Multidimensional heterostructure synergistic modulation of carbonyl iron/biomass-derived carbon composites for broadband efficient electromagnetic wave attenuation

A high-speed vehicle flying through the atmosphere between 100 and 20 km may suffer from a “communication blackout.” In this paper, a low frequency system with an on-board loop antenna to receive signals is presented as a potential blackout mitigation method. Because the plasma sheath is in the near-field region of the loop antenna, the traditional scattering matrix method that is developed for the far-field region may overestimate the electromagnetic (EM) wave's attenuation. To estimate the EM wave's attenuation in the near-field region, EM interference (EMI) shielding theory is introduced. Experiments are conducted, and the results verify the EMI shielding theory's effectiveness. Simulations are also conducted with different plasma parameters, and the results obtained show that the EM wave's attenuation in the near-field region is far below than that in the far-field region. The EM wave's attenuation increases with the increase in electron density and decreases with the increase in collision frequency. The higher the frequency, the larger is the EM wave's attenuation. During the entire re-entry phase of a RAM-C module, the EM wave's attenuations are below 10 dB for EM waves with a frequency of 1 MHz and below 1 dB for EM waves with a frequency of 100 kHz. Therefore, the low frequency systems (e.g., Loran-C) may provide a way to transmit some key information to high-speed vehicles even during the communication “blackout” period.

Use of borehole radar reflection logging to monitor steam-enhanced remediation in fractured limestone—results of numerical modelling and a field experiment

Stealth technology plays an important role in modern military conflicts, especially when used in fighter jets. Since airfoil structures have a leading edge, inlet, and surface bulge that are easily detected by radar, it is necessary to study the stealth of these structures. In this study, we investigate structures coated with radionuclides to generate plasma. Using simulation and calculation methods, the attenuation of 0.1–10 GHz electromagnetic waves propagating in plasma was studied. The results showed that the attenuation of low-frequency electromagnetic waves is greater than that of high-frequency electromagnetic waves. The attenuation of 0.1–1 GHz electromagnetic waves is found to be less than − 2.7 dB, − 3.0 dB, and − 15.6 dB at the airfoil leading edge, inlet, and surface bulge structures, respectively. We also found that the attenuation of electromagnetic waves with 0°-incidence is greater than that of waves with 10°, 20°, and 30° incidence angles. Additionally, the attenuation of electromagnetic waves decreases gradually as the incident angle increases.

The attenuation of electromagnetic (EM) waves in unmagnetized plasma generated by an inductively coupled plasma (ICP) actuator has been investigated both theoretically and experimentally. A numerical study is conducted to investigate the propagation of EM waves in multilayer plasma structures which cover a square flat plate. Experimentally, an ICP actuator with dimensions of 20 cm×20 cm×4 cm is designed to produce a steady plasma slab. The attenuation of EM waves in the plasma generated by the ICP actuator is measured by a reflectivity arch test method at incident waves of 2.3 GHz and 10.1 GHz, respectively. A contrastive analysis of calculated and measured results of these incident wave frequencies is presented, which suggests that the experiment accords well with our theory. As expected, the plasma slab generated by the ICP actuator can effectively attenuate the EM waves, which may have great potential application prospects in aircraft stealth.

In this paper, we discuss a novel underwater localization method using 3D Electromagnetic (EM) wave attenuation pattern. To calculate the EM wave attenuation in underwater, according to distance, we use the Friis-Shelkunoff (FRIIS) formula, which mainly depends on antenna properties and medium variables. The research on these variables was executed in previous works [3, 4]. In this work, 3D underwater localization method is proposed using the 3D attenuation model and depth data from the additional pressure sensor, which is realized with the several anchor nodes located in fixed positions and mobile node for receiving EM waves with an attached pressure sensor. We measured mobile node attenuation data in the underwater with position change in the x-z vertical plane. And it was compared with the theoretical 3D spatial attenuation model. The preliminary results about 3D underwater localization show good agreement with theoretical estimation.

This paper describes the electromagnetic wave (EM) attenuation by concrete blocks focusing on the frequency range 1.70 – 1.88 GHz and 3.40 – 3.80 GHz. The attenuation calculation of concrete was made according to ITU recommendation ITU-R P.2040-1 (07/2015) for conducting dielectric. Also, the attenuation calculation was made using simulated values of S 11 and S 21 parameters. These two sets of computationally derived data were compared with each other, and the differences were not significant. The values of EM wave attenuation during propagation through concrete were compared with the values from the available literature and the deviations are also minor. 5G systems use higher frequencies and the tested concrete materials shield the 5G signals better than 4G signals. The results of this research can be used in the building walls with high attenuation for 4G and 5G communication systems.

In this recent work, a ground penetrating radar (GPR) technique was proposed to evaluate the deteriorated depth of concrete bridge decks with asphalt overlays in the Korea expressway network. Air-coupled GPR was utilized in the measurement of the relative permittivity of concrete on bridge decks with asphalt overlays and the electromagnetic (EM) wave attenuation of the concrete cover of top reinforcing bars (rebars) in the pilot bridge in public service. In addition, 13 core samples were obtained from the bridge deck to carry out a detailed survey that includes visual inspection of the deterioration and measurement of chloride content with depth. The validity of the GPR technique was examined by comparing it with the results of the field investigation. Moreover, the correlation of the deteriorated depth with either the relative permittivity or EM wave attenuation was established. Results show that a GPR signal analysis method based on a dual-criteria (relative permittivity and EM wave attenuation) is more effective in analyzing the deterioration characteristics and evaluating the deteriorated depth of concrete bridge decks with asphalt overlay compared to the analysis method based on one of the two GPR properties. Results of the field test are considered to be significant wherein it establishes a relationship between the GPR property and deterioration characteristics of the bridge decks. Moreover, results show the practical applicability of the GPR technique in evaluating the deteriorated depth of the bridge decks with asphalt overlay.

The aim of the study is to identify and compare the attenuation of electromagnetic waves at 1.161 GHz and 2.45 GHz frequency between uncoated and coated woven fabric samples wherein the metal contained yarns were used in weft direction with increasing quantity per 10.5 mm long repeat of fabric length. Plain weave fabric samples were made of three different types of metal contained yarns in weft direction. The quantity of metal contained yarns per one centimeter was increased by every sample. In addition, samples were coated with polyurethane and graphite layers. The characteristics (thickness and surface density) of fabric samples were determined. The attenuation of electromagnetic (EM) waves was measured and compared for uncoated and coated samples. Two horn antennae and network analyzer were used to take measurements at 1.161 GHz and 2.45 GHz. The graphite coating made the attenuation higher for the samples with less content of metal contained yarns, but for the samples with bigger content of metal contained weft yarns, this improvement was inessential.

The phase engineering of the polarization interface is of great significance in modifying dielectric loss in electromagnetic wave (EMW) attenuation process, but hard to conduct in a complex hybrid system. Herein, a twin‐phase of β/γ‐MoCx@CN with matched Fermi level and closed work function properties in lightweight MoCx nanoflower is constructed, facilitating electron transport withdraw enhanced conductivity and polarization. Moreover, the EMW multiple dissipations among the β/γ‐MoCx@CN polarization interface is promoted, displaying better matched impedance. It delivered a remarkable minimum reflection loss (RLmin) of −74.2 dB at the thickness of 1.5 mm, which far beyond the single phased β‐MoCx@CN, γ‐MoCx@CN and reported MoCx‐based EMW absorbers. The radar cross‐section (RCS) map of β/γ‐MoCx@CN is simulated, showing a brilliant maximum reduction value of 13.6 dB m2 at the theta angle of 30°. This work presented an excellent sample of atomic‐level manipulation of interfacial polarization in dielectric MoCx EMW absorption materials.

Prediction of electron density is crucial to numerically evaluate the attenuation of electromagnetic waves in plasmas and to optimize the parameters. In this paper, a simple collisional-radiative model (CRM) to determine the electron density of Ar dielectric barrier discharge (DBD) plasmas for pressures ranging from 0.2 to 1 atm is introduced, and then, the attenuation of electromagnetic waves is analyzed. First, the radial average electron density of Ar DBD plasma is estimated by combining the measured current and a 1-D self-consist fluid numeric model. Second, based on a simple CRM, an optical emission spectroscopy method is used to determine the radial electron density distribution. Finally, according to the radial electron density distribution, the attenuation of electromagnetic waves is calculated at a frequency range from 10 MHz to 10 GHz. The result indicates that the electromagnetic waves with a relatively low frequency can be effectively attenuated by the plasma and the edge distribution of the plasma clearly affects the attenuation.

Segregated structure of poly (vinylidene fluoride-co-hexafluoropropylene) composites loaded with polyaniline@carbon nanotube hybrids with enhanced microwave absorbing properties

Lightweight electromagnetic (EM) wave absorbers made of ceramics have sparked tremendous interest for applications in EM wave interference protection at high temperatures. However, EM wave absorption by pure ceramics still faces huge challenges due to the lack of efficient EM wave attenuation modes. Inspired by the energy dissipation mechanism during fracture of lobster shells with a soft and stiff multilayered structure, we fabricate a high-performance EM wave absorption ceramic aerogel composed of an alternating multilayered wave transparent Si3N4 (N) layer and wave absorption SiC (C) layer by a simple restack method. The obtained N/C aerogel shows ultralow density (∼8 mg/cm3), broad effective absorption bandwidth (8.4 GHz), strong reflection loss (-45 dB) at room temperature, and excellent EM wave absorption performance at high temperatures up to 1000 °C. The attenuation of EM wave mainly results from a "reflection-absorption-zigzag reflection" process caused by the alternating multilayered structure. The superior absorption performance, especially at high temperatures, makes the N/C aerogel promising for next-generation wave absorption devices served in high-temperature environments.

Previously, we proposed a scheme that determines the position of a remotely operated underwater vehicle (ROV) from the signal strengths of commercial radio-frequency sensors and antennas. This scheme provides accurate position information in a structured environment but is limited to two-dimensional (2D) environments because the radiation power of the antenna depends on the elevation angle between the sending and receiving antennas. To overcome this problem, we propose a 3D localization scheme that considers the electromagnetic (EM) wave attenuation over the range of reliable elevation angles. In order to determine the reliable elevation scope, we analyzed the radiation patterns of dipole antennas. The feasibility of our approach is demonstrated in distance estimation and 3D localization experiments by varying the distance and elevation angle. Encouraged by these results, we constructed an underwater wireless sensor network in the experimental basin, and performed ROV position tracking with the depth sensor. The scheme achieved reliable localization accuracy at a fast sampling rate, demonstrating the feasibility of exploiting EM wave attenuation in localization.

Based on the complex Snell's law of lossy media, a ray tracing method is proposed to study the propagation attenuation characteristics of electromagnetic (EM) waves in plasma sheaths. The plasma sheath is modelled as layered media. This method considers the complex ray characteristics of inhomogeneous plane EM waves, tracks the propagation rays of EM waves in each layer of media, and calculates the propagation attenuation of EM waves in each layer of media according to the propagation direction of the complex rays. The attenuation during numerical cumulative propagation is the total attenuation of EM waves through the plasma sheath. By comparing the results with that obtained from the WKB method, the accuracy of the ray tracing algorithm is proved. The results of the propagation attenuation of a blunt cone model are calculated by the proposed method, and the effects of different parameters on the EM wave propagation attenuation in the plasma sheath are analysed at different heights, velocities, incident angles, and incident positions. Studying the propagation characteristics of EM waves in the plasma sheath is of importance in application for radar target tracking, blackout communication, and other issues.

With the continuous innovation of radar technology, both civilian and military radar shave more and more stringent requirements for accuracy in complex environments. Different from the previous research on long-distance electromagnetic wave propagation in rainfall environment, this paper mainly focuses on the attenuation of electromagnetic waves in the process of short-distance propagation. With the help of electromagnetic simulation software, a simulation model is established according to the precipitation of stratiform clouds in Henan Province to simulate the short-distance propagation process of electromagnetic waves in the P-band, and the electromagnetic wave attenuation is reflected by calculating the difference between the electric field energy before and after the path. The results show that in the case of short distance propagation in rainfall environment, at the same distance, with the increase of frequency, the attenuation of electromagnetic wave is also increasing, which is the same trend as that in the case of long distance propagation, and its attenuation can not be ignored under the conditions of precision guidance.