Single Frequency Band Research Articles

Electromagnetic Compatibility Study of Trackside Antenna Array Miniaturization in the Subway Tunnel

Abstract To improve the compatibility of the subway tunnel’s electromagnetic environment and reduce the radiation impact of trackside antennas on subway workers. This paper proposes a miniaturized dual-band trackside antenna array by using metamaterial units. Its operation bandwidth is 2.33~2.56 GHz and 3.24~3.45 GHz, which could simultaneously satisfy the signal cover demands of the communications-based train control (CBTC) and the civil 5G wireless communication system. The proposed miniaturized antenna array has a maximum gain of 14.4 dBi and a maximum channel capacity of 13.9 bps/Hz at a signal-to-noise ratio (SNR) of 20 dB, which can effectively improve the quality of wireless communication systems. The number of trackside antennas with a single operation frequency band is reduced, and the distance between the antennas is enlarged at the same time. Besides that, we analyze the radiation impact on the tunnel electromagnetic environment of the proposed trackside antenna array. In particular, the electromagnetic dose absorbed by the human model of a tunnel worker is quantized. The results show that the electric field strength in the tunnel reduces by 4.11% at least after antenna array miniaturization, and the specific absorption rate (SAR) absorbed by the worker model's trunk, skull, brain, heart, and liver is reduced by a maximum of 19.02%, 33.16%, 28.27%, 41.75%, and 74.54%, respectively, further lowering the human electromagnetic exposure risk. Therefore, a miniaturized trackside antenna array could reduce the interference from other radiation sources in the tunnel while providing a new idea for electromagnetic protection for subway workers.

High-efficient, polarization-insensitive, wide-angle, compact metamaterial energy harvester for S-band and C-band applications

This article proposes a polarization-insensitive compact Metamaterial (MM) energy harvester that can be used seamlessly in the S-band and C-band frequencies. It is important to focus on the limitations of many current designs of harvesters, which need to be overcome. The existing devices are large and often operate in a single frequency band, while their Energy Harvesting (EH) efficiency is low. The proposed harvester solves these problems using smart technology, using a rectangle strip with two gaps, each containing 50 Ω resistors for efficient energy collecting. Also, four hexagonal ring resonators are embedded into the cross-dumbbell configuration, connecting them with strip lines. Smaller rectangular rings surround these hexagonal rings, each with gaps labelled g1–g4. Despite its sophisticated design, the size of this harvester is (10 × 10) mm2 only. This harvester operates at frequencies of 3.5 GHz and 5.5 GHz, demonstrating remarkable absorption responses across varying polarizations and incident angles in both transverse electric (TE) and transverse magnetic (TM) modes. The simulation results indicated impressive energy harvesting efficiencies of 97% at 3.5 GHz and 98% at 5.5 GHz. In addition, experiments in an anechoic chamber with a 3 × 3 array (30 × 30) mm2 were used to confirm the efficiencies empirically. The simulated and measured results showed a strong correlation, confirming the reliability of the proposed design. The proposed MM harvester is distinguished by its high efficiency, polarization-insensitive behaviour, and compactness, making it very promising for many applications in EH.

Integration of dual band radio waves and ensemble-based approach for rice moisture content determination and localisation

Maintaining optimal moisture content in grain storage is critical to ensuring adequate supply throughout the year, but it presents a significant challenge. Current moisture measurement methods often necessitate sophisticated and costly equipment. This paper introduces an approach employing real-time rice moisture content determination and detection of spoilage (specifically wet spots) within a storage facility achieved through the utilisation of radio waves operating at 2.4 GHz and 868 MHz, along with an ensemble-based machine learning algorithm. Experimental samples spanning from 12% to 30% moisture levels were collected, then subjected to pre-processing, and subsequently employed to train the Ensemble-based Rice Moisture Content and Localisation (eRMCL) algorithm. The eRMCL produced an effective prediction of both rice moisture content and the localisation of wet spots within the grain storage unit. The results show that compared to support vector machine, random forest, and machine learning methods, the eRMCL algorithm had the best performance metrics, with an accuracy of 94.8% in predicting the moisture content and location of spoilage in storage. The measurement of moisture content and the identification of wet spots in rice storage using the dual frequency wave approach were found to be more accurate than with a single frequency band. Thus, the dual frequency band is a novel method for the determination of the moisture content of stored rice and the localisation of the spoilage area.

An ultralight, eco-friendly 3D porous carbon aerogel derived from cotton nano-cellulose for infrared stealth and microwave absorption

As multi-band military detection technology advances in the field of information warfare, stealth materials that are only applied for single frequency bands have extremely poor effectiveness in avoiding detection interference. Thus, it is urgent to develop stealth materials with compatible performance in multiple bands, especially infrared-radar compatible stealth materials. However, integrating infrared-radar compatiblity into one particular material remains a significant challenge. Inspired by the methods of structure design and component selection, this research provided a cotton nano-cellulose-based carbon aerogel with three-dimensional (3D) macro-mesoporous interface space for high-performance infrared-radar compatibility. When the density is only 0.005 ± 0.002 g cm−3, the infrared emissivity exhibits as low as 0.56 in 3–5 μm band and 0.52 in 8–14 μm band, the minimum reflection loss (RLmin) attains −19.8 dB, and the maximum effective microwave absorption bandwidth (EAB) covers 4.64 GHz. Additionally, computer simulation technology (CST) can be used to simulate the optimum radar cross section (RCS) reduction value of 15.86 dB m2, indicating that the aerogel has great potential in reducing the probability of being detected by radar detectors. Therefore, the lightweight porous carbon aerogels not only employ renewable and eco-friendly biomass materials, but also show great significance for high-performance infrared-radar compatibility, which is in favor of protecting human security all over the world.

Flexible wideband microwave meta-absorber with designable digital infrared and visible camouflage

With the widespread use of multi-spectrum detection technology, the stealth of a single frequency band cannot meet the practical application requirements. Recently, the investigation of wearable and insulated multi-spectrum compatible stealth technology has become urgent. The flexible and thermally isolated wideband microwave meta-absorber with infrared and visible camouflage has been proposed, fabricated, and measured. An infrared shielding layer (IRSL) and a radar absorbing layer (RAL) are the two main components of the absorber. IRSL is realized by specifically arranging the pre-designed patch structure with three different filling ratios, which can confuse the detection of thermal infrared in 3–14 μm. RAL is achieved by etching the structure of the lossy material to form electrical loss in plane and magnetic loss between layers, so as to realize the broadband absorption of microwave higher than 90 % from 6.2-22.2 GHz. In addition, the absorber employs flexible and thermally isolated materials, providing excellent high-temperature stability normally at temperatures up to 130 °C. These unique properties confirm the feasibility of the proposed strategy. To effectively adapt to different thermal camouflage environments, it is essential to create IR digital camouflage patterns. Moreover, the additional flexibility and thermal insulation characteristics make it powerful in compatible camouflage-stealth facilities when used in complex environments and a wide range of high temperatures.

Design of Y-shaped tri-band rectangular slot DGS patch antenna at sub-6 GHz frequency range for 5G communication

This paper presents the design and development of a rectangular slot DGS patch antenna fed by a microstrip line, designed to operate across three distinct frequency bands at 4.0 GHz, 4.9 GHz, and 5.5 GHz for 5G wireless communication applications. The antenna design outlined in this study is implemented on a Fr-4 substrate with dimensions measuring 50.5 × 41.12 × 1.5 mm3. The antenna gains at three frequency bands are 2.69 dBi, 7.27 dBi, and 11.37 dBi having impedance bandwidths of 9%, 8.9%, and 5.1%, respectively. The attained bandwidths are 356 MHz, 443 MHz, and 287 MHz for the respective frequency bands. The radiation efficiencies of the proposed antenna are 90%, 82%, and 79% of the three respective frequencies. Antenna 1 in this study exhibits single-band behavior, effectively covering the single frequency band which is 5.5 GHz (5.3578–5.9519 GHz) 5G unlicensed band 5-GHz WLAN IEEE 802.11a frequency. On the other hand, Antenna 2 demonstrates dual-band characteristics spanning the S-band 3.7 GHz (3.5619–3.8544 GHz) and C-band range 5.1 GHz (4.8496–5.2008 GHz) suitable for mid-band 5G applications. Antenna 3 proposed antenna exhibits a tri-band functionality within the C-band spectrum. The results highlight multiple-band operation, consistent high gain, high directivity, and favorable directional radiation patterns.

Ergodic Rate Analysis for Full-Duplex and Half-Duplex Networks with Energy Harvesting

Considering energy harvesting, the ergodic data rates for both in band full-duplex (FD) and half-duplex (HD) wireless communications were studied. The analytic expressions of downlink and uplink ergodic rates for the proposed system were first derived with independent and identically distributed (i.i.d.) Rayleigh fading link. It was revealed that the uplink data rate can be improved by decreasing the downlink data rate. Furthermore, the uplink/downlink data rates are also shown to be influenced by some significance parameters, for example, the power split parameter and signal-to-noise ratio (SNR) (i.e., PS/σ2) of each link. Additionally, unlike the HD, the proposed FD node is capable of harvesting energy during the communication process; however, this is at the cost of performance loss induced by the residual self-interference (RSI), which is caused by the essence of simultaneous uplink and downlink transmissions in a single frequency band.

Irregular optogenetic stimulation waveforms can induce naturalistic patterns of hippocampal spectral activity

Objective. Therapeutic brain stimulation is conventionally delivered using constant-frequency stimulation pulses. Several recent clinical studies have explored how unconventional and irregular temporal stimulation patterns could enable better therapy. However, it is challenging to understand which irregular patterns are most effective for different therapeutic applications given the massively high-dimensional parameter space. Approach. Here we applied many irregular stimulation patterns in a single neural circuit to demonstrate how they can enable new dimensions of neural control compared to conventional stimulation, to guide future exploration of novel stimulation patterns in translational settings. We optogenetically excited the septohippocampal circuit with constant-frequency, nested pulse, sinusoidal, and randomized stimulation waveforms, systematically varying their amplitude and frequency parameters. Main results. We first found equal entrainment of hippocampal oscillations: all waveforms provided similar gamma-power increase, whereas no parameters increased theta-band power above baseline (despite the mechanistic role of the medial septum in driving hippocampal theta oscillations). We then compared each of the effects of each waveform on high-dimensional multi-band activity states using dimensionality reduction methods. Strikingly, we found that conventional stimulation drove predominantly ‘artificial’ (different from behavioral activity) effects, whereas all irregular waveforms induced activity patterns that more closely resembled behavioral activity. Significance. Our findings suggest that irregular stimulation patterns are not useful when the desired mechanism is to suppress or enhance a single frequency band. However, novel stimulation patterns may provide the greatest benefit for neural control applications where entraining a particular mixture of bands (e.g. if they are associated with different symptoms) or behaviorally-relevant activity is desired.

Exploring BMI recognition through resting state, free imagination, and visual stimulation-induced EEG

In recent years, the development of Brain-Computer Interface (BCI) technology has attracted significant attention, particularly in the acquisition and application of electroencephalogram (EEG) signals. Most pertinent studies have utilized EEG to monitor neural activity states. Given that EEG does not provide direct insights into the physical states of body structures, many researchers have refrained from employing EEG to assess structural body states such as Body Mass Index (BMI). This study, for the first time, employs portable EEG detection devices combined with machine learning algorithms such as Logistic Regression (LR), Naive Bayes (NB), and Support Vector Machine (SVM) to process EEG features, enabling the application of EEG in identifying BMI. We collected EEG data from three different states: resting state, free imagination, and viewing pictures. The results demonstrate that these EEG signals can effectively differentiate subjects with higher BMI. Particularly under visual stimulation, EEG features exhibited optimal performance when subjects viewed images of high-calorie foods, with the model achieving an average accuracy of 80% and an F1 score of 75%. From the perspective of frequency bands, within a single frequency band, the β band performed notably well in classification. However, the model constructed by integrating features from various frequency bands yielded the best classification performance. These comprehensive paradigms are expected to fill the current research gap in the application of EEG and provide new methodological perspectives for further studies.

Four-channel near-field focusing metasurface lens based on frequency-polarization multiplexing

In response to the issue of traditional near-field focusing metasurfaces having a single working frequency band and limited focusing functionality, this paper proposes a four-channel focusing metasurface based on frequency-polarization multiplexing. Utilizing the principles of anisotropy and metasurface resonant phase, a metasurface unit composed of two sets of orthogonal resonators was designed. The designed units have independent transmission amplitude and phase at 15 GHz and 23 GHz, with the transmission phase of the two sets of resonators encoded in 2-bit and 1-bit based on phase differences of 90° and 180°, respectively. Based on the units, combined with the focusing principle of metasurface lenses and the principle of phase superposition, a four-channel near-field focusing metasurface lens was designed. The lens is composed of 20 × 20 units, measuring 200 × 200 mm2. Numerical simulations and experimental results demonstrate that the designed metasurface lens achieves single-point and dual-points focusing at 15 GHz under x- and y-polarized wave incidence, with the focus at the z = 70 mm plane and a maximum focusing efficiency of 48.5%. At 23 GHz under x- and y-polarized wave incidence, metasurface lens focuses electromagnetic waves at different positions, with the focus at the z = 80 mm plane and a maximum focusing efficiency of 27.8%. The metasurface lens designed by this method is expected to find applications in fields such as Medical Sensing, Microwave Imaging, and Integrated Optics.

Dielectric Behavior Characterization of RE/BaTiO3 Using Time Domain Spectroscopy: Application on High-Performance Dielectric Resonator Antennas

We are working to design dielectric resonator antennas based on binary composites made of epoxy resin (RE) and barium titanate (BaTiO3 or BT). The composite samples are prepared at room temperature and under atmospheric pressure. The dielectric properties of these composites were assessed using time domain spectroscopy (TDS). The antennas structure are designed, simulated, and optimized using electromagnetic software Ansys, HFSS. Two types of antennas are studied. The first type consists of a cylindrical dielectric resonator that gives three antenna models in terms of bandwidths, the antennas having a single frequency band, the antennas having dual-band, and the antenna covering three frequency bands, with peak gains varying between 3.68 and 8.15 dB achieved. The second type consists of dielectric resonators composed of two adjacent identical shapes each consisting of a rectangular joined with a cylindrical with the same height. The proposed antenna achieves ultra-wideband with a relative bandwidth of 97% covering the range of 6 to 17.32 GHz, and dual-band circularly polarized ( AR<3dB ), the range of the lower band is 9.62 to 10.14 GHz and the range of the upper band is 16.74 to 16.94 GHz. The focus of this research is on creating novel antennas for applications in wireless communications systems.

SEACKgram: a targeted method of optimal demodulation-band selection for compound faults diagnosis of rolling bearing

Rolling bearing plays an important role in carrying and transmitting power in rotating machinery, and the bearing fault is easy to lead to mechanical accidents, resulting in huge losses and casualties. Therefore, the condition monitoring and diagnosis of rolling bearings are very important to improve the safety of equipment. Compound fault is a common fault evolved from the initial defect, which is characterized by randomness, coupling, concealment, and secondary. The existence of these characteristics brings great challenges to the accurate diagnosis of compound faults. In the diagnosis of compound faults, the traditional methods that select the single optimal demodulation frequency band for analysis and identification sometimes cannot completely extract multiple fault components, which are prone to miss diagnosis and misdiagnosis. In order to solve this problem, the SEACKgram method is proposed by constructing a Square Envelope Unbiased Autocorrelation Correlation Kurtosis (SEACK) index. The frequency band of the original signal is divided by the Maximal Overlap Discrete Wavelet Packet Transform, and the SEACK index is used to quantitatively describe the fault signals of different frequency bands. According to the different fault periods, the resonant frequency bands of the maximum SEACK value are selected, then the resonance band signal is analyzed by square envelope spectrum, and the fault type is identified according to the fault characteristic frequency. The simulated and experimental vibration signals of rolling bearings with compound faults are used to verify the feasibility of the proposed method. The results show that the proposed SEACKgram can improve the accuracy of compound faults identification and would be applied in engineering practice to a certain extent.

Dual-band topological rainbows in Penrose-triangle photonic crystals.

Topological rainbows (TRs) possess the potential to separate and localize topological photonic states across different frequencies. However, previous works on TRs have been confined to a single-frequency band. Furthermore, the achievement of multiband TRs within a single structure is still a significant challenge. In this paper, a composed structure waveguide is designed based on Penrose-triangle photonic crystals. By adjusting the size of scatterers and introducing non-Hermitian terms, we successfully realize dual-band TRs. This achievement will not only enhance the uniformity of the electric field intensity distribution but also provide the potential to introduce a new avenue for the development of robust photonic devices dedicated to processing vast amounts of data information.

Improved End-to-End Wireless Transmission Integrating NOMA and DL-Based Autoencoder

The field of wireless communication systems has experienced significant advancements in recent years, leading to the emergence of two promising technologies: non-orthogonal multiple access (NOMA) and deep learning (DL)-based autoencoders (AE). Through power allocation, NOMA enables multiple users to share a single frequency band, while AE can compress and decompress data with high precision. Integrating NOMA and AE enables end-to-end (E2E) transmission with a superior signal-to-noise (SNR) ratio. To further enhance the wireless network's block error rate (BLER) performance, the multiple-input, multiple-output (MIMO) technique is also incorporated into the newly proposed system. With the incorporation of the MIMO signal, the system is abbreviated as the MIMO-NOMA-AE system. The suggested technique for detecting MIMO-NOMA-AE signals has demonstrated a remarkable performance gain in SNR surpassing the traditional successive interference cancellation (SIC)-based NOMA system. The proposed system also performs better than previously utilized deep neural network (DNN)-based SISO-NOMA-AE communication systems. While this method shows potential for future wireless communication systems, further research and testing are necessary to evaluate its practical feasibility and effectiveness.

Graphene-based optically transparent metasurface for microwave and terahertz cross-band stealth utilizing multiple stealth strategies

Stealth, as a miraculous physical phenomenon, has received widespread attention from the scientific and engineering communities for a long time. Optically transparent stealth devices are of significant importance for the stealth capabilities of aircraft windshields and solar panels. However, the current stealth implementations are limited to a single frequency band due to the strong dispersion of passive materials so that cross-band stealth still remains challenging. In this paper, a novel cross-wavelength stealth strategy is proposed based on multi-layer graphene transparent metasurface, which achieves stealth both in microwave and terahertz frequency bands. Strong resonance is designed to achieve high absorption in the microwave band and diffuse scattering is employed for RCS reduction in the terahertz band. Materials such as graphene and ITO are employed to achieve optical transparency and flexibility of the metasurface. The above design is implemented using numerical simulations and experiments, and the results are in good agreements. This design method that integrates multiple stealth strategies opens up a new approach for cross-band stealth, with potential applications in countering advanced electromagnetic detection.

PHS: A Pulse Sequence Method Based on Hyperbolic Frequency Modulation for Speed Measurement

The channel in the marine environment is a time-varying and space-varying channel. Pulse-truncated continuous wave (PCW) speed measurement is often used in sonar, but the instability effect of PCW signal in the channel limits the effectiveness of speed measurement. Hyperbolic frequency modulation (HFM) signal is insensitive to Doppler; therefore, HFM signals are widely used in ranging and velocity measurement of sonar and radar. However, due to the filtering effect of the marine environment, the HFM signal of a single frequency band may cause excessive transmission loss, and the echo energy may be too weak to detect the target. Based on the analysis of the influence of speed on the distance measurement of HFM signal, a pulse sequence method based on HFM for speed measurement (PHS) is proposed, which uses HFM signals of different frequency bands and pulse widths in the pulse sequence to perform speed measurement. Extensive simulation results show that PHS method not only guarantees the speed measurement but also makes full use of the energy of the HFM sequence to improve the accuracy of the distance measurement. And PHS method is valuable to the practical application of engineering.

Dual-band transmission polarization conversion metasurface and its reconfigurable-phase design

Although abundant transmission polarization conversion metasurfaces (T-PCMs) have been reported, a dual-band T-PCM has only received little attention. Moreover, a reconfigurable-phase design of the T-PCMs is limited to a single-frequency band operation. There is hardly any literature to integrate dual-band and reconfigurable-phase features into a T-PCM. Herein, a dual-band T-PCM is presented based on the Fabry-Pérot-like resonant cavity. Particularly, the T-PCM meta-atom contains dual anisotropic patches distributed in different layers, and the novel dual-patch structure introduces multiple current modes to implement dual-band operation. Further, a reconfigurable-phase design of the dual-band meta-atom is performed, and four PIN diodes are embedded in each meta-atom to realize a 1-bit reconfigurable phase. In this way, the T-PCM meta-atom can simultaneously achieve high-efficiency 90° polarization rotation and 1-bit dynamic phase manipulation in 2.3–3.0 GHz and 4.4–7.5 GHz. By changing the encoding of the T-PCM, both cross-polarized transmission and beam manipulation are demonstrated in two divided bands. A sample is fabricated and measured to validate our design, and the results confirm the simulations. With the advantages of ingenious design and a clear operation mechanism, the novel dual-patch structure can be extended to the terahertz and optics regimes.

Terahertz metamaterial-induced multiple transparency windows through bright-bright mode couplings

Metamaterials that offer optical control over multiple transparency windows have paved the way for advancements in terahertz (THz) modulation technology. In this paper, we have conducted a systematic investigation into the interaction between THz waves and “bright” split-ring resonators (SRRs). Through manipulation of the quantity and spatial arrangement of SRRs within metamaterial structures, we have successfully induced multiple transparency windows within the THz spectrum. Furthermore, we have explored the transmitted switching ratio of both the designed single transparency window and double resonance frequency bands as a function of the azimuthal angle of the THz wave. This work offers a general strategy for designing the number of electromagnetically induced transparency windows and holds the potential for realizing multichannel memories.

EEG decoding for musical emotion with functional connectivity features

Emotion refers to the subjective emotional experience that humans generate in specific situations, typically accompanied by physiological and psychological changes. In the field of emotions, multi-channel EEG emotional features can better reflect the collaborative mechanisms across multiple brain regions. Therefore, we propose a novel feature called asPLV (averaged sub-frequency phase locking value) based on the Morlet transform method to construct functional network edges. The proposed feature encompasses a comprehensive analysis of phase synchronization across sub-frequency bands spanning a wide range of frequencies and has the potential to reduce fluctuations arising from reliance on a single frequency band. We designed a music-evoked emotion experiment aimed at inducing corresponding emotions in participants while simultaneously recording their electroencephalogram (EEG) signals and extracted our proposed asPLV feature for classification. The results show that the proposed feature displays superior classification performance and generalization compared to other state-of-the-art methods. The proposed method is not only effective in successfully distinguishing between different emotions but also introduces a novel brain network metric to elucidate the collaboration and information exchange among emotion-related brain regions. Moreover, the asPLV feature could provide new insights for the development of an emotional brain-computer interface (BCI).

Aberrant dynamic and static functional connectivity of the striatum across specific low-frequency bands in patients with autism spectrum disorder

BackgroundDysfunctions of the striatum have been repeatedly observed in autism spectrum disorder (ASD). However, previous studies have explored the static functional connectivity (sFC) of the striatum in a single frequency band, ignoring the dynamics and frequency specificity of brain FC. Therefore, we investigated the dynamic FC (dFC) and sFC of the striatum in the slow-4 (0.027-0.073 Hz) and slow-5 (0.01-0.027 Hz) frequency bands. MethodsData of 47 ASD patients and 47 typically developing (TD) controls were obtained from the Autism Brain Imaging Data Exchange (ABIDE) database. A seed-based approach was used to compute the dFC and sFC. Then, a two-sample t-test was performed. For regions showing abnormal sFC and dFC, we performed clinical correlation analysis and constructed support vector machine (SVM) models. ResultsThe middle frontal gyrus (MFG), precuneus, and medial superior frontal gyrus (mPFC) showed both dynamic and static alterations. The reduced striatal dFC in the right MFG was associated with autism symptoms. The dynamic‒static FC model had a great performance in ASD classification, with 95.83 % accuracy. ConclusionsThe striatal dFC and sFC were altered in ASD, which were frequency specific. Examining brain activity using dynamic and static FC provides a comprehensive view of brain activity.