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Abstract The chip-scale hybrid optical pumping spin-exchange relaxation-free (SERF) atomic magnetometer with a single-beam arrangement has prominent applications in biomagnetic measurements because of its outstanding features, including ultrahigh sensitivity, an enhanced signal-to-noise ratio, homogeneous spin polarization and a much simpler optical configuration than other devices. In this work, a miniaturized single-beam hybrid optical pumping SERF atomic magnetometer based on a microfabricated atomic vapor cell is demonstrated. Although the optically thin Cs atoms are spin-polarized, the dense Rb atoms determine the experimental results. The enhanced signal strength and narrowed resonance linewidth are experimentally proven, which shows the superiority of the proposed magnetometer scheme. By using a differential detection scheme, we effectively suppress optical noise with an approximate five-fold improvement. Moreover, the cell temperature markedly affects the performance of the magnetometer. We systematically investigate the effects of temperature on the magnetometer parameters. The theoretical basis for these effects is explained in detail. The developed miniaturized magnetometer has an optimal magnetic sensitivity of 20 fT/Hz1/2. The presented work provides a foundation for the chip-scale integration of ultrahighly sensitive quantum magnetometers that can be used for forward-looking magnetocardiography (MCG) and magnetoencephalography (MEG) applications.

Abstract With the rapid development of various fields, including aerospace, industrial measurement and control, and medical monitoring, the need to quantify flow velocity measurements is increasing. It is difficult for traditional flow velocity sensors to fulfill accuracy requirements for velocity measurements due to their small ranges, susceptibility to environmental impacts, and instability. Herein, to optimize sensor performance, a flexible microelectromechanical system (MEMS) thermal flow sensor is proposed that combines the working principles of thermal loss and thermal temperature difference and utilizes a flexible cavity substrate made of a low-thermal-conductivity polyimide/SiO2 (PI/SiO2) composite porous film to broaden the measurement range and improve the sensitivity. The measurement results show that the maximum measurable flow velocity can reach 30 m/s with a resolution of 5.4 mm/s. The average sensitivities of the sensor are 59.49 mV/(m s−1) in the medium-to-low wind velocity range of 0–2 m/s and 467.31 mV/(m s−1) in the wind velocity range of 2–30 m/s. The sensor proposed in this work can enable new applications of flexible flow sensors and wearable devices.

Existing microfabricated atomic vapor cells have only one optical channel, which is insufficient for supporting the multiple orthogonal beams required by atomic devices. In this study, we present a novel wafer-level manufacturing process for fabricating multi-optical-channel atomic vapor cells and an innovative method for batch processing the inner sidewalls of millimeter glass holes to meet optical channel requirements. Surface characterization and transmittance tests demonstrate that the processed inner sidewalls satisfy the criteria for an optical channel. In addition, the construction of an integrated processing platform enables multilayer non-isothermal anode bonding, the filling of inert gases, and the recovery and recycling of noble gases. Measurements of the absorption spectra and free-induction decay signals of xenon-129 (129Xe) and xenon-131 (131Xe) under different pump-probe schemes demonstrate the suitability of our vapor cell for use in atomic devices including atomic gyroscopes, dual-beam atomic magnetometers, and other optical/atomic devices. The proposed micromolding technology has broad application prospects in the field of optical-device processing.

Abstract Stress tolerance plays a vital role in ensuring the effectiveness of piezoresistive sensing films used in flexible pressure sensors. However, existing methods for enhancing stress tolerance employ dome-shaped, wrinkle-shaped, and pyramidal-shaped microstructures in intricate molding and demolding processes, which introduce significant fabrication challenges and limit the sensing performance. To address these shortcomings, this paper presents periodic microslits in a sensing film made of multiwalled carbon nanotubes and polydimethylsiloxane to realize ultrahigh stress tolerance with a theoretical maximum of 2.477 MPa and a sensitivity of 18.092 kPa−1. The periodic microslits permit extensive deformation under high pressure (e.g., 400 kPa) to widen the detection range. Moreover, the periodic microslits also enhance the sensitivity based on simultaneously exhibiting multiple synapses within the sensing interface and between the periodic sensing cells. The proposed solution is verified by experiments using sensors based on the microslit strategy for wind direction detection, robot movement sensing, and human health monitoring. In these experiments, vehicle load detection is achieved for ultrahigh pressure sensing under an ultrahigh pressure of over 400 kPa and a ratio of the contact area to the total area of 32.74%. The results indicate that the proposed microslit strategy can achieve ultrahigh stress tolerance while simplifying the fabrication complexity of preparing microstructure sensing films.

Microfabricated alkali metal vapor cells are the core components for miniaturizing quantum devices, such as atomic clocks, atomic gyroscopes, and atomic magnetometers. Alkali metals are prone to thermal migration at the bonding interface during the sealing of the vapor cell, which leads to bonding failure. In this study, a non-isothermal anodic bonding process based on plasma activation was developed to achieve high-strength bonding at low temperatures using the temperature gradient to keep the alkali metal away from the bonding interface. This procedure eliminates interference from the alkali metal and significantly increases the success rate of anodic bonding of vapor cells. Simulation results for the temperature field and the residual stresses during anodic bonding demonstrate that the procedure is theoretically feasible. The effect of plasma treatment on the contact angle and roughness of the bonding surface revealed a mechanism for improving the bond strength. In addition, the construction of an integrated processing platform made it possible to perform non-isothermal anode bonding, injection of alkali metal, filling of inert gases, and recovery and recycling of noble gases. The high strength and good hermeticity of the bonding interface were demonstrated by the bond strength, cross-sectional high-resolution transmission electron microscopy observations, and leakage rate tests. Finally, the absorption spectrum and free-induction decay signal of the fabricated vapor cell were measured.

Abstract With the growing demand for thermal management of electronic devices, cooling of high-precision instruments, and biological cryopreservation, heat flux measurement of complex surfaces and at ultralow temperatures has become highly imperative. However, current heat flux sensors (HFSs) are commonly used in high-temperature scenarios and have problems when applied in low-temperature conditions, such as low sensitivity and embrittlement. In this study, we developed a flexible and highly sensitive HFS that can operate at ultralow to high temperatures, ranging from −196 °C to 273 °C. The sensitivities of HFSs with thicknesses of 0.2 mm and 0.3 mm, which are efficiently manufactured by the screen-printing method, reach 11.21 μV/(W/m2) and 13.43 μV/(W/m2), respectively. The experimental results show that there is a less than 3% resistance change from bending to stretching. Additionally, the HFS can measure heat flux in both exothermic and absorptive cases and can measure heat flux up to 25 kW/m2. Additionally, we demonstrate the application of the HFS to the measurement of minuscule heat flux, such as heat dissipation of human skin and cold water. This technology is expected to be used in heat flux measurements at ultralow temperatures or on complex surfaces, which has great importance in the superconductor and cryobiology field.

Considering the magnetic shielding requirements of both geomagnetic field and 50 Hz power-line frequency in the complex working conditions of the power grid, an electromagnetic shielding system combining active and passive modes is proposed in this article. A three-dimensional Helmholtz coil with a magnetic shielding barrel nested inside is established by the COMSOL simulation tool, and the magnetic shielding efficiency of the system is analyzed. Comparing different materials, the simulation results indicate that permalloy alloy exhibits better shielding performance than pure iron and nickel materials. Additionally, the overall shielding efficiency of the shielding barrel increases linearly with the number of multiple layers. Under the combined active and passive electromagnetic shielding conditions, the system achieves a shielding efficiency of SE = 113.98 dB, demonstrating excellent performance in shielding both AC and DC interference magnetic fields. This study provides theoretical guidance for the construction of magnetic shielding systems in electromagnetic interference environment.

Abstract Precision grinding is a key process for realizing the use of large-aperture aspherical optical elements in laser nuclear fusion devices, large-aperture astronomical telescopes, and high-resolution space cameras. In this study, the arc envelope grinding process of large-aperture aspherical optics is investigated using a CM1500 precision grinding machine with a maximum machinable diameter of Φ1500 mm. The form error of the aspherical workpiece induced by wheel setting errors is analytically modeled for both parallel and cross grinding. Results show that the form error is more sensitive to the wheel setting error along the feed direction than that along the lateral direction. It is a bilinear function of the feed-direction wheel setting error and the distance to the optical axis. Based on the error function above, a method to determine the wheel setting error is proposed. Subsequently, grinding tests are performed with the wheels aligned accurately. Using a newly proposed partial error compensation method with an appropriate compensation factor, a form error of 3.4 μm peak-to-valley (PV) for a Φ400 mm elliptical K9 glass surface is achieved.

High-temperature thin-film thermocouples (TFTCs) have attracted significant attention in the aerospace and steel metallurgy industry. However, previous studies on TFTCs have primarily focused on the two-dimensional planar-type, whose thermal sensitive area has to be perpendicular to the test environment, and therefore affects the thermal fluids pattern or loses accuracy. In order to address this problem, recent studies have developed three-dimensional probe-type TFTCs, which can be set parallel to the test environment. Nevertheless, the probe-type TFTCs are limited by their measurement threshold and poor stability at high temperatures. To address these issues, in this study, we propose a novel probe-type TFTC with a sandwich structure. The sensitive layer is compounded with indium oxide doped zinc oxide and fabricated using screen-printing technology. With the protection of sandwich structure on electrode film, the sensor demonstrates robust high-temperature stability, enabling continuous working at 1200 °C above 5 h with a low drift rate of 2.3 °C·h ^−1 . This sensor exhibits a high repeatability of 99.3% when measuring a wide range of temperatures, which is beyond the most existing probe-type TFTCs reported in the literature. With its excellent high-temperature performance, this temperature sensor holds immense potentials for enhancing equipment safety in the aerospace engineering and ensuring product quality in the steel metallurgy industry.

An intensity-demodulated fiber-optic magnetometer is proposed and experimentally investigated, which is fabricated via fusion splicing a segment of photonic crystal fiber (PCF) between single-mode fibers (SMFs), with the cladding air holes of PCF filled with magnetic fluid. Using the magneto-optical properties of the magnetic fluid, the transmission spectrum is changed with an external magnetic field. Based on the intensity variations in the transmission spectrum, the magnetic field is detected, and a sensitivity of 0.238 dB/mT is obtained at 1550.03 nm with the length of PCF 5.5 cm. By converting light signals into electrical signals, a sensitivity of 0.003 V/mT is achieved. The fiber-optic magnetometer possesses the advantages of simple fabrication, compact/robust structure, and low cost.

In this work, a novel fiber-optic sensor for 2D magnetic sensing is explored based on nanostructured magnetic fluid. The fiber-optic sensor comprises a ring-shaped fiber structure that is coated with magnetic fluid. The unique magneto-optical characteristic of the nanostructured magnetic fluid enables the fiber-optic structure to detect magnetic fields. By utilizing the 3D Monte Carlo method, the magneto-optical characteristic induced by the nanostructure changes in the magnetic fluid was analyzed. The sensor can realize 2D vector magnetic sensing by intensity demodulation and achieves a sensitivity of 2.402 dB/mT. The proposed fiber optic sensor helps in developing a high-sensitivity 2D vector magnetic field sensor, which has potential applications in the fields of navigation, electrical power systems, and biological detection.

This study discussed the application of optical fibers in addressing the problem of insufficient light harvesting and sensing health monitoring in ancient buildings. Based on three-dimensional (3D) printing technology to fix the light-harvesting lens and conducting optical fiber, develop the replacement parts that can be buried into the optical fiber of ancient buildings. By introducing the experimental application to improve the experimental quality of research and teaching. Firstly, it highlights the advantage that the optical fiber plus lens structure design can make the natural light introduced for a long time; secondly, it points out that the buried optical fiber structure design does not affect the warmth and sound insulation of the building; finally, the health monitoring of the building is realized through the proposed method of buried optical fiber sensing. The design scheme adopts a fiber optic light transmission and sensing system, which can realize the whole system’s corrosion resistance, after laying buried and low-cost operation.

A co-sputtering process for the deposition of Fe0.8Ga0.2B alloy magnetostrictive thin films is studied in this paper. The soft magnetic performance of Fe0.8Ga0.2B thin films is modulated by the direct-current (DC) sputtering power of an FeGa target and the radio-frequency (RF) sputtering power of a B target. Characterization results show that the prepared Fe0.8Ga0.2B films are amorphous with uniform thickness and low coercivity. With increasing FeGa DC sputtering power, coercivity raises, resulting from the enhancement of magnetism and grain growth. On the other hand, when the RF sputtering power of the B target increases, the coercivity decreases first and then increases because of the conversion of the films from a crystalline to an amorphous state. The lowest coercivity of 7.51 Oe is finally obtained with the sputtering power of 20 W for the FeGa target and 60 W for the B target. Potentially, this optimization provides a simple way for improving the magnetoelectric coefficient of magnetoelectric composite materials and the sensitivity of magnetoelectric sensors.

Abstract With the rapid development and application of smart homes, sensors known as ‘neurons’ have become more and more important in this field. In response to the demand for relative humidity parameter in home monitoring, a flexible relative humidity sensor based on reduced graphene oxide (RGO) and interdigital electrode for smart homes was designed and prepared in this paper. The base of the interdigital electrode structure was polyimide, and the RGO film was prepared by a spraying process. A test system for the relative humidity sensor with different saturated salt solutions was also built. The test results show that the sensor resistance and relative humidity have a linear relationship in the range of 24.6% RH–82.9% RH, and the linearity is as high as 0.987. The sensitivity of the sensor is 0.51 kΩ/% RH. The relative humidity sensor with the characteristics of flexibility and high sensitivity will have broad application prospects and value in the field of smart homes.

Abstract Flexible sensors used to detect NO2 gas generally have problems such as poor repeatability, high operating temperature, poor selectivity, and small detection range. In this work, a new spraying platform with a simple structure, low cost, and good film-forming consistency was designed and built to make a sensitive film (rGO/SnO2) for NO2 gas sensors. The relationship between the solid content of rGO and SnO2 nanoparticles, annealing temperature, and sensor performance was studied. The results show that the interdigital electrode-sensitive film formed by spraying 0.25 ml of a 0.4 wt% rGO/SnO2 mixture and annealing at 250 °C exhibited the best comprehensive performance for NO2 detection. The sensor’s response value for 100 ppm NO2 gas was 0.2640 at room temperature (25 °C), and the response time and recovery time were 412.4 s and 587.3 s, respectively. In the range of 20–100 ppm, the relationship between the response and NO2 concentration was linear, and the correlation coefficient was 0.9851. In addition, a soft-monitoring node module with an overlimit warning function for NO2 gas was designed and manufactured based on flexible electronics. Finally, the flexible sensor and node module were embedded into woven fabric that could be used to make a mask or a watch that could detect NO2 gas, realizing the practical application of flexible NO2 gas sensors in the field of wearable electronics.

Abstract A micromachined resonator immersed in liquid provides valuable resonance parameters for determining the fluidic parameters. However, the liquid operating environment poses a challenge to maintaining a fine sensing performance, particularly through electrical characterization. This paper presents a piezoelectric micromachined cantilever with a stepped shape for liquid monitoring purposes. Multiple modes of the proposed cantilever are available with full electrical characterization for realizing self-actuated and self-sensing capabilities. The focus is on higher flexural resonances, which nonconventionally feature two-dimensional vibration modes. Modal analyses are conducted for the developed cantilever under flexural vibrations at different orders. Modeling explains not only the basic length-dominant mode but also higher modes that simultaneously depend on the length and width of the cantilever. This study determines that the analytical predictions for resonant frequency in liquid media exhibit good agreement with the experimental results. Furthermore, the experiments on cantilever resonators are performed in various test liquids, demonstrating that higher-order flexural modes allow for the decoupled measurements of density and viscosity. The measurement differences achieve 0.39% in density and 3.50% in viscosity, and the frequency instability is below 0.05‰. On the basis of these results, design guidelines for piezoelectric higher-mode resonators are proposed for liquid sensing.

At present, flexible pressure-sensitive materials generally have problems with weak adhesion and poor wear resistance, which easily result in friction failure when used for plantar pressure detection. In this study, a flexible pressure sensor with the advantages of a wide detection range, fast recovery, and good abrasive resistance was designed and prepared based on the screen printing process. The pressure-sensitive unit with a structural size of 5 mm× 8 mm was a functional material system due to the use of graphene and epoxy resin. The influence of the different mass ratios of the graphene and epoxy resin on the sensing properties was also studied. The test results showed that when the mass ratio of graphene to epoxy resin was 1:4, the response time and recovery time of the sensing unit were 40.8 ms and 3.7 ms, respectively, and the pressure detection range was 2.5–500 kPa. The sensor can detect dynamic pressure at 0.5 Hz, 1 Hz, 2 Hz, 10 Hz, and 20 Hz and can withstand 11,000 cycles of bending. In addition, adhesion tests showed that the high viscosity of the epoxy helped to improve the interlayer bond between the pressure-sensitive materials and the flexible substrate, which makes it more suitable for plantar pressure detection environments, where friction is common.

Here, we present a high-precision demodulation method that supports the arrayed waveguide grating (AWG) system, which includes a 1 × 8 AWG as the primary filter with a 0.5 nm channel spacing and a 1 × 4 AWG as the auxiliary filter with a 1 nm channel spacing. The high precision is achieved through an innovative method of decoupling three channels, involving two adjacent channels of the primary filter and one channel of the secondary auxiliary filter. Simulation results show that the AWGs have a good transmission spectrum with crosstalk below −24.8 dB, non-uniformities below 0.8 dB, insertion loss below −3.7 dB, 3 dB bandwidth of 0.25 nm, and 10 dB bandwidth of 0.43 nm. The interrogation precision can reach 8 pm, with a dynamic range of 0.4 nm, corresponding to a single FBG.

Recently, an exceptional point (EP) was constructed in a coupled double-ring resonator. Generally, such non-Hermitian optical systems are realized via material selection and a spatially precise layout. However, because of material limitations, some system parameters cannot be changed after the waveguide is fabricated. In this study, We demonstrate a lithium niobate-based tunable system for controlling system dispersion and loss, the resonator structure made of lithium niobate is theoretically and numerically investigated and analyzed. Lithium niobate is chosen because it exhibits good electro-optic properties. Furthermore, the real part of the potential energy term of the non-Hermitian system is regulated using external electric field. Consequently, a frequency shift of up to 149 GHz is observed in the double characteristic peak of the transmission spectrum with a contrast of up to 0.43. In addition, a gain-influenced EP is observed in a coupled dual-ring resonator system by introducing gain material. It has potential application in future optical fiber communication, optical quantum computing, and environmental sensing.

It is particularly important to improve the performance of mid-infrared (mid-IR) electro-optic (EO) modulator, which is one of the key devices that will expand the channels of optic communication, and will be utilized in optical free space communication, optical detection for gas molecules, etc. We present and theoretically design the performance of the high-speed mid-IR EO modulator based on lithium niobate on insulator (LNOI) at λ = 3 μm. We have designed, calculated, and optimized single-mode ridge waveguide, 1 × 2 multimode interference (MMI) couplers and coplanar waveguide (CPW) electrodes structures for x-cut lithium niobate. Our device with an extinction ratio greater than 40 dB, a half-wave voltage-length product is about 12 V·cm, and a EO bandwidth up to 12 GHz with interaction length of 15 mm. The performance of interaction length of 5 mm and 10 mm mid-IR EO modulator are also proposed and simulated for a compromise consideration between the EO bandwidth and driving voltage.

With the advancement of modulation technology and the requirement for device miniaturization and integration, lithium niobate on insulator (LNOI) can be a versatile platform for this pursuit, as it can confine the transmitted light at the nanoscale, leading to a strong light–matter interaction, which can sensitively capture external variations, such as electric fields and temperature. This paper presents a compact microring modulator with versatile tuning based on X-cut LNOI. The LNOI modulator equipped with electrodes with a coverage angle of 120∘ achieved a maximum electro-optic (EO) tuning efficiency of 13 pm/V and a maximum extinction ratio of 11 dB. The asymmetry in the static or quasi-static electro-optic tuning of the microring modulator was also analyzed. Furthermore, we measured the thermal-optic effect of the device with a sensitivity of 26.33 pm/∘C, which can potentially monitor the environment temperature or compensate for devices’ functional behavior. The demonstrated efficient and versatile compact microring modulator will be an important platform for on-chip active or passive photonic components, microring-based sensor arrays and integrated optics.

Magnetometers based on nitrogen-vacancy (NV) centers in diamonds have promising applications in fields of living systems biology, condensed matter physics, and industry. This paper proposes a portable and flexible all-fiber NV center vector magnetometer by using fibers to substitute all conventional spatial optical elements, realizing laser excitation and fluorescence collection of micro-diamond with multi-mode fibers simultaneously and efficiently. An optical model is established to investigate multi-mode fiber interrogation of micro-diamond to estimate the optical performance of NV center system. A new analysis method is proposed to extract the magnitude and direction of the magnetic field, combining the morphology of the micro-diamond, thus realizing μm-scale vector magnetic field detection at the tip of the fiber probe. Experimental testing shows our fabricated magnetometer has a sensitivity of 0.73 nT/Hz1/2, demonstrating its feasibility and performance in comparison with conventional confocal NV center magnetometers. This research presents a robust and compact magnetic endoscopy and remote-magnetic measurement approach, which will substantially promote the practical application of magnetometers based on NV centers.

GaN high-electron-mobility transistor (HEMT) terahertz (THz) detectors have been widely studied and applied in the past few decades. However, there are few reports about the influence of GaN/AlGaN heterostructure material properties on the detection model at present. In this paper, a response voltage model for a GaN HEMT THz detector that considers the carrier scattering in a GaN/AlGaN heterostructure is proposed. The phonon scattering, dislocation scattering, and interface roughness scattering mechanisms are taken into account in the classic THz response voltage model; furthermore, the influence of various material parameters on the response voltage is studied. In a low-temperature region, acoustic scattering plays an important role, and the response voltage drops with an increase in temperature. In a high temperature range, optical phonon scattering is the main scattering mechanism, and the detector operates in a non-resonant detection mode. With an increase in carrier surface density, the response voltage decreases and then increases due to piezoelectric scattering and optical phonon scattering. For dislocation and interface roughness scattering, the response voltage is inversely proportional to the dislocation density and root mean square roughness (RMS) but is positively related to lateral correlation length. Finally, a comparison between our model and the reported models shows that our proposed model is more accurate.

Nano-steps, as classical nano-geometric reference materials, are very important for calibrating measurements in the semiconductor industry; therefore, controlling the height of nano-steps is critical for ensuring accurate measurements. Accordingly, in this study nano-steps with heights of 1, 2, 3 and 4 nm were fabricated with good morphology using atomic layer deposition (ALD) combined with wet etching. The roughness of the fabricated nano-steps was effectively controlled by utilizing the three-dimensional conformal ALD process. Moreover, the relationship between the surface roughness and the height was studied using a simulation-based analysis. Essentially, roughness control is crucial in fabricating nano-steps with a critical dimension of less than 5 nm. In this study, the minimum height of a nano-step that was successfully achieved by combining ALD and wet etching was 1 nm. Furthermore, the preconditions for quality assurance for a reference material and the influencing factors of the fabrication method were analyzed based on the 1 nm nano-step sample. Finally, the fabricated samples were used in time-dependent experiments to verify the optimal stability of the nano-steps as reference materials. This research is instructive to fabricate nano-geometric reference materials to within 5 nm in height, and the proposed method can be easily employed to manufacture wafer-sized step height reference materials, thus enabling its large-scale industrial application for in-line calibration in integrated circuit production lines.

To meet the need for micro-volume devices for high-precision measurement of temperature, Cu-Constantan (CuNi45) thin films with a novel array structure of thermo-electrodes were designed and fabricated. The thermo-electrodes on the probe-type substrate were deposited by magnetron sputtering technology and the profiling mask was prepared by 3D printing technology. The comprehensive performance of the temperature sensor was improved by systematic optimization of the heat treatment process and accuracy correction algorithm. Results showed that the sensor can measure with an accuracy of up to ±0.19%FS from −60 °C to 200 °C. The three-dimensional probe array temperature sensor shows great advantages in sensitivity, reliability resolution, stability, and measurement accuracy.

A nano-grating standard with accurate linewidth can not only calibrate the magnification of nano-measurement instruments, but can also enable comparison of linewidths. Unfortunately, it is still a challenging task to control the linewidth of nano-grating standards. Accordingly, in this paper, atomic layer deposition (ALD) was used to regulate the linewidth of the one-dimensional grating standards with a pitch of 1000 nm, fabricated by electron beam lithography (EBL). The standards were measured using an atomic force microscope (AFM) before and after ALD, and the linewidth and pitch of the grating were calculated through the gravity center method. The obtained results prove that the width of a single grating line in the standard can be regulated with great uniformity by precisely utilizing ALD. Meanwhile, the proposed method does not affect the pitch of grating, and the measurement uncertainty of standards is less than 0.16% of the pitch, thereby demonstrating a high surface quality and calibration reliability of the standards, and realizing the integration of linewidth and pitch calibration functions. Moreover, the precise and controllable fabrication method of the micro-nano periodic structure based on ALD technology has many potential applications in the fields of optoelectronic devices and biosensors.

Smart wearable devices are occupying an increasingly important position in scientific research and people’s life fields. As an indispensable component of smart wearable devices, sensors play a crucial role in their sensing and feedback capabilities. In this paper, we investigate the bending gesture sensing for the most dexterous part of human anatomy, the finger. Based on series-connected fiber Bragg gratings (FBGs), recognition of finger bending posture is achieved by MATLAB modeling and the cubic spline interpolation.

A side ohmic contact mode for the double channel GaN/AlGaN epitaxial layer is proposed in this paper. Rectangle transmission line model (TLM) electrodes are prepared, and the specific contact resistance is tested at the annealing temperatures from 700 °C to 850 °C. The results show that the minimum specific contact resistance is 2.58 × 10−7 Ω·cm2 at the annealing temperature of 750 °C, which is three to four times lower than the surface contact mode. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and atomic force microscope (AFM) were carried out for the analysis of the morphology, element composition, and the height fluctuation at the contact edge. With the increase in the annealing temperature, the specific contact resistance decreases due to the alloying of electrodes and the raised number of N vacancies. However, when the annealing temperature exceeds 800 °C, the state of the stress in the electrode films transforms from compressive stress to tensile stress. Besides, the volume expansion of metal electrode film and the increase in the roughness at the contact edge leads to the degradation of the side ohmic contact characteristics.

Reduced graphene oxide (rGO) fiber as a carbon-based fiber sensor has aroused widespread interest in the field of gas sensing. However, the low response value and poor flexibility of the rGO fiber sensor severely limit its application in the field of flexible wearable electronics. In this paper, a flexible and wearable nylon fiber sensor modified by rGO and ZnO quantum dots (QDs) is proposed for wide-range NO2 gas detection at room temperature. The response value of the nylon fiber sensor to 100 ppm NO2 gas is as high as 0.4958, and the response time and recovery time are 216.2 s and 667.9 s, respectively. The relationship between the sensor’s response value and the NO2 concentration value is linear in the range of 20–100 ppm, and the fitting coefficient is 0.998. In addition, the test results show that the sensor also has good repeatability, flexibility, and selectivity. Moreover, an early warning module was also designed and is proposed in this paper to realize the over-limit monitoring of NO2 gas, and the flexible sensor was embedded in a mask, demonstrating its great application potential and value in the field of wearable electronics.

A Mach–Zehnder fiber optic sensor with high refractive index response sensitivity was developed. By fabricating a waist-enlarged bitaper structure on the interference arm of a single mode–multimode–single mode (SMS) Mach–Zehnder interferometer (MZI), the spectral contrast and response sensitivity were improved. Subsequently, the response sensitivity was further improved by etching the interference arm. When a beam of light was introduced into the sensor, due to the structural mismatch between the multimode fiber and the normal transmission light, the difference between the low-order mode and the high-order mode was generated in the fiber core and the fiber cladding. In the process of transmission in the sensing arm, due to the different refractive indices of the core and cladding, the optical path difference of the high-order mode and the low-order mode was different, which eventually generated interference fringes. The experimentally measured response sensitivity of SMS MZI in the range of 1.351 RIU to 1.402 RIU is 57.623 nm/RIU; the response sensitivity of a single mode–multimode–bitaper–multimode–single mode (SMBMS) MZI is 61.607 nm/RIU; and the response sensitivity of the etched SMBMS (ESMBMS) MZI is 287.65 nm/RIU. The response sensitivity of the new ESMBMS MZI is three times higher than that of the original SMS MZI. The sensor has the characteristics of compact structure, high sensitivity, easy manufacture, and a wide range of refractive index measurements, and can be used in food processing, pharmaceutical manufacturing and other fields.

An all-fiber temperature and refractive dual-parameter-sensing Michelson interferometer is designed based on the waist-enlarged bitaper. At 5 mm from the fiber end, the waist-enlarged bitaper is manually spliced and the probe is formed. Since the input light encounters the waist-enlarged bitaper, it will excite high-order modes to transmit in the fiber cladding, and there will be an optical path difference between the basic mode and the higher-order mode. The light transmitted in the core and cladding is reflected upon encountering the fiber end face and the interference occurs due to the optical path difference between basic mode and higher-order mode. Changes in temperature and refractive index at the fiber probe can be detected by monitoring the interference fringes. The refractive response sensitivity is −191.06 dBm/RIU from 1.351 RIU to 1.4027 RIU, and the temperature response sensitivity is 0.12 nm/°C from 11 °C to 98 °C. Through the sensitivity matrix equation, the superimposed refractive index and temperature signals can be effectively demodulated. The sensor has the advantages of multi-parameter measurement, compact structure, low cost, easy fabrication and high reliability.

Two sandwiched ZnO/Metal/ZnO transparent conductive thin films, 50nm ZnO/Cu/50nm ZnO (abbreviated as ZnO(Cu)) and 50nm ZnO/Ti/Cu/Ti/50nm ZnO (abbreviated as ZnO(Ti/Cu)) were deposited by magnetron sputtering technology. The comparative analysis of experiment results shows that the introduction of the Ti layer is beneficial to the overall properties of ZnO(Ti/Cu) thin film compared to ZnO(Cu) thin film with the same metal layer thickness. The effect of the annealing temperature on the performance of the two film systems was studied. Although the carrier concentration did not always increase with annealing temperature, the sheet resistances did decrease due to the obvious increase of mobility. The transmittance of ZnO(Cu) thin films increases with annealing temperature, while that of ZnO(Ti/Cu) films increases at first and then decreases. The optical band gap of ZnO(Cu) thin films increases with temperature, but is lower than that of ZnO(Ti/Cu) thin films, whose bandgap first increases with temperature and then decreases. The figure of merit of the ZnO(Ti/Cu) film is better than that of ZnO(Cu), which shows that the overall performance of ZnO(Ti/Cu) films is better, and annealing can improve the performance of the film systems.

Flexible temperature sensors have been extensively investigated due to their prospect of wide application in various flexible electronic products. However, most of the current flexible temperature sensors only work well in a narrow temperature range, with their application at high or low temperatures still being a big challenge. This work proposes a flexible thermocouple temperature sensor based on aerogel blanket substrate, the temperature-sensitive layer of which uses the screen-printing technology to prepare indium oxide and indium tin oxide. It has good temperature sensitivity, with the test sensitivity reaching 226.7 μ V °C ^−1 . Most importantly, it can work in a wide temperature range, from extremely low temperatures down to liquid nitrogen temperature to high temperatures up to 1200 °C, which is difficult to be achieved by other existing flexible temperature sensors. This temperature sensor has huge application potential in biomedicine, aerospace and other fields.

In electrohydrostatic drive actuators, there is a demand for temperature and pressure monitoring in complex environments. Fiber Bragg grating (FBG) has become a promising sensor for measuring temperature and pressure. However, there is a cross-sensitivity between temperature and pressure. A gold-plated FBG is proposed and manufactured, and an FBG is used as a reference grating to form a parallel all-fiber sensing system, which can realize the simultaneous measurement of pressure and temperature. Based on the simulation software, the mechanical distribution of the pressure diaphragm is analyzed, and the fixation scheme of the sensor is determined. Using the demodulator to monitor the changes in the reflectance spectrum in real-time, the pressure and ambient temperature applied to the sensor are measured. The experimental results show that the temperature sensitivity of gold-plated FBG is 3 times that of quartz FBG, which can effectively distinguish the temperature changes. The pressure response sensitivity of gold-plated FBG is 0.3 nm/MPa, which is same as the quartz FBG. Through the sensitivity matrix equation, the temperature and pressure dual-parameter sensing measurement is realized. The accuracy of the temperature and pressure measurement is 97.7% and 99.0%, and the corresponding response rates are 2.7 ms/°C and 2 ms/MPa, respectively. The sensor has a simple structure and high sensitivity, and it is promising to be applied in health monitoring in complex environments with a high temperature and high pressure.

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.