Search Results (137)

This paper presents a new type of ultrasonic gyroscopic sensor based on a solid-state standing-wave vibrator, which is promising for shock-resistant applications. A theoretical model of the proposed design, which is a layered structure, and the numerical simulation of its frequency response using the developed software are presented. A test sample of the novel sensing element was made and experimental studies of its frequency response were conducted. The results showed a high correlation between the resonant frequencies both for the real sample research and numerical modeling; thus, the validity of the theoretical model was confirmed. The laboratory investigation of the developed sensing element on a test bench under rotating conditions was carried out and a shift in the standing-wave amplitude proportional to the angular velocity of rotation was revealed; thus, an informative signal for this type of gyroscopic sensor was found. It is shown that the amplitude of the output signal of the new sensor on standing waves compares favorably with the signal levels reported for similar traveling-wave solutions in previous studies. The optimization strategies for the new sensor’s design and operating mode to increase signal to noise ratio are also identified. Thus, the potential of using the developed solid-state standing-wave vibrator as a shock-resistant ultrasonic gyroscopic sensor is supported. Full article

This paper proposes a non-overlapping planar cross-arranged ultra-wideband shared-aperture base station antenna array targeting the 2 to 6 GHz application bandwidth. The low-frequency module (double-layer parasitic coupling) and the high-frequency module (chamfered slotted patch) are independently designed, and metal baffles are introduced around the antenna elements to reshape the boundary conditions and physically block the electromagnetic coupling paths. Both simulation and experimental results demonstrate that the fabricated prototype successfully exceeds the targeted 2–6 GHz spectrum, achieving an actual continuous coverage from 1.84 to 6.3 GHz. Specifically, the antenna achieves a gain higher than 5.9 dBi in the measured low-frequency band (1.84–3.72 GHz) and higher than 6.1 dBi in the high-frequency band (3.63–6.3 GHz), with a voltage standing wave ratio (VSWR) below 2 across the entire band. The metal baffles successfully correct the high-frequency radiation pattern distortion and ensure stable directional radiation over the full operating bandwidth. This design provides an efficient, robust, and manufacturable solution for 5G offshore wind power multi-band base station antennas. Full article

The failure of impedance matching between the ultrasonic power supply and the transducer can degrade machining quality, decrease machining efficiency, and reduce tool life. To enhance the detection efficiency of impedance matching status in ultrasonic machining systems, an impedance matching detection method based on the Voltage Standing Wave Ratio (VSWR) is proposed. First, by constructing a fitting model for the forward and reverse voltage and power of ultrasonic power supply, the relationship between VSWR and voltage is determined. Subsequently, a correlation model between the VSWR and tool tip amplitude, which reflects the working state of the ultrasonic system, is established. And the range of VSWR for optimal performance of system impedance matching is obtained by means of the model. Finally, the detection effectiveness of this method is verified through experiments on tool tip output amplitude under varying working conditions, and a comparison is made between this method and the phase method. The results indicate that using VSWR as a detection parameter to characterize impedance matching yields measurement values within 7% of the theoretical values. These results confirm the evaluation interval for a good working state of the system. Furthermore, experiments under varying force loads and temperatures demonstrate the reliability of the VSWR-based characterization. Compared to the traditional phase method, this approach reduces the cost of impedance matching performance detection and meets the requirements for impedance matching status detection during ultrasonic machining. Full article

Ultrasonic motors have attracted considerable attention in precision actuation applications because of their advantages over conventional electromagnetic motors, such as compact structure, high positioning accuracy, immunity to electromagnetic interference, noise-free operation, and suitability for low-temperature environments. However, conventional traveling-wave linear ultrasonic motors usually rely on boundary constraints to establish stable traveling waves, which may limit their structural flexibility and self-propelled capability. To address this issue, this paper proposes a free-boundary traveling-wave linear ultrasonic motor capable of realizing self-propelled motion. The motor features a projection structure at each end of the stator. Two piezoelectric ceramics are placed at one end for excitation, while a damping material is arranged at the other end for energy absorption. This design enables the motor to generate traveling waves without requiring fixed boundary conditions. The motor operates in the B(3,1) out-of-plane vibration mode to enhance the energy absorption capacity of the non-excited end and reduce its standing wave ratio (SWR). A finite element model of the motor is established to investigate its vibration characteristics. In addition, a novel method for estimating the standing wave ratio is proposed by using piezoelectric ceramics attached to the motor surface, replacing the traditional calculation approach. A prototype is fabricated to verify the feasibility of the proposed design. Experimental results show that the prototype achieves a minimum SWR of 1.81, a no-load speed of 42.1 mm/s, and a maximum output force of 0.465 N. These results confirm the feasibility of the proposed scheme and provide a new approach for the design of free-boundary traveling-wave linear ultrasonic motors. Full article

This study proposes a method to quantify uncertainty in the scattering parameter (S-parameter) measurements when using de-embedding techniques. After calibrating the measurement setup with reference standards, de-embedding algorithms are employed to extract the intrinsic S-parameter of the device under test (DUT). This process introduces additional complexity to the uncertainty analysis. This study investigates the sources of uncertainty inherent to vector network analyzer (VNA) measurements. Subsequently, a covariance matrix-based approach is employed to propagate these uncertainties, culminating in the quantification of S-parameter uncertainty. The effectiveness of the proposed is determined by comparing the measured S-parameters of power dividers and couplers to their nominal values, considering parameters such as balance, coupling, and voltage standing wave ratio (VSWR). Additionally, an uncertainty analysis is conducted for the power divider’s S-parameters, tracing the uncertainty sources back to the calibration standards. Full article

Objective: To investigate the changes in T-wave amplitude and Tp-Te interval on supine and standing electrocardiograms (ECGs) in pediatric postural orthostatic tachycardia syndrome (POTS), and to explore their predictive value for the therapeutic effect of metoprolol. Methods: A total of 59 children diagnosed with POTS who presented with syncope or pre-syncopal symptoms were enrolled as the POTS group, and 52 healthy children served as the control group. Supine and standing ECGs were recorded for all subjects, and T-wave amplitude and Tp-Te interval were measured. Children with POTS were followed-up after metoprolol treatment and divided into a therapeutic response group and a non-response group. Results: (1) Comparison of supine vs. standing ECGs: In the POTS group, standing posture (compared with supine posture) was associated with increased heart rate (HR), decreased T-wave amplitude in leads II, III, aVF, V4, V5, and V6, shortened Tp-Te interval in leads I, II, III, aVR, aVF, V1, V3, V4, V5, and V6, and elevated Tp-Te/QT ratio in leads aVL and V5 (all p < 0.05). (2) Comparison with the control group: The POTS group exhibited a greater HR difference (ΔHR), as well as larger differences in T-wave amplitude (ΔT-wave amplitude) between supine and standing positions in leads II, aVR, aVL, aVF, V3, and V5 (all p < 0.05). (3) Follow-up: Compared with the non-response group, the therapeutic response group showed larger ΔT-wave amplitude in leads III, aVF, V2, V3, V4, and V5, larger Tp-Te interval difference (ΔTp-Te interval) in lead V3, and larger Tp-Te/QT ratio difference (ΔTp-Te/QT ratio) in lead V3 (all p < 0.05). (4) Receiver operating characteristic curve: ΔT-wave amplitude in leads III, aVF, V2, V3, V4, and V5, ΔTp-Te interval in lead V3, and ΔTp-Te/QT ratio in lead V3 all had predictive value for the therapeutic effect of metoprolol in pediatric POTS (all p < 0.05). Conclusions: ΔHR and ΔT-wave amplitude in lead V5 between supine and standing positions are independent risk factors for pediatric POTS. A combination of five indicators—ΔT-wave amplitude in leads V2, V3, and V5, ΔTp-Te interval in lead V3, and ΔTp-Te/QT ratio in lead V3 between supine and standing ECGs—exerts a good predictive effect on the therapeutic response of pediatric POTS to metoprolol intervention. Full article

To meet the high-sensitivity requirement of ultra-high-frequency (UHF) sensors for electromagnetic waves radiated by partial discharge (PD) in power equipment of substations, this paper proposes a Koch complementary fractal UHF antenna based on the artificial magnetic conductor (AMC) metasurface. First, based on the Iterated Function System (IFS), a finite element model of the UHF Koch fractal antenna is constructed via affine transformation. Then, leveraging the in-phase reflection characteristic of the metasurface, an AMC metasurface for gain enhancement of the Koch fractal antenna is designed, and a multi-dimensional parameter joint optimization method is adopted to obtain the optimal structural parameter set of the Koch fractal antenna loaded with the AMC metasurface. Finally, experimental tests and analyses are carried out on the Koch complementary fractal UHF antenna. The results show that the antenna loaded with the AMC metasurface achieves a better voltage standing wave ratio (VSWR) and improved gain in both low and high frequency bands: the average gain increases by 35.19% in the frequency range of 0.3 GHz to 1.5 GHz, and the peak gain reaches approximately 11.5 dB with an enhancement of 120%. Full article

The ultra-high frequency (UHF)-based partial discharge (PD) detection technology for gas-insulated switchgear (GIS) has achieved large-scale applications due to its high sensitivity and real-time monitoring capabilities. However, long-term service-induced antenna corrosion in UHF sensors may lead to degraded reception characteristics. To ensure the credibility of monitoring data, on-site sensor calibration under ambient noise conditions is required. This study first analyzes the time–frequency domain characteristics of white noise received by UHF sensors in GIS environments. Leveraging the transceiver reciprocity principle of sensors, a noise reconstruction method based on external sensors is proposed to simulate on-site white noise. Subsequently, CST simulation models are established for both standard and degraded sensors, quantifying the impact of factors like antenna corrosion on performance parameters such as echo impedance S11 and voltage standing wave ratio (VSWR). Finally, the two sensor models are coupled into GIS handholes for comparative simulation analysis. Results show that antenna corrosion causes resonant frequency shifts in sensors, reducing PD signal power by 55.27% and increasing noise power by 64.11%. The signal-to-noise ratio (SNR) decreases from −9.70 dB to −15.34 dB, with evident waveform distortion in the double-exponential PD pulses. These conclusions provide theoretical references for on-site UHF sensor calibration in noisy environments. Full article

A stripline-type circulator is essential for the initial low-power characterization of vacuum electron devices such as magnetrons, enabling accurate measurements of startup behavior, oscillation frequency, and mode structure while minimizing reflections and protecting diagnostic equipment. In this study, two broadband S-band stripline circulator prototypes operating in the 2–4 GHz and 3–4 GHz bands were designed, fabricated, and experimentally characterized. A unified design methodology was implemented by using the same ferrite material and coupling angle in both structures, providing procurement simplicity, cost reduction, and technological standardization. This approach also enabled a direct assessment of how bandwidth variations influence circulator behavior. The design goals targeted a transmission efficiency above 90%, isolation exceeding 15 dB, and a voltage standing-wave ratio (VSWR) of 1.2:1. Experimental evaluations, including magnetic field mapping, low-power S-parameter measurements, and high-power tests, confirmed that both prototypes satisfy these specifications, consistently achieving at least 90% transmission across their respective operating bands. Additionally, a comparative analysis between a locally fabricated ferrite and a commercial ferrite sample was conducted, revealing the influence of material properties on transmission stability and high-power behavior. The results demonstrate that broadband stripline circulators employing a common ferrite material can be adapted to different S-band applications, offering a practical, cost-effective, and reliable solution for RF systems. Full article

In recent years, the scientific community has increasingly focused on state-of-the-art techniques, such as MIMO and mmWave transmission, aimed at enhancing the performance of telecommunication channels both quantitatively and qualitatively through various approaches. These efforts often rely on channel models designed to more accurately represent real-world conditions, thereby ensuring that the results are objective and practically applicable. In the present study, we employ one of the most scientifically reliable system- level simulators, Vienna SLS Simulator, to evaluate the performance of a wireless channel that we configure based on the latest standards (3GPP TR 36.873). We take into account the well-known non-symmetrical behavior of mMIMOs, where m stands for microwave MIMOs, in wireless communication systems and analyze the resulting changes in key performance metrics including average cell throughput, average user spectral efficiency and signal-to-interference-plus-noise ratio (SINR). We vary specific parameters such as transmission power, antenna polarization, ratio of indoor to outdoor users, and others with the aim of validating or challenging existing scientific assumptions. Particular attention is given to studying how variations in the aforementioned factors affect channel geometry and spatial uniformity, emphasizing the role of antenna geometry, polarization and user distribution in shaping channel asymmetries in mmWave MU-MIMO systems. Overall, this study provides insights into designing more balanced and efficient wireless systems in realistic urban environments. Full article

A Global Navigation Satellite System (GNSS) and Long Range (LoRa) technology play a crucial role in connected vehicles. The demand for antennas that cover both LoRa and GNSS bands is increasing. This work has developed a novel dual-band coplanar waveguide (CPW)-fed interleaved meander line antenna, incorporating a radiating element, ground plane, and feed. The antenna dimension is 90 × 90 × 1.635 mm³. The design employs a planar meander line configuration to effectively cover the 868 MHz LoRa and 1248 MHz GNSS bands. The antenna was integrated with a Frequency Selective Structure (FSS) to improve the parameters. The designed antenna provides sufficient bandwidth of 40 and 110 MHz for the LoRa and GNSS frequency bands, respectively. The CPW-interleaved meander line antenna attains a gain of −0.12 dBi at LoRa and 3.5 dBi at GNSS frequency. It achieves a voltage standing wave ratio of <2 and impedance of 50 Ω. The novelty of the proposed work is integrating FSS with a CPW-interleaved meander line antenna, which achieves dual-band operation. This dual-band low-profile configuration is suitable for connected vehicle communication. Full article

This paper addresses the long-standing question of understanding the origin and evolution of low-frequency unsteadiness interactions associated with shock waves impinging on a turbulent boundary layer in transonic flow (Mach: $1.1$ to $1.3$). To that end, high-speed experiments in a blowdown open-channel wind tunnel have been performed across a convergent–divergent nozzle for different expansion ratios (PR = 1.44, 1.6, and 1.81). Quantitative evaluation of the underlying spectral energy content has been obtained by processing time-resolved pressure transducer data and Schlieren images using the following spectral analysis methods: Fast Fourier Transform (FFT), Continuous Wavelet Transform (CWT), as well as coherence and time-lag evaluations. The images demonstrated the presence of increased normal shock-wave impact for PR = 1.44, whereas the latter were linked with increased oblique $\lambda$-foot impact. Hence, significant disparities associated with the overall stability, location, and amplitude of the shock waves, as well as quantitative assertions related to spectral energy segregation, have been inferred. A subsequent detailed spectral analysis revealed the presence of multiple discrete frequency peaks (magnitude and frequency of the peaks increasing with PR), with the lower peaks linked with large-scale shock-wave interactions and higher peaks associated with shear-layer instabilities and turbulence. Wavelet transform using the Morlet function illustrates the presence of varying intermittency, modulation in the temporal and frequency scales for different spectral events, and a pseudo-periodic spectral energy pulsation alternating between two frequency-specific events. Spectral analysis of the pixel densities related to different regions, called spatial FFT, highlights the increased influence of the feedback mechanism and coupled turbulence interactions for higher PR. Collation of the subsequent coherence analysis with the previous results underscores that lower PR is linked with shock-separation dynamics being tightly coupled, whereas at higher PR values, global instabilities, vortex shedding, and high-frequency shear-layer effects govern the overall interactions, redistributing the spectral energy across a wider spectral range. Complementing these experiments, time-resolved numerical simulations based on a transient 3D RANS framework were performed. The simulations successfully reproduced the main features of the shock motion, including the downstream migration of the mean position, the reduction in oscillation amplitude with increasing PR, and the division of the spectra into distinct frequency regions. This confirms that the adopted 3D RANS approach provides a suitable predictive framework for capturing the essential unsteady dynamics of shock–boundary layer interactions across both temporal and spatial scales. This novel combination of synchronized Schlieren imaging with pressure transducer data, followed by application of advanced spectral analysis techniques, FFT, CWT, spatial FFT, coherence analysis, and numerical evaluations, linked image-derived propagation and coherence results directly to wall pressure dynamics, providing critical insights into how PR variation governs the spectral energy content and shock-wave oscillation behavior for nozzles. Thus, for low PR flows dominated by normal shock structure, global instability of the separation zone governs the overall oscillations, whereas higher PR, linked with dominant $\lambda$-foot structure, demonstrates increased feedback from the shear-layer oscillations, separation region breathing, as well as global instabilities. It is envisaged that epistemic understanding related to the spectral dynamics of low-frequency oscillations at different PR values derived from this study could be useful for future nozzle design modifications aimed at achieving optimal nozzle performance. The study could further assist the implementation of appropriate flow control strategies to alleviate these instabilities and improve thrust performance. Full article

Wildfire activity is intensifying globally as climate change amplifies heat waves, droughts and wind extremes, threatening biodiversity. South Korea (63% forested) has experienced a sharp rise in large fires. We analysed 905 wildfires ≥ 5 ha from 1980–2024, linking burned area to maximum wind speed, relative humidity, temperature and forest structure (conifer, broadleaf and mature–stand ratios, forest cover). Pearson correlations, HC3-corrected regression, a 1000-tree Random Forest and five-fold validated XGBoost interpreted with SHAP captured linear and nonlinear effects; WUI influences were examined qualitatively. Each 1 m s⁻¹ increase in peak wind expanded burned area by ~8.5 ha, whereas a 1% rise in humidity reduced area by ~3 ha (p < 0.01). Broadleaf prevalence restrained spread, while high conifer and mature–stand proportions enlarged it. Machine learning raised explanatory power from R² = 0.62 to 0.66 and showed that very dry air, strong winds and conifer cover above half the landscape coincided with the largest events. Burned area during 2020–2024 reached 29,905 ha—sevenfold that of 2015–2019. These results imply that extreme fire weather, flammable pine fuels and expanding WUI settlements jointly elevate risk; implementing real-time meteorological thresholds, targeted fuel treatments and stricter WUI zoning can help mitigate this risk. Full article

Background and Objectives: The autonomic nervous system (ANS) orchestrates adaptation to stress; however, its reactivity is influenced by demographic, anthropometric, and psychosocial factors. While arterial stiffness and central adiposity are established cardiovascular risk markers, less is known about how maladaptive coping strategies, cumulative life stress, and quality of life influence short-term autonomic regulation. This study examined the age- and sex-specific associations between anthropometry, maladaptive coping, life stress, quality of life, and ANS adaptation in adults. Materials and Methods: In this cross-sectional study, 122 healthy adults aged 21–78 years underwent a standardized lay–stand–lay (LSL) protocol with pulse wave analysis. Hemodynamic outcomes included pulse wave velocity (PWVao), augmentation indices (AIxA and AIxB), and aortic blood pressures (SBPao and PPao). Anthropometric measures comprised BMI, waist and hip circumference, waist-to-hip ratio (WHR), and waist-to-height ratio (WHtR). Psychosocial assessments included the Young Hypercompensation Inventory (maladaptive coping), Holmes–Rahe Life Events Inventory (life stress), and EQ-5D-3L (quality of life). Associations were analyzed using mixed-effects models adjusted for covariates, with false discovery rate correction. Results: Age was the strongest determinant of autonomic reactivity: older adults showed greater recovery of augmentation indices and central pressures after orthostatic challenge. Sex differences were evident, with women displaying consistently higher augmentation indices and men showing greater PWV responses. Central adiposity (WHR, WHtR, and waist circumference) predicted blunted augmentation index reactivity, while hip circumference was protective. BMI-defined obesity showed weaker associations. Maladaptive coping, life stress burden, and quality of life were not significantly associated with ANS indices after correction for multiple comparisons. Conclusions: ANS adaptation to postural stress is largely determined by age, sex, and visceral adiposity, whereas psychosocial measures showed limited influence in this healthy adult sample. These findings highlight the demographic and anthropometric determinants of cardiovascular adaptability, suggesting that psychosocial influences may primarily act through long-term behavioral and neuroendocrine pathways. Full article

In this study, SiO₂ thin films were sputtered from a Si target using reactive HiPIMS (high-power impulse magnetron sputtering) in an argon–oxygen process gas. In order to understand the behavior of HiPIMS, the deposition process was studied by systematically varying the sputtering parameters and monitoring the current waveforms. A decaying transient was observed at the leading edge of the pulse, caused by the L-C term of the HiPIMS generator, the cable, and the target. To investigate the periodic transient, we used, to the best of our knowledge, for the first time, a standing wave ratio meter (SWR). In order to be able to deposit films with the desired properties, the target voltage and its associated current characteristics were also investigated. The formation of a distinct step-like shape in the current–voltage characteristics is observed during reactive sputtering. A simple physical model was used to determine the position and length of the plateau. The appearance of hysteresis, which is typical of reactive sputtering, was also observed. These findings may help us to better understand the mechanism of reactive HiPIMS deposition of SiO₂. Full article