Showing papers on "Frequency band published in 2020"
TL;DR: A novel scheme for joint target search and communication channel estimation, which relies on omni-directional pilot signals generated by the HAD structure, is proposed, which is possible to recover the target echoes and mitigate the resulting interference to the UE signals, even when the radar and communication signals share the same signal-to-noise ratio (SNR).
Abstract: Sharing of the frequency bands between radar and communication systems has attracted substantial attention, as it can avoid under-utilization of otherwise permanently allocated spectral resources, thus improving efficiency. Further, there is increasing demand for radar and communication systems that share the hardware platform as well as the frequency band, as this not only decongests the spectrum, but also benefits both sensing and signaling operations via the full cooperation between both functionalities. Nevertheless, the success of spectrum and hardware sharing between radar and communication systems critically depends on high-quality joint radar and communication designs. In the first part of this paper, we overview the research progress in the areas of radar-communication coexistence and dual-functional radar-communication (DFRC) systems, with particular emphasis on application scenarios and technical approaches. In the second part, we propose a novel transceiver architecture and frame structure for a DFRC base station (BS) operating in the millimeter wave (mmWave) band, using the hybrid analog-digital (HAD) beamforming technique. We assume that the BS is serving a multi-antenna user equipment (UE) over a mmWave channel, and at the same time it actively detects targets. The targets also play the role of scatterers for the communication signal. In that framework, we propose a novel scheme for joint target search and communication channel estimation, which relies on omni-directional pilot signals generated by the HAD structure. Given a fully-digital communication precoder and a desired radar transmit beampattern, we propose to design the analog and digital precoders under non-convex constant-modulus (CM) and power constraints, such that the BS can formulate narrow beams towards all the targets, while pre-equalizing the impact of the communication channel. Furthermore, we design a HAD receiver that can simultaneously process signals from the UE and echo waves from the targets. By tracking the angular variation of the targets, we show that it is possible to recover the target echoes and mitigate the resulting interference to the UE signals, even when the radar and communication signals share the same signal-to-noise ratio (SNR). The feasibility and efficiency of the proposed approaches in realizing DFRC are verified via numerical simulations. Finally, the paper concludes with an overview of the open problems in the research field of communication and radar spectrum sharing (CRSS).
846 citations
01 Dec 2020
TL;DR: An up-to-date review paper to analyze key concepts associated with the Terahertz system architecture and presents a comprehensive comparison between the THz wireless communication and its other contenders.
Abstract: Ultra-high bandwidth, negligible latency and seamless communication are envisioned as milestones that will revolutionize the way by which societies create, distribute and consume information. The remarkable expansion of wireless data traffic has advocated the investigation of suitable regimes in the radio spectrum to satisfy users’ escalating requirements and allow the exploitation of massive capacity and massive connectivity. To this end, the Terahertz (THz) frequency band (0.1-10 THz) has received noticeable attention in the research community as an ideal choice for scenarios involving high-speed transmission. As such, in this work, we present an up-to-date review paper to analyze key concepts associated with the THz system architecture. THz generation methods are first addressed by highlighting the recent progress in the devices technology. Moreover, the recently proposed channel models available for propagation at THz band frequencies are introduced. A comprehensive comparison is then presented between the THz wireless communication and its other contenders. In addition, several applications of THz communication are discussed taking into account various scales. Further, we highlight the milestones achieved regarding THz standardization activities. Finally, a future outlook is provided by presenting and envisaging several potential use cases and attempts to guide the deployment of the THz frequency band.
228 citations
TL;DR: In this paper, a 4-port multiple-input-multiple-output (MIMO) antenna array operating in the mm-wave band for 5G applications is presented, where an identical two-element array excited by the feed network based on a T-junction power combiner/divider is introduced, while the ground plane is made defected with rectangular, circular and a zigzag-shaped slotted structure to enhance the radiation characteristics of the antenna.
Abstract: We present a 4-port Multiple-Input-Multiple-Output (MIMO) antenna array operating in the mm-wave band for 5G applications. An identical two-element array excited by the feed network based on a T-junction power combiner/divider is introduced in the reported paper. The array elements are rectangular-shaped slotted patch antennas, while the ground plane is made defected with rectangular, circular, and a zigzag-shaped slotted structure to enhance the radiation characteristics of the antenna. To validate the performance, the MIMO structure is fabricated and measured. The simulated and measured results are in good coherence. The proposed structure can operate in a 25.5–29.6 GHz frequency band supporting the impending mm-wave 5G applications. Moreover, the peak gain attained for the operating frequency band is 8.3 dBi. Additionally, to obtain high isolation between antenna elements, the polarization diversity is employed between the adjacent radiators, resulting in a low Envelope Correlation Coefficient (ECC). Other MIMO performance metrics such as the Channel Capacity Loss (CCL), Mean Effective Gain (MEG), and Diversity gain (DG) of the proposed structure are analyzed, and the results indicate the suitability of the design as a potential contender for imminent mm-wave 5G MIMO applications.
156 citations
TL;DR: In this article, a ray-tracing model is used to evaluate the phase distribution in the aperture of a geodesic lens with respect to the relative permittivity distribution of axially symmetric surfaces.
Abstract: This article describes a design procedure that enables a time-efficient evaluation of the focusing properties of modulated geodesic lenses using ray tracing on the equivalent gradient-index planar lens. The method uses transformation optics to define the equivalent planar relative permittivity distribution of axially symmetric surfaces and a ray-tracing model to evaluate the phase distribution in the aperture of the lens. This approach is of interest to optimize modulated geodesic lenses having polynomial profiles, reducing their height while preserving their wideband behavior and wide angular focusing properties. The approach is validated with a specific lens design. The profile is optimized at 30 GHz, while the focusing properties are monitored over the complete Ka up-link frequency band allocated to satellite communications (i.e., 27.5–31 GHz). The manufactured prototype produces 21 beams equally spaced every 7.5° over the extended angular range of ±75°. The ray-tracing model results are compared in detail with the corresponding full-wave model results and experimental data. The manufactured design has return loss better than 15 dB over a fractional frequency bandwidth larger than 30%, in line with the predictions. Excellent scanning properties are demonstrated over an angular range of ±60° with scan losses below 1 dB and good pattern stability, including on sidelobe levels. A height reduction by a factor of 4, when compared to a conventional geodesic lens, is demonstrated with this specific design.
84 citations
TL;DR: In this article, a regulatory mechanism constituted by an electrically charged coil and a magnet ring is introduced into an HSLDS resonator to devise a semi-active quasi-zero-stiffness (QZS) resonator.
81 citations
TL;DR: The proposed method, incorporating with dual-tree complex wavelet packet transform (DTCWPT), provides improved performance compared to FK, in particular, for extracting periodic transients from noisy signals containing a variety of interferences.
79 citations
TL;DR: In this paper, a multi-layer quasi-zero stiffness (QZS) nonlinear isolator is proposed for low frequency and ultra-low frequency vibration in low frequency on-orbit instruments.
78 citations
11 Jan 2020
TL;DR: It is concluded that band ratio measures are a non-specific measure, conflating multiple possible underlying spectral changes, and recommend explicit parameterization of neural power spectra as a more specific approach.
Abstract: Band ratio measures, computed as the ratio of power between two frequency bands, are a common analysis measure in neuro-electrophysiological recordings. Band ratio measures are typically interpreted as reflecting quantitative measures of periodic, or oscillatory, activity. This assumes that the measure reflects relative powers of distinct periodic components that are well captured by predefined frequency ranges. However, electrophysiological signals contain periodic components and a 1/f-like aperiodic component, the latter of which contributes power across all frequencies. Here, we investigate whether band ratio measures truly reflect oscillatory power differences, and/or to what extent ratios may instead reflect other periodic changes—such as in center frequency or bandwidth—and/or aperiodic activity. In simulation, we investigate how band ratio measures relate to changes in multiple spectral features, and show how multiple periodic and aperiodic features influence band ratio measures. We validate these findings in human electroencephalography (EEG) data, comparing band ratio measures to parameterizations of power spectral features, and find that multiple disparate features influence ratio measures. For example, the commonly applied theta/beta ratio is most reflective of differences in aperiodic activity, and not oscillatory theta or beta power. Collectively, we show that periodic and aperiodic features can create the same observed changes in band ratio measures, and that this is inconsistent with their typical interpretations as measures of periodic power. We conclude that band ratio measures are a non-specific measure, conflating multiple possible underlying spectral changes, and recommend explicit parameterization of neural power spectra as a more specific approach. Significance Statement Neural oscillations are a ubiquitous feature of investigation in electrophysiological recordings. Frequency band ratio measures are a common approach to investigate neural oscillations, applied across cognitive and clinical neuroscience, and in recording modalities such as in electroencephalography and local field potentials. In this work we systematically investigate the methodological properties of band ratio measures. We show that band ratio measures are not specific to measuring oscillatory power, as they are intended and interpreted to do. Rather, they often reflect other features of the data, such as aperiodic, or 1/f-like, activity. These findings are significant for interpreting prior empirical and clinical research, guiding future work, and another motivation that aperiodic neural activity should be a key consideration when studying electrophysiological data.
77 citations
TL;DR: In this article, a multiple-input-multiple-output (MIMO) antenna array for broadband 5G new radio (5G NR) metal-frame smartphone applications is proposed by loading eight identical antennas into the metal frame of the smartphone to form an eight-antenna array for the sub-6 GHz 8 × 8 MIMO system.
Abstract: A multiple-input–multiple-output (MIMO) antenna array for broadband 5G new radio (5G NR) metal-frame smartphone applications is proposed. The MIMO antenna array is realized by loading eight identical antennas (Ant1–Ant8) into the metal frame of the smartphone to form an eight-antenna array for the sub-6 GHz 8 × 8 MIMO system. Each antenna element is a slot antenna type that is composed of an L-shaped open slot and a 50 Ω microstrip feedline, and good impedance matching in the upper frequency band can be achieved by loading a tuning stub to the feedline. The 10 dB impedance bandwidth of the proposed eight-antenna array can cover the 5G NR Bands n77/n78/n79 and wireless local area network (WLAN) 5 GHz band. Besides demonstrating desirable antenna efficiency of 50%–82% and envelope correlation coefficient of 12 dB. At 20 dB signal-to-noise ratio (SNR), the calculated peak channel capacity of the proposed eight-antenna array applied to an 8 × 8 MIMO system is 43.93 b/s/Hz.
75 citations
TL;DR: A novel tool called the Improved Envelope Spectrum via Feature Optimization-gram (IESFOgram) is proposed as a band selection tool for the demodulation of the bi-variable map (CSC or CSCoh) for bearing diagnostics, represented in a 1/3-binary tree and is applicable under constant and variable speed conditions.
65 citations
TL;DR: A 1-bit high-efficiency programmable metasurface is proposed to achieve completely independent functions with real-time reconfigurability controlled by FPGA hardware system in both C-band and X-band, designed with abilities of generating multi-beams or twin-beam scanning in the low frequency band while dynamic beam-scanning in high frequency band.
Abstract: Active metasurfaces pave a way for manipulating electromagnetic (EM) waves in real-time by incorporating with tunable materials or components, emerging as an attractive solution to achieve versatile EM functionalities in dynamic fashions. However, most of the active metasurfaces demonstrated so far only support tunable responses for a certain single frequency band, or have obvious frequency cross-talks that cannot provide dual-band independent operations, limiting their further uses in practical applications. Here, we propose a 1-bit high-efficiency programmable metasurface to achieve completely independent functions with real-time reconfigurability controlled by FPGA hardware system in both C-band and X-band. Specifically, the metasurface is designed with abilities of generating multi-beams or twin-beam scanning in the low frequency band while dynamic beam-scanning in high frequency band. As the experimental verifications, a double-layered metasurface has been fabricated and tested, and the measured results agree well with the simulations, demonstrating its abilities of independent, high-efficiency, real-time, and programmable manipulation of EM waves in two discrete frequency bands. The proposed concept may largely enhance the information capacity of the metasurface, bringing new degrees of freedom in achieving versatile tunable functionalities and offering useful applications in the radar and wireless communication systems.
TL;DR: It is determined that a Rogowski coil could be constructed with adequate bandwidth to cover the relevant frequency band of 1 kHz–1 MHz and found that the amplitude of the pulse and the difference in the integrated fast Fourier transform of the current signal are well correlated with the series fault.
Abstract: Series arc faults can cause fire hazards in dc distribution systems. During a series arc fault, the line impedance usually increases rapidly and the arc current includes high-frequency components. To capture the arc-induced high-frequency signals, parallel capacitors are added to the circuit. The characteristics of the currents through these capacitors permit fault detection and localization. This paper determined that a Rogowski coil could be constructed with adequate bandwidth to cover the relevant frequency band of 1 kHz-1 MHz, found that the amplitude of the pulse and the difference in the integrated fast Fourier transform of the current signal are well correlated with the series fault, described experiments to demonstrate that, over the range tested, the two parameters are robust with respect to the pressure of the atmosphere in which the arc forms, the electrode material, the speed at which the electrodes separate to initiate the arc, the switch operation, the load-type and the load change, and demonstrated that within the well-known limits of traveling wave localization, such localization can be used based on the capacitor current pulse information after it has been validated by the spectrum analysis as a fault and not a spurious signal. The proposed approach was demonstrated in two low-voltage dc cable circuits.
TL;DR: In this paper, a quasiperiodic arrangement of resonators introduces frequency band gaps in addition to the locally resonant gap and topologically nontrivial gaps with associated edge states.
Abstract: In extending the ideas of topological phases of matter to acoustic and mechanical systems, a quasiperiodic arrangement of resonators introduces frequency band gaps in addition to the locally resonant gap. Here numerical evaluation of the spectrum as a function of the quasiperiodic arrangement reveals a structure reminiscent of the famous Hofstadter butterfly. The onset of the locally resonant band gap and topologically nontrivial gaps with associated edge states is demonstrated numerically and experimentally. These structural designs can induce wave localization and attenuation over multiple frequency bands, for applications in $e.g.$ vibration isolation and energy harvesting.
TL;DR: In this paper, an ultra-compact two-port MIMO antenna working in the frequency range of 3.1-10.6 GHz with dual band-notched characteristics is presented.
Abstract: In this paper, an ultra-compact two-port MIMO antenna working in the frequency range of 3.1–10.6 GHz with dual band-notched characteristics is presented. The MIMO antenna consists of two identical octagonal-shaped radiating elements placed adjacent to each other with a connected ground plane. The overall size of the proposed two-port UWB-MIMO antenna is 19 × 30 × 0.8 mm3. In the ground plane of antenna elements, a T-shaped stub is introduced to create band-notch at 5.5 GHz. Also, an open-ended half-guided-wavelength resonator slot is introduced along the upper edge of the octagonal radiator to obtain a broader notched-band (4.37–5.95 GHz). The second band-notch is created around 7 GHz (6.52–7.45 GHz) by etching another open-ended slot from the radiating patch. The two-notch bands reject interference due to HiperLAN, WiMAX, INSAT/Super-extended C-band, downlink of X-band satellite communication and RFID service bands. A pair of L-shaped slits are introduced in the feed line to improve impedance matching, for the frequency band available between the two notches. The proposed design is fabricated on an FR-4 substrate and minimum isolation greater than 18 dB (a major portion >22 dB) and envelope correlation coefficient (ECC) less than 0.13 are obtained. The antenna gain varies in the range of 1.2–2.91 dBi with a variation of 1.71 dBi only. A radiation efficiency, greater than 70% is achieved throughout the operating frequency band.
TL;DR: Numerical comparisons show that the proposed antenna is superior to other published designs, which makes the proposed single antenna an excellent candidate for a multiple-input multiple-output (MIMO) system constructed from a number of properly allocated elements for 5G mobile communications with excellent diversity schemes.
Abstract: A compact dual-frequency ( 38 / 60 GHz ) microstrip patch antenna with novel design is proposed for 5G mobile handsets to combine complicated radiation mechanisms for dual-band operation. The proposed antenna is composed of two electromagnetically coupled patches. The first patch is directly fed by a microstrip line and is mainly responsible for radiation in the lower band ( 38 GHz ). The second patch is fed through both capacitive and inductive coupling to the first patch and is mainly responsible for radiation in the upper frequency band ( 60 GHz ). Numerical and experimental results show good performance regarding return loss, bandwidth, radiation patterns, radiation efficiency, and gain. The impedance matching bandwidths achieved in the 38 GHz and 60 GHz bands are about 2 GHz and 3.2 GHz , respectively. The minimum value of the return loss is − 42 dB for the 38 GHz band and − 47 for the 60 GHz band. Radiation patterns are omnidirectional with a balloon-like shape for both bands, which makes the proposed single antenna an excellent candidate for a multiple-input multiple-output (MIMO) system constructed from a number of properly allocated elements for 5G mobile communications with excellent diversity schemes. Numerical comparisons show that the proposed antenna is superior to other published designs.
15 Dec 2020
TL;DR: In this article, the authors proposed a general strategy to design chromatic aberration-free meta-devices with high efficiency and ultrabroadband properties, which is realized by satisfying the key criteria of desirable phase dispersion and high reflection amplitudes at the target frequency interval.
Abstract: Chromatic aberration-free meta-devices (e.g., achromatic meta-devices and abnormal chromatic meta-devices) play an essential role in modern science and technology. However, current efforts suffer the issues of low efficiency, narrow operating band, and limited wavefront manipulation capability. We propose a general strategy to design chromatic aberration-free meta-devices with high-efficiency and ultrabroadband properties, which is realized by satisfying the key criteria of desirable phase dispersion and high reflection amplitudes at the target frequency interval. The phase dispersion is tuned successfully based on a multiresonant Lorentz model, and high reflection is guaranteed by the presence of the metallic ground. As proof of the concept, two microwave meta-devices are designed, fabricated, and experimentally characterized. An achromatic meta-mirror is proposed within 8 to 12 GHz, and another abnormal chromatic meta-mirror can tune the reflection angle as a linear function. Both meta-mirrors exhibit very high efficiencies (85% to 94% in the frequency band). Our findings open a door to realize chromatic aberration-free meta-devices with high efficiency and wideband properties and stimulate the realizations of chromatic aberration-free meta-devices with other functionalities or working at higher frequency.
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TL;DR: An intelligent reflecting surface (IRS) is deployed to assist the terahertz communications and the sum-rate of user equipments (UEs) is maximized while guaranteeing the rate requirement of each UE.
Abstract: In this paper, an intelligent reflecting surface (IRS) is deployed to assist the terahertz (THz) communications. The molecular absorption causes path loss peaks to appear in the THz frequency band, and the fading peak is greatly affected by the transmission distance. In this paper, we aim to maximize the sum rate with individual rate constraints, in which the IRS location, IRS phase shift, the allocation of sub-bands of the THz spectrum, and power control for UEs are jointly optimized. For the special case of a single user equipment (UE) with a single sub-band, the globally optimal solution is provided. For the general case with multiple UEs, the block coordinate searching (BCS) based algorithm is proposed to solve the non-convex problem. Simulation results show that the proposed scheme can significantly enhance system performance.
TL;DR: In this article, the authors proposed a new design solution of a broadband microstrip antenna intended for use in 5G systems, which can be used in the LMDS (local multipoint distribution service) frequency band.
Abstract: Communication systems have been driven towards the fifth generation (5G) due to the demands of compact, high speed, and large bandwidth systems. These types of radio communication systems require new and more efficient antenna designs. This article presents a new design solution of a broadband microstrip antenna intended for use in 5G systems. The proposed antenna has a central operating frequency of 28 GHz and can be used in the LMDS (local multipoint distribution service) frequency band. The dimensions of the antenna and its parameters have been calculated, simulated, and optimized using the FEKO software. The antenna has a compact structure with dimensions (6.2 × 8.4 × 1.57) mm. Rogers RT Duroid 5880 material was used as a substrate for the antenna construction, which has a dielectric coefficient of 2.2 and a thickness of 1.57 mm. The antenna described in the article is characterized by a low reflection coefficient of −22.51 dB, a high energy gain value of 3.6 dBi, a wide operating band of 5.57 GHz (19.89%), and high energy efficiency.
TL;DR: The developed lightweight adhesive composites with graphene fillers can be used as electromagnetic absorbers in the high-frequency microwave radio relays, microwave remote sensors, millimeter wave scanners, and wireless local area networks.
Abstract: We report on the synthesis of the epoxy-based composites with graphene fillers and test their electromagnetic shielding efficiency by the quasi-optic free-space method in the extremely high-frequency (EHF) band (220-325 GHz). The curing adhesive composites were produced by a scalable technique with a mixture of single-layer and few-layer graphene layers of few-micrometer lateral dimensions. It was found that the electromagnetic transmission, T, is low even at small concentrations of graphene fillers: T<1% at a frequency of 300 GHz for a composite with only ϕ = 1 wt% graphene. The main shielding mechanism in composites with the low graphene loading is absorption. The composites of 1 mm in thickness and a graphene loading of 8 wt% provide an excellent electromagnetic shielding of 70 dB in the sub-terahertz EHF frequency band with negligible energy reflection to the environment. The developed lightweight adhesive composites with graphene fillers can be used as electromagnetic absorbers in the high-frequency microwave radio relays, microwave remote sensors, millimeter wave scanners, and wireless local area networks.
TL;DR: A controlled wide-bandwidth impedance measurement approach is presented in this paper, in which, a butterfly-type disturbance circuit and chirp pulsewidth modulation signal model are incorporated to generate the desired controlled-band width harmonics with a high aggregation as well as the average amplitude.
Abstract: The accurate information of the wide-bandwidth impedance versus the frequency is urgently needed for evaluating the system resonances, instabilities, and operations of the railway traction power system (TPS), and to avoid/control the harmonic resonance and oscillation issues. As the system topology and detailed parameters of the TPS are not fully known even timely varying, we have to obtain the detailed wide-bandwidth impedance information through exciting the harmonic disturbance into the system, and then, calculating the response information. Therefore, a controlled wide-bandwidth impedance measurement approach is presented in this paper, in which, a butterfly-type disturbance circuit and chirp pulsewidth modulation signal model are incorporated to generate the desired controlled-bandwidth harmonics with a high aggregation as well as the average amplitude. Impedance measurement results of the proposed approach have been validated through both simulation and experiment. Considering the measured errors, the proposed method is efficient in testing the wide-bandwidth impedance of the single-phase railway traction system.
TL;DR: In this paper, a broadband and tunable radar absorber is proposed by integrating graphene capacitor with resistive frequency-selective surfaces (RFSS), which can be dynamically controlled by changing the effective sheet resistance of graphene through an electrostatic field bias.
Abstract: In this communication, a broadband and tunable radar absorber is proposed by integrating graphene capacitor with resistive frequency-selective surfaces (RFSS). The microwave reflectivity can be dynamically controlled by changing the effective sheet resistance of graphene through an electrostatic field bias. The simulated results indicate that this structure can tune its reflectivity over a wide frequency band ranging from 2.9 to 15.9 GHz under the normal incidence, when the graphene resistance is varied from 120 to $700~\Omega $ /sq. The tuning range of the average reflectivity is from −4.6 to −15.3 dB. The physical mechanism of this tunable absorber is discussed by studying the electric field distribution and power loss density. We fabricated this absorber and measured its tunable reflectivity by applying different biasing voltages. The experimental results are in a good agreement with those of the simulation results. In addition, this absorber is also verified to have a good angular stability and polarization insensitivity, which will have broad prospects in the application of stealth technology.
TL;DR: In this article, a measurement of optomechanically squeezed light, performed at room temperature in a broad band near the audio-frequency regions relevant to gravitational wave detectors, was presented, where sub-Poissonian quantum noise was observed in a frequency band of 30-70 kHz with a maximum reduction of 0.7 ± 0.1 dB below shot noise at 45 kHz.
Abstract: Squeezed light—light with quantum noise lower than shot noise in some quadratures and higher in others—can be used to improve the sensitivity of precision measurements. In particular, squeezed light sources based on nonlinear optical crystals are being used to improve the sensitivity of gravitational wave detectors. In optomechanical squeezers, the radiation-pressure-driven interaction of a coherent light field with a mechanical oscillator induces correlations between the amplitude and phase quadratures of the light, which induce the squeezing. However, thermally driven fluctuations of the mechanical oscillator’s position make it difficult to observe the quantum correlations at room temperature and at low frequencies. Here, we present a measurement of optomechanically squeezed light, performed at room temperature in a broad band near the audio-frequency regions relevant to gravitational wave detectors. We observe sub-Poissonian quantum noise in a frequency band of 30–70 kHz with a maximum reduction of 0.7 ± 0.1 dB below shot noise at 45 kHz. We present two independent methods of measuring this squeezing, one of which does not rely on the calibration of shot noise. The ability to create optomechanically squeezed light at room temperature across a frequency range in the audio band could improve the measurement precision of future interferometric detectors for gravitational waves.
TL;DR: In this article, the authors investigated offline decoding analysis with different models and conditions to assess how they influence the performance and stability of the decoder and concluded that neural network-based decoders with downsampling or a wide range of frequency band features could not only improve decoder performance but also robustness with applications for stable use of BCIs.
Abstract: Previous studies of Brain Computer Interfaces (BCI) based on scalp electroencephalography (EEG) have demonstrated the feasibility of decoding kinematics for lower limb movements during walking. In this computational study, we investigated offline decoding analysis with different models and conditions to assess how they influence the performance and stability of the decoder. Specifically, we conducted three computational decoding experiments that investigated decoding accuracy: (1) based on delta band time-domain features, (2) when downsampling data, (3) of different frequency band features. In each experiment, eight different decoder algorithms were compared including the current state-of-the-art. Different tap sizes (sample window sizes) were also evaluated for a real-time applicability assessment. A feature of importance analysis was conducted to ascertain which features were most relevant for decoding; moreover, the stability to perturbations was assessed to quantify the robustness of the methods. Results indicated that generally the Gated Recurrent Unit (GRU) and Quasi Recurrent Neural Network (QRNN) outperformed other methods in terms of decoding accuracy and stability. Previous state-of-the-art Unscented Kalman Filter (UKF) still outperformed other decoders when using smaller tap sizes, with fast convergence in performance, but occurred at a cost to noise vulnerability. Downsampling and the inclusion of other frequency band features yielded overall improvement in performance. The results suggest that neural network-based decoders with downsampling or a wide range of frequency band features could not only improve decoder performance but also robustness with applications for stable use of BCIs.
TL;DR: The proposed integrated MIMO antenna configuration ascertains to be a potential contender for the forthcoming communication applications and verifies that the proposed antenna system satisfies the international human safety standards.
Abstract: This work demonstrates an integrated multiple-input multiple-output (MIMO) antenna solution for Long Term Evolution (LTE) and Millimeter-Wave (mm-wave) 5G wireless communication services. The proposed structure is comprised of a two-element LTE MIMO antenna, and a four-element 5G MIMO configuration with rectangular and circular defects in the ground plane. For experimental validation, the proposed structure is fabricated on a Rogers RO4350B substrate with 0.76 mm thickness. The overall substrate dimensions are 75 mm × 110 mm. The proposed structure is capable of operating at 5.29–6.12 GHz (LTE 46 and 47 bands) and 26–29.5 GHz (5G mm-wave) frequency bands. Additionally, the measured peak gain of 5.13 and 9.53 dB is attained respectively for the microwave and mm-wave antennas. Furthermore, the analysis of the MIMO performance metrics demonstrates good characteristics, and excellent field correlation performance across the operating bands. Furthermore, the analysis of the Specific Absorption Rate (SAR) and Power Density (PD) at the lower frequency band (5.9 GHz) and PD only at mm-Wave frequency band (28 GHz) verifies that the proposed antenna system satisfies the international human safety standards. Therefore, the proposed integrated MIMO antenna configuration ascertains to be a potential contender for the forthcoming communication applications.
TL;DR: In this paper, the authors proposed a novel metasurface with a transmission window within the wide RCS reduction band, which allows high transmission in the transparent window and also behaves as a metallic-like reflection sheet.
Abstract: Metasurfaces have been extensively investigated to achieve radar cross section (RCS) reduction over a wide frequency band. In this article, we propose the design of a novel metasurface with a transmission window within the wide RCS reduction band. The function of this metasurface is similar to rasorbers, whereas the mechanism behind the wideband RCS reduction is scattering cancellation rather than absorption. To this end, the ideal reflection and transmission properties of the metasurface unit cell are firstly revealed. And then an anisotropic unit cell composed of multilayered metallic patterns is designed to obtain the desired reflection and transmission properties. The bottom layer is composed of the typical patch-grid-patch bandpass frequency selective surface, which allows for high transmission in the transparent window and also behaves as a metallic-like reflection sheet in the RCS reduction band. Two metasurfaces, with checkerboard and aperiodic configurations, respectively, were designed, fabricated, and measured, as a proof-of-concept demonstration. A good agreement between the simulations and measured results provides a solid verification for our design. The results here provide an alternative method to open a transparent window within the RCS reduction band and may find potential applications in stealth radomes.
TL;DR: A light-responsive elastic metamaterial whose transmission spectrum can be tuned by light stimuli is introduced, and it is demonstrated that an appropriate laser illumination is effective in reversibly widening an existing frequency band gap, doubling its initial value.
Abstract: The metamaterial paradigm has allowed an unprecedented space-time control of various physical fields, including elastic and acoustic waves. Despite the wide variety of metamaterial configurations proposed so far, most of the existing solutions display a frequency response that cannot be tuned, once the structures are fabricated. Few exceptions include systems controlled by electric or magnetic fields, temperature, radio waves and mechanical stimuli, which may often be unpractical for real-world implementations. To overcome this limitation, we introduce here a polymeric 3D-printed elastic metamaterial whose transmission spectrum can be deterministically tuned by a light field. We demonstrate the reversible doubling of the width of an existing frequency band gap upon selective laser illumination. This feature is exploited to provide an elastic-switch functionality with a one-minute lag time, over one hundred cycles. In perspective, light-responsive components can bring substantial improvements to active devices for elastic wave control, such as beam-splitters, switches and filters. Here, the authors present a light-responsive elastic metamaterial whose transmission spectrum can be tuned by light stimuli. More specifically, we demonstrate that an appropriate laser illumination is effective in reversibly widening an existing frequency band gap, doubling its initial value.
TL;DR: In this article, a self-decoupled antenna array using the cancellation of two opposite couplings is proposed, where a pair of such antennas can be closely placed with inherent high isolation without using an extra decoupling structure between the antennas.
Abstract: The concept of a self-decoupled antenna array using the cancellation of two opposite couplings is proposed in this article. A pair of such antennas can be closely placed with inherent high isolation without using an extra decoupling structure between the antennas. A pertinent equivalent circuit model is presented to illustrate the physical mechanism of this new concept. It is found that the inductive and capacitive couplings between the antennas can be well canceled out with each other by properly adjusting the antenna dimensions. A demonstrating antenna array with a spacing of $0.024\lambda _{0}$ at the working frequency of 3.5 GHz and its counterpart array are first studied. The measured results show that although the proposed antenna array occupies a slightly larger size than its counterpart array, it presents better performance compared with its counterpart antenna array in port isolation (from 10 to 20 dB), total efficiency (from 68% to 80%), and envelope correlation coefficient (ECC) (from 0.14 to 0.04) throughout the desired frequency band of 3.3–3.8 GHz. A 3-D self-decoupled antenna array is designed to show that the proposed antenna can be in a compact form factor. Another self-decoupled array and its counterpart working at 2.14 GHz (long-term evolution (LTE) band 1) are studied through multi-input multi-output (MIMO) over-the-air (OTA) test when the arrays are integrated with an LTE module, showing significant improvement on the data throughput.
TL;DR: A new informative frequency band selector based on the conditional variance statistic is proposed and studied in details and it is shown that the proposed method is superior to many common alternatives based e.g. on Kurtosis or Alpha selectors, especially when non-cyclic impulses dominate over the cyclic ones.
TL;DR: In this paper, a technique is implemented for the generation of tunable circularly polarized THz wave using patterned graphene patch, which is perturbed by inserting a patterned slot to generate the set of orthogonal magnetic dipoles and hence the CP wave.
TL;DR: Two novel diagnostic methodologies are proposed based on the Cyclic Spectral Coherence (CSCoh), which allow for the automatic selection and integration of the optimal bands on the CSCoh under heavy impulsive noise, such as EMI, resulting in a spectrum with enhanced characteristic bearing fault frequencies.