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This paper proposes a double-heterostructure (DH) GaN/AlGaN epitaxial layer that contains an AlGaN interlayer. The electrical properties are characterized and compared with conventional single-heterostructure (SH) GaN/AlGaN epitaxial layers. The Hall effect measurement shows that the DH GaN/AlGaN epitaxial layer has a carrier mobility of 1815 cm2 V−1 s−1, which is approximately 20.37% higher than the SH GaN/AlGaN epitaxial layer. The weak-beam dark-field images taken by transmission electron microscopy show that the AlGaN interlayer in the DH GaN/AlGaN epitaxial layer can block dislocations. The full widths at half maximum results show that there is no significant difference in the screw dislocation density between the SH and DH GaN/AlGaN epitaxial layers. However, the edge dislocation density and the overall internal stress in the DH GaN/AlGaN epitaxial layer are less than those in the SH GaN/AlGaN epitaxial layer. Finally, the physical mechanism of how edge dislocations impact the electrical properties of a DH GaN/AlGaN epitaxial layer is discussed.

A compact vector magnetometer based on balloon-like fiber structure functionalized by magnetic fluid (MF) was proposed. To fabricate the sensor, the single mode fiber (SMF) was bent into a balloon-like structure, and then the shape was fixed by using the alcohol lamp flame. Because of the bending, the fiber core mode leaks into the cladding, thereby forming higher order cladding modes that are sensitive to the variations of external refractive index. When the structure is encapsulated in MF, due to the anisotropic distribution of ferromagnetic nanoparticles under magnetic field, the refractive index around the fiber structure also presents anisotropy. By measuring the refractive index of the MF under different magnetic-field directions and intensities, both the measurement of the magnetic field intensity and direction can be achieved. The experimental results show that a high magnetic field intensity sensitivity of 0.78 nm/mT and a high magnetic-field direction sensitivity of 0.094°/mT were obtained. Due to the simple fabricating method, low cost, and highly sensitivity, the proposed fiber vector magnetometer has potential applications in the navigation, aviation, and electric power industry.

A new fiber Bragg grating (FBG) sensor that can measure temperature, vibration, and strain is proposed in this article. The structure of this sensor is designed and optimized via theoretical analysis and the finite-element method (FEM). With an innovatively designed L-shaped cantilever (LSC), this designed sensor can better balance the vibration measurement sensitivity and the resonant frequency. The strain measurement structure is designed as a hollow square so that the reaction force of the sensor for the measured object is only $2.76\times 10^{-3}$ N/ $\mu \varepsilon $ , which ensures that the strain distribution of the measured object is not affected. The designed sensor can significantly amplify the measured strain with a measurement sensitivity (5.44 pm/ $\mu \varepsilon$ ) that is four times greater than that of the bare FBGs. This article uses single-mode FBGs inscribed by a femtosecond laser (FS-FBG) to make the sensors, and the sensing performance is analyzed. The results show that this FS-FBG-based sensor can withstand temperatures up to 1100 °C.

With the advancement and development of science and technology, the detection role of small-scale robot has become increasingly prominent, especially for environmental detection in hazardous situations such as explosion and fire. In this study, to realise the detection of carbon monoxide gas in hazardous locations, a flexible carbon monoxide sensor consisting of polyimide, interdigital electrode, and composite film is proposed and designed, which has the advantages of simple structure, high sensitivity, good flexibility, and low cost. For the interdigital electrode, the distance between the electrodes and the width of the electrode is both 50 μm, and the sizes of the polyimide substrate and the electrode area are 1.5 × 4 cm2 and 1 × 1 cm2, respectively. The composite film is made by mixing single-walled carbon nanotubes and platinum powders. The test results show that the sensitivity of the sensor is 0.0201 Ω/ppm in the range of 0–100 ppm at room temperature with a linear fit of 94.63%.

Nitrogen-vacancy (NV) colour centres in diamond have attracted extensive attention in quantum precision measurement, computation and communication. In these fields, microwave manipulation is a technology in which antenna is used to radiate special microwave to manipulate the quantum spin state of NV colour centres. In this work, high frequency structure simulator software is used to design a microstrip antenna with a resonance frequency of 2.8756 GHz. Based on simulation and experiments, near field radiation of antenna is optimised to improve its microwave manipulation quality. This antenna will be helpful in the development of hybrid quantum devices of NV centres.

A double-channel (DC) GaN/AlGaN high-electron-mobility transistor (HEMT) as a terahertz (THz) detector at 315 GHz frequency is proposed and fabricated in this paper. The structure of the epitaxial layer material in the detector is optimized, and the performance of the GaN HEMT THz detector is improved. The maximum responsivity of 10 kV/W and minimum noise equivalent power (NEP) of 15.5 pW/Hz0.5 are obtained at the radiation frequency of 315 GHz. The results are comparable to and even more promising than the reported single-channel (SC) GaN HEMT detectors. The enhancement of THz response and the reduction of NEP of the DC GaN HEMT detector mainly results from the interaction of 2DEG in the upper and lower channels, which improves the self-mixing effect of the detector. The promising experimental results mean that the proposed DC GaN/AlGaN HEMT THz detector is capable of the practical applications of THz detection.

Multiplexed fiber optic Fabry–Perot interferometer (FPI) sensors are well known for their precision, simple construction, simpler wiring, and high sensing qualities. However, the limitations on existing demodulation methods degrade the measurement accuracy of multiplexed FPI sensors and necessitate large cavity length differences. In this paper, we propose an adaptive high-precision demodulation method based on vector matching and cluster-competitive particle swarm optimization (CCPSO), which transforms cavity length demodulation into searching for the global extreme. The proposed CCPSO, which uses agglomeration within clusters and competition between clusters simultaneously, enables the improvement of the global extreme search capabilities. The theoretical analysis and experimental results show that the proposed demodulation method decreases the lower limit of the needed cavity length differences to 22 μm, which is reduced by 76.9% compared with the fast Fourier transform-based method. An accuracy of 1.05 nm is achieved with a cavity length difference of 27.5 μm and a signal-to-noise ratio of 36.0 dB for the noise.

As an important part of the world cultural heritage, ancient buildings are important carrier of human civilization and non-renewable resource, which is also the historical data for studying the social economy, culture and art, and religious beliefs in the era of ancient buildings. However, with the rapid development of society, especially the development of urban construction, environmental pollution, and tourism, the health status of ancient buildings is not optimistic. At present, the rapid development of science and technology, information technology has been widely applied to all aspects of the field of cultural heritage, such as the protection of cultural relics, ancient buildings’ protection and repair, etc. This paper presents a review of the application of sensing technology in the field of the ancient buildings’ protection, especially in fiber optic sensing technology and wireless sensor network.

Accurate temperature measurements can efficiently solve numerous critical problems and provide key information. Herein, a flexible micro-three-dimensional sensor, with a combination of platinum and indium oxide to form thermocouples, is designed and fabricated by a microfabrication process to achieve in situ real-time temperature measurements. The stability and reliability of the sensor are greatly improved by optimizing the process parameters, structural design, and preparation methods. A novel micro-three-dimensional structure with better malleability is designed, which also takes advantage of the fast response of a two-dimensional thin film. The as-obtained flexible temperature sensor with excellent stability and reliability is expected to greatly contribute to the development of essential components in various emerging research fields, including bio-robot and healthcare systems. The model of the application sensor in a mask is further proposed and designed to realize the collection of health information, reducing the number of deaths caused by the lack of timely detection and treatment of patients.

PurposeThe Fabry-Perot sapphire optical fiber sensor is an excellent choice for high-temperature sensing in civil and military fields, such as oil exploitation, engine and turbine. The purpose of this paper is to study the high-reflective film system withstanding high temperature in Fabry-Perot sapphire optical fiber high-temperature sensor. To improve the performance of the sensor and reduce the difficulty of signal acquisition, one of the key ways is to enhance the normalized light intensity of F-P sensor, which can be achieved by coating the high-reflective film system on the fiber end.Design/methodology/approachThe high-reflective film system can be achieved by a multilayer film with alternating ZrO2and Al2O3film layers whose refractive indexes are different. In addition, the optimum film alternating sequences and the influence of the number of film layers, incident angle and temperature should be obtained by numerical analysis.FindingsWith the increase of the number of film layers, the reflectivity rises gradually and the change trend is more and more gentle. A minimum of the spectral reflectivity will occur at a certain incident angle depending on the design of the periodic multilayer system. Temperature affects the reflectivity of high-reflective film system. The normalized light intensity of the F-P sensor coated with high-reflective film system enhances greatly which is helpful to the signal demodulation. The temperature response of the F-P sensor is mainly determined by the characteristics of the F-P cavity.Originality/valueHigher reflectivity, lower cost and easy signal acquisition are the most important features of the introduced high-reflective film system for the Fabry-Perot sapphire optical fiber high-temperature sensor.

We propose a nonresonant terahertz (THz) detector based on double-channel (DC) GaN/AlGaN high-electron-mobility transistor (HEMT) utilizing a technology computer-aided design platform. The hydrodynamic model is simplified as the drift-diffusion model for nonresonant THz detection simulation. Dependence of THz photoresponse on various structure parameters of the detector is analyzed by simulation. The two typical metrics, responsivity and noise equivalent power (NEP), are theoretically calculated for the optimization of the structure parameters. The optimized responsivity and NEP reach 5.8 kV/W and 50 pW/Hz0.5 at the same gate voltage, respectively, and a minimum NEP of 20 pW/Hz0.5 is obtained. The comparison between our simulation results and the experiment data of single-channel HEMT detector proves that the DC HEMT detector shows an excellent THz detection performance.

A multimode fibre Bragg grating (MMFBG) is experimentally demonstrated in this work. The light from the lead-in optical fibre transmits to the MMFBG, the Bragg gratings in multimode fibres show multiple reflection peaks due to the coupling among all bounded modes. Some reflection peaks are reflected back to the lead-out fibre core by the MMFBG. Finally, the spatial frequency spectra of the reflection peaks are detected by the detection device. As the temperature variates, the changes in the transmission spectrum will be observed. Experimental results show that the MMFBG responds to temperature and the temperature sensitivity is 0.0114 nm/oC. The MMFBG has the advantages of compact structure, anti-electromagnetic interference, and stable chemical property, which has great potential in temperature measurement.

A flexible tactile sensor was proposed to measure the three-dimensional forces. The sensor consisted of a bump structure, top and bottom electrodes, a piezoelectric sensitive layer and a substrate layer. The top and the bottom electrodes were prepared by lift-off process. When a three-dimensional force was applied, the bottom four electrodes under the bump structure would collect different charge signals, which can be detected by the different electric current variations. In the experiments, when the forces range from 0 to 10N with different angles were applied to the bump structure, the sensor can measure forces with a best non-linearity of 1.89%. This proposed tactile sensor could be used in the intelligent robotics to measure multi-dimensional force.

This paper experimentally studies the temperature and pressure response of fiber Bragg grating (FBG) and gold-plated FBG. The incident light is transmitted through the sensor and is reflected after encountering FBG. As the temperature and pressure changes, the reflection peak will change. The changes in the reflection spectrum are studied through experiments to get the temperature and pressure changes at the measured point. The experimental results show that the temperature response sensitivity of the FBG is 0.011 nm/ °C, and the response sensitivity of gold-plated FBG is 0.031 nm/ °C. The pressure response sensitivities of the sensors are 0.07nm/Mpa and 0.09nm/Mpa., respectively. Through the comparison of FBG and gold-plated FBG, temperature and pressure dual-parameter sensing is realized. The probe structure is simplified, the measurement accuracy of the sensor is improved, and the temperature and pressure dual-parameter sensor measurement in the medical, chemical, engine and other research fields are realized.

A few-mode fiber Bragg grating (FM-FBG) inscribed in a few-mode fiber (FMF) can maintain multiple reflection peaks due to the stable multiple modes in FMF. This paper studies the sensing characteristics of multiple reflection peaks for a four-mode FBG (4M-FBG) and innovatively proposes a joint-peak demodulation method based on one FM-FBG to reduce measurement error in temperature or strain sensing. This joint-peak demodulation method, theoretically explained and experimentally verified, provides the possibility of generating miniature sensors with high measurement accuracy and stable measurement performance. The potential of 4M-FBG for simultaneous measurement of strain and temperature is studied in this paper. By measuring the changes of wavelength and intensity of the reflection peaks, temperature and strain can be measured effectively.

The optical fiber temperature and refractive index sensor combined with the hollow needle structure for medical treatment can promote the standardization of traditional acupuncture techniques and improve the accuracy of body fluid analysis. A double-parameter sensor based on fiber Bragg grating (FBG) is developed in this paper. The sensor materials are selected through X-ray diffraction (XRD) analysis, and the sensor sensing principle is theoretically analyzed and simulated. Through femtosecond laser writing pure silica fiber, a high temperature resistant wavelength type FBG temperature sensor is obtained, and the FBG is corroded by hydrofluoric acid (HF) to realize a high-sensitivity intensity-type refractive index sensor. Because the light has dual characteristics of energy and wavelength, the sensor can realize simultaneous dual-parameter sensing. The light from the lead-in optical fiber is transmitted to the sensor and affected by temperature and refractive-index, then, the reflection peak is reflected back to the lead-out fiber by the FBG. The high temperature response and the refractive index response of the sensor were measured in the laboratory, and the high temperature characteristics of the sensor were verified in the accredited institute. It is demonstrated that the proposed sensor can achieve temperature sensing up to 1150 °C with the sensitivity of 0.0134 nm/°C, and refractive sensing over a refractive range of 1.333 to 1.4027 with the sensitivity of −49.044 dBm/RIU. The sensor features the advantages of two-parameter measurement, compact structure, and wide temperature range, and it exhibits great potential in acupuncture treatment.

In the paper, the flexible temperature sensor based on polyimide is designed and fabricated by magnetron sputtering technology. The impact of vacuum degree, sputtering power, and argon flow rate on the roughness and deposition rate of two thermo-electrodes [indium tin oxide (ITO)/indium oxide (In2O3)] is investigated with orthogonal experiment. The thermoelectric properties of the sensor are greatly improved by low temperature heat treatment. The sensitivity of the ITO film and In2O3 film increases by 2.61 times and 2.89 times, respectively, after 1 h low-temperature heat treatment. According to the comprehensive evaluation, an innovative step annealing process is proposed to optimize the heat treatment of the prepared thermo-electrodes. The fabricated flexible thin film thermocouples exhibit great operating characteristics in the low temperature measurement range. When the hot end's temperature reaches 181.5 °C, the thermoelectric force can reach 7.84 mV and the average Seebeck coefficient can reach 50.55 µV/°C. The repeatability and hysteresis error of the sensor is ±0.88% and 1.90%, respectively. The sensor in this work shows great application potential for in situ real-time temperature measurement in robotic dexterous hands, electronic skin, and foldable devices.

As the perfect combination of fiber optics and nanotechnology, micro-nano fiber is one of the frontier research directions in fiber optics and micro-nano photonics developed in recent years. In this paper, a high-sensitivity temperature sensor is proposed and realized based on the micro-nano fiber structure. The degree of linearity and sensitivity of the sensor are 98.6% and -0.0121 dBm / °C, respectively. Besides, the preparation process and influencing factors of micro-nano fiber are also introduced and discussed in detail. The configuration features the advantages of high sensitivity, simple structure, low transmission loss, low cost, and easy fabrication, making it a good candidate for the field of temperature measurement.

WRe26-In2O3 (WRe26 (tungsten-26% rhenium) and In2O3 thermoelectric materials) thin film thermocouples (TFTCs) have been fabricated based on magnetron sputtering technology, which can be used in temperature measurement. Many annealing processes were studied to promote the sensitivity of WRe26-In2O3 TFTCs. The optimal annealing process of the thermocouple under this kind of RF magnetron sputtering method was proposed after analyzing the properties of In2O3 films and the thermoelectric voltage of TFTCs at different annealing processes. The calibration results showed that the WRe26-In2O3 TFTCs achieved a thermoelectric voltage of 123.6 mV at a temperature difference of 612.9 K, with a sensitivity of up to 201.6 &micro, V/K. Also, TFTC kept a stable thermoelectric voltage output at 973 K for 20 min and at 773 K for two hours. In general, the WRe26-In2O3 TFTCs developed in this work have great potential for practical applications. In future work, we will focus on the thermoelectric stability of TFTCs at higher temperatures.

An optical fibre Fabry–Perot interferometer (FPI) is proposed and experimentally demonstrated in this work. In the fast Fourier transform spectrum of the FPI transmission spectrum, a higher order model is separated from the transmission spectrum and the spatial frequency spectrum of the higher order model is detected. As the temperature changes, the shifts of the spatial frequency spectrum will be observed. The sensitivity of the temperature is 0.128 µm−1 K−1. The proposed sensor features the advantages of easy fabrication, compact structure and stable chemical property, and exhibits great potential in high-temperature measurement.

An optical Mach-Zehnder interferometer (MZI) composed of a short section of thin-core fiber (TCF) which inserted into a standard single-mode fiber (SMF) with two waist-enlarged bitapers was proposed for high temperature measurement. MZIs with different lengths were fabricated, and the relationship between length and interference period was studied. The fast Fourier transform (FFT) method was used to determine the transmitted spectra of MZIs, and the results indicate that LP01 and LP02 modes are the main modes. The MZI has a high temperature sensitivity of 0.087 nm/°C with a good linearity of 99.8% from 30 to 1000 °C. Because it has advantages of compact size, easy fabrication, high sensitivity, high mechanical strength and wide sensing range, the MZI can be used for high sensitivity temperature measurement.

In the present study, a high-performance n-type temperature sensor was developed by a new and facile synthesis approach, which could apply to ambient temperature applications. As impacted by the low sintering temperature of flexible polyimide substrates, a screen printing technology-based method to prepare thermoelectric materials and a low-temperature heat treatment process applying to polymer substrates were proposed and achieved. By regulating the preparation parameters of the high-performance n-type indium oxide material, the optimal proportioning method and the post-treatment process method were developed. The sensors based on thermoelectric effects exhibited a sensitivity of 162.5 μV/°C, as well as a wide range of temperature measurement from ambient temperature to 223.6 °C. Furthermore, it is expected to conduct temperature monitoring in different scenarios through a sensor prepared in masks and mechanical hands, laying a foundation for the large-scale manufacturing and widespread application of flexible electronic skin and devices.

In this paper, an optical fiber MEMS (Micro-Electro-Mechanical System) micro pressure sensor based on BM (beam-membrane) structure is proposed. The most important part of the sensor is composed of a sensitive silicon diaphragm and a dual fiber collimator. In the designed optic fiber micro pressure sensor, the sensitive silicon diaphragm creatively utilizes a BM structure made by MEMS manufacturing technology. By comparing other structures and performing simulations, the BM structure has better linearity while ensuring its sensitivity is concluded. The BM structure is used to reflect light, and the dual-fiber collimator is used to transmit and receive light. The measurement range of the sensor is from 0KPa to 10KPa. The intensity demodulation makes the whole system easier to realize and ensures the performance of the sensor. By setting up the sensor experimental platform and conducting experiments, the sensitivity of the designed sensor is −0.252db/KPa.

Nowadays, studies based on quantum effect of nitrogen-vacancy (NV ) color centers in diamond have received extensive attention, such as quantum computing, quantum information and quantum precision measurement. In these fields, microwave manipulation is one kind of critical technology in which antenna was used to radiate special magnetic pulse to manipulate the quantum state of NV color centers. In this study, High Frequency Structure Simulator software (HFSS ) is used to design microstrip antenna whose resonance frequency is 2.87GHz. Based on simulation and experiment, near field radiation of the sample is optimized to improve its magnetic field. Besides, wide bandwidth and high radiation efficiency is achieved through a sandwich structure. This antenna will be helpful in guiding the development of hybrid quantum devices of NV centers, especially for precision measurement sensing.

In this paper, a novel optical fiber surface plasmon resonance (SPR) magnetic field sensor is proposed and experimentally demonstrated. The structure is fabricated by splicing a section of photonic crystal fiber between two multimode fibers. After the structure is coated with 10 nm Cr and 50 nm Au, the high refractive index (RI) sensitivity, from 1973.72 nm RIU−1 to 3223.32 nm RIU−1 in the range of 1.3326–1.3680, verifies the SPR sensor, which is higher than the structure based on single mode fiber with the same coating. In addition, the microscopic mechanism of the tunable characteristics of magnetic fluid RI with the ambient magnetic field is simulated by the molecular dynamics method. To measure the external magnetic field, the sensing region of the SPR sensor is fully inserted in a capillary tube, which is filled with magnetic fluid and sealed with UV glue. A maximum sensitivity of 4.42 nm mT−1 is achieved in the range of 0–24 mT, experimentally. Due to high sensitivity, simple manufacturing and compact size, the proposed sensor possesses attractive application prospects in environmental monitoring, power transmission and biomedical applications.

Autonomous wireless sensor nodes (WSN) for information acquisition and status monitoring, play an important role in the boom area of the internet of things (IoT) and industry 4.0. Self-sustained power supply is an important pursuit in massive practical applications but yet to be developed. Here we propose a novel hybrid piezoelectric generator (PEG) and triboelectric nanogenerator (TENG) to form a novel self-sustainable WSN. The PEG consisting of a hinged-hinged PZT bimorph and two T shaped proof mass, has an output power of 6.5 mW excited in 25 Hz at 1.0 g. PEG also shows broadband characteristics thanks to the impact of the TENG and tunable frequency due to the axial force. 30 serial LEDs in sine vibration and 20 serial LEDs in shock vibration are lighted up with the proposed double voltage rectifier circuit by PEG, which can serve as alarming signals in vibration and drop monitoring. The triboelectric accelerometer shows good linearity with a sensitivity of 15 V/g in 0–1.5 g with an optimized gap of 1.5 mm. After low power design, Arduino nano and RF transceiver can be sustainably powered by PEG, and send the TENG acceleration signal wirelessly by Zigbee. A VR train monitoring demonstration has been conducted showing the great prospect of the self-sustainable WSN in harsh environments.

In this paper, a novel micro-displacement sensor with double optical fiber probes is proposed and designed, which can realize the highly sensitive sensing of longitudinal or lateral micro-displacements. The optical fiber probes are made through photopolymer formulation, and the effects of reaction time and optical power on the growth length of the probe are illustrated. The relationship between light intensity and longitudinal micro-displacement is a power function in the range of 0–100 μm at room temperature with a correlation coefficient of 98.92%. For lateral micro-displacement, the sensitivity is −2.9697 dBm/μm in the range of 0–6 μm with a linear fit of 99.61%. In addition, the linear correlation coefficient decreases as the initial longitudinal distance increases, and the function of these correlation coefficients is also linear with a linearity of 96.14%. This sensor has a simple manufacturing process, low cost, high sensitivity, and fast response speed. It is suitable for harsh environments such as strong electromagnetic interference and corrosivity, and has a broad application prospect in the field of micro-displacement sensing.

In this paper, indium oxide (In2O3) and platinum (Pt) are selected as thermoelectric materials to form a kind of temperature sensor. The thermoelectric property of In2O3 is optimized by heat treatment that the Seebeck coefficient is greatly increased with the increase of heat treatment time at 200°C. The sensitivity of the flexible thin film thermocouples combined with Pt increased from -40.43μV/°C to -176.06μV/°C with the same temperature difference between hot junction and cold junctions, increasing by 4.35 times. The treated flexible Pt/In2O3 TFTCs based on polyimide exhibits a maximum output voltage of 34.33mV and an ultra-high sensitivity of 204.35μV/°C, which is one of the highest values reported for thermocouples deposited onto flexible substrate in the low temperature measurement. In repeatability test and stability test, the sensor also shows great characteristics in repeatability, stability and the temperature drift. In practical manipulator measurement, it can realize accurate measurement of the temperature of the measured object, which has an excellent application prospect of industrial robot and biomedicine.

This paper investigates optical characteristics of ZnO/Cu/ZnO multilayer optical thin film by numerical simulation and it is further verified by experiments. The influences of Cu and ZnO thickness on the optical characteristics of ZnO/Cu/ZnO thin films are studied. The results show that the transmittances of ZnO/Cu/ZnO thin film decrease with the increase of thickness of Cu layer but are nonlinear with the ZnO thickness. The maximal light transmission in the visible region is obtained by controlling the thickness of Cu and ZnO films.

A novel probe-type thin film thermocouple has been fabricated successfully for high temperature measurement applications. WRe26 (tungsten–26% rhenium)–In2O3 thermoelectric materials were used in the thermocouples to achieve high thermoelectric output and high temperature resistance. The films were deposited on a cylindrical substrate by magnetron sputtering technology. The annealing process of the thermocouples was studied to achieve optimal performance. The calibration results showed the thermoelectric output of WRe26–In2O3 thin film thermocouples reached 93.7 mv at 700 °C, and its sensitivity was 165.5 µV/°C under the temperature of the cold junction, which was 133.8 °C. The thermocouples developed in this work have great potential for practical applications.

Wireless sensor nodes (WSNs) for temperature and humidity monitoring are commonly used in a cold chain logistics container. Energy harvesting technology is expected to realize the sustainable self-power supply for the WSN. Low amplitude and broadband vibration energy harvesting performance are the key points in train application. In this study, two piezoelectric vibration energy harvesters (PVEHs) are designed and simulated via COMSOL. Their low resonant frequencies and high electromechanical sensitivities are realized by big L-shaped mass blocks with different material densities. Their broadband vibration energy harvesting performance is achieved by the stopper and series connection. Experimental data are shown at an acceleration of 0.5 m/s2; PVEH-1 and PVEH-2 have maximum powers of 0.24 mW and 0.1 mW when excited at the resonant frequencies of 13.1 Hz and 18.8 Hz, respectively, and they both have the optimal load resistance of 40 kΩ. Two circuit design styles of two PVEHs, independent and series styles, are proposed for broadband vibration energy harvesting. Experimental results show that the series style has a wider operating frequency bandwidth and shorter charging time. Two PVEHs in series style can be effectively used for power supply of the temperature and humidity WSN in the broadband frequency range of 8.7-22.0 Hz above charging root mean square voltage of 5 V at the acceleration of 3.0 m/s2. This scheme is promised to be applied to the cold chain logistics train container.

A multimode fiber Bragg grating (MMFBG) is experimentally demonstrated in this paper. The light from the lead-in optical fiber is transmitted to the MMFBG, Bragg gratings in multimode fibers show multiple reflection peaks due to the coupling between all bounded modes. Some reflection peaks are reflected back to the lead-out fiber core by the MMFBG. Finally, the spatial frequency spectra of the reflection peaks are detected by the detection device. As the temperature change, the shifts of the spatial frequency spectrum will be observed. Experimental results show that the MMFBG responds to temperature and the valve of temperature sensitivity is 0.0114 nm/°C. The MMFBG features the advantages of anti-electromagnetic interference, compact structure and stable chemical property, and it exhibits great potential in temperature measurement.

A fourier analysis applied to the Fabry-Perot interferometer(FPI) transmission spectrum for temperature measurement is proposed and experimentally demonstrated in this paper. In the fast Fourier transform (FFT) spectrum of the FPI transmission spectrum, a higher order model is separated from the transmission spectrum and the spatial frequency spectra of the higher order model is detected. As the temperature change, the shifts of the spatial frequency spectrum will be observed. The sensitivity of the temperature is 0.00012/(nm · °C). The proposed sensor features the advantages of easy fabrication, compact structure and stable chemical property, and it exhibits great potential in high temperature measurement.

A combined sensor to simultaneously measure strain, vibration, and temperature has been developed. The sensor is composed of two Fiber Bragg gratings (FBGs) and a vibration gainer. One FBG is used to measure strain, while the other measures vibration and temperature. The gainer has a mass block which is used to increase its sensitivity to vibration. The main beam of the vibration gainer was designed as a trapezoid in order to reduce the strain gradient while sensing vibration. In addition, an interrogation method was used to eliminate interactions between measured parameters. Experiments were carried out to analyze the performance of the proposed sensor. For individual strain measurement in the range of 0&ndash, 152 &mu, &epsilon, the sensitivity and nonlinearity error were 1.878 pm/&mu, and 2.43% Full Scale (F.S.), respectively. For individual temperature measurement in the range of 50&ndash, 210 &deg, C, the sensitivity and nonlinearity error were 29.324 pm/&deg, C and 1.88% F.S., respectively. The proposed sensor also demonstrated a sensitivity of 0.769 pm/m&middot, s&minus, 2 and nonlinearity error of 1.83% F.S. for vibration measurement in the range of 10&ndash, 55 m/s2. Finally, simultaneously measuring strain, temperature, and vibration resulted in nonlinearity errors of 4.23% F.S., 1.89% F.S., and 2.23% F.S., respectively.

Fiber Bragg gratings (FBGs) have become a promising sensor element for measuring temperature, strain and other parameters. However, there exists a cross-sensitivity between temperature and strain. An all-fiber sensing system composed of gold-plated FBGs and acrylic FBGs has been proposed and fabricated, which can achieve simultaneous measurement of axial strain and temperature. Using a spectrometer to monitor the shift in the transmission spectrum in real time, the strain and ambient temperature applied to the sensor can be measured conveniently. The experimental results show that the temperature sensitivity of a gold-plated FBG is 3.2 times of that of an acrylate-plated FBG, which can distinguish the temperature changes efficiently. In other words, its sensitivity is increased 2.2 times compared with ordinary fiber grating. The strain sensitivity of gold-plated FBG and acrylate-plated FBG is the same, which is 1.19 pm/µe. The sensor has the advantages of having a simple structure and high sensitivity and can be used to monitor the running state of rail traffic.

An ordinary optical fiber ultra-high temperature sensor based on infrared radiation with the advantages of simple structure and compact is presented. The sensing system consists of a detection fiber and a common transmission fiber. The detector fiber is formed by annealing a piece of ordinary fiber at high temperature twice, which changes the properties of the fiber and breaks the temperature limit of ordinary fiber. The transmission fiber is a bending insensitive optical fiber. A static calibration system was set up to determine the performance of the sensor and three heating experiments were carried out. The temperature response sensitivities were 0.010 dBm/K, 0.009 dBm/K and 0.010 dBm/K, respectively, which indicate that the sensor has good repeatability. The sensor can withstand a high temperature of 1823 K for 58 h with an error of less than 1%. The main reason why the developed ordinary optical fiber sensor can work steadily for a long time at high temperature is the formation of &beta, cristobalite, which is stable at high-temperature.

A temperature multipoint sensing system based on three cascade Mach&ndash, Zehnder interferometers (MZIs) is introduced. The MZIs with different lengths are fabricated based on waist-enlarged fiber bitapers. The fast Fourier transformation is applied to the overlapping transmission spectrum and the corresponding interference spectra can be obtained via the cascaded frequency spectrum based on the inverse Fourier transformation. By analyzing the drift of interference spectra, the temperature response sensitivities of 0.063 nm/&deg, C, 0.071 nm/&deg, C, and 0.059 nm/&deg, C in different furnaces can be detected from room temperature up to 1000 &deg, C, and the temperature response at different regions can be measured through the sensitivity matrix equation. These results demonstrate feasibility of multipoint measurement, which also support that the temperature sensing system provides new solution to the MZI cascade problem.

A nano-scale dual-step was made by Focused Ion Beam (FIB). The shape of the nano two-step was measured using Atom Force Microscope (AFM). The parameter values in different location of the nano dual-step are compared, including the height h, the base surface roughness Rabase, the first-step surface roughness Rastep1, the second-step surface roughness Rastep2 and the sidewall inclination θ1, θ2. It was shown that the control of z direction was difficulte when the size was ≤ 50 nm.

In this paper, nanolines are fabricated on photoresist using electron beam lithography (EBL) technique. The trapeziform of the cross-section is studied through analysis of the top-down scan electron microscope (SEM) image of the nanolines. Width is not adequate to describe the nanolines. From the SEM image it can be observed that the edge of the nanolines is not straight. Fractal dimension is used to describe the line-edge roughness (LER) of the nanolines. Three different methods are used to calculate the width of the nanolines. Comparing three different values and uncertainty, the true value of the nanolines has been found.

In this paper, we describes an integrated MEMS tactile tri-axial micro-force probe sensor based on piezoresistive for Minimally Invasive Surgery (MIS) as it's micro-structure, three-dimensional measurement and high resolution up to be micronewton (μN) scale. The sensor is 4×4×20.9mm3. The sensing element of the sensor is fabricated on Silicon on Insulator (SOI) wafer by surface and bulk micromachining technology. It uses four cantilever beams supporting the suspended mass. Twelve relief pieoresisters formed by iron implant and Inductive Couple Plasmas (ICP) etching technology are placed on the beams to detect the applied force. The pyrex glass bonded on the bottom of the SOI wafer by anodic bonding technology is the overload protection element. The tactile element is the quartz fiber probe which is no-pollution, low cost, small size and easy to process. It is glued on suspended mass of the sensing element by epoxy resin. After fabrication, the sensor is packaged and tested by precision test bench and analytical balance. The experimental results illustrate that the sensor has excellent characteristics especially with resolution better than 3µN.