Microwave and Optical Technology Letters最新文献

A gas analyzer has been developed using cavity ring-down spectroscopy (CRDS) technology, designed to simultaneously measure the concentrations of CO₂ and CO. These gases are critical indicators of transformer insulation degradation. The analyzer covers a CO₂ concentration range from a few ppm to several thousand ppm and can measure CO/CO₂ concentration ratios from 0.076 to 0.8. The selected absorption lines for CO and CO₂ are centered at 6337.99 and 6338.59 cm⁻¹, respectively. The two candidate lines are proximate to each other and nonoverlapping. The experimental results indicate that the system accurately fits the measured and calculated signals, enabling concentration measurements at the ppm level. This confirms its ability to measure the gas concentrations and ratios critical for assessing the condition of transformer insulation. This CRDS-based system offers a reliable and sensitive method for early detection of potential transformer faults.

The integration of health monitoring and wearable antenna technologies has enhanced patient assessment and the provision of healthcare. Traditional health monitoring methods have evoked a surge in interest toward embroidered antennas as a viable solution for constant physiological monitoring in a noninvasive way. This study examines the performance of an embroidered wearable textile (EWT) antenna intended for breathing rate applications. The antenna is seamlessly integrated into a commercially available T-shirt, extending the confines of “smart” textiles. The compact (45 mm × 26 mm) EWT antenna operates in 2.4 and 5.8 GHz with gains of 2.07 and 5.85 dBi, respectively. Crumpling and stretching analysis have also been investigated to ensure antenna's mechanical stability and reliability. Subsequently a specific absorption rate analysis has also been performed to quantify the radiation within specified limits.

This study explores tightly coupling technology applied in the design of an ultra-wideband (UWB), compact, dual-polarized antenna. The proposed design utilizes tightly coupling effects to achieve UWB performance, with a notable feature being its double-dipole topology. This topology significantly reduces the difficulty of impedance matching across the ultra-wide band. To suppress the significant edge effect that occurs in tightly coupled dipoles, coupled grounded posts are added to the surrounding dipoles, effectively attenuating edge reflections and significantly expanding the bandwidth to lower frequencies. A periodic patch superstrate is loaded above the dipoles to improve the impedance matching and radiation performance. A prototype was fabricated and measured, showing a bandwidth is 1.8–12.5 GHz (149.7%) with VSWR $��\; ��<��$ 2.2, fully covering the S, C, and X bands. The proposed antenna is printed on a thin substrate and its size is very small, only $��\; ��33�\; �\times �\; �33�\; �\times �\; �18.2��$ mm ($��\; ��0.2�\; �\times �\; �0.2�\; �\times �\; �0.11�\; �{\lambda }_L��$), where the $��\; ��{\lambda }_L��$ is the wavelength of the lowest operating frequency.

This paper aims to study the effect of eliminating some elements from the original planar array (OPA) to generate a useful flat-top coverage pattern (FTCP) using a genetic algorithm. The study involves dividing the fully planar array (i.e., OPA) into two regions with an unequal number of elements. The first region includes the elements located in the core (center) of the array, and the remaining elements are the second region, and their location is within the boundary (side) of the array. Only the elements of the first region are included in the optimization process, while the elements of the second region are eliminated in the form of a specific geometric composition without affecting the FTCP generation. Comparing the OPA that N×M elements with the first region (active subarray) elements, it is noted that the number of elements has been reduced from N×M to (N − 2x) × (M − 2y) to reduce the complexity of the system as much as possible without affecting the performance in general. Different boundary subarray shapes are presented in this paper with different numbers of elements. The obtained results showed the effectiveness of the proposed method in generating FTCP close to its counterpart in the OPA.

A new decoupling method for microstrip antenna arrays has been proposed in this paper, which is based on characteristic mode analysis. This method works by suppressing the nonworking mode that contributes the most to mutual coupling. An eight-element microstrip antenna array is designed as the reference antenna, and for this antenna, mode suppression is achieved by etching gaps on the patch and adding metal columns between the patch and the ground. The antenna array after the mode suppression is fabricated and measured. The results show that the measured S₃₄ after the mode suppression is below −21 dB, whereas the simulated S₃₄ of the reference antenna array is about −15 dB. This indicated a 7–10.5 dB reduction in coupling across the band. Additionally, the measured ActiveS₃ after the mode suppression is still below −11 dB. Besides, the measured and simulated normalized array patterns after the mode suppression agree well at different frequencies.

Based on the improved YOLOv8n, a steel plate defect detection and recognition method is proposed to address the high labor costs and workload of traditional tasks. SPPFELAN processes inputs in parallel to enhance computational efficiency by executing multiple pooling operations simultaneously. The parallel feature fusion module PscSE, using a mixed-dimension SE attention mechanism (scSE), captures global and channel-related information better, improving characterization capability. The EIOU loss function addresses the ambiguous aspect ratio definition of CIOU loss, enhancing detection accuracy and accelerating convergence. Results show the YOLOv8n-PscSE-SPPFELAN model achieves 76.9% [email protected] on the Northeastern University steel plate dataset, a 4.6% improvement over the original YOLOv8n, with a computation amount of 7.7 GFLOPs, reducing resource usage and greatly improving detection speed.

Microstrip antennas are increasingly utilized in space-borne applications, spanning areas such as RFID, mobile communication, and healthcare. This paper introduces a novel wearable ultra-wideband (UWB) microstrip patch antenna, distinctively designed in a star shape. The antenna, with a total volume of 1172 mmÂş, is crafted on a semiflexible substrate using RT/duroid 5880. It exhibits a low loss tangent of 0.0004 and a relative permittivity of 2.2. The proposed design achieves a resonant frequency of 3.4 GHz, an impressive reflection coefficient of −39 dB, and an extensive bandwidth of 5.6 GHz, ranging from 2.8 to 8.4 GHz. Although the antenna demonstrates modest gain and directivity, its expansive bandwidth is a significant attribute. This wideband antenna is proposed as an ideal candidate for wearable biomedical applications, leveraging its substantial bandwidth and unique design characteristics.

A common design solution of wideband filtering antennas inspired by the synthesis of a flat-top gain curve is proposed by using mutual coupling effects. The realization of a frequency-varied flat-top gain curve based on specially designed subarrays is analyzed. Analysis results conclude a design process of generating filtering response based on shorting pins and parasitic structures. A single-layer rectangle patch array loaded with parasitic shorted patches is designed and analyzed for the validation. The proposed antenna possesses an impedance bandwidth of 4.95–6.05 GHz and a peak realized gain of 11.2 dBi. Besides, the design has its out-of-band rejection levels higher than 15 dB.

In this paper, an enhancement gain of compact CPW-Fed antenna using a single layer frequency selective surfaces (FSSs) reflector for ultra-wideband (UWB) applications is presented. A hexagonal CPW-Fed antenna with a size of 30 × 30 mm² is realized to provide a UWB bandwidth operation. In this study, a novel design of an FSS unit cell with reduction and a small size of 8 × 8 mm² is proposed. It allows one to achieve a UWB band-stop response between 3 and 11.5 GHz. The FSS reflector has 7 × 7 units with a total size of 56 × 56 mm². This reflector is placed below the antenna at a distance of 20 mm. The main objective of this contribution is to improve the gain level of the antenna, where the proposed antenna achieves an improvement of realized gain of 6.2 dBi with increasing from 2.2 to 8.4 dBi. The antenna became more directive after the integration of the FSS reflector with a directional radiation pattern. The numerical and experimental results are in good concordance with the simulated one. This study is performed in terms of voltage standing wave ratio, radiation pattern, realized gain, and radiation efficiency.

This paper presents a novel additively manufactured wideband dual circularly polarized (CP) open-ended waveguide (OEW) antenna, which adopts a pair of wedge-shaped outer ridges acting as a circular polarizer. Study found that compared to the con- ventional designs that employ internal polarization converting structures, such outer ridges are capable of achieving wider axial ratio bandwidth (ARBW) and better reflection coefficients. On each ridge, two rectangular slots are designed to suppress the higher order mode caused by the increased waveguide size, and further expanding the ARBW. The proposed antenna is fed by two differential ports. By switching the feeding ports, the CP states can be altered to either right-handed CP (RHCP) or left-handed CP (LHCP). In terms of configuration, the proposed antenna has a simple one-piece structure and is fabricated by using dielec- tric 3-D printing technology. To form the waveguide walls, its partial surfaces are coated by copper films through electroplat- ing. The proposed antenna features easy fabrication and light weight. Experimental results show that the proposed antenna has an impedance bandwidth of larger than 47.6% (8–13 GHz) with reflection coefficients lower than −15 dB, while the 3-dB ARBW is 37.7% from 8.4 to 12.3 GHz.