Operation In Extreme Environments Research Articles

Ultrathin, flexible, and high-performance bacterial cellulose/copper nanowires film for broadband electromagnetic interference shielding and photothermal conversion

The swift advancements in wearable electronics, implantable medical devices, fifth-generation mobile communication, unmanned aerial vehicles, and military stealth technology have led to a surge in demand for highly flexible multifunctional films. Consequently, the enhancement of electromagnetic radiation and the requirement for normal operation in extreme environments have posed significant challenges for flexible electromagnetic interference (EMI) shielding films. In this paper, ultra-thin, flexible bacterial cellulose (BC)/copper nanowires (CuNWs) (BCu) films with Janus structure are prepared by the combination of microwave-assisted hydrothermal synthesis and vacuum filtration method, which can be used for broadband EMI shielding and photothermal conversion. BCu films demonstrate exceptional mechanical properties, boasting a tensile strength range from 48.5 to 77.3 MPa, accompanied fracture strain 4.1–5.9 %. When CuNWs mass in Janus film increases to 10 mg, the conductivity of BCu-4 Janus films can reach 4761.90 S cm−1. The ultra-strong EMI shielding effectiveness (SE, above 56.00 dB) is achieved in 6–26.5 GHz for BCu-4 film with an ultra-thin thickness (16 μm). Moreover, the specific EMI SE of BCu-4 is as high as 4294.38 dB mm−1. Furthermore, BCu Janus films exhibit outstanding photothermal conversion performance. A saturation temperature of BCu-4 Janus film reaches as high as 75 °C under irradiation of one sunlight (100 mW cm−2). The facile and collaborative strategy is provided for fabricating ultra-thin, flexible multifunctional Janus films with EMI shielding and photothermal conversion capabilities, addressing EMI problems in modern electronic technology and offering new avenues for applications in various fields.

Thermo‐Mechanically Stable, Liquid Metal Embedded Soft Materials for High‐Temperature Applications

AbstractLiquid‐metal embedded elastomers (LMEEs) have been demonstrated to show a variety of excellent properties, including high toughness, dielectric constant, and thermal conductivity, with applications across soft electronics and robotics. However, within this scope of use cases, operation in extreme environments – such as high‐temperature conditions – may lead to material degradation. While prior works highlight the functionality of LMEEs, there is limited insight on the thermal stability of these soft materials and how the effects of liquid metal (LM) inclusions depend on temperature. Here, the effects on thermal stability, including mechanical and electrical properties, of LMEEs are introduced. Effects are characterized for both fluoroelastomer and other elastomer‐based composites at temperature exposures up to 325 °C, where it is shown that embedding LM can offer improvements in thermo‐mechanical stability. Compared to elastomer like silicone rubber that has been previously used for LMEEs, a fluoroelastomer matrix offers a higher dielectric constant and significant improvement in thermo‐mechanical stability without sacrificing room temperature properties, such as thermal conductivity and modulus. Fluoroelastomer‐LM composites offer a promising soft, multi‐functional material for high‐temperature applications, which is demonstrated here with a printed, soft heat sink and an endoscopic sensor capable of wireless sensing of high temperatures.

Additive manufacturing of functionally gradient refractory coatings using substrate dilution and in-situ carbide formation

Enabling operations in extreme environments remains a top priority for the space, defense, and energy sectors, driving the demand for ultra-high-temperature materials. Traditional materials employed in these sectors have limited operating temperatures and thus novel alternatives are of interest. Refractory metals and carbides have excellent high-temperature properties, however, their high melting points and susceptibility to cracking during solidification make them challenging to process, especially through additive manufacturing (AM) technologies. In this work, Directed Energy Deposition (DED) was used to create a functionally graded refractory coating (W-WC-Nb system on a titanium substrate) by integrating titanium into the refractory matrix through substrate dilution. By developing a new W-based alloy then adding titanium from the substrate along the build direction, a crack-free microstructure was formed within layers closer to the substrate. Additionally, an in-situ carbide formation strategy was explored, creating titanium carbide and niobium carbide phases that could improve the high-temperature and corrosion properties without the need to overcome processing difficulties associated with these high-melting carbides. These strategies allow for the development of new material systems with tailored properties and improved processibility of refractory material systems.

An experimental methodology to study impulsive hydrodynamic loading of air-backed composite plates

Sandwich composites in marine vessels are frequently exposed to impulsive hydrodynamic loading during operation in extreme environments. The response of sandwich composites to impulsive hydrodynamic loading has yet to be fully investigated due to the lack of full-field, simultaneous measurement techniques. Here, we propose an experimental framework for the study of the dynamic response of sandwich composites to hydrodynamic loading. We focus on a fiber-reinforced plate positioned at the air-water interface subjected to impulsive hydrodynamic loading. The interaction between the plate and the water is studied through a combined visualization technique based on particle image velocimetry (PIV) and digital image correlation (DIC). The velocity and pressure fields are quantified through PIV, and, simultaneously, the out-of-plane vibration of the plate is inferred from DIC. Repeated measurements were conducted for a range of hydrodynamic loading conditions. Our experiments unveiled a rich multimodal response that is strongly coupled with the flow physics. This work constitutes a first step toward an experimental understanding of fluid-structure interaction of air-backed sandwich composites.

Ultrasensitive UV-C detection based on MOCVD-grown highly crystalline ultrawide bandgap orthorhombic κ-Ga2O3

Orthorhombic κ-Ga2O3, as one of the Ga2O3 polymorphs, is considered a promising as ultrawide bandgap material for extreme environment devices. It is considered more superior than the conventional group III-V compound semiconductors and silicon carbides in extreme environments demanding material/device characteristics of high-voltage, high-temperature, high-pressure, high-impact, and high-radiation. In this study, we demonstrate ultrasensitive ultraviolet-C (UV-C) detection using Si-doped orthorhombic κ-Ga2O3 photodetectors. A 150 nm thick κ-Ga2O3 film was grown on a 2-inch diameter sapphire (α–Al2O3) wafer via metal organic chemical vapor deposition (MOCVD) method. The crystallinity of orthorhombic κ-Ga2O3 film was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The ultrawide bandgap of approximately 4.9 eV was confirmed by UV transmittance measurement. For UV-C detection analysis, a planar device with a channel length of 20 μm was fabricated using Au/Ti metal contacts on the orthorhombic κ-Ga2O3 film. The device doped under 15 sccm SiH4 flow rate showed ultrahigh photoresponse of ∼72.1 A/W, Ion/Ioff of ∼14, and decent rise (∼0.35 s) and decay (∼1.79 s). Our results will contribute to the understanding on a new material phase of κ-Ga2O3, as well as on developing optoelectronics devices with high radiation hardness suitable for operation in extreme environments.

(Invited, Digital Presentation) The Challenges of Overcoming Defects in GaN Hemts for Operation in Extreme Environments

GaN high electron mobility transistors (HEMTs) are known to contain a high density of crystal defects. The material properties of GaN such as high breakdown voltage, carrier mobility, critical electric field strength, and higher thermal conductivity than Si, make it an ideal candidate material for use in power switches in extreme environments. In high power environments (>1.5kV), vertical GaN device geometry is emerging as an effective technique to improve performance, but the more mature lateral GaN HEMT technology is being consistently improved upon to increase breakdown voltage and overall performance in the high-power regime. In high temperature environments, GaNs wide bandgap helps in preventing unwanted thermal generation of carriers, but devices also experience increased gate-leakage current and ohmic contact resistance degradation at high temperatures. The role of defects in these limiting factors of GaN HEMT performance in extreme high power and high temperature environments is reviewed.

Work schedule and seasonal influences on sleep and fatigue in helicopter and fixed-wing aircraft operations in extreme environments

Sleep and fatigue were investigated in aviation search and rescue, firefighting, emergency medical services and offshore transfer operations in 210 participants, for 21 days each, across 17 datasets in seven countries. Sleep data were collected using wrist-worn actigraphs and sleep diaries. Sustained attention was assessed using a 5-min Psychomotor Vigilance Task (PVT). Duty information was provided from corporate IT systems. Despite the number of 24 h operations, most work occurred during daytime hours, and most sleep occurred at night. There were seasonal changes in work and sleep patterns, with naps used to augment total sleep time. The proportion of sleep occurring during duty varied from zero to 30%. Differences in PVT response times were trivial to small. Legislation that defines flight, duty time and minimum rest limits assume that sleep is not obtained during duty periods, apart from some napping under Fatigue Risk Management Systems (FRMS). However, especially in cases where the aviation service requires waiting for tasks (e.g. search and rescue, emergency medical response), this assumption may not always hold. FRMS should accommodate different modes of working that safely facilitate sleep during duty time where appropriate.

Ti doped SiOC precursor to activate gyroid sensing structures

Ti-doped polymer-derived SiOC ceramic has multi-functional sensing capability due to its semiconductive properties. Their mechanical and chemical stability provide reliable support for their long-term service and safe operation in extreme environments. The sensing properties of Ti-doped SiOC (SiTiOC) can be optimized by modulation carrier concentration. Meanwhile, it can be fabricated by 3D printing as structural-strengthened components, promising for abnormal environmental signals warning under harsh conditions. In this work, SiTiOC gyroid structures were constructed by vat photopolymerization. The resulting components had thermistor characteristics with a negative temperature coefficient. After the Ti doping, the structures exhibited a high conductivity of 1.10 S/m, as the Ti ions formed an efficient percolation network by introducing acceptor impurities. The structures also had piezoresistive capability as the conductive phases can generate a tunneling-percolation conduction effect. They can detect a strain of less than 0.5%. Furthermore, the structures can realize n-butanol sensing for their p-type semiconductor properties. The components also had an excellent mechanical performance with the compressive strength and Young's modulus of 92.83 MPa and 4.28 GPa, respectively, ensuring reliable service under pressure loading.

Electron mobility and velocity in Al0.45Ga0.55N-channel ultra-wide bandgap HEMTs at high temperatures for RF power applications

Ultra-wide bandgap AlGaN has attracted recent attention as a promising channel material for next-generation high electron mobility transistors (HEMTs) for RF power due to its high critical field, excellent transport properties, and potential for operation in extreme environments. However, the effects of temperature on the transport properties are not fully understood. Here, Al0.62Ga0.38N/Al0.45Ga0.55N HEMTs have been fabricated and characterized up to 150 °C at DC and RF to evaluate the effect of temperature on electron mobility and carrier velocity. Measured results indicate that both mobility and carrier velocity exhibit modest dependence on temperature, suggesting that AlGaN channel HEMTs are promising for future RF power applications.

A Holistic Approach to Human-Supervised Humanoid Robot Operations in Extreme Environments.

Nuclear energy will play a critical role in meeting clean energy targets worldwide. However, nuclear environments are dangerous for humans to operate in due to the presence of highly radioactive materials. Robots can help address this issue by allowing remote access to nuclear and other highly hazardous facilities under human supervision to perform inspection and maintenance tasks during normal operations, help with clean-up missions, and aid in decommissioning. This paper presents our research to help realize humanoid robots in supervisory roles in nuclear environments. Our research focuses on National Aeronautics and Space Administration (NASA’s) humanoid robot, Valkyrie, in the areas of constrained manipulation and motion planning, increasing stability using support contact, dynamic non-prehensile manipulation, locomotion on deformable terrains, and human-in-the-loop control interfaces.

Unmanned Aircraft Systems Performance in a Climate-Controlled Laboratory

Despite many research studies focus on strategies to improve autopilot capabilities and bring artificial intelligence onboard Unmanned Aircraft Systems (UAS), there are still few experimental activities related to these vehicle performance under unconventional weather conditions. Air temperature and altitudes directly affect thrust and power coefficients of small scale propeller for UAS applications. Reynolds numbers are usually within the range 10,000 to 100,000 and important aerodynamic effects, such as the laminar separation bubbles, occur with a negative impact on propulsion performance. The development of autonomous UAS platforms to reduce pilot work-load and allow Beyond Visual Line of Sight (BVLOS) operations requires experimental data to validate capabilities of these innovative vehicles. High quality data are needed for a deep understanding of limitations and opportunities of UAS under unconventional flight conditions. The primary objective of this article is to present the characterization of a propeller and a quadrotor capabilities in a pressure-climate-controlled chamber. Mechanical and electrical data are measured with a dedicated test setup over a wide range of temperatures and altitudes. Test results are presented in terms of thrust and power coefficient trends. The experimental data shows low Reynolds numbers are responsible for degraded thrust performance. Moreover, details on brushless motor capabilities are also discussed considering different temperature and pressure conditions. The experimental data collected in the test campaign will be leveraged to improve UAS design, propulsion system modelling as well as to provide guidelines for safe UAS operations in extreme environments.

Automatic Fracture Characterization Using Tactile and Proximity Optical Sensing.

This paper demonstrates how tactile and proximity sensing can be used to perform automatic mechanical fractures detection (surface cracks). For this purpose, a custom-designed integrated tactile and proximity sensor has been implemented. With the help of fiber optics, the sensor measures the deformation of its body, when interacting with the physical environment, and the distance to the environment's objects. This sensor slides across different surfaces and records data which are then analyzed to detect and classify fractures and other mechanical features. The proposed method implements machine learning techniques (handcrafted features, and state of the art classification algorithms). An average crack detection accuracy of ~94% and width classification accuracy of ~80% is achieved. Kruskal-Wallis results (p < 0.001) indicate statistically significant differences among results obtained when analysing only integrated deformation measurements, only proximity measurements and both deformation and proximity data. A real-time classification method has been implemented for online classification of explored surfaces. In contrast to previous techniques, which mainly rely on visual modality, the proposed approach based on optical fibers might be more suitable for operation in extreme environments (such as nuclear facilities) where radiation may damage electronic components of commonly employed sensing devices, such as standard force sensors based on strain gauges and video cameras.

Crew-Friendly Countermeasures Against Musculoskeletal Injuries in Aviation and Spaceflight.

Aviation and space medicine face many common musculoskeletal challenges that manifest in crew of rotary-wing aircraft (RWA), high-performance jet aircraft (HPJA), and spacecraft. Furthermore, many astronauts are former pilots of RWA or HPJA. Flight crew are exposed to recurrent musculoskeletal risk relating to the extreme environments in which they operate, including high-gravitational force equivalents (g-forces), altered gravitational vectors, vibratory loading, and interaction with equipment. Several countermeasures have been implemented or are currently under development to reduce the magnitude and frequency of these injuries. Cervical and lumbar spine, as well as extremity injuries, are common to aviators and astronauts, and occur in training and operational environments. Stress on the spinal column secondary to gravitational loading and unloading, ± vibration are implicated in the development of pain syndromes and intervertebral disk pathology. While necessary for operation in extreme environments, crew-support equipment can contribute to musculoskeletal strain or trauma. Crew-focused injury prevention measures such as stretching, exercise, and conditioning programs have demonstrated the potential to prevent pre-flight, in-flight, and post-flight injuries. Equipment countermeasures, especially those addressing helmet mass and center of gravity and spacesuit ergonomics, are also key in injury prevention. Furthermore, behavioral and training interventions are required to ensure that crew are prepared to safely operate when faced with these exposures. The common operational exposures and risk factors between RWA and HPJA pilots and astronauts lend themselves to collaborative studies to develop and improve countermeasures. Countermeasures require time and resources, and careful consideration is warranted to ensure that crew have access to equipment and expertise necessary to implement them. Further investigation is required to demonstrate long-term success of these interventions and inform flight surgeon decision-making about individualized treatment. Lessons learned from each population must be applied to the others to mitigate adverse effects on crew health and well-being and mission readiness.

Predicting the Validity of Expert Judgments in Assessing the Impact of Risk Mitigation Through Failure Prevention and Correction.

Operational risk management of autonomous vehicles in extreme environments is heavily dependent on expert judgments and, in particular, judgments of the likelihood that a failure mitigation action, via correction and prevention, will annul the consequences of a specific fault. However, extant research has not examined the reliability of experts in estimating the probability of failure mitigation. For systems operations in extreme environments, the probability of failure mitigation is taken as a proxy of the probability of a fault not reoccurring. Using a priori expert judgments for an autonomous underwater vehicle mission in the Arctic and a posteriori mission field data, we subsequently developed a generalized linear model that enabled us to investigate this relationship. We found that the probability of failure mitigation alone cannot be used as a proxy for the probability of fault not reoccurring. We conclude that it is also essential to include the effort to implement the failure mitigation when estimating the probability of fault not reoccurring. The effort is the time taken by a person (measured in person-months) to execute the task required to implement the fault correction action. We show that once a modicum of operational data is obtained, it is possible to define a generalized linear logistic model to estimate the probability a fault not reoccurring. We discuss how our findings are important to all autonomous vehicle operations and how similar operations can benefit from revising expert judgments of risk mitigation to take account of the effort required to reduce key risks.

Human reliability assessment for complex physical operations in harsh operating conditions

This paper presents a methodology for quantifying the effect of harsh environmental conditions on the reliability of human actions in performing complex physical operations. A review of current human reliability techniques confirms that there is a lack of methodology for quantifying human errors while conducting complex physical operations in extreme environments. The developed methodology is based on a hierarchical Bayesian network accounting for causal dependencies among environmental factors, human error modes, and scenario-based activities. Also, a new model is developed with three reference points (awareness of the situation, access to a system, and action) that derives human error modes (HEMs) from physiological failure mechanisms and helps an analyst identify the root causes of human errors. The proposed methodology is applied to estimate the likelihood of human error in two different scenarios in harsh operating conditions in floating offshore structures. The two scenarios are a set of different human activities in a workplace under defined operational and environmental conditions. The proposed methodology helps enhance the safety of human performance while considering effective physical factors. It will also help to reform current regulations for working in harsh environments.

An Experimental Analysis on Propeller Performance in a Climate-controlled Facility

Despite many commercial applications make extensive use of Unmanned Aircraft Systems (UAS), there is still lack of published data about their performance under unconventional weather conditions. In the last years, multirotors and fixed wing vehicles, commonly referred to as drones, have been studied in wind environments so that stability and controllability have been improved. However, other important weather variables have impact on UAS performance and they should be properly investigated for a deeper understanding of such vehicles. The primary objective of our study is the preliminary characterization of a propeller in a climate-controlled chamber. Mechanical and electrical data have been measured while testing the propeller at low pressure and cold temperatures. Test results point out that thrust and electric power are strongly affected by air density. A comparison between the experimental data and the results of the Blade Element Theory is carried out to assess the theory capability to estimate thrust in unconventional environments. The overlap between experimental data and theory computation is appropriate despite geometrical uncertainties and corroborate the need of a reliable aerodynamic database. Propeller performance data under unconventional atmospheres will be leveraged to improve UAS design, propulsion system modelling as well as provide guidelines to certify operations in extreme environments.

Memristor-Based Hybrid Fault Tolerant Structure With Concurrent Reconfigurability

Fault tolerance is one of the main issues of electronic devices especially for controlling and monitoring of the operations in extreme environments. In this letter, a new memristor-based hybrid approach has been proposed, which combines attractive features of the both static and dynamic methods to introduce a new concurrent reconfigurable structure. The simulation results show that the proposed structure tolerates transient and permanent faults during the run-time with minimum delay, power consumption, and area overhead in comparison to the related works. The proposed work also reaches to minimum silicon protection factor with zero pause time during fault recovery phase.

Polymer‐Derived Ultra‐High Temperature Ceramics (UHTCs) and Related Materials

Ultra‐high temperature ceramics (UHTCs) represent an emerging class of materials capable of providing mechanical stability and heat dissipation upon operation in extreme environments, e.g., extreme heat fluxes, chemically reactive plasma conditions. In the last few decades, remarkable research efforts and progress were done concerning the physical properties of UHTCs as well as their processing. Moreover, there are vivid research activities related to developing synthetic access pathways to UHTCs and related materials with high purity, tunable composition, nano‐scaled morphology, or improved sinterability. Among them, synthesis methods considering preceramic polymers as suitable precursors to UHTCs have received increased attention in the last few years. As these synthesis techniques allow the processing of UHTCs from the liquid phase, they are highly interesting, e.g., for the fabrication of ultra‐high temperature ceramic composites (UHT CMCs), additive manufacturing of UHTCs, etc. In the present review, UHTCs are in particular discussed within the context of their physical properties as well as energetics. Moreover, various synthesis methods using preceramic polymers to access UHTCs and related materials (i.e., (nano)composites thereof with silica former phases) are summarized and critically evaluated.

Impedance Field Expression of Bilateral Control for Reducing Data Traffic in Haptic Transmission

It is expected that bilateral control will find broad applications such as mobile robot exploration and operations in extreme environments. However, the transmission of vivid haptic sensation requires a rapid data-transfer rate of haptic data due to the short sampling period and high-frequency communication. The objective of this paper is aimed at the traffic reduction of haptic data by exploiting an impedance field equivalence of a standard bilateral control. The proposed approach theoretically clarifies the equivalence of the standard bilateral control and impedance control in terms of haptic transmission. Based on this equivalence, the same performance of a standard bilateral control can be achieved by only communicating the force information that determines the equilibrium position of the impedance control. The validity of the proposed approach is confirmed through both simulations and experiments. The obtained results show that the proposed approach successfully reduced the amount of communicated haptic data without any disadvantages compared with the standard acceleration-based bilateral system. This paper shows novel interpretation that haptic transmission is realized by controlling the equilibrium force, which contributes reducing data traffic in haptic transmission and understanding motion generation.

Bottom-Up Synthesis and Mechanical Behavior of Refractory Coatings Made of Carbon Nanotube-Hafnium Diboride Composites.

We use aligned carbon nanotube (CNT) forests as scaffolds to deposit hafnium diboride (HfB2) and fabricate millimeter-thick ultrahigh-temperature composite coating. HfB2 has a melting temperature of 3250 °C, which makes it an attractive candidate for applications requiring operation in extreme environments. Compared to typical refractory HfB2 processing, which requires temperatures exceeding 1500 °C, we use conformal HfB2 chemical vapor deposition (CVD) to coat CNT forests at a low temperature of 200 °C. During this process, nanometer-thin HfB2 films grow on the CNT surface and uniformly fill tall CNT forests, thus transforming nanometer film deposition to a scalable HfB2 coating technology. The conformal HfB2 coating process uses static (S-) CVD, where the precursor is fed into a closed system, enabling highly conformal coating and economically efficient utilization of the HfB2 precursor reaching 85%. The modulus and compressive strength of the composites are measured using flat-punch indentation of micropillars having various coating thickness. Filling the CNTs with HfB2 strengthens their node morphology and effectively enhances the mechanical properties. We study the nonlinear behavior of the material to extract a unique modulus value that describes the stress-strain response at any applied compression. At the highest HfB2 coating thickness of 45 nm, the solid fraction is increased from 2% for the bare CNTs to 36% for the composite; the modulus and strength reach 107 and 1.5 GPa, respectively. An analytical model is used to explain the mechanism of the measured structure-mechanical property scaling. Finally, the process is used to fabricate CNT-HfB2 films having 1.7 mm height, a centimeter square area, and only 5.8 × 10-6 nm/nm thickness gradient to demonstrate the potential for scalability.