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.

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.

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.

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.

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.

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.

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.

Least square fitting demodulation technique for the interrogation of an optical fiber Fabry-Perot sensor with arbitrary reflectivity.

A novel Fabry-Perot (F-P) demodulation technique based on least square fitting for arbitrary reflectivity F-P sensors is proposed. The demodulation method was simulated and analyzed to verify feasibility of the algorithm. Two different finesse F-P interferometers constructed with a reflector bracket were used to make the stability experiments and the stepping experiments. The results show that the demodulation technique can interrogate the cavity length of F-P interferometers with different fineness in a wide range, and the demodulation error is less than 12 nm.

The analgesic efficacy compared ultrasound-guided continuous transverse abdominis plane block with epidural analgesia following abdominal surgery: a systematic review and meta-analysis of randomized controlled trials.

BACKGROUND: This review and meta-analysis aims to evaluate the analgesic efficacy of continuous transversus abdominis plane (TAP) block compared with epidural analgesia (EA) in adults after abdominal surgery. METHODS: The databases PubMed, Embase and Cochrane Central Register were searched from inception to June 2019 for all available randomized controlled trials (RCTs) that evaluated the analgesic efficacy of continuous TAP block compared with EA after abdominal surgery. The weighted mean differences (WMDs) were estimates for continuous variables with a 95% confidence interval (CI) and risk ratio (RR) for dichotomous data. The pre-specified primary outcome was the dynamic pain scores 24 h postoperatively. RESULTS: Eight trials including 453 patients (TAP block:224 patients; EA: 229 patients) ultimately met the inclusion criteria and seven trials were included in the meta-analysis. Dynamic pain scores after 24 h were equivalent between TAP block and EA groups (WMD:0.44; 95% CI: 0.1 to 0.99; I2 = 91%; p = 0.11). The analysis showed a significant difference between the subgroups according to regularly administering (4 trials; WMD:-0.11; 95% CI: - 0.32 to 0.09; I2 = 0%; p = 0.28) non-steroidal anti-inflammatory drugs (NSAIDs) or not (3 trials; WMD:1.02; 95% CI: 0.09 to 1.96; I2 = 94%; p = 0.03) for adjuvant analgesics postoperatively. The measured time of the urinary catheter removal in the TAP group was significantly shorter (3 trials, WMD:-18.95, 95% CI:-25.22 to - 12.71; I2 = 0%; p < 0.01), as was time to first ambulation postoperatively (4 trials, WMD:-6.61, 95% CI: - 13.03 to - 0.19; I2 = 67%; p < 0.05). CONCLUSION: Continuous TAP block, combined with NSAIDs, can provide non-inferior dynamic analgesia efficacy compared with EA in postoperative pain management after abdominal surgery. In addition, continuous TAP block is associated with fewer postoperative side effects.

MEMS-Based Reflective Intensity-Modulated Fiber-Optic Sensor for Pressure Measurements.

A reflective intensity-modulated fiber-optic sensor based on microelectromechanical systems (MEMS) for pressure measurements is proposed and experimentally demonstrated. The sensor consists of two multimode optical fibers with a spherical end, a quartz tube with dual holes, a silicon sensitive diaphragm, and a high borosilicate glass substrate (HBGS). The integrated sensor has a high sensitivity due to the MEMS technique and the spherical end of the fiber. The results show that the sensor achieves a pressure sensitivity of approximately 0.139 mV/kPa. The temperature coefficient of the proposed sensor is about 0.87 mV/°C over the range of 20 °C to 150 °C. Furthermore, due to the intensity mechanism, the sensor has a relatively simple demodulation system and can respond to high-frequency pressure in real time. The dynamic response of the sensor was verified in a 1 kHz sinusoidal pressure environment at room temperature.

Fiber-optic Fabry-Perot pressure sensor based on sapphire direct bonding for high-temperature applications.

In this study, a fiber-optic Fabry-Perot (FP) high-temperature pressure sensor based on sapphire direct bonding is proposed and experimentally demonstrated. The sensor is fabricated by direct bonding of two-layer sapphire wafers, including a pressure diaphragm wafer and a cavity-etched wafer. The sensor is composed of a sensor head that contains a vacuum-sealed cavity arranged as an FP cavity and a multimode optical fiber. The external pressure can be measured by detecting the change in FP cavity length in the sensor. Experimental results demonstrate the sensing capabilities for pressures from 20 kPa to 700 kPa up to 800°C.

Al2O3-Based a-IGZO Schottky Diodes for Temperature Sensing.

High-temperature electronic devices and sensors that operate in harsh environments, especially high-temperature environments, have attracted widespread attention. An Al2O3 based a-IGZO (amorphous indium-gallium-zinc-oxide) Schottky diode sensor is proposed. The diodes are tested at 21⁻400 °C, and the design and fabrication process of the Schottky diodes and the testing methods are introduced. Herein, a series of factors influencing diode performance are studied to obtain the relationship between diode ideal factor n, the barrier height ФB, and temperature. The sensitivity of the diode sensors is 0.81 mV/°C, 1.37 mV/°C, and 1.59 mV/°C when the forward current density of the diode is 1 × 10-5 A/cm², 1 × 10-4 A/cm², and 1 × 10-3 A/cm², respectively.

Batch-producible MEMS fiber-optic Fabry-Perot pressure sensor for high-temperature application.

A fiber-optic Fabry-Perot pressure sensor based on a micro-electro-mechanical system (MEMS) and CO2 laser fusion technology is developed and experimentally demonstrated for high-temperature application. The sensing heads are batch-fabricated by anodically bonding the micromachined Pyrex glass wafer and local gold-plated silicon wafer. The separated sensing head and the single-mode fiber are fused together to form the Fabry-Perot cavity using the CO2 laser. In order to improve the measurement accuracy in a high-temperature environment, a fiber Bragg grating is used as a temperature sensor for temperature decoupling. The experimental results show that the fiber-optic Fabry-Perot pressure sensor has a maximum nonlinearity of 0.4%. The maximal error of the pressure after temperature decoupling is less than 1.05% over a pressure range of 0-0.5 MPa and a temperature range of 20°C-350°C. The batch fabrication technology makes the sensors low cost and high uniformity.

Microbubble-based fiber-optic Fabry-Perot pressure sensor for high-temperature application.

Using arc discharge technology, we fabricated a fiber-optic Fabry-Perot (FP) pressure sensor with a very low temperature coefficient based on a microbubble that can be applied in a high-temperature environment. The thin-walled microbubble can be fabricated by heating the gas-pressurized hollow silica tube (HST) using a commercial fusion splicer. Then, the well-cut single-mode fiber (SMF) was inserted into the microbubble, and they were fused together. Thus, the FP cavity can be formed between the end of the SMF and the inner surface of the microbubble. The diameter of the microbubble can be up to 360 µm with the thickness of the wall being approximately 0.5 µm. Experimental results show that such a sensor has a linear sensitivity of approximately -6.382 nm/MPa, -5.912 nm/MPa at 20°C, and 600°C within the pressure range of 1 MPa. Due to the thermal expansion coefficient of the SMF being slightly larger than that of silica, we can fuse the SMF and the HST with different lengths; thus, the sensor has a very low temperature coefficient of approximately 0.17 pm/°C.

Fiber-optic Fabry-Perot pressure sensor based on low-temperature co-fired ceramic technology for high-temperature applications.

In this study, a novel batch-producible fiber-optic Fabry-Perot (FP) pressure sensor based on a low-temperature co-fired ceramic technology is proposed and experimentally demonstrated for high-temperature applications. The sensor is fabricated by inserting a well-cut single-mode fiber (SMF) into a zirconia fiber ferrule, followed by insertion of the overall structure into an alumina sensor head. The FP cavity in the sensor is formed by placing the end face of the SMF in parallel to the diaphragm. The external pressure can be detected by demodulating the FP cavity length of the sensor. A theoretical analysis indicates that the pressure sensitivity can be designed flexibly by adjusting the parameters of the ceramic diaphragm, radius, and thickness. Experimental results demonstrate that the pressure sensor exhibits a high linear sensitivity of approximately 0.1 µm/kPa at room temperature in the pressure range up to 160 kPa. The repeatability error and nonlinear error of three repeatable experiments are approximately 2.60% and smaller than 0.101%, respectively. The temperature coefficient and coefficient of the pressure-sensitivity changes with temperature are 0.023 µm/°C and 0.205 nm/(kPa°C) in the temperature range of 20°C-300°C.

A Ceramic Diffusion Bonding Method for Passive LC High-Temperature Pressure Sensor.

Alumina ceramic is a highly promising material for fabricating high-temperature pressure sensors. In this paper, a direct bonding method for fabricating a sensitive cavity with alumina ceramic is presented. Alumina ceramic substrates were bonded together to form a sensitive cavity for high-temperature pressure environments. The device can sense pressure parameters at high temperatures. To verify the sensitivity performance of the fabrication method in high-temperature environments, an inductor and capacitor were integrated on the ceramic substrate with the fabricated sensitive cavity to form a wireless passive LC pressure sensor with thick-film integrated technology. Finally, the fabricated sensor was tested using a system test platform. The experimental results show that the sensor can realize pressure measurements above 900 °C, confirming that the fabricated sensitive cavity has excellent sealing properties. Therefore, the direct bonding method can potentially be used for developing all-ceramic high-temperature pressure sensors for application in harsh environments.

A Room-Temperature CNT/Fe3O4 Based Passive Wireless Gas Sensor.

A carbon nanotube/Fe3O4 thin film-based wireless passive gas sensor with better performance is proposed. The sensitive test mechanism of LC (Inductance and capacitance resonant) wireless sensors is analyzed and the reason for choosing Fe3O4 as a gas sensing material is explained. The design and fabrication process of the sensor and the testing method are introduced. Experimental results reveal that the proposed carbon nanotube (CNT)/Fe3O4 based sensor performs well on sensing ammonia (NH3) at room temperature. The sensor exhibits not only an excellent response, good selectivity, and fast response and recovery times at room temperature, but is also characterized by good repeatability and low cost. The results for the wireless gas sensor's performance for different NH3 gas concentrations are presented. The developed device is promising for the establishment of wireless gas sensors in harsh environments.

A Novel Metamaterial Inspired High-Temperature Microwave Sensor in Harsh Environments.

A high-temperature sensor based on a metamaterial unit cell is proposed in this paper. The wireless passive temperature sensing method is based on the electromagnetic backscatter principle, and thus has the advantages of higher quality, lower environmental interference, and anti-low frequency interference. We developed a finite-element method-based model for the sensor via high-frequency simulation software (HFSS). A double split-ring resonator (SRR) with an outer ring length of 13 mm was designed on alumina ceramic substrate. The sensor was fabricated at 2.42 GHz using micromechanical technology and screen printing technology. When the temperature increased from 28 to 1100 °C, the resonant frequency decreased from 2.417 to 2.320 GHz with an average sensitivity of 95.63 kHz/°C. As the sensor is easily designed and fabricated, it can be used for chipless radio frequency identification (RFID) tags by simply changing the size of rings. Furthermore, emerging 3D printing technology and commercial desktop inkjet printers will be used to realize the rapid low-cost preparation of the sensor, enabling its wide range of applications in aerospace, military, manufacturing, transportation, and other fields.

Microwave Backscatter-Based Wireless Temperature Sensor Fabricated by an Alumina-Backed Au Slot Radiation Patch.

A wireless and passive temperature sensor operating up to 800 °C is proposed. The sensor is based on microwave backscatter RFID (radio frequency identification) technology. A thin-film planar structure and simple working principle make the sensor easy to operate under high temperature. In this paper, the proposed high temperature sensor was designed, fabricated, and characterized. Here the 99% alumina ceramic with a dimension of 40 mm × 40 mm × 1 mm was prepared in micromechanics for fabrication of the sensor substrate. The metallization of the Au slot patch was realized in magnetron sputtering with a slot width of 2 mm and a slot length of 32 mm. The measured resonant frequency of the sensor at 25 °C is 2.31 GHz. It was concluded that the resonant frequency decreases with the increase in the temperature in range of 25-800 °C. It was shown that the average sensor sensitivity is 101.94 kHz/°C.

Substrate Integrated Waveguide (SIW)-Based Wireless Temperature Sensor for Harsh Environments.

This paper presents a new wireless sensor structure based on a substrate integrated circular waveguide (SICW) for the temperature test in harsh environments. The sensor substrate material is 99% alumina ceramic, and the SICW structure is composed of upper and lower metal plates and a series of metal cylindrical sidewall vias. A rectangular aperture antenna integrated on the surface of the SICW resonator is used for electromagnetic wave transmission between the sensor and the external antenna. The resonant frequency of the temperature sensor decreases when the temperature increases, because the relative permittivity of the alumina ceramic increases with temperature. The temperature sensor presented in this paper was tested four times at a range of 30⁻1200 °C, and a broad band coplanar waveguide (CPW)-fed antenna was used as an interrogation antenna during the test process. The resonant frequency changed from 2.371 to 2.141 GHz as the temperature varied from 30 to 1200 °C, leading to a sensitivity of 0.197 MHz/°C. The quality factor of the sensor changed from 3444.6 to 35.028 when the temperature varied from 30 to 1000 °C.