Temperature-Decoupled Single-Crystal MgO Fiber-Optic Fabry-Perot Vibration Sensor Based on MEMS Technology for Harsh Environments.

A high-temperature-resistance single-crystal magnesium oxide (MgO) extrinsic Fabry-Perot (FP) interferometer (EFPI) fiber-optic vibration sensor is proposed and experimentally demonstrated at 1000 °C. Due to the excellent thermal properties (melting point > 2800 °C) and optical properties (transmittance ≥ 90%), MgO is chosen as the ideal material to be placed in the high-temperature testing area. The combination of wet chemical etching and direct bonding is used to construct an all-MgO sensor head, which is favorable to reduce the temperature gradient inside the sensor structure and avoid sensor failure. A temperature decoupling method is proposed to eliminate the cross-sensitivity between temperature and vibration, improving the accuracy of vibration detection. The experimental results show that the sensor is stable at 20-1000 °C and 2-20 g, with a sensitivity of 0.0073 rad (20 °C). The maximum nonlinearity error of the vibration sensor measurement after temperature decoupling is 1.17%. The sensor with a high temperature resistance and outstanding dynamic performance has the potential for applications in testing aero-engines and gas turbine engines.

A Waterproof Flexible Paper-Based Thermoelectric Generator for Humidity and Underwater Environments.

A thermoelectric generator (TEG) is one of the important energy harvesting sources for wearable electronic devices, which converts waste heat into electrical energy without any external stimuli, such as light or mechanical motion. However, the poor flexibility of traditional TEGs (e.g., Si-based TE devices) causes the limitations in practical applications. Flexible paper substrates are becoming increasingly attractive in wearable electronic technology owing to their usability, environmental friendliness (disposable, biodegradable, and renewable materials), and foldability. The high water-absorbing quality of paper restricts its scope of application due to water failure. Therefore, we propose a high-performance flexible waterproof paper-based thermoelectric generator (WPTEG). A modification method that infiltrates TE materials into cellulose paper through vacuum filtration is used to prepare the TE modules. By connecting the TE-modified paper with Al tape, as well as a superhydrophobic layer encapsulation, the WPTEG is fabricated. The WPTEG with three P-N modules can generate an output voltage of up to 235 mV at a temperature difference of 50 K, which can provide power to portable electronic devices such as diodes, clocks, and calculators in hot water. With the waterproof property, the WPTEG paves the way for achieving multi-scenario applications in humid environments on human skin.

Extensible multi-wavelength interrogation method for arbitrary cavities in low-fineness multi-cavity Fabry-Pérot interferometric sensors.

To the best of our knowledge, a novel extensible multi-wavelength (EMW) method to interrogate arbitrary cavities in low-fineness fiber-optic multi-cavity Fabry-Pérot interferometric (LFMFPI) sensors is proposed and experimentally demonstrated. Based on the derived model of the LFMFPI sensor with any amount of cascaded cavities, theoretically, variation in each cavity of a LFMFPI sensor can be extracted simultaneously once the necessary parameters are acquired in advance. The feasibility of this method is successfully demonstrated in simulations and experiments utilizing LFMFPI sensors. In experiments with the LFMFPI sensor, optical path differences (OPD) of 78 nm and 2.95 µm introduced by temperature variation in two cavities, and the OPD induced by vibration with the amplitude from 5.891 nm to 38.116 nm were extracted, respectively. The EMW method is potential in multi-parameter sensing for pressure, vibration, and temperature.

Temperature, pressure, and humidity SAW sensor based on coplanar integrated LGS.

This paper presents a surface acoustic wave (SAW) sensor based on coplanar integrated Langasite (LGS) that is fabricated using wet etching, high-temperature bonding, and ion beam etching (IBE) processes. The miniaturized multiparameter temperature‒pressure-humidity (TPH) sensor used the MXene@MoS2@Go (MMG) composite to widen the humidity detection range and improve the humidity sensitivity, including a fast response time (3.18 s) and recovery time (0.94 s). The TPH sensor was shown to operate steadily between 25-700 °C, 0-700 kPa, and 10-98% RH. Coupling issues among multiple parameters in complex environments were addressed by decoupling the Δf-temperature coupling factor to improve the accuracy. Therefore, this work can be applied to simultaneous measurements of several environmental parameters in challenging conditions.

Temperature Sensors Integrated with an Electrochromic Readout toward Visual Detection.

Temperature sensors have attracted great attention for personal health care and disease diagnosis in recent years. However, it is still a great challenge to fabricate reliable and highly sensitive temperature sensors that can convert physiological signals into easily readable signals in a convenient way. Herein, an integrated smart temperature sensor system based on a traditional temperature sensor and electrochromic display is proposed for real-time visual detection of temperature. Significantly, a voltage-regulated electrochromic device (ECD) based on tungsten oxide (WO3) and polyaniline (PANI) as the real-time visualization window was integrated into the platform to provide feedback on the temperature change. The ECD would change its color from green to blue based on the electrical signal of the temperature sensor, resulting in a visualized readout that can be monitored through our naked eye. Additionally, the smart temperature sensor system possesses an extremely durable property and cycle stability, remaining around 90% of the initial value even after 15,000 s continuous cycle. Thus, the novel design and low power consumption advantages make it a good candidate to pave the way for developing interactive wearable electronics and intelligent robots as real-time temperature feedback systems.

High-Temperature Fiber-Optic Fabry-Perot Vibration Sensor Based on Single-Crystal Sapphire.

In this paper, a fiber-optic Fabry-Perot (F-P) vibration sensor that can work at 800 °C is proposed. The F-P interferometer is composed of an upper surface of inertial mass placed parallel to the end face of the optical fiber. The sensor was prepared by ultraviolet-laser ablation and three-layer direct-bonding technology. Theoretically, the sensor has a sensitivity of 0.883 nm/g and a resonant frequency of 20.911 kHz. The experimental results show that the sensitivity of the sensor is 0.876 nm/g in the range of 2 g to 20 g at an operating frequency of 200 Hz at 20 °C. The nonlinearity was evaluated from 20 °C to 800 °C with a nonlinear error of 0.87%. In addition, the z-axis sensitivity of the sensor was 25 times higher than that of the x-axis and y-axis. The vibration sensor will have wide high-temperature engineering-application prospects.

Multi-Channel MEMS-FAIMS Gas Sensor for VOCs Detection.

Aimed at the problems of a large equipment size, long time and high price of environmental VOC gas detection, the FAIMS-VOC gas sensor was designed and prepared according to the principle that the ionization energy of the common VOC gas is less than 10.6 eV. The sensor is small in size, fast in detection, low in power consumption, and can work continuously. The sensor was fabricated through the MEMS process, a specific process which included photolithography, etching, anodic bonding, etc. The sensor is 5160 µm long, 5300 µm wide and 800 µm high. We built a test system to detect two typical VOC gases: isobutylene and acetone. The results show that in the detection of isobutylene gas and acetone gas, the sensor voltage value changes with the change of gas concentration. The linearity of testing isobutylene is 0.961, and the linearity of testing acetone is 0.987. When the isobutylene gas concentration is 50 ppm, the response time is 8 s and the recovery time is 6 s; when the acetone gas concentration is 50 ppm, the response time is 9 s and the recovery time is 10 s. In addition, the sensor demonstrates good repeatability and stability, which are conducive to the detection of VOCs in the environment.

Recent Progress of Nanodiamond Film in Controllable Fabrication and Field Emission Properties.

The interest in the field electron emission cathode nanomaterials is on the rise due to the wide applications, such as electron sources, miniature X-ray devices, display materials, etc. In particular, nanodiamond (ND) film is regarded as an ideal next-generation cathode emitter in the field emission devices, due to the low or negative electron affinity, small grain size, high mechanical hardness, low work function, and high reliability. Increasing efforts are conducted on the investigation of the emission structures, manufacturing cost, and field emission properties improvement of the ND films. This review aims to summarize the recent research, highlight the new findings, and provide a roadmap for future developments in the area of ND film electron field emitter. Specially, the optimizing methods of large-scale, high-quality, and cost-effective synthesis of ND films are discussed to achieve more stable surface structure and optimal physical properties. Additionally, the mainstream strategies applied to produce high field emission performance of ND films are analyzed in detail, including regulating the grain size/boundary, hybrid phase carbon content, and doping element/type of ND films; meanwhile, the problems existing in the related research and the outlook in this area are also discussed.

Probe type TFBG-excited SPR fiber sensor for simultaneous measurement of multiple ocean parameters assisted by CFBG.

The tilted fiber Bragg grating(TFBG), chirped fiber Bragg grating(CFBG), Vernier effect and metal surface plasmon resonance(SPR) effect are effectively combined to form a probe type fiber sensor for simultaneous measurement of seawater salinity, temperature and depth(STD). The SPR effect excited by the TFBG is achieved by covering a gold layer around the TFBG, which is used to measure the refractive index (RI) of seawater. The core mode of TFBG is used to detect the change of seawater temperature and the measurement of TFBG reflection spectrum is realized by inscribing a CFBG after the TFBG, which makes the sensor have a probe type design and more beneficial to practical applications. The fusion of quartz micro-spheres on the end face of the sensing fiber and the parallel connection of an Fabry Perot(F-P) interference cavity enables the use of Vernier effect to detect the depth of the ocean. Femtosecond laser line-by-line method is used to the inscribing of TFBG, which allows the grating parameters to be changed flexibly depending on the desired spectrum. The experimental results show that the temperature sensitivity is 10.82pm/°C, the salinity sensitivity is 0.122nm/g/Kg, the depth sensitivity is 116.85 pm/m and the depth can be tested to 1000 m or even deeper.

Process method of Si3N4 ceramic brazing sealed cavity for high-temperature application.

The process method of a Si3N4 ceramic sealed cavity is realized by vacuum brazing and chemical reaction at 1,100°C and 0.5 MPa pressure. Through the combination of Si3N4 ceramic polishing and thinning, inductively coupled plasma etching, and high-temperature metal filler (Ti-Zr-Cu-Ni) brazing process, a vacuum-sealed cavity suitable for high-temperature environments was prepared. The cross section of the bonding interface was characterized by scanning electron microscope (SEM) and energy dispersive spectrometer (EDS), which indicated that the two Si3N4 ceramic were well bonded, the cavity structure remained intact, and the bonding interface strength exceeded 5.13 MPa. Furthermore, it retained its strong bonding strength after in high-temperature environments of 1,000, 1,050, and 1,100°C for 1 h. This indicates that a brazed vacuum-sealed cavity can be used in high-temperature environments. Through the proposed method, pressure sensor that can withstand high temperatures can be developed.

Fabrication of an all-silica microsphere-lens on optical fiber for free-space light coupling and sensing in extreme environments.

In this paper, an all-silica microsphere-lens was designed and fabricated on the fiber end face, which can effectively improve the coupling efficiency of free-space light. In the production process, a coreless silica fiber with specific length was spliced on the end face of the fiber and melted by a CO2 laser fusion splicer. Due to the effect of surface tension, the coreless silica fiber would form a microsphere-lens on the fiber end face and the diameter of the microsphere-lens could be adjusted by controlling the light-passing time of the CO2 laser fusion splicer. Through experiments, it can be found that the 3 dB bandwidth optical coupling distance of the microsphere-lens with a diameter of 270 µm is about 200 µm, and the focus depth is about 450 µm. In order to verify the feasibility of using the microsphere-lens in the fiber-optic Fabry-Perot sensors, a Fabry-Perot interferometer was constructed by using the microsphere-lens and the single-mode fiber end face. The experimental results showed that the interference spectrum of the Fabry-Perot interferometer has a good contrast ratio. Integrating the advantages of all-silica structure, simple manufacturing process, low cost, small size, and sturdy construction, the proposed microsphere-lens is expected to be a potential candidate for free-space light coupling and fiber-optic sensors in extreme environments.

Towards two-dimensional color tunability of all-solid-state electrochromic devices using carbon dots.

Electrochromic devices (ECDs) that display multicolor patterns have gradually attracted widespread attention. Considering the complexity in the integration of various electrochromic materials and multi-electrode configurations, the design of multicolor patterned ECDs based on simple approaches is still a big challenge. Herein, it is demonstrated vivid ECDs with broadened color hues via introducing carbon dots (CDs) into the ion electrolyte layer. Benefiting from the synergistic effect of electrodes and electrolytes, the resultant ECDs presented a rich color change. Significantly, the fabricated ECDs can still maintain a stable and reversible color change even in high temperature environments where operating temperatures are constantly changing from RT to 70°C. These findings represent a novel strategy for fabricating multicolor electrochromic displays and are expected to advance the development of intelligent and portable electronics.

Wireless LC Conformal Temperature Sensor Based on Ag Film (9912-K FL) for Bearing Temperature Measurement.

As the key component of aero-engines and industrial gas turbines, a bearing's working temperature at high speed is close to 300 ℃. The measurement of an engine bearing's temperature is of great significance to ensure flight safety. In this study, we present a wireless LC conformal temperature sensor for bearing temperatures, which integrates silver on the bearing surface in situ through a screen-printing process. This process makes Ag film (9912-K FL) firmly adhere to the bearing surface and realizes wireless measurements for bearing temperatures in situ. A high-temperature holding experiment of the prepared sensor was conducted, and the results showed that the sensor can work stably for 10 h at 300 ℃. We tested the designed wireless LC conformal temperature sensor at 20−270 ℃. The results showed that the proposed temperature sensor attained as good accuracy and stability in the temperature range 20−270 ℃. The sensitivity of the temperature measurements was 20.81 KHz/℃ when the bearing rotateds, the maximum repeatability was 0.039%, the maximum uncertainty was 0.081%, and the relative error was stable within 0.08%.

Remifentanil pretreatment attenuates brain nerve injury in response to cardiopulmonary bypass by blocking AKT/NRF2 signal pathway.

OBJECTIVE: This study aimed to explore the effect and mechanism of remifentanil on cardiopulmonary bypass (CPB)-induced cerebral nerve injury. METHODS: After pretreating with remifentanil, or dexmedetomidine (DEX), SD rats were subjected to the CPB for 2 h. The data of body temperature, blood gas and mean arterial pressure (MAP) and hematocrit (HCT) were recorded at different time points. The cerebral tissue water content of rats was determined and immunohistochemical (IHC) and H&E assays on the hippocampal CA1 region of rats was performed. The levels of interleukin (IL)-6, IL-10, soluble protein-100ß (S100ß) and neuron-specific enolase (NSE) were analyzed by ELISA, and those of the indexes for oxidative stress (malondialdehyde (MDA) and superoxide dismutase (SOD)) were detected by the commercial kits. Morris water maze was used to evaluate the learning and memory abilities. Western blot/qRT-PCR were used to detect the protein/mRNA expressions in hippocampus. RESULTS: CPB increased the levels/expressions of IL-6, IL-10, S100ß, NSE, MDA, cleaved caspase-3, Bax and decreased those of Bcl-2, SOD, p-AKT, HO-1, in serum and parietal cortex tissue, with increased brain water content, lesions in the hippocampal CA1 area, swimming distance, brain nerve injury and decreased escape latency, retention time on platform and times of crossing the platform of rats. The preconditioning of remifentanil or DEX partially attenuated CPB-induced injury and -decreased expressions on p-AKT and HO-1, while further promoting CPB-induced expression of nuclear Nrf2 expression and inhibiting that of cytoplasm Nrf2. CONCLUSION: This paper demonstrates that remifentanil preconditioning could partially attenuate CPB-induced brain nerve injury of rats.

Humidity Sensor Based on rGO-SDS Composite Film.

Based on the humidity testing requirements in different environments, this paper investigates the humidity sensitivity of reduced graphene oxide (rGO)-sodium dodecyl sulfate (SDS) composite film humidity sensor. In the experiments, rGO-SDS dispersions with a concentration of 5 mg/mL were prepared, and a microelectromechanical system (MEMS) process was used to prepare the interdigital electrodes. The dispersions were then drop-coated on the interdigital electrodes and dried on a heated plate at 100 °C. The surface characteristics of the rGO-SDS films transferred onto SiO2-Si substrates were analyzed by scanning electron microscopy, raman spectroscopy and atomic force microscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, and tested by a correlation system, which showed a linear relationship between humidity variation and the resistance variation of the sensor in the ambient humidity range of 25-95% RH. At room temperature, the linearity of the sensor is about 0.98431 and the sensitivity is about 11.41432 Ω/% RH. At 100 °C, the correlation of the sensor is about 0.95046 and the sensitivity is about 1.0145 Ω/% RH; with a response time of only 9 s at ambient humidity from 25% RH to 95% RH, the sensor has very good repeatability and stability.

An Accelerometer Based on All Silica In-Line Fiber Fabry-Perot Etalon for High Temperature up to 800 °C.

High-temperature accelerometers have been widely used in aerospace, nuclear reactors, automobile technologies, etc. In this paper, a fiber-optic Fabry-Perot accelerometer (FOFPA) with a cantilever beam for high temperature is designed and experimentally demonstrated. The FOFPA is formed by bonding an all-silica in-line fiber Fabry-Perot etalon (ILFFPE) to one surface of the uniform cantilever beam with the lumped mass at the free end for acceleration measurement. The all silica in-line fiber FP etalon is made by welding two gold-coat single-mode fiber (GSMF) and a hollow silica glass tube (HST). The research results indicate that the sensitivity of the FOFPA is 0.02328rad/g, and the resonance frequency is 1146.6 Hz in the range of 1 g ~ 10 g. The high-temperature performance of the FOFPA was also evaluated. From 20 °C to 800 °C, the temperature drift is about 0.3178 nm/°C. The FOFPA has the potential of being applicable in higher temperatures compared to conventional accelerometers.

Acetone Sensor Based on FAIMS-MEMS.

In this paper, to address the problems of large blood draws, long testing times, and the inability to achieve dynamic detection of invasive testing for diabetes, stemming from the principle that type 1 diabetic patients exhale significantly higher levels of acetone than normal people, a FAIMS-MEMS gas sensor was designed to detect acetone, which utilizes the characteristics of high sensitivity, fast response, and non-invasive operation. It is prepared by MEMS processes, such as photolithography, etching, and sputtering, its specific dimensions are 4000 µm in length, 3000 µm in width and 800 µm in height and the related test system was built to detect acetone gas. The test results show that when acetone below 0.8 ppm is introduced, the voltage value detected by the sensor basically does not change, while when acetone gas exceeds 1.8 ppm, the voltage value detected by the sensor increases significantly. The detection accuracy of the sensor prepared by this method is about 0.02 ppm/mV, and the voltage change can reach 1 V with a response time of 3 s and a recovery time of 4 s when tested under 20 ppm acetone environment; this has good repeatability and stability, and has great prospects in the field of non-invasive detection of type 1 diabetes.

An optimized pulse coupled neural network image de-noising method for a field-programmable gate array based polarization camera.

The quality of polarization images is easy to be affected by the noise in the image acquired by a polarization camera. Consequently, a de-noising method optimized with a Pulse Coupled Neural Network (PCNN) for polarization images is proposed for a Field-Programmable Gate Array (FPGA)-based polarization camera in this paper, in which the polarization image de-noising is implemented using an adaptive PCNN improved by Gray Wolf Optimization (GWO) and Bi-Dimensional Empirical Mode Decomposition (BEMD). Unlike other artificial neural networks, PCNN does not need to be trained, but the parameters of PCNN such as the exponential decay time constant, the synaptic junction strength factor, and the inherent voltage constant play a critical influence on its de-noising performance. GWO is able to start optimization by generating a set of random solutions as the first population and saves the optimized solutions of PCNN. In addition, BEMD can decompose a complicated image into different Bi-Dimensional Intrinsic Mode Functions with local stabilized characteristics according to the input source image, and the decomposition result is able to lower the complexity of heavy noise image analysis. Moreover, the circuit in the polarization camera is accomplished by FPGA so as to obtain the polarization image with higher quality synchronously. These two schemes are combined to attenuate different types of noises and improve the quality of the polarization image significantly. Compared with the state-of-the-art image de-noising algorithms, the noise in the polarization image is suppressed effectively by the proposed optimized image de-noising method according to the indices of peak signal-to-noise ratio, standard deviation, mutual information, structural similarity, and root mean square error.

An LC Wireless Passive Pressure Sensor Based on Single-Crystal MgO MEMS Processing Technique for High Temperature Applications.

An LC wireless passive pressure sensor based on a single-crystalline magnesium oxide (MgO) MEMS processing technique is proposed and experimentally demonstrated for applications in environmental conditions of 900 °C. Compared to other high-temperature resistant materials, MgO was selected as the sensor substrate material for the first time in the field of wireless passive sensing because of its ultra-high melting point (2800 °C) and excellent mechanical properties at elevated temperatures. The sensor mainly consists of inductance coils and an embedded sealed cavity. The cavity length decreases with the applied pressure, leading to a monotonic variation in the resonant frequency of the sensor, which can be retrieved wirelessly via a readout antenna. The capacitor cavity was fabricated using a MgO MEMS technique. This MEMS processing technique, including the wet chemical etching and direct bonding process, can improve the operating temperature of the sensor. The experimental results indicate that the proposed sensor can stably operate at an ambient environment of 22-900 °C and 0-700 kPa, and the pressure sensitivity of this sensor at room temperature is 14.52 kHz/kPa. In addition, the sensor with a simple fabrication process shows high potential for practical engineering applications in harsh environments.

Dual-wavelength demodulation technique for interrogating a shortest cavity in multi-cavity fiber-optic Fabry-Pérot sensors.

This paper demonstrates, for the first time, a novel demodulation technique that can be applied for interrogating a shortest cavity in multi-cavity Fabry-Pérot (F-P) sensors. In this demodulation technique, using an amplified spontaneous emission (ASE) light source and two optical fiber broadband filters, the interference only occurs in a shortest F-P cavity that is shorter than the half of the coherence length. Using a signal calibration algorithm, two low-coherence interference optical signals with similar coherence lengths were calibrated to obtain two quadrature signals. Then, the change in the cavity length of the shortest F-P cavity was interrogated by the two quadrature signals and the arctangent algorithm. The experimental results show that the demodulation technique successfully extracted 1 kHz and 500 Hz vibration signals with 39.28 µm and 64.84 µm initial cavity lengths, respectively, in a multi-cavity F-P interferometer. The demodulation speed is up to 500 kHz, and the demodulation technique makes it possible for multi-cavity F-P sensors to measure dynamic and static parameters simultaneously. The results show that the demodulation technique has wide application potential in the dynamic measurement of multi-cavity F-P sensors.