Search Results (951)

This paper presents a novel method for integrating multiple filters into a single board that can be reconfigured through design modifications. The primary objective is to introduce a scalable three-in-one filter, referred to as a triplexer, suitable for diverse applications. The proposed filter is well-suited to applications such as multi-band RF front ends, software-defined radios (SDRs), test instrumentation requiring selectable responses, and compact wireless sensor nodes. The manuscript develops a mathematical model for each filter, enabling adjustment of the cutoff frequency to different values. The model is then expanded to capture the interactions among the three filters and is validated in MATLAB. An experimental four-port filter sample is fabricated to validate the concept. It comprises a $2.85$ GHz low-pass filter (LPF), a $5.10$ GHz band-pass filter (BPF), and a $6.30$ GHz high-pass filter (HPF). The proposed triplexer is designed using step impedance and coupled lines, providing a systematic design approach suitable for various applications due to its adaptability and straightforward structure. The methodology includes calculations in MATLAB, full-wave EM simulation, fabrication on RT/Duroid 5880, and measurements with a four-port network analyzer. The measured results show strong agreement with both calculated and simulated results. Full article

This study introduces two compact wideband substrate-integrated waveguide (SIW) filters fabricated using thin-film technology. The wideband bandpass response is achieved by incorporating interdigital capacitor (IDC) structures into a half-mode SIW (HMSIW) transmission line. An equivalent LC circuit model is formulated to analyze the influence of IDC parameters on the generation of transmission zeros. For the first filter (BPF 1), a third-order IDC coupling configuration is employed, resulting in a 1 dB passband spanning 11 GHz to 18 GHz, a minimum insertion loss of 0.66 dB, three transmission zeros that enhance stopband performance, and a compact core dimension of $0.49{\lambda }_g\times 0.29{\lambda }_g$. For further miniaturization, a modified HMSIW transmission line incorporating a metal-insulator-metal (MIM) capacitor at the equivalent magnetic wall is proposed. This design effectively reduces the transverse dimension of the waveguide while maintaining the original cutoff frequency. Utilizing this configuration, the second bandpass filter (BPF 2) was designed and fabricated employing double-layer ceramic thin-film technology. The resulting filter exhibits a 1 dB passband spanning 10 GHz to 18 GHz, a compact footprint measuring $0.44{\lambda }_g\times 0.23{\lambda }_g$, a minimum insertion loss of 0.58 dB, and features three transmission zeros. The fabricated and measured results of both filters show good agreement with simulations. Compared with previously reported wideband SIW filters, the proposed designs demonstrate comprehensive advantages in fractional bandwidth, insertion loss, out-of-band suppression, and circuit size, providing effective filtering solutions for high-density integration of microwave and millimeter-wave RF systems. Full article

Composite materials are extensively used in the aeronautical and aerospace industries for their high strength-to-weight ratios but are vulnerable to barely visible impact damage (BVID), which can severely compromise structural integrity. Digital shearography (DS) provides a non-contact, full-field solution for subsurface inspection; however, low signal-to-noise ratios in raw phase maps often hinder precise damage identification. This study explores a post-processing methodology utilizing a band-pass filtering algorithm and temporal summation to isolate damage-related spatial frequencies. An in-house digital shearography system was used to inspect a carbon-fiber-reinforced polymer (CFRP) plate subjected to 13.5 J and 26.2 J impacts. Twelve phase maps, acquired during the thermal cooling stage, were processed using a multi-pass filters to systematically analyze different frequency ranges. Results demonstrate that summing multiple filtered phase maps significantly enhances the contrast of damage signatures compared to single phase maps or traditional unwrapping techniques. Furthermore, quantitative assessment using image quality metrics, such as the generalized contrast-to-noise ratio (gCNR), confirmed that optimal frequency selection is essential for an accurate damage delineation. This approach provides a robust framework for improving the reliability and sensitivity of non-destructive testing in composite structures. Full article

Recent advances in metasurface-based research have enabled significant reductions in the size and weight of optical devices. By employing metallic nanostructures with subwavelength dimensions, color filtering can be achieved through phenomena such as extraordinary optical transmission (EOT), which allows specific bands of visible light to pass through. However, conventional EOT-based color filters often suffer from strong side peaks outside the desired transmission band, degrading color purity and hindering accurate color reproduction. In this study, we propose an ultrathin, polarization-independent color filter based on a nanohole array that utilizes the EOT effect while effectively suppressing unwanted side peaks. To achieve this, we introduce a modified design in which additional metallic triangular edges are placed around a hole in a conventional hole array. This configuration suppresses higher-order diffraction modes and enables selective transmission at RGB wavelengths, thereby improving spectral selectivity and overall color performance. Full article

This article presents a novel compact high-Q bandpass filter (BPF) utilizing a 3-D stacked stripline configuration. T-shaped stepped impedance resonators (SIRs) are employed to achieve miniaturization. By folding the filter geometry from an inline arrangement into a U-shape along the broadside direction, both broadside and edge coupling structures are realized, enabling various cross-coupling schemes for flexible placement of transmission zeros (TZs). A comprehensive analysis of both electric and magnetic coupling structures is conducted to support the overall filter design. To validate the concept, a tenth-order general Chebyshev BPF prototype centered at 3.485 GHz with a 1 dB bandwidth of 380 MHz is designed, fabricated, and measured. The filter is constructed by vertically soldering two patterned sheet metal layers together with three stacked cavities. Despite having an electrical size of only 0.58 × 0.23 × 0.19 λ_g³, the filter exhibits a high unloaded Q-factor (Q_u) of 1200, along with up to six TZs and a spurious-free frequency range extending to 12 GHz. Measured results show an insertion loss of 0.58 dB at the center frequency and a return loss of better than 20 dB within the passband, demonstrating favorable agreement with simulations. Featuring solid electrical performance, the proposed filter is ideally suited for 5G and 5G-Advanced (5G-A) communication base stations. Full article

A brain–computer interface (BCI) enables direct communication between the brain and external devices by translating neural activity into executable control commands. Among electroencephalography (EEG)-based paradigms, steady-state visual evoked potential (SSVEP) is widely adopted due to its high signal-to-noise ratio, robustness, and minimal calibration requirements. While SSVEP-based spellers have been extensively investigated, many existing systems rely on high-channel-density EEG recordings and computationally complex processing pipelines, and are primarily designed for alphabetic input structures. In this study, we present an SSVEP-based Korean speller that integrates the Cheonjiin keyboard layout to support intuitive composition of Hangul syllables. The proposed system adopts a simple configuration, employing only five visual stimulation frequencies (6.67–12 Hz) and two occipital EEG channels (O1 and O2), with real-time frequency recognition performed using canonical correlation analysis (CCA) within a 1.5 s sliding window. EEG signals were acquired at 200 Hz using an OpenBCI Ganglion board, band-pass filtered (5–45 Hz), and processed with harmonic sinusoidal reference templates for multi-frequency classification. The proposed interface generates five control commands (up, down, left, right, and select), enabling directional cursor navigation and character confirmation on a 4 × 4 virtual Cheonjiin keyboard. Experimental validation with three healthy participants demonstrated an average classification accuracy of approximately 82% and an information transfer rate (ITR) of 31.2 bits/min. Frequency-domain analysis revealed clear spectral peaks at the stimulation frequencies and their harmonics, indicating reliable SSVEP responses. The proposed system employs a simple two-channel configuration integrated with a Korean language-specific input structure, demonstrating that reliable SSVEP-based communication can be realized without computationally intensive algorithms or high-cost EEG acquisition systems. These findings demonstrate that reliable SSVEP-based communication can be achieved using a low-channel configuration without reliance on high-cost EEG equipment. Full article

This study examined temporal scalp electroencephalography (EEG) absolute power and brief self-reported psychological state measures before and after participation in a Life Story Program (LSP) in older adults. Five older women participated in the study. For each participant, pre- and post-assessments were scheduled at approximately the same time of day and included a brief four-item questionnaire and biosignal acquisition in a controlled seated environment. EEG was recorded at 500 Hz from T5 and T6 during an eyes-closed resting condition. For EEG analysis, only non-speaking segments were used; the initial 3–5 min stabilization period was excluded, and the subsequent 10 min of data were analyzed. One participant was excluded after outlier screening, resulting in a final EEG sample of four participants. EEG preprocessing included linear detrending, 60 Hz notch filtering, 0.5–50 Hz band-pass filtering, artifact rejection, and Welch-based estimation of absolute power in the delta, theta, alpha, beta, and gamma bands. Given the small sample size, all analyses were treated as exploratory. Questionnaire responses remained generally stable across assessments. No statistically significant pre–post differences were observed after false discovery rate correction, although small reductions, particularly in the gamma band, were observed. These findings should be interpreted as preliminary observations requiring confirmation in larger controlled studies with broader multichannel EEG coverage and more robust recording configurations. Full article

The need to isolate tides during model runtime, such as for data assimilation of sea level anomaly and tidal transports and for internal wave drag parameterization, has motivated the adaptation or development of three online filters for tidal isolation: a recursive climatological filter (RCF), an online harmonic analysis (OHA) and a streaming band-pass filter (SBP). Here, we evaluated these approaches and showed that, although derived from different mathematical frameworks, all three show identical frequency responses, characterized by passbands of equal magnitude centered on target frequencies and zero phase shift. In practice, however, OHA is more costly, while SBP suffers from discretization errors. Both RCF and OHA also allow the extraction of time-varying harmonic constants, allowing additional applications. Given its low cost and being free from discretization error, we further assessed RCF for de-tiding modelled coastal sea levels. We found that long-term nodal modulations become increasingly influential as the passband narrows and adaptation time increases, leading to degraded filter skill. This issue is mitigated by using constituent-dependent passbands accounting for nodal effects. Overall, the RCF effectively and efficiently isolates coastal tides and storm surges, with extreme peak surge differences of 2.0 ± 1.2% relative to those obtained from conventional harmonic analysis. Full article

This study introduces an automated computational tool to evaluate the phase velocity of the highly dispersive A₀ mode using only two signals measured along the wave propagation path. The algorithm combines the zero-crossing technique with automated spectral decomposition, utilizing a bank of bandpass filters with adaptive bandwidths. Validated through theoretical and experimental analysis of an aluminium plate near 300 kHz, the results demonstrate that using a two-signal set and variable filter widths significantly improves accuracy and extends the measurable frequency range of the dispersion curve. Experimental results demonstrate that by applying various filter widths, the phase velocity dispersion curve segment can be reconstructed over a frequency range exceeding 65% of the signal’s spectral width at the −40 dB level. The reconstruction yielded an average relative error of 0.8% ± 1.2%, while the best-case scenario showed an error of just 0.3% ± 0.4%. Implementing automated filter parameter selection on a signal pair offers a time-efficient alternative to traditional spatial scanning, significantly simplifying data collection while reducing labour and time requirements. Full article

This paper proposes a millimeter-wave miniature on-chip bandpass filter (BPF) implemented using a 0.18 μm CMOS process. To address the issues of insufficient coupling capability, limited control of transmission zeros, and excessive chip area in traditional on-chip filters, a folded cross-interdigital coupling structure is proposed to enhance coupling efficiency and reduce size. The design incorporates metal–insulator–metal (MIM) capacitors to increase the coupling capacitance between resonators without increasing the area, and utilizes a defected ground structure (DGS) to modify the current distribution at the ground plane, generating additional transmission zeros to improve selectivity. An LC equivalent circuit model was established and verified through full-wave electromagnetic simulation, and the design was validated through chip fabrication and on-wafer measurements. The measurement results show an insertion loss of 3.36 dB and a fractional bandwidth of 49.1% at 32 GHz, with two transmission zeros. The core dimensions are 0.25 mm × 0.18 mm. This design achieves a good balance between miniaturization, selectivity, and insertion loss, making it suitable for millimeter-wave SoC applications. Full article

This work presents a portable polarimetric multispectral imaging (PMSI) system operating in the visible to shortwave infrared range (VNIR–SWIR: 400–1700 nm) and its application to target detection, discrimination from aquatic backgrounds, and polymer identification. The instrument integrates two synchronized cameras with motorized bandpass filters and piezoelectric polarization control, enabling the acquisition of 48 wavelength–polarization measurements per capture. This configuration allows the extraction of both intensity-based and polarimetric features, including the degree of linear polarization (DoLP). A complete radiometric and polarimetric calibration framework is implemented, encompassing system response characterization, polarization-dependent gain correction, and reflectance normalization under variable illumination. Experiments conducted on a representative set of 16 polymer materials show that polarimetric information consistently improves class separability compared to intensity-only features, with a mean gain of 6.9 (95% CI: 6.35–8.47). Although the correlation between intensity- and DoLP-based separability is moderate (r = 0.44), the results indicate complementary identification capability. Material recoverability was further evaluated using spectral unmixing techniques (VCA, N-FINDR, and PPI), with VCA offering the best accuracy–complexity trade-off on the calibrated Stokes reflectance dataset. Despite these gains, identification among chemically similar polyethylene variants remains challenging due to limited spectral and polarimetric contrast. An underwater detectability study under natural illumination reveals strong wavelength-dependent constraints: SWIR penetration is limited to 4 cm, whereas VNIR bands (430–550 nm) preserve detectability up to 20 cm, with DoLP enhancing edge visibility. These results motivate future validation in more complex aquatic conditions and with increased spectral dimensionality. Full article

We aim to elucidate the sedimentary cyclicity of the Middle Jurassic Bath–Bajocian Formation in the northern S Oilfield of the West Siberian Basin, address the lack of high-resolution Milankovitch cycle research in this region, and support hydrocarbon exploration and development. This study employs the gamma-ray (GR) logging data of Well 79 as the primary dataset. Using Acycle V2.8 software implemented on the MATLAB 2020b platform, we conducted a systematic astrochronological analysis. After improving data quality through preprocessing procedures—including outlier removal, linear interpolation, and detrending—we identified significant cyclic signals via spectral analysis. These cyclicities were subsequently validated using multitaper spectral analysis (MTM), sliding spectral analysis, COCO correlation testing, and wavelet analysis. Band-pass filtering was then applied to facilitate sequence subdivision and sedimentation rate estimation. The results reveal well-preserved Milankovitch cyclicity in the Bath–Bajocian Formation of Well 79. The observed cycle thicknesses corresponding to the 405 kyr long eccentricity, 100 kyr short eccentricity, 41 kyr obliquity, and 20 kyr precession are 34.57 m, 8.26 m, 3.44 m, and 1.73 m, respectively, with thickness ratios deviating by less than 5% from the theoretical 20:5:2:1 proportion. Sliding spectral analysis indicates an alternating pattern of increasing and decreasing sedimentation rates. Based on the identified orbital signals, 12 fourth-order sequences and 52 fifth-order cycles were recognized. Sedimentation rates among the three wells range from 6.49 to 12.08 cm/kyr, averaging 9.29 cm/kyr, and exhibit a decreasing trend from west to east. These findings provide a robust astrostratigraphic framework for refined stratigraphic division and reservoir prediction in the study area. Full article

Objective: This prospective study investigated the use of H-scan ultrasound (US) imaging as a novel component of a multiparametric radiomic analysis framework for characterizing human breast cancer response to neoadjuvant chemotherapy (NAC) before and early after treatment initiation. Methods: Thirty breast cancer patients scheduled for NAC were scanned using a clinical US system (Logiq E9, GE HealthCare) equipped with a 9L-D linear array transducer. Radiofrequency (RF) data was obtained at baseline (pre-NAC) and after 10% and 30% of the complete dose of chemotherapy. The RF data was analyzed by a bank of 256 frequency-shifted bandpass filters to form H-scan US frequency images. Grayscale texture features were extracted from both B-scan and H-scan US images. In addition, US attenuation coefficient and speckle statistics based on the Nakagami and Burr distributions were estimated from the RF data. Data classification of tumor and peri-tumoral regions was performed using a novel three-dimensional (3D) score map based on support vector machine (SVM) modeling. Unlike conventional classifiers that report only a single prediction score, a 3D score map provides a visual representation of the classifier decision space, enabling interpretation of class separation and treatment-induced shifts in multiparametric US measurements. Results: The dataset was split into 10 disjoint partitions (90% training, 10% testing) to compute area under the receiver operating characteristic curve (AUC), sensitivity, specificity, and accuracy measures. Actual patient response to NAC was assessed at surgery and categorized as either pathologic complete response (pCR) or non-pCR. Multiparametric US and data classification results at pre-NAC found AUC values of 0.78 after using only tumor information (p < 0.01), which increased to 0.81 with inclusion of peri-tumoral information (p < 0.01). Significant differences in multiparametric US measures from both cancer response types was found after integration of patient data collected at 10% completion of the NAC regimen (i.e., first NAC cycle), yielding an improved AUC of 0.86 (p < 0.001). Conclusions: Multiparametric US imaging with radiomic features from both the tumor and peri-tumoral regions is a promising noninvasive approach for monitoring early breast cancer response to NAC. Full article

Graph Neural Networks (GNNs) have emerged as the standard for learning representations from graph-structured data. While traditional architectures relying on message-passing mechanisms excel in homophilic settings, they essentially function as fixed low-pass filters. However, this smoothing operation limits their ability to generalize to heterophilic graphs, where connected nodes often exhibit dissimilar labels and high-frequency signals are crucial for discrimination. Furthermore, existing Mixture-of-Experts (MoE) methods for graphs often suffer from local-view routing, failing to capture global structural context during expert selection. To address these challenges, this paper proposes SS-AdaMoE, a novel Spatio-Spectral Adaptive Mixture of Experts framework designed for robust node classification across diverse graph patterns. Specifically, a Dual-Domain Expert System is constructed, integrating heterogeneous spatial aggregators with learnable spectral filters based on Bernstein polynomials. This allows the model to adaptively capture arbitrary frequency responses—including high-pass and band-pass signals—which are overlooked by standard GNNs. To resolve the locality bias, a Hierarchical Global-Prior Gating Network augmented by a Linear Graph Transformer is introduced, ensuring that expert selection is guided by both local node features and global topological awareness. Extensive experiments are conducted on five benchmark datasets spanning both homophilic and heterophilic networks. The results demonstrate that SS-AdaMoE consistently outperforms baselines, achieving accuracy improvements of up to 2.65% on Chameleon and 1.41% on Roman-empire over the strongest MoE baseline, while surpassing traditional GCN architectures by margins exceeding 28% on heterophilic datasets such as Texas. These findings validate that the synergy of learnable spectral priors and global gating effectively bridges the gap between spatial aggregation and spectral filtering. Full article

This paper presents an ultra-miniaturized and high-quality factor embedded loaded coaxial substrate integrated waveguide (ELCSIW) filter. Integrating a substrate-integrated coaxial resonator with a capacitively loaded air cavity achieves a 99% reduction in size compared to a conventional SIW cavity. Incorporating an air gap in the capacitive loading structure significantly enhances the resonator’s quality factor. A comprehensive analysis of the miniaturization factor and quality factor in relation to cavity structure dimensions is performed. Guidelines for fabricating the highly loaded cavity are presented. To demonstrate the benefits of this technique, a two-pole band-pass filter with a 6.3% bandwidth at 1.1 GHz is designed, fabricated, and measured. The overall footprint of the filter is 10.5 mm × 20.5 mm, which is comparable to 0.07 ${\lambda }_g$× 0.14 ${\lambda }_g$. The measured insertion loss is 0.54 dB, and the upper band is spurious-free up to 7 times the resonant frequency. The exceptional performance and compactness of the loaded coaxial substrate integrated waveguide cavities highlight their immense potential for compact advanced wireless systems. Full article