Radiation through plasma adjoining a conducting surface.
Wave propagation in inhomogeneous media next to conducting surface that contains radiating element
WAVE PROPAGATION↗
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Results for “surface wave”
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Surface acoustic wave stabilized oscillators
A number of 401.2 MHz surface acoustic wave (SAW) controlled oscillators were built and tested. The performance of these oscillators was evaluated for possible use as stable oscillators in communication systems. A short term frequency stability of better than 1 x 10 to the minus 9th power for one second was measured for the SAW oscillators. Long term frequency drift was measured and was found to be dependent on SAW design and packaging. Drift rates ranging from 15 ppm in twenty weeks to 2.5 ppm in twenty weeks were observed. Some further improvement was required. The temperature dependence of the saw oscillators was evaluated and it was concluded that some form of temperature compensation will be necessary to meet the requirements of some communication systems.
Parker, T. E.↗
Surface acoustic wave sensor for refrigerant leakage detection
A SAW sensor is optimized for detection of refrigerant leakage in a refrigerant system or other gases, vapors, explosives or chemicals of interest. The SAW sensor includes a piezoelectric substrate; an interdigitated transducer deposited on the piezoelectric substrate, the interdigitated transducer having an input portion that receives input surface acoustic waves and an output portion that emits output surface acoustic waves; and a refrigerant sensor film located between the input portion and the output portion of the interdigitated transducer, the refrigerant sensor film including a sorbent material that is selected for preferential adsorption of a target refrigerant over atmospheric gases. Adsorption of the target refrigerant by the sorbent material results in a frequency shift of a frequency of the output surface acoustic waves relative to a frequency of the input surface acoustic waves. The sorbent material may be a metal organic framework (MOF) material, a covalent organic framework (COF) material, a porous organic cage or organic macrocyles such as calix [n] arene and its related derivatives.
Kunapuli, Raghuit Prasad↗
Steepening of Waves at the Duskside Magnetopause
Surface waves at the magnetopause flanks typically feature steeper, i.e., more inclined leading (antisunward facing) than trailing (sunward facing) edges. This is expected for Kelvin-Helmholtz instability (KHI) amplified waves. Very rarely, during northward interplanetary magnetic field (IMF) conditions, anomalous inverse steepening has been observed. The small-scale tetrahedral configuration of the Magnetospheric Multiscale spacecraft and their high time resolution measurements enable us to routinely ascertain magnetopause boundary inclinations during surface wave passage with high accuracy by four-spacecraft timing analysis. At the dusk flank magnetopause, 77%/23% of the analyzed wave intervals exhibit regular inverse steepening. Inverse steepening happens during northward IMF conditions, as previously reported and, in addition, during intervals of dominant equatorial IMF. Inverse steepening observed under the latter conditions may be due to the absence of KHI or due to instabilities arising from the alignment of flow and magnetic fields in the magnetosheath.
Plaschke, F.↗
Enhancement of Photoemission on p-Type GaAs Using Surface Acoustic Waves
We demonstrate that photoemission properties of p-type GaAs can be altered by surface acoustic waves (SAWs) generated on the GaAs surface due to dynamical piezoelectric fields of SAWs. Multiphysics simulations indicate that charge-carrier recombination is greatly reduced, and electron effective lifetime in p-doped GaAs may increase by a factor of 10× to 20×. It implies a significant increase, by a factor of 2× to 3×, of quantum efficiency (QE) for GaAs photoemission applications, like GaAs photocathodes. Conditions of different SAW wavelengths, swept SAW intensities, and varied incident photon energies were investigated. Essential steps in SAW device fabrication on a GaAs substrate are demonstrated, including deposition of an additional layer of ZnO for piezoelectric effect enhancement, measurements of current–voltage (I–V) characteristics of the SAW device, and ability to survive high-temperature annealing. Results obtained and reported in this study provide the potential and basis for future studies on building SAW-enhanced photocathodes, as well as other GaAs photoelectric applications.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
A 200 MHz surface acoustic wave mass microbalance
The principle of operation of the surface acoustic wave (SAW) piezoelectric crystals used as microgravimetric sensors in mass microbalances is discussed. Special attention is given to a SAW 200-MHz crystal developed for measuring molecular deposition on spacecrafts, whose operating frequency does not depend on the thickness of the crystal. The frequency stability of the 200 MHz SAW device is better than 5 x 10 exp -9, which corresponds to a lower limit-of-detection of 3 x 10 exp -12 g for a signal-to-noise ratio of 3. A block diagram of the 200 MHz SAW mass microbalance and a schematic diagram of SAW resonator are presented together with performance data of this device.
Bowers, William D.↗
Modeling of a Surface Acoustic Wave Strain Sensor
NASA Langley Research Center is investigating Surface Acoustic Wave (SAW) sensor technology for harsh environments aimed at aerospace applications. To aid in development of sensors a model of a SAW strain sensor has been developed. The new model extends the modified matrix method to include the response of Orthogonal Frequency Coded (OFC) reflectors and the response of SAW devices to strain. These results show that the model accurately captures the strain response of a SAW sensor on a Langasite substrate. The results of the model of a SAW Strain Sensor on Langasite are presented
Wilson, W. C.↗
Long-Range Transhorizon Lunar Surface Radio Wave Propagation in the Presence of a Regolith and a Sparse Exospheric Plasma
Long-range, over-the-horizon (transhorizon) radio wave propagation is considered for the case of the Moon. In the event that relay satellites are not available or otherwise unwarranted for use, transhorizon communication provides for a contingency or backup option for non line-of-sight lunar surface exploration scenarios. Two potential low-frequency propagation mechanisms characteristic of the lunar landscape are the lunar regolith and the photoelectron induced plasma exosphere enveloping the Moon. Although it was hoped that the regolith would provide for a spherical waveguide which could support a trapped surface wave phenomena, it is found that, in most cases, the regolith is deleterious to long range radio wave propagation. However, the presence of the plasma of the lunar exosphere supports wave propagation and, in fact, surpasses the attenuation of the regolith. Given the models of the regolith and exosphere adopted here, it is recommended that a frequency of 1 MHz be considered for low rate data transmission along the lunar surface. It is also recommended that further research be done to capture the descriptive physics of the regolith and the exospheric plasma so that a more complete model can be obtained. This comprehensive theoretical study is based entirely on first principles and the mathematical techniques needed are developed as required; it is self-contained and should not require the use of outside resources for its understanding.
Manning, Robert M.↗
Generation and detection of 50 GHz surface acoustic waves by extreme ultraviolet pulses
In this work, we use femtosecond extreme ultraviolet pulses derived from a free electron laser to excite and probe surface acoustic waves (SAWs) on the (001) surface of single crystal SrTiO 3 . SAWs are generated by a pair of 39.9 nm pulses crossed at the sample with the crossing angle defining the SAW wavelength at 84 nm. Detection of SAWs is performed via diffraction of a time-delayed 13.3 nm probe pulse by SAW-induced surface ripples. Despite the low reflectivity of the sample in the extreme ultraviolet range, the reflection mode detection is found to be efficient because of an increase in the diffraction efficiency for shorter wavelengths. We describe a methodology for extracting the SAW attenuation in the presence of a thermal grating, which is based on measuring the decay of oscillations at twice the SAW frequency. The proposed approach can be used to study ultrahigh frequency SAWs in a broad range of materials and will bridge the wave vector gap in surface phonon spectroscopy between Brillouin scattering and He atom scattering.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Report on the LLNL Global Full-waveform Inversion Workflow and Progress
LLNL has developed the SPiRaL global seismic tomography model based upon millions of body wave travel times and surface wave dispersion curves in the period range of 25-200 seconds (Simmons et al., 2021). The motivation to construct the SPiRaL model (which stands for S-, P-, Rayleigh, and Love waves) is based upon the guidance provided by a 3-D model workshop held in Berkeley in 2007 and documented in a paper by Zucca et al. (2009). It was concluded in Zucca et al. (2009) that a “practical and obtainable” model is one that predicts body wave travel times for event location while also predicting surface wave velocities for moment tensor estimation. We have largely followed that guidance which has led to the construction of SPiRaL. Looking forward, we now seek to improve the global model through full waveform inversion (FWI). This necessitates the development/customization of an efficient and flexible modeling workflow to automate the process using LLNL’s supercomputing platforms. This report briefly outlines the work that being performed at LLNL to develop the necessary tools and framework to update the SPiRaL global model with full waveform information.
58 GEOSCIENCES↗
Apparatus for acoustically coupling an ultrasonic transducer with a body
An apparatus for acoustically coupling an ultrasonic transducer with a body along whose surface waves are to be transmitted includes a wedge having a first surface for acoustically contacting a subject surface area of a body to be measured, on which surface waves are to be transmitted, and a second surface for accoustically contacting an ultrasonic transducer. The wedge includes a cylinder in which the second surface is present and which is movably disposed in a recess in a block in which the first surface is present, for orienting the first surface and the second surface relative to each other so that ultrasonic waves emitted by the ultrasonic transducer generate surface waves which travel on the subject surface area of the body when the ultrasonic transducer is in acoustic contact with the second surface and the first surface is in acoustic contact with the subject surface area of the body. In the preferred embodiment, there is a third surface which is orientable relative to the first surface so that ultrasonic waves emitted by an ultrasonic transducer in contact with the third surface generate surface waves which travel on the subject surface area of the body when the first surface is an acoustic contact with the subject surface area of the body.
Marshall, Scot H.↗
Characterization Test Report for the Mnemonics-UCS Wireless Surface Acoustic Wave Sensor System
The scope of this testing includes the Surface Acoustic Wave Sensor System delivered to KSC: two interrogator (transceiver) systems, four temperature sensors, with wooden mounting blocks, two antennas, two power supplies, network cables, and analysis software. Also included are a number of additional temperature sensors and newly-developed hydrogen sensors
Duncan, Joshua J.↗
Seismic effects from major basin formation on the Moon and Mercury
Grooved and hilly terrains are reported which occur at the antipode of major basins on the Moon (Imbrium, Orientale) and Mercury (Caloris). Order-of-magnitude calculations, for an Imbrium-size impact on the Moon, indicate P-wave-induced surface displacements of 10 m at the basin antipode that would arrive prior to secondary ejecta. Comparable surface waves are reported which would arrive subsequent to secondary ejecta impacts and would increase in magnitude as they converge at the antipode. Other seismically induced surface features include: subdued, furrowed crater walls produced by landslides and concomitant secondary impacts; emplacement and leveling of light plains units owing to seismically induced "fluidization" of slide material; knobby, pitted terrain around old basins from enhancement of seismic waves in ancient ejecta blankets; and the production and enhancement of deep-seated fractures that led to the concentration of farside lunar maria in the Apollo-Ingenii region.
Schultz, P. H.↗
Validity of modifying Mie theory to describe scattering by nonspherical particles
A calculation procedure has been developed (Chylek et al., 1976) for determining the scattering properties of irregularly shaped, randomly oriented particles. The procedure uses a modified form of the Mie theory for spheres with equivalent cross-sectional areas. The validity of the procedure is examined with reference to the work of Welch and Cox (1978). Particular consideration is given to: (1) the assumption that surface waves constitute the only major difference between scattering by spherical and nonspherical particles, (2) the identification of certain properties of the Mie coefficients with surface waves, and (3) the technique of removing surface waves from the Mie theory. It is concluded that the idea of determining the scattering properties of random orientations of irregular particles by eliminating surface waves from the Mie expansion is valid. It is also found that the technique for removing the resonances leads to the introduction of substantial fictitious absorption.
Acquista, C.↗
Irradiation-induced Degradation of Surface Acoustic Wave Devices Fabricated on Bulk AlN
Here, recent work to evaluate the prospects for surface acoustic wave (SAW) devices fabricated on bulk aluminum nitride (AlN) for elevated temperature and radiation environments is reported and discussed. The design and fabrication of an array of SAW devices using commercial wafers is described, including the non-standard fabrication approach taken to overcome the stress-induced warpage of the 50 mm diameter AlN substrates. Radio frequency performance characterization of the SAW devices, with resonance frequencies ranging from 0.5 GHz to 1.5 GHz, is described. The linear temperature coefficient of frequency (TCF) near room temperature was measured and is compared to theoretical results from other investigators. Further, the effects of 8 MeV Al ion irradiation at 300°C and 500°C to damage levels of 0.01, 0.1 and 1 displacements per atom (dpa), as a proxy for neutron irradiation, was investigated. The ion irradiation damage was observed to decrease the SAW resonant frequency, and this effect is characterized and discussed. Significant degradation in the conductivity of the Ti/Al electrodes of the SAW devices was also observed and characterized. These experimental results provide a basis for further investigation of the prospects for development of SAW sensor devices in bulk AlN material for application in elevated temperature and radiation environments.
36 MATERIALS SCIENCE↗
Radar imaging of the ocean surface
Techniques for obtaining radar images of the ocean surface are briefly described, and examples of radar images of a variety of ocean surface wave types obtained by synthetic-aperture radar are presented and discussed. Observations described include deep-ocean waves, discrete wave trains, internal waves as surface manifestations, slicks, and eddies.
Elachi, C.↗
SAR internal wave signature experiment
Internal wave and surface wave observations by research vessels will be conducted in conjunction with aircraft SAR images. Synthetic Aperture Radar Internal Wave Signature Experiment (SARSEX) provides an opportunity to acquire aircraft and spacecraft SAR imagery of internal waves with appropriate sea truth data. Objectives are to investigate basic mechanisms (both hydrodynamic and electromagnetic) responsible for internal wave signatures and quantitatively test theories and models for predicting internal wave signatures from given ocean and radar parameters.
Winokur, R. S.↗
Real-time measurement of materials properties at high temperatures by laser produced plasmas
Determination of elemental composition and thermophysical properties of materials at high temperatures, as visualized in the context of containerless materials processing in a microgravity environment, presents a variety of unusual requirements owing to the thermal hazards and interferences from electromagnetic control fields. In addition, such information is intended for process control applications and thus the measurements must be real time in nature. A new technique is described which was developed for real time, in-situ determination of the elemental composition of molten metallic alloys such as specialty steel. The technique is based on time-resolved spectroscopy of a laser produced plasma (LPP) plume resulting from the interaction of a giant laser pulse with a material target. The sensitivity and precision were demonstrated to be comparable to, or better than, the conventional methods of analysis which are applicable only to post-mortem specimens sampled from a molten metal pool. The LPP technique can be applied widely to other materials composition analysis applications. The LPP technique is extremely information rich and therefore provides opportunities for extracting other physical properties in addition to the materials composition. The case in point is that it is possible to determine thermophysical properties of the target materials at high temperatures by monitoring generation and transport of acoustic pulses as well as a number of other fluid-dynamic processes triggered by the LPP event. By manipulation of the scaling properties of the laser-matter interaction, many different kinds of flow events, ranging from shock waves to surface waves to flow induced instabilities, can be generated in a controllable manner. Time-resolved detection of these events can lead to such thermophysical quantities as volume and shear viscosities, thermal conductivity, specific heat, mass density, and others.
Kim, Yong W.↗