The present disclosure relates to thruster mechanisms and, more particularly, relates to electrostatic thrusters and accelerators using nano- and micro-sized particles with micro- and nano-electromechanical systems (MEMS/NEMS) fabrication technology.
This section provides background information related to the present disclosure which is not necessarily prior art. This section also provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
The Nano-particle Field Extraction Thruster (nanoFET) concept is an approach for nano-particle acceleration to high speeds. According to the present teachings, nano-particles can be delivered without being suspended in a liquid. Particles can be completely dry, lightly lubricated, or treated to minimize particle cohesion. Sieve-like structures and mechanical vibration are used to overcome particle cohesion and adhesion effects to move particles from storage to the nanoFET charging and extraction grid. In addition to aerospace propulsion applications, nanoFET acceleration of nano-particles can be utilized in materials processing, nanoprinting, and biomedical applications, to name a few.
Sieve-like structures can be placed between the extraction and acceleration grids in the nanoFET and its particle reservoir with characteristics dimensions close to that of the nano-particles and larger. Multiple sieve grids can be used. The smallest structures can be based on MEMS/NEMS technology. The mechanical vibrations are accomplished via a combination of one or more external vibrating sources and integrated sources that are part of the MEMS/NEMS structures.
Using high speed nano-particles, it is possible to modify material surface properties for improved performance in materials processing. By this method, sputtering, deposition, and implantation are feasible. An important subcategory of this includes enabling improved semiconductor performance through use of nano-particles in fabrication.
Nanometer and micron-scale printing on a wide variety of materials (e.g., paper, plastics, semiconductors, and other targets) are possible for applications such as high security printing, high resolution marking, and direct circuit fabrication including for semiconductor devices. Using the nanoFET architecture of the present teachings, it is possible to consider precise, nanometer placement of particles and control of the energy of deposition.
Furthermore, biomedical applications will benefit from the ability to energetically inject nano-particles in-vivo. This allows the opportunity for treatments through the skin and drug placement at a cellular level. It will be a tool for both treatment and research.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a”, “an” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.
When an element or layer is referred to as being “on”, “engaged to”, “connected to” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to”, “directly connected to” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.
The following nomenclature will be used throughout the present teachings:
The use of charged and accelerated micro- or nano-particles was first presented by the inventors of the present application in U.S. Pat. No. 7,516,610, issued on Apr. 14, 2009, the teachings of which are hereby incorporated by reference. A principal focus of the '610 patent was the extraction of nano-particles suspended in insulating and conducting liquids.
With reference to
In some embodiments, liquidless nanoFET system 10 consists of a particle storage reservoir 14 directly against sieve electrode system 12 with a biasing member 16, such as a spring or control piston, that supplies pressure to help urge particles 100 through sieve electrode system 12. It should be understood, however, that biasing member 16 can be replaced with other urging devices and, in some cases, gravitational forces can be used in place of a dedicated biasing member.
In some embodiments, liquidless nanoFET system 10 can comprise a vibrational source 17. Vibrational source 17 can be a vibrating member or, in some cases, can be other mechanical or acoustical devices capable of imparting a mechanical or other force to disrupt the bond between adjacent particles, surfaces, or other matter.
Sieve electrode system 12 comprises at least one, but preferably a plurality, of through-hole openings or orifices 18 extending from a first side of sieve electrode system 12 to a second side thereof. The first side is adjacent particle storage reservoir 14 and receives particle 100 therefrom. The second side is in communication with a volume 25 discussed below. In some embodiments, the through-hole openings 18 of sieve electrode system 12 are sized slightly larger than the size of particle 100 so that only one particle is capable of passing through each sieve orifice 18 at a time. This assists in breaking the clumped nano-particle powder within particle storage reservoir 14 into individually isolated particles 100. However, it should be appreciated that in some embodiments where extraction of individual particles is not required, openings 18 can be sized such that two or more particles 100 can pass therethrough simultaneously.
Liquidless nanoFET system 10 further comprises a charging grid 20 and an acceleration grid 22, stacked above sieve electrode system 12 and in communication with volume 25, which can collectively be referred to as grid 23. It should be appreciated, however, that in some embodiments acceleration grid 22 can be eliminated and in some embodiments a plurality of acceleration grids 22 can be used. The construction and operation of charging grid 20 and acceleration grid 22 are similar to that described in commonly-assigned U.S. Pat. No. 7,516,610. Briefly, an electrical potential (i.e., Vac, Vch, etc.) can be applied between adjacent electrodes to define electric field therebetween (i.e., Eac, Ech, etc.) acting upon the associated particle. In other words, electric potentials are applied across the conducting sieve electrode system 12 and the charging grid 20 and acceleration grid 22 to generate the charging and accelerating electric fields used to charge and accelerate the individual particles 100 that pass through sieve electrode system 12. Once a particle 100 has charged and lifted off from sieve electrode system 12, the applied electric field accelerates particle 100 to high speeds through vias 28, 30 formed in charging grid 20 and accelerating grid 22, respectively.
As briefly described above, in some embodiments, a variety of vibrational sources 17 can be used to overcome particle cohesion and adhesion effects to move particles from storage to the nanoFET charging grid 20 and accelerating grid 22. These vibrational sources can, in some embodiments, move the entire nanoFET structure, sieve electrode system 12 structure only (as shown), and/or use surface acoustic devices that launch surface waves on the charging side of sieve electrode system 12 (opposite side from particle reservoir 14). One specific example is an axial ring piezoelectric device to vibrate the interface between particle 100 and sieve electrode system 12. When a vibration and backpressure are applied, particles 100 that come in contact with sieve electrode system 12 pass through orifice 18 of sieve electrode system 12 and the vibration motion force acts in combination with the applied charging electric field to extract individual particles and launch them through the acceleration grids 22. As the frequency of an oscillating piezoelectric device is increased, the resulting inertial force is amplified. Therefore, as the vibration frequency and/or amplitude is varied, the mass flow rate of particles 100 can be effected.
As an example, the inertial force that facilitates particle passage through sieve electrode system 12 and particle liftoff after charging may be provided by a piezoelectric stack, as illustrated in
The nanosieve that typically require micron to nanometer scale sized 3-dimensional structures are fabricated using micro and nano electromechanical system (MEMS/NEMS) manufacturing technologies. Specific sieve substrate materials depend on specific applications, but include semiconductor, conductors, as well as silicon nitride, ceramics, and other insulators and conductors. The second side of the sieve electrode system 12 must be conducting as defined by the bulk material of sieve electrode system 12 or by metal coatings such as gold or platinum or others. The nanosieve through-holes can be defined using similar techniques as for charging grid 20 and acceleration grids 22. Examples include semiconductor fabrication techniques to define structures using etching based on photons (photolithography) or electron beams (E-beam lithography), or direct surface milling using focused ion beams (FIB) to define the structures. Sieve electrode system 12 as shown in
Previous studies working with nanometer and micron sized particles explain that particles on this size scale have a strong tendency to adhere to each other (cohesion) and to other objects that they contact (adhesion). Therefore, an understanding of the adhesion and cohesion forces and how to overcome them is extremely important to the development of the liquidless nanoFET system 10 to assure that most particles 100 do not clump together through cohesion or stick to sieve electrode system 12 through adhesion. The present disclosure presents a theoretical analysis of the adhesion and cohesion forces. In addition, the electric force arising from the charging electric field acting on the charged particles is investigated, both theoretically and experimentally, as a method to overcome the adhesion force and achieve particle removal from the source electrode 12. Finally a proof-of-concept experiment with the goal of demonstrating the feasibility of overcoming the cohesion force with liquidless nanoFET system 10 is presented.
There are four primary forces generally credited for the adhesion and cohesion of small particles. The relative magnitude of these forces is dependent on the size of particles 100, the materials involved, and the environmental conditions. The most dominant of these forces when considering dry, conducting particles smaller than several hundred microns is the van der Waals force.
The van der Waals force between atoms arises when an apolar atom momentarily has a dipole moment due to the movement of its electrons with respect to its nucleus. This momentary dipole creates an electric field, which induces dipole moments in neighboring atoms. The resulting dipoles attract each other as the positive end of one atom aligns with the negative end of another.
The van der Waals force between macroscopic bodies is calculated by taking the summation of the van der Waals forces between the atoms of the different bodies. The van der Waals force density between two infinite parallel planar surfaces is calculated to be dependent on the Lifshitz-van der Waals constant, h, and the separation between the surfaces, z.
The Lifshitz-van der Waals constant has units of energy and is a function of the material combination involved. The values for select materials are published, but are disputed by many authors. It is accepted that typical values of the Lifshitz-van der Waals constant range from 0.6 to 9.0 eV. According to Curran, a minimum separation distance of 4 Angstroms is acceptable when evaluating the van der Waals force.
Using the van der Waals force density between two parallel planar surfaces given in Equation (1), the adhesion force between a spherical particle and an infinite planar surface (Equation (2)) and the cohesion force between two spherical particles (Equation (3)) are approximately calculated.
The simple expressions for the adhesion and cohesion van der Waals forces scale directly with particles' radii and inversely with the square of the minimum separation.
A comparison of the van der Waals forces reveals that the adhesion and cohesion forces scale the same with particle 100 size, but the adhesion force is approximately twice the cohesion force when using particles of the same size.
The plot in
The removal of micro- and nano-particles from surfaces is important to many applications, particularly in the MEMS and pharmaceutical industries. A few techniques currently used for particle removal are ultrasonic vibration, mechanical vibration, and laser irradiation. These techniques work by accelerating particles relative to the surface. This section investigates an alternative method of particle removal using high strength electric fields, which lends itself nicely to the design of micro- and nano-particle thrusters, which use high strength electric fields to charge particles 100 when they are in contact with the source electrode. This section presents the electric force on a spherical conducting particle when in contact with an infinite planar electrode and applies this force to determine the required electric field to overcome the van der Waals adhesion force.
The model for spherical particle removal from a planar electrode is shown in
The complete derivation of the electric force on the spherical particle 100 when in contact with the source electrode is beyond the scope of these teachings. Felici calculated it when assuming particle is much smaller than the electrode gap (d<<D).
Fel≈5.5πr2∈EBG2 (4)
Using the model for the electric force on a conducting particle in contact with the source electrode from Equation (4) and the van der Waals adhesion force from Equation (2), the threshold background electric field for particle removal can be calculated when the van der Waals force is dominant. It is important to include the gravitational force on the particle in this calculation to show where the adhesion force becomes more important than gravity.
By combining Equations (2), (4), and (5), the threshold background electric field for overcoming the adhesion force is estimated when particle 100 is much smaller than the electrode gap.
It is important to note that the threshold electric field can be broken down into two terms: the adhesion dominant term and the gravitational dominant term. The adhesion dominant term scales inversely with the square root of the size of particle 100 while the gravitational term scales directly with the square root of the size of particle 100.
The plot of the threshold electric field clearly illustrates the two regimes. Particles much larger than the centimeter range lie within the gravitational regime and particles much smaller than millimeter range lie within the adhesion regime. Both forces affect particles between these two ranges significantly. According to the plot, it may be possible to remove spherical particles with diameters as small as tens of nanometers when keeping the background electric field less than approximately 100 MV/m, which is below the level required for electron emission.
To experimentally investigate the van der Waals adhesion force and to overcome this force by way of an electric force, the system depicted in
The goals of the experiment are to measure the threshold electric field required for removing conducting spherical particles from the electrode surface for various particles in the adhesion dominant regime, investigate the effects of particle size on the adhesion force, and investigate the effects of particle 100 and electrode materials on the adhesion force.
The experiment is performed by depositing approximately 100 conducting spherical micro-particles (204) on the surface of the bottom electrode. To prevent these particles from clumping together through cohesion, particles 100 are passed through a micro-sieve to separate the clumps into individual particles prior to placement onto the electrode surface. In some embodiments, it is desirable to have particles 100 separated by a distance of at least ten times their diameter to ensure that neighboring particles do not affect the electric field profile at their surfaces. Once particles 100 are deposited, the upper electrode 200 is secured in place to provide the correct uniform electrode gap, which can be defined through the use of a spacer, such as 1.0 mm or 4.0 mm thick. Next, the voltage across the electrodes 200, 202 is increased incrementally to generate the strong electric field within the gap 208. At each voltage increment, a photograph of the particles remaining in contact with the source electrode 202 is taken to provide visual evidence of the number of particles removed. The process is repeated until all of the particles have been removed. Finally, the number of particles removed from the electrode surface 206 at each voltage increment is counted, providing an experimental measurement of the threshold electric field required for particle removal.
The particles removed from the source electrode 202 during testing are accelerated across the electrode gap 208 towards the upper electrode and onto the Kapton® tape 212, where they remain trapped. The Kapton® tape 212 serves to collect the removed particles so that they do not oscillate between the electrodes 200, 202 and disrupt the particles still adhered to the bottom electrode 202. The Kapton® tape 212 used for this experiment had a thickness of approximately 25 μm and typically has a relative dielectric constant of approximately 2.7.
The experiment was performed with four different spherical particle sizes, ranging in diameter from 53 microns to 305 microns, which are all in the adhesion dominant regime. Table 1 lists the mean diameters, tolerances, materials, densities, and manufacturers of the particles.
The photos in
The experiment was performed with two different electrode materials-gold and platinum. These materials were chosen because they do not oxidize when exposed to the atmosphere unlike most other metals. When manufacturing the electrodes, the two biggest concerns were controlling the surface flatness and the surface roughness. Controlling surface flatness is important for reducing the error in the applied electric field since a warped surface can lead to varying electric field strengths at the electrode surface. The surface roughness is important because the model for the van der Waals adhesion force assumes that the surface of the electrode is perfectly smooth.
To minimize the surface roughness and control the flatness, the electrodes were fabricated using plasma vapor deposition of the metals onto glass wafers. All depositions were performed using the EnerJet Evaporator at the Lurie Nanofabrication Facility (LNF) located at the University of Michigan. The gold electrodes were fabricated by depositing 300 nm of gold on top of a 30 nm adhesion layer of chromium, and the platinum electrodes were fabricated by depositing 100 nm of platinum on top of a 10 nm adhesion layer of titanium.
The electrodes are circular with 50 mm diameters and were deposited onto 100 mm glass wafers. A thin tail of metal stretches from the electrode and wraps around the wafer to provide an electrical connection on the reverse side.
An atomic force microscope (AFM) was used to measure the surface roughness of both the gold and platinum electrodes, and both were found to have a surface roughness on the order of 20 nm. The effects of the electrode surface roughness are presented in an upcoming section.
The experiment was performed in the Ultra High Vacuum (UHV) chamber at the Space Electrodynamics and Tether Systems (SETS) laboratory at the University of Michigan, which is pumped by a mechanical roughing pump and a turbo pump and has an ultimate pressure on the order of 10−9 Torr. Each experiment was performed at a pressure less 40 nTorr to prevent arcing within the electrode gap.
Before presenting the experimental results, it is important to recall that the Lifshitz-van der Waals constant from Equation (2) is not well known for most material combinations. Further, in the cases of reported values, many authors are not in agreement. Therefore, the present disclosure does not assume any values for the Lifshitz-van der Waals constant when analyzing the results. Instead, values for the Lifshitz-van der Waals constant that best fit the experimental results are evaluated and used for comparison between the test cases. The threshold electric field for particle removal is defined as the field strength at which 50% of the particles in contact with the source electrode are removed.
The experimental data is plotted against the theoretical threshold electric fields when using the Lifshitz-van der Waals constants evaluated to provide the best fit. Table 2 lists the evaluated Lifshitz-van der Waals constants for the four material combinations used in
The spread of the threshold electric field required for particle removal is larger than expected.
Potential reasons for the spread in the electric field required for particle removal are presented herein, which include the spread in particle size, particle and electrode surface roughness, and the surface deformation.
While the measured threshold electric fields trend as predicted by the model for each material combination, the evaluated Lifshitz-van der Waals constants for the two particle materials are quite different. The evaluated Lifshitz-van der Waals constants may be reasonable measurements of the actual values, or the difference may also be a result of uncontrolled variables in the experiment. In addition, the spread of the electric fields required for the removal of all the particles is quite large, which may also result from uncontrolled variables in the experiment. This section examines three variables in the experiment.
The first experimental variable to consider is the spread in particle size, which may contribute to the spread in the electric fields required for particle removal. Using the tolerances on particle diameters given in Table 1 and the predicted threshold electric field from Equation (6), the expected electric field spread can be calculated. Table 4 lists the approximate expected electric field spread resulting from particle size spread along with the measured spread to remove 15%-85% and 33%-67% of the particles.
The calculations in Table 4 suggest that the spread in particle size can lead to a spread in the electric field, but not enough to account for the entire spread in the experimental data.
The second experimental variable is possible deformation of particle 100 and/or the source electrode by compression. The model presented in Equation (2) assumes that particle 100 is a perfect sphere and that the electrode is a perfect plane, but, due to defects in particle 100 and/or the electrode, this is most likely not the case. The compression of either particle 100 or the electrode leads to a contact area between the two greater than just the point contact that is assumed. An increase in the contact area leads to an increase in the adhesion force.
Approximating the change in the adhesion force due to the deformation of particle 100 and/or the electrode is not straightforward because the exact geometry after deformation has occurred is unknown and can be quite complex. To approximate the change in the adhesion force resulting from deformation, all of the deformation is assumed to be at the bottom of particle 100. Using Equation (1), the adhesion force with a compressed particle is calculated to be a function of the contact area radius, rc.
Assuming that the electric force on particle 100 does not change significantly if particle 100 experiences a small deformation, which is appropriate as long as the deformation occurs at the bottom of particle 100, the new threshold electric field is calculated by modifying Equation (6) and assuming that particle 100 is in the adhesion dominant regime.
The deformation of particle 100 may lead to an error in the evaluated values of the Lifshitz-van der Waals constant from the experimental results.
In addition to increasing the error in the evaluated values for the Lifshitz-van der Waals constant, particle deformation may also be a source of the spread in the electric field required to remove all particles 100.
Comparing the theoretical spread in the electric field with the measured spread from Table 3, it is very possible that a small deformation could make significant contributions.
The final experimental variable that may potentially influence the electric field spread that is discussed in the present teachings is the surface roughness of both particle 100 and the electrode surface. The surface roughness of the materials in contact can lead to an increase or decrease in the adhesion van der Waals force depending on their relative roughness and alignment. Due to the complexity and large number of variations of surface roughness and alignments, it is not possible to provide a general relationship between the adhesion force and the materials surface roughness. Only in the case when the exact geometry of the two surfaces is known, can Equation (1) be integrated to find the adhesion force.
Sketch (a) from
As stated earlier, there exist many other possible orientations between particle 100 and electrode surfaces, and their effects on the adhesion force can be determined by understanding how the contact area changes. Since the surface roughness affects the adhesion force by changing the contact area, it is reasonable to expect that the error in the evaluated values for the Lifshitz-van der Waals constants and the resulting spread of the electric field required for particle removal are on the same order of magnitude as the case of particle deformation.
Based on the analysis presented in this subsection, it is possible that the evaluated values for the Lifshitz-van der Waals constants deviate from the actual values due to the deformation of particles 100 and/or the electrode and the surface roughness of particles and the electrode. The large spread in the electric field required for particle removal is most likely contributed to significantly by the same two experimental variables, and to a lesser extent, the spread in particle size.
As discussed in a previous section, the Lifshitz-van der Waals constant is used to calculate the van der Waals force between two macroscopic materials and is a measure of the energy of the van der Waals interaction. For materials in atmosphere or vacuum, its value generally ranges from 0.6 to 9.0 eV and is obtained using dielectric spectroscopy.
Calculating the Lifshitz-van der Waals constant is beyond the scope of the present teachings, but is known to be difficult due to the lack of available optical data. Table 5 lists the expected ranges of the Lifshitz-van der Waals constants for a couple of the experimental material combinations using published values. For comparison, the evaluated values of the Lifshitz-van der Waals constants from the experimental results are included in the table.
Note that the evaluated Lifshitz-van der Waals constants lay outside the range of predicted values for the given material properties, but are close to the expected range for all material combinations. There is possible error in the evaluated values as discussed in the previous subsection. But, according to Visser:
This section presents the feasibility of overcoming the cohesion force by using a method of transporting the dry particles 100 through sieve electrode system 12 to separate the clumped powder into individually isolated particles 100 prior to charging and acceleration as presented in the introduction. The details of the design and optimization of sieving electrode system 12 is beyond the scope of the present teachings. Results from a proof-of-concept experiment are presented with the goal of demonstrating the feasibility of this delivery system. The main goals of the proof-of concept experiment are to demonstrate the functionality of the first prototype by confirming that particles are charged, accelerated and ejected individually.
To experimentally investigate the method of delivering individual dry spherical particles through an ultra-fine sieve prior to charging and accelerating, the prototype shown in
Sieve electrode system 12 is electrically connected to ground while the charging grid 20 and the collection anode 300 are biased positive using a high voltage power supply to generate the charging electric field. Note that this prototype does not include any additional accelerating grids, but stacking additional grids above the charging grid 20 is possible. To verify that particles 100 were ejected individually and not clumped in groups, ejected particles were collected on glass slides placed just above the orifice in the charging grid and imaged using a scanning electron microscope (SEM).
The effects of the adhesion and cohesion forces on the liquidless nanoFET system 10 were presented along with potential methods of overcoming them. For conducting particles in a dry environment, the dominant adhesion and cohesion force is the van der Waals force, which scales directly with the size of particle 100. Overcoming the adhesion force by removing spherical conducting particles from a planar source electrode by way of applied electric fields was investigated. The electric force responsible for particle removal scales directly with the square of the size of particle 100 while the adhesion force scales directly with the size of particle 100. This suggests that as the size of particle 100 decreases, the required electric field for removal increases. The models developed predict that particles with diameters down to hundreds or even tens of nanometers can be removed from a planar electrode. It should be appreciated that methods of reducing the required electrical force, such as the use of mechanical vibration, are also anticipated and discussed herein.
To investigate the particle removal model, eight test cases, involving 4 particle sizes and 2 electrode materials, were studied. The tests agreed reasonably well with the model when using values of the Lifshitz-van der Waals constants close to the expected ranges for all materials. But, the values evaluated from the experimental data disagree with published values for the specific material combinations. Note that many authors are not in agreement on the published values. In addition, the spread in the electric fields required to remove particles was large. The possible error in the Lifshitz-van der Waals constants and the spread of the electric fields may be attributed primarily to the surface roughness and deformation of both particles 100 and the electrode.
Overcoming the cohesion force in part by delivering particles 100 through an ultra-fine sieve was confirmed by performing a simple proof-of-concept experiment.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.
This application claims the benefit of U.S. Provisional Application No. 61/082,061, filed on Jul. 22, 2008. The entire disclosure of the above application is incorporated herein by reference.
This invention was made with government support under Grant Nos. FA9550-07-C-0144 and FA9550-09-C-0079 awarded by Air Force Office of Scientific Research. The government has certain rights in the invention.
Number | Date | Country | |
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61082610 | Jul 2008 | US |