Showing papers in "Sensors and Actuators A-physical in 2021"
TL;DR: This paper aims to provide references for the further research on the efficient fabrication of flexible capacitive pressure sensors and effective usage of such sensors in high sensitivity requirements of application areas.
Abstract: Flexible pressure sensors have played a great role in acquiring information from human and automatics because of their wide use in electronic skin, soft robot, human-machine interaction and so on. Among a variety of flexible pressure sensors, capacitive pressure sensor has many advantages like simple structure, insensitive to temperature and humidity, low power consumption, etc. It is easy to fabricate such kind of pressure sensor, nevertheless, how to improve its sensitivity to broaden the high effective application has been a hotspot issue in recent years. In this paper, a large amount of research outputs on sensitivity improvement have been reviewed for flexible capacitive pressure sensor, including the aspects from introduction of performance evaluation indicators, working principle, generally used materials and capacitor structures to the methods of how to improve the sensitivity of capacitive pressure sensors. Then, the effective ways to obtain high sensitivity of pressure sensors have been compared and the development trend of flexible capacitive pressure sensor is prospected. This paper aims to provide references for the further research on the efficient fabrication of flexible capacitive pressure sensors and effective usage of such sensors in high sensitivity requirements of application areas.
80 citations
TL;DR: In this article, the authors summarize the recent progress on QCM gas sensors and QCM humidity sensors based on graphene materials and graphene composites, and the challenges for future works related to the development of QCM sensors coated by graphene materials or graphene composite materials.
Abstract: Graphene and graphene-based materials have shown great potential for detecting gases and humidity due to their high specific surface areas. Quartz crystal microbalance (QCM) sensors have been massively developed because they have high sensitivity, consume low energy, and can be readily modified. Recently, QCM coated by graphene composites has been explored to sensitively and selectively detect various gases and humidity. Herein, we summarize the recent progress on QCM gas sensors and QCM humidity sensors based on graphene materials and graphene composites. We start from an introduction to the sensing principle of QCM, synthesis and preparation of graphene materials used for QCM sensing material, application of graphene materials and graphene composites for sensing materials of QCM gas sensors and humidity sensors, and the mechanism of those sensors. We mainly summarize the recent advances in the performances of QCM gas sensor and QCM humidity sensor coated with pristine graphene, graphene oxide, reduced graphene oxide, and various graphene-based composite materials, including chemical, polymer, metal oxide, and other carbon-based materials. The challenges for future works related to the development of QCM sensors coated by graphene materials or graphene composites are also elaborated.
75 citations
TL;DR: The metric of Normalized Power Density (NPD) is introduced to compare and assess the energy generation capability of PEHs with several widely-used piezoelectric materials and in different scales.
Abstract: Piezoelectric energy harvesters (PEHs) promote the construction of a smarter world through powering electric devices with energy scavenged from environmental vibrations by means of piezoelectric effect. To enable the piezoelectric effect, piezoelectric materials are usually attached to mechanical structures (e.g. flexible beams) that can deform due to mechanical vibration and produce strain in piezoelectric material. The mechanical structure for energy harvesting in nature is a Compliant Mechanism (CM). A large variety of structural solutions have been proposed aiming to expend the working frequency range and maximizing the energy output of PEHs. To advance PEHs, a comprehensive review on existing structural solutions and materials is necessary. According to structural characteristics of current PEHs from the aspect of CMs, designs in state of the art are analyzed and categorized into five configurations, mono-stable, multi-stable, multi-degrees-of-freedom, frequency up-conversion and stress optimization. For each configuration, working principles and compatibilities with miniaturization to MEMS scale are analyzed and assessed. Additionally, several CMs are first proposed for PEHs in different configurations as inspirations and references to prompt the development of PEHs. Piezoelectric materials are also important factors in enhancing the energy harvesting performance. Characters of several widely adopted piezo-materials are summarized and compared. The metric of Normalized Power Density (NPD) is introduced to compare and assess the energy generation capability of PEHs with several widely-used piezoelectric materials and in different scales. A NPD-Volume graph is first presented based on the data collected in literature. It shows that PEHs with PZT have the highest NPD and stable energy generation performance in a wide volume range. Both the structural categorization and NPD-Volume graph provide guidance and reference for design and optimization of PEHs.
66 citations
TL;DR: This review paper attempts to systematically summarize environment perception technology and discuss the new challenges currently faced, including the advantages, disadvantages and applicable occasions of several commonly used sensing methods to provide a clear selection guide.
Abstract: Environmental perception technology is the guarantee of the safety of driverless vehicles. At present, there are a lot of researches and reviews on environmental perception, aiming to realize unmanned driving while ensuring the safety of human life. However, the technology is facing new challenges in the new era. This review paper attempts to systematically summarize environment perception technology and discuss the new challenges currently faced. To this end, we first summarized the advantages, disadvantages and applicable occasions of several commonly used sensing methods to provide a clear selection guide. The new challenges faced by environmental perception technology are discussed from three aspects: technology, external environment and applications. Finally, the article also points out the future development trends and efforts of environmental perception technology.
62 citations
TL;DR: In this article, the optical and electrical features of the Al/(PCBM/NiO:ZnO)/p-Si structures/diodes were investigated and compared via currentvoltage/time (I-V/t) and capacitance/conductance-voltage-frequency (C/G-V-f) characteristics in dark and various illumination intensities (20, 40, 60, 80, 100 mW/cm2) at room temperature.
Abstract: In this study, metal-oxide (NiO:ZnO) nanocomposites mixed with different weight-percentages (2, 10, 20 % NiO) content were coated on the p-Si wafer via spin-coating method. The optical and electrical features of the Al/(PCBM/NiO:ZnO)/p-Si structures/diodes were investigated and compared via current-voltage/time (I–V/t) and capacitance/conductance-voltage-frequency (C/G–V-f) characteristics in dark and various illumination intensities (20, 40, 60, 80, 100 mW/cm2) at room temperature. Main electrical parameters of them such as ideality factor (n), barrier height (Φb), rectification ratio (RR = IF/IR) and series resistance (Rs) were calculated for each percentage (2, 10, and 20 % NiO). Experimental results show that the best percentages of NiO is 20 % in respect of high value of RR and low Rs, but the value of n increases with increasing in percentages. The transient photocurrent increases with increasing illumination level. The slope (m) of the double-logarithmic Iph-P plots were found as 0.67, 0.87 and 0.82, respectively, and these slopes confirmed that these nanocomposites exhibit photoconduction behaviour and hence Al/(PCBM/NiO:ZnO)/p-Si structure can be used a photo device/sensor. The observed changes in the I with illumination, C and G with frequency are the results of interface states (Nss) located at (PCBM/NiO:ZnO)/p-Si interface and so reorder and restructure of them under illumination, bias voltage, and frequency.
62 citations
TL;DR: In this paper, various fabrication methods to synthesize metal-oxide-based heterostructure with different morphologies and dimensions have been reviewed and different types of mechanisms that improved the gas sensing performance, have been discussed.
Abstract: Recently, atmospheric pollution has become a critical problem for modern society. The detection and monitoring of gases are the major problems nowadays. Metal oxides play a crucial role in the detection of different gases owing to their change in electrical or optical parameters relative to the adsorption/desorption of gas. The sensitivity and selectivity of the metal oxide-based gas sensor can be improved by the incorporation of heterostructures. The heterostructures-based gas sensor may improve the sensing performance due to their facilitating catalytic activity, increasing adsorption rate, and creating a charge carrier depletion layer that produces a larger modulation in resistance. In this article, various fabrication methods to synthesize metal-oxide-based heterostructure with different morphologies and dimensions have been reviewed. Also, different types of mechanisms that improved the gas sensing performance, have been discussed. The heterostructures have different types of structures such as mixed heterostructure, multilayered heterostructure, core-shell, decorated heterostructure, hollow heterostructure, and one-dimensional, two dimensional, or three-dimensional hierarchical heterostructures; hence improvement in important sensing parameters of the sensor can be obtained. A compositional contribution of an individual metal oxide within a composite exhibits the capability to tune the response and selectivity of the composite towards a particular gas.
61 citations
TL;DR: In this article, a review of the various microstructures of CNT-based conductive networks are reviewed, such as uniform mixing, aligned structure, multilayered structure, porous structure, nanomesh structure, island-bridge structure, wavy structure, microarray structure, wrinkled structure, weaving structure.
Abstract: Flexible resistive-type strain sensors are attracting wide attention due to their extensive potential applications. Carbon nanotubes (CNTs) with outstanding conductivity and mechanical properties can be assembled by various methods to form different conductive strain sensing networks within elastic polymers due to its nanoscale structure. Herein, the shapes of strain sensors are introduced including film, fiber and yarn, fabric, foams and gels. The various microstructures of CNT-based conductive networks are reviewed, such as uniform mixing, aligned structure, multilayered structure, porous structure, nanomesh structure, island-bridge structure, wavy structure, microarray structure, wrinkled structure, weaving structure. The lithographic processes, solution-based processing methods (such as dropping casting, spraying, ultrasonication, dip coating, sizing coating, layer-by-layer (LBL) assembly), chemical vapor deposition, printing technology (such as screen printing, inkjet printing, 3D printing) and electrospun technology were used to fabricate these conductive networks. The sensing performance and working mechanisms of these strain sensors with different conductive networks have been summarized and analyzed. Furthermore, their applications in the fields of personal healthcare, body motion detection, smart robot, human-machine interaction and structural health monitoring are reviewed. Finally, the existing challenges and prospective research directions are discussed. The CNT-based resistance-type strain sensors will be greatly promoted through innovations in integrating multidisciplinary technologies in future.
54 citations
TL;DR: In this paper, the authors investigated the transient magnetoelectric (ME) response of the symmetric Terfenol-D/PZT/Terfenol D laminate structure driven by transient current.
Abstract: This paper investigates the transient magnetoelectric (ME) response of the symmetric Terfenol-D/PZT/Terfenol-D laminate structure driven by transient current. The time-domain output voltages are investigated in detail under the currents generated by the square, sine, and triangle transient voltages. The damping oscillation phenomenons at natural frequency are observed with the fast-changing current and weaken when the width of the transient currents are equal to the times of the natural period of laminate. Furthermore, the transient ME responses driven by the 8/20μs lightning current are also investigated. For detecting the amplitude of the 8/20μs lightning current, the detection sensitivity reaches 6.8 mV/A in the range of 90–2742 A. These results show that the ME composite is an ideally sensing device for the lightning current sensing.
50 citations
TL;DR: This review summarizes the latest research progress of piezoresistive pressure sensors, capacitive pressure sensor, and piezoelectric pressure sensors and discusses the current challenges and potential prospects of flexible pressure sensors.
Abstract: Flexible pressure sensors with high sensitivity, high flexibility, lightness and easy integration have been extensively researched in the fields of electronic skin, wearable devices, medical diagnosis, physical health detection and artificial intelligence. This review summarizes the latest research progress of piezoresistive pressure sensors, capacitive pressure sensors, and piezoelectric pressure sensors. In addition, high-performance flexible pressure sensors designed for different application requirements such as self-powered pressure sensors, multifunctional pressure sensors, and self-healing pressure sensors are also discussed. After a comprehensive description of the latest flexible pressure sensors, we discussed the current challenges and potential prospects of flexible pressure sensors. Exploring new sensing mechanisms, seeking new functional materials, and developing novel integrated technologies for flexible devices will be the key direction in the sensor field in the future.
50 citations
TL;DR: This work helps to understand how to develop geometrical soft robots’ designs for nonlinear 4D printing problems using ML and FEM.
Abstract: This paper presents a method for four-dimensional (4D) printing of soft pneumatic actuator robot (SPA)s, using nonlinear machine learning (ML) and finite element model (FEM). A FEM is developed to accurately simulate experimental actuation to obtain training data for the ML modeling. More than a thousand data training samples from the hyperelastic material FEM model generated to use as training data for the ML model, which was developed to predict the geometrical requirements of the 4D-printed SPA to realize the bending required for specific tasks. The ML model accurately predicted FEM and experimental data and proved to be a viable solution for 4D printing of soft robots and dynamic structures. This work helps to understand how to develop geometrical soft robots’ designs for nonlinear 4D printing problems using ML and FEM.
47 citations
TL;DR: In this article, an efficient fabrication route based on consolidated graphene oxide (GO) nanoplatelets inside the polyvinyl chloride (PVC) in presence tricresyl phosphate (TCP) plasticizer by In-situ method was addressed.
Abstract: Fabricating high response humidity sensors can create new-fashioned applications and avenues for stakeholder interaction. Thus, this paper addresses an efficient fabrication route based on consolidated graphene oxide (GO) nanoplatelets inside the polyvinyl chloride (PVC) in presence tricresyl phosphate (TCP) plasticizer by In-situ method. The structure of synthesized GO was verified by X-ray diffraction (XRD) and Fourier transform infrared imaging microscopic analysis (FT-IR-IM). Three different proportions of GO (i.e., 1, 3 and 6 wt.%) were used to fabricate plasticized PVC sensors. The morphology of sensors was investigated by atomic force microscopy (AFM) and transmission electron microscopy (TEM) techniques. The AFM & TEM images showed that better dispersion of GO nanoplatelets in the PPVC matrix occurred at 1 and 3 wt.%. Furthermore, other measurements such as Raman spectroscopy, mechanical properties and thermogravimetric analysis (TGA) were conducted on the fabricated PVC sensors. Also, the humidity sensing properties were tested in a wide range of relative humidity (11–85 % RH) and frequency (100 Hz–100 kHz). The data manifested that the optimum measuring frequency was 1 kHz. Moreover, the obtained results from humidity sensing at 1 kHz exhibited that sensor 3 (PPVC/GO-3%) possessed higher sensitivity, lower hysteresis with ultrafast response speed (∼ 4 s) and recovery time (∼ 6 s) compared to other sensors. This result reveals excellent possibility of using sensor 3 as humidity sensing for intelligent food packaging and other practical applications.
TL;DR: In this paper, a robust and self-powered tilt sensor based on annular liquid-solid interfacing triboelectric nanogenerator (TENG) is proposed and systematically investigated.
Abstract: Ship's attitude information is of great significance for navigation safety, cargo handling monitoring, and operation management. It is highly desired to develop an electromechanical integrated tilt sensor which can work well under harsh environment. In this paper, a robust and self-powered tilt sensor based on annular liquid-solid interfacing triboelectric nanogenerator (TENG) is to be proposed and systematically investigated. The TENG tilt sensor is composed of an annular polytetrafluoroethylene (PTFE) tube with copper electrodes segment disposed on the surface and the internal liquid which is encapsulated in PTFE tube with no air bubble. Studies on electrode width and liquid type are conducted to reasonably design the TENG sensor structure and improve its sensitivity. By conducting the durability test, the TENG tilt sensor demonstrates stable output performance and high sensitivity characteristics in low-frequency and low-amplitude inclination conditions. Moreover, the TENG tilt sensor hardly fails due to parts wear since there are no moving parts in it. The advantage of durability, maintenance-free, and independent with the external environment are highlighted in a harsh environment with high humidity, high salinity and strong magnetic field. Therefore, the present TENG tilt sensor is of practical significance for improving the automation and intelligence of ships.
TL;DR: In this paper, the performance of resistive and capacitive sensors was investigated, compared and discussed, and it was shown that the capacitive sensor is better than the resistive sensor during a long period.
Abstract: The demand for stretchable strain sensors has increased exponentially due to their ideal interaction with the human body. However, developing stretchable strain sensors with balanced properties such as a low Young’s modulus, easy fabrication, low cost, large deformation, and fast response time remains a challenge. In this study, we simultaneously prepared two high-performance types of stretchable strain sensors (resistive and capacitive sensors) based on customized compliant electrode. The electrode was developed by embedding multi-walled carbon nanotubes (MCNTs) into plasticized polyvinyl chloride (PVC) using the solvent casting method. The resistive strain sensor was fabricated by the compliant electrode and 3 M 4905 tapes in a sandwich structure. The capacitive sensor was obtained after simple stacking steps based on the preparation of resistive sensor. Then, the performance of the resistive and capacitive sensors was investigated, compared and discussed. The results show that both resistive and capacitive sensors have good static and dynamic performance. The two types of sensors have maximum tensile strain of more than 100 %, low Young's modulus less than 200 kPa, and fast response time less than 140 ms. The linearity of capacitive sensor is better than that of resistive sensor. The repeatability of capacitive sensor is better than that of resistive sensor during a long period. The resistive sensor has higher sensitivity (1.16) than the capacitive sensor (0.44), and has better signal anti-interference capability. Finally, the developed resistive and capacitive sensor were used to monitor the motion status of human joints and the motion angle of human joint, respectively, resulting in accurate sensing of human movement.
TL;DR: A green mode of synthesis of silver nanoparticles using Trigonella foenum-graecum (fenugreek) with minimal scale size and ultra-stable features was described in this article.
Abstract: A biogenic approach in the synthesis of nanoparticles has been the current trend in nanoscience attributed to the fact that it is an environmentally benign process which is safe to be used in biomedical applications. The present study describes a green mode of synthesis of silver nanoparticles using Trigonella foenum-graecum (fenugreek) with minimal scale size and ultra-stable features. The synthesized nanoparticles were characterized using UV–vis spectroscopy which showed a maximum absorption peak at 443 nm. The electronmicrographs of transmission and scanning electron microscopes predominantly spherical and not aggregated nanoparticles with an irregular array of an average diameter of 82.53 nm. The photocatalytic activity of silver nanoparticles was assessed by depredating Rhodamine B dye under light irradiation. The photodegradation of Rhodamine B dye was time-dependent followed by a complete photodegradation (nearly 93 %) with decoloration after 216 h. Further, the antibacterial activity of the silver nanoparticles was evaluated using three different bacterial strains and the zones of inhibition were shown to be (14, 2.0 mm), (5.0, 2.0 mm) and (10, 0.9 mm) for E. coli, S. aureus and Bacillus cereus, respectively.
TL;DR: In this paper, the shape memory alloy (SMA) wires were embedded eccentrically over the entire length of the printed structure to provide the actuation bending force, while the resistive wires are embedded into the SMP layer of the hinges to change the temperature and the bending stiffness of the actuator hinges via Joule heating.
Abstract: Soft composite actuators can be fabricated by embedding shape memory alloy (SMA) wires into soft polymer matrices. Shape retention and recovery of these actuators are typically achieved by incorporating shape memory polymer segments into the actuator structure. However, this requires complex manufacturing processes. This work uses multimaterial 3D printing to fabricate composite actuators with variable stiffness capable of shape retention and recovery. The hinges of the bending actuators presented here are printed from a soft elastomeric layer as well as a rigid shape memory polymer (SMP) layer. The SMA wires are embedded eccentrically over the entire length of the printed structure to provide the actuation bending force, while the resistive wires are embedded into the SMP layer of the hinges to change the temperature and the bending stiffness of the actuator hinges via Joule heating. The temperature of the embedded SMA wire and the printed SMP segments is changed sequentially to accomplish a large bending deformation, retention of the deformed shape, and recovery of the original shape, without applying any external mechanical force. The SMP layer thickness was varied to investigate its effect on shape retention and recovery. A nonlinear finite element model was used to predict the deformation of the actuators.
TL;DR: The promising development directions of intelligent robotic welding technologies are discussed, including the hardware developments of vision sensors, optimization of image processing algorithms, the combination of passive vision and active vision, multi-sensor information fusion, and applications of artificial intelligence.
Abstract: Vision-based sensors play an essential role in robotic welding, which attract increasing attention by scholars because of its non-contact characteristic, high precision, fast detection, and strong adaptability. This paper summarizes the recent research developments of vision sensor-based intelligent robotic welding and analyzes their characteristics and application scenarios in the welding process. The applications of vision sensing technologies are illustrated, especially in visual calibration, initial welding position guidance, weld seam tracking, weld pool monitoring, correlation deformation detection, and defect identification. At the end of this paper, the promising development directions of intelligent robotic welding technologies are discussed, including the hardware developments of vision sensors, optimization of image processing algorithms, the combination of passive vision and active vision, multi-sensor information fusion, and applications of artificial intelligence.
TL;DR: In this paper, nanocrystalline ZnS thin films were deposited on p-Si substrates, and the crystalline quality of the as-deposited thin films was studied using X-ray diffraction and scanning transmission electron microscopy (STEM).
Abstract: The chemical bath deposition method has been widely used to synthesize low-cost and large scalable UV light photodetectors. Herein, nanocrystalline ZnS thin films were deposited on p-Si substrates. The crystalline quality of the as-deposited ZnS thin films was studied using X-ray diffraction (XRD) and scanning transmission electron microscopy (STEM). It was found that ZnS films showed good crystallinity with the growth direction along the (111) planes of a cubic zinc blend structure, as confirmed by both XRD and STEM analysis. The crystallite size was calculated to be 2.49 nm which is very close to the Bohr radius. Optical measurements revealed a blue shift of 5 nm which indicates quantum confinement effects in the as-deposited ZnS films. Furthermore, the morphology and grain size of ZnS film was estimated from scanning electron microscopy (SEM). Photoluminescence (PL) measurements showed evidence of multiple emissions in the as-deposited ZnS films, indicating the presence of commonly known intrinsic defects, for instance, Zn and S vacancies. The fabricated heterojunction ZnS/p-Si yields a high sensitivity (1.98 × 10 4 ), fast response and high peak detectivity (4.29 × 1012). The device showed a good responsivity of (68.98 mA/W) without biasing towards the UV light (350 nm) regime. Moreover, the linear Dynamic Range of 85.92 dB and the External Quantum Efficiency (EQE) of 23.42 % was obtained that can be utilized for UV photodetectors applications.
TL;DR: In this article, a soft robotic fabric gripper that can be fabricated by a facile and highly scalable process of apparel engineering is presented, which includes a multi-fingered design that comprises hydraulic-driven, sheet-shaped fabric bending actuators.
Abstract: Fluid-driven soft grippers possess conformable grasping characteristics that differ from their rigid counterparts. Despite advances, their inherent low-stiffness due to constituent materials causes them to be inferior in many high-load applications. Existing fabrication methods of soft grippers that mostly rely on molding silicone elastomers, despite being simple, are not easily scalable. This article presents the design of a soft robotic fabric gripper that can be fabricated by a facile and highly scalable process of apparel engineering. The proposed robotic gripper features a multi-fingered design that comprises hydraulic-driven, sheet-shaped fabric bending actuators. Its performance is enhanced by incorporating a bio-inspired gecko adhesive and a thermo-responsive variable stiffness filament. Experimental studies demonstrate that adding the variable stiffness filament and gecko adhesive improves the holding force of the gripper up to 655 % and 507 % in the gripping and pull-out configurations, respectively. The variable stiffness filament features a relatively good cooling speed of only 31 s by ambient cooling. A simple analytical model was also developed to characterize the deformation of the fabric bending actuators. To monitor the gripper bending motion, a new soft fabric sensor comprising a conductive composite of liquid metal and carbon particles was developed. The sensor was configured in a sheet-like shape and can be easily integrated into the gripper, which has been usually absent for other fabric grippers. The materials employed by this gripper design are commercially available for a reasonable budget, enabling the gripper to be both cost-effective and have potential applications where both gentle grasping and high load capacity are required.
TL;DR: In this article, a pre-strained piezoresistive sensor fiber-matrix composites is used to predict the detachment of fiber inside the matrix, observed by visual inspection.
Abstract: Combining conductive fillers like carbon black with elastomers allows the development of soft elastomer strain sensors that can reach very large elongations, an important requirement for many robotic applications. However, when the conductive filler is introduced in the polymer, significant stiffening occurs, affecting the mechanical properties, e.g. Young’s Modulus, of the soft structure. In this attempt, single piezoresistive fiber composites were successfully fabricated, without drastically increasing the stiffness. Two silicone elastomers that are widely used in robotic applications were examined as matrix materials. Furthermore, modeling the stresses exerted on the fiber inside the composite was successfully used to predict the detachment of fiber inside the matrix, observed by visual inspection. For the PDMS based composite, pre-straining improved sensor properties, which could be confirmed for the monitoring of the movement of the crane robot. The results showed that the pre-strained piezoresistive sensor fiber-matrix composites positions of the robot crane can be monitored even at low strains.
TL;DR: In this article, a 2-dimensional graphitic carbon nitride g-C3N4 (GCN) is proposed as a metal-free catalyst comprising of carbon and nitrogen, which is exploited extensively in many gas sensing applications.
Abstract: The composition of gas or air mixture in a particular gas sensing environment greatly influences the properties, such as surface conductivity of metallic oxide-based gas sensors. In the recent years many native metallic oxide gas sensors, for instance, CuO, ZnO, SnO2, WO3, and α-Fe3O4 have been extensively exploited for their selectivity and sensing abilities towards different gases. Most of the researches has been conducted recently and is focused on addition of variety of dopants, mostly metal based oxide semiconductors-based gas sensors. A 2-dimensional graphitic carbon nitride g-C3N4 (GCN) is a novel metal-free catalyst comprising of carbon and nitrogen, which is exploited extensively in many gas sensing applications, owing to its excellent chemical stability and substrate characteristics. Various metal oxide semiconductors based heterojunction can be constructed with GCN. The enhanced gas sensing properties are related to the heterojunctions of GCN nanosheets made with semiconductors. The present review aim to shed a further light on the designing and construction of heterojunctional structures based on adding metal oxide nanostructures with GCN for improved gas sensing capabilities.
TL;DR: In this article, the authors reviewed the recent advances on performance indices, classification, structural composition, optimization and modeling method, and control of PEACM and provided a guideline on further development of the micro gripper.
Abstract: The piezoelectric-actuated compliant microgripper (PEACM) plays an essential role in the application fields such as biomedical engineering, microelectronics, and optical engineering. As compared with other categories of grippers, PEACM exhibits the advantages of high accuracy of displacement, large power to weight ratio, low energy consumption, and fast response speed. This paper reviews the recent advances on performance indices, classification, structural composition, optimization and modeling method, and control of PEACM. First, the gripper's performance indices and classifications are elaborated, which is beneficial to determine the design goal. Then, the compliant mechanisms adopted in the microgripper design are discussed, including the flexible hinge, displacement amplifier, and guiding mechanism. In addition, the optimization and modeling methods of the microgripper are presented. Popular types of position/force sensors and different displacement/force control strategies employed in the microgripper are surveyed. Moreover, the prospect on future development trend of the PEACM is discussed. The paper provides the reader with an overview of the recent advances on PEACM design and also a guideline on further development of the microgripper.
TL;DR: Different techniques that have been used to mimic this elegant physiological transport mechanism that is commonly found in nature are summarized and provided a starting point for researchers designing peristaltic micropumps for a broad range of applications.
Abstract: This report presents a review of progress on peristaltic micropumps since their emergence, which have been widely used in many research fields from biology to aeronautics. This paper summarizes different techniques that have been used to mimic this elegant physiological transport mechanism that is commonly found in nature. Peristaltic micropumps are defined as micropumps without specific rectification components, distinguishing them from other mechanical micropumps. Peristaltic micropumps are classified in terms of fluidic transportation into continuous-scheme with actuation along the flow path (miniaturized peristaltic pumps), and discrete-scheme where actuation is perpendicular to fluidic path (peristaltic membrane micropumps). Important parameters in peristalsis are presented, such as the operating frequency, stroke volume, and various actuation sequences, along with introducing design rules and analysis for optimizing actuation sequences. Actuation methods such as piezoelectric, motor, pneumatic, electrostatic, and thermal are discussed with their advantages and disadvantages for application in peristaltic micropumps. This review evaluates research efforts over the past 30 years with comparison of key features and outputs, and suggestions for future development. The analysis provides a starting point for researchers designing peristaltic micropumps for a broad range of applications.
TL;DR: In this article, a micron-scale graphene-based ammonia gas sensor using aerosol-jet printing technology was presented, which exhibited high response sensitivity (∼4.64 % for 4.35 ppm NH3 and ∼52.01 % for 97.19 ppm NH 3), short adsorption / desorption time ranging from 50 s to 150 s, good reversibility and repeatability.
Abstract: High-sensitivity ammonia gas sensors are paramount to many fields in our industries and lives. Due to its complicated fabrication processes, large size and long recovery time of most existing ammonia gas sensors, we present a micron-scale graphene-based ammonia gas sensor using aerosol-jet printing technology. The graphene sensor exhibited high response sensitivity (∼4.64 % for 4.35 ppm NH3 and ∼52.01 % for 97.19 ppm NH3, respectively), short adsorption / desorption time ranging from 50 s to 150 s, good reversibility and repeatability. Further employment of micro-heater close to the sensing line reduced desorption time more than ∼14.3 % when 10 V being applied onto the heater. Such design of the ammonia gas sensor by aerosol-jet printing can give an insight for graphene-based ammonia gas sensors, which may pave a way for the convenient integration with other sensors in portable instruments for coal miners and pathfinders etc.
TL;DR: This work evaluates the suitability of different mechanical micropumps and actuation mechanisms for drug administration and summarizes outstanding technical solutions that ensure sufficient fluidic performance, guarantee a safe use, and fulfil the specific requirements of medical microdosing.
Abstract: There is an increasing amount of research on microfluidic actuators with the aim to improve drug dosing applications. Micropumps are promising as they reduce the size and energy consumption of dosing concepts and enable new therapies. Even though there are evident advantages, there are only few examples of industrial microdosing units and micropump technology has not yet found widespread application. To answer the evoked question of what limits the application of microdosing technology for drug delivery, this work provides a comprehensive insight into the subject of drug dosing. We highlight and analyse specific microfluidic challenges and requirements in medical dosing: safety relevant aspects, such as prevention of freeflow and backflow; dosing-specific requirements, such as dosing precision and stability; and system-specific aspects, such as size, weight, and power restrictions or economic aspects. Based on these requirements, we evaluate the suitability of different mechanical micropumps and actuation mechanisms for drug administration. In addition to research work, we present industrial microdosing systems that are commercially available or close to market release. We then summarize outstanding technical solutions that ensure sufficient fluidic performance, guarantee a safe use, and fulfil the specific requirements of medical microdosing.
TL;DR: A comprehensive review of hydrophones, their design considerations, physical aspects, and structures by reviewing many publications that have been published over the last two decades is presented.
Abstract: This paper presents a comprehensive review of hydrophones, their design considerations, physical aspects, and structures by reviewing many publications that have been published over the last two decades. The investigation of the fundamental aspects and essential considerations of hydrophones in the literature are distributed in different papers and have not been brought together in a conclusive manner. This paper has collected and classified all the information about hydrophones including the parameters that affect their performance as well as their features. We have categorized the hydrophones according to their mechanism of operation, structure design, frequency response, and application. The literature has been summarized in a way that enables the readers' easy referral to appropriate designs for their desired application scenarios.
TL;DR: In this article, the morphological, compositional, and structural properties of synthesized SnO2 nanowires were examined using field emission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and high-resolution transmission electron microscope, respectively.
Abstract: A unique combination of high response and fast response-recovery is still a challenge in the development of room-temperature gas sensors. Herein, we demonstrated the on-chip growth of nanojunction-networked SnO2 NW sensors to work under UV-radiation at room temperature. The morphological, compositional, and structural properties of synthesized SnO2 nanowires were examined using field emission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy, respectively. The results presented the SnO2 NWs with smooth surfaces were entangled between the Pt electrode. Besides, the internal properties showed the SnO2 NWs were crystallized as the tetragonal rutile structure of SnO2. The use of UV-radiation with the optimum intensity of 50 μW/cm2 increased the gas response to 5 ppm NO2 up to 7-fold, while response and recovery times decreased about 8- and 4-fold, respectively. Moreover, alternative use of pulsed UV-radiation (provided only during the air recovery phase) can enhance significant gas response as compared with continuous UV-radiation. The enhancement of gas response could be attributed to the photo-adsorption and -desorption of NO2 molecule due to the photogeneration of electron-hole pairs. The combination of NW-NW nanojunctions and pulsed UV-radiation is expected to be a novel strategy for high-performance room temperature gas sensors.
TL;DR: In this article, the authors reviewed and summarized various changes and improvements made to die attachment, wire bonding, phosphor coating, encapsulation processes, and thermal management of light-emitting diodes.
Abstract: Light-emitting diodes (LEDs) are considered an ideal substitute for low-efficiency traditional light sources with broad applications in all scientific disciplines. For the past recent years, several developments and innovations have been reported that strengthen the reliability and thermal efficiency of speeding up the LED packaging process. This paper reviews and summarizes various changes and improvements made to die attachment, wire bonding, phosphor coating, encapsulation processes, and thermal management. It also covers the reasons for choosing the materials at every stage of LED packaging. Moreover, the review reveals a broad scope for future research, particularly on thermal management by nanoparticles and improved light intensity by different synthesized phosphors.
TL;DR: A portable sitting posture monitoring system to recognize the user's sitting posture and feedback the results in real time and achieve the optimal balance between classification accuracy and hardware resource consumption is proposed.
Abstract: Poor sitting posture is one of the main inducements that lead to a series of skeletal muscle diseases. Sitting posture monitoring system can remind the user to maintain the correct sitting posture to prevent the harm of poor sitting posture to the body. In this paper, we proposed a portable sitting posture monitoring system to recognize the user's sitting posture and feedback the results in real time. A pressure sensor array is used to collect sitting postures related information, while the collected data can be displayed on a computer. The proposed system was designed to recognize seven types of sitting postures, including sitting upright, leaning forward, leaning backward, leaning left, leaning right, cross left leg, and cross right leg. Seven machine learning algorithms were implemented for comparation. The results showed that a five-layer Artificial Neural Network could achieve the highest accuracy of 97.07 %. To enhance system performance and reduce hardware cost, we further optimized the size of the sensor array. An 11 × 13 sensor array combined with Random Forest algorithm realized the optimal balance between classification accuracy (96.26 %) and hardware resource consumption. The final system prediction time is 19 us on the Raspberry Pi, which could satisfy the practical application requirement on the embedded platform.
TL;DR: In this paper, the authors proposed a rapid and controllable acoustothermal microheater using AlN/Si thin-film SAWs, which can be integrated into a single lab-on-a-chip.
Abstract: Temperature control within a microreactor is critical for biochemical and biomedical applications. Recently acoustothermal heating using surface acoustic wave (SAW) devices made of bulk LiNbO3 substrates have been demonstrated. However, these are generally fragile and difficult to be integrated into a single lab-on-a-chip. In this paper, we propose a rapid and controllable acoustothermal microheater using AlN/Si thin film SAWs. The device’s acoustothermal heating characteristics have been investigated and are superior to other types of thin film SAW devices (e.g., ZnO/Al and ZnO/Si). The dynamic heating processes of the AlN/Si SAW device for both the sessile droplet and liquid within a polydimethylsiloxane (PDMS) microchamber were characterized. Results show that for the sessile droplet heating, the temperature at a high RF power is unstable due to significant droplet deformation and vibration, whereas for the liquid within the microchamber, the temperature can be precisely controlled by the input power with good stability and repeatability. In addition, an improved temperature uniformity using the standing SAW heating was demonstrated as compared to that of the travelling SAWs. Our work shows that the AlN/Si thin film SAWs have a great potential for applications in microfluidic heating such as accelerating biochemical reactions and DNA amplification.
TL;DR: Pure CuS and CuO@CuS core-shell heterostructure based photo detectors with high performance are synthesized by simple and cost-effective two-step chemical co-precipitation method.
Abstract: Development of photo detectors based on different semiconducting materials with high performance has been in progress in recent past, however, there is a lot of difficulties in developing the more effective photo detectors-based devices with high responsivity, detectivity and quantum efficiency. Hence, we have synthesized pure CuS and CuO@CuS core-shell heterostructure based photo detectors with high performance by simple and cost-effective two-step chemical co-precipitation method. The phase purity of CuS and CuO@CuS composite was observed by XRD analysis and the result were verified with Raman spectroscopy studies. Sphere like morphology of pure CuS and core-shell structure formation of CuO@CuS are observed with scanning and transmission electron microscopes. The presence of expected elements has been confirmed with EDX elemental mapping. Light harvesting photodiodes were fabricated by using n-type silicon substrate through drop cost method. Photo sensitive parameters of fabricated diodes were analyzed by I–V characteristics. The p-CuO@CuS (1:1)/n-Si diode owned a maximum photosensitivity (Ps) ∼ 7.76 × 104 %, photoresponsivity (R) ∼ 798.61 mA/W, external quantum efficiency ( E Q E )∼309.66 % and specific detectivity (D*) ∼ 8.19 × 1011 Jones when compared to p-CuS/n-Si diode. The obtained results revealed that the core/shell heterostructure of CuO@CuS is the most appropriate for photo detection.