Biomimetic-inspired highly sensitive flexible capacitive pressure sensor with high-aspect-ratio microstructures

The high sensitivity flexible capacitive pressure sensor (FCPS) manufactured in a fast and efficient way has friendly man-machine interaction function. In this paper, a high-sensitivity FCPS is developed by using a two-step template method to reproduce biomimetic microtower polydimethylsiloxane (PDMS) from the lotus leaf surface. The capacitive sensor is composed of a PDMS dielectric layer and the Cu nanowire electrodes sandwiching in the middle, with a high sensitivity of ~1.207 kPa⁻¹, a low detection limit of less than 0.02 kPa and a fast response time of 61.6 ms. Particularly, the sensing performance can be kept basically unchanged when bent at a 5 mm radius. Moreover, the FCPS can withstand 4000 repeated tests and maintain stable performance, and the sensitivity is almost the same in the process of loading and unloading, suggesting the high robustness. These results demonstrates the FCPSs have potential applications in electronic wearables, human health monitoring and uneven surface applications.     

Fiber optic Fabry-Perot pressure sensor with low sensitivity to temperature changes for downhole application

Pressure and temperature are two important parameters in reservoir engineering. The fiber optic sensors can be used for permanent downhole monitoring. In this paper, we propose an extrinsic fiber Fabry-Perot interferometer (EFPI) sensor for pressure measurement with low sensitivity variation. The pressure sensitivity of EFPI sensor and of the fiber Bragg grating (FBG) sensors have been measured. The experimental pressure sensitivity for EFPI and FBG sensors are measured to be 2.75 × 10⁻⁸ 1/kPa and 1.52 × 10⁻⁸ 1/kPa, respectively. The temperature cross-sensitivity problem of the EFPI sensor has been solved by a new technique. The temperature sensitivity of EFPI sensor has been decreased to 1.2 × 10⁻⁶/°C, while the temperature sensitivity of non-compensated EFPI sensor has been measured to be 16.4 × 10⁻⁶/°C. The results show that the EFPI sensor has a higher pressure sensitivity and good capability to decrease temperature sensitivity in comparison to FBG sensor.     

Unidirectional sensitive flexible sensor for bending measurements

The measurement of bending direction and bending angles is essential in the multiaxial servo-controlled system, especially for collaborative robots. However, most flexible sensors developed for bending measurements cannot distinguish bending directions due to their sensitivity to both positive and negative bending. Also, these sensors usually exhibit simultaneous response to normal pressure, which results in additional calibration. Here, a unidirectional-sensitive flexible capacitive sensor is proposed. A simple asymmetric pyramidal microstructure was designed to create uneven responses to positive and negative bending and minimum response to normal pressure based on the fringe effect. The fabricated sensor shows a relative capacitance change of nearly 0.9 in the sensitive direction and only 0.05 in the other direction as the sensor bends from flat to the curvature radius of 10 mm. Also, the sensor shows negligible sensitivity even under a normal pressure force as high as 16 N, either in planar or bending condition.     

基于微结构银纳米线的透明电子皮肤器件

Transparent, flexible electronic skin holds a wide range of applications in robotics, humanmachine interfaces, artificial intelligence, prosthetics, and health monitoring. Silver nanowire are mechanically flexible and robust, which exhibit great potential in transparent and electricconducting thin film. Herein, we report on a silver-nanowire spray-coating and electrodemicrostructure replicating strategy to construct a transparent, flexible, and sensitive electronic skin device. The electronic skin device shows highly sensitive piezo-capacitance response to pressure. It is found that micropatterning the surface of dielectric layer polyurethane elastomer by replicating from microstructures of natural-existing surfaces such as lotus leaf, silk, and frosted glass can greatly enhance the piezo-capacitance performance of the device. The microstructured pressure sensors based on silver nanowire exhibit good transparency, excellent flexibility, wide pressure detection range (0-150 kPa), and high sensitivity (1.28 kPa^-1).     

Temperature self-compensation fiber-optic pressure sensor based on fiber Bragg grating and Fabry–Perot interference multiplexing

A high performance multiplexed fiber-optic sensor consisted of diaphragm-based extrinsic Fabry–Perot interferometer (DEFPI) and fiber Bragg grating (FBG) is proposed. The novel structure DEFPI fabricated with laser heating fusion technique possesses high sensitivity with 5.35 nm/kPa (36.89 nm/psi) and exhibits ultra-low temperature dependence with 0.015 nm/°C. But the ultra-low temperature dependence still results in small pressure measurement error of the DEFPI (0.0028 kPa/°C). The designed stainless epoxy-free packaging structure guarantees the FBG to be only sensitive to temperature. The temperature information is created to calibrate the DEFPI's pressure measurement error induced by the temperature dependence, realizing effectively temperature self-compensation of the multiplexed sensor. The sensitivity of the FBG is 10.5 pm/°C. In addition, the multiplexed sensor is also very easy to realize the pressure and the temperature high-precise high-sensitive simultaneous measurement at single point in many harsh environmental areas.     

Large-range liquid level sensor based on an optical fibre extrinsic Fabry–Perot interferometer

We propose an efficient approach to develop large-range liquid level sensors based on an extrinsic Fabry–Perot optical fibre interferometer with an all fused-silica structure and CO₂ laser heating fusion bonding technology. The sensor exhibits signatures of a high sensitivity of 5.3 nm/kPa (36.6 nm/psi), a resolution of 6.8 Pa (9.9×10⁻⁴ psi) and an extreme low temperature dependence of 0.013 nm/°C. As a result, a high resolution of the water level measurement of approximately 0.7 mm on the length scale of 5 m and small errors of the water pressure measurement induced by the temperature dependence within 0.0025 kPa/°C (0.00036 psi/°C, water level 0.25 mm/°C) are achieved, thus providing useful applications for the detection of the large-range liquid level in harsh environments.     

High-sensitivity Fabry-Perot interferometric pressure sensor based on a nanothick silver diaphragm

We present a fiber-optic extrinsic Fabry-Perot interferometer pressure sensor based on a nanothick silver diaphragm. The sensing diaphragm, with a thickness measured in a few hundreds of nanometers, is fabricated by the electroless plating method, which provides a simple fabrication process involving a high-quality diaphragm at a low cost. The sensor exhibits a relatively linear response within the pressure variation range of 0-50 kPa, with a high pressure sensitivity of 70.5 nm/kPa. This sensor is expected to have potential applications in the field of highly sensitive pressure sensors.     

Capacitive position measurement for high-precision space inertial sensor

Low noise position measurement is fundamental for space inertial sensors, and at present the capacitive position sensor is widely employed for space inertial sensors. The design for the possible suppression of the front-end electric noises for a capacitive sensor is presented. A prototype capacitive sensor with 2×10⁻⁶pF/Hz1/2 at frequency above 0.04 Hz is achieved and further improvements are discussed.      

Fast piezoresistive sensor and UV photodetector based on Mn‐doped ZnO nanorods

A low cost hydrothermal synthesis method to synthesize Mn‐doped ZnO nanorods (NRs) with controllable morphology and structure has been developed. Ammonia is used to tailor the ammonium hydroxide concentration, which provides a source of OH^– for hydrolysis and precipitation during the growth instead of HMT. The morphological, chemical composition, structural, and electronic structure studies of the Mn‐doped ZnO NRs show that the Mn‐doped ZnO NRs have a hexagonal wurtzite ZnO structure along the c‐axis and the Mn ions replace the Zn sites in the ZnO NRs matrix without any secondary phase of metallic manganese element and manganese oxides observed. The fabricated PEDOT:PSS/Zn_0.85Mn_0.15O Schottky diode based piezoresistive sensor and UV photodetector shows that the piezoresistive sensor has pressure sensitivity of 0.00617 kPa^–1 for the pressure range from 1 kPa to 20 kP and 0.000180 kPa^–1for the pressure range from 20 kPa to 320 kPa with relatively fast response time of 0.03 s and the UV photodetector has both relatively high responsivity and fast response time of 0.065 A/W and 2.75 s, respectively. The fabricated Schottky diode can be utilized as a very useful human‐friendly interactive electronic device for mass/force sensor or UV photodetector in everyday living life. This developed device is very promising for small‐size, low‐cost and easy‐to‐customize application‐specific requirements. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Progress in pressure measurements with luminescence sensors

Abstract

Various luminescence sensors for pressure measurements are compared with the generally used ruby sensor. Typical advantages and disadvantages of different luminescence sensors based on lanthanide ions in various hosts are discussed. Emphasis is given to the sensor based on Sm^2?: MFCl (M =Sr, Ba) with respect to its sensitivity, temperature dependence and range of applicability.     

Green sonochemical synthesis and fabrication of cubic MnFe2O4 electrocatalyst decorated carbon nitride nanohybrid for neurotransmitter detection in serum samples

The binary nanomaterials and graphitic carbon based hybrid has been developed as an important porous nanomaterial for fabricating electrode with applications in non-enzymatic (bio) sensors. We report a fast synthesis of bimetal oxide particles of nano-sized manganese ferrite (MnFe₂O₄) decorated on graphitic carbon nitride (GCN) via a high-intensity ultrasonic irradiation method for C (30 kHz and 70 W/cm²). The nanocomposites were analyzed by powder X-ray diffraction, XPS, EDS, TEM to ascertain the effects of synthesis parameters on structure, and morphology. The MnFe₂O₄/GCN modified electrode demonstrated superior electrocatalytic activity toward the neurotransmitter (5-hydroxytryptamine) detection with a high peak intensity at +0.21 V. The appealing application of the MnFe₂O₄/GCN/GCE as neurotransmitter sensors is presented and a possible sensing mechanism is analyzed. The constructed electrochemical sensor for the detection of 5-hydroxytryptamine (STN) showed a wide working range (0.1–522.6 μM), high sensitivity (19.377 μA μM⁻¹ cm⁻²), and nano-molar detection limit (3.1 nM). Moreover, it is worth noting that the MnFe₂O₄/GCN not only enhanced activity and also promoted the electron transfer rate towards STN detection. The proposed sensor was analyzed for its real-time applications to the detection of STN in rat brain serum, and human blood serum in good satisfactory results was obtained. The results showed promising reproducibility, repeatability, and high stability for neurotransmitter detection in biological samples.     

Evaluation of acoustoelectric UV sensor according to ZnO thin film properties

This paper presents an improvement of the acoustoelectric effect by sensitivity and response of ultraviolet (UV) sensors by changing the argon/oxygen ratio. The acoustoelectric sensor is a delay-line type with a center frequency of 240.2625 MHz and fabricated on a piezoelectric substrate. Aluminum thin films were deposited as interdigitated transducers and patterned, and the ZnO thin film was deposited as a UV sensing layer by controlling the ratio of argon and oxygen with an RF magnetron sputtering. By increasing the oxygen partial pressure during ZnO deposition, the photoconductivity increased by 6.5 times, thereby increasing the frequency change related to the sensitivity of the sensor. The sensitivity to UV light was 110.4 Hz cm²/μW under an argon/oxygen ratio of 6:4, which is an increase of 5.1 times from 21.76 Hz cm²/μW obtained under a ratio of 10:2. In addition, the response and recovery times were improved by 2.85 times and 3.02 times, respectively.     

光纤菲佐气体压力传感器的波分频分复用方法

设计了一种新的光纤菲佐气体压力传感器,结合波分复用技术和空间频率复用技术,实现了不同腔长的光纤菲佐气体压力传感器的复用.给出了该复用系统的结构,阐述了其工作原理,最后利用实验验证了该方法的可行性.针对该系统中的串扰问题提出了基于参数化谱估计的Pisarenko谐波分解方案,使可复用的传感器腔长差降至100 μm左右,大大提高了系统的复用能力.实验结果表明：该系统在单个传感器气体压力分辨率达0.76% F.S(量程为0~150 kPa),复用的传感器数目可达80个以上,可满足实际工程应用中多点气压测量的需要.     

差分谐振式压力微传感器灵敏度匹配特性（英）

谐振式压力微传感器因其高精度、高稳定性及准数字输出等特性而广泛应用于气压监测、航空航天等领域。相较于其他结构,差分谐振式具有灵敏度高、线性度好及温度漂移小等优势。然而,要获得差分谐振式压力微传感器的最优性能,仍需解决差分谐振梁灵敏度不匹配的问题。在仿真与实验的基础上,对差分谐振式压力微传感器的灵敏度匹配特性进行了相关研究。根据研究结果,对传感器的结构参数进行了优化设计。两谐振梁的设计灵敏度为46 Hz/kP,实验结果显示中心梁的实际灵敏度为45 Hz/kPa,边梁的实际灵敏度为-44 Hz/kPa,差分输出的线性度高达0.999 999 9。     

差分谐振式压力微传感器灵敏度匹配特性（英）

谐振式压力微传感器因其高精度、高稳定性及准数字输出等特性而广泛应用于气压监测、航空航天等领域。相较于其他结构,差分谐振式具有灵敏度高、线性度好及温度漂移小等优势。然而,要获得差分谐振式压力微传感器的最优性能,仍需解决差分谐振梁灵敏度不匹配的问题。在仿真与实验的基础上,对差分谐振式压力微传感器的灵敏度匹配特性进行了相关研究。根据研究结果,对传感器的结构参数进行了优化设计。两谐振梁的设计灵敏度为46 Hz/kP,实验结果显示中心梁的实际灵敏度为45 Hz/kPa,边梁的实际灵敏度为-44 Hz/kPa,差分输出的线性度高达0.999 999 9。     

Bend-insensitive long-period fiber grating sensors

A novel bend-insensitive long-period fiber grating (LPFG) sensor written using focused CO₂ laser pulses is demonstrated, for the first time, to our knowledge. It is found that the central wavelength shift of such a LPFG is only −0.018 nm even for a curvature of 1.1 m⁻¹ at the most bend-insensitive position of the LPFG. Experimental results show that the bend sensitivity of the central wavelength of the LPFG has a periodic distribution along its circular directions. Such a bend-insensitive sensor could be used to solve the problem of cross-sensitivity between bend and other measurands, such as temperature, strain or refractive index, which is an unsolved problem for LPFG sensors in practice. In addition, the bend sensitivity of the LPFG can be adjusted by selecting its circular positions.     

Refractive index sensors based on Ag-metalized nanolayer in microstructured optical fibers

We propose refractive index sensors based on Ag-metalized nanolayer in microstructured optical fibers. The surface plasmon resonance modes and the sensing properties are theoretically analyzed using finite element method (FEM). In the calculation, Drude–Lorentz model is used to describe the Metal Dielectric constant. The calculation results show that the sensitivity of Ag-metalized SPR sensor can reach 1500 nm/RIU corresponding to a resolution of 6.67 × 10^?5 RIU. Comparing with conventional detecting material-Au under the same structure, the sensitivity and 3 dB bandwidth of our device are better.     

Laser-Patterned Carbon-Supported Graphitic Carbon Nitride Quantum Dots for Flexible Nanozyme-Based Fluoride Sensor

Graphitic carbon nitride quantum dots (g-CNQDs)-based colorimetric sensors are typically solution-based and hence incompatible with wearable electronics. Today's competitive technology demands safe and reliable, high-performance sensors suitable for integration with sophisticated electronics—all at a low cost. Herein, a flexible and reusable solid-state fluoride ion sensor manufactured by combining the intriguing surface properties of laser-patterned carbon (LP-C) with the sensitivity of g-CNQDs is reported. LP-C is obtained by direct IR-laser writing onto polyimide films, and g-CNQDs are synthesized via a solvent-free and zero-waste green process. The hybrid of LP-C and g-CNQDs (g-CNQDs/LP-C), mimics the natural enzyme horseradish peroxidase and oxidizes the chromogenic substrate 3,3’,5,5’-tetramethylbenzidine in the presence of H₂O₂ in acidic media. The highly selective and user-friendly nanozyme sensors feature a lower limit of detection of 0.568 ± 0.006  × 10⁻⁶ m (23.8 ± 1.5 µg L⁻¹) with linearity in the range of 0.5 × 10⁻⁶ to 100  × 10⁻⁶ m . A sensing mechanism based on the electronic transitions of g-CNQDs and LP-C, the two variants of nitrogen-containing carbon used in this work, is established. Finally, the device is tested for fluoride ion sensing in natural water samples collected from the Uhl river in Mandi, India.     

Frequency and power dependence of ultrasonic degassing

We investigated the time variation of ultrasonic degassing for air-saturated water and degassed water with a sample volume of 100 mL at frequencies of 22, 43, 129, 209, 305, 400, 514, 1018, and 1960 kHz and ultrasonic power of 15 W. Ultrasonic degassing was evaluated by dissolved oxygen concentration. Ultrasonic degassing was also investigated at a frequency of 1018 kHz and ultrasonic powers of 5, 10, 15, and 20 W. The dissolved oxygen concentration varied with the ultrasonic irradiation time and became constant after prolonged ultrasonic irradiation. The constant dissolved oxygen concentration value depended on the frequency and ultrasonic power but not the initial dissolved oxygen concentration. The degassing rate at 101.3 kPa was higher in the frequency range of 200 kHz to 1 MHz. The frequency dependence of the degassing rate was almost the same as that of the sonochemical efficiency obtained by the potassium iodide (KI) method. Ultrasonic degassing in the frequency range of 22–1960 kHz was also investigated under reduced pressure of 5 kPa. Degassing was accelerated when ultrasonic irradiation was applied under reduced pressure. However, under a reduced pressure of 5 kPa, the lower the frequencies, the higher is the degassing rate. The sonochemical reaction rate was examined by the KI method for varying dissolved air concentrations before ultrasonic irradiation. Cavitation did not occur when the initial dissolved oxygen concentration was less than 2 mg·L⁻¹. Therefore, the lower limit of ultrasonic degassing under 101.3 kPa equals 2 mg·L⁻¹ dissolved oxygen concentration. A model equation for the time variation of dissolved oxygen concentration due to ultrasonic irradiation was developed, and the degassing mechanism was discussed.     

Fiber curvature sensor based on spherical-shape structures and long-period grating

A novel curvature sensor based on optical fiber Mach–Zehnder interferometer (MZI) is demonstrated. It consists of two spherical-shape structures and a long-period grating (LPG) in between. The experimental results show that the shift of the dip wavelength is almost linearly proportional to the change of curvature, and the curvature sensitivity are −22.144 nm/m⁻¹ in the measurement range of 5.33–6.93 m⁻¹, −28.225 nm/m⁻¹ in the range of 6.93–8.43 m⁻ and −15.68 nm/m⁻¹ in the range of 8.43–9.43 m⁻¹, respectively. And the maximum curvature error caused by temperature is only −0.003 m⁻¹/°C. The sensor exhibits the advantages of all-fiber structure, high mechanical strength, high curvature sensitivity and large measurement scales.