Frequency Selectivity Research Articles

Miniaturized bandpass filter with ultrawide-stopband and high selectivity using glass-based IPD technology

A miniaturized bandpass filter (BPF) with ultrawide-stopband and high selectivity performance is proposed by virtue of glass-based integrated passive devices (IPD) technology. The proposed BPF consists of two modified second-order units and an impedance inverter. In the modified second-order units, two capacitors are added to the traditional second-order Chebyshev bandpass filter, which can generate two additional transmission zeros locating in the lower and upper bands, respectively. Moreover, these two modified second-order units are cascaded to improve the selectivity and achieve the ultrawide-stopband of the proposed BPF. In addition, the cascaded impedance inverter is introduced to further improve impedance matching of the proposed BPF. The proposed BPF is fabricated using glass-based IPD technology and measured by on-wafer probing. The fabricated BPF has a compact size of 1.0 mm × 1.0 mm × 0.35 mm. The measured results show that the fabricated BPF can cover the wide operating band from 3.3 GHz to 5.0 GHz with an insertion loss of 1.4 dB, a return loss better than 17.5 dB in the passband, and an upper stopband suppression better than 21.6 dB up to 43.5 GHz (10.48f0). In addition, the fabricated BPF can achieve a good frequency selectivity with a rectangular coefficient of 1.33. The simulated and measured results exhibit good agreements.

The serotonergic psychedelic DOI impairs deviance detection in the auditory cortex.

Psychedelics are known to induce profound perceptual distortions, yet the neural mechanisms underlying these effects, particularly within the auditory system, remain poorly understood. In this study, we investigated the effects of the psychedelic compound 2,5-Dimethoxy-4-iodoamphetamine (DOI), a serotonin 2A receptor agonist, on the activity of neurons in the auditory cortex of awake mice. We examined whether DOI administration alters sound-frequency tuning, variability in neural responses, and deviance detection (a neural process reflecting the balance between top-down and bottom-up processing). Our results show that while DOI does not alter the frequency selectivity of auditory cortical neurons in a consistent manner, it increases trial-by-trial variability in responses and consistently diminishes the neural distinction between expected (standard) and unexpected (oddball) stimuli. This reduction in deviance detection was primarily driven by a decrease in the response to oddball sounds, suggesting that DOI dampens the auditory cortex's sensitivity to unexpected events. These findings provide insights into how psychedelics disrupt sensory processing and shed light on the neural mechanisms underlying the altered perception of auditory stimuli observed in the psychedelic state.

Artificial basilar membrane/hair cell integrated acoustic system for keyword spotting in noisy environments inspired by human cochlea

We report a novel speech recognition method using a noise-robust acoustic sensor system that integrates a spatially frequency-separating sensor with a nonlinear amplification algorithm, mimicking the cochlea’s basilar membrane and hair cells. The multichannel piezoelectric artificial basilar membrane (ABM) sensor detects specific sound frequencies with high sensitivity over 0.2–6 kHz. The signal processing model of the Artificial Hair Cell inspired by the signal transduction mechanism of inner hair cells, simultaneously enhances the frequency selectivity of ABM sensors and improves noise robustness. In a 0 dB SNR noisy environment, it effectively detected the voice signal with a maximum SNR of 57 dB. Furthermore, we converted the frequency-separated signals for speech sounds in various noisy environments into heatmap images and utilized them as input for a CNN-based speech recognition algorithm. Consequently, our system demonstrated noise-robust recognition performance with 94 % accuracy, even in noisy environments.

Effects of ipsilateral, contralateral, and bilateral noise precursors on psychoacoustical tuning curves in humans

Cochlear tuning and hence auditory frequency selectivity are thought to change in noisy environments by activation of the medial olivocochlear reflex (MOCR). In humans, auditory frequency selectivity is often assessed using psychoacoustical tuning curves (PTCs), a plot of the level required for pure-tone maskers to just mask a fixed-level pure-tone probe as a function of masker frequency. Sometimes, however, the stimuli used to measure a PTC are long enough that they can activate the MOCR by themselves and thus affect the PTC. Here, PTCs for probe frequencies of 500 Hz and 4 kHz were measured in forward masking using short maskers (30 ms) and probes (10 ms) to minimize the activation of the MOCR by the maskers or the probes. PTCs were also measured in the presence of long (300 ms) ipsilateral, contralateral, and bilateral broadband noise precursors to investigate the effect of the ipsilateral, contralateral, and bilateral MOCR on PTC tuning. Four listeners with normal hearing participated in the experiments. At 500 Hz, ipsilateral and bilateral precursors sharpened the PTCs by decreasing the thresholds for maskers with frequencies at or near the probe frequency with minimal effects on thresholds for maskers remote in frequency from the probe. At 4 kHz, by contrast, ipsilateral and bilateral precursors barely affected thresholds for maskers near the probe frequency but broadened PTCs by reducing thresholds for maskers far from the probe. Contralateral precursors barely affected PTCs. An existing computational model was used to interpret the results. The model suggested that despite the apparent differences, the pattern of results is consistent with the ipsilateral and bilateral MOCR inhibiting the cochlear gain similarly at the two probe frequencies and more strongly than the contralateral MOCR.

MXene-based kirigami designs: showcasing reconfigurable frequency selectivity in microwave regime

Today’s wireless environments, soft robotics, and space applications demand delicate design of devices with tunable performances and simple fabrication processes. Here we show strain-based adjustability of RF/microwave performance by applying frequency-selective patterns of conductive Ti3C2Tx MXene coatings on low-cost acetate substrates under ambient conditions. The tailored performances were achieved by applying frequency-selective patterns of thin Ti3C2Tx MXene coatings with high electrical conductivity as a replacement to metal on low-cost flexible acetate substrates under ambient conditions. Under quasi-axial stress, the Kirigami design enables displacements of individual resonant cells, changing the overall electromagnetic performance of a surface (i.e., array) within a simulated wireless channel. Two flexible Kirigami-inspired prototypes were implemented and tested within the S, C, and X (2-4 GHz, 4-8 GHz, and 8-12 GHz) microwave frequency bands. The resonant surface, having ~1/4 of the size of a standard A4 paper, was able to steer a beam of scattered waves from each resonator by ~25°. Under a strain of 22%, the resonant frequency of the wired co-planar resonator was shifted by 400 MHz, while the reflection coefficient changed by 158%. Deforming the geometry impacted the spectral response of the components across three arbitrary frequencies in the 4-10 GHz frequency range. With this proof of concept, we anticipate implementing thin films of MXenes on technologically relevant substrates, achieving multi-functionality through cost-effective and straightforward manufacturing.

Sensing and frequency selecting with toroidal resonance in metasurface

A double M-shaped metasurface is proposed and produced to realize a high Q-factor resonance at 13 GHz. The numerical and experimental results show that the high Q excitation of the structure is caused by the strong toroidal dipole. The novel toroidal metasurface can be a refractive index sensor with a high sensitivity of 3.2 GHzRIU−1. In addition, the double layer metasurface can achieve frequency selection with a bandwidth of 0.27 GHz. The proposed metasurface further extends the application of toroidal dipole in the field of sensing, frequency selective surface and so on.

Acoustic Metasurfaces for Efficient Modulation and Demodulation of OAM Multiplexed Signals in Acoustic Communication

Abstract Orbital angular momentum (OAM) multiplexing has been suggested as a potential solution to increase the data capacity of acoustic communication systems. A method of modulation and demodulation of OAM multiplexed signals using acoustic metasurfaces is proposed in this manuscript. The amplitude and phase of independent acoustic orbital angular momentum (AOAM) multiplexed signal provide orthogonal degrees of freedom. By designing appropriate acoustic metasurfaces and combining them with binary differential phase coding techniques, we demonstrated that efficient modulation and fast demodulation of AOAM multiplexed signals can be achieved. Orthogonal acoustic spiral modes prevent mode coupling and crosstalk, enhancing acoustic multiplexing. The resonance-based structure provides signal frequency selectivity, boosting efficiency and simplifying terminal equipment for practical applications, which leads to the creation of high-capacity acoustic communication systems.

Exact synthesis of couple‐line based wideband four‐way filtering power divider with unequal power division

AbstractIn this paper, a coupled‐line‐based wideband four‐way filtering power divider (FPD) with unequal power division is presented. It is composed of three groups of coupled lines (CLs), four types of open‐ended stubs, and three kinds of resistors. By setting the CLs in each group with different parameters, unequal power distribution is obtained. Besides, open‐ended stubs with different characteristic impedances are inserted to each output port to generate two extra transmission zeros, at the same time maintaining good impedance matchings. Resistors are inserted to each group of the CLs to improve the isolations. By applying twice parity mode analysis, the exact synthesis of the proposed FPD is first derived. For demonstration, a prototype with power division ratio of 1:1.2:1.5:1.8 is designed and manufactured. Measurement results verified that more than 60% fractional bandwidth (FBW) is obtained under the criterion of 10 dB return loss and 10 dB isolation. Besides, the 3 dB passband FBWs for the four outputs reach 70% with high frequency selectivity and low insertion loss. And more than 15 dB out‐of‐band rejections are achieved for both the lower and upper stopbands.

Weak signal detection capacity of type-II Morris–Lecar neuron system under presynaptic bombardments

The information encoding mechanism of the neuronal system is quite complex and is sensitive to environmental conditions. Neuronal noise, especially synaptic random inputs, is a natural part of the brain. Theoretical and experimental studies have revealed that noise plays a vital role in signal frequency selectivity and weak sensory input perception of the neuronal system. There is a consensus that sufficiently intense noise can trigger rhythmic brain activity, and these noise-induced oscillations could improve signal processing of the neuronal system, particularly when the external signal frequency aligns with the frequency of the noise-induced rhythm. Such behavior in response to noise in the signal-processing mechanism of biological systems is elucidated by stochastic resonance. In this regard, this paper systematically analyzes the stochastic resonance in a Type-II Morris–Lecar neuron under excitatory and inhibitory background spike bombardments. Our results indicate that Morris–Lecar Type II neurons enhance their signal coding capacity by exploiting background synaptic activity. In addition, it has been revealed that the biological properties of the background synaptic connections of neurons that oscillate at different frequencies, such as delta, theta, alpha, beta, and gamma bands, are different. On the other hand, it has been found that neurons adapt to the properties of pre-synaptic neurons to encode weak signals. This study ensures novel insights into the functional role of background synaptic input in neuronal coding mechanisms by demonstrating a biophysical factor of stochastic resonance via numerical analyses. Furthermore, our results show that the properties of the background synaptic inputs significantly determine what kind of signal to encode or not. These results are an important indicator of the signal frequency selectivity of neurons, such as auditory cells.

Polarization-insensitive cross-polarization converter with high frequency selectivity based on an antenna-resonator-antenna module

In this paper, a novel transmission-type polarization-insensitive frequency selective polarization converter (PIFSPC) is proposed. The overall structural scheme of the proposed PIFSPC is based on an antenna-resonator-antenna (ARA) module, which is composed of a receiving patch antenna, double “S-shaped” half-wavelength resonators, and a transmitting patch antenna. By adopting cross-coupling, high frequency selectivity is achieved, and through the utilization of a staggered rotationally symmetric structure, polarization insensitivity is attained. The prototype possesses four transmission poles and two zeros on the polarization conversion spectrum, and it shows insensitivity to the polarization direction of incident electromagnetic waves. The frequency selectivity of the prototype at the lower and upper band edges is 425 dB/GHz and 283 dB/GHz respectively. The cross-polarization conversion rate (PCR) is over 95% within the passband from 4.93 GHz to 5.09 GHz for arbitrarily polarized azimuth incident waves, and its thickness is merely 0.052λ0. The operation bandwidth and frequency selectivity of the prototype can be readily altered. A prototype is fabricated and measured, with excellent consistency between simulations and experiments. It indicates the feasibility of integrating frequency selection and polarization conversion. The proposed PIFSPC has extensive application prospects in enhancing the anti-interference ability and electromagnetic compatibility in the fields of communication, measurement, and microwave detection.

Local control of polarization and geometric phase in thermal metasurfaces.

Thermal emission from a hot body is inherently challenging to control due to its incoherent nature. Recent advances have shown that patterned surfaces can transform thermal emission into partially coherent beams with tailored directionality and frequency selectivity. Here we experimentally demonstrate polarization-selective, unidirectional and narrowband thermal emission using single-layer metasurfaces. By implementing polarization gradients across the surface, we unveil a generalization of the photonic Rashba effect from circular polarizations to any pair of orthogonal polarizations and apply it to thermal emission. Leveraging pointwise specification of arbitrary elliptical polarization, we implement a thermal geometric phase and leverage it to prove previous theoretical predictions that asymmetric chiral emission is possible without violating reciprocity. This general platform can be extended to other frequency regimes in efforts to compactify metasurface optics technologies without the need for external coherent sources.

Pro bono in the real World: A comprehensive review of the literature and recommendations for meaningful engagement

Background and PurposeThe APA’s Ethical Principles for Psychologists explicitly addresses and humbly encourages pro bono work: “psychologists strive to contribute a portion of their professional time for little or no compensation or personal advantage.” Yet, there is ambiguity surrounding the specifics, including frequency, time commitment, eligible services, and fair selection process to determine who will receive services. Materials and Methods: This manuscript provides the results of a comprehensive literature review on pro bono work. Initially focused on psychological assessment (e.g., neuropsychological, psychoeducational), the literature search expanded to therapy, community-based practice, and fee/paid assessment studies due to the dearth of literature. The purpose of the review to explore pro bono services in order to better understand in the future how services impact a child’s access to education, family engagement, and school relationships. Results: Two primary and secondary searches were completed. The primary search investigated the involvement of the family system when working with children and adolescents. The secondary search looked at the effectiveness of psychological, neuropsychological, and psychoeducational assessments to bolster results and provide additional recommendations and future directions. Discussion: The paper also features detailed recommendations based on the search results for how clinicians can engage meaningfully in pro bono work in their current practice along four main themes: community clinic, crisis, equity, and family support. Conclusion: Finally, future directions will address the substantial gaps in the literature on this subject.

Chaotic resonance in hybrid scale-free neural networks

It has been recently shown that weak signal response of a neuron can be amplified with the help of chaotic fluctuations at an optimal intensity. This phenomenon is referred to as chaotic resonance (CR). Here, we numerically investigate the signal detection ability of nervous system via CR using hybrid coupled scale-free networks of Hodgkin-Huxley (H-H) neurons. Firstly, we find that chaotic internal fluctuations are prone to enhance signal response of neuron population, even with a weak connectivity, more than that of single isolated cell's. We show that gap junctions can satisfy the stability against such variability and the quality of perception due to synchronizability. We also show that intense hybrid network interaction with strong chemical coupling can induce the similar degree of stability and decent quality of CR performance. Our results imply that a balanced connectivity may respond to weak signals efficiently in the presence of optimal chaotic fluctuations and exhibit frequency selectivity.

Design and Implementation of Transparent Cross‐Polarization Interference Compensation in a Wideband Dual‐Polarization Satellite Receiver

ABSTRACTIn this paper, simultaneous transmission on two orthogonal antenna polarizations in a polarization division multiplexing (PDM) fashion is studied for wideband satellite communication links using dual‐polarization satellite receivers for the purpose of doubling the data rate. In order to mitigate the cross‐polarization interference (XPI), a new digital blind and transparent XPI compensation method is proposed, coined as XPI correlation learning estimation and adaptive reduction (XPI‐CLEAR). The received signal‐to‐noise‐and‐interference ratio (SNIR) and packet‐error rate (PER) performance with this non‐data‐aided and non‐decision‐directed method is assessed in a comprehensively modelled XPI channel with effects such as depolarization due to atmospheric conditions, imperfect cross‐polarization discrimination (XPD) of the antennas at the transmitter and the receiver, memory effects due to frequency selectivity of the XPD, and differential frequency offset (DFO) between the two channels. The application of the XPI‐CLEAR method presents considerable energy efficiency improvements for all the studied XPI channel effects, and is particularly beneficial for higher order modulation. A low‐complexity hardware implementation with symbol rates up to 500 MBaud validates the XPI‐CLEAR method as a practical solution to increase the data rates of the satellite air interface and to achieve the doubling of the throughput of the satellite link by the use of PDM.

A robust medical image zero-watermarking algorithm using Collatz and Fresnelet Transforms

Zero-watermarking in medical images is an emerging field that focuses on calculating the invisible data (key) using medical imagery to ensure data integrity and authenticity without compromising diagnostic accuracy. This paper introduces a robust zero-watermarking technique leveraging the Collatz and Fresnelet Transforms. The Forward Collatz Transform (FCT) is initially applied to create a secure and encrypted embedding pattern for medical images. Subsequently, the Fresnelet Transform (FT) is employed, offering superior localization and frequency selectivity. From the fresnelet values, we extract two strongest Oriented FAST and Rotated BRIEF (ORB) points to enhance watermark robustness, resulting in a 64-bit perceptual image hash. Our approach adopts a dual-layer security strategy by combining FCT and Cyclic-Shift-Transformation (CST) methods, significantly fortifying the protection of watermark image data. The watermark can be efficiently extracted using the Inverse Collatz Transform (ICT). A comprehensive performance analysis evaluates our system under single, double, and multiple attacks on medical images. Our experiments clearly show that our system outperforms existing methods in medical image watermarking, demonstrating its resilience against various manipulations. This approach can significantly improve data security and reliability in medical imaging applications.

Linear analysis of a swirling jet with a realistic swirler model

The dynamics of an axisymmetrical swirling jet is studied via global linear stability and resolvent analyses. The modeled flow represents a combustor-like swirling jet, that is turbulent, compressible, non-parallel, and enclosed. In particular, the computational domain embeds a realistic axisymmetrical swirler model to resolve the mode conversion process. Swirl fluctuations are non-negligible on this configuration representative of a swirl burner, and match the analytical mode shapes of inertial waves of an inviscid uniform flow as obtained from global stability analysis. The stability map presents two eigenvalues driving a modal amplification. These eigenmodes couple a standing acoustic wave sustained in the mixing duct and the combustion chamber with the Kelvin-Helmholtz mechanism at the mixing duct exit and the acoustic-vorticity mode conversion process at the swirler, and act as a frequency selection criterion. Finally, the most amplified forcing from the resolvent analysis is similar to an unsteady heat source in the combustion chamber, and the identified optimal amplification mechanism is likely to be triggered in reacting flow with unsteady heat release rate.

Transformation of neural coding for vibrotactile stimuli along the ascending somatosensory pathway

In mammals, action potentials fired by rapidly adapting mechanosensitive afferents are known to reliably time lock to the cycles of a vibration. How and where along the ascending neuraxis is the peripheral afferent temporal code transformed into a rate code are currently not clear. Here, we probed the encoding of vibrotactile stimuli with electrophysiological recordings along major stages of the ascending somatosensory pathway in mice. We discovered the main transformation step was identified at the level of the thalamus, and parvalbumin-positive interneurons in thalamic reticular nucleus participate in sharpening frequency selectivity and in disrupting the precise spike timing. When frequency-specific microstimulation was applied within the brainstem, it generated frequency selectivity reminiscent of real vibration responses in the somatosensory cortex and could provide informative and robust signals for learning in behaving mice. Taken together, these findings could guide biomimetic stimulus strategies to activate specific nuclei along the ascending somatosensory pathway for neural prostheses.

High‐selectivity wideband four‐way filtering power divider with input absorptive feature

AbstractIn the paper, a high‐selectivity wideband four‐way filtering power divider with input absorptive feature is presented. It consists of two parallel‐coupled lines (CLs), two three‐coupled lines (TCLs), two open‐ended stepped branches, one absorptive branch, and two isolation resistors. The wideband filtering response is achieved by cascading the TCLs and CLs. While high selectivity is obtained by loading the open‐ended stepped branch, where two extra transmission zeros are generated. In addition, wide absorptive bandwidth with good isolations between adjacent output ports are realized by combining the absorptive branch with the isolation resistors. Equations are derived by using the two‐parity mode analysis, and main parameters are investigated in detail. For validation, a prototype was designed and fabricated. Test results show that the 3‐dB FBW can reach 87% with a 10‐dB input absorptive FBW of 200%. Besides, for the output ports with 10‐dB return loss and 10‐dB isolation, the FBWs are 94% and 91.5%, respectively. It also features high frequency selectivity and low insertion loss.

A frequency selection network for medical image segmentation

Existing medical image segmentation methods may only consider feature extraction and information processing in spatial domain, or lack the design of interaction between frequency information and spatial information, or ignore the semantic gaps between shallow and deep features, and lead to inaccurate segmentation results. Therefore, in this paper, we propose a novel frequency selection segmentation network (FSSN), which achieves more accurate lesion segmentation by fusing local spatial features and global frequency information, better design of feature interactions, and suppressing low correlation frequency components for mitigating semantic gaps. Firstly, we propose a global-local feature aggregation module (GLAM) to simultaneously capture multi-scale local features in the spatial domain and exploits global frequency information in the frequency domain, and achieves complementary fusion of local details features and global frequency information. Secondly, we propose a feature filter module (FFM) to mitigate semantic gaps when we conduct cross-level features fusion, and makes FSSN discriminatively determine which frequency information should be preserved for accurate lesion segmentation. Finally, in order to make better use of local information, especially the boundary of lesion region, we employ deformable convolution (DC) to extract pertinent features in the local range, and makes our FSSN can focus on relevant image contents better. Extensive experiments on two public benchmark datasets show that compared with representative medical image segmentation methods, our FSSN can obtain more accurate lesion segmentation results in terms of both objective evaluation indicators and subjective visual effects with fewer parameters and lower computational complexity.

Composite scattering characteristics analysis of micro-ellipsoidal periodic structure optical surface and microdefects

In order to adjust and detect micro-nano periodic structure optical surface accurately and efficiently, the problem of composite scattering between micro-ellipsoidal periodic structure optical surface and pore defects is studied use the multi-resolution time domain (MRTD) approach. A calculation model is established for the intensity distribution of composite scattering, which is modulated by the micro-ellipsoidal periodic structure optical surface and microdefects. Results are in good agreement with those obtained using CST Microwave Studio software and the finite-different time-domain (FDTD) approach, which demonstrates the effectiveness of the calculation model and method. By combining the field distribution of the micro-ellipsoidal periodic structure optical surface containing microdefects with the optical response at different wavelengths, it is necessary to study the influence of various parameters of the micro-ellipsoidal structure and microdefects on the optical system of metamaterials. The effects of the parameters such as roughness, structure of micro-ellipsoidal unit, defect sizes and buried depths on the composite scattering characteristics are analyzed numerically. The results provide technical support for the fields of functional surface design, ultrasensitive detection, scattering peak orientation and frequency selection.