High Response Time Research Articles

Plasmonic Pt nanoparticles triggered efficient charge separation in TiO2/GaN NRs hybrid heterojunction for the high performance self-powered UV photodetectors

Solar radiation, especially the UV-A light rays (320–400 nm) exposure causes severe health hazard such as skin-related cancer and premature aging. Owing to the significance of UV-A photodetection, a high-performance UV-A photodetectors (PD) with high sensitivity, large detectivity and fast response time, have attracted great attention in various optoelectronic applications. Herein, we report a self-powered (SP) UV PD based on Pt nanoparticles (NP) decorated TiO2/GaN nanorods (NRs) hybrid heterojunction. The proposed Pt NP@TiO2/GaN NRs hybrid device demonstrates pronounced photoelectric performances including a large responsivity (44.6 A/W), superior detectivity (1.57 × 1014 Jones) and high electronic quantum efficiency (8.65 × 103 %) under the UV light intensity (λ = 382 nm, 1.32 mW/cm2) at zero bias, which are relatively much higher as compare to the pristine counterparts. In addition, the hybrid PD showed a short response/recovery times of 180 ms/200 ms, with a remarkable reproducibility and long-term stability towards the UV light. The impressive photoresponse properties of the hybrid SP PD are ascribed to the large photon absorption endorsed by the localized surface plasmonic resonance effect of Pt NP and the adequate built-in potential at the TiO2 and GaN NRs heterojunction interface, which further endows the effective separation and transport of photogenerated charge carriers. Furthermore, the plausible mechanism for the high-performances of hybrid UV PD is demonstrated in detailed using the energy band diagram. Our work reveals that the integral advantages of hybrid heterostructures, have a significant potential for the practical applications of advanced optoelectronics and high-performance SP UV-A PD.

Quartz crystal based sensor head design and analysis for robot torque sensor application

Background: In recent years, with the gradual development of robot human-computer interaction, robots need to meet the precise control of more complex motion. Torque sensors play an important role. The traditional strain gauge sensor uses a metal strain gauge as the sensitive element, which means that the sensor has a slow response, low resolution and can easily be affected by external signal noise. Aiming at these deficiencies of strain gauge sensors, a sensor with cutting quartz square sheet as the sensor head is proposed. Methods: In order to study the application of quartz square sensing head in the sensor, firstly, COMSOL (5.6) simulation modeling is used to obtain the stress relationship between square quartz sheet and circular quartz sheet. Then the calculation formula of the force frequency coefficient of the circular quartz sheet is modified to obtain the calculation formula of the force frequency coefficient of the square quartz sheet, and the feasibility of the formula is verified by practical experiments. Next, the theoretical simulation and experimental research on the buckling limit force of quartz wafer are carried out, and the formula of buckling limit force in the process of quartz wafer installation is modified. Finally, the designed sensitive head is installed on the elastomer structure for verification. The frequency signal is collected by SGS-THOMSON Microelectronics 32 with a sampling rate of 1000Hz. Results: The main performances of the sensor are range 150nm, sensitivity 350Hz / nm, linearity 98.14%, hysteresis 0.51%, repeatability 98.44%, resolution 0.02%. Conclusions: As the sensitive unit of the torque sensor, the designed quartz wafer can obtain high response time and high resolution, solve the problems of low resolution and slow response time of the traditional strain gauge torque sensor, and reduce the use cost of the sensor.

Biosensor based on coupled enzyme reactions for determination of arginase activity

The determination of the enzymatic activity requires constant and reproducible measuring conditions, therefore highly stable potentiometric biosensor operating on the basis of coupled enzyme reactions is proposed for arginase activity determination. Glassy carbon electrode was covered with polyazulene ion-to-electron transducing layer, which ensured improved stability of the prepared sensor. The sensor’s selectivity was obtained by applying NH4+-selective membrane on the transducing layer, which was further biofunctionalized with urease via covalent immobilization. The immobilized urease served as an auxiliary enzyme in the arginase-urease coupled enzyme assay. Thanks to obtained high stability (low drift coefficient ∼ 0.9 mV/h) and short response time (36 s), the developed urea biosensor enabled continuous monitoring the coupled enzyme reactions indirectly, through measurement the ammonium ion concentration. Arginase activity and Michaelis-Menten constant for arginine-arginase pair under defined experimental conditions, in particular constant concentration of manganese ions, was determined. Mathematical description of the coupled enzyme reactions kinetics is discussed and used to analyse the reactions with auxiliary enzyme immobilized on the electrode surface. The proposed method of determining arginase activity with use of highly stable potentiometric urease-based biosensor, allows obtaining results in the units of absolute arginase activity.

Nano-Patterned Ionogel Film for High-Sensitivity and Recyclable Flexible Pressure Sensor

Flexible pressure sensors have drawn tremendous attention in the past decades due to their widely advanced applications in electronic skin, intelligent robots and wearable devices. Most existing pressure sensors are developed based on capacitive sensing mechanism, but the sensitivity of such sensors still need to be improved. Herein a high-sensitivity pressure sensor was developed based on the P(VDF-HFP)/[Emim][BF₄] ionogel film. The ionogel film has the characteristics of good mechanical flexibility, good ionic conductivity, high dielectric constant and uniformed nanocone array structure, so the flexible pressure sensor which incorporates it as the dielectric layer shows a high sensitivity (22.38 kPa^−1 within 0–3 kPa, and 15.17 kPa^−1 within 3–15 kPa), fast response (0.29 s) and relaxation (0.16 s) time and good long-term stability. The good solubility of the P(VDF-HFP) copolymer in acetone and the non-crosslinking of the [Emim]^+ and [BF₄]^− within the copolymer network give the ionogel the ability to be recycled, thus endowing the critical component of the pressure sensor with 100% recyclability of structure and function. In addition, the sensor was successfully applied to identify fingertip force and map the pressure distribution of different objects, demonstrating that the pressure sensor can be used as part of wearable devices and human–machine interfaces to sense pressure.

Energy-Efficient Cluster Formation in IoT-Enabled Wireless Body Area Network.

Wireless sensor network is widely used in different IoT-enabled applications such as health care, underwater sensor networks, body area networks, and various offices. A sensor node may face operational difficulties due to low computing capacity. Moreover, mobility has become an open challenge in the healthcare wireless body area network that is highly affected by message loss due to topological manipulation. In this article, an enhanced version of the well-known algorithm MT-MAC is proposed, namely DT-MAC, to ensure successful message delivery. It considers node handover mechanism among virtual clusters to ensure network integrity and also uses the concept of minimum connected dominating set for network formation to achieve efficient energy utilization. It is then compared with well-known algorithms such as MT-MAC. The simulation results show that an increase in little latency of roughly 3 percent in using the proposed protocol improves the MT-MAC's packet delivery by 13–17 percent and the response time by around 15 percent. Therefore, the algorithm is best fitted for real-time applications where the high packet delivery and response time are required.

PtTe2-based terahertz photodetector integrated with an interdigital antenna

Two-dimensional materials such as graphene and black phosphorus have attracted considerable attention owing to their peculiar properties and unique applications, serve also as potential candidates for terahertz (THz) photodetection. Recent works have shown that the responsivity and sensitivity of photodetectors have been improved largely. However, there are still a few bottlenecks imposed by the fundamental limits of optical properties that impede further improvement of THz photodetection. With the continuous exploration of two-dimensional materials, especially the topological quantum states of the Dirac semimetals, which possesses uniquely non-linear optical effects, chiral anomaly and other quantization phenomena, provide a new platform for the study of fast and efficient THz photodetection. In this work, we experimentally demonstrated THz photodetectors based on Dirac semimetal-PtTe2 integrated with an interdigital antenna, which gives rise to high responsivity and fast response time in the meantime at room temperature. The achieved photocurrent responsivity is over 62 mA/W (0.12 THz) in the self-powered mode, with the noise equivalent power (NEP) is less than 60 pW/Hz0.5 (0.12 THz), and the performance has been significantly improved by applying finite voltage. Our results provide a new approach for developing high-performance THz photodetectors based on type-II Dirac semimetals.

Overall High-Performance Near-Infrared Photodetector Based on CVD-Grown MoTe2 and Graphene Vertical vdWs Heterostructure

Two-dimensional (2D) materials, such as graphene and transition metal dichalcogenides (TMDCs), are highly appealing in the fields of electronics, optoelectronics, energy, etc. Graphene, with high conductivity and high carrier mobility, is an excellent candidate for transparent electrodes. TMDCs have remarkably strong light absorption in the range of visible to infrared wavelength. High-performance photodetectors are expected to achieve through the combination of graphene and TMDCs. Nowadays, near-infrared (NIR) photodetectors play significant roles in many areas. MoTe2 with bandgap energy of about 1.0 eV in its bulk form is a promising material for cost-saving NIR photodetectors. Thus far, only a few of the reported studies on NIR photodetectors built on MoTe2/graphene heterostructures have achieved high responsivity and short response time simultaneously in one device. In this study, we fabricate graphene–MoTe2–graphene vertical van der Waals heterostructure devices through chemical vapor deposition (CVD) growth, wet transfer method, and dry etching technique. Under 1064 nm laser illumination, we acquire responsivity of as high as 635 A/W and a response time of as short as 19 μs from the as-fabricated device. Moreover, we acquire higher responsivity of 1752 A/W and a shorter response time of 16 μs from the Al2O3-encapsulated device. Our research drives the application of 2D materials in the NIR wavelength range.

Carbon-metal oxide nanocomposites for selective detection of toxic and hazardous volatile organic compounds (VOC) – A review

Recently carbon nanostructures i.e. graphene and its derivatives, carbon nanotubes (CNT) and fullerene combined with different metal oxides have provided researchers a lot of opportunities for the sensing of volatile organic compounds (VOCs). The synergistic effect of both nanocarbon and metal oxide assuredly makes the nanocomposite suitable for reliable and stable sensors. Studies on hybrid structures by many researchers had shown improved sensing parameters in terms of high sensitivity, selectivity, fast response and recovery time at room temperature. In the present review we have reported the nanocomposites of carbon nanostructures and metal oxides for efficient and selective detection of toxic and hazardous VOCs.

Soft Robot Skin With Conformal Adaptability for On-Body Tactile Perception of Collaborative Robots

Robot skin, as the physical interface between collaborative robots (cobots) and the external environments, could mediate on-body tactile signals for cobots to respond timely once a collision occurs during tasks and thus avoid damages to both cobots and surroundings. To achieve effective on-body tactile perception, robot skin should possess adequate conformal adaptability to be covered on various complex contours on the cobot, such as joints, while maintaining accurate and rapid sensing performance. In this letter, a soft robot skin consisting of an array of force-sensing units and a substrate with a serpentine structure was developed, both of which were made of porous material. The serpentine structure endows the developed skin with stretchable attributes. Thus, the skin could be conformally attached to complex surfaces of a cobot with less local stress, which was validated by finite element analysis. Taking the advantage of porous microstructure, the sensing units embedded in the substrate have exhibited high sensitivity and fast response time under external force, which are essential factors in real-time collision detection. Finally, experimental validation was carried out to verify the feasibility of deploying the developed soft robot skin on a robot arm to provide on-body tactile perception for a cobot.

The Effect of AAC Display Types on Message Production and Its Relationship with Reading Ability in Patients with Cognitive-Communication Disorders

Objectives: To provide empirical evidence that can be applied in medical settings, this study aimed to examine the effects of AAC display types on message production ability in patients with cognitive-communication disorders who are hospitalized and the correlation with the patients’ reading abilities.Methods: Twenty patients with cerebral vascular accidents who were diagnosed with cognitive-communication disorders participated in this study. Message production abilities were examined by measuring accuracy scores and response times under three AAC display conditions: (1) text-based visual scene display (VSD), (2) mixed type (text and graphic symbol-based) of VSD, and (3) graphic symbol-based GRID.Results: The graphic symbol-based GRID showed significantly high accuracy scores and short response time compared to the text-based VSD. There was no significant difference between the graphic symbol-based GRID and the mixed type of VSD in terms of accuracy scores and response time. In addition, significant correlations between the VSD type of display and the reading task scores were found.Conclusion: This study showed that the VSD types of AAC display do not enhance the communication efficacy more than the graphic symbol-based GRID in medical settings. It is at odds with a previous study that claims the effectiveness of text-based VSD without considering patients’ reading ability. These results suggest that rather than perceiving VSD itself to be more effective than other display types, it is important to provide individual graphic symbols so that reading impaired patients can understand the meaning of each message.

Analysis Model of Spoken English Evaluation Algorithm Based on Intelligent Algorithm of Internet of Things.

With the in-depth promotion of the national strategy for the integration of artificial intelligence technology and entity development, speech recognition processing technology, as an important medium of human-computer interaction, has received extensive attention and motivated research in industry and academia. However, the existing accurate speech recognition products are based on massive data platform, which has the problems of slow response and security risk, which makes it difficult for the existing speech recognition products to meet the application requirements for timely translation of speech with high response time and network security requirements under the condition of network instability and insecurity. Based on this, this paper studies the analysis model of oral English evaluation algorithm based on Internet of things intelligent algorithm in speech recognition technology. Firstly, based on the automatic machine learning and lightweight learning strategy, a lightweight technology of automatic speech recognition depth neural network adapted to the edge computing power is proposed. Secondly, the quantitative evaluation of Internet of things intelligent classification algorithm and big data analysis in this system is described. In the evaluation, the evaluation method of oral English characteristics is adopted. At the same time, the Internet of things intelligent classification algorithm and big data analysis strategy are used to evaluate the accuracy of oral English. Finally, the experimental results show that the oral English feature recognition system based on Internet of things intelligent classification algorithm and big data analysis has the advantages of good reliability, high intelligence, and strong ability to resist subjective factors, which proves the advantages of Internet of things intelligent classification algorithm and big data analysis in English feature recognition.

Self-biased high sensitivity near-infrared photodetector based on nanocrystalline indium nitride film

Most photodetectors based on nanoparticles have been designed to be powered by an external power source, which is used to simulate the photo-created carriers in order to generate a photocurrent. This clearly increases the weight and size of the device. As a consequence, their applications in areas like in-situ wireless environmental sensing and medical therapy monitoring are strictly limited. Constructing self-powered (0 V bias voltage) systems that can operate autonomously, wirelessly, and sustainably is an important research direction for next-generation nanodevices. In this study, a novel near-infrared self-powered photodetector based on indium nitride nanocrystals (InN-NCs) film that operates without an external power source is fabricated. A cost-effective and simple radio frequency technique was used to growth the film onto silicon substrate. The photodetector has good self-powered photo-response properties under NIR (850 nm) light, including high sensitivity (1300) and good response time (rise time 160 ms and decay time 210 ms).

Bi-functional carbon doped and decorated ZnO nanorods for enhanced pH monitoring of dairy milk and adsorption of hazardous dyes

This study demonstrates a simple and low-cost process for the in-situ doping and decoration of ZnO nanorods with carbon (CC–ZnO). In CC–ZnO, C-doping decreased the charge density (1.75 × 1018 cm−3) at the non-active sites of ZnO and decreased the charge transfer resistance (101 Ω) at the C-doped-ZnO/electrolyte interface by suppressing native defects and reducing the Schottky barrier height (–0.20 eV), respectively. Moreover, C-decoration enhanced the amphoteric performances of ZnO to react efficiently with H+ and OH− ions in an aqueous electrolyte, demonstrating a high pH sensitivity (48 mV/pH) and fast response time (7 s). Moreover, C-decoration enhanced the dispersion stability (92 h for 7.5 mg/mL concentration) and surface area (43.08 m2·g−1) of CC–ZnO in liquid phase, improving the monolayer adsorption capacity (119.40 mg/g) for the removal of rhodamine B (RhB) from aqueous solution. The optimum concentration and pH value of CC–ZnO and aqueous solution were determined to be 25 mg and 6.5, respectively, for maximum (84 %) removal of RhB in the initial five hours of reaction. Adsorption rate analysis revealed that CC–ZnO removed RhB through pseudo-second-order kinetics.

A Human-Machine Interface Based on an EOG and a Gyroscope for Humanoid Robot Control and Its Application to Home Services

The human-machine interface (HMI) has been studied for robot teleoperation with the aim of empowering people who experience motor disabilities to increase their interaction with the physical environment. The challenge of an HMI for robot control is to rapidly, accurately, and sufficiently produce control commands. In this paper, an asynchronous HMI based on an electrooculogram (EOG) and a gyroscope is proposed using two self-paced and endogenous features, double blink and head rotation. By designing the multilevel graphical user interface (GUI), the user can rotate his head to move the cursor of the GUI and create a double blink to trigger the button in the interface. The proposed HMI is able to supply sufficient commands at the same time with high accuracy (ACC) and low response time (RT). In the trigger task of sixteen healthy subjects, the target was clicked from 20 options with ACC of 99.2% and RT 2.34 s. Furthermore, a continuous strategy that uses motion start and motion stop commands to create a certain robot motion is proposed to control a humanoid robot based on the HMI. It avoids the situation that combines some commands to achieve one motion or converts the certain motion to a command directly. In the home service experiment, all subjects operated a humanoid robot changing the state of a switch, grasping a key, and putting it into a box. The time ratio between HMI control and manual control was 1.22, and the number of commands ratio was 1.18. The results demonstrated that the continuous strategy and proposed HMI can improve performance in humanoid robot control.

A hybrid photodetector of graphene/TiO2/inorganic PbS quantum dots for fast response

Hybrid graphene/quantum dots photodetectors have been obtained up to 109 A W−1 ultrahigh responsivity, but the major challenge of these architectures is the slow photoresponse speed, especially the delay time of these configurations is mostly on the second time scale. Herein, we propose a hybrid photodetector of graphene/TiO2 films/inorganic PbS quantum dots, which bridge the gap between high sensitivity and fast response time at visible band detection. Under 635 nm light illumination, the device shows a high responsivity of 1.2 × 104 A W−1, a fast decay time of 35 ms, and a specific detectivity of 1.5 × 1012 Jones at 1 V bias. The high responsivity is ascribed to the photogating effect, and the major findings hold great promise for application in optoelectronics.

A New Strategy of 3D Printing Lightweight Lamellar Graphene Aerogels for Electromagnetic Interference Shielding and Piezoresistive Sensor Applications

AbstractLamellar 3D structures are beneficial to raise the electrical properties of graphene aerogels like electrical conductivity, electromagnetic interference (EMI) shielding efficiency (SE) and pressure sensitivity. In this paper, a strategy of 3D printing lamellar graphene aerogel (LGA) based on shear‐thinning and ice‐growth‐inhibition mechanisms is demonstrated. A well‐designed slit extrusion printhead is used to produce shear thinning graphene oxide (GO) water‐based dispersions. Tert‐butyl alcohol is added into GO water‐based dispersions to inhibit ice growth which will destroy the GO flakes arrangement. After freeze‐drying and chemical reduction of the printed GO samples, the lightweight LGAs are prepared. Comparing to the traditional way, the strategy in this paper shows much better size and shape scalable freedom. The LGA exhibits electrical conductivity up to 705.6 S m−1, which is rather high for graphene‐based aerogels. Benefiting from the lamellar structure and high electrical conductivity, the aerogel achieves up to 68.75 dB EMI SE at X‐band with the thickness of 3 mm, while the absolute EMI SE can reach up to 15351.9 dB cm3 g−1. The LGA can also be used as a piezoelectric pressure sensor, which exhibits high compressible stress and rapid response time.

High-performance ultraviolet photodetectors based on 2D layered In4/3P2Se6 nanoflakes

Ultraviolet photodetectors (UV PDs) based on 2D layered materials have attracted much attention because of the great applications in the fields of biology, healthcare, and space science, as well as the unique optical and electrical properties of 2D layered materials. Many UV PDs have been reported. However, high performance UV PDs with high responsivity and ultrafast light response time still need to be explored further. Here, we synthesized layered In4/3P2Se6 nanoflakes via the chemical vapor conversion (CVC) method. The UV PDs based on as-grown In4/3P2Se6 nanoflakes exhibit a very high light switching ratio of up to 6 × 105 at room temperature, which is ascribed to the large photocurrent and an ultralow dark current of ∼80 fA. Meanwhile, an ultrafast rise and a decay time of ∼ 470 μs/440 μs are achieved. The according responsivity, external quantum efficiency, and special detectivity are 4.31 A W−1, 1485.2%, and 6.3 × 1012 Jones, respectively, which are excellent performance among the UV PDs based 2D layered materials. Notably, it has both high responsivity and fast light response time, better than other 2D layered semiconductor photodetectors. Our finding demonstrates In4/3P2Se6 nanoflakes are promising materials for high performance UV PDs in the future.

Real-time quantification for sulfite using a turn-on NIR fluorescent probe equipped with a portable fluorescence detector

Sulfur dioxide and its derivative sulfite widely existed in air, water as the environment pollutant. Sulfite is also commonly used as preservative and additive in fresh fruits, vegetables, wines and pharmaceutical materials. Due to sulfite is closely related with human diseases, it is very urgent for the sensitive and rapid quantification of sulfite in various samples. In our study, a turn-on near infrared (NIR) fluorescent probe (MDQ) was developed for sulfite detection based on a Michael addition reaction, with high sensitivity (LOD 4.16 nmol/L), selectivity and fast response time (400 s). Using MDQ, a quantify method for sulfite in traditional Chinese medicines (TCMs) was developed with the advantages of high precision, accuracy and convenient operation. Furthermore, according to the photophysical property of MDQ, a portable fluorescence detector is designed to quantify sulfite for TCMs and surface water in Dalian city of China. Therefore, the developed fluorescent probe MDQ and portable fluorescent detector as a rapid inspection instrument were successfully used to real-time monitor the sulfite in various complex samples.

Bdot probe and Rogowski coil cross-calibration and sensor fusion in pulsed direct current capacitor discharges.

Bdot probes and Rogowski coils are used in the measurement of transient magnetic fields and currents, respectively. They both share the mechanism of creating an induced electromotive force response via Faraday's law, which scales linearly with the pulsed magnetic field. High power capacitor direct current (DC) discharge systems release a single pulse of current that is both very high and very fast (≲1 ms). To capture these transient data and characterize these systems, high current tolerant and fast response time sensors are required. While these measuring devices have been well studied and utilized for almost 100 years, a comprehensive and detailed description of the custom design, calibration, and sensor fusion application of these tools for use in various pulsed DC capacitor value discharges is largely missing in the literature. Using robust analytical calculations, finite element analyses, and empirical methods, we have developed a sensor fusion protocol for current and magnetic field probes (with relative errors of ±13% and ±15%, respectively) for use in any geometry of high speed pulsed DC current calibrated capacitor discharge systems. This paper comprehensively outlines the design and sensor fusion methodologies that allow for the deployment of in-house built Bdot probes and Rogowski coils to a wide range of pulsed DC systems and demonstrates their use in a characteristic plasma environment.

Structural and Electrical Properties of Glucose Biosensors Based on ZnO and ZnO-CuO Nanostructures

Background: Nanostructured metal oxides have stimulated tremendous efforts for sightseeing glucose bio-sensing applications. They have been mostly investigated to fabricate highly sensitive, stabilized and ultrafast biosensors. Objective: Fabrication and characterization of glucose biosensors based on zinc oxide (ZnO) nanostructured thin films modified by copper oxide (CuO) nanostructures in order to obtain stabilized ZnO:CuO biosensors with high sensitivity and fast response time. Methods: The components of the investigated biosensors are synthesized using the hydrothermal solgel method by dip-coating the sensing layer on indium tin oxide-coated glass substrates (ITO). The structural and electrical properties of the fabricated biosensors are investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and I-V characteristics. Results: SEM micrographs indicate that ZnO nanostructures exhibit an interconnected sheet-like patterns. These sheets are thin and distributed randomly on the ITO substrate. SEM images of ZnO:CuO reveal that the morphology of nanostructured thin films is composed of flower-like patterns. The XRD patterns of ZnO and modified ZnO:CuO thin films subjected to thermal annealing show that thin films exhibit a high degree of crystallinity with minor traces of impurity phases. The biosensors' key parameters are calculated and interpreted by measuring the I-V characteristics to elucidate the sensitivity and reproducibility of measurements performed for various glucose concentrations. Furthermore, the electric current response of ZnO and ZnO:CuO biosensors are found to be linear and quadratic as a function of glucose concentration, respectively. The introduction of CuO into ZnO thin films leads to the enhancement of the sensitivity of the synthesized glucose biosensors for a high degree of precision in measuring glucose levels. Conclusion: Both sensors exhibit average sensitivities in the range (from 1 to 10 μA mM−1 cm−2) with quite good reproducibility. The unique property of this sensor is its ability to measure glucose concentrations at neutral pH conditions (i.e. pH = 7) using a simple, low cost and novel sensor design.