Frequency Selectivity Research Articles

Active Regulation of Elastic Waves in a Type of Two-Dimensional Periodic Structures With Piezoelectric Springs

Abstract Wave propagations exhibit direction and frequency selectivity in two-dimensional (2D) periodic structures, which provides possibilities to regulate wave dispersion and bandgap properties. Most of current researches focus on regulations of 1D waves, and there are few works about active regulations of 2D waves, especially in the structures with strong nonlinearities that have remarkable influences on dispersions. In this work, two types of 2D periodic nonlinear lattice structures with piezoelectric springs, which include a monatomic and a diatomic structure, are designed to implement controllable dispersion and propagation direction of 2D waves. Considering the strong nonlinearities caused by the cubic spring, dynamic models of the wave propagations in the two kinds of periodic structures are established, and an improved incremental harmonic balance (IHB) method is developed to implement efficient and accurate calculations of the 2D wave propagation. Influences of active and structural parameters on dispersion and bandgap properties are comprehensively studied, and the regulation ability of the piezoelectric springs is demonstrated where the proportional voltage constant is the active control parameter with particle displacements as the feedback. Results also show that a piezoelectric modulated bandgap and a critical wave vector region are created by positive and negative proportional constants, respectively, which indicate that the structures can be used to filter a wide range of low-frequency long-wavelength noises and waves at particular directions. The properties predicted by the improved IHB method are verified by numerical experiments.

Frequency Selection in a MEMS Flexural Beam Resonator by Electrostatic Actuation

Frequency Selection in a MEMS Flexural Beam Resonator by Electrostatic Actuation

Image Restoration via Frequency Selection.

Image restoration aims to reconstruct the latent sharp image from its corrupted counterpart. Besides dealing with this long-standing task in the spatial domain, a few approaches seek solutions in the frequency domain by considering the large discrepancy between spectra of sharp/degraded image pairs. However, these algorithms commonly utilize transformation tools, e.g., wavelet transform, to split features into several frequency parts, which is not flexible enough to select the most informative frequency component to recover. In this paper, we exploit a multi-branch and content-aware module to decompose features into separate frequency subbands dynamically and locally, and then accentuate the useful ones via channel-wise attention weights. In addition, to handle large-scale degradation blurs, we propose an extremely simple decoupling and modulation module to enlarge the receptive field via global and window-based average pooling. Furthermore, we merge the paradigm of multi-stage networks into a single U-shaped network to pursue multi-scale receptive fields and improve efficiency. Finally, integrating the above designs into a convolutional backbone, the proposed Frequency Selection Network (FSNet) performs favorably against state-of-the-art algorithms on 20 different benchmark datasets for 6 representative image restoration tasks, including single-image defocus deblurring, image dehazing, image motion deblurring, image desnowing, image deraining, and image denoising.

Ultrabroadband vernier cascaded microring filters based on dispersive Si3N4 waveguides

A viable candidate for use in silicon photonics and microwave photonics is the hybrid external cavity laser (ECL) chip, which offers a high extinction ratio, ultrabroadband mode-hopping-free tuning range, and small linewidth. It requires a photonic filter device with an ultrabroadband operating bandwidth and adjustable frequency selection capability. The Vernier cascaded microring filter is a prevailing filter technique that usually ignores chromatic dispersion and will result in noticeable frequency variations, particularly over a large frequency range. Based on dispersive Si3N4 waveguides, we develop ultrabroadband Vernier cascaded microring filters and examine the impact of chromatic dispersion. For the same waveguide geometry, the filter’s effective free spectral range (FSR) varies by more than 400 GHz with and without the dispersion. Furthermore, these Vernier filters, which are made of anomalous and normal dispersive waveguides respectively, exhibit mode hopping at the opposite frequency side. It leads to a sudden mode number leap and, consequently, a diversified dispersion condition for the convoluted filtering frequency. We show that this phenomenon is caused by the interplay between half of the FSR difference, and the accumulated frequency difference caused by the chromatic dispersion. Finally, the use of thermal-optical tuning enables accurate frequency tuning. Our findings offer a valuable resource for the engineering of hybrid ECLs at the chip scale.

Broadband circularly polarized filtering patch antenna based on metasurface

AbstractIn this paper, a single‐fed broadband circularly polarized (CP) filtering patch antenna based on metasurface is proposed. It consists of a corner‐truncated square patch, a nonuniform metasurface, and a U‐shaped strip. By placing the metasurface above the driven patch antenna, a radiation null is realized at the upper band, and an additional axial ratio (AR) minimum is simultaneously generated to enhance the CP bandwidth. Besides, two more radiation nulls are achieved at each side of the band edges by introducing a U‐shaped strip underneath the patch and embedding a shorting pin into the patch, which further improves the frequency selectivity and suppresses the radiation level. Measured results show that the designed antenna has a wide impedance bandwidth of 19.7% (4.8–5.85 GHz), a CP bandwidth of 19.9% (4.75–5.8 GHz), and an in‐band average gain of 7 dBic with suppression level of more than 18 dB at out of band.

2.09 μm single-frequency all-polarization-maintaining Ho-doped fiber laser based on dynamic Bragg grating frequency selection

We demonstrated a 2.09 μm single-frequency all-polarization-maintaining (all-PM) Ho-doped fiber (HDF) laser pumped by a 1940 nm Tm-doped fiber (TDF) laser. The oscillator employed a ring cavity scheme to enhance the net gain at the wavelength, with two circulators utilized to guarantee unidirectional laser operation and eliminate the spatial hole burning (SHB) effect in the gain fiber. An unpumped HDF was used as a fiber saturable absorber (FSA) to construct a powerful dynamic Bragg grating (DBG) for frequency selection. By optimizing the output coupling ratio, FSA length and FBG temperature, a maximum single-frequency output power of 57.9 mW was obtained with a center wavelength of 2089.73 nm. Furthermore, we recorded and discussed the rapid switching of longitudinal mode states through FBG temperature tuning, as well as the optical bistability of longitudinal modes induced by saturable absorption in the oscillator. Finally, a power level of 1 W with a polarization extinction ratio of 17 dB was successfully achieved by a first-stage HDF amplifier.

Microwave absorption properties of flexible fabric coating containing Ni decorated carbon fiber with frequency selection surface incorporation

Reasonable application of double-loss absorber is one of the effective ways to improve the absorption performance of materials. In this study, Nickel (Ni) plated carbon fiber was successfully prepared by electroless plating, and Ni particles with different crystal forms were obtained by high temperature heat treatment. In addition, the modified magnetic carbon fiber is mixed with strong magnetic FeSiAl powders to improve its electromagnetic properties to obtain excellent absorbing performance. The structural characterization and analysis of the composite powders showed that the nickel particles were successfully attached to the carbon fiber surface. Further exploration of the Ni plated carbon fiber after heat treatment, the composite powders had the best absorption performance, and the minimum reflection loss value could reach −19.11 dB. Combined with the periodic frequency selection surface (FSS), the minimum reflection loss and effective bandwidth are further improved, which are −51.76 dB and the whole X band frequency range. This work helps to developing the flexible fabric coating with strong absorbility and thin thickness.

Estimation of Cochlear Frequency Selectivity Using a Convolution Model of Forward-Masked Compound Action Potentials.

Frequency selectivity is a fundamental property of the peripheral auditory system; however, the invasiveness of auditory nerve (AN) experiments limits its study in the human ear. Compound action potentials (CAPs) associated with forward masking have been suggested as an alternative to assess cochlear frequency selectivity. Previous methods relied on an empirical comparison of AN and CAP tuning curves in animal models, arguably not taking full advantage of the information contained in forward-masked CAP waveforms. To improve the estimation of cochlear frequency selectivity based on the CAP, we introduce a convolution model to fit forward-masked CAP waveforms. The model generates masking patterns that, when convolved with a unitary response, can predict the masking of the CAP waveform induced by Gaussian noise maskers. Model parameters, including those characterizing frequency selectivity, are fine-tuned by minimizing waveform prediction errors across numerous masking conditions, yielding robust estimates. The method was applied to click-evoked CAPs at the round window of anesthetized chinchillas using notched-noise maskers with various notch widths and attenuations. The estimated quality factor Q10 as a function of center frequency is shown to closely match the average quality factor obtained from AN fiber tuning curves, without the need for an empirical correction factor. This study establishes a moderately invasive method for estimating cochlear frequency selectivity with potential applicability to other animal species or humans. Beyond the estimation of frequency selectivity, the proposed model proved to be remarkably accurate in fitting forward-masked CAP responses and could be extended to study more complex aspects of cochlear signal processing (e.g., compressive nonlinearities).

Frequency selectivity in monkey auditory nerve studied with suprathreshold multicomponent stimuli

Data from non-human primates can help extend observations from non-primate species to humans. Here we report measurements on the auditory nerve of macaque monkeys in the context of a controversial topic important to human hearing. A range of techniques have been used to examine the claim, which is not generally accepted, that human frequency tuning is sharper than traditionally thought, and sharper than in commonly used animal models. Data from single auditory-nerve fibers occupy a pivotal position to examine this claim, but are not available for humans. A previous study reported sharper tuning in auditory-nerve fibers of macaque relative to the cat. A limitation of these and other single-fiber data is that frequency selectivity was measured with tonal threshold-tuning curves, which do not directly assess spectral filtering and whose shape is sharpened by cochlear nonlinearity. Our aim was to measure spectral filtering with wideband suprathreshold stimuli in the macaque auditory nerve. We obtained responses of single nerve fibers of anesthetized macaque monkeys and cats to a suprathreshold, wideband, multicomponent stimulus designed to allow characterization of spectral filtering at any cochlear locus. Quantitatively the differences between the two species are smaller than in previous studies, but consistent with these studies the filters obtained show a trend of sharper tuning in macaque, relative to the cat, for fibers in the basal half of the cochlea. We also examined differences in group delay measured on the phase data near the characteristic frequency versus in the low-frequency tail. The phase data are consistent with the interpretation of sharper frequency tuning in monkey in the basal half of the cochlea. We conclude that use of suprathreshold, wide-band stimuli supports the interpretation of sharper frequency selectivity in macaque nerve fibers relative to the cat, although the difference is less marked than apparent from the assessment with tonal threshold-based data.

Design nano cluster high Q-factor perfect plasmonic absorber for bacteria detection in the optical range

Plasmonic nanostructures enable strong light absorption at the nanometer scale, making them highly attractive for a variety of applications including sensing, imaging, and spectroscopy. In this work, we propose and simulate a dual-band plasmonic absorber based on a Pentamer and split ring resonator (SRR) hybrid structure. The absorber operates at terahertz frequencies of 209 and 229 THz, corresponding to free-space wavelengths of 1310 nm and 1430 nm. At the lower frequency band, the absorber provides perfect absorption up to 100 %, while at the higher band, the absorption is 95 %. The high absorption selectivity at the two target bands is enabled by the hybrid heptamer-SRR design. The central Pentamer consists of a central nanodisk surrounded by four peripheral nanodisks with precise dimensions and spacing. This Pentamer provides a dual-band response tuned to the desired frequencies. To further enhance the quality factor and absorption, the Pentamer is encircled by an SRR designed to boost the Q-factor. At 229 THz, the SRR pushes the quality factor to around 635, significantly higher than typical plasmonic absorbers. The final optimized design enables strong absorption together with high Q-factor and frequency selectivity. It exhibits sensitivity around 450 nm/RIU and a Figure of Merit of 227 RIU−1. The full-wave simulation is used for designing the absorber in CST Microwave Studio to optimize the dimensions for maximum dual-band absorption for biosensing applications. This absorber can be realistically fabricated for terahertz sensing applications such as detecting bacteria as studied.

The impact of local pinning sites in magnetic tunnel junctions with non-homogeneous free layers

Pinning at local defects is a significant road block for the successful implementation of technological paradigms which rely on the dynamic properties of non-trivial magnetic textures. Here, a comprehensive study of the influence of local pinning sites for non-homogeneous magnetic layers integrated as the free layer of a magnetic tunnel junction is presented, both experimentally and with corresponding micromagnetic simulations. The pinning sites are found to be extremely detrimental to the frequency controllability of the devices, a key requirement for their use as synapses in a frequency multiplexed artificial neural networks. In addition to describing the impact of the local pinning sites in the more conventional NiFe, a vortex-based magnetic tunnel junction with an amorphous free layer is presented which shows significantly improved frequency selectivity, marking a clear direction for the design of future low power devices.

Frequency selection rule for the HDHF Lissajous scanning imaging with a low-voltage one axis actuated PZT scanner based on an asymmetric fiber cantilever.

Lissajous micro scanners are very attractive in compact laser scanning applications for biomedical endoscopic imaging, such as confocal microscopy, endomicroscopy or optical coherence tomography. The scanning frequencies have a very important effect on the quality of the resulting Lissajous scanning imaging. In this paper, we propose a frequency selection rule for high definition and high frame-rate (HDHF) Lissajous scanning imaging, by deriving the relationship among the scanning field of view (FOV), actuation frequencies and pixel size based on the characteristics of the scanning trajectory. The minimum sampling rate based on the proposed frequency selection rule is further discussed. We report a lead zirconate titanate piezoelectric ceramic (PZT) based Lissajous fiber scanner to achieve HDHF Lissajous scanning imaging. Based on the frequency selection rule, different frequency combinations are calculated, under which the Lissajous fiber scanner can work at the frame rate (FR) of 10 Hz, 20 Hz, 40 Hz and 52 Hz. The trajectory evolution of the Lissajous scanning at the frame rate of 10 Hz has been obtained to verify the applicability of the proposed rule. The measured resolution of the scanner is 50.8 lp/mm at the unit optical magnification, and the measured FOV at the FR of 10 Hz and 40 Hz are 1.620 mm ×1.095 mm and 0.405 mm ×0.27 mm, respectively. HDHF Lissajous scanning images of the customized spatial varying binary pattern are obtained and reconstructed at the FR of 10 Hz and 40 Hz, demonstrating the practicability of the frequency selection rule.

Frequency Selectivity of the Auditory System in Females with Anemia: An Indian Scenario

Frequency Selectivity of the Auditory System in Females with Anemia: An Indian Scenario

Vibration-based monitoring of agro-industrial machinery using a k-Nearest Neighbors (kNN) classifier with a Harmony Search (HS) frequency selector algorithm

Monitoring the status of rotating components is important in modern machinery. The goal of this study is to evaluate the feasibility of using a k-Nearest Neighbors (kNN) classifier combined with a Harmony Search (HS) algorithm, to detect the operational status of rotating components within agricultural machines. Vibration data, the source data, were acquired from four accelerometers located along the chassis of a harvester. Five operational statuses of three rotating components of the harvester were studied: engine (low/maximum speed), thresher, and chopper (on/off and balanced/unbalanced). The methodology includes vibration signal acquisition, data preprocessing, smoothing, preselection of frequencies, Brute Force (BF) and Harmony Search frequency selection, and classification with kNN. The input frequencies for the classifier were chosen with either BF search or HS. The main results of the study were: i) the preselection of frequencies reduced the training time between 92.2% and 95.6%; ii) the smoothing stage improved accuracy; iii) HS reduced the training time between 82% and 90% in comparison with BF, reaching accuracies of nearly 100% in the five operational statuses with only 2 input frequencies; iv) similar levels of accuracy were obtained when using data from the accelerometers at different locations. The results suggested that it was feasible to predict the operational status of rotating components of agricultural machines using a kNN classifier with the combination of preselection, smoothing, and the HS algorithm. This feasibility was achieved both in terms of accuracy and computational burden, building upon previously proposed methods.

Effect of Earthing-Up Frequency on Growth and Yield of Anchote (Coccinia abyssinica) Varieties at Gimbi District, Western Ethiopia

Anchote (Coccinia abyssinica (Lam.) Cogn) is a tuberous root crop native to Ethiopia. It is a good source of protein, carbohydrates, calcium, and iron. However, little attention has been given to the improvement of genetic and agronomic practices such as selection of variety, staking, weeding, fertilizer application, and earthing-up frequency. Thus, the attainable yield is below the potential. The experiment was arranged in a 3 × 5 factorial arranged in a randomized complete block design (RCBD) with three replications with the objective of determining the effect of earthing-up frequency on the growth and yield of anchote varieties. The interaction effect of earthing-up frequencies and varieties significantly affected anchote leaf number plant−1, shoot dry weight plant−1, unmarketable tuber weight ha−1, vine diameter, shoot fresh weight plant−1, tuber fresh weight plant−1, marketable tuber weight ha−1, and total tuber yield ha−1. Total tuber yield ha−1 was perfectly correlated with tuber fresh weight plant−1 (r = 1), and all parameters were significantly correlated with tuber dry matter plant−1, and tuber dry matter plant−1 was positively and significantly correlated with total tuber yield ha−1 (r = 0.46). Consequently, the highest total tuber yield was observed from earthing-up four times (26.94 t ha−1) and three times (26.88 t ha−1) with Desta 01, while the lowest was observed from the control with Acc405 (15.11). The highest economical tuber yield was obtained from three times earthing-up frequency (26.878 t ha−1, 25.50 t ha−1, and 23.92 t ha−1 for Desta 01, Acc405, and Acc173), and the lowest was observed from the control (22.83 t ha−1, 15.11 t ha−1, and 21.11 t ha−1 for Desta 01, Acc405, and Acc173), respectively. Therefore, for the study area, it is better to apply three times earthing-up frequencies (35 days, 49 days, and 63 days from planting date for once, twice, and three times earthing-up, respectively) with Desta 01 variety followed by Acc405. Since the experiment was conducted using irrigation, it is suggested to be repeated under rainfed conditions to draw a definite conclusion.

Fully Reconfigurable Photonic Filter for Flexible Payloads

Reconfigurable photonic filters represent cutting-edge technology that enhances the capabilities of space payloads. These advanced devices harness the unique properties of light to deliver superior performance in signal processing, filtering, and frequency selection. They offer broad filtering capabilities, allowing for the selection of specific frequency ranges while significantly reducing Size, Weight, and Power (SWaP). In scenarios where satellite communication channels are crowded with various signals sharing the same bandwidth, reconfigurable photonic filters enable efficient spectrum management and interference mitigation, ensuring reliable signal transmission. Furthermore, reconfigurable photonic filters demonstrate their ability to adapt to the dynamic space environment, withstanding extreme temperatures, radiation exposure, and mechanical stress while maintaining stable and reliable performance. Leveraging the inherent speed of light, these filters enable high-speed signal processing operations, paving the way to various space payload applications, such as agile frequency channelization. This capability allows for the simultaneous processing and analysis of different frequency bands. In this theoretical study, we introduce a fully reconfigurable filter comprising two decoupled ring resonators, each with the same radius. Each resonator can be independently thermally tuned to achieve reconfigurability in both central frequency and bandwidth. The precise reconfiguration of both central frequency and bandwidth is achieved by using the thermo-optic effect along the whole ring resonator path. A stopband rejection of 45 dB, with a reconfigurable bandwidth and central frequency of 20 MHz and 180 MHz, respectively, has been numerically achieved, with a maximum electrical power of 11.50 mW and a reconfiguration time of 9.20 µs, by using the scattering matrix approach, where the elements have been calculated through Finite Element Method-based and Beam Propagation Method-based simulations. This performance makes the proposed device suitable as key building block of RF optical filters, useful in the next-generation telecommunication payload domain.

A validation of an entropy-based artificial intelligence for ultrasound data in breast tumors

BackgroundThe application of artificial intelligence (AI) in the ultrasound (US) diagnosis of breast cancer (BCa) is increasingly prevalent. However, the impact of US-probe frequencies on the diagnostic efficacy of AI models has not been clearly established.ObjectivesTo explore the impact of using US-video of variable frequencies on the diagnostic efficacy of AI in breast US screening.MethodsThis study utilized different frequency US-probes (L14: frequency range: 3.0-14.0 MHz, central frequency 9 MHz, L9: frequency range: 2.5-9.0 MHz, central frequency 6.5 MHz and L13: frequency range: 3.6-13.5 MHz, central frequency 8 MHz, L7: frequency range: 3-7 MHz, central frequency 4.0 MHz, linear arrays) to collect breast-video and applied an entropy-based deep learning approach for evaluation. We analyzed the average two-dimensional image entropy (2-DIE) of these videos and the performance of AI models in processing videos from these different frequencies to assess how probe frequency affects AI diagnostic performance.ResultsThe study found that in testing set 1, L9 was higher than L14 in average 2-DIE; in testing set 2, L13 was higher in average 2-DIE than L7. The diagnostic efficacy of US-data, utilized in AI model analysis, varied across different frequencies (AUC: L9 > L14: 0.849 vs. 0.784; L13 > L7: 0.920 vs. 0.887).ConclusionThis study indicate that US-data acquired using probes with varying frequencies exhibit diverse average 2-DIE values, and datasets characterized by higher average 2-DIE demonstrate enhanced diagnostic outcomes in AI-driven BCa diagnosis. Unlike other studies, our research emphasizes the importance of US-probe frequency selection on AI model diagnostic performance, rather than focusing solely on the AI algorithms themselves. These insights offer a new perspective for early BCa screening and diagnosis and are of significant for future choices of US equipment and optimization of AI algorithms.

An mmWave dual-band integrated substrate gap waveguide single cavity filter with frequency selectivity

An mmWave dual-band integrated substrate gap waveguide single cavity filter with frequency selectivity

A Three-Dimensional Incident Angle-Insensitive Circular Polarization Frequency Selective Slab With High Frequency Selectivity

A Three-Dimensional Incident Angle-Insensitive Circular Polarization Frequency Selective Slab With High Frequency Selectivity

Physiological sensing system integrated with vibration sensor and frequency gel dampers inspired by spider.

Recent advances in bioelectronics in mechanical and electrophysiological signal detection are remarkable, but there are still limitations because they are inevitably affected by environmental noise and motion artifacts. Thus, we develop a gel damper-integrated crack sensor inspired by the vibration response of the viscoelastic cuticular pad and slit organs in a spider. Benefitting from the specific crack structure design, the sensor possesses excellent sensing behaviors, including a low detection limit (0.05% strain), ultrafast response ability (3.4 ms) and superior durability (>300 000 cycles). Such typical low-amplitude fast response properties allow the ability to accurately perceive vibration frequency and waveform. In addition, the gel damper exhibits frequency-dependent dynamic mechanical behavior that results in improved stability and reliability of signal acquisition by providing shock resistance and isolating external factors. They effectively attenuate external motion artifacts and low-frequency mechanical noise, resulting in cleaner and more reliable signal acquisition. When the gel damper is combined with the crack-based vibration sensor, the integrated sensor exhibits superior anti-interference capability and frequency selectivity, demonstrating its effectiveness in extracting genuine vocal vibration signals from raw voice recordings. The integration of damping materials with sensors offers an efficient approach to improving signal acquisition and signal quality in various applications.