Fast Response Research Articles

Electronic Effect Driven Specific and Sensitive Recognition toward GHB.

Precise detection of a trace substance that intrinsically possesses weak chemical activity and less-distinctive spatial structure is of great significance, but full of challenges, as it could not be effectively recognized via either an active covalent reaction process or multiple noncovalent interactions toward its simple structure. Here, the electronic-effect-driven recognition strategy was proposed to visually sense an illicit drug, γ-hydroxybutyric acid (GHB), which was treated as an analyte model due to its inherent simple structure. In particular, a sensing system composed of two probes substituted by the nitro (-NO2) and the hydrogen (-H), was constructed with the characteristic yellow coloring and blue fluorescence, as well as high sensitivity (0.586 ng/mL), fast response (0.2 s), and specific recognition, even in the presence of 22 interferents. In addition, a portable eyeshadow box-like sensing chip was fabricated and proven to be reliable and feasible in sensing GHB disguised in liquors for self-protection in a covert manner. Hence, this work developed an electronic-effect-driven modulation strategy of the recognition interaction between the probe and the analyte and, thus, would open up a new thought for detecting the analyte with weak activity and a simple structure, as well as propel the relevant application in real scenarios.

Flexible Nanofiber Pressure Sensors with Hydrophobic Properties for Wearable Electronics

In recent years, flexible pressure sensors have received considerable attention for their potential applications in health monitoring and human–machine interfaces. However, the development of flexible pressure sensors with excellent sensitivity performance and a variety of advantageous characteristics remains a significant challenge. In this paper, a high-performance flexible piezoresistive pressure sensor, BC/ZnO, is developed with a sensitive element consisting of bacterial cellulose (BC) nanofibrous aerogel modified by ZnO nanorods. The BC/ZnO pressure sensor exhibits excellent mechanical and hydrophobic properties, as well as a high sensitivity of −15.93 kPa−1 and a wide range of detection pressure (0.3–20 kPa), fast response (300 ms), and good cyclic durability (>1000). Furthermore, the sensor exhibits excellent sensing performance in real-time monitoring of a wide range of human behaviors, including mass movements and subtle physiological signals.

Pd–Ta alloy films hydrogen sensors based on partially coated π -phase-shifted FBG

A fiber-optic hydrogen sensor based on Pd–Ta alloy films partially coated π-phase-shifted fiber-Bragg grating (FBG) is proposed and experimentally demonstrated. Three types of Pd–Ta alloy films with different Ta content were prepared via co-sputtering technology. Material characterization shows the transformation of Pd–Ta alloy to amorphous phase with the increase of Ta content, and the phase transition between α-PdTaHx and β-PdTaHx is inhibited at 2 % hydrogen concentration. Hydrogen sensing experiments show that in-situ temperature compensation is possible with Pd/Ta films partially coated on π-phase-shifted FBG. Moreover, the sensor's hysteresis phenomenon was eliminated with an increase in Ta content due to the first-order phase transition. Pd–Ta alloy films hydrogen sensor with a Ta content of 27 % is capable of in-situ temperature compensation, fast response, good stability, and reliability.

A wirelessly programmable, skin-integrated thermo-haptic stimulator system for virtual reality

Sensations of heat and touch produced by receptors in the skin are of essential importance for perceptions of the physical environment, with a particularly powerful role in interpersonal interactions. Advances in technologies for replicating these sensations in a programmable manner have the potential not only to enhance virtual/augmented reality environments but they also hold promise in medical applications for individuals with amputations or impaired sensory function. Engineering challenges are in achieving interfaces with precise spatial resolution, power-efficient operation, wide dynamic range, and fast temporal responses in both thermal and in physical modulation, with forms that can extend over large regions of the body. This paper introduces a wireless, skin-compatible interface for thermo-haptic modulation designed to address some of these challenges, with the ability to deliver programmable patterns of enhanced vibrational displacement and high-speed thermal stimulation. Experimental and computational investigations quantify the thermal and mechanical efficiency of a vertically stacked design layout in the thermo-haptic stimulators that also supports real-time, closed-loop control mechanisms. The platform is effective in conveying thermal and physical information through the skin, as demonstrated in the control of robotic prosthetics and in interactions with pressure/temperature-sensitive touch displays.

N-doped TiO2/rGO: synthesis, structure, optical characteristics, and humidity sensing applications

In the current study, the effect of rGO ratio on the N-dopped TiO2 has been synthesized through sol–gel method. The prepared N-doped TiO2/rGO composites were examined for humidity sensing applications. The relationship between optical properties and the humidity sensing properties was studied. The structure, morphology, and bonding interaction have been examined using XRD, FT-IR, PL and HRTEM respectively. The average particle size as estimated from XRD and HRTEM was found to be about 9 nm. The optical properties have been studied using UV/ Vis. Spectroscopy. Further, optical parameters including refractive index and optical band gap energy have been estimated. The humidity sensing behavior of the resultant composites were evaluated in a wide range of humidity (7%–97% RH) at different testing frequencies. The optical band gap was found to be decreased as the amount of rGO increase. Among all prepared samples, both the optical parameters and humidity sensing experiments confirmed that the 0.5% rGO@N-dopped TiO2 sample is the best candidate for the humidity sensing applications. The best optimum testing frequency was demonstrated to be 50 Hz. The sensor demonstrates a fast response and recovery times of 13 s and 33 s with low hysteresis and large sensitivity. The humidity sensing mechanism was studied using complex impedance spectroscopy at different RH levels under testing frequency range from 50 Hz to 5 MHz and testing voltage of 1 VAC. The produced structure demonstrated a promising material for humidity measuring devices.

Binary Nematic Liquid Crystals Mixture with Enhanced Electro-Optics Properties for Photonic Applications

Purpose: In this work, we mix two simple nematic liquid crystals (NLCs) and investigated the binaryNLCs mixtures of 7CB/PCH5 of different mixing ratios. Methodology: The pure liquid crystals 7CB and PCH5 and binary mixtures of them of high temperature stability were thermally analyzed by differential scanning calorimetry. The mixture 7CB/PCH5:30/70 wt% has the highest thermal stability with a nematic-isotropic (N-I) transition temperature at 50oC. The electrooptic properties of 7CB, PCH5, and the mixture 7CB/PCH5:30/70 wt% at room temperature were also investigated using an amplitude modulated electric signal (1 kHz - 100 Hz) by increasing diving peak voltage from 0 V to 10 V. The threshold volage is relatively reduced for the binary mixture in comparison to that value for PCH5. In comparison to the pure LCs, the mixture 7CB/PCH5:30/70 wt% has the fastest response times of values 2.36 ms total time response, 0.41 ms rise time, and 1.95 ms fall time. It has also the highest contrast ratio. Moreover, it has a maximum measured transmission that is higher than those for PCH5 and 7CB by about 17 % and 8%, respectively, at a field strength of 2V/mm. Findings: The obtained results indicate that the electrooptic properties of PCH5 was improved when mixed with a proper ratio of 7CB, of lower cost, more stablity , and higher potential for photonic applications. Unique Contriburibution to Theory, Practice and Policy: This expermental study shows that simply by mixing two relatively low cost NLCs materials, one of high thermal stability and low electro-optic properties with other one of low thermal stability and better electro-optic properties; this would improve the stability, response, and transmition of the binary mixture. If the a suitable driving method is applied, without doping with other orgnic or inorganic matrial.

Broad‐range, high‐linearity, and fast‐response pressure sensing enabled by nanomechanical resonators based on 2D non‐layered material: β‐In2S3

AbstractTwo‐dimensional (2D) non‐layered materials, along with their unique surface properties, offer intriguing prospects for sensing applications. Introducing mechanical degrees of freedom is expected to enrich the sensing performances of 2D non‐layered devices, such as high frequency, high tunability, and large dynamic range, which could lead to new types of high performance nanosensors. Here, we demonstrate 2D non‐layered nanomechanical resonant sensors based on β‐In2S3, where the devices exhibit robust nanomechanical vibrations up to the very high frequency (VHF) band. We show that such device can operate as pressure sensor with broad range (from 10−3 Torr to atmospheric pressure), high linearity (with a nonlinearity factor as low as 0.0071), and fast response (with an intrinsic response time less than 1 μs). We further unveil the frequency scaling law in these β‐In2S3 nanomechanical sensors and successfully extract both the Young's modulus and pretension for the crystal. Our work paves the way towards future wafer‐scale design and integrated sensors based on 2D non‐layered materials.image

An optimal feedforward circuit with null audio susceptibility in feedback‐controlled buck converter

AbstractThe ability to manage abrupt disturbances in input supply voltage and sudden fluctuations in load represents a fundamental requirement for DC‐DC buck converters. While feedback control systems typically address such transients, certain applications necessitate even faster transient responses. This paper introduces an input voltage feedforward scheme (IVFS) integrated with voltage mode feedback controllers to enhance closed‐loop performance. Relevant transfer functions resulting from the inclusion of the feedforward circuit are derived, and an optimal condition for audio susceptibility nullification is identified. This scheme ensures an additional attenuation in magnitude of audio susceptibility, in contrast to the buck converter without feedforward. In the time domain, the incorporation of IVFS results in a 20% reduction in percentage overshoot for a 12‐8‐12 step in supply voltage. Additionally, for a 12‐15‐12 step, the percentage overshoot and settling time are completely eliminated. Various active and passive parasitics are included in modeling of the buck converter to aid in designing the feedforward and feedback controller. A Type‐III controller is employed as a feedback controller to assess the closed‐loop performance. A hardware prototype is built to demonstrate the efficacy of the proposed feedforward scheme. The implementation of the entire circuit is straightforward due to its requirement of only a few discrete components, namely, analog multiplier, and error amplifier.

Ultraefficient Ammonia Gas Sensors Based on Pt‐Loaded WO3 Nanobars

Herein, unloaded WO3 (WO3) and Pt‐loaded WO3 (Pt‐WO3) nanobars are successfully synthesized through simple hydrothermal and impregnation methods. X‐ray diffractometer analysis confirms the formation of a monoclinic WO3 structure. Surface analysis reveals that the Pt impregnation results in a significant increase in the specific surface area of WO3 nanobars. The gas‐sensing performance of sensors based on nanobars is measured toward ammonia (NH3) with varying NH3 concentrations at different operating temperatures. Compared with the pristine WO3 sensor, the Pt‐WO3‐based sensor with an optimal Pt content of 1 wt% exhibits a relatively low optimum operating temperature of 250 °C and a superior response of 960–50 ppm NH3. Furthermore, the Pt‐WO3‐based sensor also displays fast response, excellent NH3 selectivity to ammonia, moderate humidity dependence, and good stability. Therefore, the developed hydrothermal and impregnation methods could be a suitable alternative procedure for the synthesis of Pt‐WO3 nanobars useful for advanced NH3‐sensing applications.

Synthesis and application of a novel fluorescent probe based on benzothiazole for detection of hydrazine in real samples

ABSTRACT A novel fluorescence enhancement type probe 2-(1, 3-benzothiazol-2-yl)-5-(diethylamino)phenyl thiophene-2-carboxylate (PTN) for the detection of hydrazine (N2H4) was designed and synthesised. The fluorescence of the probe PTN solution increased dramatically upon the addition of N2H4 and its appearance changed from nearly colourless to dazzling blue. The simple structure and readily available fluorescent probe provide a novel approach for the quantitative detection of N2H4 in the linear range from 0 to 37.5 μM, with a detection limit down to 56 nM, fast response (within 5 min), strong anti-interference ability, easy operation (test paper), and a wide range of pH from 6 to 10. Furthermore, the probe PTN was able to detect N2H4 in actual water samples and image the exogenous N2H4 signal in colorimetric test strips and living zebrafish.

Dual Virtual Series–Parallel Emulation with Inertial Voltage Feedforward Controller for DC Microgrid

The impacts of nonlinearities from the I–V curve cause large oscillation and fluctuation occur in the PV attached DC voltage, BDC, load current, and solar current during low penetration of irradiance. PV system nonlinearities, weak damping, and lack of inertia causes lead to stability issues for DC microgrids. The stability of the system has been shifted to an unstable region during low penetration discussed for traditional controllers. In this paper, dual virtual series and parallel emulation with inertia feedforward controller have been introduced to mitigate fluctuations, initial DC notching, and damping issue for the DC microgrid system. This control method simulates the characteristics of the DC machine's robust and versatile method of DC/DC converter. The crossover frequency of the system has been reduced during low penetration with SPIEC which is not sufficient to prevent the oscillation and notching of the system. The system stability is enhanced through the proposed controller during low penetration analysed by pole-zero plots. During low penetration, the system pole has been shifted to a stable region towards the left side of the s-plane by the proposed controller to the traditional controller. The transient performance like oscillation, overshoot, and DC initial notching is resolved by the feed-forward current controller. However, the steady-state error is resolved by the voltage restoration controller. The proposed controller aims to enhance the power sharing among the energy storage and PV system under constant/variable loads. The oscillation, overshoot, and DC initial notching of the energy storage and PV have been discussed and made fast dynamic response by the proposed controller.

High-Performance CsPbBr3-Silicon Heterojunction Photodetectors Fabricated by Chemical Vapor Deposition

Abstract Inorganic perovskite cesium lead halide (CsPbBr3) has attracted extensive research attention due to its excellent photoelectric properties and long-term stability to water, oxygen, light and heat. In this work, high crystallinity CsPbBr3 microcrystals with different morphologies and grain sizes were synthesized by one-step chemical vapor deposition (CVD) on silicon (Si) wafers and silicon nanowires (SiNWs), respectively. Characterization results show that the CsPbBr3 microcrystals grown on SiNWs (CsPbBr3-SiNWs) display more compact and uniform morphologies than those grown on Si wafer (CsPbBr3-Si). Moreover, CsPbBr3-SiNWs exhibits higher detectivity and larger on/off ratio than CsPbBr3-Si, which are 5.1×1012 Jones over 3.4×1012 Jones, and 51.3 over 14.7, respectively. Furthermore, CsPbBr3-SiNWs shows a faster photo response with a rise/fall time of 0.22 s/0.28 s than 0.26 s/0.32 s in CsPbBr3-Si. In addition, the CsPbBr3-SiNWs photodetector maintained 90% of its original photocurrent after 60 days of exposure to air, showing excellent stability. These results strongly suggest a promising fabrication approach for constructing perovskite-based heterojunction optoelectronic devices with high performance and excellent stability.

High gain NiO/ZnO heterojunction photodiodes operated in Deep-ultraviolet region

Epitaxially matched (0001) Al2O3 single substrates are utilized to design p-n heterojunctions (p-NiO/n-ZnO) as they offer low defect density for device fabrication due to small lattice mismatches. Using the radio frequency sputtering technique, the NiO/ZnO thin film-based heterojunction has been fabricated by varying the n-type film's (ZnO) thickness for ultra-violet (UV) photodiode application. It has been investigated how different ZnO film thicknesses affect junction parameters and photoresponse properties. The high photosensitivity (∼ 104), enhanced current gain (∼ 105) and fast response obtained at very low UV intensity (0.62μW/cm2) at 300 nm wavelength are attributed to the internal gain mechanism (recombination tunnelling and space-charge limited current conduction with the remarkable effect of the presence of excess free oxygen) in these devices. The prepared heterojunction photodiode with high speed and deep-UV sensitivity can be a potential solution for visible blind UV detection.

Porous Dielectric Structure and Response Speed of Moisture Sensors

We made moisture sensors using α-Al2O3 films as porous dielectric materials deposited through the anodic spark deposition (ASD). In this study, a variety number of small pores has been studied to investigate the response speed of moisture sensors. Three different surface morphologies have been studied using scanning electron microscopy (SEM). Sample DM23 has the maximum number of small pores. Small pores are defined as pore size ranging from 40 nm to several hundred nm. Sample TA40 has the minimum number of small pores. Sample FW06 has the medium number of small pores. We found that the sensor made from dielectric material with the maximum number of small pores has the fastest response speed, and that from the minimum number of small pores has the slowest response speed either from high humidity to low humidity or from low humidity to high humidity.

Development of Grid-Forming and Grid-Following Inverter Control in Microgrid Network Ensuring Grid Stability and Frequency Response

This paper proposes a control strategy for grid-following inverter control and grid-forming inverter control developed for a Solar Photovoltaic (PV)–battery-integrated microgrid network. A grid-following (GFL) inverter with real and reactive power control in a solar PV-fed system is developed; it uses a Phase Lock Loop (PLL) to track the phase angle of the voltages at the PCC and adopts a vector control strategy to adjust the active and reactive currents that are injected into the power grid. The drawback of a GFL inverter is that it lacks the capability to operate independently when the utility grid is down due to outages or disturbances. The proposed grid-forming (GFM) inverter control with a virtual synchronous machine provides inertia to the grid, generates a stable grid-like voltage and frequency and enables the integration of the grid. The proposed system incorporates a battery energy storage system (BESS) which has inherent energy storage capability and is independent of geographical areas. The GFM control includes voltage and frequency control, enhanced islanding and black start capability and the maintenance of the stability of the grid-integrated system. The proposed model is validated under varying irradiance conditions, load switching, grid outages and temporary faults with fault ride-through (FRT) capability, and fast frequency response and stability are achieved. The proposed model is validated under varying irradiance conditions, load switching, grid outages and line faults incorporating fault ride-through capability in GFM-based control. The proposed controller was simulated in a 100 MW solar PV system and 60 MW BESS using the MATLAB/Simulink 2023 tool, and the experimental setup was validated in a 1 kW grid-connected system. The percentage improvement of the system frequency and voltage with FRT-capable GFM control is 69.3% and 70%, respectively, and the percentage improvement is only 3% for system frequency and 52% for grid voltage in the case of an FRT-capable GFL controller. The simulation and experimental results prove that GFM-based inverter control achieves fast frequency response, and grid stability is also ensured.

High‐Performance and High Bandwidth Electroadhesive Clutch Enabled by Fracture Mechanics and a Dielectric Nanoparticle‐Based High‐k Composite

AbstractClutches are integral components in robotic systems, enabling programming of system stiffness and precise control over a wide range of motion types. While different types of clutches exist, electroadhesive (EA) clutches present several key advantages, such as flexibility, low mass, low power consumption, simplicity, and fast response. Achieving high EA stress in EA clutches has remained a challenge, however, necessitating high voltage input or a large contact area to achieve the desired force. In this work, an EA clutch is proposed with a high EA stress achieved by taking fracture mechanics into account and using a high dielectric composite layer while still maintaining a comparable high switching speed to other dielectric‐based EA clutches. The maximum EA stress is observed to be 108.8 N cm−2, which is four times larger than what has been reported previously among dielectric‐based EA clutches at room temperature. This high EA stress clutch can facilitate miniaturization and lower the operating voltage as well as extend to high load capacity applications. The proposed approach holds promise for advancements in various domains, including haptics (both kinesthetic and cutaneous), exoskeletons, walking robots, and other systems that require compliance, low mass, and precise force control.

Buck converter with switched capacitor charge compensation for fast transient response

Buck converter with switched capacitor charge compensation for fast transient response

Performance optimization and testing of a novel energy coupled actuated high-speed valve based on peak-and-hold driving strategy

High-speed on/off valve acts as critical enabling component of digital hydraulics, which has been challenging the traditional hydraulic system by providing efficient and effective hydraulic control solutions. The high-speed on/off valve that ideally fits the digital hydraulic system is expected to achieve fast response and long stroke with affordable energy consumption. This not only requires developing advanced actuation mechanism but also demands extensive study on the driving strategy. This study focuses on investigating the Peak-and-hold driving strategy applied to a novel high speed on/off valve-energy coupling actuated valve (ECAV), in order to achieve target performance with optimized energy consumptions. This work has developed an electro-mechanical coupled physics model based on commercial finite element solver COMSOL. This model helps to investigate the performance of ECAV under different peak-and-hold driving parameters and thereby recommend the optimal peak-and-hold driving strategy. Then, the experimental testing on the prototype ECAV has been conducted to validate the simulated performances. The measurement results showed that the prototype ECA using the optimal peak & hold solution demonstrated significant advantage in energy saving targeting at response of 10 ms for 1.5 mm stroke, especially compared to a typical step input signal.

Research on improved active disturbance rejection control strategy for hydraulic-driven Stewart stabilization platform

Purpose In response to the severe lag in tracking the response of the Stewart stability platform after adding overload, as well as the impact of nonlinear factors such as load and friction on stability accuracy, a new error attenuation function and a parallel stable platform active disturbance rejection control (ADRC) strategy combining cascade extended state observer (ESO) are proposed. Design/methodology/approach First, through kinematic modeling of the Stewart platform, the relationship between the desired pose and the control quantities of the six hydraulic cylinders is obtained. Then, a linear nonlinear disturbance observer was established to observe noise and load, to enhance the system’s anti-interference ability. Finally, verification was conducted through simulation. Findings Finally, stability analysis was conducted on the cascaded observer. Experiments were carried out on a parallel stable platform with six degrees of freedom involving rotation and translation. In comparison to traditional PID and ADRC control methods, the proposed control strategy not only endows the stable platform with strong antiload disturbance capability but also exhibits faster response speed and higher stability accuracy. Originality/value A new error attenuation function is designed to address the lack of smoothness at d in the error attenuation function of the ADRC controller, reducing the system ripple caused by it. Finally, a combination of linear and nonlinear ESOs is introduced to enhance the system's response speed and its ability to observe noise and load disturbances. Stability analysis of the cascade observer is carried out, and experiments are conducted on a six-degree-of-freedom parallel stable platform with both rotational and translational motion.

Liquid crystalline elastomer self-oscillating fiber actuators fabricated from soft tubular molds.

The self-oscillation of objects that perform continuous and periodic motions upon unchanging and constant stimuli is highly important for intelligent actuators, advanced robotics, and biomedical machines. Liquid crystalline elastomer (LCE) materials are superior to traditional stimuli-responsive polymeric materials in the development of self-oscillators because of their reversible, large and anisotropic shape-changing ability, fast response ability and versatile structural design. In addition, fiber-shaped oscillators have attracted much interest due to their agility, flexibility and diverse oscillation modes. Herein, we present a strategy for fabricating fiber-shaped LCE self-oscillators using soft tubes as molds. Through the settlement of different configuration states of the soft tubes, the prepared fiber-shaped LCE oscillators can perform continuous rotational self-oscillation or up-and-down shifting self-oscillation under constant light stimuli, which are realized by photoinduced repetitive self-winding motion and self-waving motion, respectively. The mechanism of self-oscillating movements is attributed to the local temperature oscillation of LCE fibers caused by repetitive self-shadowing effects. LCE self-oscillators can operate stably over many oscillating cycles without obvious performance attenuation, revealing good robustness. Our work offers a versatile way by which LCE self-oscillators can be conveniently designed and fabricated in bulk and at low cost, and broadens the road for developing self-oscillating materials for biological robotics and health care machines.