the lightning channel is located at close distances to the electrodes. Indeed, the level of induced electromagnetic fields caused by a nearby lightning channel can still be too high and potentially dangerous. The computations are performed using an efficient Method of Moments (MoM) numerical tool based on surface-wire integral equations for a stratified medium in the frequency range from dc to several MHz. Numerical results demonstrate that the frequency dependency of the soil parameters results in a decrease of the potential rise of the grounding electrodes, with respect to the case where the parameters are assumed constant.

A Simple Polarization-Insensitive and Wide Angular Stable Circular Ring Based Undeca-Band Absorber for EMI/EMC Applications

Abstract: In this article, a closed ring resonator-based absorber with eleven consecutive absorption peaks is proposed over X and K bands with an average absorption rate of 96.29%. The proposed design consists of circular ring resonators embedded in the circularly slotted square patch printed on the top of the grounded FR-4 substrate. The surface current distributions well illustrates the reason behind the electromagnetic (EM) wave absorption. The design is polarization insensitive for normal incidence and wide angular stable up to 45° for TE (60° for TM) polarization. The structure is fabricated on a single-layered FR-4 dielectric substrate with a periodicity of ${{\boldsymbol{\lambda }}_{\boldsymbol{o}}}$ /2.32 and thickness of ${{\boldsymbol{\lambda }}_{\boldsymbol{o}}}$ /16.74, where ${{\boldsymbol{\lambda }}_{\boldsymbol{o}}}$ is the free-space wavelength at the lowest resonant frequency. A transmission line-based equivalent circuit model has been illustrated and good agreement is observed with full-wave simulations. This article's novelty lies in the absorption mechanism of eleven consecutive absorption peaks, demonstrating the controllability of the absorptivity peaks and resonant frequency. To the best of the authors’ knowledge, the proposed absorber demonstrates the highest number of near-unity successive absorption bands with better angular stability. The proposed structure was checked for radar cross section reduction application with an X -band antenna and results show 19.7-dBsm reduction at normal incidence.

Modeling and Suppression of Electromagnetic Interference Noise on Motor Resolver of Electric Vehicle

Abstract: Electromagnetic interference (EMI) couplings between motor drive system and resolver circuit induce considerable EMI noise in resolver, which has a serious impact on the excitation and feedback signals of resolver. In order to suppress the EMI noise effectively, it is necessary to study the coupling mechanism between the motor drive system and the resolver circuit. In this article, an EMI estimation model of resolver is proposed. An electric vehicle motor drive system is used for analysis. Coupling effects between permanent-magnet synchronous machine and variable reluctance resolver are investigated and modeled. Impedance measurement and numerical simulation are used to extract model parameters. Based on the estimation model, the conversion of common-mode (CM) noise to differential-mode (DM) noise in resolver circuit is analyzed. The estimation model is validated by comparing simulated results and measured results. Then, a CM choke is designed in the resolver circuit to suppress the coupled EMI noise. This modeling method is applicable for analyzing the EMI noise coupling between motor drive system and other low-voltage sensitive circuits.

An Effective EMTR-Based High-Impedance Fault Location Method for Transmission Lines

Abstract: This article summarizes the electromagnetic time-reversal (EMTR) technique for fault location, and further numerically validates its effectiveness when the fault impedance is negligible. In addition, a specific EMTR model considering the fault impedance is derived, and the correctness of the model derivation is verified by various calculation methods. Based on this, we found that when the fault impedance is large, the existing EMTR methods might fail to accurately locate the fault. We propose an EMTR method that improves the location effect of high-impedance faults by injecting double-ended signals simultaneously. Theoretical calculations show that this method can achieve an accurate location for high-impedance faults. To further illustrate the effectiveness, the proposed method is compared with the existing EMTR methods and the most commonly used traveling wave-based method using wavelet transform. The simulation results show that the proposed double-ended EMTR method can effectively locate high-impedance faults, and it is more robust against synchronization errors compared with the traveling wave method. In addition, the proposed method does not require the knowledge or a priori guess of the unknown fault impedance.

A Novel Ultrawideband Absorptive Common-Mode Filter Design Using a Miniaturized and Resistive Defected Ground Structure

Abstract: An ultrawideband absorptive common-mode filter (A-CMF) with a newly developed defected ground structure (DGS) is proposed in this article. The DGS miniaturized to a subwavelength size is able to totally suppress the common-mode noise while maintaining the signal integrity of the differential mode. In addition, the reflection and radiation of the common-mode noise are negligible in the stopband. For quick design, a simplified equivalent circuit model is also proposed. This model can be employed to estimate the resistances of the lumped resistors embedded in the DGS to obtain a very wide absorption band. In the demonstrated example, the fractional bandwidth determined by a 90% absorption efficiency can achieve as large as 104% around 3.55 GHz for an A-CMF realized on a simple two-layer printed circuit board. Such a widely absorptive bandwidth is never achieved before to our knowledge. The design methodology is validated by full-wave simulation. Finally, real measurement of the design is also carried out to confirm the design and analysis.

Transient Analysis of ESD Protection Circuits for High-Speed ICs

Abstract: Electrostatic discharge (ESD) failures in high-speed integrated circuits (ICs) cause critical reliability problems in electronic devices. Transient voltage suppressor (TVS) diodes are installed on high-speed I/O traces to improve system-level ESD protection. To protect the circuit, the majority of ESD current must flow into the external TVS diode rather than into the IC, but due to turn- on behavior, the TVS diode may not snap back when needed and the IC's internal protection may take most of the current. These race conditions between the internal and external ESD protection circuits were investigated for a universal serial bus(USB) interface board. The transient turn- on behavior of the on-chip and off-chip protection circuitry was characterized by measurements and by system efficient ESD design (SEED) simulations. The effect of transmission line pulses (TLP pulses) and power supply voltages of different sizes on the response of the protection circuitry were monitored and compared with SEED simulations. SEED models showed good agreement with measurements and were used to study the impact of passive components added to a high-speed trace or within the IC package on the ESD protection response. Results show the importance of properly accounting for the parasitic resistance and inductance between the on-chip diode and off-chip TVS diode, as well as the length of the transmission line when choosing the external TVS device. Results also show that testing must be performed using mid-level events to account for possible problems due to race conditions.

Ultra-Wideband Polarization Insensitive Thin Absorber Based on Resistive Concentric Circular Rings

Abstract: Eliminating stray and suppressing unwanted radiation in a high frequency circuit is difficult. It becomes a challenge to achieve an ultra-wide absorption band in a thin-single-layer microwave absorber. In this article, a novel polarization-independent, ultra-wideband, light-weight, thin microwave absorber has been investigated numerically and experimentally. The proposed absorber unit cell consists of two concentric circular rings loaded with lumped resistances placed on top surface of a dielectric substrate. Unit cell size is 0.28 λL * 0.28 λL * 0.067 λL, which is compact in configuration (where λL is the wavelength corresponding to lowest frequency of operation). The proposed design provides more than 90% absorption in the frequency range of 6.7 GHz to 20.58 GHz (fractional bandwidth of 101.7%). The novelty of the proposed work lies in designing a wideband and ultra-thin absorber by using optimum unit cell geometry, resistance loading, and air column loading. Combination of these techniques results in a very wide band absorber design. Four fold structural symmetricity makes the absorber polarization insensitive. The absorber is compact, light-weight (used air as spacer), and thin (only 0.067 λL thick) and provides an alternative to construct wideband absorber for electromagnetic interference reduction.

EMI in a Cardiac Implantable Electronic Device (CIED) by the Wireless Powering of a Left Ventricular Assist Device (LVAD)

Abstract: This article deals with the electromagnetic interference (EMI) in a cardiac implantable electronic device (e.g., implantable cardioverter-defibrillator or cardiac resynchronization therapy) generated by a left ventricular assisted device (LVAD) powered by a wireless power transfer (WPT) system. Wireless LVAD, not yet available in the market, is currently being investigated for many aspects spanning from electronics, hydraulic, electrical feeding, mechanical, and its possible impact on other implanted devices, such as a cardiac implantable electronic device (CIED). No results are yet published on possible EMI effects produced by the WPT coil currents in the pacing leads of a CIED implanted in the same patient with the LVAD. To this aim, the next generation of wireless LVADs with transcutaneous WPT system is first described, and, then, used to predict the induced voltage by the WPT system on a CIED lead. The obtained results demonstrate as the proposed WPT system, tested in accordance with the ISO 14117 standard, does not interfere with other CIEDs.

Heatsink Preselection Chart to Minimize Radiated Emission in Broadband on the PCB

Abstract: In this article, the type of heatsinks and the horizontal/vertical orientation of them on the printed circuit boards are investigated to reduce electromagnetic interference (EMI) effects caused by the heatsink on the electronic components on the mainboard. The circular, rectangular, and square heatsinks with the equal base area are designed, simulated, and measured in the 1–10 GHz band. All parameters such as the reflection coefficient, electric field values, and radiation pattern are obtained and compared with each other to specify both selection priority of heatsink type and its orientation in a certain frequency range. As a novelty, both the effect of heatsink type and its orientation on EMI performance is investigated to prepare a heatsink selection handout by using simulation and measurement results. While the radiation emission (RE) of the circular type is the lowest between 1.8–3.6 and 5.8–7.8 GHz bands, the RE of the rectangular one is the lowest in 3.6–5.8 and 9.2–10 GHz. Also, for 1–10 GHz range, horizontal orientation is preferred for 10% of the whole frequency region, while vertical orientation is better for 24% regardless of the heatsink type.

Exposure Assessment of Array Antennas at 28 GHz Using Hybrid Spherical Near-Field Transformation and FDTD Method

Abstract: To protect humans from overexposure to electromagnetic (EM) fields above 6 GHz, recently revised International Commission on Non-Ionizing Radiation Protection guidelines and IEEE standard specify the basic restrictions in terms of absorbed power density (APD) and epithelial power density, respectively. To assess the EM exposure resulting from the 5G mmWave array antenna, we adopted a hybrid method that combines spherical near-field measurements and numerical dosimetry with spherical near-field transformation. Four array antennas working at 28 GHz were used as the radiation sources. The incident power density (IPD), APD, and temperature rise in a stratified body model and anatomical partial body models corresponding to different body locations were evaluated for various antenna-body distances. The results were validated by comparison with the full-wave simulations. The differences in peak spatial-average IPD and APD between two methods are below 0.08 and 1.05 dB, respectively, for the simulated cases and generally decrease with the increasing antenna-body distance. The highest heating factor for the peak spatial-average APD was approximately 0.025°C/(W/m2). The results also show that the differences in APD and temperature rise caused by various exposed body locations are marginal.

Electromagnetic Cavity Resonance Equalization With Bandpass Negative Group Delay

Abstract: This article deals with an original equalization method of 3-D electromagnetic (EM) cavity resonance by using bandpass negative group delay (NGD) function Based on the equivalent circuit, the S -matrix model of the equalized EM cavity is introduced The design equations of the NGD function are established in function of the cavity physical parameters The feasibility of the equalization method is validated with a 42×28×38 cm rectangular cavity containing two communicating monopole antennas By considering the TE110-mode, a significant equalization is realized with improvement of transmission coefficient flatness from 4 dB to less than 03 dB In addition to the magnitude, the NGD equalization method enables to outstandingly reduce spikes of 3-D EM cavity group delay With the proof of concept, the GD is reduced from more than 4 to 1 ns

Wave Propagation Characteristics and Electromagnetic Transient Analysis of Underground Cable Systems Considering Frequency-Dependent Soil Properties

Abstract: The accurate estimation of the influence of the imperfect earth on the propagation characteristics of conductors is a crucial issue in electromagnetic (EM) transient analysis. In this aspect, the frequency-dependence of the soil electrical properties should be also considered. The effects of the dispersion of soil electrical properties on EM propagation have been investigated mostly for overhead transmission lines. This article presents a detailed EM transient analysis of underground cable systems taking into consideration the frequency-dependent (FD) soil properties. A generalized earth formulation of cable earth return impedance and shunt admittance is adopted. Propagation characteristics and transient responses are calculated by using both FD soil models and constant soil properties, as well as approximate earth formulations, neglecting the influence of the imperfect earth on shunt admittances; significant differences are observed. Guidelines for the accurate evaluation of earth conduction effects on the transient performance of underground cable systems are also introduced.

Machine Learning-Based Prediction of MRI-Induced Power Absorption in the Tissue in Patients With Simplified Deep Brain Stimulation Lead Models

Abstract: Interaction of an active electronic implant such as a deep brain stimulation (DBS) system and magnetic resonance imaging (MRI) radiofrequency (RF) fields can induce excessive tissue heating, limiting MRI accessibility. Efforts to quantify RF heating mostly rely on electromagnetic (EM) simulations to assess individualized specific absorption rate (SAR), but such simulations require extensive computational resources. Here, we investigate if a predictive model using machine learning (ML) can predict the local SAR in the tissue around tips of implanted leads from the distribution of the tangential component of the MRI incident electric field, E tan. A dataset of 260 unique patient-derived and artificial DBS lead trajectories was constructed, and the 1 g-averaged SAR, 1 g SARmax, at the lead-tip during 1.5 T MRI was determined by EM simulations. E tan values along each lead's trajectory and the simulated SAR values were used to train and test the ML algorithm. The resulting predictions of the ML algorithm indicated that the distribution of E tan could effectively predict 1 g SARmax at the DBS lead-tip ( R = 0.82). Our results indicate that ML has the potential to provide a fast method for predicting MR-induced power absorption in the tissue around tips of implanted leads such as those in active electronic medical devices.

Broadband Microwave Absorption Properties of a Frequency-Selective Surface Embedded in a Patterned Honeycomb Absorber

Abstract: In this article, a patterned honeycomb absorber (PHA) with an embedded frequency-selective surface (FSS) was proposed for broadband applications The impedance of the FSS embedded in a homogeneous honeycomb absorber (HA) was first analyzed, which suggested that directly combining an FSS with a homogeneous HA was unreliable Subsequently, a PHA was developed to adjust the input impedance Using the PHA, an FSS embedded in patterned honeycomb absorber structure with a wide absorption band was developed The consistency between the simulated and measured results verifies the analysis and design principle The proposed absorber may be very suitable for various microwave applications owing to its low cost, lightweight, high strength, and environmental friendliness

Three-Dimensional Printing of Honeycomb Microwave Absorbers: Feasibility and Innovative Multiscale Topologies

Abstract: In this article, we propose to apply 3-D printing technology to the design and realization of honeycomb microwave absorbers. First, printability of simple honeycomb structures, made of a lossy dielectric material, was evaluated and validated by measurement in the 2–18 GHz frequency band. Effective dielectric properties of honeycomb structures with different dimensions are also discussed. Then, the interest of 3-D printing technology was highlighted by the design, fabrication, and measurement of a multiscale honeycomb absorber that can significantly increase the relative bandwidth. The 3-D printed honeycomb absorbers are compared with others technologies. The potential of this technology was also illustrated by the fabrication and measurement of a pyramidal honeycomb absorber that demonstrates an absorption level of more than 22.9 dB over the 2–18 GHz frequency band.

GPR-Based EMI Prediction for UAV's Dynamic Datalink

Abstract: The datalink of an unmanned aerial vehicle (UAV) is vulnerable to external electromagnetic interference (EMI) The characteristic parameters of the EMI signal can be definitively detected by a developed monitoring platform mounted on the UAV, but it is impossible to determine the lost-link thresholds of the datalink in any state by experiment because the state of the datalink varies dynamically with the flight distance and the UAV's attitudes In this case, whether a certain state of the UAV's datalink will be interrupted or not by the EMI cannot be evaluated In this article, a method of EMI prediction for the UAV's dynamic datalink based on the Gaussian process regression (GPR) is proposed, two indicators, including the interfering frequency and the operation signal power of the datalink, are taken as the training inputs, and the lost-link thresholds of the datalink obtained by the EMI injection test are taken as the training targets The results show that this method can effectively fit the training samples and determine a 95% confidence interval of the predictive outputs, which has a low predictive error, less than 22 dB Compared with the methods of the layer recurrent neural network and support vector machine, the GPR method has higher predictive accuracy and a stronger generalization ability Therefore, the detected EMI characteristic parameters can be used as new input samples to predict the lost-link thresholds in any condition On this basis, the EMI margin can be calculated to evaluate the degree of the anti-EMI redundancy of the UAV's datalink, which can be used for the active adaptation of the UAV's datalink to EMI in the future

Isolation Improvement of Compact Microbase Station Antenna Based on Metasurface Spatial Filtering

Abstract: A compact high-isolation multiple-input multiple-output (MIMO) microbase station antenna consisting of two dual-polarized antenna elements is presented. The symmetrical magnetic coupling feeding network is used to feed the radiation patch of the dual-polarized antenna and to improve the isolation of the antenna element. By introducing parasitic square patches, the radiation characteristics and isolation of the dual-polarized antenna are improved. In addition, a modified closed-loop metasurface unit is designed and used to construct an isolation wall. When dual-polarized antenna elements are used to assemble a MIMO antenna, the proposed metasurface structure is inserted between them to reduce the coupling between MIMO antenna elements, regarded as a spatial band-stop filter to suppress the spatial electromagnetic waveform of the elements. After loading the metasurface isolation wall, the maximum increase of isolation is 9.17 dB at the center frequency point of 2.6 GHz. For antenna element ports and cross-polarized ports, the isolations are greater than 30 dB, and the isolation of the same polarized ports is better than 25 dB within the frequency band from 2.45 to 2.8 GHz. At the same time, the reflection coefficients of the ports of the elements are less than −15 dB. Finally, a prototype of the proposed MIMO microbase station antenna was fabricated and tested, and the experimental results are proximity with the simulation responses.

Analytical Evaluation of the Low-Frequency Magnetic Shielding of Thin Planar Magnetic and Conductive Screens

Abstract: A recent analytical formulation for the low-frequency magnetic shielding effectiveness of a thin metal screen against a circular loop source is extended to the case of a screen exhibiting both magnetic and conductive properties. The presence of magnetic properties introduces a series impedance in the equivalent network of the structure, in addition to the shunt admittance associated with the screen conductivity. However, the fields scattered by the two elements do not interact and hence can be treated independently; furthermore, the series impedance gives rise to integrals akin to those stemming from the shunt admittance. A generalized analytical formulation for a combined magnetic and conductive screen is thus obtained, that is favorably compared with both classical approximate formulations and exact results.

Improved Coplanar Couplers Based WPT Systems for Adaptive Energy Harvesting on Power Towers

Abstract: Wireless power transfer (WPT) technology is promising for energy harvesting and electronics powering on power towers. This article presents an improved coplanar couplers based WPT system for adaptive energy harvesting on the towers. Magnetic flux analyses of conventional coaxial coils indicate that the significance of the adaptive and extensible performance in this application. Improved coplanar couplers are further proposed to reduce magnetic flux interactions between the WPT and high-voltage components and promote the performances, which include discrete transmitter windings, vertical receiver coil, and high-permeability layers. Related parameters are determined based on a concluded flow from a sequence of simulations. Moreover, performances of the WPT and high-voltage systems under operating conditions are simulated. The design does not break the high-voltage characteristic and shows robust performances from comparisons. Experimental results prove the effectiveness of the design with a 22.53% efficiency and an 18.98 W output power. Such an adaptive insulator-independent energy supply solution can be extended to different high-voltage towers.

Lightning Performance Evaluation of Transmission Line Based on Data-Driven Lightning Identification, Tracking, and Analysis

Abstract: Lightning performance evaluation is aimed at classifying transmission lines into different risk levels of thunderstorm-induced trip-out. Its applications range from better lightning protection guidance, arrester installation design, transmission line retrofits, and line corridor design. Previous studies fail to consider the real-time lightning intensity, which is an essential factor of lightning trip-out that must not be ignored. This article proposes a novel lightning performance evaluation model based on the idea that the tower, which has a record of lightning trip-out with weaker real-time lightning intensity, is more susceptible to trip out, which means low lightning performance. In order to quantify the lightning intensity, this article puts forward a new definition of lightning intensity which includes three kinds of real-time characteristics, that is the location, the current of lightning strike, and the number of times the lightning movement track crosses the transmission line. More specifically, with the rapid development of lightning location system, a novel Lightning Identification, Tracking, and Analysis algorithm is proposed to search lightning movement track based on a database of 17 million lightning records. When lightning trip-out happens, the lightning performance level is graded according to the real-time lightning intensity. By comparing the similarity of static characteristics, the lightning performance level is extended to the tower, which has no record of lightning trip-out. By comparison with the traditional model, the proposed model is closer to the actual situation and can significantly improve the accuracy of lightning performance evaluation, which is improved by 66.7%.

Design and Analysis of Single Sided Modified Square Loop UWB Frequency Selective Surface

Abstract: In this article, a compact frequency selective surface (FSS) is implemented using a modified metallic square loop structure for ultrawide band (UWB) stop behavior. The proposed structure exhibits wideband rejection over the entire UWB, ranging from 3.1 to 10.8 GHz. The proposed structure manifests polarization independent characteristics and provides a stable frequency response for normal and oblique angles under both transverse electric (TE) and transverse magnetic (TM) incident polarization. The angular stability for various polarization angles is also obtained. This structure provides a −10dB wide impedance bandwidth of 110.79%. The maximum relative deviation in between transmission zero frequency and angularly incident frequency is 5.9% and 6.2% at 80˚ TE and TM polarized wave, respectively, with attenuation more than 45 dB. The unit cell of the proposed FSS is imprinted on single-layer FR4 substrate of the dimensions 6 × 6 mm2, which is 0.062× 0.062 λ, where λ is the wavelength of lower cut-off frequency and is by far the smallest design for the desired UWB rejection FSS.

Hierarchical Attention-Based Machine Learning Model for Radiation Prediction of WB-BGA Package

Abstract: Rapid increase in operating frequency of integrated chips and intricacy of electronic packages outpaces the ability of conventional methods in coping with the growing complexity of electromagnetic interference (EMI) issues. To address it, several machine learning (ML) methods––deep neural network (DNN), convolutional neural network, support vector regression, K-nearest neighbor, and linear regression are constructed to acquire the best ML model to accurately and rapidly predict the maximum 3-m radiated electric field of a wire-bond ball grid array package. The key hyperparameters of different ML models are tuned respectively to attain the least prediction error for each model. Among the optimized ML models, the prediction accuracy of the DNN model is the highest. In this article, a hierarchical attention-based DNN model is proposed and discussed in depth to reduce the number of training datasets, and identify the structural parameters with large contributions to radiation prediction. These structural parameters with contributions can guide the packaging design. The DNN model with attention-weight input requires fewer training datasets than the original DNN model. Furthermore, the experimental measurement for EMI radiation of a test package board is implemented, and the far-field results show the effectiveness and feasibility of the DNN model.

Dual-Polarization Absorptive/Transmissive Frequency-Selective Surface With Tunable Passband

Abstract: A dual-polarization frequency-selective structure with a tunable passband and two absorptive bands is presented. Based on an equivalent circuit model (ECM), the working principle is investigated first. The values of components in the ECM are derived from the required performances and are mapped to the structure of an initial design, which is designed by cascading of an absorptive frequency-selective surface (FSS) realized with dipole-like elements and a lossless bandpass FSS achieved with square ring slot. For tuning the passband, varactors and biasing networks are added into the initial design. The adding of the varactors and biasing networks significantly affects the performance, and brings about the emergence of singular resonances. The approaches for mitigating the effects and the techniques for suppressing the singular resonances are proposed. Simulated results show that, between two absorptive bands, a passband is tuned from 3.33 to 5.13 GHz if the capacitances are decreased from 0.5 to 0.15 pF. A prototype is fabricated and measured. Measured results show that the passband is altered from 3.56 to 4.35 GHz as the reverse bias voltage of the used varactors is increased from 6 to 18 V.

Performance Analysis of Incident Power Density Evaluation by Inverse Source Method for Compliance Assessment at Quasi-Millimeter and Millimeter Wave Bands

Abstract: In modern communication systems including the fifth-generation mobile communication system (5G), quasi-millimeter, and millimeter wave frequencies above 6 GHz are utilized. At these frequencies, the incident power density is employed as a metric to assess the compliance of wireless devices to human exposure limits in international guidelines and national regulations. In this article, the performance of the inverse source method (ISM) for incident power density evaluation is investigated in terms of accuracy and operational costs, i.e., measurement and computational costs. The ISM is based on the surface equivalence theorem, and it reconstructs the incident power density close to the device under test from a field measured in a more distant region. The comparison of the performance between the ISM and the conventional plane-wave spectrum method by computational simulation shows that the ISM has an advantage over the conventional method in robustness to the truncation of the measurement region. The ISM reduces the number of measurement points to a quarter for the reconstruction of the spatially averaged incident power density in an error less than 0.4 dB. These findings in the computational simulations are also validated by the measurements of a standard horn antenna and array antennas operated at 28 GHz.

Effective Grounding of the Photovoltaic Power Plant Protected by Lightning Rods

Abstract: This article discusses the lightning protection performance of a grounding grid for photovoltaic (PV) systems protected by independent lightning rods Several grounding grid configurations are investigated, and the transferred voltages between the dc cables and supporting structures at different points in the PV system are evaluated using the finite difference time domain (FDTD) method In the PV system without a dedicated grounding grid for supporting structures, the transferred voltage is very high, and is even worse if the soil resistivity is high Installing a dedicated grounding grid, which is very costly in a large PV power plant, can reduce the amplitude of the transferred voltage and eliminate the residual voltage effectively It is found that the arrangement using a bonding network is superior to other grounding improvement approaches in lightning protection More importantly, the proposed approach is simple to implement and cost-effective With the bonding network, the soil with high soil resistivity will not lead to severe overvoltage in the system It is highly recommended to be adopted in the PV power plant protected by independent lightning rods

Additive Manufacturing of PLA-Based Microwave Circuit-Analog Absorbers

Abstract: Fused filament fabrication (FFF) was used to additively manufacture (3-D print) two-prototype circuit-analog (CA) absorbers. The CA absorbers consist of a lossy frequency selective surface (FSS), substrate, and ground plane. In this article, the FSS and substrate were manufactured using two different FFF materials to make a cohesive structure manufactured during a single printing procedure. To design the CA absorbers, the complex permittivity of FFF printed polylactic acid (PLA), bronze-, brass-, copper-, and iron-powder infused PLAs, and a graphite-PLA composite was measured using a free-space materials measurement system. Out of the candidate materials measured, graphite PLA and standalone PLA were selected as the FSSs and substrates, respectively. Complex permittivity data from the selected materials were input to Computer Simulation Technology Microwave Studio so that a genetic algorithm could optimize absorber dimensions. Reflectivity of the printed absorbers was measured using a free-space measurement setup. Measured reflectivity data were compared to that from simulations. A simulated-geometric tolerance study corroborated differences noted between ideal models and measured data. The results showed that FFF techniques can be used for CA-absorber designs and that 3-D printing settings can ultimately affect absorber performance.

Effect of Incidence Angle on the Spatial-Average of Incident Power Density Definition to Correlate Skin Temperature Rise for Millimeter Wave Exposures

Abstract: This article reports on an intercomparison study on the effect of the incidence angle on the spatial average of incident power density (PD) and resultant temperature rise using computational and thermographic measurement approaches. Two definitions of the spatial average of incident PD—the peak spatial-average normal component of the Poynting vector and peak spatial-average norm of the Poynting vector—were compared. First, an intercomparison of incident PD and temperature rise in a layered skin model was conducted for a 4 × 4 dipole array antenna. The variations caused by antenna type, antenna-body distance, and skin model to these definitions were then discussed. The results revealed that both definitions are in good agreement and correlate with the peak temperature rise for small or moderate incidence angles. The heating factor was enhanced for transverse-magnetic-like polarized waves for peak spatial-average normal component of the Poynting vector for large-angle incidences because of the Brewster effect. The normal incidence scenario was confirmed to be essential for considering the peak skin temperature rise.

Response of 10-kV Metal-Oxide Surge Arresters Excited by Nanosecond-Level Transient Electromagnetic Disturbances

Abstract: Nanosecond-level transient electromagnetic disturbance (TED), including very fast transient overvoltage caused by operation of disconnectors, high-altitude electromagnetic pulse, and many other fast transients may interfere or even damage the electrical equipment. As one of the main overvoltage protective equipment, the protective performance of metal-oxide surge arresters (MOAs) under nanosecond-level TED should be investigated and then compared with that under microsecond-level TED, especially the lightning impulse. Based on a testing platform containing a 400-kV pulse generator with adjustable rise time from 5 to 100 ns, the behaviors of nonlinearity, fast impulse response, and converting impedances of three types of 10-kV MOAs under TED with different rise time were explored experimentally in this article. The peak residual voltages of 10-kV MOAs under TED with the rise time of 5 ns at 5 kA are 50.2–60.7% higher than those under the lightning impulse. The rise time of TED has significant influence on the peak voltage and impedance converting behaviors of MOAs. A circuit model of 10-kV MOAs under nanosecond-level TED is built and validated by experimental results, which can be applied in insulation coordination and design of protective devices against TED.