Showing papers on "Frequency band published in 2021"
TL;DR: The simulation results show that the proposed Fast Entrogram can effectively extract periodic pulses, and it is verified by experimental signals that the method can be applied to fault diagnosis of bearing inner and outer rings.
88 citations
TL;DR: In this paper, an electromagnetic Stewart platform with high static and low dynamic stiffness is explored to reduce the vibration in six degrees of freedom (6-dofs) and simultaneously harvest energy.
76 citations
TL;DR: In this article, highly sensitive piezoelectric mobile acoustic sensor (PMAS) is demonstrated by exploiting an ultrathin membrane for biomimetic frequency band control, which can cover the entire voice spectrum.
Abstract: Flexible resonant acoustic sensors have attracted substantial attention as an essential component for intuitive human-machine interaction (HMI) in the future voice user interface (VUI). Several researches have been reported by mimicking the basilar membrane but still have dimensional drawback due to limitation of controlling a multifrequency band and broadening resonant spectrum for full-cover phonetic frequencies. Here, highly sensitive piezoelectric mobile acoustic sensor (PMAS) is demonstrated by exploiting an ultrathin membrane for biomimetic frequency band control. Simulation results prove that resonant bandwidth of a piezoelectric film can be broadened by adopting a lead-zirconate-titanate (PZT) membrane on the ultrathin polymer to cover the entire voice spectrum. Machine learning-based biometric authentication is demonstrated by the integrated acoustic sensor module with an algorithm processor and customized Android app. Last, exceptional error rate reduction in speaker identification is achieved by a PMAS module with a small amount of training data, compared to a conventional microelectromechanical system microphone.
70 citations
TL;DR: In this article, a high-resolution imaging radar system is proposed to enable high-fidelity four-dimensional (4D) sensing for autonomous driving, i.e., range, Doppler, azimuth, and elevation, through a joint sparsity design in frequency spectrum and array configurations.
Abstract: We propose a high-resolution imaging radar system to enable high-fidelity four-dimensional (4D) sensing for autonomous driving, i.e., range, Doppler, azimuth, and elevation, through a joint sparsity design in frequency spectrum and array configurations. To accommodate a high number of automotive radars operating at the same frequency band while avoiding mutual interference, random sparse step-frequency waveform (RSSFW) is proposed to synthesize a large effective bandwidth to achieve high range resolution profiles. To mitigate high range sidelobes in RSSFW radars, optimal weights are designed to minimize the peak sidelobe level such that targets with a relatively small radar cross section are detectable without introducing high probability of false alarm. We extend the RSSFW concept to multi-input multi-output (MIMO) radar by applying phase codes along slow time to synthesize a two-dimensional (2D) sparse array with hundreds of virtual array elements to enable high-resolution direction finding in both azimuth and elevation. The 2D sparse array acts as a sub-Nyquist sampler of the corresponding uniform rectangular array (URA) with half-wavelength interelement spacing, and the corresponding URA response is recovered by completing a low-rank block Hankel matrix. Consequently, the high sidelobes in the azimuth and elevation spectra are greatly suppressed so that weak targets can be reliably detected. The proposed imaging radar provides point clouds with a resolution comparable to LiDAR but with a much lower cost. Numerical simulations are conducted to demonstrate the performance of the proposed 4D imaging radar system with joint sparsity in frequency spectrum and antenna arrays.
64 citations
TL;DR: In this paper, a step-by-step hydrothermal method was used to texture rod-like TiO2 semiconductor with different mass ratios on the a few layers of WS2 nanosheets.
63 citations
TL;DR: In this paper, the authors proposed an all-metal wideband phase correcting structure (AWPCS) with none of these limitations and is designed based on the relative phase error extracted by postprocessing the actual near-field distributions of any EM sources.
Abstract: Electromagnetic (EM) metasurfaces are essential in a wide range of EM engineering applications, from incorporated into antenna designs to separate devices like radome. Near-field manipulators are a class of metasurfaces engineered to tailor an EM source’s radiation patterns by manipulating its near-field components. They can be made of all-dielectric, hybrid, or all-metal materials; however, simultaneously delivering a set of desired specifications by an all-metal structure is more challenging due to limitations of a substrate-less configuration. The existing near-field phase manipulators have at least one of the following limitations; expensive dielectric-based prototyping, subject to ray tracing approximation and conditions, narrowband performance, costly manufacturing, and polarization dependence. In contrast, we propose an all-metal wideband phase correcting structure (AWPCS) with none of these limitations and is designed based on the relative phase error extracted by post-processing the actual near-field distributions of any EM sources. Hence, it is applicable to any antennas, including those that cannot be accurately analyzed with ray-tracing, particularly for near-field analysis. To experimentally verify the wideband performance of the AWPCS, a shortened horn antenna with a large apex angle and a non-uniform near-field phase distribution is used as an EM source for the AWPCS. The measured results verify a significant improvement in the antenna’s aperture phase distribution in a large frequency band of 25%.
54 citations
TL;DR: In this article, an efficient wideband polarization-rotation thin metasurface based on oval pattern is presented to manipulate the polarization of incident electromagnetic waves in reflect band, where the oval pattern was split by strip lines to outperform the results.
Abstract: An efficient wideband polarization-rotation thin metasurface based on oval pattern is presented. The aim of this structure is to manipulate the polarization of incident electromagnetic waves in reflect band. The oval pattern is split by strip lines to outperform the results. It is shown that the proposed polarization converter converts the incident linearly or circularly polarized waves into orthogonal counterpart over a frequency band of 10.2–20.5 GHz. A prototype of the proposed structure is fabricated to validate the numerical simulation. The experimental and simulation results confirm that polarization conversion ratio (PCR) is greater than 90% at the same frequency band with high stability to oblique incidence angle. Numerical simulation reveals that the strong electric and magnetic resonances between top and bottom layers lead to wideband polarization conversion. Equivalent impedance surface method is discussed to further analysis the polarization conversion mechanism.
52 citations
TL;DR: In this article, a single layer MIMO antenna for 5G 28 GHz frequency band applications is proposed and investigated, which operates in the Ka-band, which is the most desirable frequency band for mm-wave communication.
Abstract: In this paper, a novel single layer Multiple Input–Multiple Output (MIMO) antenna for Fifth-Generation (5G) 28 GHz frequency band applications is proposed and investigated. The proposed MIMO antenna operates in the Ka-band, which is the most desirable frequency band for 5G mm-wave communication. The dielectric material is a Rogers-5880 with a relative permittivity, thickness and loss tangent of 2.2, 0.787 mm and 0.0009, respectively, in the proposed antenna design. The proposed MIMO configuration antenna element consists of triplet circular shaped rings surrounded by an infinity-shaped shell. The simulated gain achieved by the proposed design is 6.1 dBi, while the measured gain is 5.5 dBi. Furthermore, the measured and simulated antenna efficiency is 90% and 92%, respectively. One of the MIMO performance metrics—i.e., the Envelope Correlation Coefficient (ECC)—is also analyzed and found to be less than 0.16 for the entire operating bandwidth. The proposed MIMO design operates efficiently with a low ECC, better efficiency and a satisfactory gain, showing that the proposed design is a potential candidate for mm-wave communication.
52 citations
TL;DR: In this paper, an on-line chatter monitoring using the fast kurtogram (FK) and the frequency band power (FBP) is proposed to resolve the problem of noisy signals.
Abstract: The spectral kurtosis (SK) is a useful tool for locating the non-stationary component in the single source signal. It has been verified by the mechanical fault diagnosis. The fast kurtogram (FK) is an improvement method based on the SK. However, for the signals with lower signal noise ratio (SNR), FK is not able to locate the chatter. In this paper, an on-line chatter monitoring using the FK and the frequency band power (FBP) is proposed to resolve this problem. Through the application of the FK, the frequency band with the largest SK can be found. In order to enhance the SK, a bandpass filter is designed. However, for the unstable cutting process, SK is not increased at all. Hence, FBP is adopted to monitor the chatter according to the energy change. The proposed method is verified by the milling experiments and satisfactory detection results are obtained.
48 citations
TL;DR: A systematic topological optimization method based on material-field series expansion (MFSE) framework for full and directional band gap acoustic metamaterials design that can generate meaningful optimized topologies of PnCs for the full frequency band and directional propagation with a broad frequency range is developed.
48 citations
TL;DR: In this article, a three-beam impact energy harvester (TIEH) was proposed to enhance the energy harvesting efficiency for low-frequency rotational motion, which includes three beams, including the excitation beam, the harvesting beam and the protection beam.
TL;DR: A performance comparison with the state-of-the-art mm-wave end-fire antennas in terms of operational bandwidth, electrical size, and various MIMO performance parameters shows the worth of the proposed work.
Abstract: In this paper, an end-fire antenna for 28 GHz broadband communications is proposed with its multiple-input-multiple-output (MIMO) configuration for pattern diversity applications in 5G communication systems and the Internet of Things (IoT). The antenna comprises a simple geometrical structure inspired by a conventional planar helical antenna without utilizing any vias. The presented antenna is printed on both sides of a very thin high-frequency substrate (Rogers RO4003, er = 3.38) with a thickness of 0.203 mm. Moreover, its MIMO configuration is characterized by reasonable gain, high isolation, good envelope correlation coefficient, broad bandwidth, and high diversity gain. To verify the performance of the proposed antenna, it was fabricated and verified by experimental measurements. Notably, the antenna offers a wide −10 dB measured impedance ranging from 26.25 GHz to 30.14 GHz, covering the frequency band allocated for 5G communication systems with a measured peak gain of 5.83 dB. Furthermore, a performance comparison with the state-of-the-art mm-wave end-fire antennas in terms of operational bandwidth, electrical size, and various MIMO performance parameters shows the worth of the proposed work.
DOI•
08 Nov 2021TL;DR: In this article, a simple radar-absorbing structure with square pore was designed and prepared by 3D printing and coating dipping methods to verify the reliability of the design in this paper.
Abstract: To broaden the absorbing frequency band of radar-absorbing material (RAM), a simple radar-absorbing structure (RAS) with square pore was designed and prepared by 3D printing and coating dipping methods to verify the reliability of the design in this paper. On this basis, the gradient optimization design of sheet resistance of the structure was carried out to investigate the effect of gradient sheet resistance on the radar-absorbing performance. The results show that the sheet resistance and wall thickness of the structure have significant influence on the reflection loss peak and the absorbing bandwidth. When the side length L = 15 mm, the sheet resistance R = 500 Ω/sq, the height H = 20 mm, and the wall thickness w = 1.0 mm, the effective radar-absorbing bandwidth with a reflection loss below −10 dB can reach 15.82 GHz in the frequency band of 1–18 GHz. After the gradient optimization design of sheet resistance, the radar-absorbing bandwidth is wider and the absorbing curve is flatter, the gradient design of sheet resistance with appropriate tolerance can further improve the radar-absorbing performance of broadband. This RAS provided a new technical way for the development of “thin, light, wide, and strong” RAMs. (1) The schematic diagram and equivalent circuit model of square-hole structure; (2) The simulation and test results of the square-hole structure
TL;DR: In this article, the frequency band characteristics of vibrational triboelectric nanogenerators (TENGs) were systematically elaborated and a mechanical model of V-TENG was established to explore its working mechanism for wide-band vibrational energy harvesting.
Abstract: Micromechanical vibration, as one of the most prevalent forms of energy in an ambient environment, has surpassing application potentials as the power source for self-powered electronics. A triboelectric nanogenerator (TENG) can effectively convert vibrational energy to electricity, which has the unique benefit of a wide-band over a traditional vibration energy harvester due to the contact electrification mechanism. Herein, the frequency band characteristics of vibrational TENG (V-TENG) were systematically elaborated. The mechanical model of V-TENG was established to explore its working mechanism for wide-band vibrational energy harvesting. By simulation analysis and experimental validation, the bandwidth dependence of V-TENG on acceleration magnitude, proof mass, stiffness, and gap distance was investigated in detail. With optimized structural parameters, an ultra-wide-band vibration energy harvester (UVEH) was developed by a tandem spring-mass structure. Within the ultra-wide-band range from 3 to 45 Hz, the UVEH can invariably illuminate 36 serial light-emitting diodes (LEDs) and charge a 33 μF capacitor to 1.5 V within 35 s. This work has quantitatively studied frequency band characteristics of V-TENG and provided a promising strategy for wide-band vibrational energy harvesting from a machine, bridge, water wave, and human motion.
TL;DR: The results indicate that the ACK can simultaneously extract the wheelset tread damage and bearing fault-related vibration component, and it is superior to the other traditional methods.
TL;DR: A novel sensor for detecting and measuring angular rotation and proximity, intended for rapid prototyping machines, based on a complementary split-ring resonator driven by a conductor-backed coplanar waveguide, which has a planar topology.
Abstract: This article presents a novel sensor for detecting and measuring angular rotation and proximity, intended for rapid prototyping machines. The sensor is based on a complementary split-ring resonator (CSRR) driven by a conductor-backed coplanar waveguide (CBCPW). The sensor has a planar topology, which makes it simple and cost-effective to produce and accurate in measuring both physical quantities. The sensor has two components, a rotor and a stator: the first of these (the CSRR) can rotate around its axis and translate along the plane normal to the ground of the CBCPW. A detailed theoretical and numerical analysis, along with a circuit model, of the unique sensor design is presented. The proposed sensor exhibits linear response for measuring angular rotation and proximity in the range of 30°–60° and 0–200 μm, respectively. Another distinctive feature of the rotation and proximity sensor is the wide frequency band of applicability, which is an integral part of its novel design and is implemented through various dielectric material loadings on the CSRR. In the prototype of the proposed device, the stator (CBCPW) is fabricated on a 0.508-mm-thick RF-35 substrate, whereas the CSRR-based rotor is fabricated on TLY-5 and RF-35 substrates. The angular rotation, proximity, operating band selection, and sensitivity are measured using a vector network analyzer and are found to be good matches to the simulated and theoretical results.
TL;DR: In this article, a dual-band fully reconfigurable circularly polarized (CP) reflectarray (RA) antenna for satellite communication applications in the Ku band is proposed, which operates with the downlink and uplink beams at frequency bands of 10.8-11.8 GHz and 14-15.4 GHz, respectively.
Abstract: This work presents the design and experimental validation of a dual-band fully reconfigurable circularly polarized (CP) reflectarray (RA) antenna for satellite communication applications in the Ku band. The proposed structure operates with the downlink and uplink beams at frequency bands of 10.8-11.8 GHz and 14-15.4 GHz, respectively. Simultaneous and independent beam control is provided over each of the two bands. The constituent unit cell is composed of two interleaved circular loops of different sizes to address the two frequency bands. Each loop is loaded using four varactor diodes. The loops are symmetrically loaded in the transverse plane to provide an isotropic response suitable for CP applications. A phase range of more than 300∘ is achieved in both bands as the capacitive loading varies, with an average of 2 dB loss in the lower frequency band and 3 dB loss in the higher band. In this paper, the response of the unit cell is studied through full-wave simulations and verified through quasi-optical (QO) measurements, and the fully tunable performance of the reflectarray is validated through measurements in a near-field anechoic chamber.
TL;DR: In this paper, the working mechanism of a wideband absorber designed with an adjustable and highly selective notch band was studied, in which the narrow notch band is independently controlled by the lower lossless layer of the absorber, whereas the upper lossy layer loaded with lumped resistors realizes absorption.
Abstract: In this article, the working mechanism of a wideband absorber designed with an adjustable and highly selective notch band is studied, in which the narrow notch band is independently controlled by the lower lossless layer of the absorber, whereas the upper lossy layer loaded with lumped resistors realizes absorption. We present two instances with geometrically controlled and electrically controlled notch bands, respectively. Without decreasing absorption performance, the notch position can be flexibly adjusted throughout the entire frequency band by simply modifying the dimension of the lossless frequency-selective surface (FSS) or changing the capacitance of the varactor, i.e., using geometric control or electrical control. The narrow notch band allows two wide absorption bands to be retained on both sides; therefore, good stealth performance is still guaranteed. Equivalent circuit models (ECMs) are proposed to further explain the principle. The frequency-domain simulation, ECM, time-domain simulation, and experimental results are in good agreement and validate the adjustability and high selectivity of the notched absorbers. At the end of this article, an FSA-backed monopole antenna is simulated and measured, which clearly illustrates that these FSAs can serve as the ground plane for antennas and realize out-of-band RCS reduction.
TL;DR: In this article, a Ka-band monolithic low-noise amplifier with high gain and high dynamic range (DR) was designed and implemented in a 100-nm gallium nitride (GaN)-on-Si technology.
Abstract: A Ka -band monolithic low-noise amplifier (LNA) with high gain and high dynamic range (DR) has been designed and implemented in a 100-nm gallium nitride (GaN)-on-Si technology. The LNA is designed as the first stage of a high DR receiver in an frequency modulated continuous wave (FMCW) radar for the detection of small drones. The three-stage monolithic microwave integrated circuit (MMIC) LNA has a linear gain of 26 dB and a noise figure (NF) of 2 dB in the frequency band 33–38 GHz. The output 1-dB compression point (P1dB) and output IP3 at 37 GHz are 20 and 28.4 dBm, respectively. To our knowledge, this combination of NF, gain, and DR performance represents the state of art in this frequency band.
Posted Content•
TL;DR: In this article, the impact of the radiation patterns of the antennas and unit cells of the RISs is formulated in terms of an angle-dependent loss factor, which gives more accurate estimates of the path loss of RISs comprised of unit cells with a deep sub-wavelength size.
Abstract: Reconfigurable intelligent surfaces (RISs) provide an interface between the electromagnetic world of the wireless propagation environment and the digital world of information science. Simple yet sufficiently accurate path loss models for RISs are an important basis for theoretical analysis and optimization of RIS-assisted wireless communication systems. In this paper, we refine our previously proposed free-space path loss model for RISs to make it simpler, more applicable, and easier to use. In the proposed path loss model, the impact of the radiation patterns of the antennas and unit cells of the RIS is formulated in terms of an angle-dependent loss factor. The refined model gives more accurate estimates of the path loss of RISs comprised of unit cells with a deep sub-wavelength size. The free-space path loss model of the sub-channel provided by a single unit cell is also explicitly provided. In addition, two fabricated RISs, which are designed to operate in the millimeter-wave (mmWave) band, are utilized to carry out a measurement campaign in order to characterize and validate the proposed path loss model for RIS-assisted wireless communications. The measurement results corroborate the proposed analytical model. The proposed refined path loss model for RISs reveals that the reflecting capability of a single unit cell is proportional to its physical aperture and to an angle-dependent factor. In particular, the far-field beamforming gain provided by an RIS is mainly determined by the total area of the surface and by the angles of incidence and reflection.
TL;DR: In this paper, a multi-band integration of the bivariable map around multiple resonant frequencies that are carriers of the bearing damage signature is proposed, which is applied, tested and evaluated on experimental data and the results are compared with state-of-the-art band selection tools.
TL;DR: In this article, a planar circularly polarized (CP) planar array antenna is proposed for the upcoming 5G millimeter-wave (mm-wave) applications, where the antenna element is fed by a slot etched on the substrate integrated waveguide (SIW) for convenient integration.
Abstract: A novel wideband circularly polarized (CP) planar array antenna is proposed in this article for the upcoming fifth-generation (5G) millimeter-wave (mm-wave) applications. The antenna element is fed by a slot etched on the substrate integrated waveguide (SIW) for convenient integration. It consists of two additional semicircle patches and two suspend metal posts which are working as the newly proposed polarizers for broadband CP operation. The combined patch, post, and slot generate totally four CP modes which greatly expand the antenna 3 dB axial ratio (AR) bandwidth. The antenna operating mechanism and the design procedure are illustrated in detail. The simulated results for the antenna element show an AR bandwidth of 41.28% from 25.66 to 39.01 GHz, an impedance bandwidth of wider than 44.62% from 24.41 to 38.43 GHz, and a gain of 7.25 ± 1 dBic over the frequency band. The antenna shows a stable pattern and wide AR/impedance overlapping bandwidth (25.66–38.43 GHz), which covers most of the current 5G mm-wave bands. To enhance the antenna gain for practical application, a planar $4 \times 4$ antenna array fed by a fully incorporated SIW network is designed, fabricated, and measured. The measured results for the array demonstrate an AR bandwidth of 36.51% from 25.3 to 36.6 GHz, an impedance bandwidth of 40.21% from 24.42 to 36.71 GHz, and a peak gain of 19 dBic. The proposed antenna features a novel broadband CP working principle, low profile, and good radiation performance, which is well suited for 5G mm-wave applications.
TL;DR: A dual-broadband dual-polarized magnetoelectric dipole (ME-dipole) antenna with a shared aperture for 5G applications is proposed in this paper.
Abstract: A dual-broadband dual-polarized magnetoelectric dipole (ME-dipole) antenna with a shared aperture for 5G applications is proposed in this communication. The antenna is operated at the 2.35–3.93 GHz (N41 and N78) and 24–34 GHz (N257 and N258) dual fifth-generation (5G) bands. Each band exhibits a dual-polarized radiation, and more importantly, the two bands shared the same radiation aperture. In the millimeter-wave (MM-wave) band, the proposed antenna can generate two-dimensional (2-D) multiple beams with dual-polarization, and the switching range at each plane is about ±20°. The antenna is composed of two kinds of ME-dipole. The MM-wave band uses an ME-dipole feeding through the substrate-integrated waveguide (SIW) as the source to excite four horn antennas with inclined inner walls to achieve high-gain 2-D switching with dual-polarization. The lower frequency band combines the four horn antennas to achieve a large dual-polarized ME-dipole antenna. The antenna operating mechanism and the design procedure are illustrated in detail. The measured results show that a −10 dB impedance bandwidth of 33.91% (24–33.91 GHz) and 50.31% (2.35–3.93 GHz) is achieved. The peak gain of the proposed antenna in the two bands is 10.67 dBi (3.8 GHz) and 14.85 dBi (32.2 GHz), respectively. Due to the robust characteristics of the ME-dipole and horn antenna, the antenna shows a stable pattern and a wide impedance bandwidth, which covers most of the current 5G microwave and MM-wave bands. The antenna features a shared aperture, large frequency ratio, dual-broadband, dual-polarization, and 2-D multiple beams, which are well suited for the 5G base station applications.
TL;DR: A comparative analysis with state-of-the-art works exhibits that the presented design possesses advantages of compact size and multiple operating modes.
Abstract: This paper presents a compact and simple reconfigurable antenna with wide-band, dual-band, and single-band operating modes. Initially, a co-planar waveguide-fed triangular monopole antenna is obtained with a wide operational frequency band ranging from 4.0 GHz to 7.8 GHz. Then, two additional stubs are connected to the triangular monopole through two p-i-n diodes. By electrically switching these p-i-n diodes ON and OFF, different operating frequency bands can be attained. When turning ON only one diode, the antenna offers dual-band operations of 3.3–4.2 GHz and 5.8–7.2 GHz. Meanwhile, the antenna with single-band operation from 3.3 GHz to 4.2 GHz can be realized when both of the p-i-n diodes are switched to ON states. The proposed compact size antenna with dimensions of 0.27λ0 × 0.16λ0 × 0.017λ0 at the lower operating frequency (3.3 GHz) can be used for several wireless applications such as worldwide interoperability for microwave access (WiMAX), wireless access in the vehicular environment (WAVE), and wireless local area network (WLAN). A comparative analysis with state-of-the-art works exhibits that the presented design possesses advantages of compact size and multiple operating modes.
TL;DR: In this paper, a multifunctional metasurface (MFMS) based on graphene and photosensitive silicon (Si) is proposed, which integrates three functions: broadband absorption, broadband linear and circular polarization conversions in the THz band.
Abstract: With the development of metasurfaces and the improvement of manufacturing technology, it is important and imperative to design novel metasurfaces that can flexibly manipulate terahertz (THz) waves. In this paper, a multifunctional metasurface (MFMS) based on graphene and photosensitive silicon (Si) is proposed, which integrates three functions: broadband absorption, broadband linear and circular polarization conversions in THz band. For absorption mode, the MFMS can absorb above 90% energy in the frequency band of 1.74-3.52 THz with the relative bandwidth of 67.6%. For both linear-linear and circular-circular polarization conversion modes, the relative bandwidth with over 90% polarization conversion rates (PCRs) reaches 49.3% in the frequency band of 1.54-2.55 THz. The working mechanism of the MFMS is analyzed by the surface current distributions, and its properties of the absorption and polarization conversion under oblique incident angles are investigated, respectively. The proposed metasurface has promising prospects in terahertz devices such as modulators, smart switches and other terahertz devices.
TL;DR: A novel formulation of the frequency band constraint based on a modified Heaviside function is proposed, which is continuous and differentiable and derived and used in a gradient-based optimization method, which validates the effectiveness of the developed method.
Abstract: Engineering structures usually operate in some specific frequency bands. An effective way to avoid resonance is to shift the structure’s natural frequencies out of these frequency bands. However, in the optimization procedure, which frequency orders will fall into these bands are not known a priori. This makes it difficult to use the existing frequency constraint formulations, which require prescribed orders. For solving this issue, a novel formulation of the frequency band constraint based on a modified Heaviside function is proposed in this paper. The new formulation is continuous and differentiable; thus, the sensitivity of the constraint function can be derived and used in a gradient-based optimization method. Topology optimization for maximizing the structural fundamental frequency while circumventing the natural frequencies located in the working frequency bands is studied. For eliminating the frequently happened numerical problems in the natural frequency topology optimization process, including mode switching, checkerboard phenomena, and gray elements, the “bound formulation” and “robust formulation” are applied. Three numerical examples, including 2D and 3D problems, are solved by the proposed method. Frequency band gaps of the optimized results are obtained by considering the frequency band constraints, which validates the effectiveness of the developed method.
TL;DR: The proposed improved frequency band selection method called maximum envelope based-Autogram (MEAutogram) can reduce the calculation amount through overcoming the influence of irrelevant components on the segmentation position, which can be adaptively determined according to the characteristics of signal.
TL;DR: In this paper, an inverse design procedure of a metasurface in an ultra-wide working frequency band is presented in which the output unit cell structure can be directly computed by a specified design target.
Abstract: Beyond the scope of conventional metasurface, which necessitates plenty of computational resources and time, an inverse design approach using machine learning algorithms promises an effective way for metasurface design. In this paper, benefiting from Deep Neural Network (DNN), an inverse design procedure of a metasurface in an ultra-wide working frequency band is presented in which the output unit cell structure can be directly computed by a specified design target. To reach the highest working frequency for training the DNN, we consider 8 ring-shaped patterns to generate resonant notches at a wide range of working frequencies from 4 to 45 GHz. We propose two network architectures. In one architecture, we restrict the output of the DNN, so the network can only generate the metasurface structure from the input of 8 ring-shaped patterns. This approach drastically reduces the computational time, while keeping the network’s accuracy above 91%. We show that our model based on DNN can satisfactorily generate the output metasurface structure with an average accuracy of over 90% in both network architectures. Determination of the metasurface structure directly without time-consuming optimization procedures, an ultra-wide working frequency, and high average accuracy equip an inspiring platform for engineering projects without the need for complex electromagnetic theory.
TL;DR: In this paper, a phototube is incorporated into a simple neural circuit, and then the output voltage and dynamics become sensitive to external illumination within a specific frequency band, and the firing modes are also dependent on the amplitude and frequency band in the illumination.
Abstract: Inspired by the photoelectric effect, a phototube is incorporated into a simple neural circuit, and then the output voltage and dynamics become sensitive to external illumination within a specific frequency band. The firing modes are also dependent on the amplitude and frequency band in the illumination. In this paper, the signal outputs from a chaotic circuit are used as external optical signals, which are filtered and encoded by a phototube. Then, the functional neural circuit is excited to present a variety of firing modes and patterns. An exponential function of the filtering wave is proposed to discover the biophysical mechanism for frequency selection in the retina as most of wave bands of the external illumination are absorbed in the cathode material of the phototube while a specific band is effective in inducing a photocurrent for stimulating the visual neurons. Based on our light-sensitive neural circuit and model, external illumination is filtered and firing modes in the neuron are reproduced; furthermore, the mode transition induced by parameter shift is also investigated in detail. This result discovers the signal processing mechanism in the visual neurons and provides helpful guidance for designing artificial sensors for encoding optical signals and for repairing abnormalities in the retina of the visual system.
TL;DR: An exhaustive review of recent related-works of THz band antenna, fabrication and measurement are presented, and challenges of the THzband antenna design, fabrication, measurement are addressed.