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Jackson, H. W.

Publications and source records attributed to Jackson, H. W..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Microwave Induced Direct Bonding of Single Crystal Silicon Wafers

We have heated polished doped single-crystal silicon wafers in a single mode microwave cavity to temperatures where surface to surface bonding occurred. The absorption of microwaves and heating of the wafers is attributed to the inclusion of n-type or p-type impurities into these substrates. A cylindrical cavity TM (sub 010) standing wave mode was used to irradiate samples of various geometry's at positions of high magnetic field. This process was conducted in vacuum to exclude plasma effects. This initial study suggests that the inclusion of impurities in single crystal silicon significantly improved its microwave absorption (loss factor) to a point where heating silicon wafers directly can be accomplished in minimal time. Bonding of these substrates, however, occurs only at points of intimate surface to surface contact. The inclusion of a thin metallic layer on the surfaces enhances the bonding process.

Budraa, N. K.↗
NASA NTRS1996

Conductive Sphere in a Radio Frequency Field: Theory and Applications to Positioners, Heating, and Noncontact Measurements

An electrically conductive spherical sample located in an electromagnetic field excited by rf (radio frequency) current in a system of coaxial coils is treated theoretically. Maxwell's equations are solved exactly and all integrals in the formulas for the fields are evaluated analytically for the case where the sphere is on the axis and the coil system is modeled by a stack of filamentary circular loops. Formulas are also derived for electromagnetic force exerted on the sphere, excess impedance in the coil system due to the presence of the sphere, and power absorbed by the sphere. All integrals in those formulas have been evaluated analytically. Force measurements are presented and they are in excellent agreement with the new theory. A low-power electromagnetic levitator that is accurately described by the theory has been demonstrated and is discussed. Experimental measurements of excess impedance are presented and compared with theory, and those results are used to demonstrate an accurate noncontact method for determining electrical conductivity. Theoretical formulas for power absorption are evaluated numerically and their usefulness in both rf heating and in making noncontact measurements of a number of thermophysical properties of materials is discussed.

Jackson, H. W.↗
NASA NTRS1996

Comparison of Finite-Difference and Analytical Microwave Calculation Methods

Normal modes and power absorption distribution in microwave cavities containing lossy dielectric samples were calculated for problems of interest in materials processing. The calculations were performed both using a commercially available finite-difference electromagnetic solver and by numerical evaluation of exact analytic expressions.

power↗
NASA NTRS1995

Steady State Temperature Profile in a Cylinder Heated by Microwaves

We have developed a new theory to calculate the steady state temperature profile in a cylindrical sample positioned along the entire axis of a cylindrical microwave cavity. Temperature profiles were computed for alumina rods of various radii contained in a cavity excited in one of the TM0n0 modes with n = 1, 2, or 3. Sample surface and center temperatures will be presented as a function of total sample absorbed power or electric field strength at the sample surface. An approach for attaining more uniform heating within the sample by reducing the magnitude of the inverted temperature profile using a concentric outer cylindrical tube will be discussed. Also, parametric studies will be reported for model calculations in which the total hemispherical emissivity was varied at boundaries of the sample and surrounding tube and at the cavity wall. The results will be discussed in the context of controlling both the average sample temperature and the temperature distribution in the sample during microwave processing.

steady-state↗
NASA NTRS1995

Steady State Temperature Profile in a Cylinder Heated by Microwaves

A new theory has been developed to calculate the steady state temperature profile in a cylindrical sample positioned along the entire axis of a cylindrical microwave cavity. Temperature profiles where computed for- alumina rods of various radii contained in a cavity excite in one of the TM(sub OnO) modes with n = 1, 2 or 3. Calculations where also performed with a concentric outer cylindrical tube surrounding the rod to investigate hybrid heating. The parameters studies of the sample center and surface temperature where performed as a function of the total power transmitted into the cavity. Also, the total hemispherical emissivity was varied at boundaries of the rod, surrounding tube, and cavity walls. The result are discussed in the context of controlling the average rod temperature and the temperature distribution in the rod during microwave processing.

Jackson, H. W.↗
NASA NTRS1993

Transient Temperature Behavior of a Sphere Heated by Microwaves

We have developed a model for microwave heating of a sphere in a rectangular resonant cavity. The model calculates transient temperature distributions within a sphere during the approach to steady state conditions or on the path to thermal runaway.

microwave heating microwave absorption↗
NASA NTRS1992

Microwave processing of materials in microgravity

The Jet Propulsion Laboratory is investigating the use of microwave energy as a controlled heating and positioning source for the processing of materials in the microgravity environment of space. Ground-based studies of the positioning capabilities of microwave forces are presented. The ability to quickly and efficiently control the heating of a variety of materials is demonstrated, and the heating of several representative materials is presented. A compact cold-wall microwave furnace compatible with future flight experiments in a shuttle mid-deck cannister is evaluated. The development of a hybrid containerless processing facility that will serve both as an acoustic positioning chamber and a microwave-heating cavity is also proposed. The design characteristics of a cold-wall furnace and hybrid heater/positioner are reviewed.

Barmatz, M.↗
NASA NTRS1992

Steady state temperature profile in a sphere heated by microwaves

A new theory has been developed to calculate the microwave absorption and resultant temperature profile within a sphere positioned in a single mode rectangular cavity. This theory is an extension of a total absorption model based on Mie scattering results. Temperature profiles have been computed for alumina spheres at the center of a rectangular cavity excited in the TM354 mode. Parametric studies reveal significant structure in those profiles under special conditions that are associated with electromagnetic resonances inside the spheres. Anomalous behavior similar to thermal runaway occurs at moderate temperatures when there is enhanced absorption associated with resonant conditions in the sphere.

Barmatz, M.↗
NASA NTRS1991

Microwave absorption by a lossy dielectric sphere in a rectangular cavity

A new theory of absorption of microwave power by a lossy dielectric sphere in a resonant rectangular chamber is developed here. In this treatment, resonant modes of the cavity are resolved into traveling plane-wave fields, and Mie's theory of scattering and absorption of a plane electromagnetic wave by a sphere is utilized. The fields in the cavity containing the sphere are found by superposition of results for the individual scattering problem for each traveling plane wave. Absorbed power is then calculated by evaluating the time-averaged Poynting vector and integrating over the surface of the sphere. Applications of microwave power absorption are discussed, with particular emphasis on processing of materials. Numerical studies based on the newly derived formulas are presented. The results exhibit the manner in which microwave absorption is influenced by a number of different experimentally controllable parameters. The examples considered were chosen with a view toward designing experiments and apparatus for containerless processing of materials in the microgravity environment of space.

Jackson, H. W.↗
NASA NTRS1991

Method for calculating and observing microwave absorption by a sphere in a single mode rectangular cavity

A new theory of microwave absorption by a lossy dielectric sphere in a single mode rectangular cavity has been recently developed. The absorption was treated in the framework of an electromagnetic scattering problem. That theory is summarized here and calculated results that bear on optimizing the processing of materials are illustrated. Methods for observing power absorption and other results predicted by the scattering model are discussed. Cavity perturbation theory provides a bridge between theoretical calculations and experimental observations, and a special problem that arises when an established version of cavity perturbation theory is applied to spheres is identified, analyzed, and resolved. The direct problem of predicting shifts in frequency and Q from model calculations is discussed for a sphere in a cavity when the sphere's complex dielectric constant is known. Also, the inverse problem of determining the complex dielectric constants from measured values of those shifts is considered. The small sphere limit, where an electrostatic or quasistatic model is valid, is treated in detail, and planned work on parallel problems for larger spheres is described.

Jackson, H. W.↗
NASA NTRS1990

Third-sound propagation in thick films of superfluid He-4

Atkins' (1959) basic theory of third sound in thick films of superfluid He-4 is extended here to include a heat source for exciting third sound. A one-dimensional model obeying periodic boundary conditions is developed which can represent a variety of experimentally important configurations. General solutions for the model equations are found which give a complete description of third-sound waves in terms of displacement of the film surface, superfluid velocity, and temperature change as functions of space and time. Algebraic expressions for quantities that occur in general formulas are found for special excitation signals. The structure of third sound is calculated for the first time and the results are found to be inconsistent with previous findings. A direct method for accurately measuring the vaporization coefficient is also presented.

Jackson, H. W.↗
NASA NTRS1990

JPL research to develop a He-3/He-4 dilution refrigerator for space applications

A research program to develop a He-3/He-4 solution refrigerator for space applications is underway. The results of the effort to use an electric field as a substitute for gravity to control the He-3/He-4 mixture interface that separates phases in terrestrial units are described. Further, experimental results obtained from an engineering model of a single-cycle dilution refrigerator with a mixing chamber capable of operating in a zero-gravity environment are described. Future research and development plans are outlined, in particular the need to test the operation of a single-cycle as well as a continuously operating dilution refrigerator in space.

Petrac, D.↗