Search Results (5,423)

Carbon-based materials, including graphene, carbon nanotubes, laser-induced graphene, and pyrolyzed glassy carbon, are widely used in sensing applications due to their high conductivity, large surface area, and tunable surface chemistry. Meanwhile, microfluidic systems enable precise fluid handling, reduced sample consumption, and enhanced analytical performance through improved mass transport and device miniaturization. The integration of carbon-based materials with microfluidic platforms has enabled the development of compact, portable, and highly sensitive devices for water monitoring. This review summarizes recent advances in carbon-based microfluidic sensors for water monitoring applications. Key carbon materials and their sensing mechanisms, particularly electrochemical transduction, are discussed. Various microfluidic integration strategies, including paper-based devices, polymer-based devices, MEMS-based systems, and flexible platforms, are highlighted, with emphasis on mass transport enhancement and overall system performance. Representative recent advances in carbon-based microfluidic sensors for water monitoring, including the detection of heavy metal ions, nutrients, and emerging contaminants, are reviewed. Finally, challenges related to scalable manufacturing, long-term operational stability, biofouling/surface fouling, and reproducible system integration are discussed, together with future perspectives on intelligent carbon-based microfluidic platforms featuring AI-assisted analytics, sense-response functionality, and self-healing and dynamic antifouling capabilities for water monitoring. These advances are expected to enable real-time, low-cost, and field-deployable water monitoring systems for environmental protection and public health management. Overall, this review highlights the critical role of integrating carbon-based sensing materials with microfluidic engineering in advancing next-generation water monitoring technologies. Full article

Smart manufacturing requires real-time monitoring of multidimensional forces at the interface between the tool and workpiece in computer numerical control (CNC) machining. In this study, an innovative iKIT wireless extrasensory toolholder is introduced that is capable of high-fidelity, in situ, high-frequency sensing and monitoring of the cutting force, torque, and two-way bending moments. The hardware design of the system is outlined, highlighting a high-bandwidth miniature wireless transmission method and noncontact power supply and energy storage solution suitable for rotating machining environments. To assess the system performance, comprehensive milling tests were performed on aluminum alloy materials, and the relationship between the process parameters and changes in multidimensional mechanical loads was thoroughly examined. The experimental findings demonstrate that the smart toolholder detects precisely how parameter variations affect the loads. Multidimensional mechanical signals (torque and two-way bending moments) show a strong positive correlation with the feed rate and axial depth of cut, confirming the impact of the material removal rate on the system loads. Conversely, these signals are negatively correlated with spindle speed, accurately reflecting the effects of thermal softening and a reduced friction coefficient in aluminum alloys during high-speed cutting. This study not only offers a dependable hardware framework for integrating miniaturized sensors into toolholders, but also delivers accurate data to support digital twin models and adaptive control in machining processes. Full article

Microrobots navigating the human body require biocompatible actuators capable of functioning in physiological fluids. The microalga Euglena gracilis offers precise phototactic control; however, its operational stability in simulated physiological environments remains unproven. Here, we report that a stepwise acclimation process preserves the robotic functionality of E. gracilis in 100% phosphate-buffered saline (PBS), 100% fetal bovine serum (FBS), and a NaCl solution at a concentration equivalent to PBS (137 mM). We compared direct transfer against a graduated adaptation protocol, evaluating morphology, swimming speed, motility rate, and phototaxis. Direct transfer to each medium caused near-total immobilization, whereas stepwise acclimation retained motility. Acclimated cells exhibited size reduction (miniaturization) while maintaining their characteristic eccentricity. These adapted cells sustained a negative phototactic response among the remaining motile population, supporting optical controllability despite reduced swimming speed. These results indicate that stepwise acclimation allows E. gracilis to retain partial motility and phototactic controllability under simulated physiological saline conditions, and that the observed miniaturization and preserved photo-responsiveness may be useful features for future biohybrid microrobotics. Full article

Gel-based materials are emerging as lightweight, mechanically compliant, and electromagnetically tunable platforms for next-generation antennas, electromagnetic interference (EMI) shields, microwave absorbers, and radomes. This review summarizes recent progress in hydrogel-, aerogel-, ionogel-, organohydrogel-, and xerogel-based electromagnetic materials, with emphasis on how network structure, pore architecture, solvent phase, and functional fillers regulate permittivity, conductivity, impedance matching, and attenuation. The device-level roles of gels are discussed in miniaturized and reconfigurable antennas, absorption-dominated shielding systems, broadband microwave absorbers, high-temperature wave-transparent radomes, and metamaterial, energy-harvesting, and bioelectronic systems. Particular attention is paid to the mechanisms of dipolar relaxation, ionic conduction, interfacial polarization, conduction loss, magnetic loss, and multiple scattering. Finally, key challenges are identified, including hydrogel dehydration and freezing, aerogel fragility, ionogel cost and leakage, limited long-term reliability, and the lack of standardized performance metrics. Future directions toward durable, scalable, multifunctional, and device-integrated gel-based electromagnetic materials are proposed. Full article

Moisture content is a critical parameter during processing and storage. Although conventional microwave-based moisture detection methods enable rapid and non-destructive measurement, they are often hindered by high cost and susceptibility to design limitations and environmental fluctuations. In this study, a partial ground plane technique combined with a beveled partial ground and corner truncation topology is employed to enhance antenna architecture. By accounting for the nonlinear relationship between antenna dimensions and operating bandwidth, the bandwidth is significantly broadened without increasing the antenna footprint. A novel microstrip antenna is developed using low-cost epoxy resin (FR4) as the substrate. To address the instability and narrow bandwidth often associated with microstrip antennas, an electromagnetic simulation model was constructed using HFSS. This model characterizes the relationship between dimensional parameters and bandwidth, facilitating antenna optimization. Simulation results demonstrate that the operating frequency remains stable at 915 MHz, while the operating bandwidth is expanded from 0.91–0.92 GHz to 0.6–1.1 GHz without increasing the antenna size, thereby satisfying the requirements for material moisture detection. The proposed antenna is integrated into the moisture detection circuit developed in this study, and its stability is evaluated under various environmental conditions. Results indicate that the novel microstrip antenna achieves high detection performance and is robust against environmental variations, while offering reduced fabrication costs. This study provides a new direction for the miniaturization and cost reduction of moisture detection systems. Full article

The contribution of this paper is to propose the design and experimental validation of split-type dual- and tri-band bandpass filters (BPFs) based on highly miniaturized substrate-integrated coaxial cavities (SICCs). The proposed split-type multiband filter design achieves exceptional circuit-area efficiency within the SIW-related (substrate-integrated waveguide) split-type filter category. The size-reduced SICCs are fabricated using two substrates of different thicknesses. The coupling matrix method is employed to synthesize the responses of the example dual- and tri-band filters. The proposed dual-band filter achieves a circuit size of 0.17 λ_d × 0.17 λ_d, with insertion losses of 0.78 and 0.89 dB for the two passbands, and isolation between the passbands exceeding 15 dB. For the tri-band filter, the circuit size is 0.27 λ_d × 0.34 λ_d, with the insertion losses of 0.96, 2.6, and 1.21 dB across the three passbands, accompanied by similarly effective isolation. Experimental results validate the circuit designs and performance, demonstrating strong agreement between measured and simulated data. Full article

In this study, an ecofriendly microfluidic microbial biocathode electrolysis cell is developed for hydrogen production. Low-cost microbial catalysts are employed on single-walled carbon nanotube cathodes instead of noble metal (platinum) catalysts. The channel layer for the electrolyte flow is fabricated from polydimethylsiloxane and coated with Parylene C to minimize oxygen permeability. A miniaturized electrolysis cell is constructed by depositing electrodes onto a glass substrate and bonding them to a polydimethylsiloxane channel layer via plasma surface treatment. The establishment of the biocathode during the start-up procedure is analyzed, and the hydrogen production performance of the biocathode microbial electrolysis cell (MEC) is evaluated under various applied voltages and electrolyte flow rates. At higher applied voltages and optimal flow rates, biofilm formation is well-developed, resulting in a peak hydrogen production rate of 14.8 m³ H₂ m⁻³ d⁻¹. The developed MEC biocathode demonstrates significant performance, achieving a current density of 0.22 A m⁻², corresponding to 69% of that of a platinum-catalyzed cathode MEC, while exhibiting a substantially longer operating duration of 12 h. These results demonstrate the potential to overcome the inherent limitations of biocathodes, thereby addressing the high cost and low durability of conventional platinum-catalyzed MECs. Compared with conventional MEC systems, the proposed microfluidic configuration enables membraneless operation with reduced internal resistance and rapid biofilm formation, demonstrating its potential as a compact and cost-effective platform for biohydrogen production. Full article

Magnetic fluid tilt sensors possess excellent shock resistance and strong adaptability to extreme environments, making them a highly promising new type of angle measurement device. This paper proposes a new miniaturized tilt sensor structure composed of a central permanent magnet, restoring magnets at both ends, magnetic fluid, and a Hall element. The inner diameter of the new sensor is only 8 mm and the overall length is 110 mm. The numerical electromagnetic field simulation model of the tilt sensor was established using COMSOL v6.1. Simulation analyses were conducted on the magnetic flux density distribution of the permanent magnet and the restoring force between permanent magnets. The structural dimensions of the central permanent magnet and restoring magnet were determined through analysis based on the simulation results. Subsequently, static and dynamic performance tests were conducted on the tilt sensor. The results demonstrate that the novel tilt sensor delivers excellent repeatability and low hysteresis error. The measurement range of the sensor is −35° to +35°, with a repeatability error of 0.46%, hysteresis error of 0.71%, linearity of 4.52%, and static sensitivity of 32.5 mV/°, as well as good dynamic response stability. Full article

We present in this paper a low-power impulse-radio ultra-wideband (IR-UWB) transmitter architecture for neural implants. It features a duty-cycled phase-locked loop (PLL) and a co-designed compact fractal antenna. To suppress the carrier frequency drift inherent in open-loop ring oscillators while maintaining ultra-low power consumption, a hybrid PLL-oscillator upconversion scheme integrated with a switch-controlled voltage-holding module is proposed. Operating at a 10% duty cycle, the PLL consumes merely 90 $\mu$W and achieves a locking frequency of 4.25 GHz with a peak-to-peak jitter of 2.14 ps. Furthermore, to eliminate the bulky output matching network, an 8 mm × 10 mm coplanar-waveguide-fed fractal antenna is co-designed to present the conjugate impedance required by the power amplifier output, significantly advancing the miniaturization and energy efficiency of the neural implant. The complete transmitter was fabricated in TSMC 40 nm CMOS, with a supply voltage of 1.0 V, and in vitro wireless experiments through 18 mm of porcine tissue validated the design with a total power consumption of 0.58 mW. Full article

The passive nature of gravity matching navigation, along with its concealment and freedom from error accumulation over time, is essential for reducing inertial navigation system (INS) errors and enabling high-precision autonomous underwater positioning. The current paper provides a systematic review of major technologies in the field, including the development of underwater gravimeters, construction of gravity reference maps, suitable area selection, optimization of matching algorithms, gravity–inertial integrated navigation, and path planning. We discuss hardware developments, including classical sensors, gradiometers, and quantum sensors, as well as methodological concepts such as multi-source sensor data fusion, intelligent area selection, algorithm optimizations, connections between multiple filters, and intelligent trajectory design. Despite a relatively well-developed technical infrastructure, several bottlenecks remain, including the low engineering maturity of high-end hardware, poor algorithmic performance under extreme conditions, over-reliance on simulation, and weak module integration. Future research should focus on hardware miniaturization, cross-domain intelligent adaptive algorithms, multi-condition real-world validation, and the transition from loosely coupled to tightly coupled architectures to achieve improved accuracy and robustness. Full article

Text entry remains a bottleneck for productivity-oriented Virtual Reality (VR), especially in scenarios where optical hand tracking is unstable because of self-occlusion, poor lighting, or out-of-view interaction. We present SlideRing, a dual-thumb wearable text-entry method that senses thumb-to-finger micro-gestures with two miniature Inertial Measurement Units (IMUs). SlideRing defines a 30-command interaction space from two hands, three target fingers, and five gesture types, then maps these commands to a full alphabetic keyboard through two complementary strategies: an ergonomic layout optimized for low movement cost and a QWERTY-compatible layout optimized for learnability. To decode subtle inertial signals, we design a dual-stream recognition model with a Statistical Feature Encoder, a Temporal Feature Encoder, and a context-aware gating module for joint finger–action classification. In offline evaluation, the model reaches 96.5% target-finger accuracy and 94.2% action-type accuracy. In a five-day text-entry study, the ergonomic layout improves from 7.43 to 15.75 words per minute (WPM), while the QWERTY-compatible layout improves from 10.55 to 15.25 WPM. The ergonomic layout reduces physical demand, whereas the QWERTY-compatible layout lowers initial mental load. These results suggest that IMU-based thumb-to-finger input has the potential to provide robust, low-visual-demand text entry for constrained VR environments. Full article

Understanding indoor and outdoor airborne organic mixtures, including semi-volatile organic compounds (sVOCs), remains challenging as quantitative monitoring is often costly and difficult to scale across buildings and individuals. Here we present a low-cost, miniaturised passive sampler-based methodology for static and wearable deployment to generate time-integrated chemical fingerprints and source prioritisation. New sampler devices containing replicate 9 mm sorbent discs (Tenax^® TA and/or polydimethylsiloxane) were deployed for 28 days in indoor (kitchen, bedroom) and outdoor (roadside) environments and worn by five participants; extracts were analysed by liquid extraction and gas chromatography–mass spectrometry (GC-MS) using conservative, transparent criteria for tentative compound identification. Across the household deployments, 52 compounds met inclusion criteria and distinct room-specific and outdoor chemical signatures were observed. Wearable deployments also produced differentiable chemical profiles, with greater similarity among co-inhabitants, but still could differentiate co-habitant activities based on exposure. These results demonstrate the feasibility of using miniature passive samplers to obtain reproducible, information-rich profiles that can help discriminate environments and exposure scenarios. Full article

Soft robots built from compliant materials and deformable structures are increasingly used in medical intervention, wearable assistance, delicate manipulation, and environmental exploration, where conventional rigid robots are limited by high mechanical impedance and poor morphological adaptability. However, their transition from laboratory prototypes to deployable systems remains constrained by coupled bottlenecks in materials, actuation, sensing, modeling, control, energy supply, and manufacturing. This review summarizes recent advances in soft robotics through an evaluative framework covering actuation and materials, modeling and simulation, control strategies, multimodal sensing, and representative applications. Instead of treating these topics as independent descriptions, we compare the underlying mechanisms, measurable performance indicators, strengths, limitations, and application boundaries. Three conclusions emerge. First, no single actuation strategy can simultaneously maximize output force, response speed, energy efficiency, durability, miniaturization, and untethered operation. Second, high-fidelity continuum models improve physical accuracy but remain difficult to use for real-time control, whereas reduced-order and data-driven models improve efficiency at the cost of generalization, interpretability, or contact fidelity. Third, practical soft robots will depend on system-level integration of embedded sensing, physics-informed learning, robust control, reliable materials, and scalable fabrication. Future progress should therefore prioritize standardized benchmarks, lifecycle reliability, energy-autonomous operation, and task-specific comparisons with rigid robotic systems. Full article

This paper presents a corrugated Vivaldi antenna architecture targeting sub-6 GHz and millimeter-wave frequency bands for 5G CubeSat applications, combining experimental validation at sub-6 GHz with a simulation-based scaling study at 26.5 GHz. Existing CubeSat antenna designs either target a single frequency band or rely on complex metamaterial structures incompatible with nanosatellite fabrication constraints. To address this gap, a single-element corrugated Vivaldi antenna measuring 90 mm × 80 mm is designed, fabricated on FR-4 substrate, and experimentally validated at 3.5 GHz, confirming a wide impedance bandwidth of 2.75 GHz and a peak gain of 9.6 dBi. The strong agreement between CST Studio Suite simulations and measurements validates the electromagnetic solver configuration, which is subsequently applied, as a simulation-based design study, to a geometrically scaled version on Taconic RF-60A substrate operating at 26.5 GHz. The miniaturized single-element version achieves a simulated 17 GHz ultra-wideband response and 6 dBi gain in a 7.32 mm × 6.32 mm footprint. Two- and four-element array configurations at 26.5 GHz demonstrate systematic simulated gain progression to 9 dBi and 13 dBi, respectively, with beamwidth narrowing from 49${}^{\circ }$ to 30${}^{\circ }$. All 26.5 GHz designs are simulated with lossy copper metallization ($\sigma =5.8\times {10}^7$ S/m) and are entirely simulation-based; experimental mmWave validation is a designated target for future work. These results establish a validated design and scaling roadmap for corrugated Vivaldi antennas spanning sub-6 GHz and millimeter-wave bands, offering a cost-effective and CubeSat-compatible solution for high-data-rate inter-satellite communication links. Full article

The final stage of urban logistics does not end at the building entrance but continues within complex, vertically structured indoor environments, where conventional ground-based delivery systems face limitations in efficiency, flexibility, and scalability. This study introduces the concept of last-meter delivery, defined as unmanned aerial vehicle (UAV)-enabled transport from the building envelope to the recipient within global navigation satellite system (GNSS)-denied, building-regulated indoor space, and systematically reviews the literature from two traditionally separate domains: indoor-UAV operation in GNSS-denied spaces, and outdoor-UAV-based logistics. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, 297 studies are synthesized through a two-stream thematic synthesis. The review makes three contributions. First, a unified analytical framework is developed across four dimensions (spatial mobility, logistical capability, social acceptance, and operational coordination) through which the two bodies of literature are shown to be largely complementary, with the gaps in one stream coinciding with the strengths of the other. Second, indoor aerial delivery is found to be subject to a distinct set of operational constraints, including micro-scale navigation accuracy, strict geometric safety envelopes, close human–UAV interaction, and privacy sensitivity, implying that indoor transport-UAVs cannot be realized through simple miniaturization of outdoor platforms but require precision-oriented, human-centric, and building-aware design. Third, the four dimensions are translated into a building-management-oriented indicator framework covering spatial compliance, handover standardization, building information modeling (BIM) integration, occupant consent, and liability allocation, reframing last-meter requirements in terms that are actionable for building planners and facility managers. By framing these challenges within the last-meter perspective, this review identifies the gap between current last-mile theories and emerging in-building aerial logistics and provides a structured foundation for future research. Full article