Search Results (99)

This paper reports magnetic microscopy using high-sensitivity room-temperature tunnel magnetoresistance (TMR) devices for thin geological sections. The sensitivity region of the TMR sensor has dimensions of 178 µm (L) × 0.1 µm (W) × 100 µm (H), consisting of two TMR devices. Magnetic images were obtained for a vertically magnetized Hawaii basalt thin section in two sensor configurations, with the sensor length aligned parallel to the X- (lift-off = 174 μm) and Y-axes (lift-off = 200 μm), without introducing anisotropic distortion in the magnetic images. Although the magnetic images obtained with a scanning SQUID microscope (SSM) were similar, slight discrepancies were observed in the high-spatial-resolution region. A magnetic point source (50 μm × 50 μm) with a perpendicular magnetization film was prepared for evaluation. The SSM measurements showed a clear magnetic dipole at an angle of approximately 1° from the vertical direction. The FWHMs for both the SSM and TMR sensors increased linearly with lift-off. However, the peak magnetic fields, magnetic moments, and dipole tilts of the TMR sensor were significantly larger than those of the SSM sensor. This discrepancy may be due to the vertical extent of the active region of the TMR sensor, as well as due to sensor noise and drift. Full article

This study demonstrates a Mach–Zehnder-type internal-state atom interferometer in a sodium F = 1 spinor Bose–Einstein condensate (BEC), which is realized by applying a three-pulse radio-frequency sequence ($\pi /2$–$\pi$–$\pi /2$) to manipulate the two magnetic sublevels $|1,-1⟩$ and $|1,0⟩$. Phase-scanning experiments show that the visibility remains at a high level across all three pulse stages ($V>0.77$). In the hold-time scanning measurements, the visibility decays exponentially with hold time, yet the system maintains good coherence. This work establishes a foundation for precision measurements based on internal-state atom interferometers, as the approach simplifies the experimental apparatus while maintaining good quantum coherence and high-contrast interference fringes. Full article

The pulsed power switch serves as a critical component in pulsed power systems. The electric radiation generated by switching operations threatens the miniaturization of pulsed power systems, causing significant electromagnetic interference (EMI) to nearby signal circuits. The pseudospark switch’s (PSS) exceptionally fast transient response, a key enabler for sophisticated pulsed power systems, is also a major source of severe EMI. This study investigated the electric field radiation from a high voltage PSS within a capacitor discharge unit (CDU), using a near-field scanning system based on an electro-optic probe. The time-frequency distribution of the radiation was characterized, identifying contributions from three sequential stages: the application of the trigger voltage, the main gap breakdown, and the subsequent oscillating high voltage. During the high-frequency oscillation stage, the distribution of the peak electric field radiation aligns with the predictions of the dipole model, with a maximum value of 43.99 kV/m measured near the PSS. The spectral composition extended to 60 MHz, featuring a primary component at 1.24 MHz and distinct harmonics at 20.14 MHz and 32.33 MHz. Additionally, the impacts of circuit parameters and trigger current on the radiated fields were discussed. These results provided essential guidance for the electromagnetic compatibility (EMC) design of highly-integrated pulsed power systems, facilitating more reliable PSS applications. Full article

The analysis of ground-penetrating radar data generally relies on the visual identification of structures on selected profiles and their interpretation in terms of buried features. In simple cases, inverse modelling of the acquired data set can facilitate interpretation and reduce subjectivity. These methods suffer from severe restrictions due to antenna resolution limits, which prevent the identification of tiny structures, particularly in forensic, stratigraphic, and engineering applications. Here, we describe a technique to obtain a high-resolution characterization of the underground, based on the forward modelling of individual traces (A-scans) of selected radar profiles. The model traces are built by superposition of Ricker wavelets with different polarities, amplitudes, and arrival times and are used to create reflectivity diagrams that plot reflection amplitudes and polarities versus depth. A thin bed is defined as a layer of higher or lower permittivity relative to the surrounding material, such that the top and bottom reflections are subject to constructive interference, determining the formation of an anomalous peak in the trace (tuning effect). The proposed method allows the detection of ultra-thin layers, well beyond the Rayleigh vertical resolution of GPR antennas. This approach requires a preliminary estimation of the instrumental uncertainty of common monostatic antennas and takes into account the frequency-dependent attenuation, which causes a spectral shift of the dominant frequency acquired by the receiver antenna. Such a quantitative approach to analyzing radar data can be used in several applications, notably in stratigraphic, forensic, paleontological, civil engineering, heritage protection, and soil stratigraphy applications. Full article

The multidimensional parameter measurement of microwave signals, including temporal, spatial, and frequency, is essential for electronic warfare and radar systems. In this article, we present a photonic scheme for real-time microwave frequency and angle-of-arrival (AOA) measurement based on stimulated Brillouin scattering (SBS). In the proposed system, the unknown signal under test (SUT) received by adjacent antennas is injected into a dual-drive Mach–Zehnder modulator (DDMZM). Two branches of the SUT with phase difference interfere in the optical domain, converting phase difference into the power of optical sidebands. These optical sidebands are scanned by combining SBS with frequency-to-time mapping (FTTM) to achieve simultaneous measurement of the AOA and frequency. Consequently, the frequency and AOA of the SUT are mapped to the time interval and normalized amplitude of the output electrical pulses, respectively. Results show that the system can achieve the frequency measurement of multiple RF signals in the range of 5–15 GHz and AOA measurement in the range of −70° to 70°, with measurement errors of ±5 MHz and ±2°, respectively. Furthermore, the frequency measurement range can be flexibly adjusted by tuning the pump optical driving signals. Full article

In this study, 8-ply 3K carbon fiber fabrics were spray-coated with Ag/RGO nanoparticles at varying weight ratios (0, 2.5, and 5 w/w). Composite specimens were fabricated, consisting of an unmodified control sample (neat) and three different variants containing 0.075 w/w% RGO, 0.26 w/w% AgRGO, and 0.45 w/w% AgRGO, respectively. The effects of RGO and AgRGO contents on the electrical conductivity, flexural properties, dynamic mechanical properties, and electromagnetic interference shielding (EMI) performance of these composites were investigated. Additionally, the distribution of RGO and AgRGO on the surfaces and interfaces of carbon fibers was examined using field emission scanning electron microscopy to determine the microstructure–property relationship. The increase in the Ag ratio in the AgRGO filler material in the composite from 2.5 to 5 resulted in an increase in both the through-the-thickness and surface conductivity values by 3.5 times, reaching maximum conductivity values (273 × 10⁻³ S/m and 256 × 10⁻³ S/m, respectively). Composites containing filler material with an Ag/RGO weight ratio of 2.5 achieved a total electromagnetic shielding efficiency of 18 dB at the X-band frequency region, without loss in flexural strength, while the maximum total electromagnetic shielding efficiency value of 22.68 dB was obtained when the Ag/RGO weight ratio was 5. With a maximum SE_T value these composites might be suitable for use in areas that do not require primary load-bearing applications, such as satellite, antenna, and avionics system housings. Full article

This study investigates the influence of laser processing parameters on the surface roughness and color formation of AISI 304 stainless steel. Experiments were conducted to explore how raster step, scanning speed, frequency, linear energy density, and overlap coefficient affect the surface characteristics of laser-marked zones. It was found that increasing the raster step from 20 µm to 80 µm led to a consistent increase in surface roughness (from 1.23 µm to 1.47 µm at 20 kHz and 25 mm/s), accompanied by a shift in color from dark brown to lighter yellow hues. In contrast, increasing scanning speed (from 25 mm/s to 125 mm/s) caused a nonlinear reduction in roughness (e.g., from 1.23 µm to 0.76 µm at 20 kHz and Δx = 20 µm), resulting in a lighter surface color. Frequency was identified as a critical factor; increasing it from 20 kHz to 100 kHz resulted in a threefold decrease in roughness (from 1.23 µm to 0.25 µm at 20 µm raster step and 125 mm/s), which correlated with a shift to brighter yellow tones. Higher linear energy density values (1.60–8.00 J/cm) increased roughness and darkened the surface color, while higher overlap coefficients produced the opposite trend. The study highlights the relationship between surface nanostructuring and the formation of stable interference colors, providing quantitative parameters for achieving desired chromatic effects. These findings establish a basis for the industrial application of laser color marking, where both aesthetic differentiation and functional enhancements—such as corrosion resistance, hydrophobicity, and antibacterial properties—are essential. Future research will focus on quantitatively evaluating the functional properties, including corrosion resistance, hydrophobicity, and durability, of the colored surfaces produced under optimized parameters. This research aims to further develop laser marking as a foundational tool for both aesthetic and functional surface engineering. Full article

The remarkable growth of high-frequency electronic systems has raised concerns about electromagnetic interference (EMI), emphasizing the need for lightweight and efficient shielding materials. In this study, ternary composites based on polypyrrole (PPy), graphene oxide (GO), and silver nanowires (AgNWs) were synthesized through chemical oxidative polymerization of pyrrole monomer and embedded into polycaprolactone (PCL) matrices to create flexible films. Structural and morphological analyses confirmed the successful incorporation of all components, with scanning electron microscopy showing granular PPy, sheet-like GO, and fibrous AgNWs, while spectroscopic studies indicated strong interfacial interactions without damaging the PPy backbone. Thermomechanical analysis revealed that GO increased stiffness and defined the glass transition, whereas AgNWs improved toughness and energy dissipation; their combined use resulted in balanced properties. EMI shielding effectiveness (SE) was tested in the X-band (8–12 GHz). Pure PPy exhibited poor shielding ability, while the addition of GO and AgNWs significantly enhanced performance. The highest EMI SE values were observed in PPy/GO–AgNWs composites, with an average SE of 16.05 dB at 20 wt% of the composite in the PCL matrix, equivalent to about 84.4% attenuation of incident waves. These results demonstrate that the synergistic integration of GO and AgNWs into PPy matrices enables the creation of lightweight, flexible films with advanced EMI shielding properties, showing great potential for next-generation electronic and aerospace applications. Full article

This study reports the synthesis, structural characterization, and electromagnetic shielding performance of tantalum (Ta)-doped nickel ferrite (NiFe₂O₄) composites reinforced with chopped strands. Ta-doped NiFe₂O₄ powders were prepared via the conventional mixed-oxide route and sintered at 1200 °C for 4 h, resulting in a well-crystallized single-phase spinel structure. Comprehensive structural and chemical analyses were carried out using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS), confirming the successful incorporation of Ta into the NiFe₂O₄ lattice and the uniform microstructural distribution. The ferrite powders were subsequently embedded with chopped strands and epoxy resin through hot pressing to fabricate composites with varying filler contents. The electromagnetic interference (EMI) shielding effectiveness (SE) of the composites was systematically evaluated in the 7–18 GHz frequency range using a network analyzer (NA). The optimized composite, with a thickness of 1.2 mm, demonstrated a maximum SE of 34.74 dB at 17.4 GHz, primarily attributed to interfacial polarization, dipolar relaxation, and multiple scattering effects induced by the chopped strands. The results indicate that the shielding performance of the composites can be precisely tuned by modifying the filler concentration and microstructural characteristics, enabling selective frequency-band applications. Overall, this work highlights the potential of Ta-doped NiFe₂O₄/chopped strand composites as lightweight, cost-effective, and high-performance candidates for advanced microwave absorption and electromagnetic shielding applications in defense, and next-generation communication technologies. Full article

This paper presents a high-sensitivity multi-point seawater temperature detection system based on the virtual Vernier effect, achieved through multiplexed Fabry–Perot (FP) cavities combined with optical frequency-modulated continuous wave (FMCW) interferometry. To address the nonlinear frequency scanning issue inherent in FMCW systems, this paper implemented a software compensation method. This approach enables accurate positioning of multiple FP sub-sensors and effective demodulation of the sensing interference spectrum (SIS) for each FP interferometer (FPI). Through digital signal processing (DSP) algorithms and spectral demodulation, each sub-FP sensor generates an artificial reference spectrum (ARS). The virtual Vernier effect is then achieved by means of a computational process that combines the SIS intensity with the corresponding ARS intensity. This eliminates the need for physical reference arrays with carefully detuned spatial frequencies, as is required in traditional Vernier effect implementations. The sensitivity amplification can be dynamically adjusted with the modulation function parameters. Experimental results demonstrate that an optical fiber link of 82.3 m was achieved with a high spatial resolution of 23.9 $\mathsf{\mu }\mathrm{m}$. Within the temperature range of ${30 }^{\circ }\mathrm{C}$ to ${70 }^{\circ }\mathrm{C}$, the temperature sensitivities of the three enhanced EIS reached −275.56 $\mathrm{pm}{/}^{\circ }\mathrm{C}$, −269.78 $\mathrm{pm}{/}^{\circ }\mathrm{C}$, and −280.67 $\mathrm{pm}{/}^{\circ }\mathrm{C}$, respectively, representing amplification factors of 3.32, 4.93, and 6.13 compared to a single SIS. The presented approach not only enables effective multiplexing and spatial localization of multiple fiber sensors but also successfully amplifies weak signal detection. This breakthrough provides crucial technical support for implementing quasi-distributed optical sensitization sensing in marine environments, opening new possibilities for high-precision oceanographic monitoring. Full article

A green and cost-effective method was employed to efficiently synthesize conductive silica–silver (SiO₂/PCPA/Ag) core–shell structured microspheres. The SiO₂ microspheres were initially functionalized with poly(catechol-polyamine), followed by the in situ reduction of Ag ions to Ag nanoparticles on the surface of the SiO₂ microspheres using an electroless plating process. Analysis using scanning electron microscopy confirmed the successful formation of a dense and uniform silver layer on the surface of the SiO₂ microspheres. The valence state of the silver present on the surface of the SiO₂ microspheres was determined to be zero through analyses conducted using an X-ray photoelectron spectrometer and X-ray diffractometer. Consequently, the SiO₂/PCPA/Ag microspheres, upon initial preparation, demonstrated a notable conductivity of 1005 S/cm, which was further enhanced to 1612 S/cm following additional heat treatment aimed at rectifying defects within the silver layer. The resulting rubber composites displayed a low electrical resistivity of 5.4 × 10⁻³ Ω·cm and exhibited a significant electromagnetic interference (EMI) shielding effectiveness exceeding 100 dB against both X-band and Ku-band frequencies, suggesting promising potential for utilization as a material for conducting and EMI shielding purposes. Full article

A novel polarization-reconfigurable 1 × 8 array beam-scanning antenna based on a switchable vertically crossed balanced feed (VCBF) structure is presented. The designed VCBF structure can provide a stable 180° phase difference by utilizing spatial symmetry, enabling the synthesis of two linear polarizations (LP). The parasitic patch layer loaded directly above the VCBF can effectively enhance the operating frequency bandwidth of the antenna. In the array design, by controlling the amplitude and phase input at each port, scanning angles of ±45°, ±40°, and ±30° can be achieved under two LP at 3.0, 3.5, and 4.0 GHz. The simulation and measurement results indicate that the designed antenna has a wideband characteristic with a relative bandwidth of 28.6% and stable polarization reconfigurability. Benefiting from the advantages of polarization reconfigurability and beam-scanning capabilities, the antenna is highly suitable for applications in wireless communication systems that require polarization anti-interference. Full article

The large size and metal-enclosed casings of oil-immersed power transformers present significant challenges for patrol robots attempting to accurately locate their position within the transformer. Therefore, this paper proposes a three-dimensional spatial localization method for transformer patrol robots using a nine-element ultrasonic array. This method is based on wavelet decomposition and weighted filter beamforming (WD-WFB) algorithms. To address the issue of strong noise interference in the field, the ultrasonic localization signals are adaptively decomposed into wavelet coefficients at different frequencies and scales. An improved semi-soft thresholding function is applied to the decomposed wavelet coefficients to reduce noise and reconstruct the localization signals, resulting in localization signals with low distortion and a high signal-to-noise ratio(SNR). To overcome the limitations of traditional beamforming algorithms regarding interference resistance and signal resolution, this paper presents an improved WFB algorithm. By obtaining the energy distribution of the scanning area and determining the position of the maximum energy point, the spatial position of the transformer patrol robot can be determined. The test results show that the proposed improved semi-soft threshold function demonstrates superior denoising performance compared to traditional threshold functions. When compared to the soft threshold function, it achieves improvements of 15.32% in SNR and 15.57% in normalized correlation coefficient (NCC), along with a 48.91% reduction in root mean square error (RMSE). Compared with the hard threshold function, the improvement is even more significant: the SNR is improved by 60.55%, the NCC is improved by 24.90%, and the RMSE is reduced by 58.77%. The denoising effect was significantly improved compared to the traditional threshold function. In a 1200 mm × 1000 mm × 1000 mm transformer test box, the improved WFB algorithm in this paper was used to perform multiple localizations of the transformer patrol robot at different positions after denoising the field signals using the semi-soft threshold function. The maximum relative localization error was 3.47%, and the absolute error was within 2.6 cm, meeting engineering application requirements. Full article

The timely detection of delamination is essential for preventing catastrophic failures and extending the service life of carbon fiber-reinforced polymers (CFRP). Full wavefields in CFRP encapsulate extensive information on the interaction between guided waves and structural damage, making them a widely utilized tool for damage mapping. However, due to the multimodal and dispersive nature of guided waves, interpreting full wavefields remains a significant challenge. This study proposes an end-to-end delamination imaging approach based on UNet++ using 2D frequency domain spectra (FDS) derived from full wavefield data. The proposed method is validated through a self-constructed simulation dataset, experimental data collected using Scanning Laser Doppler Vibrometry, and a publicly available dataset created by Kudela and Ijjeh. The results on the simulated data show that UNet++, trained with multi-frequency FDS, can accurately predict the location, shape, and size of delamination while effectively handling frequency offsets and noise interference in the input FDS. Experimental results further indicate that the model, trained exclusively on simulated data, can be directly applied to real-world scenarios, delivering artifact-free delamination imaging. Full article

Stripe noise along the scanning direction significantly degrades the quality of high-resolution infrared line-scan images and impairs downstream tasks such as target detection and radiometric analysis. This paper presents a lightweight, single-frame, reference-free non-uniformity correction (NUC) method tailored for such images. The proposed approach enhances the directionality of stripe noise by projecting the 2D image into a 1D row-mean signal, followed by adaptive guided filtering driven by local median absolute deviation (MAD) to ensure spatial adaptivity and structure preservation. A spectral-entropy-constrained frequency-domain masking strategy is further introduced to suppress periodic and non-periodic interference. Extensive experiments on simulated and real datasets demonstrate that the method consistently outperforms six state-of-the-art algorithms across multiple metrics while maintaining the fastest runtime. The proposed method is highly suitable for real-time deployment in airborne, satellite-based, and embedded infrared imaging systems. It provides a robust and interpretable framework for future infrared enhancement tasks. Full article