Sharp Frequency Research Articles

Physical model for acoustic resonance in annular cavity structure

A physical model for acoustic resonance in the annular cavity structure is developed to represent the typical characteristic when acoustic resonance occurs. Firstly, the measurement of sound pressure in the casing and rotor blades vibration is operated in a multistage high pressure compressor. The sharp peak frequency and discrete multi-tone occur in the frequency spectrum of sound pressure in the compressor, and the vibration of the first stage of rotor blades synchronously presents the high amplitude. The frequencies associated with rotor blades vibration can be calculated with rotating sound source theory. It is also confirmed that acoustic resonance occurs in the multistage compressor. With acoustic similarity principle, an annular cavity model is established to simulate the typical characteristics of acoustic resonance in the compressor based on Large Eddy Simulation (LES) and Lighthill acoustic analogy. The coupling relationship between cavity acoustic mode and disc vibration mode shape is expounded when acoustic resonance occurs in the model. And acoustic resonance will be locked in the certain flow rate range. All these characteristics match well with those occur in the multistage high pressure compressor.

Analysis and Design of Reflectarray Antennas Based on Delay Lines: A Filter Perspective

The analysis and design of reflectarray (RA) antennas based in delay lines is introduced for the first time from a filter perspective. To this purpose, each unit-cell of the RA is considered as a network composed of two ports, one being the delay line and the other one the free-space. This approach allows to borrow the coupling matrix formalism from filter theory and apply it to design unit-cells exhibiting broadband operation together with very sharp frequency responses. The concept is demonstrated with the aid of planar printed unit-cells coupled to substrate integrated waveguides (SIWs) through slots, a configuration that offers significant advantages to shape its frequency response while providing relatively low loss. With the aim of validation, a third order filter structure integrated in SIW-based unit-cells has been experimentally tested using the waveguide simulator technique, at a center frequency of 9 GHz. Measurements demonstrate a high-quality linear phase variation and range, and large frequency selectivity together with broadband response for the element of about 18%. The experimental results show the feasibility of this approach for the design of broadband reflectarray antennas exhibiting sharp gain responses. To illustrate the concept, a medium size reflectarray has been theoretically designed using the proposed unit cell at 9 GHz, showing a directive beam with 35.8 dB gain, sharp gain selectivity over 18 dB, and confirms the wide band operation with 20.3% bandwidth for a 3 dB gain variation.

Design and implementation of sharp edge FIR filters using hybrid differential evolution particle swarm optimization

The filter is an important building block of modern communication and electronic systems. Based on well-defined bandwidth, it extracts the desired portion of the spectrum when the raw input signal is applied. Efficacy of filtering depends on the preciseness of bandwidth to avoid co-channel interference and signal loss. In addition, it must provide higher stopband attenuation and passband attenuation very close to unity with a tolerable quantity of pass/stop band ripple. Design/implementation of sharp edge modern FIR filter is structured as a multi-objective, constrained, complex, and highly nonlinear (hence multimodal) error minimization challenge. Hence, this work proposes a novel objective (normalized error fitness) function and a robust hybrid algorithm for the effective searching of the optimal filter coefficients for providing excellent sharp edge frequency response during the filtering action. Most popular particle swarm optimization (PSO) and differential evolution (DE) algorithm are effectively combined together to frame the proposed hybrid DE-PSO algorithm for enhancing the exploration and exploitation abilities of it. The proposed hybrid algorithm is validated using twelve different benchmark functions. Through simulations, the qualitative performance of the proposed approach is compared with the conventional PSO, DE, real-coded genetic algorithm and the Parks–McClellan method.

Compact Differential-Fed Planar Filtering Antennas

This paper proposes novel low-profile differential-fed planar antennas with embedded sharp frequency selectively. The antennas are compact and easy to integrate with differential devices without matching baluns. The antenna design is formulated as a topology optimization problem, where requirements on impedance bandwidth, directivity, and filtering are used as the design objectives. The optimized antennas operate over the frequency band 6.0–8.5 GHz. The antennas have reflection coefficients below −15 dB, cross-polarization levels below −42 dB, a maximum gain of 6.0 ± 0.5 dB, and a uniform directivity over more than 130° beamwidth angle in the frequency band of interest. In addition, the antennas exhibit sharp roll-off between the operational band and frequencies around the 5.8 GHz WiFi band and the 10 GHz X-band. One antenna has been fabricated with a good match between simulation and measurement results.

Hair Bundle Stimulation Mode Modifies Manifestations of Mechanotransduction Adaptation.

Sound detection in auditory sensory hair cells depends on the deflection of the stereocilia hair bundle which opens mechano-electric transduction (MET) channels. Adaptation is hypothesized to be a critical property of MET that contributes to the auditory system's wide dynamic range and sharp frequency selectivity. Our recent work using a stiff probe to displace hair bundles showed that the fastest adaptation mechanism (fast adaptation) does not require calcium entry. Using fluid-jet stimuli, others obtained data showing only a calcium-dependent fast adaptation response. Because cochlear stereocilia do not move coherently and the hair cell response depends critically on the magnitude and time course of the hair bundle deflection, we developed a high-speed imaging technique to quantify this deflection in rat cochlear hair cells. The fluid jet delivers a force stimulus, and force steps lead to a complex time course of hair bundle displacement (mechanical creep), which affects the hair cell's macroscopic MET current response by masking the time course of the fast adaptation response. Modifying the fluid-jet stimulus to generate a hair bundle displacement step produced rapidly adapting currents that did not depend on membrane potential, confirming that fast adaptation does not depend on calcium entry. MET current responses differ with stimulus modality and will shape receptor potentials of different hair cell types based on their in vivo stimulus mode. These transformations will directly affect how stimuli are encoded.SIGNIFICANCE STATEMENT Mechanotransduction by sensory hair cells represents a key first step for the sound sensing ability in vertebrates. The sharp frequency tuning and wide dynamic range of sound sensation are hypothesized to require a mechanotransduction adaptation mechanism. Recent work indicated that the apparent calcium dependence of the fastest adaptation differs with the method of cochlear hair cell stimulation. Here, we reconcile existing data and show that calcium entry does not drive the fastest adaptation process, independent of the stimulation method. With force stimulation of the hair bundle, adaptation manifests differently than with displacement stimulation, indicating that the stimulation mode of the hair bundle will affect the hair cell receptor current and stimulus coding.

Design of Tunable Devices at Terahertz Frequencies Based on Quasi-Photonic Crystals Incorporated with Graphene

In this study, we present a new theoretical model including Thue-Morse and double-period sequences as quasi-photonic crystals are incorporation with graphene and investigate the transmission properties of the THz waves in both structures using a straightforward computational method. We also consider properties of nonlinear conductivity in addition to surface linear conductivity for graphene. We observe the sharp peaks and proper forbidden bands are created in the range of 0.3 THz to 30 THz. In addition, we find that by considering the nonlinear term of graphene and engineering the structural parameters such as the chemical potential of graphene, number of layers and the incidence wave angle, transmission levels of peaks enhance scientifically and quality factor improve considerably. These results show that it would be possible to design of high-Q tunable filters with multi-stop bands in the THz regime which can reduce the noise associated with THz frequency peaks and increase the number of sharp frequency peaks.

Digital Nonlinear Metasurface with Customizable Nonreciprocity

AbstractRecently, investigation of metasurface has been extended to nonreciprocity through breaking time‐reversal symmetry. Among a number of magnetless strategies, nonlinearity is an important nonreciprocal principle amenable to the metasurface. As passive analog‐based devices, most of the existing nonlinear nonreciprocal metasurfaces are inherently characterized by the relatively unchangeable performance, sharp frequency response, and hysteresis loops. Here, an analog–digital–analog mechanism is proposed to realize the nonlinear nonreciprocity, which provides a digitally reconfigurable solution for a family of nonreciprocal performance within a shared hardware architecture. This concept is validated by a metasurface prototype with the integration of a digital module at microwave frequencies. Based on the proposed mechanism, the properties can be customized as demanded, ranging from a normal reciprocal response to a variety of nonreciprocal functions, including electromagnetic (EM) diode and EM unidirectional limiting functions, which have been experimentally demonstrated with direction reversibility and threshold tunability. The proposed metasurface is also underpinned by the nonhysteretic performance and wide operating bandwidth, thereby potentially making it an inexpensive and stable candidate for advanced manipulations of EM waves.

Sharp Skirt Dual-Mode Bandpass Filter with Overlay Plate to Control Upper Passband Edge

This paper presents design and analytical model for Sharp Skirt Dual-Mode Bandpass Filter for RF receivers. Proposed filter is designed using open stub loaded H shaped resonator. Based on analytical model insertion loss S21 and return loss S11 for proposed filter are demonstrated. Inductive Overlaying plate is proposed to control upper passband edge of proposed filter to improve frequency selectivity with fixed center frequency. The proposed filter has sharp frequency selective range from 5.1GHz to 9.2GHz. With overlay plate, frequency selective range is tuned to 5.1GHz-8.6GHz. Without overlaying plate the proposed filter has return loss greater than 10dB and insertion loss of 0.7dB. Lower and upper passband edges are at 5.1GHz and 9.2GHz with attenuation level of 52dB and 54dB respectively. With overlaying plate, the filter has same S 11 and S 21 parameters, but upper passband edge is shifted from 9.2GHz to 8.6GHz.

Effects of developmental noise exposure on inhibitory cell densities and perineuronal nets in A1 and AAF of mice

Within the auditory cortex, there are two primary-like regions considered to be ‘core’ cortical fields, the primary auditory cortex (A1) and the anterior auditory field (AAF). Both fields have sharp frequency tuning, tonotopic organization, and inputs from the ventral division of the medial geniculate body of the thalamus. AAF seems to be more specialized for faster spectrotemporal processing than A1, but the underlying mechanisms are unclear. A1 has been studied extensively in developmental plasticity, but how AAF changes with developmental experience is less clear. To address potential cellular correlates of processing differences between the two fields, we used immunohistochemistry to quantify the density of GABA, parvalbumin (PV), and somatostatin (SOM) cells in A1 and AAF of mice. We also compared the density of perineuronal nets (PNN) between A1 and AAF. PNNs are a specialized assembly of extracellular matrix involved in network maturation and plasticity. Finally, we compared the effects of developmental noise exposure on inhibitory and PNN cell density in these two core regions. In adult mice, there were more PV cells and PNNs surrounding cell bodies in AAF than in A1. Moderate level noise exposure during early development leads to 1) increased GABA and SOM cell density in both A1 and AAF, and 2) decreased PNN cell density in A1, but not AAF. Inhibitory cells without PNN appear to be more susceptible to changes following developmental noise exposure in both fields. Deep layers (5/6) are more susceptible to change in PNN density compared to superficial layers (1–4) of A1. Results are consistent with altered cortical gain control models and impaired maturation of cortex in response to noisy environments, and suggest that PNNs may be more prone to modification in A1 than AAF.

ALMA Band 3 polarimetric follow-up of a complete sample of faint PACO sources

Abstract We present Atacama Large Millimetre/submillimiter Array (ALMA) high sensitivity ($\sigma _\mathrm{ P} \simeq 0.4\,$ mJy) polarimetric observations at $97.5\,$ GHz (Band 3) of a complete sample of 32 extragalactic radio sources drawn from the faint Planck–ATCA Co-eval Observations (PACO) sample (b < −75°, compact sources brighter than $200\,$ mJy at $20\,$ GHz). We achieved a detection rate of $~97\, {\rm per\, cent}$ at $3\, \sigma$ (only 1 non-detection). We complement these observations with new Australia Telescope Compact Array (ATCA) data between 2.1 and $35\,$GHz obtained within a few months and with data published in earlier papers from our collaboration. Adding the co-eval GaLactic and Extragalactic All-sky Murchison widefield array (GLEAM) survey detections between $70\,$ and $230\,$ MHz for our sources, we present spectra over more than 3 decades in frequency in total intensity and over about 1.7 decades in polarization. The spectra of our sources are smooth over the whole frequency range, with no sign of dust emission from the host galaxy at mm wavelengths or of a sharp high frequency decline due, for example, to electron ageing. We do however find indications of multiple emitting components and present a classification based on the number of detected components. We analyse the polarization fraction behaviour and distributions up to $97\,$ GHz for different source classes. Source counts in polarization are presented at $95\,$ GHz.

Frequency-dependent entrainment of striatal fast-spiking interneurons.

Striatal fast-spiking interneurons (FSIs) fire in variable-length runs of action potentials at 20-200 spikes/s separated by pauses. In vivo, or with fluctuating applied current, both runs and pauses become briefer and more variable. During runs, spikes are entrained specifically to gamma-frequency components of the input fluctuations. We stimulated parvalbumin-expressing striatal FSIs in mouse brain slices with broadband noise currents added to direct current steps and measured spike entrainment across all frequencies. As the constant current level was increased, FSIs produced longer runs and showed sharper frequency tuning, with best entrainment at the stimulus frequency matching their intrarun firing rate. We separated the contributions of previous spikes from that of the fluctuating stimulus, revealing a strong contribution of previous action potentials to gamma-frequency entrainment. In contrast, after subtraction of the effect inherited from the previous spike, the remaining stimulus contribution to spike generation was less sharply tuned, showing a larger contribution of lower frequencies. The frequency specificity of entrainment within a run was reproduced with a phase resetting model based on experimentally measured phase resetting curves of the same FSIs. In the model, broadly tuned phase entrainment for the first spike in a run evolved into sharply tuned gamma entrainment over the next few spikes. The data and modeling results indicate that for FSIs firing in brief runs and pauses firing within runs is entrained by gamma-frequency components of the input, whereas the onset timing of runs may be sensitive to a wider range of stimulus frequency components.NEW & NOTEWORTHY Specific types of neurons entrain their spikes to particular oscillation frequencies in their synaptic input. This entrainment is commonly understood in terms of the subthreshold voltage response, but how this translates to spiking is not clear. We show that in striatal fast-spiking interneurons, entrainment to gamma-frequency input depends on rhythmic spike runs and is explained by the phase resetting curve, whereas run initiation can be triggered by a broad range of input frequencies.

Differential Inhibitory Configurations Segregate Frequency Selectivity in the Mouse Inferior Colliculus.

Receptive fields and tuning curves of sensory neurons represent the neural substrates that allow animals to efficiently detect and distinguish external stimuli. They are progressively refined to create diverse sensitivity and selectivity for neurons along ascending central pathways. However, the neural circuitry mechanisms have not been directly determined for such fundamental qualities in relation to sensory neurons' functional organizations, because of the technical difficulty of correlating neurons' input and output. Here, we obtained spike outputs and synaptic inputs from the same neurons within characteristically defined neural ensembles, to determine the synaptic mechanisms driving their diverse frequency selectivity in the mouse inferior colliculus. We find that the synaptic strength and timing of excitatory and inhibitory inputs are configured differently and independently within individual neurons' receptive fields, which segregate sensitive and selective neurons and endow neural populations with broad receptive fields and sharp frequency tuning. By computationally modeling spike outputs from integrating synaptic inputs and comparing them with real spike responses of the same neurons, we show that space-clamping errors did not qualitatively affect the estimation of spike responses derived from synaptic currents in in vivo voltage-clamp recordings. These data suggest that heterogeneous inhibitory circuits coexist locally for a parallel but differentiated representation of incoming signals.SIGNIFICANCE STATEMENT Sensitivity and selectivity are functional qualities of sensory systems to facilitate animals' survival. There is little direct evidence for the synaptic basis of neurons' functional variance within neural ensembles. Here we adopted a novel framework to fill such a long-standing gap by uniting population activities with single cells' spike outputs and their synaptic inputs. Furthermore, the effects of space-clamping errors on subcortical synaptic currents were evaluated in vivo, by comparing recorded spike responses and simulated spike outputs from computationally integrating synaptic inputs. Our study illustrated that the synaptic strength and timing of inhibition relative to excitation can be configured differently for neurons within a defined neural ensemble, to segregate their selectivity. It provides new insights into coexisting heterogeneous local circuits.

Resolving Phonon Fock States in a Multimode Cavity with a Double-Slit Qubit

We resolve phonon number states in the spectrum of a superconducting qubit coupled to a multimode acoustic cavity. Crucial to this resolution is the sharp frequency dependence in the qubit-phonon interaction engineered by coupling the qubit to surface acoustic waves in two locations separated by $\sim40$ acoustic wavelengths. In analogy to double-slit diffraction, the resulting self-interference generates high-contrast frequency structure in the qubit-phonon interaction. We observe this frequency structure both in the coupling rate to multiple cavity modes and in the qubit spontaneous emission rate into unconfined modes. We use this sharp frequency structure to resolve single phonons by tuning the qubit to a frequency of destructive interference where all acoustic interactions are dispersive. By exciting several detuned yet strongly-coupled phononic modes and measuring the resulting qubit spectrum, we observe that, for two modes, the device enters the strong dispersive regime where single phonons are spectrally resolved.

Iterative Bayesian denoising based on variance stabilization using Contourlet Transform with Sharp Frequency Localization: application to EFTEM images

BackgroundDue to the presence of high noise level in tomographic series of energy filtered transmission electron microscopy (EFTEM) images, alignment and 3D reconstruction steps become so difficult. To improve the alignment process which will in turn allow a more accurate and better three dimensional tomography reconstructions, a preprocessing step should be applied to the EFTEM data series.ResultsExperiments with real EFTEM data series at low SNR, show the feasibility and the accuracy of the proposed denoising approach being competitive with the best existing methods for Poisson image denoising. The effectiveness of the proposed denoising approach is thanks to the use of a nonparametric Bayesian estimation in the Contourlet Transform with Sharp Frequency Localization Domain (CTSD) and variance stabilizing transformation (VST). Furthermore, the optimal inverse Anscome transformation to obtain the final estimate of the denoised images, has allowed an accurate tomography reconstruction.ConclusionThe proposed approach provides qualitative information on the 3D distribution of individual chemical elements on the considered sample.

An Adaptive and Secure Holographic Image Watermarking Scheme.

A novel adaptive secure holographic image watermarking method in the sharp frequency localized contourlet transform (SFLCT) domain is presented. Based upon the sine logistic modulation map and the logistic map, we develop an encrypted binary computer-generated hologram technique to fabricate a hologram of a watermark first. Owing to the enormous key space of the encrypted hologram, the security of the image watermarking system is increased. Then the hologram watermark is embedded into the SFLCT coefficients with Schur decomposition. To obtain better imperceptibility and robustness, the entropy and the edge entropy are utilized to select the suitable watermark embedding positions adaptively. Compared with other watermarking schemes, the suggested method provides a better performance with respect to both imperceptibility and robustness. Experiments show that our watermarking scheme for images is not only is secure and invisible, but also has a stronger robustness against different kinds of attack.

Lowpass Filter with Wide Stopband Based on T-Shaped Resonator Loaded Step-Impedance Hairpin Resonator

A lowpass filter with wide stopband based on stepped impedance hairpin resonator is proposed. Multiple transmission zeros are created in the stopband region by different size T-shaped resonator to achieve wide stopband. A lowpass filter with 3dB cutoff frequency (fc) at 3.2GHz is designed, simulated and fabricated. Experimental results indicate that stopband can be extended to more than 7fc with a rejection level of 20dB after loading T-shaped resonator. The insertion loss is lower than 0.4dB and return loss is better than 16dB in the passband. Excluding the feed lines, the size of the filter is less than 0.26λg X 0.06λg. The modified filter is of good value in engineering application for its small size, sharp cutoff frequency response and wide stopband.

Hybrid secure and robust image watermarking scheme based on SVD and sharp frequency localized contourlet transform

In this paper, using singular value decomposition (SVD) and sharp frequency localized contourlet transform (SFLCT) a secure and robust image watermarking procedure is introduced. The SVD and SFLCT are applied on both watermark and original images and using the properties of the SVD and utilizing the advantages of the SFLCT, noticeable results of the watermarking requirements are obtained. Since most of the SVD based watermarking schemes are not resistant against ambiguity attacks and suffer from the false positive problem, this objection is resolved without adding extra steps to the watermarking algorithm and the suggested scheme is secure and resistant against ambiguity attacks. The simulation of the scheme is implemented and its robustness against various types of attacks is experimented. In comparison with some of the recent schemes this procedure shows high imperceptibility, capacity and robustness and these features make the scheme a suitable choice for the image processing applications.

Review on Design of Frequency Selective Surfaces based on Substrate Integrated Waveguide Technology

The spectacular development of frequency selective surfaces (FSS) as a spatial filter, absorbers and reflectors made them feasible for the aerospace and defence applications. The intervention of substrate integrated waveguide (SIW) technology into FSS results in the improvement of unit cell structures and better performance by isolating them from inter-element interference. Such FSS structures with SIW cavities upholds the FSS properties and improves their selectivity and performance. Considering the diversity in applications of introducing SIW cavity technology into FSS, the aim of this paper is to furnish a study on the glimpse of EM design techniques to analyze this type of structures. Design topologies of narrowing bandwidth, dual resonance, the design of FSS with sharp sideband edges and frequency selective polarization rotating structures are presented. Further, a novel design for improving the bandwidth of reflective FSS is discussed based on SIW technology. Fabrication techniques pertaining to this type of structures are presented in brief.

Acoustical Measurement of Natural Lightning Flashes: Reconstructions and Statistical Analysis of Energy Spectra

AbstractTwenty‐seven natural flashes of three thunderstorms which occurred during October 2012 in Southern France are acoustically reconstructed and analyzed in the [0.1 − 180]‐Hz frequency bandwidth and the [0.3 − 20]‐km distance range. A 50‐m triangular array of four recalibrated microphones sampled at 500 Hz has been used for the recording. A novel method of separation of return strokes from intracloud discharges within the acoustical signal is detailed and systematically applied. It shows the possibility to separate nearby cloud‐to‐ground (CG) events or nearby and distant CGs of the same flash. The separation method yields a total of 36 return stroke signals and spectra, along with some intracloud signals. The combination of reconstruction, separation, and frequency analysis provides new insights on the origin of thunder infrasound, showing unambiguously that thunder infrasound originate dominantly from return strokes. Apart from the higher amplitude of CGs, no clear difference between intracloud and CG spectra is observed. No sharp frequency peaks can be put into evidence. The spectral variability with distance is highlighted, especially for the total acoustic energy and the center frequency and bandwidth. A link between acoustic energy and impulse charge moment change is also found, though only by a small number of data.

The susceptibility of cochlear outer hair cells to cyclodextrin is not related to their electromotile activity

Niemann-Pick Type C1 (NPC1) disease is a fatal neurovisceral disorder caused by dysfunction of NPC1 protein, which plays a role in intracellular cholesterol trafficking. The cholesterol-chelating agent, 2-hydroxypropyl-β-cyclodextrin (HPβCD), is currently undergoing clinical trials for treatment of this disease. Though promising in alleviating neurological symptoms, HPβCD causes irreversible hearing loss in NPC1 patients and outer hair cell (OHC) death in animal models. We recently found that HPβCD-induced OHC death can be significantly alleviated in a mouse model lacking prestin, an OHC-specific motor protein required for the high sensitivity and sharp frequency selectivity of mammalian hearing. Since cholesterol status is known to influence prestin’s electromotility, we examined how prestin contributes to HPβCD-induced OHC death in the disease context using the NPC1 knockout (KO) mouse model (NPC1-KO). We found normal expression and localization of prestin in NPC1-KO OHCs. Whole-cell patch-clamp recordings revealed a significant depolarization of the voltage-operating point of prestin in NPC1-KO mice, suggesting reduced levels of cholesterol in the lateral membrane of OHCs that lack NPC1. OHC loss and elevated thresholds were found for high frequency regions in NPC1-KO mice, whose OHCs retained their sensitivity to HPβCD. To investigate whether prestin’s electromotile function contributes to HPβCD-induced OHC death, the prestin inhibitor salicylate was co-administered with HPβCD to WT and NPC1-KO mice. Neither oral nor intraperitoneal administration of salicylate mitigated HPβCD-induced OHC loss. To further determine the contribution of prestin’s electromotile function, a mouse model expressing a virtually nonelectromotile prestin protein (499-prestin) was subjected to HPβCD treatment. 499-prestin knockin mice showed no resistance to HPβCD-induced OHC loss. As 499-prestin maintains its ability to bind cholesterol, our data imply that HPβCD-induced OHC death is ascribed to the structural role of prestin in maintaining the OHC’s lateral membrane, rather than its motor function.