Large Frequency Range Research Articles

Subharmonic eigenvalue orbits in the spectrum of pulsating Poiseuille flow

Spectral degeneracies where eigenvalues and eigenvectors simultaneously coalesce, also known as exceptional points, are a natural consequence of the strong non-normality of the Orr–Sommerfeld operator describing the evolution of infinitesimal disturbances in parallel shear flows. While the resonances associated with these points give rise to algebraic growth, the development of non-modal stability theory exploiting specific perturbation structures with much larger potential for transient energy growth has led to waning interest in spectral degeneracies. The appearance of subharmonic eigenvalue orbits, recently discovered in the periodic spectrum of pulsating Poiseuille flow, can be traced back to the coalescence of eigenvalues at exceptional points. We present a thorough analysis of the spectral properties of the linear operator to identify exceptional points and accurately map the prevalence of subharmonic eigenvalue orbits for a large range of pulsation amplitudes and frequencies. This information is then combined with solutions of the linear initial value problem to analyse the impact of the appearance of these orbits on the temporal evolution of linear disturbances in pulsating Poiseuille flow. The periodic amplification phases are shown to be heralded by repeated non-normal growth bursts that are intensified by the formation of subharmonic orbits involving the leading eigenvalues. These bursts are associated with the change of alignment of the perturbation from the decaying towards the amplified branch of the subharmonic eigenvalue orbits in a so-called branch transition process.

A Fractional Model of Complex Permittivity of Conductor Media with Relaxation: Theory vs. Experiments

Moving from the study of plasmonic materials with relaxation, in this work we propose a fractional Abraham–Lorentz-like model of the complex permittivity of conductor media. This model extends the Ciancio–Kluitenberg, based on the Mazur–de Groot non-equilibrium thermodynamics theory (NET). The approach based on NET allows us to link the phenomenological function of internal variables and electrodynamics variables for a large range of frequencies. This allows us to closer reproduce experimental data for some key metals, such as Cu, Au and Ag. Particularly, our fitting significantly improves those obtained by Rakic and coworkers and we were able to operate in a larger range of energy values. Moreover, in this work we also provide a definition of a substantial fractional derivative, and we extend the fractional model proposed by Flora et al.

Fourier Subspace-Based Deep Learning Method for Inverse Design of Frequency Selective Surface

Frequency selective surface (FSS) is critical for electromagnetic (EM) radiation protection due to its high spatial filtering performance, especially for active FSS. Recently, the artificial neural network (ANN) has shown great potential in solving EM inverse problems and rapid industrial design. In such an inverse model with ANN, it establishes the relationship between the given inputs of S-parameters and the desired structure parameters or material parameters. However, faced with applications where S-parameters vary in a large frequency range with different curve shapes, such as multiband microwave devices, equal interval sampling may result in high-dimensional inputs and will require a more complicated neural network. In this work, we present a Fourier subspace-based deep learning method (FS-BDLM) for FSS inverse design, where the dimension of the input is largely reduced by using Fourier subspace to represent the most salient features of the desired S-parameter performance. Compared with existing deep learning methods, the proposed technique makes inverse neural models more compact and more stable to noise contaminations. The validation of the proposed FS-BDLM is conducted both numerically and experimentally through two dual-passband FSS design examples, where the well-designed FSS is fabricated to validate the technique.

Toward Completely Sampled Extracellular Neural Recording During fMRI.

This work aims to estimate severe fMRI scanning artifacts in extracellular neural recordings made at ultrahigh magnetic field strengths in order to remove the artifact interferences and uncover the complete neural electrophysiology signal. We build on previous work that used PCA to denoise EEG recorded during fMRI, adapting it to cover the much larger frequency range (1-6000 Hz) of the extracellular field potentials (EFPs) observed by extracellular neural recordings. We examine the singular value decomposition (SVD)-PCA singular value shrinkage (SVS) and compare two shrinkage rules and a sliding template subtraction approach. Additionally, we present a new technique for estimating the singular value upper bounds in spontaneous neural activity recorded in the isoflurane anesthetized rat that uses the temporal first difference of the neural signal. The approaches are tested on artificial datasets to examine their efficacy in detecting extracellular action potentials (EAPs: 300-6000 Hz) recorded during fMRI gradient interferences. Our results indicate that it is possible to uncover the EAPs recorded during gradient interferences. The methods are then tested on natural (non-artificial) datasets recorded from the cortex of isoflurane anesthetized rats, where both local field potential (LFP: 1-300 Hz) and EAP signals are analyzed. The SVS methods are shown to be advantageous compared to sliding template subtraction, especially in the high frequency range corresponding to EAPs. Our novel approach moves us towards simultaneous fMRI and completely sampled neural recording (1-6000Hz with no temporal gaps), providing the opportunity for further study of spontaneous brain function and neurovascular coupling at ultrahigh field in the isoflurane anesthetized rat.

Photonic Generation of Reconfigurable Ternary Modulated Microwave Signals with a Large Frequency Range

A photonic scheme generating ternary modulated signals, which include amplitude, phase, and frequency modulated signals, has been proposed and demonstrated. This scheme is based on a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM), where the X-DPMZM is used to generate an optical frequency comb (OFC), and the Y-DPMZM is utilized to accomplish ternary modulation. The key feature of this scheme is that ternary modulated signals with eight wavebands can be obtained by using only the DP-DPMZM in situations of different input signals. In the simulation, a 2.5 Gbit/s amplitude shift keying (ASK), phase shift keying signal (PSK), or an 8 GHz bandwidth linearly frequency modulated (LFM) signal are obtained. The generated signals have eight wavebands with a large frequency range from 10 GHz to 80 GHz. Moreover, the recovery and pulse compression performances of the generated signals are evaluated.

Aberration-corrected transmission electron microscopy with Zernike phase plates

We explore the possibility of applying physical phase plates (PPs) in combination with aberration-corrected transmission electron microscopy. Phase-contrast transfer characteristics are calculated and compared for a thin-film based Zernike PP, a hole-free (HF) or Volta PP and an electrostatic Zach PP, considering their phase-shifting properties in combination with partial spatial coherence. The effect of slightly converging illumination conditions, often used in high-resolution applications, on imaging with PPs is discussed. Experiments with an unheated Zernike PP applied to various nanomaterial specimens and a qualitative analysis clearly demonstrates the general compatibility of PPs and aberration-corrected transmission electron microscopy. Calculations and experiments show the benefits of the approach, among which is a strong phase-contrast enhancement of a large range of spatial frequencies. This allows the simultaneous imaging of atomic-resolution structures and morphological features at the nanometer scale, with maximum phase contrast. The calculations can explain why the HFPP damps contrast transfer at higher spatial frequencies.

Back-Gate Lumped Resistance Effect on AC Characteristics of FD-SOI MOSFET

In this work, the impact of a large lumped resistor connected to the back-gate (B-G) of an fully depleted silicon-on-insulator (FD-SOI) transistor is studied. A related transition in the frequency responses of output conductance and capacitance is evidenced experimentally by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> -parameters measurements in a large frequency range up to 40 GHz. However, present compact model does not correctly reproduce the B-G/substrate network behavior. This calls for a model accounting for both n-well and substrate networks. A small-signal equivalent circuit including distributed elements is thus proposed and compared with experimental results.

Three dimensional vibroacoustic topology optimization of hearing instruments using cut elements

The focus of this article is on level set based topology optimization of vibroacoustic hearing instruments. The goal is to demonstrate the applicability of the proposed framework for optimization of 3D industrial scale hearing instruments. The framework employs an immersed boundary cut element method to handle the modeling of complex design geometries on fixed unstructured meshes. Utilization of unstructured meshes allows for optimizing small parts of a complex hearing instrument without disturbing the overall geometry. The remaining parts of the model which are not included in the optimization process are modeled with segregated approach. The design parameterization is based on an explicit level set approach, for which the nodal level set values are linked to the mathematical design variables. The optimization problem is solved using mathematical programming and the sensitivities are obtained with a discrete adjoint approach. A validation study is carried out comparing the proposed cut element model to a body fitted mesh for a large range of frequencies. The optimization framework is then applied on the tube and the suspension structures of a hearing instrument system considering two sets of material properties for the design parts. The optimization considers the minimization of sound pressure on the microphone surface for discrete frequencies aiming to reduce the feedback paths and to increase the amplification that the device can deliver to the user. Both optimization cases improve the performance of the hearing instrument system by effectively reducing the sound pressure on the microphone surface for the considered frequency range.

Information transmission in recurrent networks: Consequences of network noise for synchronous and asynchronous signal encoding.

Information about natural time-dependent stimuli encoded by the sensory periphery or communication between cortical networks may span a large frequency range or be localized to a smaller frequency band. Biological systems have been shown to multiplex such disparate broadband and narrow-band signals and then discriminate them in later populations by employing either an integration (low-pass) or coincidence detection (bandpass) encoding strategy. Analytical expressions have been developed for both encoding methods in feedforward populations of uncoupled neurons and confirm that the integration of a population's output low-pass filters the information, whereas synchronous output encodes less information overall and retains signal information in a selected frequency band. The present study extends the theory to recurrent networks and shows that recurrence may sharpen the synchronous bandpass filter. The frequency of the pass band is significantly influenced by the synaptic strengths, especially for inhibition-dominated networks. Synchronous information transfer is also increased when network models take into account heterogeneity that arises from the stochastic distribution of the synaptic weights.

Ultrasound water-marking for simultaneous B-scan imaging and bio-telemetry

Ultrasound imaging technology has undergone a revolution during the last decade due to the availability of transducers that can operate over a large range of frequencies, and also due to the availability of high-speed, high-resolution analog-to-digital converters and signal processors. The large data acquisition and computational bandwidth afforded on these portable and bench-top ultrasound imaging systems could potentially be leveraged for designing energy-efficient bio-telemetry links that can be used for communicating with devices implanted in vivo. In this paper, we discuss an ultrasound water-marking approach that can be used for simultaneous imaging and bio-telemetry. The trade-off involves supporting a reasonable data-rate bio-telemetry link and at the same time minimizing artifacts due to bio-telemetry data in the B-scan images. Specifically, we exploit a variance-based signal representation where the image background noise is modulated to encode the data to be transmitted or sensed. Using a B-scan ultrasound imaging system and a phantom setup we show that the approach can support biotelemetry links at sub-nanowatt transmission power and at depths greater than 10 cm.

Design and characterization of a broadband multi-node bulk acoustic wave device for acoustofluidic applications

The classic approaches to generate the Acoustic Radiation Force (ARF) in a standing wave cavity are based on the use of a specific height for the cavity and a narrow-band acoustic frequency to reach the resonance. We present a robust multi-node cavity working over a broadband range of frequency. This approach allows large acoustophoresis manipulations. The design of a transparent cavity and the use of a broadband ultrasonic transducer allowed the characterization of the acoustic energy and the comparison with a simple 1-D model. The acoustic properties of the system were estimated through the effects of the acoustic radiation forces on particles suspension. From the particle velocities induced by the ARF, measured with a Particle Image Velocimetry (PIV) approach, we deduced the acoustic energy over a large frequency range. The automation of the setup allowed the acquisition of a large amount of data to make parametric studies. The results show a wide continuous operating range for the acoustic radiation forces. Furthermore, the occurrence of the resonance peaks allows an increase by a factor ten of the force magnitude. This broadband effect also enables an accurate control of the node positions by tuning the proper acoustic frequency.

A 0.5 V Sub-Threshold CMOS Current-Controlled Ring Oscillator for IoT and Implantable Devices

A current-controlled CMOS ring oscillator topology, which exploits the bulk voltages of the inverter stages as control terminals to tune the oscillation frequency, is proposed and analyzed. The solution can be adopted in sub-1 V applications, as it exploits MOSFETS in the subthreshold regime. Oscillators made up of 3, 5, and 7 stages designed in a standard 28-nm technology and supplied by 0.5 V, were simulated. By exploiting a programmable capacitor array, it allows a very large range of oscillation frequencies to be set, from 1 MHz to about 1 GHz, with a limited current consumption. Considering, for example, the five-stage topology, a nominal oscillation frequency of 516 MHz is obtained with an average power dissipation of about 29 µW. The solution provides a tuneable oscillation frequency, which can be adjusted from 360 to 640 MHz by controlling the bias current with a sensitivity of 0.43 MHz/nA.

Mode tracking method based on information entropy prejudging mode swapping

Mode tracking based on correlation is a common method to achieve reasonable mode ordering in characteristic mode analysis (CMA). However, it is time-consuming to traverse the correlation calculation with all frequency points. For this reason, it is proposed to use information entropy in determining the frequency points of mode swapping in advance, which effectively improves the computational efficiency of CMA. Meanwhile, it is pointed out that for higher-order modes or electrically large structures, pseudo-degenerate modes are prone to appear, which results in mode swapping. In a large frequency range, the reactance property of a mode can be reversed, causing a change in the physical meaning of the mode. Therefore, CMA is best performed in the frequency range adapted to the structure size. Numerical analysis examples show the feasibility of this mode tracking method and confirm the rationality of mode performance analysis.

Analytical Study on the Low-Frequency Vibrations Isolation System for Vehicle’s Seats Using Quasi-Zero-Stiffness Isolator

Improving the vibration isolation for the seat of small vehicles under low excitation frequencies is important for providing good comfort for the driver and passengers. Thus, in this study, a compact, low-dynamic, and high-static stiffness vibration isolation system has been designed. A theoretical analysis of the proposed quasi-zero stiffness (QZS) isolator system for vehicle seats is presented. The isolator consists of two oblique springs and a vertical spring to support the load and to achieve quasi-zero stiffness at the equilibrium position. To support any additional load above the supported weight, a sleeve air spring is used. Furthermore, the two oblique springs are equipped with a horizontal adjustment mechanism that is aimed to reach higher frequencies with the existed stroke when a heavy load is applied. The proposed system can be fitted for small vehicles, especially for B-segment and C-segment cars. Finally, the simulation results reveal that the proposed system has a large isolation frequency range compared to that of the linear isolator.

Angle-dependent acoustic reflectivity of gillnets and their modifications to reduce bycatch of odontocetes using sonar imaging

Incidental capture in gillnets is the most pressing threat for small cetaceans worldwide. One reason why small, echolocating cetaceans entangle in gillnets may be their inability to acoustically detect gillnets and classify them as obstacles. To increase the overall acoustic reflectivity as well as alter the perceived image to simulate an impenetrable barrier, small reflective objects – 8 mm wide acrylic glass spheres – were attached to standard gillnets. This study investigates the acoustic reflectivity of standard gillnets and modified gillnets with different numbers of spheres/m², at several angles of ensonification across a large frequency range. The acoustic reflectivity of standard gillnets is very low and decreases with angle of ensonification. Gillnets equipped with the spheres have substantially higher acoustic backscattering strength, and exhibit a positive relation between backscattering strength and inclination, i.e. gillnets ensonified from an angle have an even larger echo than when ensonified perpendicularly. Gillnets with sphere-sphere distance of 20 cm perform best, while the acoustic backscatter of gillnets with 40 cm and 60 cm sphere-distances is similar. The acoustic image (echogram) of the gillnet with spheres demonstrates a distinct highly visible acoustic pattern, potentially rendering the spheres an effective way to reduce bycatch of small cetaceans.

A continuum model reproducing the multiple frequency crossovers in acoustic attenuation in glasses

Structured metamaterials are at the core of extensive research, promising for acoustic and thermal engineering. Nevertheless, the computational cost required for correctly simulating large systems imposes to use a continuous model to describe the effective behavior without knowing the atomistic details. Crucially, a correct description needs to describe both the extrinsic interface-induced and the intrinsic atomic scale-originated phonon scattering, especially when the component material is made of glass, a highly dissipative material in which wave attenuation is strongly dependent on frequency as well as on temperature. In amorphous systems, the effective acoustic attenuation triggered by multiple mechanisms is now well characterized and exhibits a nontrivial frequency dependence with a double crossover of power laws. In this work, we propose a continuum viscoelastic model based on the hierarchical strategy multi-scale approach, able to reproduce well the phonon attenuation in a large frequency range, spanning three orders of magnitude from GHz to THz with a ω2−ω4−ω2 dependence, including the influence of temperature.

Optimization of Matching Layers to Extend the Usable Frequency Band for Underwater Single-Crystal Piezocomposite Transducers.

The ongoing robotic revolution in oceanic science puts new requirements on sonar technology. Small platforms require compact multi-purpose transducers, with strict requirements on power consumption and heat dissipation. Introducing single-crystal ferroelectrics as the active material of the transmitter can be one way of meeting the new requirements. The large electromechanical coupling coefficient of single crystals can enable an extension of the usable frequency band compared to conventional PZT. For the applications considered in this work, the usable frequency band is restricted by both the transmitted acoustic power and the reactive electrical power. Single crystals as the active materials can double the usable band, but the acoustic matching required for this can be difficult to obtain in practice. We investigated an air-backed, plane 1-3 composite transducer, matched to water by acoustic matching layers. For many applications, the diversity provided by a large usable frequency range is more important than a flat acoustic power response, and the transducer can be used far beyond the -3-dB limit. We defined the usable band by requiring maximum -12-dB ripple in transmitted acoustic power and maximum 50% reactive power. The matching layers were optimized to maximize the usable band according to this definition, in contrast to the conventional approach where matching layers are optimized for maximally flat response. Under the chosen definitions, our modeling showed that with a single crystal as the active material we could achieve 188% usable frequency band relative to the resonance frequency, compared to 121% for a PZT.

EFFICIENT INCREMENTAL SIMULATION OF “1/f” NOISES

Large-scale simulations and analysis of the original powers of 2 geometric source sum algorithm for simulating [Formula: see text] noise confirm that it provides a reasonably accurate approximation to an exact [Formula: see text] spectral density with a Gaussian amplitude distribution over any arbitrarily large frequency range. This incremental algorithm is computationally efficient with a computation time, after initialization, that varies linearly with the number of samples generated. A new variation allows non-integer and random ratios for the geometric sequence that reduces variations about the exact power-law spectral density and, by varying individual source amplitudes, produces generalized [Formula: see text] noises.

Enhanced energy storage performance in (1-x)Bi0.85Sm0.15FeO3-xCa0.5Sr0.5Ti0.9Zr0.1O3 relaxor ceramics

Producing dielectric ceramics with favorable energy storage density, efficiency, and thermal stability has become an urgent task for developing energy storage devices. In this work, the innovative Pb-free (1-x)Bi0.85Sm0.15FeO3-xCa0.5Sr0.5Ti0.9Zr0.1O3 [(1-x)BSF-xCSTZ, x = 0.0, 0.1, 0.2, 0.3 and 0.4] ceramics were fabricated via traditional solid phase sintering approach. Their structures, electrical characteristics, and energy storage properties were researched comprehensively. The results verified that all the samples form solid solutions with pseudo-cubic perovskites structure. The density of ceramic samples is improved accompanied by gradually refined grain size upon increasing the CSTZ doping content. Interestingly, an excellent recoverable density of ∼3.3 J/cm3 with high efficiency of ∼78% is received at x = 0.3 under the average breakdown electric field of 350 kV/cm. The energy storage performances remained stable in a broad temperature range of 20 – 110 ℃, a large frequency range of 1 Hz – 1 kHz, and beyond 105 repeated charging-discharging cycles. The enhanced energy storage performances of BSF ceramics by introducing CSTZ result from the improved relaxor behavior and the increased electric breakdown strength. Our strategy for relaxor modulation with a sealed sintering method to achieve high energy storage performance can be valuable in BiFeO3-based ceramic capacitors.

A Microfluidic Dielectric Spectroscopy System for Characterization of Biological Cells in Physiological Media.

Dielectric spectroscopy (DS) is a promising cell screening method that can be used for diagnostic and drug discovery purposes. The primary challenge of using DS in physiological buffers is the electrode polarization (EP) that overwhelms the impedance signal within a large frequency range. These effects further amplify with the miniaturization of the measurement electrodes. In this study, we present a microfluidic system and the associated equivalent circuit models for real-time measurements of cell membrane capacitance and cytoplasm resistance in physiological buffers with 10 s increments. The current device captures several hundreds of biological cells in individual microwells through gravitational settling and measures the system’s impedance using microelectrodes covered with dendritic gold nanostructures. Using PC-3 cells (a highly metastatic prostate cancer cell line) suspended in cell growth media (CGM), we demonstrate stable measurements of cell membrane capacitance and cytoplasm resistance in the device for over 15 min. We also describe a consistent application of the equivalent circuit model, starting from the reference measurements used to determine the system parameters. The circuit model is tested using devices with varying dimensions, and the obtained cell parameters between different devices are nearly identical. Further analyses of the impedance data have shown that accurate cell membrane capacitance and cytoplasm resistance can be extracted using a limited number of measurements in the 5 MHz to 10 MHz range. This will potentially reduce the timescale required for real-time DS measurements below 1 s. Overall, the new microfluidic device can be used for the dielectric characterization of biological cells in physiological buffers for various cell screening applications.