Engineering topics

Schemmel, Peter J.

Publications and source records attributed to Schemmel, Peter J..

7 records

NASA NTRS2020

Microwave Photoelasticity: A Resonant Wavelength Approach Applied to PEEK Polymer

Every nondestructive testing (NDT) technique has its unique set of advantages and limitations. Currently, the only existing noncontact NDT method capable of measuring sub-surface stresses, in optically opaque materials, at near-real-time speeds and over large areas is Microwave Photoelasticity (MP). This paper presents a new MP approach, which correlates changes in resonant wavelengths to changes in stress. In addition to a theoretical outline of the approach, the design and operation of an instrument capable of conducting these measurements is described. Finally, the technique is demonstrated by conducting measurements on polyetheretherketone, commonly known as PEEK, polymer. Between the W-Band frequencies of 105 to 115 GHz, PEEK’s stress-optic-coefficient was determined to be of 𝐶𝐶 = −0.20 ± 0.02 1/GPa.

Schemmel, Peter J.↗

NASA NTRS2019

Refractive Index of Polyaryletherketone (PEEK) at X- and W-Band

This report details refractive index measurements of polyaryletherketone (PEEK) thermoplastic between X-band (8 to 12 GHz) and W-band (75 to 110 GHz) frequencies. Scattering-parameter data are collected using both traditional waveguide and modified free-space techniques. The complex-valued refractive index is calculated using the standard Nicolson-Ross-Weir method. Results indicate that PEEK’s refractive index is n = 1.783 – 0.001i across X-band and n = 1.792 – 0.007i across W-band. Therefore, PEEK exhibits a moderate real refractive index component and low transmission loss. Coupled with its favorable mechanical and thermal properties, this makes PEEK an ideal material to inspect using NASA’s submillimeter radiofrequency-based technology.

Polyaryletherketone↗

NASA NTRS2019

Mitigating Interference from Urban Air Mobility Vehicles on Satellite Communication Links by Using Vortex Radiometry

Vortex radiometers (VR) establish an early warning system for communication systems by generating concentric annular beam patterns around the active link. Received power peaks are monitored as interfering signals traverse overhead, allowing the VR to estimate source velocity. From this information the VR determines 1) when a fade will occur, 2) how long the fade will persist for and 3) how intense the fade will be. This paper demonstrates how VRs can be used to increase the resilience of communication systems used in urban air mobility applications.

vortex radiometry↗

NASA NTRS2019

Mitigating Interference from Urban Air Mobility Vehicles on Satellite Communication Links by Using Vortex Radiometry

Vortex radiometers (VRs) establish an early warning system for communication channels by generating concentric annular beam patterns around the active link. Peaks in received power are monitored as interfering signals traverse overhead, allowing the VR to estimate source velocity. From this information the VR determines 1) when a fade will occur, 2) how long the fade will persist for and 3) how intense the fade will be. This paper demonstrates how VRs can increase the resilience of communication systems used in urban air mobility applications.

Schemmel, Peter J.↗

NASA NTRS2019

Vortex Radiometry: Enabling Frequency Agile Communications

Exponential proliferation of UAVs and CubeSats puts NASA's high priority communication systems at risk. UAVs and CubeSats are easy to acquire, modify and build, making it extremely likely that some will be used in unauthorized ways. While these systems provide several benefits to society, their increased use also increases the probability of unintentional signal interference, and even deliberate jamming of NASA's communication systems.This paper presents an algorithm to determine 1) when an interference induced fade will occur, 2) how long the fade will persist for and 3) how intense the fade will be. The algorithm requires data collected from Vortex Radiometers (VRs), which probe the RF environment using annular antenna beam patterns. A set of numerical simulations show that a multi-beam VR system can instruct a cognitive antenna to switch between Ka- and X-Band communications, in order to avert interference from small diameter noise sources. Analysis of the simulation results indicate that practical VR systems will require several concentric annular beam patterns, in order to mitigate fades from noise sources of various sizes. The paper concludes by identifying technology challenges that need to be overcome to achieve these capabilities.

Orbital Angular Momentum↗

NASA NTRS2019

Reducing Aviation Fuel Costs with Non-Destructive Testing

Thermal barrier coatings (TBCs) are absolutely critical to the efficient and safe operation of gas turbine engines (GTEs). Manufacturing TBCs is a complex chemical, thermal and mechanical process that requires precise control. And yet, the variation in life of a TBC operated within a GTE is large. This variation ultimately reduces operational performance via a designed reduction to the turbine entry temperature, T4.This paper makes the case for developing advanced THz and sub-millimeter based nondestructive testing (NDT) techniques, capable of estimating when TBC components will fail. Such a technique could identify TBCs with low expected remaining useful lifetimes, directly after production. These TBCs could be re-manufactured, thereby not only improving their own expected useful life, but also the mean lifetime of the entire manufacturing population. A series of calculations demonstrates that TBCs with enhanced life characteristics can withstand higher T4 temperatures. Assuming that a GTE is to operate at a constant thrust, this increased temperature can be traded for a reduction in fuel flow. An analysis comparing fuel savings to manufacturing costs shows that substantial savings are achievable.

microwaves↗

NASA NTRS2019

Vortex Radiometry: Fundamental Concepts

Vortex radiometers (VRs) enable communication systems to maximize data throughput by determining when to employ fade mitigation most efficiently. With this information, communication systems can optimize mitigation strategies before actual fades occur. Doing so maximizes the time over which the link is available, and therefore maximizes data throughput. This paper presents the fundamental concepts of vortex radiometry, including the creation of annular beam patterns through the use of orbital angular momentum (OAM). These concepts are simulated on a 100 Mbps (Megabits per second) GEO (Geosynchrous Earth Orbit)-to-ground Ka-Band communication link. During the simulation a noise source traverses across the link, and without VR capabilities the link is disrupted. However, when the situation is repeated with VR capabilities enabled, the antenna is able to increase receiver gain and maintain the link. VRs are uniquely suited to provide communication systems with the ability to optimize receiver parameters and maximize data throughput, making them critical to enabling next generation communication networks.

Orbital Angular Momentum↗