Frequency Range Research Articles

Wideband bandpass filter with ultra-wide stopband based on cross-shaped parallel coupled lines

A broadband out-of-band rejection capability and multiple transmission zeros of wideband bandpass filter are proposed and validated in this article, which employ quadruple anti-parallel coupled-line structures to form a novel cross-shaped resonator planar topology. The centered frequency of the single wideband bandpass filter designed for verification is located at 2.4 GHz (f 0) with a fractional bandwidth of 50%. The interaction of crossed multiple anti-coupled lines with a lowpass-loaded fan constitutes the wideband with nine transmission zeros in the 5 f 0 frequency range for improved suppression extending to 26.5 GHz (10.7 f 0) with a suppression level of 12.5 dB. Moreover, the designed prototype filter is implemented and tested with a measured minimum insertion loss of 0.9 dB. Good agreement between the measured and simulated results is attained to successfully validate the correctness of the proposed design approach.

RCS-reduced patch antenna with wide frequency tuning range based on absorbing metasurface

A frequency-tunable patch antenna with reduced radar cross section (RCS) based on absorbing metamaterial is proposed. By controlling the external voltage of the varactor diodes, the working frequency of the patch can be adjusted. Through an investigation of the composite structure of the patch and absorbing metamaterial, RCS reduction is achieved over the entire wide tunable frequency range of the antenna. Measured results illustrate that the proposed patch antenna can dynamically operate in the range from 2.28 to 3.6 GHz with a gain variation of 7.1–8.7 dBi. Meanwhile, the RCS can be reduced by at least 7 dB and up to 20 dB in a fractional bandwidth of 44.9% of the antenna under a normal incidence. In comparison to conventional RCS-reduced antennas, the proposed one features a broader frequency tuning range and has potential value in wideband radar systems under complex electromagnetic interference environments.

Dynamic tensile viscoelastic properties of porcine periodontal ligament.

The periodontal ligament plays a significant role in orthodontic and masticatory processes. To explicitly investigate the effects of dynamic force amplitude and frequency on the dynamic tensile properties of the periodontal ligament, in vitro tensile experiments were conducted using a dynamic mechanical analysis at various dynamic force amplitudes across a wide frequency range. Storage modulus, loss modulus, and loss factor values were measured. A Maxwell constitutive model based on modulus was established to describe the dynamic mechanical properties of the periodontal ligament. The results showed that the storage modulus ranged from 29.53MPa to 158.24MPa, the loss modulus ranged from 3.26MPa to 76.16MPa, and the loss factor values all increased with higher frequencies and higher dynamic force amplitudes. Based on the parameters obtained from the fitting results, it is evident that the short-term response has a more pronounced impact on the elastic response of the periodontal ligament than the long-term response. Increasing the dynamic force amplitude and its frequency amplified the viscous effects of the periodontal ligament and enhanced energy dissipation. The proposed constitutive model further demonstrated that the periodontal ligament acts as a viscoelastic biomaterial. These findings have implications for future research on the periodontal ligament.

Frequency-extended inverse design of transmission-type linear-to-circular polarization control metasurface based on deep learning

Due to the parameter range limitations of the training dataset, traditional inverse prediction network models can only predict structure parameters of the metasurface within a limited frequency range. When the given design targets exceed the prediction range of network models, the predicted results will not match the actual results. This paper proposes a frequency-extended inverse design method (FEIDM) based on deep learning to address the problem. The method can automatically collect the required data and train the network model based on the center working frequency of the design targets, thereby achieving accurate prediction of metasurface structural parameters and effectively reducing labor and computational costs. Taking the transmission-type linear-to-circular polarization control metasurface as an example, the unit cell of the metasurface is first established in the paper. The structural parameters and corresponding electromagnetic parameters are collected without changing the unit size of the metasurface, and an initial inverse prediction network model (IIPNM) is constructed. The research results indicate that its predictable center working frequency range is 3–5.5 GHz. Using the design concept proposed in this paper, a program is constructed, it can automatically achieve data collection, target extraction, network model training, and prediction. Four given design targets are predicted. Among them, the center working frequencies of the three design targets are outside the initial predictable range. The predicted results meet the requirements of the given target, verifying the effectiveness of the proposed scheme. Finally, a set of parameters is selected to fabricate, and the experimental results are consistent with the simulation results. The research results can provide a reference for the efficient prediction of metasurface structural parameters over a wide frequency band.

Ultra-thin wideband frequency tunable metamaterial absorber and its application for antenna radar cross section reduction

A metamaterial absorber (MMA) with broadband and efficient absorption performance based on ultra-thin dielectric layer is proposed. In this unique configuration, the absorption frequency of the MMA can be continuously and dynamically tuned across a wide frequency range by manipulating the reverse voltage of the central varactor diode. From both the equivalent circuit and field distribution perspectives, we analyze the mechanisms behind broadband tuning and superior absorption. Simulation and experimental results demonstrate that the absorption peak of MMA can be continuously tuned over a range of 5.16–8.16 GHz, with the absorption rate consistently exceeding 90%, and the thickness is only 0.5 mm. Integrating MMA array with a microstrip patch antenna in a suitable manner can dynamically mitigates the radar cross section (RCS) within the associated frequency range, with virtually negligible impact on the antenna’s radiation performance.

Phase delays between mouse globus pallidus neurons entrained by common oscillatory drive arise from their intrinsic properties, not their coupling.

A hallmark of Parkinson's disease is the appearance of correlated oscillatory discharge throughout the cortico-basal ganglia (BG) circuits. In the primate globus pallidus (GP), where the discharge of GP neurons is normally uncorrelated, pairs of GP neurons exhibit oscillatory spike correlations with a broad distribution of pairwise phase delays in experimental parkinsonism. The transition to oscillatory correlations is thought to indicate the collapse of the normally segregated information channels traversing the BG. The large phase delays are thought to reflect pathological changes in synaptic connectivity in the BG. Here we study the structure and phase delays of spike correlations measured from neurons in the mouse external GP (GPe) subjected to identical 1-100 Hz sinusoidal drive but recorded in separate experiments. First, we find that spectral modes of a GPe neuron's empirical instantaneous phase response curve (iPRC), elucidate at what phases of the oscillatory drive the GPe neuron locks when it is entrained, and the distribution of phases at which it spikes when it is not. Then, we show that in this case the pairwise spike cross-correlation equals the cross-correlation function of these spike phase distributions. Finally, we show that the distribution of GPe phase delays arises from the diversity of iPRCs, and is broadened when the neurons become entrained. Modeling GPe networks with realistic intranuclear connectivity demonstrates that the connectivity decorrelates GPe neurons without affecting phase delays. Thus, common oscillatory input gives rise to GPe correlations whose structure and pairwise phase delays reflect their intrinsic properties captured by their iPRCs.Significance Statement The external globus pallidus (GPe) is a hub in the basal ganglia, whose neurons impose a barrage of inhibitory synaptic currents on neurons of the subthalamic nucleus, substantia nigra and internal globus pallidus. GPe neurons normally fire independently, but in experimental parkinsonism, they become correlated in the frequency range associated with the pathological rhythms seen in human Parkinson's disease, raising the possibility that they may be generators of the pathological oscillation. We drove individual pallidal neurons with an oscillatory input over a wide range of frequencies. Cross-correlations of these neurons reproduced many of the features seen in parkinsonism, suggesting that their correlated oscillations might derive from a shared input rather than internal interconnections.

High birefringence low loss nearly zero flat dispersion similar to slotted core photonic crystal fibers

Abstract Studying high-performance photonic crystal fibers (PCF) is of significant scientific importance for terahertz (THz) waveguide systems. This study introduces a novel PCF design with a core composed of the smallest sub-wavelength units resembling a slotted structure, aiming to achieve high birefringence and low loss. The optical properties of the proposed PCF are analyzed through simulations, yielding impressive results. The PCF exhibits an ultra-high birefringence of 0.07848, a minimum limiting loss of 10−17 dB/cm, and an effective material loss as low as 0.04251 cm−1. Moreover, it demonstrates near-zero flat dispersion of −0.012 ± 0.074 ps/THz/cm over a broad frequency range of 1.2–2.2 THz. This fiber stands out by not only providing high birefringence but also by striking an optimal balance among birefringence, transmission loss, and dispersion for THz waveguides. The implications of this work are profound for the development of THz communication systems, THz polarization-maintaining transmission, and sensing applications. Furthermore, it established an important benchmark for the design of THz-PCFs that prioritize high birefringence, low loss, and near-zero flat dispersion, offering an essential reference for future research and development in this field.

Heart rate variability and stroke or systemic embolism in patients with atrial fibrillation.

Stroke remains one of the most serious complications in atrial fibrillation (AF) patients and has been linked to disturbances of the autonomic nervous system. We hypothesized that impaired cardiac autonomic function might be associated with an enhanced stroke risk in AF patients. We enrolled 1922 AF patients who were either in sinus rhythm (SR-group, n=1121) or AF (AF-group, n=801) on a 5-minute resting ECG recording. HRV triangular index (HRVI), standard deviation of normal-to-normal intervals, root mean square root of successive differences of normal-to-normal intervals, mean heart rate, 5-min total power and power in the high frequency, low frequency and very low frequency range were calculated. We constructed Cox regression models to examine the association of HRV parameters with the composite endpoint of stroke or systemic embolism. Mean age was 71±8 years in the SR group and 75±8 in the AF group. 37 patients in the SR group (3.4%) and 60 patients in the AF group (8.0%) experienced a stroke or systemic embolism during a follow-up time of 5 years. In patients with SR, HRVI <15 was the strongest HRV parameter to be associated with stroke or systemic embolism (hazard ratio 3.04; 95% confidence interval 1.3-7.0; p=0.009) after adjustment for multiple confounders. In the AF group, we found no HRV parameter to be associated with the composite endpoint. HRVI measured during SR on a single 5-minute ECG recording is independently associated with stroke or systemic embolism in AF patients. HRV analysis in SR may help to improve risk stratification in AF patients.

The Phononic Properties and Optimization of 2D Multi-Ligament Honeycombs

Honeycomb structures have attracted much attention for their excellent characteristics of reducing vibration and noise in recent years. In this study, through band analysis of different ligament structures, we aim to optimize the design of a steel structure that can isolate most of the noise in the 1500–5000 Hz range. The present study examines several different chiral structures. We calculate the band gaps of chiral structures under different geometric configurations and identify the variations in band gaps with geometric layouts. It is found that compared to other chiral structures, the triligaments chiral structure exhibits excellent band gap characteristics. The calculation results demonstrate that enhancing axial symmetry while filling central nodes can effectively enhance the structure’s band gap properties. Frequency–response functions of different lattice structures are computed, and the results align with the calculations of band structures. This study then analyzes the influence of the number of periods on the magnitude of vibration attenuation, revealing that under the same number of periods, the wider the band gap of the structure, the greater the vibration attenuation. Both the triligaments chiral structure and the vertical triligaments structure possess ideal band gap widths, effectively suppressing wave propagation. Subsequently, harmonic response analyses and transient wave calculations further validate the accuracy of the band structure and frequency–response curve calculations. Our study results provide a new way to design a sound insulation structure that can isolate noise signals within the frequency range from 1500 to 5000 Hz in engineering.

Differential BroadBand (1–16 GHz) MMIC GaAs mHEMT Low-Noise Amplifier for Radio Astronomy Applications and Sensing

A broadband differential-MMIC low-noise amplifier (DLNA) using metamorphic high-electron-mobility transistors of 70 nm in Gallium Arsenide (70 nm GaAs mHEMT technology) is presented. The design and results of the performance measurements of the DLNA in the frequency band from 1 to 16 GHz are shown, with a high dynamic range, and a noise figure (NF) below 1.3 dB is obtained. In this work, two low-noise amplifiers (LNAs) were designed and manufactured in the OMMIC foundry: a dual LNA, which we call balanced, and a differential LNA, which we call DLNA. However, the paper focuses primarily on DLNA because of its differential architecture. Both use a 70 nm GaAs mHEMT space-qualified technology with a cutoff frequency of 300 GHz. With a low power bias Vbias/Ibias (5 V/40.5 mA), NF &lt; 1.07 dB “on wafer” was achieved, from 2 to 16 GHz; while with the measurements made “on jig”, NF = 1.1 dB, from 1 to 10 GHz. Furthermore, it was obtained that NF &lt; 1.5 dB, from 1 to 16 GHz, with a figure of merit equal to 145.5 GHz/mW. Finally, with the proposed topology, several LNAs were designed and manufactured, both in the OMMIC process and in other foundries with other processes, such as UMS. The experimental results showed that the NF of the DLNA MMIC with multioctave bandwidth that was built in the frequency range of the L-, S-, C-, and X-bands was satisfactory.

A Novel FSS Loaded Circular Slot Monopole Antenna for Microwave Breast Imaging Application

Breast cancer continues to be a major contributor to women's global mortality rates, emphasizing the need to explore alternative and supplementary early-stage detection techniques. This study delves into a circular slot monopole ultra-wideband (UWB) antenna equipped with a frequency-selective surface (CSMA-FSS) for early detection microwave imaging applications. To expand the impedance bandwidth of the traditional circular monopole antenna, a circular slit is introduced on a monopole structure. Additionally, a 10 × 10 unit cell FSS structure is integrated into the antenna as a far-field reflecting plane to enhance gain characteristics. The antenna, crafted with dimensions of 50 × 50 × 1.6 mm³ and a 1.6 mm thick FR4 substrate, operates across the ultra-wideband frequency spectrum, spanning from 3.1 GHz to 12 GHz, while consistently maintaining a reflection coefficient (S 11) value of – 10 dB or lower. Notably, the antenna showcases a gain of over 5 dBi across the entire 3.1 GHz to 12 GHz frequency range. The suggested antenna is ideal for microwave imaging applications due to its broad impedance bandwidth, impressive gain, and excellent directivity. Furthermore, it maintains a relatively uniform group delay, with a deviation of ±0.5 ns throughout the UWB band. In the time domain characteristics, the antenna exhibits excellent pulse handling capabilities and strong signal correlation, featuring an S 21 value of less than – 25 dB. The characteristics, observed in both the time and frequency domains, suggest that the proposed antenna holds significant potential for substantially enhancing breast cancer imaging system.

Research on abnormal vibration of high-speed train based on wheel-rail coupling modal analysis

During dynamic line testing of a high-speed train, it was observed that the vehicle exhibited significant abnormal vertical vibrations under specific track conditions. The frequency of this vibration varies with the train speed and exhibits harmonics through analysis. As the speed approaches 400 km/h, the peak frequency is close to 44 Hz, corresponding to the system structure's natural frequency. A finite element model of the wheel-rail coupling was established for modal analysis, which revealed that the coupling between the bogie and the track will form a bogie P2 force resonance mode, which closely matches the frequency range of the abnormal vibrations. A dynamic model of vehicle-track rigid-flexible coupling was established, to simulate vibration reproduction and the bogie P2 force resonance mode variation law. Additionally, irregularities of specific wavelengths on the track can excite this mode, leading to a significant increase in amplitude. Some sections of the track line have slab warping, with a wavelength of approximately 2.45m. The frequency range of excitation formed when the vehicle speed approaches 400 km/h is close to that of the bogie P2 resonance mode. As a result, coupling resonance occurs between the vehicle and track systems, ultimately causing abnormal vibrations.

Impact of Zinc Oxide on Dielectric Properties of Forsterite Coated Titanium Based Medical Implants

Abstract Zinc oxide-doped forsterite solutions are synthesized through the sol-gel approach by varying the weight percentage of zinc oxide. These solutions are then applied to titanium (Ti) substrates to form zinc oxide-doped forsterite coated Ti substrate samples using the dip-coating method. The structural and surface morphology analyses of the samples are conducted using X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM). Dielectric properties, encompassing dielectric constant, dielectric loss, alternating current conductivity, loss tangent, and relaxation time are explored at room temperature over a frequency range of 200 MHz to 20 GHz utilizing a Vector Network Analyzer (VNA) setup. The impact of zinc oxide on the structure, morphology, and dielectric properties of the samples, particularly in medical implant applications, is extensively discussed. The results indicate that samples with a higher weight percentage of zinc oxide demonstrate superior dielectric characteristics.

Oxide semiconductor based deep‐subthreshold operated read‐out electronics for all‐printed smart sensor patches

AbstractThe ability to fabricate an entire smart sensor patch with read‐out electronics using commercial printing techniques may have a wide range of potential applications. Although solution‐processed oxide thin film transistors (TFTs) are capable of providing high mobility electron transport, resulting in large ON‐state current and power output, there is hardly any literature report that uses the printed oxide TFTs at the sensor interfaces. Here, printed amorphous indium‐gallium‐zinc oxide (a‐IGZO)‐based deep‐subthreshold operated TFTs that comprise signal amplifiers and analog‐to‐digital converters (ADCs) that can successfully digitalize the analog sensor signals up to a frequency range of 1 kHz are reported. In addition, exploiting the high current oxide TFTs, a current drive circuit placed after the ADC unit has been found useful in producing easy‐to‐detect visual recognition of the sensor signal at a predefined threshold crossover. Notably, the entire smart sensor patch is demonstrated to operate at a low supply voltage of ≤2 V, thereby ensuring that it can be an on‐chip energy source compatible and standalone detection unit.

Material Damping Estimation within Low-, Medium- and High-Frequency Ranges

When considering the dynamic response of mechanical systems, material damping is a main factor to account for. It largely affects phenomena at different time scales, from the transient response of the system, to its modal response, up to the acoustic wave propagation within the bulk and at the contact interfaces. Nevertheless, despite the key role of the material damping in the mechanical response, its estimation within a wide frequency range is still a challenge, when considering the existing technics. Moreover, the material damping varies largely with respect to frequency and the actual approaches for its estimation are limited within restricted frequency ranges. An approach for estimating the material damping within the overall frequency range does not exist in the literature. This paper proposes an approach where structural and acoustic technics are combined with an energy statistical approach, for identifying the trend of material damping within a larger frequency range. The approach is here applied to polycarbonate (PC) material. The results highlighted that the material damping in the low–medium frequency range (1[Formula: see text]Hz-several kHz) fits with the Rayleigh damping model. On the other hand, the damping in the higher frequency range (106 Hz) showed a stabilization with the increase of the frequency.

Analysis of fusion alphas interaction with RF waves in D-T plasma at JET

Abstract This work studies the influence of RF waves in ICRH range of frequency on fusion alphas during the recent JET D-T campaign. Fusion alphas from D-T reactions are born with energies of about 3.5MeV and therefore have significant Doppler shift enabling synergistic interaction between them and RF waves at broad range of frequencies including the ones foreseen for future fusion machines ITER and SPARC. Resonant interaction between RF waves and alphas, also called synergistic effects, will modify the alpha distribution and ultimately will have an impact on alpha orbit losses and heating. Data from JET 3.43T/2.3MA pulses based on the hybrid scenario during the DTE2 campaign were used for the analysis in this study. The impact of synergistic effects on alpha orbit losses and alpha heating is assessed. Conclusions are based on analysis of experimental data for fast alphas losses, i.e. measurements from neutral particle analyser, fast ion losses scintillator detector, Faraday cups, and TRANSP simulations. Experimental data and TRANSP analysis indicate that there are indeed changes in the alphas’ distribution function due to interaction with RF waves. Data from the scintillator detector and the Faraday cups were compared for pulses with and without ICRH power and versus cases with enhanced alpha losses due to MHD activities. The trends from these diagnostics consistently show no additional alpha losses due to interaction with RF waves. TRANSP predictions for the impact of the synergistic effects on alpha heating show up to 42% increase in alpha electron heating and up to 25% increase in alpha ion heating. These effects however become negligibly small, less than 1%, when alpha heating is compared to the total auxiliary hearting power in the investigated JET pulses.

Changes in hearing function and intracochlear morphology after electrode array insertion in minipigs

Background In temporal bone specimens from long-term cochlear implant users, foreign body response within the cochlea has been demonstrated. However, how hearing changes after implantation and fibrosis progresses within the cochlea is unknown. Objectives To investigate the short-term dynamic changes in hearing and cochlear histopathology in minipigs after electrode array insertion. Material and Methods Twelve minipigs were selected for electrode array insertion (EAI) and the Control. Hearing tests were performed preoperatively and on 0, 7, 14, and 28 day(s) postoperatively, and cochlear histopathology was performed after the hearing tests on 7, 14, and 28 days after surgery. Results Electrode array insertion had a significant effect for the frequency range tested (1 kHz–20kHz). Exudation was evident one week after electrode array insertion; at four weeks postoperatively, a fibrous sheath formed around the electrode. At each time point, the endolymphatic hydrops was found; no significant changes in the morphology and packing density of the spiral ganglion neurons were observed. Conclusions and Significance The effect of electrode array insertion on hearing and intracochlear fibrosis was significant. The process of fibrosis and endolymphatic hydrops seemed to not correlate with the degree of hearing loss, nor did it affect spiral ganglion neuron integrity in the 4-week postoperative period.

Broadband spin-decoupled metasurface for independent wavefront manipulations of orthogonal circularly-polarized waves

Abstract Metasurfaces endowed with spin-decoupled functionalities offer the capability to meticulously customize the electromagnetic wavefronts of incident dual orthogonal circularly-polarized (CP) waves in a desirable manner, that holds immense potential for broadening their application fields. Nevertheless, a major lack that persists in most spin-decoupled metasurfaces is the limited bandwidth or the intricate design requirements. Herein, we propose a broadband spin-decoupled metasurface, consisted of weak-resonant mirror-symmetry unit structures, that enables independent and distinct wavefront manipulations under the incidence of orthogonal CP waves. As a demonstration, we present a dual-channel metasurface that integrates geometric and propagation phases to generate vortex waves with two distinct modes in a wide frequency range from 10 GHz to 16 GHz. Both simulated and experimental results&amp;#xD;are consistent and collectively confirm the validity of our proposed metasurface. The research provides a practical and efficient avenue for constructing spin-decoupled metasurface within a broad frequency band.

Development of a novel, concentric micro-ECoG array enabling simultaneous detection of a single location by multiple electrode sizes.

Detection of the epileptogenic zone is critical, especially for patients with&#xD;drug-resistant epilepsy. Accurately mapping cortical regions exhibiting high activity during&#xD;spontaneous seizure events while detecting neural activity up to 500 Hz can assist clinicians'&#xD;surgical decisions and improve patient outcomes. We designed, fabricated,&#xD;and tested a novel hybrid, multi-scale micro-electrocorticography (micro-ECoG) array with&#xD;a unique embedded configuration. This array was compared to a commercially available&#xD;microelectrode array (Neuronexus) for recording neural activity in rodent sensory cortex&#xD;elicited by somatosensory evoked potentials and pilocarpine-induced seizures. Main results&#xD;Evoked potentials and spatial maps recorded by the multi-scale array ("micros", "mesos", and&#xD;"macros" refering to the relative electrode sizes, 40 micron, 1 mm, and 4 mm respectively)&#xD;were comparable to the Neuronexus array. The SSEPs recorded with the micros had higher&#xD;peak amplitudes and greater signal power than those recorded by the larger mesos and macro.&#xD;Seizure onset events and high-frequency oscillations (∼450 Hz) were detected on the multi-&#xD;scale, similar to the commercially available array. The micros had greater SNR than the mesos&#xD;and macro over the 5-1000 Hz frequency range during seizure monitoring. During cortical&#xD;stimulation experimentation, the mesos successfully elicited motor effects. &#xD;Previous studies have compared macro- and microelectrodes for localizing seizure activity in&#xD;adjacent regions. The multi-scale design validated here is the first to simultaneously measure&#xD;macro- and microelectrode signals from the same overlapping cortical area. This enables direct&#xD;comparison of microelectrode recordings to the macroelectrode recordings used in standard&#xD;neurosurgical practice. Previous studies have also shown that cortical regions generating&#xD;high-frequency oscillations are at an increased risk for becoming epileptogenic zones. More&#xD;accurate mapping of these micro seizures may improve surgical outcomes for epilepsy patients.

Frequency effect on low‐cycle fatigue behavior of pseudoelastic NiTi alloy

AbstractThis study presents experimental results on the effect of loading frequency during low‐cycle fatigue on the fracture mechanism and properties of pseudoelastic NiTi wire. The uniaxial tensile tests were performed in stress‐controlled mode over the 0.1–10 Hz frequency range. It was shown that the number of cycles before specimen failure decreased with increasing frequency from 0.1 Hz to 1 Hz but increased at frequencies above 1 Hz. It was fractographically shown that fatigue striations were observed on the fracture surfaces of specimens tested at all loading frequencies. A new type of fatigue striations was described on fracture specimens tested at frequencies up to 1 Hz. They are characterized by different spacing between successive striations with a change in the slope of the fracture at the transitions between them. This feature may be associated with forward and reverse phase transformations during half‐periods of loading and unloading of nitinol.