Multi-frequency Bands Research Articles

The design of radio frequency energy harvesting and radio frequency-based wireless power transfer system for battery-less self-sustaining applications

In this paper, the RF energy harvesting system and RF-based wireless power transfer system are proposed and designed for battery-less self-sustaining application. For energy harvesting, the designed antenna array improves the received RF power effectively and also can harvest RF energy in multi-frequency bands. For wireless power transfer, the proposed helical antenna realizes the system design in miniaturization. Subsequently, the T shape LC matching network are designed between the antenna and the rectifying circuit to obtain more power transmission. The measured results show that the proposed Wi-Fi rectifier and 433 MHz rectifier offer a maximum conversion efficiency of 66.8% and 76% in case of the input power is −3 dBm and 0 dBm, respectively. Finally, the performance of the RF-based wireless power transfer system and RF energy harvesting system are attested by experimentally measurement, the measured results indicate that these systems can be used to power electronic.

Wave-equation traveltime inversion with multifrequency bands: Synthetic and land data examples

We have developed a wave-equation traveltime inversion method with multifrequency bands to invert for the shallow or intermediate subsurface velocity distribution. Similar to the classical wave-equation traveltime inversion, this method searches for the velocity model that minimizes the squared sum of the traveltime residuals using source wavelets with progressively higher peak frequencies. Wave-equation traveltime inversion can partially avoid the cycle-skipping problem by recovering the low-wavenumber parts of the velocity model. However, we also use the frequency information hidden in the traveltimes to obtain a more highly resolved tomogram. Therefore, we use different frequency bands when calculating the Fréchet derivatives so that tomograms with better resolution can be reconstructed. Results are validated by the zero-offset gathers from the raw data associated with moderate geometric irregularities. The improved wave-equation traveltime method is robust and merely needs a rough estimate of the starting model. Numerical tests on the synthetic and field data sets validate the above claims.

Optimized Wishart Network for an Efficient Classification of Multifrequency PolSAR Data

High-resolution wide-area images are required in the diverse field of research ranging from urban planning and disaster prediction to agriculture and geology. Sometimes the image is taken under harsh weather conditions or at night time. Current optical remote sensing technology does not have the capability to acquire images in such conditions. Synthetic aperture radar (SAR) uses microwave signal which has a long-range propagation characteristic that allows us to capture images in difficult weather conditions. In addition to this, some polarimetric SAR (PolSAR) systems are also capable of capturing images using multifrequency bands simultaneously resulting into a multitude of information in comparison to the optical images. In this letter, we propose a single-hidden layer optimized Wishart network (OWN) and extended OWN for classification of the single-frequency and multifrequancy PolSAR data, respectively. Performance evaluation is conducted on a single-frequency as well as multifrequency SAR data obtained by Airborne Synthetic Aperture Radar. We observed that for combining multiple band information, proposed single-hidden layer network outperforms deep learning-based architecture involving multiple hidden layers.

Gravitational-wave standard siren and cosmology

The discoveries of gravitational-wave (GW) event GW170817, caused by the coalescence of binary neutron-star, as well as the electromagnetic counterparts in multi-frequency bands, mark the coming of multimessenger GW astronomy. By observing the GW waveform of compact binary coalescence, one can independently determine its luminosity distance, which indicates that this kind of GW sources can be treated as “standard sirens to study the expansion history of the Universe. This provides a novel method for the research of cosmology. In this article, we introduce the basic principle of GW sources as “standard sirens, and focus on various methods to determine the distance and redshift of GW events. We also discuss the detection capabilities of constraining cosmological parameters for (second-generation and third-generation) ground-based GW detectors and space-based GW detectors. In particular, we investigate the potential constraints on the Hubble constant and equation-of-state of dark energy.

Joint Estimation of Effective Brain Wave Activation Modes Using EEG/MEG Sensor Arrays and Multimodal MRI Volumes.

In this letter, we present a new method for integration of sensor-based multifrequency bands of electroencephalography and magnetoencephalography data sets into a voxel-based structural-temporal magnetic resonance imaging analysis by utilizing the general joint estimation using entropy regularization (JESTER) framework. This allows enhancement of the spatial-temporal localization of brain function and the ability to relate it to morphological features and structural connectivity. This method has broad implications for both basic neuroscience research and clinical neuroscience focused on identifying disease-relevant biomarkers by enhancing the spatial-temporal resolution of the estimates derived from current neuroimaging modalities, thereby providing a better picture of the normal human brain in basic neuroimaging experiments and variations associated with disease states.

Identifying Resting-State Multifrequency Biomarkers via Tree-Guided Group Sparse Learning for Schizophrenia Classification.

The fractional amplitude of low-frequency fluctuations (fALFF) has been widely used as potential clinical biomarkers for resting-state functional-magnetic-resonance-imaging-based schizophrenia diagnosis. How-ever, previous studies usually measure the fALFF with specific bands from 0.01 to 0.08 Hz, which cannot fully delineate the complex variations of spontaneous fluctuations in the resting-state brain. In addition, fALFF data are intrinsically constrained by the brain structure, but most of the traditional methods have not consider it in feature selection. For addressing these problems, we propose a model to classify schizophrenia in multifrequency bands with tree-guided group sparse learning. In detail, we first acquire the fALFF data in multifrequency bands (i.e., slow-5: 0.01-0.027 Hz, slow-4: 0.027-0.073 Hz, slow-3: 0.073-0.198Hz, and slow-2: 0.198-0.25 Hz). Then, we divide the whole brain into different candidate patches and select those significant patches related to schizophrenia using random forest-based important score. Moreover, we use tree-structured sparse learning method for feature selection with the above patch spatial constraint. Finally, considering biomarkers from multifrequency bands can reflect complementary information among multiple-frequency bands, we adopt the multikernel learning method to combine features of multifrequency bands for classification. Our experimental results show that these biomarkers from multifrequency bands can achieve a classification accuracy of 91.1% on 17 schizophrenia patients and 17 healthy controls, further demonstrating that the multifrequency bands analysis can better account for classification of schizophrenia.

Brain Regional Homogeneity Changes in Cirrhotic Patients with or without Hepatic Encephalopathy Revealed by Multi-Frequency Bands Analysis Based on Resting-State Functional MRI.

ObjectiveTo investigate brain regional homogeneity (ReHo) changes of multiple sub-frequency bands in cirrhotic patients with or without hepatic encephalopathy using resting-state functional MRI.Materials and MethodsThis study recruited 46 cirrhotic patients without clinical hepatic encephalopathy (noHE), 38 cirrhotic patients with clinical hepatic encephalopathy (HE), and 37 healthy volunteers. ReHo differences were analyzed in slow-5 (0.010−0.027 Hz), slow-4 (0.027−0.073 Hz), and slow-3 (0.073−0.198 Hz) bands. Routine analysis of (0.010−0.080 Hz) band was used as a benchmark. Associations of abnormal ReHo values in each frequency band with neuropsychological scores and blood ammonia level were analyzed. Pattern classification analyses were conducted to determine whether ReHo differences in each band could differentiate the three groups of subjects (patients with or without hepatic encephalopathy and healthy controls).ResultsCompared to routine analysis, more differences between HE and noHE were observed in slow-5 and slow-4 bands (p < 0.005, cluster > 12, overall corrected p < 0.05). Sub-frequency band analysis also showed that ReHo abnormalities were frequency-dependent (overall corrected p < 0.05). In addition, ReHo abnormalities in each sub-band were correlated with blood ammonia level and neuropsychological scores, especially in the left inferior parietal lobe (overall corrected p < 0.05 for all frequency bands). Pattern classification analysis demonstrated that ReHo differences in lower slow-5 and slow-4 bands (both p < 0.05) and higher slow-3 band could differentiate the three groups (p < 0.05). Compared to routine analysis, ReHo features in slow-4 band obtained better classification accuracy (89%).ConclusionCirrhotic patients showed frequency-dependent changes in ReHo. Sub-frequency band analysis is important for understanding HE and clinical monitoring.

No-reference image quality assessment with center-surround based natural scene statistics

In this paper, we propose an efficient no-reference image quality assessment (NR-IQA) method dubbed Center-Surround based Blind Image Quality Assessment (CS-BIQA). Our proposed method employs the Difference of Gaussian (DoG) model to decompose images into several frequency bands, considering the center-surround effect and multi-channel attribute of human visual system (HVS). The integrated natural scene statistics (NSS) features can be further derived from all DoG bands. After that, regression models between the integrated features and associated subjective assessment scores are learned on the training dataset. Subsequently, the learned models are used to predict the quality scores of test images. The main contribution of this paper is twofold. Firstly, the empirical distributions of DoG bands of images are proven to be a Gaussian-like distribution. And thus, the NSS features can be employed to represent the perceptual quality of images. Secondly, different types of distortions are observed to affect different frequency components of images. So, the integrated features extracted from multi-frequency bands are employed in CS-BIQA to achieve stronger distinguishable capability of image quality. Excessive experiments are conducted to indicate that our proposed CS-BIQA metric can represent the perceptual characteristics of HVS. The results on popular IQA databases demonstrate that the CS-BIQA metric is competitive with the state-of-the-art relevant IQA metrics. Furthermore, our proposed method has very low computational complexity, making it more suitable for real-time applications.

Compact Left-Handed Meta-Atom for S-, C- and Ku-Band Application

A new compact left-handed meta-atom for S-, C- and Ku-band applications is presented in this paper. The proposed structure provides a wide bandwidth and exhibits left-handed characteristics at 0°, 90°, 180° and 270° (xy-axes) rotations. Besides, the left-handed characteristics and wide bandwidth of 1 × 2, 2 × 2, 3 × 3 and 4 × 4 arrays are also investigated at the above-mentioned rotation angles. In this study, the meta-atom is designed by creating splits at the outer and inner square-shaped ring resonators, and a metal arm is placed at the middle of the inner ring resonator. The arm is also connected to the upper and lower portions of the inner ring resonator, and later, the design appears as an I-shaped split ring resonator. The commercially available, finite integration technique (FIT)-based electromagnetic simulator CST Microwave Studio is used for design and simulation purposes. The measured data comply well with the simulated data of the unit cell for 1 × 2, 2 × 2, 3 × 3 and 4 × 4 arrays at every rotation angle. Owing to the effective medium ratio (EMR) of 8.50 at 0° and 180° rotations, the proposed meta-atom structure is compact in size. Moreover, due to the quality factor of 82, the designed meta-atom is flexible for high-performance antenna, filter and sensor applications. Therefore, the meta-atom integrated antenna shows multi frequency bands with the highest peak gain of 5 dBi, which is used as the long distance radio communication frequency.

A Study on Wireless Technologies to Improve Communication Performance by Utilizing Multi-frequency Bands

A Study on Wireless Technologies to Improve Communication Performance by Utilizing Multi-frequency Bands

Few-layer black phosphorus: A bright future in electromagnetic absorption

Few-layer black phosphorus (FL-BP) was prepared by liquid phase exfoliation (LPE) and composites with different weight ratio of FL-BP reveal high electromagnetic absorption (EA) performance in multi-frequency bands. A composite loaded with 30wt.% of FL-BP showed the broadest effective EA at bandwidth of 6.20GHz under the thickness of 2.5mm. Furthermore, when the loading ratio increased to 50wt.%, FL-BP based absorber has effective EA bandwidth in S (2–4GHz) band.

Depth-Perception Preserved Content Remapping Based on Cornsweet Illusion for 3D Display

Usually, there is a limited depth of field (DOF) for automultiscopic three-dimensional (3D) displays, which requires modifying light fields of 3D scenes to fit into the DOF constraint of a target display. A novel depth-perception preserved 3D content remapping method is presented based on Cornsweet illusion, which uses Cornsweet profile to enhance the depth-perception by augmenting the contrast at the edges. The original depth map is decomposed into multifrequency bands and remapped by reducing the low-frequency bands while preserving the high-frequency parts, which leads to Cornsweet profiles with the preserved perceptual depth. The manipulation of the multifrequency bands is processed in logarithmic domain with a well-designed monotonic mapping function. The tradeoff between displayed blur and depth preservation is achieved by adopting the available objective metric based on human vision system. A warping-based view synthesis method is adopted to retarget the light field according to the modified depth map. Experimental results show that the displayed modified 3D light field appears sharp, and the original perception of depth is maximally preserved.

Combining the absorptive and radiative loss in metasurfaces for multi-spectral shaping of the electromagnetic scattering.

The absorptive and radiative losses are two fundamental aspects of the electromagnetic responses, which are widely occurring in many different systems such as waveguides, solar cells, and antennas. Here we proposed a metasurface to realize the control of the absorptive and radiative loss and to reduce the radar cross section (RCS) in multi-frequency bands. The anti-phase gradient and absorptive metasurfaces were designed that consists of metallic square patch and square loop structure inserted with resistors, acting as an phase gradient material in the X and Ku band, while behaving as an absorber in the S band. The simulation and experiment results verified the double-band, wideband and polarization-independent RCS reduction by the absorptive and anti-phase gradient metasurfaces.

Miniaturised printed elliptical nested fractal multiband antenna for energy harvesting applications

This study presents the design, optimisation, simulation and fabrication of a novel printed elliptical nested fractal (planar) antenna for multiband operation. The proposed antenna is intended to function as the receptor element in radio-frequency energy harvesting applications. The simple microstrip structure and the compact size of the antenna ease its fabrication and allow it to be integrated with other electronic circuitry. It consists of nested elliptical structures fed by 50 Ω microstrip line with complementary elliptical ground along with rectangular ground plane. The added Hilbert structures at both sides of the antenna feeding line on the top layer enhance its performance to operate in multi-frequency bands. This antenna exhibits good radiation and reflection characteristics at 910 MHz (global system of mobile (GSM 900)), 2.4 GHz (Bluetooth/wireless local area network), 3.2 GHz (Radiolocation, third generation (3G)), 3.8 GHz (for long-term evolution, 4G) and additional 5 GHz band (wireless fidelity signals). The overall dimension of antenna is 41 mm (width) × 44 mm (length) × 1.778 mm (thickness). To the best knowledge of the authors, this is the widest bandwidth antenna to be developed at these small dimensions covering major standards from 900 MHz up to 6 GHz for electromagnetic energy harvesting applications.

High Frequency Generation Based-On Nonlinear Micro Ring Resonator for Frequency Band Enhancement

Propose the simulation of THz carrier frequencies using the small device and a Gaussian beam propagating within the device system. We found that the generated output power with the high frequency can be achieved. This consisted of a serial nonlinear micro ring resonator system for generating pulse and signal filter by Add/Drop filter, a technology optical communication by the micro ring resonator which generates the THz frequency multiple, whereas channel capacity in term of multi frequency bands can be provided by optical Add/Drop multiplexing. The increase in the number of channel capacity can be obtained by the increase in frequency density, while the security was introduced by the specific frequency filter, which was operated by the central operator. The optical micro ring resonators for THz frequency generation and enhancement are reviewed. The advantage of proposed system can be implemented by using the simultaneous optical communication system.

An integrated 0.38–6 GHz, 9–12 GHz fully differential fractional-N frequency synthesizer for multi-standard reconfigurable MIMO communication application

A wide-band fully differential fractional-N frequency synthesizer for multi-standard application is presented. The single fully differential LC---VCO with 28.5 % tuning rang and a set of dividers, quadrature self-mixer are designed to accomplish the multi-frequency bands with the frequency band from 0.38 to 6 GHz and from 9.0 to 12 GHz. It covers several wireless standards. A novel high isolation multiplexer is presented to achieve the frequency band selection. This chip was implemented with 65 nm CMOS technology and the maximum consumption is 20.05 mA from 1.2 V power supply. It occupies an active area of 1.5 mm2. The measured typical phase noise of the frequency synthesizer is ?114.6 dBc/Hz from 1 MHz offset for 4.85 GHz output.

Multi-band, highly absorbing, microwave metamaterial structures

A further example of multi-band absorption using ultra-thin, polarization-insensitive, wide-angled metamaterial absorbers that operate in multi-frequency bands within the microwave regime is presented in this work. The basic structure geometry is utilised to create multi-band highly absorbing structures by incorporating the scalability property of the metamaterials. Simulation results verify the structure’s ability for high absorption. The multi-band absorbers are promising candidates as absorbing elements in scientific and technical applications because of its multi-band absorption, polarization insensitivity, and wide-angle response. Finally, the current distributions for those structures are presented to gain a better insight into the physics behind the multiple absorption mechanism.

Fault Feature Extraction for Shaft System of Hydraulic Machinery Based on Wavelet Packet

Shaft fault is the most common fault for hydraulic machinery. In this paper, wavelet packet energy spectrum analysis method was used for multi frequency bands division of shaft monitoring signals. The variable bands frequency energy can construct feature vectors needed for fault diagnosis based on support vector machine, by integrating the procedure of wavelet packet analysis method and online monitoring technology, feature can be extracted in real time, and it make possible for real-time fault diagnosis and prediction of hydraulic machine.

Moho depth and crustal composition in Southern Africa

Abstract We present new results on structure, thickness, and composition of the crust in southern Africa based on 6300 seismic receiver functions at 85 stations. Application of Hk-stacking to the entire SASE dataset and use of multi-frequency bands improve resolution substantially. We observe a highly heterogeneous crustal structure with short wavelength variations in thickness (H), Vp/Vs-ratio (composition), and Moho sharpness, which defines ~ 20 blocks that do not everywhere coincide with surface tectonic features. In the Zimbabwe Craton, the Tokwe block has H = 35–38 km and Vp/Vs = 1.74–1.79 whereas the thicker crust in the Tati block (H = 47–51 km) may be related to deformation of the Archean crust along the cratonic margin. Two distinct crustal blocks with similar crustal thickness (42–46 km) but significantly different Vp/Vs-ratios are recognized in the Limpopo Belt. Extreme values of 1.90–1.94 at the dyke swarms in eastern Limpopo, and 1.84 at the Olifants River Dyke Swarm and easternmost Bushveld Intrusion Complex (BIC) indicate voluminous magmatic intrusions in the whole crust. We find no evidence for magmatic intrusions in the central (inferred) part of BIC, where the crust is thick (45–50 km) and Vp/Vs is low (1.68–1.70). This thick crustal root may have deflected rising magmas to form the two BIC lobes. Most of central Kaapvaal has thin (35–40 km) crust and Vp/Vs ~ 1.74. These characteristics are similar to the Tokwe block in Zimbabwe Craton and may indicate delamination of pre-existing lower crust, which is further supported by a very sharp Moho transition. The exposed cross-section in the Vredefort impact crater is non-representative of cratonic crust due to shallow Moho (34 km) and high Vp/Vs ~ 1.80 attributed to shock metamorphism. High Vp/Vs = 1.76 is typical of the Witwatersrand Basin, and anomalously low Vp/Vs = 1.66–1.67 marks the Kaapvaal–Kheis–Namaqua transition. Highly heterogeneous crust, both in thickness and Vp/Vs-ratio is typical of the Namaqua–Natal and Cape Fold Belts.

A TEMPORAL MULTI-FREQUENCY ENCODING TECHNIQUE FOR CHIPLESS RFID BASED ON C-SECTIONS

A time domain chipless RFID tag based on cascaded microstrip coupled transmission line sections (C-sections), which can operate in multi-frequency bands is presented. The group delay characteristics of the C-sections are exploited to generate the tag Identiflcation (ID). The tag comprises cascaded commensurate group of C-sections and two cross-polarized ultra wide-band (UWB) antennas. Since the proposed tag can operate in multi-frequency bands, this paper proves the possibility of increasing the coding capacity compared to the existing time domain designs. A tag operating at ISM (Industrial Scientiflc and Medical) bands at 2.45GHz and 5.8GHz together with conformance of frequency and power regulations is discussed elaborately. The prototype of the device is fabricated and validated experimentally. The time domain characteristic of the tag is also validated experimentally by interrogating a short pulse. Furthermore, measurement results using commercial Ultra Wide Band (UWB) radar which can be used as a chipless RFID reader is also incorporated. The obtained results conflrm the concept and the possibility of using temporal multi-frequency in chipless RFID.