Harsh Environment Sensors Research Articles

Research on Dust Effect for MEMS Thermal Wind Sensors

This communication investigated the dust effect on microelectromechanical system (MEMS) thermal wind sensors, with an aim to evaluate performance in practical applications. An equivalent circuit was established to analyze the temperature gradient influenced by dust accumulation on the sensor’s surface. The finite element method (FEM) simulation was carried out to verify the proposed model using COMSOL Multiphysics software. In experiments, dust was accumulated on the sensor’s surface by two different methods. The measured results indicated that the output voltage for the sensor with dust on its surface was a little smaller than that of the sensor without dust at the same wind speed, which can degrade the measurement sensitivity and accuracy. Compared to the sensor without dust, the average voltage was reduced by about 1.91% and 3.75% when the dustiness was 0.04 g/mL and 0.12 g/mL, respectively. The results can provide a reference for the actual application of thermal wind sensors in harsh environments.

Sensorless control of switched reluctance motor based on a simple flux linkage model

Introduction. The operation of switched reluctance motor requires prior knowledge of the rotor position, obtaining from either low resolution photocoupler based position sensor or high resolution shaft encoder, to control the on/off states of the power switches. Problem. However, using physical position sensor in harsh environment will inevitably reduce the reliability of the motor drive, in which sensorless control comes into play. Novelty. In this paper, a sensorless control scheme of switched reluctance motor is proposed. Methodology. The method is based on a simple analytical model of the flux-linkage curves rather than the conventional approach that normally uses a look-up table to store all the data points of the flux-linkage curves. By measuring the phase current, rotor position can be deduced from the analytical model. Practical value. Simulation results are given and the proposed sensorless scheme is verified to provide a moderate position estimation accuracy in a wide speed range in both unsaturated and saturated conditions.

Fiber Optic Sensors for Harsh and High Radiation Environments in Aerospace Applications.

In the upcoming space revolutions aiming at the implementation of automated, smart, and self-aware crewless vehicles and reusable spacecraft, sensors play a significant role in the control systems. In particular, fiber optic sensors, with their small footprint and electromagnetic immunity, represent a great opportunity in aerospace. The radiation environment and the harsh conditions in which these sensors will operate represent a challenge for the potential user in the aerospace vehicle design and the fiber optic sensor specialist. We present a review that aims to be a primer in the field of fiber optic sensors in radiation environments for aerospace. We review the main aerospace requirements and their relationship with fiber optics. We also present a brief overview of fiber optics and sensors based on them. Finally, we present different examples of applications in radiation environments for aerospace applications.

Demonstration of a silicon gated field emitter array based low frequency Colpitts oscillator at 400 °C

Silicon gated field emitter arrays have been used as a vacuum transistor to demonstrate a 152 kHz Colpitts oscillator. The transfer and output characteristics of the 1000 × 1000 silicon arrays were measured using a collector placed ≈ 1 mm away with a gate voltage up to 40 V and a collector voltage up to 200 V. The data were used to establish an LTspice transistor model based on a field emission tip model and a collector current model that fit the characteristics. Then, the LTspice model was used to design a low frequency Colpitts oscillator. Furthermore, experiments were carried out to successfully demonstrate the oscillation. Oscillation frequency was 152 kHz with a peak to peak voltage of 25 V for a tip to ground series resistance value of 10 kΩ at 50 V on the gate and 210 V on the collector. Further, the oscillator was also tested at 50, 100, 200, 300, and 400 °C. It was observed that frequency shifts for each temperature which is due to the change in the overall capacitance of the test setup. This type of device could be used as a temperature sensor in harsh environments.

Trustworthiness of Process Monitoring in IIoT Based on Self-Weighted Dictionary Learning

Process monitoring, a typical application of industrial Internet of Things (IIOT), is crucial to ensure the reliable operation of the industrial system. In practice, due to the harsh environment and unreliable sensors and actuators, it is often difficult for IIoT to collect enough tagged and highly reliable data, which further degrades the process monitoring performance and makes the monitoring results not trustworthy. In order to reduce the negative impact of these unreliable factors, a self-weighted dictionary learning process monitoring method is proposed. In particular, a label propagation classifier is implemented from the labeled data to unlabeled data to obtain a credible label prediction. Subsequently, considering the interference of low-quality data and label information, we reweight the classification loss and label-consistency constraints to enhance the trustworthiness of feature extraction. Finally, a novel iterative optimization algorithm that combines the block coordinate descent method with the alternating direction multiplier method is developed to ensure the convergence speed of the learned classifier and dictionary. Extensive experiments indicate that the proposed method can guarantee the trustworthiness of the process monitoring results.

Wear-Resisting and Stable 4H-SiC/Cu-Based Tribovoltaic Nanogenerators for Self-Powered Sensing in a Harsh Environment.

Tribovoltaic nanogenerators (TVNGs) are an emerging class of devices for high-entropy energy conversion and mechanical sensing that benefit from their outstanding real-time direct current output characteristics. Here, a self-powered TVNG was fabricated using a small-area 4H-SiC semiconductor wafer and a large-area copper foil. Thus, the cost of materials remains low compared to devices employing large-scale semiconductors. The 4H-SiC/metal-TVNGs (SM-TVNGs) presented here are sensitive to vertical force and sliding velocity, making them appropriate for mechanical sensing. Notably, owing to the modulated bindingtons and surface states, these SM-TVNGs performed well in a harsh environment, namely, in high-temperature and high-humidity conditions. In addition, the SM-TVNGs exhibited an excellent wear-resisting property. On these bases, we designed a self-powered and real-time monitoring device able to estimate the number of staff present in various areas of a deep mining site, a high-temperature and high-humidity environment. This work not only discloses basic physics behind the tribovoltaic effect but also sheds light on possible applications of SM-TVNGs for wear-resisting and stable mechanical sensors in harsh environments.

Au–Au Bonding-Associated Lapping and Polishing Technique for Sapphire-Based Fabry–Perot Acoustic Sensor Applied for Harsh Environment

This article presents a sapphire-based Fabry–Perot acoustic sensor with potential for application in harsh environment acoustic sensing. The key component of the sensor is a thin sapphire diaphragm with a diameter of 20 mm and thickness down to 10 proposed Au–Au bonding-associated lapping and polishing technique. Microfabrication characterizations have corroborated the availability of realizing wafer-class thin sapphire diaphragm fabrication by employing the Au–Au bonding-associated lapping and polishing technique, and the diaphragm can be then easily transferred and assembled as a sensor. The strategy for optimizing the stripping phenomenon during lapping is also proposed. Acoustic calibration experiment through a plane wave tube indicates the sensitivity of 13.58 mV/Pa at 10 kHz and the frequency response range of 100250 kHz. The temperature tolerance experiment through the muffle furnace shows that no structural damage or optical spectrum invalidity occurs even if the environmental temperature reaches 800°, which indicates a high working temperature of the sensor up to 80°. Major findings and future application directions of this article are concluded as: 1) realization of an innovative sapphire-based Fabry–Perot acoustic sensor that shows significant potential in applications of numerous key industrial domains, such as aerospace engineering, and 2) a novel approach for achieving wafer-class sapphire ultrathin diaphragm fabrication, which might offer innovative methods for the optimization of sapphire-based harsh environment sensors and give reference to the sapphire lapping process as demanded in the gallium nitride (GaN)-based light-emitting diodes (LED) industry.

A Review of MEMS Vibrating Gyroscopes and Their Reliability Issues in Harsh Environments

Micro-electromechanical systems (MEMS) vibrating gyroscopes have gained a lot of attention over the last two decades because of their low power consumption, easy integration, and low fabrication cost. The usage of the gyroscope equipped with an inertial measurement unit has increased tremendously, with applications ranging from household devices to smart electronics to military equipment. However, reliability issues are still a concern when operating this inertial sensor in harsh environments, such as to control the movement and alignment of mini-satellites in space, tracking firefighters at an elevated temperature, and assisting aircraft navigation in gusty turbulent air. This review paper focuses on the key fundamentals of the MEMS vibrating gyroscopes, first discussing popular designs including the tuning fork, gimbal, vibrating ring, and multi-axis gyroscopes. It further investigates how bias stability, angle random walk, scale factor, and other performance parameters are affected in harsh environments and then discusses the reliability issues of the gyroscopes.

Temperature and strain sensitivities of a groove bonded fiber Bragg grating at room and cryogenic temperatures

Optical fiber Bragg gratings (FBGs) are well suited for applications as temperature or/and strain sensors in harsh environments, e.g., detecting thermal hot spots in high-temperature superconductor (HTS) fusion energy magnets at cryogenic temperatures and high radiation environments. To maximize the signal-to-noise ratio (SNR) of the FBGs to a hot spot, we propose to have them mounted in V-shaped grooves of HTS' copper former. To investigate the differences between different adhesives on transferring strain and heat in this configuration, five arrays of FBGs are mounted in the V-shaped grooves of a copper dog-bone using Scotch-Weld epoxy, Stycast 2850 FT, Apiezon N, and Loctite 5145 silicone. The copper is cycled through tensile forces in a modified universal tensile tester, subjected to a thermal cycle between 293 K and 77 K, and exposed to heat pulse propagations at 293 K and 80 K. The FBGs that are bonded using Stycast show the highest temperature and strain sensitivities at room and cryogenic temperatures. No major differences in the temperature and strain sensitivities have been found between Ormocer and polyimide coated FBGs. Apiezon N is found to transfer strain consistently well below 245 K, which is comparable with other bonding materials in the temperature range between 77 K and 110 K. The FBGs bonded with the four adhesives in the V-groove configurations are shown to have comparable SNRs to a temperature rise of 20 K at 80 K. This paper emphasizes the importance of maximizing the thermal strain transferred from the host material through the bonding agents to achieve high temperature sensitivity of FBGs.

Optical Sensor, Based on an Accelerometer, for Low-Frequency Mechanical Vibrations.

This article documents the design, manufacture, and testing of a silicon inertial optical sensor for low-frequency (lower than 2 kHz) applications. Three accelerometer designs optimized by parameterization using Finite Element Analysis were considered. The accelerometers were manufactured and the one with the highest performance at low frequency was chosen for testing, which was attached to a steel package. The feasibility of using probes, based on micro-machined sensing elements, to measure mechanical vibrations with high resolution was also studied. The detection is performed with an air interferometer, eliminating the need for electric signals that are susceptible to electromagnetic interference and large temperature variations. From the fabrication technology using only a silicon wafer with both sides etched, the frequency response of the sensor, temperature operation (higher than 85 °C) and with a resolution of 17.5 nm, it was concluded that is achievable and feasible to design and manufacture an optical vibration sensor for potential harsh environments with a low cost.

Electromechanical properties of housed piezoelectric CTGS resonators at high temperatures – Modeling of housing influence

Abstract The use of piezoelectric sensors in harsh environments requires their protection by housing. Therefore, it is essential to select materials used for the housing carefully. They should not only withstand the same conditions as the active element while providing protection for it, but also influence the piezoelectric component as little as possible. Mechanical stress or electric short-cut of the signals must be avoided as it leads to strong damping and to reduction of e. g. mass or temperature resolution. Therefore, understanding of housing impact on the piezoelectric sensor plays an important role in research and development. Housed as well as unhoused CTGS resonators are analyzed at temperatures up to 1000 °C. The electrical impedance in the vicinity of the resonance frequency is acquired and modeled by electric equivalent circuits that are fitted to the data. The circuit models describing unhoused and housed CTGS resonators are an extension of the Butterworth-van Dyke equivalent circuit. Analysis of the data reveals that the realized housing impacts the behavior of the CTGS resonators only slightly above ca. 600 °C, whereas this influence is negligible for typical applications.

Guided-Mode-Resonance Reflectors for Performance Enhancement of Sapphire Based Fabry-Perot Sensors in Harsh Environment

This paper presents a guided-mode resonance (GMR) reflector for sapphire based Fabry-Perot (F-P) sensors that enables tunable or wideband high reflectance with high temperature resistance,which is expected to effectively regulate the performance of F-P sensors and offer a novel approach for designing F-P sensors in harsh environments. Intrinsic and extrinsic GMR gratings are proposed, and their optical and thermal properties are investigated and compared through numerical simulations, such as rigorous coupled-wave analysis and finite element analysis methods. The quantitative results indicate high feasibility for harsh environment applications and the potential for adopting different demodulation methods. Significant enhancement in the F-P sensor performance is obtained through analysis based on the F-P interference model, and the spectrum fineness and sensor sensitivity can be enhanced by at least one order of magnitude. The GMR reflector can be extended to other types of F-P sensors, demonstrating significant potential in high-temperature applications.

A General gm/Id Temperature-Aware Design Methodology Using 180 nm CMOS up to 250 °C

The advent of the Internet-of-Things brings new challenges in circuit design. The presence of circuits and sensors in harsh environments brought the need for methodologies that account for them. Since the beginning of the transistors, the temperature is known for having a significant impact on performance, and even though very low temperature sensitivity circuits have been proposed, no general methodology for designing them exists. This paper proposes a general gm over Id technique for designing temperature-aware circuits that can be used either on measurement data, analytically, or based on simulation models. This model is validated using measurements up to 250°C of X-FAB XT018 transistors and later with a circuit design example.

Modeling and Optimization of Laser Cladding Fixation Process for Optical Fiber Sensors in Harsh Environments.

In order to overcome the shortcomings of the poor shear resistance of the bare optical fiber whose coating layer falls off due to harsh conditions, such as on aero-engines and the marine environment, the coaxial powder feeding laser cladding method (CPFLCM) is proposed to connect the optical fiber sensor and the substrate. The concentration field model of the powder flow is established in sections, the effective number model of particles and the corresponding laser attenuation rate are obtained. Through simulation, the influence of relevant parameters of laser cladding on the temperature field was analyzed, and the accurate parameters of laser cladding were optimized. Finally, the temperature rise trajectory of the substrate temperature field was verified by using the fiber grating temperature sensor. Through experiments, the quality of the molten pool and the optical transmission loss of the optical fiber sensor were analyzed, and the consistency of the simulation optimization parameters was verified. Through this paper, it can be concluded that the proposed CPFLCM can realize the effective connection of the optical fiber sensor to the substrate. It is of great significance in the application of optical fiber sensors in harsh environments of oceans and aerospace.

Inductive proximity sensors within a ceramic package manufactured by material extrusion of binder-coated zirconia

The embedding of electric components into additively manufactured structures offers enormous potential for extending the functionality and applications of parts produced by additive manufacturing (AM). However, the production of electric components embedded with 3D-printed ceramic structures has been a significant challenge due to the complexity of the manufacturing process and the high-temperature post-processing it requires. In the present study, an inductive proximity sensor with a 3D-printed ceramic housing and embedded sensing elements was designed and produced using a hybrid manufacturing process in which the printing process is paused and a sensing element is embedded into the printed structure. Sensing elements materials were carefully selected and intra-sensor structures were developed to ensure that the sensing element would survive in a high-temperature sintering environment. In the developed process, binder-coated zirconia containing 87 wt% was used as feedstock in a piston-based material extrusion process to fabricate the ceramic housing for the sensor, and platinum wire was used in the sensing element. The subsequent debinding and sintering processes achieved a nearly fully dense ceramic housing that protects the sensor in harsh environments. The successfully fabricated sensor was tested by measuring the change of distance between the inductive and metallic target and determining if the changes in distance would alter the inductance of the sensor. Results show that the sensing element maintains functionality throughout each fabrication step, and the fully packaged sensor also demonstrates the ability to work properly at high temperatures (in the range of 200–400 °C). At a frequency of 2 MHZ and a voltage of 1 V, the inductive sensor has a measurement range of approximately 7.0 mm. Additive manufacturing of the sensor housing enabled precise control of the geometry, dimensions, and infill density. Because the developed methodology allows for control of the type and structure of the sensing element, it can be used in the manufacture of a wide variety of sensors or smart components.

Influence of substrate temperature on the microstructure of YSZ films and their application as the insulating layer of thin film sensors for harsh temperature environments

Thin film sensors are employed to monitor the health of hot-section components of aeroengine intelligence (for instance, blades), and electrical insulating layers are needed between the metal components and thin film sensors. For this purpose, the electrical insulation characteristics of an yttria-stabilized zirconia (YSZ)/Al2O3 multilayer insulating structure were investigated. First, YSZ thin films were deposited by DC reactive sputtering at various substrate temperatures, and the microstructural features were investigated by scanning electron microscopy and X-ray diffraction. The results indicate that the micromorphology of the YSZ thin film gradually became denser with increasing substrate temperature, and no new phases appeared. The compact and uniform topography of the YSZ thin film improved the insulation properties of the multilayer insulating structure and enhanced the adhesion of the thin film sensors. In addition, the electrical insulation properties of the YSZ/Al2O3 multilayer insulating structure were evaluated via insulation resistance tests from 25 to 800 °C, in which the YSZ thin film was deposited at 550 °C. The results show that the insulation resistance of the multilayer structure increased by an order of magnitude compared with that of the conventional Al2O3 insulating layer, reaching 135 kΩ (5.1 × 10−6 S/m) at 800 °C. Notably, the insulation resistance was still greater than 75 kΩ after annealing at 800 °C for 5 h. Finally, the shunt effect of the YSZ/Al2O3 multilayer insulating structure was estimated using a PdCr thin film strain gauge. The relative resistance error was 0.24%, which demonstrates that the YSZ/Al2O3 multilayer insulating structure is suitable for thin film sensors.

All-sapphire fiber-optic pressure sensors for extreme harsh environments.

In this paper, an all-sapphire fiber-optic Fabry-Perot (F-P) pressure sensor is proposed. The sapphire pressure-sensitive diaphragm with low surface roughness is fabricated by MEMS wet etching. The direct bonding process is adopted to bond the sapphire-sensitive diaphragm and substrate together. And the sapphire fiber is adopted to be the lead-in fiber to ensure the sensor's resistance to high temperature. The performance of the sensor is tested within a pressure range of 0.1∼5 MPa and within the temperature range from room temperature to 1200°C. Experimental results show that the sensor could work stably at the temperature of 1200°C. The pressure sensitivity reaches up to 15nm/MPa. The nonlinearity of the sensor is 0.96% FS (full scale), and the relative resolution reaches 0.12%FS. The all-sapphire F-P sensor could be used for high-pressure testing in a high-temperature environment.

A Superhydrophobic Hydrogel for Self‐Healing and Robust Strain Sensor with Liquid Impalement Resistance

Main observation and conclusionThe superhydrophobic strain sensor is a fantastic direction, which could protect the strain sensor in harsh environment. Nevertheless, the self‐healing superhydrophobic strain sensor has not been reported. In this research, we developed a superhydrophobic strain sensor, which demonstrated excellent self‐healing, mechanical robustness, and liquid impalement resistance simultaneously. The key innovation is to partially embed hydrophobic graphene and carbon nanotubes into the hydrogel matrix. The hodrogel substrate endows the sample with self‐healing property. The graphene, carbon nanotubes and hydrogel together lead to an accurate and real‐time monitoring of human motion. Furthermore, the prepared sample demonstrated super‐robust superhydrophobicity, which retained superhydrophobicity after many kinds of damage (such as 1000% stretch, 10000 stretching‐releasing cycles, hand‐rub, tape‐peeling, and high‐speed drop/jet impact).

FBG-Based Sensor for the Assessment of Heat Transfer Rate of Liquids in a Forced Convective Environment.

The assessment of heat transfer is a complex task, especially for operations in the oil and gas industry, due to the harsh and flammable workspace. In light of the limitations of conventional sensors in harsh environments, this paper presents a fiber Bragg grating (FBG)-based sensor for the assessment of the heat transfer rate (HTR) in different liquids. To better understand the phenomenon of heat distribution, a preliminary analysis is performed by constructing two similar scenarios: those with and without the thermal insulation of a styrofoam box. The results indicate the need for a minimum of thermal power to balance the generated heat with the thermal losses of the setup. In this minimum heat, the behavior of the thermal distribution changes from quadratic to linear. To assess such features, the estimation of the specific heat capacity and the thermal conductivity of water are performed from 3 W to 12 W, in 3 W steps, resulting in a specific heat of 1.144 cal/g °C and thermal conductivity of 0.5682 W/m °C. The calibration and validation of the HTR sensor is performed in a thermostatic bath. The method, based on the temperature slope relative to the time curve, allowed for the measurement of HTR in water and Kryo 51 oil, for different heat insertion configurations. For water, the HTR estimation was 308.782 W, which means an uncertainty of 2.8% with the reference value of the cooling power (300 W). In Kryo 51 oil, the estimated heat absorbed by the oil was 4.38 kW in heating and 718.14 kW in cooling.

Operational Parameters for Sub-Nano Tesla Field Resolution of PHMR Sensors in Harsh Environments.

The resolution of planar-Hall magnetoresistive (PHMR) sensors was investigated in the frequency range from 0.5 Hz to 200 Hz in terms of its sensitivity, average noise level, and detectivity. Analysis of the sensor sensitivity and voltage noise response was performed by varying operational parameters such as sensor geometrical architectures, sensor configurations, sensing currents, and temperature. All the measurements of PHMR sensors were carried out under both constant current (CC) and constant voltage (CV) modes. In the present study, Barkhausen noise was revealed in 1/f noise component and found less significant in the PHMR sensor configuration. Under measured noise spectral density at optimized conditions, the best magnetic field detectivity was achieved better than 550 pT/√Hz at 100 Hz and close to 1.1 nT/√Hz at 10 Hz for a tri-layer multi-ring PHMR sensor in an unshielded environment. Furthermore, the promising feasibility and possible routes for further improvement of the sensor resolution are discussed.