Search Results (276)

This paper describes the design and implementation of an automated irrigation control system that uses data collected by a wireless sensor network. Each sensor node, built on a custom-designed printed circuit board, includes sensors for light intensity, temperature, and a custom soil moisture sensor. Data is transmitted to a central control node via ESP-NOW, where it is processed and compared with configurable thresholds retrieved from Google Sheets over Wi-Fi. Irrigation is triggered automatically when conditions meet the remotely defined thresholds. A key contribution is the development and testing of a custom soil moisture sensor, with results compared to commercial models. The system supports low-power operation through deep sleep modes, enabling long-term field deployment. The novelty lies in the complete integration of hardware, software, and cloud-based control, providing a flexible and low-cost solution for precision agriculture. The system can be deployed in greenhouses or open fields and serves as a platform for future research in smart irrigation. The fundamental aspect is a very user-friendly solution for any farmer attributable to easy accommodation to the Google Sheets interface, no maintenance cost over the cloud account, and up to 45 days of battery life or a built-in alternative for solar power. Full article

Following the integrated optical assembly and single printed circuit board co-layout design concept for electrical circuits, this paper develops a field-programmable gate array (FPGA) based, miniaturized, eight-channel microwave photonic transceiver stabilization system for the joint regulation of lasers and Mach–Zehnder modulators (MZMs). The integrated single-board hardware enables high-precision, high-reliability automatic temperature control (ATC), automatic power control (APC), and arbitrary closed-loop control of the MZMs bias point, overcoming the drawbacks of discrete single-channel, independent control schemes reported in previous works, which lack expandability for large radar arrays. The laser sub-module supports continuously adjustable drive current and multi-level protection, achieving wavelength stability of 0.01 nm and an output optical power fluctuation of less than 0.02%. The MZM control unit delivers wide-range, high-stability bias drift suppression with arbitrary bias point stability up to 0.05 dB. All static and dynamic performance indicators of the proposed module are characterized using a dedicated experimental setup comprising optical power meters, optical spectrum analyzers, temperature cycling chambers, and vector signal analyzers. Leveraging FPGA-based parallel hardware logic, the system features low latency, low jitter, cross-channel mismatch compensation, and excellent timing synchronization, with a compact overall footprint of 180 mm × 120 mm that matches the size of radar antenna panels and supports flexible array scaling. The proposed integrated module meets the low-noise, high-reliability, and high-integration requirements of radio-over-fiber links in microwave photonic radars. It effectively advances the practical engineering deployment of microwave photonic radar systems. Full article

Organic memristive devices are promising components for neuromorphic systems. Although based on solution-processable materials, their fabrication often involves complex, resource-intensive processes. Here, we report the fabrication of organic memristive devices using aerosol jet printing to deposit both the active channel based on proprietary polyaniline-based bioink and PEDOT:PSS electrodes. Polymers printing has been carried out both on rigid and flexible substrates, the latter with the aim of demonstrating a flexible device not subjected to films delamination upon bending. By optimizing printing parameters, we achieved devices exhibiting high ON/OFF current ratios exceeding 100 and rapid switching dynamics, with performance comparable on glass and Kapton supports. Morphological and electrical characterizations revealed that channel thickness and uniformity critically influence resistive switching behavior. These findings demonstrate that aerosol jet printing enables scalable, low-material-consumption production of flexible organic memristive devices suitable for neuromorphic applications, potentially facilitating their integration into complex, energy-efficient bio-inspired circuits. Full article

Flexible strain sensors have attracted considerable attention in gait recognition owing to their ability to adhere directly to the skin near joints and transduce local deformation. In existing work, however, sensor placement and orientation are largely determined by anatomical experience, while multi-channel classification still relies on back-end digital processors, whose power consumption and latency constrain system practicality in wearable scenarios. This paper presents an integrated design path that proceeds from skin-mechanics theory through sensor-layout optimization to analog-domain front-end inference. On the layout side, the lines-of-non-extension (LoNE) theory is employed to convert the selection of sensor attachment angles from empirical judgment into a calculable mechanics problem; guided by the spatial course of LoNE in the ankle and knee regions, the positions and angles of the nine sensors are determined individually—channels perpendicular to the LoNE capture maximum strain, channels offset by 45 degrees supplement non-sagittal-plane information, and a channel aligned along the LoNE provides a near-zero-strain reference. On the circuit side, the mathematical equivalence between the weighted summation of a linear classifier and Kirchhoff’s current law (KCL) nodal current superposition is exploited to map the classification operation onto current aggregation in an analog circuit, yielding an in-sensor computing (ISC) front end in which the nine-channel weighted summation is completed in a single analog step. The sensors are fabricated by screen-printing a liquid-metal–polymer composite conductive ink onto a TPU film substrate, with a gauge factor RSD of $6.8\%$ and a tensile linearity $R^2>0.99$. Using walking, running, and stair descent as verification targets, the analog classifier reaches 99% accuracy at the circuit-level functional-verification stage. On real multi-subject data, it achieves $87.0\%\pm 8.4\%$ accuracy under intra-subject cross-session validation, with an analog-domain inference response faster than $100\mathsf{\mu }\mathrm{s}$. This design path is not bound to a specific joint or sensor material; when the layout methodology is extended to additional joint regions and the circuit architecture incorporates multiple outputs to cover more classification categories, the same workflow remains applicable, offering a promising low-power, lightweight technical solution for wearable motion monitoring. Full article

This paper presents a compact modified monopole antenna tailored for 5G NR on-glass automotive applications operating in the n78 band. The design overcomes 3D radiation pattern limitations inherent in conventional monopole and inverted-F antennas (IFAs). Unlike traditional structures where auxiliary branches serve impedance matching or grounding, this design integrates open- and short-circuited stubs with a coplanar waveguide (CPW) feed to eliminate discrete components. By utilizing a resonant mechanism distinct from IFAs, it enables precise control over the current distribution and phase on the radiator to achieve passive 3D beam shaping without active switches or arrays. This suppresses the inherent elevation null, enhancing upper-hemisphere radiation. A prototype operating from 3.3 to 3.6 GHz was fabricated on a flexible printed circuit (FPC) and verified on a glass substrate. This study focuses strictly on radiation characteristics at the antenna element level; to ensure a focused investigation on dielectric-antenna interactions, large-scale vehicle body scattering and full-scale vehicle integration are excluded from this scope. The results, including S-parameters, gain, total efficiency, and 3D patterns, demonstrate superior elevation coverage and comparable impedance performance under on-glass boundary conditions. The proposed methodology offers a high-feasibility, low-complexity, and cost-effective solution for passive 3D radiation control in on-glass 5G wireless links. Full article

High-power 355 nm ultraviolet (UV) lasers, leveraging their short wavelength, high photon energy, and high absorption across a broad range of materials, have become indispensable light sources for precision manufacturing, semiconductor processing, and laser direct imaging (LDI). In this paper, we demonstrate a high-power 355 nm UV laser system based on a narrow-linewidth polarization-maintaining (PM) Yb-doped fiber laser and cascaded frequency conversion. A single-frequency semiconductor laser is employed as the seed source, with its spectral linewidth broadened to 0.32 nm (full width at half maximum, FWHM) via phase modulation to suppress stimulated Brillouin scattering (SBS). Through a PM master oscillator power amplifier (MOPA) architecture, a maximum average output power of 899 W at 1064 nm is achieved with a beam quality factor of M² = 1.12 (M²_x = 1.11, M²_y = 1.13). By employing lithium triborate (LiB₃O₅, LBO) crystals for extracavity cascaded second-harmonic generation (SHG) and sum-frequency generation (SFG), a maximum green output power of 613.7 W at 532 nm is obtained, corresponding to a SHG conversion efficiency of 68.2%, and a maximum UV output power of 227.1 W at 355 nm is achieved, with a total conversion efficiency of 25.2%. At the maximum output power, the UV beam quality factors are M² = 1.16 (M²_x = 1.24 and M²_y = 1.09), and the power fluctuation is better than ±1.5% root-mean-square (RMS) over 8 h of continuous operation. These results indicate that the cascaded frequency conversion approach based on narrow-linewidth PM fiber lasers possesses the capability for further scaling to higher-power single-path high-brightness UV output and can provide high-brightness UV sources for applications such as flexible printed circuit (FPC) laser cutting, flat-panel display laser direct imaging, and semiconductor wafer scribing. Full article

Urban pipelines are essential infrastructure components in modern cities. Their curved and confined structures make sensing difficult to achieve. In conventional flexible sensing devices, pressure and bending signals often interfere with each other. To address this problem, we propose an integration strategy for multi-array sensors on flexible printed circuits. The approach integrates laser-induced graphene pressure sensors and bending sensors on a polydimethylsiloxane substrate with flexible printed circuits. This integration enables stable and reliable signal acquisition and the device shows good performance under pressure loading. It has high linearity (R² > 0.99), low hysteresis (2.68%), and a fast response time (~50 ms) in the range of 0–120 kPa. The sensing architecture is based on geometry-induced strain-field differentiation, which suppresses pressure–bending cross-interference and improves multimodal signal discrimination through structural design. Pressure mainly produces isotropic signals, while bending generates anisotropic strain signals. We test the device in simulated pipeline environments. Protrusion defects and corrosion defects generate different signal patterns. These differences allow clear defect identification. The device further supports spatial posture sensing and bending-state monitoring in complex curved pipeline conditions. Full article

SITSCAN CS is an original tactile system, which was primarily developed to investigate pressure distribution on uneven surfaces, e.g., chairs; however, due to its flexibility and modular conception, it can be utilized in other industrial or medical applications too. It consists of a flexible, PET-based PCB print-made sensing plate with active area of 50 × 50 cm with a placed matrix of 50 × 50 individual sensors. It uses the piezoresistive effect of the conductive ink layer as the transducing technology between the applied pressure and the output electrical signal. The tactile system further consists of control electronic circuits which process the measured data with up to 1000 fps with a maximal possible resolution 80 × 80 sensing points. The acquired data can be visualized, stored and further processed by means of the respective PC control program. The article describes the theoretical basis for the tactile system, as well as its development, construction, technical specifications and the testing process. Full article

This work presents the design and implementation of a flexible RFID tag based on a biocompatible and environmentally friendly conductive polymer, PEDOT:PSS, which is deposited onto a polyimide/fabric substrate using screen-printing techniques. The complete system consists of a dipole antenna based on PEDOT:PSS and a compact inductive metallic loop on a separate flexible printed circuit board (PCB) designed to match the capacitive impedance of a commercial RFID chip. The modular architecture, with the integrated circuit (IC) mounted on a reusable PCB substrate, shows efficient power transfer while allowing for easy disassembly, recycling, and consequently circularity of the PEDOT:PSS antenna and IC. By leveraging biocompatible materials and additive manufacturing processes, the proposed approach contributes to the advancement of sustainable and low-impact wireless technologies, addressing environmental concerns in next-generation electronics. Full article

Reliable potato quality monitoring during postharvest handling requires compact sensing systems that can acquire chemically relevant information while operating on irregular tuber surfaces. In this study, a Flexible Spectral Sensing Gripper (FSSG) was developed by integrating a low-cost 12-channel visible/near-infrared (Vis/NIR) spectral sensor array, electronic components, and an ESP32-S microcontroller onto a flexible printed circuit (FPC) substrate encapsulated with PDMS. By embedding the sensing units into the grasping interface, the FSSG enables conformal, multi-point spectral acquisition during potato handling, reducing optical-coupling uncertainty associated with unstable contact. Spectral reflectance data were collected from potato tubers, and dry matter content (DMC) and starch content (SC) were determined by standard chemical analysis as reference values. Multiple linear regression (MLR) and partial least squares regression (PLSR) models were compared under Norm, SNV, MSC, SNV-Norm, and MSC-Norm preprocessing conditions, and support vector machine (SVM) classification was used to distinguish healthy and artificially induced deteriorated samples. Normalization combined with MLR provided the best performance among the evaluated regression approaches, achieving cross-validation coefficients of determination ($R_{CV}^2$) of 0.847 and 0.817 and RPD values of 2.557 and 2.345 for DMC and SC, respectively. The SVM model achieved 98.67% accuracy for healthy versus artificially induced deteriorated potato samples. Overall, the FSSG demonstrates the value of combining gripper-integrated spectral sensing with interpretable chemometric modeling for potato quality screening. The FSSG enables real-time non-destructive quality prediction and disease-detected classification of potatoes, improves sorting accuracy and production efficiency, and provides general sensing solutions for controlled-environment agriculture, cold-chain logistics, and value-added processing of agricultural products. Full article

Background: Endovascular aortic aneurysm repair (EVAR) is considered the gold standard for the treatment of abdominal aortic aneurysms. However, the performance of stent-grafts used during this procedure may be affected by their structural design, particularly in anatomically challenging, tortuous iliac arteries. This study aimed to evaluate the hemodynamic performance of different stent-graft limb designs in an in vitro EVAR simulation using compliant three-dimensional (3D)-printed iliac artery models with controlled angulations. Methods: Four commercially available stent-grafts (Anaconda^®, Endurant II^®, Treo^®, Zenith Spiral-Z^®) representing different stent-strut configurations (including O-ring, Z-stent, and spiral designs) were deployed in compliant 3D-printed vascular phantoms simulating severe iliac angulations of 75°, 90°, and 105°. The models were incorporated into a pulsatile flow circuit, and pressure and flow velocity were measured proximally and distally to the angulated segment. Results: Across all tested angulations, the O-ring-based design demonstrated the most favorable hemodynamic performance. In particular, the Anaconda stent-graft showed the smallest pressure loss and the lowest increase in distal flow velocity, especially in the 90° and 105° models. These findings suggest that O-ring-supported structures provide greater flexibility and conformability in severely angulated iliac segments. Conclusions: In this controlled in vitro setting, stent-grafts with O-ring strut morphology better preserved flow conditions than other tested configurations in tortuous anatomy. These results suggest that stent-graft structural design may influence device behavior in challenging iliac anatomy under controlled in vitro conditions. These findings should be considered hypothesis-generating bench data and do not represent direct evidence for clinical device selection. Full article

In this study, a flexible, lightweight high-frequency underwater transducer (FT) was designed and fabricated. To ensure the flexibility and reliability of the transducer, a flexible piezoelectric composite material with a same-side electrode configuration and a perforated flexible printed circuit (FPC) were designed. First, finite element simulation analysis was performed on the flexible piezoelectric composites to optimize the structural parameters. Next, using a cutting and infusion method combined with reflow soldering, the piezoelectric composites and FPC were integrated to form a flexible sensing element. Finally, a flexible packaging process for the underwater transducer was investigated, resulting in a flexible underwater transducer with a thickness of only 5.3 mm. The results of underwater electroacoustic comparison tests show that the transmission and reception performance of the FT differs by less than 0.5 dB from that of conventional rigid transducers. This demonstrates that the flexible underwater transducer developed in this study not only possesses the advantages of flexibility and can be conformally mounted on curved surfaces but also achieves acoustic performance comparable to that of traditional rigid transducers, thereby providing new insights for the lightweight development of underwater transducers. Full article

Solid rocket motor (SRM) is a reliable and cost-effective aerospace propulsion system, by virtue of its advantages in terms of simple structure, long storage life, low cost, and ease of manufacturing. However, cracks and interfacial delamination may occur at the interface owing to the interface stress resulting from the complex service scenarios throughout the entire life cycle of the SRM. Therefore, it is crucial to monitor the interface stress for health assessment of the SRM. To achieve non-destructive in situ monitoring of interface stress, this paper proposes a novel embedded wireless flexible sensor (EWFS). Through theoretical analysis, the expression of the relationship between the input and output signals of EWFS is formulated. The response patterns of the output signals under different interface stresses are investigated. A prototype of the EWFS comprising the flexible printed circuit board (FPCB) and polydimethylsiloxane (PDMS) is fabricated, along with an interface stress-testing system established for experiments. The experimental results indicate that the EWFS exhibits a sensitivity of 27.2 mV·MPa⁻¹, a linearity error of 1.73%, a maximum hysteresis error of 2.67%, and a stability error of 0.023%. Full article

A dual-band flexible wearable MIMO antenna with two operating modes, namely low-frequency narrowband and high-frequency broadband, is proposed and investigated in this paper. The antenna is based on a polyimide (PI) flexible printed circuit (FPC) substrate and has a compact size (90 mm × 40 mm × 0.1 mm), enabling easy integration into helmet-mounted devices. The antenna elements are fed by a coplanar waveguide (CPW) and integrated with a ground decoupling structure, achieving an isolation of at least 23.4 dB between the two ports across the entire operating frequency band. In addition, the impedance-matching characteristics of the antenna under bending conditions and the Specific Absorption Rate (SAR) of this MIMO antenna in a 1 g human-tissue model at 3.7 GHz and 4.6 GHz were evaluated. The results indicate that the antenna’s key electromagnetic performance remains relatively stable under bending conditions, and the SAR values comply with international limit requirements, verifying its feasibility for application in head-worn terminals. With an impedance bandwidth of −10 dB, this antenna achieves dual-band coverage at 3.42–3.84 GHz (relative bandwidth of 11.6%) and 4.37–7.80 GHz (relative bandwidth of 56.4%), effectively meeting the requirements of 5G/6G communication frequency bands. Full article

To address the issue of significantly reduced coupling coefficient and limited transmission efficiency in traditional flat solenoid magnetic couplers within wireless power transfer (WPT) systems under horizontal lateral offset conditions, this paper proposes a design method for a concave flat solenoid coil magnetic coupler for engineering applications, aiming to achieve high misalignment tolerance. An equivalent model of the LCC/S compensation circuit is established, its output characteristics are analyzed, and the parameter configuration method for its resonant elements is derived. Secondly, from the perspective of winding arrangement, the mechanism by which the coil winding method, turn spacing, and port concavity angle affect the uniformity of magnetic field distribution and the retention rate of the coupling coefficient is analyzed in detail, and corresponding parameter trade-off and optimization methods are proposed. Subsequently, a simulation model of multiple configuration magnetic couplers is established based on Ansys/Maxwell, comparing the magnetic field distribution and coupling coefficient variation of different structures under horizontal offset conditions. The results show that the concave structure with a non-uniform arrangement and a port concavity angle of 30° can still maintain a high coupling coefficient and stable transmission performance under a maximum horizontal offset equal to 60% of the corresponding transmitter-side characteristic dimension. To achieve lightweight and integrated design, the receiver is designed with a flexible printed circuit board (FPC) coil structure, meeting the miniaturization and high power density requirements of low-to-medium power portable devices. Finally, a 100 W experimental prototype was built. Experimental results show that within an offset range of ±15 mm on the X-axis and ±30 mm on the Y-axis at the receiver, the system output voltage fluctuation is controlled within 4%, and the maximum transmission efficiency reaches 87.3%. These results verify the feasibility and practical applicability of the proposed magnetic coupler with high misalignment tolerance. Full article