Raytheon Technologies (Singapore)

Abstract The safe and reliable operation of insulation material used in key high voltage components under extreme environmental conditions represents the major concerns for manufacturers and operators of More Electric Aircrafts (MEA). Surface discharge occurring in high current carrying components in DC power system diminishes the insulation material’s performance and life, especially at high‐temperature conditions. Here, the surface discharge behaviour of two commonly used high‐temperature insulation materials, ethylene‐tetrafluoroethylene (ETFE) and polyetheretherketone (PEEK) is studied at different temperatures under ramp and DC voltages. Extracted partial discharge (PD) features are presented and the impact of voltage polarity on surface discharge propagation is discussed. Our studies reveal that, while both materials exhibit non‐linear PD behaviour with respect to their electrical conductivity, ETFE generally shows PDs with higher intensity at high temperature above 100°C with a higher possibility of surface discharge due to its lower permittivity. Overall, the PD mechanism in high‐temperature, DC voltage applications is explored, and a basis for the selection of high‐temperature PD suppressing materials is developed.

Abstract The thermodynamics of reduction in variable valence oxides are important in a vast number of fields in which point defects, and in particular oxygen vacancies, control material functionality. Here, we present, by way of an example measurement of the material YMnO 3‐ δ , for which the vacancy formation energy has not been previously reported, best practices for material characterization. Sample mass is recorded by thermogravimetric analysis at temperatures from 600 to 1500°C under five different gas atmospheres, with oxygen partial pressure ranging from 0.081 to 7.66 × 10 –5 atm. Because YMnO 3‐ δ displays relatively small nonstoichiometry, less than 0.09, over the range of conditions examined, a large sample was required to record the modest mass changes. In the more oxidizing conditions, equilibrium behavior was recorded using a finite heating rate of 10°C min –1 . In the more reducing conditions, absolute mass changes with temperature were large such that the evolved oxygen increased the oxygen partial pressure in the sample vicinity, precluding equilibration under finite heating. Accordingly, a temperature‐stepped protocol with long isothermal holds was employed. Analysis of the results from these stepped measurements required interpolation, which was carried out on the ln( δ ) versus 1/ T plane. In the nonpolar, centrosymmetric phase ( P 6 3 / mcm and δ ≥ 0.016), the enthalpy of reduction was found to be 304 ± 4 kJ (mol‐O) –1 , as averaged over the δ range 0.020–0.035. While YMnO 3‐ δ is known to incorporate oxygen excess in its ambient temperature, polar phase ( P 6 3 cm ), the conditions leading to such behavior were not included in this study.

Abstract A micromechanics‐based modeling approach that allows for the simultaneous consideration of deformation, damage, and oxidation associated with each constituent of silicon carbide (SiC)‐based ceramic matrix composites (CMC), including the fiber, fiber coating, and matrix, is described. Chemical kinetics models from the literature are combined with a progressive damage model. Rupture predictions of unnotched and notched stress‐hold (creep) specimens are compared with experimental measurements from a SiC/SiC CMC to assess the efficacy of the modeling approach. Techniques of improving creep rupture life are explored using the model.

Raytheon Technologies Research Center (RTRC) is currently developing a high power-density motor (12kW/kg) under the ARPA-E ASCEND program. In this paper, we present innovative and unique aspects of a "triple rotor" tightly coupled with a planetary gearbox (GB). The rotor design is unique and makes full use of the electromagnetic potential of permanent magnets (PM). The high speed of the motor is reduced to the target application speed by a planetary GB embedded within the profile of the "inner rotor". The design is guided by the stress and rotordynamics analysis and the GB modeling. Also presented is the risk reduction hardware built to validate the manufacturing process. The program is continuing and in the next 2 years, the RTRC team, supported by Collins Aerospace, will build and test a full 250kW demo. The test results will be presented in a paper on the demonstration.

As Computer Mediated Communications (CMCs) advance, businesses have sought alternatives to face-to-face (F2F) meetings to increase productivity for geographically dispersed teams while saving time and money. However, critical differences between CMCs and F2F impact multiple aspects of communication performance. In order to investigate these variations, the current research investigated the communication effectiveness in three distinct scenarios: video conferencing (VC), virtual reality (VR), and face-to-face (F2F). The study involved an electrical circuit repair task and the administration of multiple surveys to gather data from a total of 104 participants, focusing on four dependent variables: shared situational awareness, usability, mental workload, and performance confidence. For all the variables, results showed significantly better scores in VR and F2F conditions than in VC, but there was no significant difference between the VR and F2F conditions. These findings can inform technology developers in improving communication performance in computer mediated contexts, especially by using VR.

Abstract In a classical chemical vapor infiltration (CVI) process, the competing effects of chemical kinetics and reagent gas transport lead to non‐uniform depositions such that outer layers of a preform densify faster leaving the core highly porous. Currently, CVI must be performed at a sufficiently low temperature to achieve good densification quality which leads to high processing time and cost. Volumetric heating of the preform, especially through microwaves, can create temperature inversion such that the core is hotter than the outer surface and potentially, overcome the challenges associated with isothermal CVI. Direct numerical simulations (DNS) of densification under various such temperature distributions indicate that microwave heating in CVI processing can lead to better (uniform) densification of porous preforms. The role of key parameters describing the temperature distributions on the densification behavior is investigated. Strategic temporal control of the temperature distribution shows that processing times can be reduced by almost half while maintaining a good densification quality similar to that of low‐temperature isothermal processing. Inside‐out densification due to the inverted temperature profile is a key distinguishing characteristic of microwave assisted CVI.

Due to the COVID-19 pandemic and compulsory social distancing, researchers in educational fields started to investigate alternatives to face-to-face (F2F) training methods with greater focus, such as video conferencing (VC) and virtual reality (VR) applications. This study investigated the differences between VC, VR and F2F training conditions by evaluating the level of body ownership and agency perceived by trainees. An electrical circuit repair task and multiple surveys were used to gather data from 106 participants in the form of four dependent variables: a circuit knowledge test, task completion rate, number of the subtasks completed by failing participants, and test phase duration. The study included two visits by each participant to measure knowledge retention while there were no training and surveys in Visit 2. Results showed significantly higher circuit learning and knowledge retention scores in F2F and VR conditions than in VC. Also, regarding the retention of knowledge, participants had significantly better knowledge retention in Visit 1 than Visit 2. The authors hope the results of this study enable training developers to enhance the learning process in computer mediated communications.

Abstract In this work, TiO 2 thin films deposited by the atomic layer deposition (ALD) method were treated with a special N 2 O plasma surface treatment and used as the gate dielectric for AlGaN/GaN metal insulator semiconductor high electron mobility transistors (MISHEMTs). The N 2 O plasma surface treatment effectively reduces defects in the oxide during low-temperature ALD growth. In addition, it allows oxygen atoms to diffuse into the device cap layer to increase the barrier height and thus reduce the gate leakage current. These TiO 2 films exhibit a dielectric constant of 54.8 and a two-terminal current of 1.96 × 10 −10 A mm −1 in 2 μ m distance. When applied as the gate dielectric, the AlGaN/GaN MISHEMT with a 2 μ m-gate-length shows a high on/off ratio of 2.59 × 10 8 and a low subthreshold slope (SS) of 84 mV dec −1 among all GaN MISHEMTs using TiO 2 as the gate dielectric. This work provides a feasible way to significantly improve the TiO 2 film electrical property for gate dielectrics, and it suggests that the developed TiO 2 dielectric is a promising high- κ gate oxide and a potential passivation layer for GaN-based MISHEMTs, which can be further extended to other transistors.

The paper proposes airborne quadruple-three-phase power train architectures featuring low electromagnetic emissions and reduced dc-link ripple current. The paper first identifies the conflict of achieving minimized common-mode voltage (CMV) and dc-link ripple current jointly using a dual three-phase drive system. Then drive systems consisting of four three-phase winding sets are proposed. It shows that in contrast to the dual three-phase drive with proper modulation methods and winding displacements, the CMV and ripple current reach their best cancellation simultaneously. The proposed system and related operating methods ideally achieve complete common-mode voltage (CMV) cancellation and up to 67% dc ripple current reduction compared to the single-three-phase solution. The superior cancellation feature results in a six times smaller dc-link capacitor and ten times smaller electromagnetic interference (EMI) filter for a ±500 V, 250 kW power-train inverter design. A 250-kW quadruple three-phase high-altitude prototype for electrified aircraft was designed based on the proposed architecture using SiC Mosfets. Experimental results are provided to validate the approach.

In this paper, we propose efficient quantum algorithms for solving nonlinear stochastic differential equations (SDE) via the associated Fokker-Planck equation (FPE). We discretize the FPE in space and time using two well-known numerical schemes, namely Chang-Cooper and implicit finite difference. We then compute the solution of the resulting system of linear equations using the quantum linear systems algorithm. We present detailed error and complexity analyses for both these schemes and demonstrate that our proposed algorithms, under certain conditions, provably compute the solution to the FPE within prescribed <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\epsilon$</tex> error bounds with polynomial dependence on state dimension <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d$</tex> . Classical numerical methods scale exponentially with dimension, thus, our approach, under the aforementioned conditions, provides an exponential speed-up over traditional approaches.

In this paper, we discuss an analysis method to describe the human and automation roles in increasingly autonomous aviation systems. Specifically, we discuss the relationship between humans and automation in the performance of individual functions in two dimensions, related to their responsibility and authority for the control loops associated with an individual intended function. This work builds upon concepts and terminology proposed by ASTM International in Autonomy Design and Operations in Aviation: Terminology and Requirements Framework (TR1) published in 2019 and is based in part on the on-going work of an ASTM Working Group (WK76044) under F39 Aircraft Systems. TR1 presented a Contextual Framework for analysis of automated aviation functions, and the working group is developing a practice for its implementation.The role of the human vs. the role of automation, which has been extensively discussed in the past, is fundamental to the implementation of the Contextual Framework. As such, it is worth a fresh look, particularly against the backdrop of the Contextual Framework. Our work has led to an analysis of the system state, which at any given time is defined by the role of the human and the role of automation in a two-dimensional space. We refer to this as Dimensional Role Analysis which uses a directed graph approach to clearly depict the nominal operating mode, the revisionary modes, and the triggering events that would cause transition. The analysis approach helps to establish clear delineations as to the responsibility and authority of humans and automation in the performance of individual intended functions. This work makes a clear distinction between authority, responsibility, and accountability consistent with the work of ASTM.Using the concepts and language presented in this paper could add clarity to discussions in the aviation community, as proponents seek to certify and obtain operational approval for increasingly autonomous systems in aviation. While this paper focuses on aircraft control, these approaches could also apply to other safety critical systems.

Raytheon Technologies Research Center (RTRC) is currently developing a high power-density (12kW/kg) motor under the ARPA-E ASCEND program. A key element of the unique motor design is the outer rotor that utilizes pre-stressed magnets wrapped between a very thin inner sleeve and a metallic-composite hybrid outer sleeve. In this paper, we first present the trades and thermomechanical analysis leading to the outer rotor design which meets performance requirements and safety margin in the desired operating space. Further we discuss challenges associated with manufacturing the outer rotor and a unique method used to fabricate a prototype. Lastly, we discuss the nondestructive evaluation (NDE) conducted to understand the prototyping output. The issues revealed by the evaluation will be addressed in future prototyping

Abstract The drop freezing process is described by a phase-field model. Two cases are considered: when the freezing is triggered by central nucleation and when nucleation occurs on the drop surface. Depending on the environmental temperature and drop size, different morphological structures develop. Detailed dendritic growth was simulated at the first stage of drop freezing. Independent of the nucleation location, a decrease in temperature within the range from ~−5° to −25°C led to an increase in the number of dendrites and a decrease in their width and the interdendritic space. At temperatures lower than about −25°C, a planar front developed following surface nucleation, while dendrites formed a granular-like structure with small interdendritic distances following bulk nucleation. An ice shell grew in at the same time (but slower) as dendrites following surface nucleation, while it started forming once the dendrites have reached the drop surface in the case of central nucleation. The formed ice morphology at the first freezing stage predefined the splintering probability. We assume that stresses needed to break the ice shell arose from freezing of the water in the interdendritic spaces. Under this assumption, the number of possible splinters/fragments was proportional to the number of dendrites, and the maximum rate of splintering/fragmentation occurred within a temperature range of about −10° to −20°C, is in agreement with available laboratory and in situ measurements. At temperatures &lt; −25°C, freezing did not lead to the formation of significant stresses, making splintering unlikely. The number of dendrites increased with drop size, causing a corresponding increase in the number of splinters. Examples of morphology that favors drop cracking are presented, and the duration of the freezing stages is evaluated. Sensitivity of the freezing process to the surface fluxes is discussed.

In this paper we apply guided policy search (GPS) based reinforcement learning framework for a high dimensional nonlinear optimal control problem arising in an additive manufacturing process. The problem comprises of controlling the process parameters so that layer-wise deposition of material leads to desired geometric characteristics of the resulting part surface while minimizing the material deposited. A realistic simulation model of the deposition process along with carefully selected set of guiding distributions generated based on iterative Linear Quadratic Regulator is used to train a neural network policy using GPS. A closed loop control based on the trained policy and in-situ measurement of the deposition profile is tested experimentally, and shows promising performance.

This work presents the experimental realization of a printed-circuit beamformer designed using shape optimization. Shape optimization of the printed-circuit beamformer is enabled through the use of a circuit network solver that utilizes reduced-order models of printed-circuit unit cells to rapidly evaluate device responses, and the adjoint variable method to evaluate gradients. The designed beamformer is patterned on a microwave substrate and interfaces with a 3-D printed tapered aperture antenna. It produces nine orthogonal beams and has isolated input ports that are impedance matched. Experimental results for the performance of the 3-D printed antenna and the beamformer will be presented at the conference.