Electromagnetic Environment Research Articles

NEAT Based Approach for Cognitive Covert Communication Assisted by UAV-IRS

Abstract To address the security vulnerabilities inherent in cognitive radio technology amidst extensive control information and data exchanges, this paper introduces the use of unmanned aerial vehicle equipped with intelligent reflecting surfaces (UAV-IRS) as relay nodes to facilitate covert communications for cognitive users. Given the complexities and dynamics of the electromagnetic environment, which involve multiple interconnected and constantly changing communication resources, as well as high-dimensional data, we propose the NeuroEvolution of Augmenting Topologies based Resource Optimisation Algorithm Method (NEAT-ROAM). This advanced algorithm continuously optimizes and adapts the network structure in response to the external environment, ensuring robust and secure communication in dynamic and challenging scenarios. The algorithm not only provides superior covert communication performance but also exhibits fast convergence, which can be applied to the problem of assisting covert communication under mobile conditions using UAV-IRS.

Thickness-controlled HsGDY/N-doped double-shell hollow carbon tubes for broadband high-performance microwave absorption

With the increasing deterioration of the electromagnetic environment, it is important to develop new and efficient electromagnetic wave-absorbing materials. In this work, bilayer hollow HsGDY/NC nanotubes with controllable thickness are constructed by introducing high conductivity polydopamine (PDA) and hydrogen-substituted graphdiyne (HsGDY) followed by the etching and carbonization. Subsequently, the effects of the composition, coating order, and structural characteristics of nanotubes on the electromagnetic parameters are thoroughly investigated, thereby analyzing the microwave absorption mechanism. The impedance matching of HsGDY/NC is optimized by changing the thickness of NC layer, while utilizing unique multi-heterogeneous interfaces and hierarchical conductive structures that enhance the interface polarization and conductive loss. As a result, HsGDY@NC-3 displays the optimal absorbing performance with an effective absorption bandwidth (EAB) of 7.8 GHz (10.1–17.9 GHz) and a minimum reflection loss (RLmin) of −47.18 dB at the filler content of only 11 %. This work broadens the application scopes of HsGDY and provides a novel insight into the design of lightweight, high-efficiency, and wide-frequency microwave absorbers, which is expected to be a potentially effective microwave-absorbing material.

The Impact of Mobile Phone Electromagnetic Waves on the Neurons and Blood Brain Barrier Integrity in the Chick Embryo

The electromagnetic environment surrounding us has dramatically evolved over the past decade, with the proliferation of Wi-Fi, Bluetooth, and other wireless technologies becoming commonplace in our daily lives. Mobile phones emit non-ionizing low-frequency electromagnetic waves (EW). To examine the effects of EW on living cells, this study aims to explore the impact of cell phone EW on the developing brain of chick embryos. The fertilized eggs were allowed to develop under exposure to electromagnetic waves emitted by cell mobile. A cell phone was placed inside the incubator with 20 eggs and was called from outside on a precise schedule. The same number of fertilized eggs were placed in another incubator without a mobile phone and served as the control. Embryos were sacrificed on days 10 and 15, and the cerebral cortex and cerebellum were removed and sent for electron microscopy. In the control group, cerebral neurons appeared healthy, with a large, centrally placed nucleus, visible oligodendrocytes, and a less dense extracellular matrix. In contrast, neurons from the exposed group were smaller, fewer in number, with unclear nuclear margins, signs of shrinkage, and apoptosis and a dense extracellular matrix. In the cerebellum, the exposed group revealed a reduced number of Purkinje neurons and noticeable mitochondrial swelling. The blood-brain barrier remained intact in the control group but was compromised in the exposed group. We conclude that electromagnetic waves emitted by cell phones adversely affect the normal development of the brain in chick embryos.

All Inorganic Scintillating Fiber for Thermal Neutron Detection

AbstractThermal neutron detection with scintillating fibers has excellent scientific and technological potential for remote and spatially resolved detection. However, most fibers are polymers, and developing all‐inorganic scintillating fibers remains a significant challenge. Herein, all‐inorganic scintillating fibers and prototype neutron detection devices are successfully constructed for neutron detection. The scintillating fibers with a perfect waveguide configuration and tunable size have been fabricated through the melt‐in‐tube method. The interactions between the thermal neutron and scintillating fiber have been theoretically analyzed. The dependence of the neutron absorption ability on the core diameter, cladding thickness, and 6Li abundance has been investigated. Guided by the above experimental and theoretical results, the configuration of the scintillating fiber and the corresponding neutron detection prototype device has been built. Its practical application for neutron detection has been demonstrated, and importantly, the single thermal neutron event can be successfully monitored. The device shows great promise for neutron detection applications in special scenarios such as tiny space and electromagnetic interference environments.

Swarm Investigation of Ultra-Low-Frequency (ULF) Pulsation and Plasma Irregularity Signatures Potentially Associated with Geophysical Activity

Launched on 22 November 2013, Swarm is the fourth in a series of pioneering Earth Explorer missions and also the European Space Agency’s (ESA’s) first constellation to advance our understanding of the Earth’s magnetic field and the near-Earth electromagnetic environment. Swarm provides an ideal platform in the topside ionosphere for observing ultra-low-frequency (ULF) waves, as well as equatorial spread-F (ESF) events or plasma bubbles, and, thus, offers an excellent opportunity for space weather studies. For this purpose, a specialized time–frequency analysis (TFA) toolbox has been developed for deriving continuous pulsations (Pc), namely Pc1 (0.2–5 Hz) and Pc3 (22–100 mHz), as well as ionospheric plasma irregularity distribution maps. In this methodological paper, we focus on the ULF pulsation and ESF activity observed by Swarm satellites during a time interval centered around the occurrence of the 24 August 2016 Central Italy M6 earthquake. Due to the Swarm orbit’s proximity to the earthquake epicenter, i.e., a few hours before the earthquake occurred, data from the mission may offer a variety of interesting observations around the time of the earthquake event. These observations could be associated with the occurrence of this geophysical event. Most notably, we observed an electron density perturbation occurring 6 h prior to the earthquake. This perturbation was detected when the satellites were flying above Italy.

Formal estimation of wireless network services for signal strength and electromagnetic wave association in an International Green University

The United Nations focuses on 17 urgent problems to call for action in all countries. Goal 7 of the 17 urgent problems is based on affordable and clean energy. Since 2017, National Taitung University (NTTU) has dedicated more time and effort to attain the wisdom, health, sustainability and aesthetics as an international green university. To accomplish this, we adhere and construct a safe radiofrequency and electromagnetic wave environment to achieve healthy and sustainable campus objectives. According to the UI GreenMetric World University Rankings, NTTU was ranked 74th in 2021, 67th in 2022 and 58th in 2023. In this study, we propose a formal estimation of wireless network services for classrooms or smart spaces to achieve the goal of safe radiofrequency and electromagnetic waves. Inside classrooms or smart spaces, better wireless signal strength and safer electromagnetic waves are achieved. Moreover, the proposed method can be used to determine the quantity of wireless access points for a given classroom or smart space to avoid unsafe electromagnetic waves and inappropriate energy consumption. The experimental results show that all benchmarks meet the wireless exposure limits of the WHO and physician safe technologies in the NTTU.

Multifunctional carbon Fiber@TiO2/C aerogels derived from MXene for pressure tunable microwave absorption

Developing microwave absorption (MA) materials with dynamically tunable performance stands as a pivotal endeavor to fulfill the escalating demands of electronic devices and military equipment in complex electromagnetic environments. This study presents advanced hierarchical CF@TiO2/C aerogels with pressure tunable MA performance, engineered through a novel in-situ oxidation process of MXene on carbon fiber (CF) substrates. This process facilitates the formation of a two-dimensional (2D) TiO2/C hybrid layer, which significantly enhances the polarization loss capabilities of the aerogels while maintaining excellent mechanical resilience. The unique architecture of these aerogels facilitates the modulation of their electrical conductivity and permittivity via pressure, thus enabling dynamically adjustable MA performance. Upon compression (50 %), the CF@TiO2/C aerogels showcase an outstanding effective absorption bandwidth (EAB) of 7.84 GHz, accompanied by a remarkable minimum reflection loss (RLmin) of −74.38 dB. Notably, the EAB of CF@TiO2/C aerogels can be precisely tuned from 4 to 18 GHz (covering the C-band, X-band, and Ku-band), with maximum changes in RLmin values (ΔRLmin) reaching as high as 59.30 dB, indicating substantial tunability under varying pressure. Moreover, the CF@TiO2/C aerogels also demonstrate outstanding thermal insulation and pressure sensing performance, highlighting their potential for multifunctional applications. This research not only sheds light on the intricate interplay between nanostructured materials and electromagnetic waves interactions but also sets a new strategy for the design of multifunctional, tunable microwave absorbers suitable for complex electromagnetic environments in modern electronic and military applications.

Specific emitter identification unaffected by time through adversarial domain adaptation and continual learning

Timely identifying the emitter of target signals is crucial for communication security in complex electromagnetic environments. Specific emitter identification (SEI) is a technique to identify emitters using the hardware fingerprints of emitters. In this paper, the impact of changes in hardware fingerprints over time on SEI is solved, which significantly deteriorates identification performance. This issue is addressed from two aspects: one is mitigating the impact of these changes, and the other is tracking and adapting to them. For the aspect of mitigating impact, an alternating adversarial domain adaptation (AADA) method is proposed to eliminate the time-varying component in hardware fingerprints. Subsequently, a feature map calculation method using weighted Euclidean distance is designed, preserving the main parameters of feature maps for each emitter. For the aspect of tracking and adapting to changes, a continual learning method was designed based on feature maps of each emitter. This approach incorporates the selective annotation of unlabeled new data with an iterative optimization training process. To validate the effectiveness of the proposed method, we independently collected comprehensive time-variant datasets as well as simpler datasets with varying receivers and environments. The proposed method was tested on these datasets and compared with existing conventional and advanced methods. The experimental results indicate that the proposed SEI method exhibits superior recognition performance. Compared to existing methods, it achieved an average recognition accuracy improvement of over 8% on the time-variant dataset, and demonstrated enhanced robustness against these three types of variations.

Nonlinear electrodynamics and its possible connection to relativistic superconductivity: an example

Abstract This work presents an illustrative example suggesting a potential connection between the Heisenberg–Euler (HE) model of nonlinear electrodynamics (NLED) and relativistic superconductivity. Within a cylindrical coordinate system, we derive nonlinear Maxwell’s equations from the HE Lagrangian to the fourth order in the electromagnetic (EM) field. By considering static electric and magnetic fields with Gaussian radial profiles, we compute the corresponding HE current density. In parallel, we explore relativistic type-II superconductivity in analogy with the Ginzburg–Landau (GL) theory. We calculate the vortex-supercurrent density of the condensate and propose a link between this current and the HE current. This connection enables the derivation of the relativistic order parameter state. The problem considered in this article may contribute to the understanding of superconductivity in strong EM environments within the broader framework of NLED.

Test and evaluation of radar systems operating in the modern electromagnetic spectrum

AbstractModern radar systems are critical infrastructure in defence and civilian applications. In the defence domain, modern radars operate in a highly contested, congested, and constrained electromagnetic environment. In the context of operating in this challenging environment, the challenges across the system life cycle are examined in testing modern radar systems which are characterised by advanced features, such as multi‐function capability, advanced digital signal processing, high resolution, wideband, and frequency agile systems that incorporate phase array and active electronically scanned array capabilities. The challenges and key objectives in testing these sophisticated modern radar systems are highlighted, as well as the enabling technologies that can support Test & Evaluation of such systems. An architecture for Hardware‐in‐the‐Loop testing, which leverages modular and flexible commercial‐of‐the‐shelf hardware, is proposed together with an application software that allows the testing of radar with a radar target generator.

Seamlessly merging radar ranging and imaging, wireless communications, and spectrum sensing for 6G empowered by microwave photonics

To facilitate intelligent interconnection among people, machines, and things, the next generation of communication technology must incorporate various sensing functions besides high-speed wireless communications. Integration of radar, wireless communications, and spectrum sensing is being investigated for 6G with increased spectral efficiency, enhanced system integration, and reduced cost. Microwave photonics, a technique that combines microwave engineering and photonic technology is considered an effective solution for implementing the integration and breaking the bottleneck problems of electronic solutions. Here, we show a photonics-assisted joint radar, wireless communications, and spectrum sensing system that enables precise perception of the surrounding physical and electromagnetic environments while maintaining high-speed communication. Communication signals and frequency-sweep signals are merged optically using a shared system architecture and hardware to achieve signal level sharing, ultimately simultaneously achieving high-accuracy radar ranging and imaging with a measurement error within ± 4 cm and an imaging resolution of 25 × 24.7 mm, high-data-rate wireless communications at 2 Gbaud, and wideband spectrum sensing with a frequency measurement error within ±10 MHz in a 6 GHz bandwidth.

Hygienic problems of using terahertz electromagnetic radiation (literature review)

The purpose of the work is to review and analyze domestic and foreign scientific works, systematize the scope of application of terahertz electromagnetic radiation (EMR) to determine hygienic problems in the field of health risk prevention in the development and use of modern radioelectronic devices. The literature search was conducted on the databases: eLibrary, Web of Science, and fifty. During the study of scientific literature, from over fifty works were analyzed, there 36 sources were selected 36 sources corresponded to the purpose of the study. Today, the urgent tasks are to predict the parameters of a complex electromagnetic environment in open areas and inside buildings using mobile communication standards 4, 5 and 6G, scientific justification of hygienic standards for the combined effects of the electromagnetic factor, methodological approaches to monitoring EMR levels, including the development of domestic selective EMR meters in a wide range of frequencies (radio frequency and terahertz ranges)

Superbunched Radiation of a Tunnel Junction due to Charge Quantization.

A chaotic light source is characterized by the fact that many independent emitters radiate photons with a random optical phase. This is similar compared to a tunnel junction where many independent channels are able to emit photons due to a coupling to an electromagnetic environment. However, in a recent experiment it has been observed that a tunnel junction can deviate from the expectation of chaotic light and is able to emit strongly correlated, superbunched photons. Motivated by this, we study the correlation of the radiation and show that the superbunching originates from the emission of multiple photons which is possible due to the quantization of charge.

Bi-functional flexible Ag2Se/Polyvinylidene fluoride composite films for thermal energy conversion and electromagnetic interference shielding by solution 3D printing

Developing bi-functional thermoelectric (TE) and electromagnetic interference (EMI) shielding materials is an effective way for the integrated electronic devices to face the accumulated thermal energy and complicated electromagnetic environment. Herein, flexible Ag2Se/polyvinylidene fluoride (Ag2Se/PVDF) composite films were successfully prepared through solution 3D printing and subsequent annealing treatment. As Ag2Se content increased, both the power factor and average total EMI shielding effectiveness (SET) were boosted. When the mass fraction of Ag2Se was 85 wt%, a power factor of 904.6 μW m−1K−2 at 360 K was achieved for the ASP-85 composite film. Meanwhile, this ASP-85 composite film shown the outstanding SET value of 56.1 dB at 52 μm thickness. Flexible Ag2Se/PVDF composite films displayed the excellent thermal energy conversion and EMI shielding capacity.

Multi-spectrum compatible electrochromic device combining microwave transmission with ultra-wide emissivity modulation

The potential of polyaniline (PANI)-based electrochromic devices (ECDs) to offer adaptive anti-surveillance stealth in the visible/infrared bands is considerable. However, the incompatibility between infrared and radar stealth renders it challenging to achieve compatibility between the two with PANI-based ECDs. In this work, an etched electrode with frequency-selective surface configurations is initially designed for selective transmission and reflection of microwaves. Subsequently, a stellate PANI is prepared on the electrode surface by introducing triphenylamine (TPA) modification into the long molecular chain of disordered PANI, and assembled into a multi-spectrum compatible ECD. The results demonstrate that the ECD can achieve efficient transmission between 10.2–13.9 GHz, with a transmission rate approaching 90 % at 11.92 GHz, and enables the visible characteristics to switch between jungle dark green and desert earthy yellow. Furthermore, thermal-infrared emissivity (ε) modulation is achieved in the atmospheric transmission windows of 3–5 μm and 8–14 μm, with maximum emissivity change (Δε) of 0.61 and 0.73, respectively. The ECD demonstrated the capacity to exceed the limitations of static camouflage associated with existing multi-spectrum stealth materials, and exhibited a high degree of adaptability in intelligent electromagnetic confrontation environments.

Research on Spatial Electric Field Measurement of DC Line with MEMS Electric Field Sensor

Abstract As more and more UHVDC transmission lines are put into operation or under construction, the demand for space electromagnetic environment monitoring around transmission lines is increasingly urgent. In view of the lack of effective measuring instruments and methods for spatial DC electric field, this paper studies the spatial electric field measurement of DC line with a field mills MEMS electric field sensor. The relationship between the output current of the sensor and the intensity of the DC electric field is derived. In view of the error caused by the space accumulation of induced charge on the cover of the sensor, the structure of the sensor is further designed. In the new structure design, the shielding electrode grounding method is used to solve the accumulation of space charge on the shielding sheet. After calibrating and testing the response characteristics of the sensor in the performance test platform, the sensor is used in the DC line space electric field simulation test experiment. The output results of MEMS sensor at different spacing and voltage levels are consistent with the electric field distribution law. The measurement results prove that the designed structure is feasible to measure the space electric field of DC line, which is important for monitoring the electromagnetic environment.

Research and implementation of a large-bandwidth real-time radar jamming simulator.

The electromagnetic environment faced by modern radar is becoming increasingly complex. One effective means to improve the performance of radar systems is testing in an anti-jamming ability test chamber, where the increased complexity has also led to higher performance requirements for radar jamming simulators. Based on the requirements for modern radar system testing, this paper presents a study of a large-bandwidth real-time radar jamming simulator and describes its overall design architecture; the simulator covers the L-Ku and Ka frequency bands and the instantaneous bandwidth is ≥2GHz, which means that the system is able to simulate 11 interference patterns. Synchronous control of the system is realized in 1ms through use of the reflection memory interrupt mechanism, the synchronous pulse signal mechanism, synchronous timing design, and a real-time control software architecture. An overall design scheme for real-time simulation of a radar target jamming echo is given and baseband signal processing resources are saved through information preprocessing, a large-capacity high-speed storage board is designed to improve the data reading speed, a multiphase filtering structure is used to achieve high sampling rates and save hardware resources, and a high-speed parallel computing method is used to improve computing efficiency; the actual measured baseband signal processing time is less than 500ns. Finally, a measurement platform is built, and the main interference patterns are verified through experimental measurements.

A novel spike detection model for dynamic stress monitoring of bogie frame

The fatigue evaluation of the bogie frame is an important part of the structural health monitoring of the vehicle. During the dynamic stress monitoring, some signal spikes, which are much larger than the normal fluctuation range due to the interference of the complex electromagnetic environment, affect the accuracy of the structural damage assessment and need to be accurately detected and replaced. Aiming at the drawbacks of traditional detection methods that are overly dependent on engineering experience and not universal, a novel spike detection model is proposed in this paper. By the process of data transformation, spike region features are effectively separated. Based on the isolation forest algorithm, the normalized anomaly score of each point is calculated, and the threshold is determined adaptively. The spike detection rate and damage sensitivity are proposed as the evaluation indices of the detection effect of the method. The results show that the spike detection rate is improved by 7.86% on average, and the damage sensitivity is improved by 15.59% on average. The spike detection model in this paper is significantly improved compared to the existing methods.

A three-band narrow-band terahertz perfect absorber for patch antennas and other sensors

We have studied a multi-mode resonance and actively tunable high-sensitivity terahertz perfect absorber using a microstructured Dirac semimetal. The absorber is composed of gold-dielectric-Dirac semimetal three-layer structure, which has good optical sensing characteristics. The absorber produces three perfect absorption modes (>95%) in the range of 2–6 THz, with a minimum bandwidth (FWHM) of 0.18 THz. We studied the adaptability of the device response mode to the actual complex electromagnetic environment by simulating the deflection incident angle. In addition, we also analyzed the influence of various parameter variables on the absorption performance, which provides a clearer idea and more possibilities for the wider application of the device. In terms of sensing detection, the absorber has a maximum refractive index sensitivity S of 610 GHz/RIU and a maximum figure of merit FOM of 3.4 in the ambient refractive index range of 1 to 1.8. Finally, we also realized the tunable absorption frequency of the absorber in 60–80 meV. We believe that based on the good optical properties of the absorber, the device has potential application value in communication technology, space exploration and so on.

A Generalisable Heartbeat Classifier Leveraging Self-Supervised Learning for ECG Analysis During Magnetic Resonance Imaging.

Electrocardiogram (ECG) is acquired during Magnetic Resonance Imaging (MRI) to monitor patients and synchronize image acquisition with the heart motion. ECG signals are highly distorted during MRI due to the complex electromagnetic environment. Automated ECG analysis is therefore complicated in this context and there is no reference technique in MRI to classify pathological heartbeats. Imaging arrhythmic patients is hence difficult in MRI. Deep Learning based heartbeat classifier have been suggested but require large databases whereas existing annotated sets of ECG in MRI are very small. We proposed a Siamese network to leverage a large database of unannotated ECGs outside MRI. This was used to develop an efficient representation of ECG signals, further used to develop a heartbeat classifier. We extensively tested several data augmentations and self-supervised learning (SSL) techniques and assessed the generalization of the obtained classifier to ECG signals acquired in MRI. These augmentations included random noises and a model simulating MRI specific artefacts. SSL pretraining improved the generalizability of heartbeat classifiers in MRI (F1=0.75) compared to Deep Learning not relying on SSL (F1=0.46) and another classical machine learning approach (F1=0.40). These promising results seem to indicate that the use of SSL techniques can learn efficient ECG signal representation, and are useful for the development of Deep Learning models even when only scarce annotated medical data are available.