Search Results (2,477)

Based on monolithic microwave integrated circuit (MMIC) technology, this paper presents the design and implementation of a low-cost, highly integrated Ka-band sixteen-channel transmit/receive (T/R) module, specifically tailored to meet the application requirements of phased array antennas in airborne and spaceborne radar systems, satellite communications, and 5G/6G millimeter-wave networks. The proposed module employs an MMIC-based single-channel dual-chip discrete architecture, optimally integrating amplitude-phase multifunction chips and transmit-receive multifunction chips in terms of both fabrication process and performance characteristics, achieving a favorable balance between high performance and high-integration density. Using low-cost, low-temperature co-fired ceramic (LTCC) substrates, full-silver conductive paste, and a nickel–palladium–gold plating process, a novel “back-to-back” thin-slice packaging technique is presented to improve integration, lower manufacturing costs, and boost long-term reliability. Furthermore, the design incorporates glass insulators and a direct array interconnection scheme, which significantly minimizes transmission losses and reduces interface dimensions. The final module measures 70.3 mm × 26.2 mm × 10.9 mm and weighs only 34 g. Experimental results demonstrate a transmit output power of at least 23 dBm, a receive gain exceeding 26 dB, and a noise figure below 3.5 dB, achieving a 22.5–58% reduction in volume per channel while maintaining competitive RF performance. To improve testing effectiveness and guarantee data consistency, an automated radio frequency (RF) test system based on Python 3.11.5 was also developed. This work provides a practical technical approach for the engineering realization of Ka-band phased array systems. Full article

Ultrasonic testing is a prevalent method for non-destructive evaluation of railway rails; however, conventional Time-of-Flight (ToF) approaches applied in practical dry-coupled inspections often rely on simplified assumptions regarding wave propagation velocity and neglect complex waveform characteristics. This paper presents a robust depth estimation framework for surface-breaking cracks that enhances sizing accuracy through effective velocity calibration and Hilbert envelope extraction. Unlike standard methods that assume the free-space speed of sound in air (343 m/s) for wave propagation within the air-filled gap of a surface-breaking crack, we propose an effective velocity model derived from in situ calibration to account for the boundary layer viscosity and thermal conduction effects within narrow crack geometries. The signal processing chain incorporates spectral analysis, band-pass filtering, and Hilbert Transform-based envelope detection to mitigate noise and resolve phase ambiguities. Experimental validation on steel specimens with controlled defects (0.2–10.0 mm) demonstrates that the proposed method achieves an exceptional linear correlation (R² ≈ 0.9976). The calibrated effective velocity was determined to be 289.3 m/s, approximately 15.6% lower than the speed of sound in air, confirming the significant influence of confinement effects. Furthermore, excitation parameters were optimized, identifying that high-voltage excitation (≥110 V) and a tuned pulse width (≈150 ns) are critical for maximizing the signal-to-noise ratio. The results confirm that combining physical model calibration with advanced signal analysis significantly reduces systematic errors, paving the way for portable, high-precision rail inspection systems. Full article

Background: Load carriage is an essential part of the occupational work of many jobs, yet there is little research on the hemodynamic responses to load carriage. It is known that front load carriage elicits larger increases in arterial stiffness than load carried on the side of the body. However, the hemodynamic forward and reflected pulse wave responses to load carriage are unknown and could relate to cardiac risk. Methods: We compared responses to 30 s front load carriage between 45 females and 23 males, with pre- and post-carry hemodynamics assessed using pulse wave analysis. Results: We found increases (p < 0.001) in arterial stiffness (24.8% females; 32.4% males), forward pulse wave (5.8 mmHg females; 5.7 mmHg males), and reflected pulse wave (6.8 mmHg females; 9.9 mmHg males). Pre- and post-carriage forward and reflected pulse waves were lower in females (p < 0.05). Compared to males, females overall had more relationships between the change in vascular measurements and other variables. We found an inverse relationship between changes in myocardial supply–demand (SEVR) and changes in forward pulse wave in females (r = −0.37, p < 0.001) but not males. Also, a direct relationship between changes in SEVR and changes in aortic DBP (r = 0.30, p = 0.04) and changes in resting DBP (r = 0.35, p = 0.02) existed in females. Conclusions: The data suggest that sex-related differences in hemodynamic responses exist. Females may experience a larger drop in estimated myocardial supply–demand balance accompanied by lower diastolic filling. Employers should be aware of these inherent cardiac risks with load carriage in their female employees. Full article

With the deepening of fifth-generation mobile communication technology (5G) commercialization and the surge in demand for intelligent connectivity of all things, the sixth-generation mobile communication technology (6G) has entered a phase of technological breakthroughs. The innovation in antenna design will determine the upper limits of 6G communication. This paper systematically reviews the research progress on antenna technology for 6G communications, focusing on operating frequency bands, antenna structure design, and materials and packaging technologies. The development of 6G communication technology drives antenna research toward higher-frequency bands, with the current research focus extending from the millimeter wave (mmWave) band to the terahertz (THz) band. Compared to the traditional mmWave band, the THz band shows significant advantages in performance indicators. At the antenna structure level, its development trend is mainly reflected in the following three aspects: size miniaturization, scale expansion and distributed deployment, and expansion of frequency bands and functions. New materials and advanced packaging have become key enabling technologies: materials with low-loss characteristics and tunable surface conductivity have become research focuses. Meanwhile, advanced packaging processes achieve miniaturization and high-performance integration of antenna systems. This review aims to provide a systematic technical reference for the research and engineering development of next-generation 6G antennas. Full article

Continuous blood pressure (BP) monitoring is essential for the prevention and management of cardiovascular diseases. Traditional cuff-based methods cause discomfort during repeated measurements, and wearable sensors require direct skin contact, limiting their applicability. Radar-based contactless BP measurement has emerged as a promising alternative. However, radar pulse wave (RPW) signals are susceptible to motion artifacts, respiratory interference, and environmental clutter, posing persistent challenges to estimation accuracy and robustness. In this paper, we propose MARU-MTL, a Mamba-enhanced multi-task learning framework for continuous BP estimation using a single millimeter-wave radar sensor. To address signal quality degradation, a Variational Autoencoder-based Signal Quality Index (VAE-SQI) mechanism is proposed to automatically screen RPW segments without manual annotation. To capture long-range temporal dependencies across cardiac cycles, we integrate a Bidirectional Mamba module into the bottleneck of a U-Net backbone, enabling linear-time sequence modeling with respect to the segment length. We also introduce a multi-task learning strategy that couples BP regression with arterial blood pressure waveform reconstruction to strengthen physiological consistency. Extensive experiments on two datasets comprising 55 subjects demonstrate that MARU-MTL achieves mean absolute errors of 3.87 mmHg and 2.93 mmHg for systolic and diastolic BP, respectively, meeting commonly used AAMI error thresholds and achieving metrics comparable to BHS Grade A. Full article

This study investigates the temporal and spatial variations in sea level anomaly (SLA) and sea surface wind in the East China Sea (ECS) from 1993 to 2021 using AVISO altimetry data and ERA5 reanalysis wind data. Empirical Orthogonal Function (EOF) and trend analyses were applied to identify dominant modes and long-term changes. Results reveal pronounced seasonal SLA variability, with lower levels in winter/spring and higher levels in summer/autumn, strongly modulated by monsoon winds. The first EOF mode of SLA accounted for 52.73% of variance, showing basin-coherent seasonal fluctuations, while the second mode (7.79%) reflected contrasts between coastal and Kuroshio-influenced regions. The ECS experienced an average sea level rise of 3.77 mm/year, exceeding 6 mm/year along the Jiangsu and Zhejiang–Fujian coasts. Sea surface wind stress variability was greatest in the northern Taiwan Strait and southwest of the Ryukyu Islands, but decreased along the Zhejiang coast. Sea level anomalies (SLAs) in the East China Sea exhibit clear multi-scale coupling with the wind field. The seasonal SLA variability in the East China Sea is jointly modulated by local Ekman forcing due to wind stress, while also being potentially linked to the Kuroshio and open-ocean Rossby waves. These findings underscore the role of wind forcing in regional sea level changes and provide insight for coastal management under climate change. Full article

Structural health monitoring (SHM) technology enables the monitoring and assessment of the condition of various materials and structures. Lamb-guided waves (LW) are widely used to detect damage in large-scale plate structures. One of the parameters used for these purposes is the time-of-flight (ToF) of ultrasonic LW signals. In the presented feasibility study, the ToF was determined based on the idea that the zero-crossings of this signal, filtered by several filters, are concentrated around the maximum of the signal envelope. This ToF detection method, unlike threshold- and peak-based methods, avoids uncertainties in signal and noise levels and does not require a signal detection threshold. Compared to the correlation method, no reference signal is required. It has been established that the curves of signal propagation times with varying distance depend on the group and phase velocities of signal propagation and have phase jumps. The proposed methodology for assessing plate inhomogeneities involves comparing signal propagation time curves with and without damage. This methodology has been verified both through theoretical modeling and experimental research. The experimental studies used a 6 mm thick steel specimen with artificial defects of various diameters (10–35 mm). The A₀ mode of Lamb waves with a central frequency of 150 kHz was excited in the steel plate. For experimentally obtained B-scans, the ToF distributions of signals along the scan trajectories were calculated. By comparing the defective and defect-free ToF curves, critical points of the experimental curves were determined, which were used to estimate the dimensions of the defects. Both in the case of theoretical modeling and in the result of experimental measurements, it was determined that the proposed methodology can be used to determine the inhomogeneities of plates. Full article

Honeycomb sandwich panels are widely used in aerospace, yet they are vulnerable to low-velocity impacts. Implementing effective localization is challenging because, unlike single-layer structures, the multi-layer energy dissipation capabilities of honeycomb core induce rapid stress wave attenuation and reverberations, degrading signal quality. This paper designs a testing platform for low-velocity impact and proposes a template matching method based on wavelet denoising and error outlier weighting. This method is based on 16 FBG sensors uniformly arranged on the panel, dividing the panel into 25 $\times$ 25 grids, with five impacts in each grid forming a template library. Similarity matching is performed by calculating the Euclidean distance between the template library and test signals, combined with wavelet denoising and outlier weighting to compute the average localization accuracy. The results show that for a honeycomb panel measuring 500 mm $\times$ 500 mm $\times$ 20 mm, the basic method yields an average localization accuracy of 21.29 mm. When error outlier weighting is applied, the accuracy improves to 12.36 mm. Finally, by combining outlier weighting with Sym5 wavelet denoising, the average error is further reduced to 8.53 mm. These results demonstrate that the proposed method mitigates the effects of signal instability in honeycomb structures, providing a robust and precise solution for aerospace SHM where traditional methods fall short. Full article

Blood pressure estimation through pulse wave analysis (PWA) aims to establish the relationship between features of pulse waveforms and blood pressure. This study is the first to investigate the connection between features of carotid artery diameter waveforms and variations in blood pressure, as well as to develop a blood pressure estimation model based on these features. A dataset was constructed from 14 subjects, with data collected across various physiological states and time points. For each subject, carotid artery diameter waveforms were measured using ultrasound, while synchronous blood pressure data were recorded with a reference device. A total of 52 morphological features were extracted from the diameter waveforms and their first and second derivatives. The influence of different models and feature combinations on blood pressure estimation was analyzed using various machine learning approaches. Ultimately, optimal models were developed for each subject to dynamic blood pressure fluctuations. On independent test data where blood pressure fluctuations exceeded 25 mmHg, the mean absolute error (MAE) of the estimates was 3.3 ± 4.1 mmHg. Even after a period of two days or more, the models remained effective, yielding a MAE of 4.2 ± 5.3 mmHg. Full article

4D millimeter-wave radar provides a promising solution for robust perception in adverse weather. Existing detectors still struggle with sparse and noisy point clouds, and maintaining real-time inference while achieving competitive accuracy remains challenging. We propose SGE-Flow, a streamlined PointPillars-based 4D radar 3D detector that embeds lightweight spatiotemporal geometric enhancements into the voxelization front-end. Velocity Displacement Compensation (VDC) leverages compensated radial velocity to align accumulated points in physical space and improve geometric consistency. Distribution-Aware Density (DAD) enables fast density feature extraction by estimating per-pillar density from simple statistical moments, which also restores vertical distribution cues lost during pillarization. To compensate for the absence of tangential velocity measurements, a Transformer-based Inter-frame Flow (IFF) module infers latent motion from frame-to-frame pillar occupancy changes. Evaluations on the View-of-Delft (VoD) dataset show that SGE-Flow achieves 53.23% 3D mean Average Precision (mAP) while running at 72 frames per second (FPS) on an NVIDIA RTX 3090. The proposed modules are plug-and-play and can also improve strong baselines such as MAFF-Net. Full article

Additive manufacturing is transforming high-frequency electronics prototyping by offering a sustainable and cost-effective alternative to traditional methods. This work addresses and demonstrates two areas: the use of 3D printing for millimeter-wave (mmWave) antennas, and chip-to-chip or chip-to-PCB interconnects. Both approaches facilitate reduced material waste. A 47 GHz series-fed microstrip patch array was printed on flexible Kapton using aerosol jet technology, showing performance comparable to etched arrays on Roger’s substrates. Crucially, the Kapton film can be peeled off after testing, allowing the reuse of expensive low-loss substrates. Therefore, this method supports rapid, low-waste prototyping. To address future chip-to-chip and chip-to-PCB mmWave interconnect limitations, XTPL’s Ultra-Precise Dispensing (UPD) was used to fabricate 3D-printed micro-interconnects. At 73 GHz, these interconnect structures achieved return loss better than 10 dB and insertion loss under 1 dB—outperforming traditional bondwires. Together, these results show 3D printing’s potential to enable sustainable, high-performance mmWave RF systems. Full article

Background: Atrial arrhythmias represent a frequent long-term complication in patients with atrial septal defects (ASDs). Interatrial block (IAB), reflecting delayed or impaired conduction across Bachmann’s bundle, has been proposed as an electrophysiological substrate predisposing to atrial arrhythmogenesis. However, evidence regarding its prevalence and clinical correlates in pediatric patients with ASD remains limited. The present study aimed to characterize interatrial conduction patterns and assess the occurrence of IAB in children with large secundum ASD undergoing percutaneous closure. Methods: Between January 2020 and March 2024, 37 consecutive pediatric patients (median age 6 years, range 5–11) with large ostium secundum ASD were included in a retrospective analysis of a prospectively maintained institutional database. Standard 12-lead electrocardiograms were recorded before and within 24 h after defect closure. P-wave morphology and duration were systematically analyzed, and IAB was classified according to the Bayés de Luna criteria. Results: The median Qp/Qs ratio was 1.69 (1.32–2.24), with a mean pulmonary artery pressure of 19 mmHg (17–22). IAB was identified in 24.3% of patients before the procedure, predominantly as first-degree IAB. Following device implantation, IAB prevalence (29.7%) and P-wave parameters remained unchanged, with no significant differences compared with baseline. No associations were observed between IAB and defect size, hemodynamic burden, or device characteristics, whereas anthropometric variables, including weight, height, and body surface area, showed a significant correlation with IAB occurrence. During a median follow-up of 199 days, no atrial arrhythmias were documented. Conclusions: In this pediatric cohort with large ASD, IAB was present in approximately one quarter of patients and appeared unrelated to anatomical or procedural factors, supporting the hypothesis of an underlying congenital conduction abnormality. Early recognition of IAB may therefore have implications for long-term arrhythmic risk stratification in this population. Full article

Frequency-Modulated Continuous-Wave (FMCW) millimeter-wave (mmWave) radars, originally developed for automotive applications, can be also explored for environmental sensing due to their compact size, low cost, and robustness under adverse environmental conditions. However, measurements obtained from commercial automotive radars are often affected by environmental noise and intrinsic self-interference caused by coupling between transmitting and receiving patch antennas, which can degrade the reliability of relative power-based range profiles. In this paper, the performance of the AWR1843BOOST FMCW mmWave radar from Texas Instruments is investigated, with particular emphasis on noise due to antenna coupling. A sub-optimal post-processing technique based on Noise Environmental Measurement (NEM) removal is proposed to remove both deterministic noise, associated with antenna coupling, and stochastic noise, related to environmental contributions. The proposed approach is validated through controlled laboratory experiments involving different targets characterized by distinct dielectric properties, including a metallic object, an absorbing object, and a target with varying degrees of wetness. The experimental results demonstrate that the NEM removal technique significantly enhances the clarity of the backscattered target’s relative power, preserving differences between target values, and improves the radar’s sensitivity to material properties and water content. Measurements accomplished at the electromagnetic and remote sensing laboratory of the Università degli Studi di Napoli Parthenope confirmed the soundness of the proposed NEM removal technique and the sensitivity of the AWR radar to the dielectric properties of targets. Full article

Traveling wave ultrasonic motors (TWUMs) are critical components in precision systems, yet their performance is susceptible to degradation under dynamic disturbances in harsh operating environments. This paper presents a monolithic U-shaped rotor designed to intrinsically achieve quasi-zero stiffness (QZS). Unlike conventional QZS systems that rely on assembling discrete positive and negative stiffness elements, the proposed design generates the target mechanical characteristic through the tailored nonlinear response of a unified U-shaped structure, thereby improving preload stability. Through exploring the critical parameters of the rotor cross-section, the finite element method (FEM) is employed to optimize the geometry configuration and characterize the mechanical performances. The simulation results show the QZS behavior demonstrating a stable force plateau of 320 ± 10 N across a 0.7 mm displacement range. A maximum von Mises stress of 788 MPa is obtained, well within the material’s safety margin, thereby ensuring the structural integrity. Experimental tests validate the effectiveness of the proposed design. This compact, monolithic U-shaped rotor provides a robust and reliable QZS solution, demonstrating significant potential for enhancing the stability of TWUMs in applications prone to harsh environments such as wide-range temperature fluctuations, thermal cycling conditions, and shock environments. Full article

This study addresses the impact-induced failure of drilling pump valves caused by uncontrolled disc–seat collisions by proposing a novel valve design incorporating a two-stage buffering mechanism. The design employs a wave spring as the primary buffer and an elastic sealing ring as the secondary buffer, effectively mitigating impact through staged energy dissipation. A nonlinear stiffness model of the wave spring, accounting for the transition between line and surface contact modes, was developed. Strong fluid–structure interaction transients were simulated using dynamic meshing and user-defined functions. A parametric study was conducted by systematically varying cylindrical spring stiffness (7.7–15 N/mm), preload (110–160 N), and wave spring type (D85 to D110). Results show that, compared to a conventional valve, the two-stage mechanism reduces impact velocity by 24.2%, accelerates opening response by 17.9%, and extends the closing phase by 0.28%. Increasing wave spring stiffness (from D85 to D110) decreases opening delay time by 98.7% and attenuates peak velocity by 44.4%. Optimized hybrid spring parameters can minimize closing delay height by 27.3%. By reducing seat erosion and suppressing vibration-induced failure, the two-stage buffering mechanism effectively extends valve service life and enhances operational reliability in high-cycle drilling operations. Full article