System and method for separating electrically conductive particles

A system and method for separating an electrically conductive particulate material, such as gold, from other materials. A ferromagnetic core is formed in a torroidal-like shape and is provide with a gap. A coil is wound around the core and an alternating current is applied to the coil to induce an alternating magnetic field at the gap. A stream of particles is directed into the gap. The frequency of the alternating current is set according to the specific resistivity of the particulate material which is to be separated from the rest of the material and according to the size of the particles which are to be separated from the rest of the material. By properly adjusting or setting the frequency of the alternating magnetic field, the first particles are imparted a trajectory which is different than the trajectory of the second particles in the particle stream. In order to account for the size of the particle, the present invention increases the frequency of the alternating magnetic field as the size of the first particles decreases. The present invention has particular application for separating particles of gold from other materials.

BACKGROUND 
1. The Field of the Invention 
This invention relates to apparatus used to separate particles consisting 
of one material from one or more other materials. More particularly, the 
present invention relates to apparatus and methods utilizing 
electromagnetic force to separate particles consisting of one electrically 
conductive material of interest, such as a valuable metal, from other 
conductive and nonconductive materials. 
2. The Prior Art 
There are many occasions in scientific and industrial applications where 
materials must be separated from one another. Particularly in the mining 
industry, valuable metals must be efficiently separated from other 
materials which are found in the ore. 
In many industrial applications, separation of particles having different 
sizes and densities relies on the earth's gravity as well as some 
additional process such as filtration. All such arrangements which have 
been devised utilizing gravity to separate particles of different 
densities include one or more drawbacks as are recognized in the art. For 
example, such arrangements may require water as a carrier for the 
particles to be separated. Disadvantageously, the water must be removed 
from the particles after separation. Moreover, in some mining locations, 
water is not readily available. 
In order to provide efficient separation without water, various apparatus 
and techniques have been proposed which also utilize some electromagnetic 
properties of materials, rather than density alone, to separate materials. 
While the task of separating magnetic materials from nonmagnetic materials 
is a relatively easy one, the task of separating a nonmagnetic materials 
from other nonmagnetic materials utilizing the magnetic properties of the 
materials has been the subject of research in the industry. Still, many 
problems and drawbacks exist with the proposed schemes. Particularly in 
the mining industry, there have been numerous attempts to separate 
materials from one another, for example gold from other materials, based 
on the differing magnetic properties of the materials. 
One example of a previous scheme is represented by U.S. Pat. No. 5,057,210 
to Julius. The Julius reference recognizes that the creation of eddy 
currents in conductive materials allows a magnetic field to move a 
nonmagnetic material. The Julius reference, however, utilizes rotating 
permanent magnets to generate a changing magnetic field and thus does not 
recognize critical aspects of the use of induced eddy currents in 
electrically conductive, nonmagnetic materials as will be explained 
shortly. 
Another example of a previous scheme is represented by U.S. Pat. No. 
5,161,695 to Roos. The Roos reference also recognizes that the creation of 
eddy currents in conductive materials allows a changing magnetic field to 
move particles of a nonmagnetic material. The Roos reference, however, 
utilizes permanent magnets, as does the Julius reference, and thus does 
not recognize critical aspects of utilizing induced eddy currents to cause 
movement of nonmagnetic particles. The scheme of the Roos reference is 
ineffective as will be apparent shortly. 
In view of the shortcomings inherent in the previously proposed schemes to 
separate nonmagnetic materials using magnetic force, it would be a 
significant advance in the art to provide a more efficient system and 
method of separating electrically conductive nonmagnetic materials. 
BRIEF SUMMARY AND OBJECTS OF THE INVENTION 
In view of the above described state of the art, the present invention 
seeks to realize the following objects and advantages. 
It is a primary object of the present invention to provide a practical 
system and method for separating electrically conductive nonmagnetic 
materials. 
It is also an object of the present invention to provide a system and 
method for separating electrically conductive nonmagnetic materials which 
does not rely on moving mechanical parts to achieve separation of the 
materials. 
It is a further object of the present invention to provide a system and 
method for separating electrically conductive nonmagnetic materials from 
each other which does not require any liquid. 
It is also an object of the present invention to provide a system and 
method for separating electrically conductive, nonmagnetic particles 
wherein an magnetic field which induces eddy currents in the particles 
also causes movement of the particles which are to be separated. 
It is a still further object of the present invention to provide a system 
and method for separating electrically conductive, nonmagnetic particles 
which could not otherwise be separated using flotation or filtration 
schemes. 
It is also an object of the present invention to provide a system and 
method for separating electrically conductive, nonmagnetic particles 
wherein characteristics such as the specific resistivity and the size of 
the particle determine the separation of one material from other 
materials. 
These and other objects and advantages of the invention will become more 
fully apparent from the description and claims which follow or may be 
learned by the practice of the invention. 
The present invention provides a system for separating a first electrically 
conductive particulate material from one or more other materials. The 
present invention is particularly intended for use with materials in 
particulate form but can also be used with materials in other forms. The 
present invention can also be used in conjunction with other separation 
technologies, such as flotation and filtration, which are known in the 
art. For example, the separation techniques of the present invention can 
be used before or after materials have been subjected to other separation 
techniques known in the art. 
The present invention includes means for localizing a magnetic field at a 
first location. The magnetic field is an alternating or oscillating field. 
It is preferred that the magnetic field have a strength of at least 1 
kilogauss (kGs) and have a frequency of, for example, at least 10 
kilohertz (kHz). In contrast with the prior art, the present invention 
considers the size of the particle when selecting the frequency. As the 
size of the particle to be separated decreases, the frequency preferably 
increases. For example, a frequency of 10 kHz may be used for the largest 
particles needing separation, a frequency of 20 kHz if medium size 
particles are to be separated, and a frequency of 40 kHz or higher for the 
smallest particles which are to be separated. 
The means for localizing a magnetic field can desirably include a core of 
ferromagnetic material formed in a torroidal-like shape, at least one gap 
formed in the core, and an electrical conductor wound around the core, the 
conductor being capable of carrying electrical current and inducing a 
magnetic flux in the gap. Alternatively, other structures which can be 
devised by those skilled in the art can function as the means for 
localizing. For example, a coil with a plurality of gaps and without a 
core can function as the means for localizing. 
A means for directing a material stream to the gap is also provided. The 
material stream comprises both the desirable first particles which consist 
of an electrically conductive, nonmagnetic material and a second material 
which can consist of one or a plurality of other materials. A means for 
setting the velocity of the material stream is preferably provided. 
The present invention may also include means for sorting the particulate 
material according to size and conveying the first electrically conductive 
particulate material to the means for directing a material stream to the 
first location. As will be explained, the present invention utilizes 
heretofore unrecognized principles that allow separation of electrically 
conductive, nonmagnetic particles more efficiently than before. 
The present invention exploits the characteristics of particle electrical 
specific resistivity and particle size. Thus, in contrast to the 
previously proposed schemes, the present invention considers the size of 
the particles in the separation process. For example, some embodiments of 
the present invention preferably include means for sorting particles 
having a diameter not larger than about five millimeters and more 
preferably not larger than about two millimeters. Embodiments of the 
present invention may also comprise means for measuring the size of the 
particles of the electrically conductive particulate material so that the 
operation of the system can be adjusted for best efficiency. Moreover, in 
contrast to the previously proposed schemes, the present invention 
considers the specific resistivity of the particles in the separation 
process. 
The present invention also includes means for generating an alternating 
current and for applying it to the means for localizing a magnetic field. 
The frequency of the alternating current is set according to the specific 
resistivity (or conductivity) of the desired material and the size of the 
particles comprising the desired material. Selected embodiments of the 
present invention preferably include means for increasing the frequency of 
the alternating current as the size of the first particles decreases. 
The means for localizing a magnetic field and the means for generating an 
alternating current cooperate together to induce an alternating magnetic 
field at a location, for example the gap, where separation occurs. 
Separation occurs as a result of the alternating magnetic field deflecting 
the path of the desired material a different amount than the other 
material present in the stream is deflected. Structures are also included 
to function as a means for gathering the first particles as they are 
separated from the material stream. 
The method of the present invention preferably includes the steps of 
generating an alternating magnetic field, introducing a stream of 
particles into the magnetic field, the stream of particles including both 
the desired first particles and undesired second particles. The step of 
adjusting the frequency of the alternating magnetic field is carried out 
in accordance with the specific resistivity and the size of the first 
particles. By properly adjusting or choosing the frequency of the 
alternating magnetic field, the first particles are imparted a trajectory 
which is different than the trajectory of the other particles in the 
particle stream. In order to adjust for the size of the particle, the 
present invention increases the frequency of the alternating magnetic 
field as the size of the first particles decreases. 
Since the size of the particles greatly influences the separation process, 
it may be desirable to pre-sort the particles according to size or adjust 
the size of the particles before being subjected to the alternating 
magnetic field. Moreover, it is desirable to adjust the velocity of the 
particles in the particle stream as they enter the magnetic field. 
The particle stream is subjected to the magnetic field for a period of time 
while the first particles are gathered into one location and the remaining 
material gathered into another location. The present invention has 
particular application for separating particles of gold from other 
materials.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
General Discussion 
As explained earlier, the disadvantages of utilizing gravitational force in 
order to separate materials, particularly in the mining industry, has lead 
to the proposal of schemes which utilize the electrical properties of 
materials to carry out the separation. Still, the proposed scheme 
inherently includes several drawbacks and disadvantages which have 
hitherto not been recognized. 
In order to most clearly explain the operation of the present invention, 
and the critical differences between the present invention and the 
existing art, a general discussion setting forth the underlying principals 
of the present invention will first be provided followed by examples of 
specific embodiments utilizing the principals of the present invention. 
In the following discussion and examples, the illustrative material to be 
separated and gathered is gold. It is to be understood, however, that the 
present invention, in contrast to some teachings in the prior art, can be 
used to separate many different electrically conductive materials, both 
precious metals and other conductive materials. Gold is used as an example 
because of the interest in the mining industry to separate gold particles 
from other materials either in a gold mining operation or as a secondary 
product in some other type of mining operation. Gold is a very dense 
element, having a density of 19.3 gram/cm.sup.3, which makes it possible 
to separate gold using sedimentation, flotation, or some other technique 
involving the force of gravity as has been common in the mining industry. 
Still, there are some circumstances where these techniques cannot be used 
and where the present invention is particularly advantageous. 
The present invention utilizes the differences in the specific resistivity 
between different electrically conductive materials. As is well known, 
gold is a good electrical conductor having specific resistivity (R) of 
2.42 .mu..OMEGA..multidot.cm. As will be explained more fully shortly, the 
present invention also considers, in contrast to the prior arrangements, 
the size of the particle. 
In a magnetic field, the force exerted on an electrically conductive 
particle possessing a magnetic moment M is expressed by Expression (1). 
EQU F.sub.B =(M.multidot..gradient.)B=(.gradient.B).multidot.M (1) 
where 
##EQU1## 
M is magnetic moment. 
The force F is used in accordance with the present invention to move 
selected electrically conductive, nonmagnetic particles in a desired 
direction, while not substantially moving or moving to a lesser extent 
other particles, as will be described. Nonmagnetic materials, including 
particles consisting of gold and other precious and valuable metals, do 
not inherently exhibit their own magnetic moment M. But electrically 
conductive particles can exhibit their own magnetic moment M if subjected 
to an alternating magnetic field. 
EQU B=B.sub.o e.sup.i.omega.t (2) 
When a conductive particle is subjected to an alternating magnetic field, 
the magnetic moment M which is acquired by the particle is attributed to 
eddy currents, also referred to as Foucault currents, induced in the 
particle by the electric field. Expression (3) describes the magnetic 
moment M acquired by a particle. 
EQU M=.alpha.VB (3) 
It will be appreciated that in Expression (3), .alpha. is a coefficient of 
magnetic polarization and V=4/3.pi.a.sup.3 represents the volume of a 
particle. The coefficient of magnetic polarization (.alpha.), in turn, 
depends on the magnetic field frequency f=2.pi..omega., the specific 
resistivity of the material R (which in the case of a gold particle will 
be taken as 2.42 .mu..OMEGA..multidot.cm), and the diameter of the 
particle d=2a. Expression (4) provides a value for the coefficient of 
magnetic polarization (.alpha.). See Landau, L. D. & Lifshitz, E. M., 
Elektrodianamika sploshnyh sred Moscow (1982) which is now incorporated 
herein by reference. 
##EQU2## 
From Expression (4), it will be seen that the coefficient of magnetic 
polarization is a complex variable which includes real and imaginary parts 
as shown in Expression (5). 
EQU .alpha.=.alpha..sub.1 +i.alpha..sub.2 (5) 
Reference will now be made to FIG. 1. FIG. 1 is chart showing the frequency 
dependence of the real part .alpha..sub.1 and the imaginary part 
.alpha..sub.2 of the coefficient of magnetic polarization .alpha. for a 
particle of gold having a radius (a) equal to 1 mm. 
From the data set forth in FIG. 1, it will be appreciated that the force 
acting upon a particle being subjected to a magnetic field which is 
alternating or oscillating in time is actually a composite of two 
oscillating functions: magnetic field and magnetic moment M. Importantly, 
the magnetic moment M is delayed in phase by an angle expressed by: 
.phi.=arctan (.alpha. .sub.1 /.alpha..sub.2). 
Significantly, it should be appreciated that (a) the size of the particle, 
(b) the resistivity of the particle, and (c) the frequency of the 
oscillating magnetic field must all considered when separating 
electrically conductive, nonmagnetic particles such as gold. The 
previously proposed techniques and methods have all ignored one or more of 
these parameters. 
When the frequency at which the magnetic field oscillates is relatively 
low, the calculated depth of the "skin layer" .delta. is much greater than 
particle size d. As will be understood by those skilled in the art, the 
so-called skin effect is the tendency of alternating currents to flow only 
near the surface of a conductor. The skin effect becomes more pronounced 
as the frequency of the alternating or oscillating current increases. 
The depth below the surface of the particle at which the current density 
decreases to an established ratio of the value of the current density at 
the surface of the particle is referred to herein as the "skin layer." 
When the depth of the skin layer is much greater than the size of the 
particle the coefficient of magnetic polarization .alpha. is purely 
imaginary. This condition is shown by Expression (6). 
##EQU3## 
In the case where the depth of the skin layer .delta. is much greater than 
the size of the particle, the phase of the magnetic moment M lags the 
magnetic field by . Because the phase of the magnetic moment M lags the 
magnetic field by the force acting upon a particle oscillates at a double 
frequency resulting in the average value of the force &lt;F.sub.B &gt; applied 
to the particle being equal to zero as expressed by Expression (7). 
EQU F.sub.B .about.e.sup.-2i.omega.t, &lt;F.sub.B &gt;=0, when .delta.&gt;&gt;d (7) 
In contrast, at relatively high frequencies, that is when the depth of the 
skin layer .delta. is much smaller than the particle size d, the 
coefficient of magnetic polarization .alpha. is purely real, i.e., 
-.alpha..sub.1 .alpha..sub.2, when .delta.&gt;&gt;d. In the case where the 
frequency is high enough, the time-averaged value of the force &lt;F.sub.B &gt; 
applied to the particle is not equal to zero but becomes equal to a 
half-value of amplitude as represented by Expression (8). 
##EQU4## 
From the preceding explanation, it will be understood that as the frequency 
increases to a point where a limit-derived magnetic particle polarization 
is reached the averaged dynamic movement of a particle (that is the 
movement of the particle averaged over many high frequency cycles) is 
determined by superposition of the magnetic force &lt;F.sub.B &gt; and the 
ambient gravitational force m g =-.gradient.u which leads to Expression 
(9). 
##EQU5## 
where u=mgz (the potential energy of a particle .epsilon. a gravitational 
field). 
From the preceding discussion, it will be appreciated that the movement of 
a particle in a magnetic field which is oscillating at an appropriately 
"high" frequency, as defined above, is equivalent to movement of the 
particle in a potential field with effective potential energy U.sub.eff as 
described in Expression (10). 
##EQU6## 
As will be appreciated by those skilled in the art, the integral of the 
movement described by Expression (10) is effective full energy as set 
forth in Expression (11). 
##EQU7## 
From the integral expressed in Expression (11), an absolute value of the 
particle's speed can be expressed as set forth in Expression (12). 
##EQU8## 
As will be appreciated, represents the density of gold, which is assumed 
to equal 19.3 g/cm.sup.3. The coefficient of polarization, at an 
appropriately high frequency, is given by 
##EQU9## 
From the foregoing, it will be appreciated that the present invention 
recognizes those principals which are necessary to efficiently separate 
nonmagnetic, electrically conductive particles which have heretofore not 
been understood and not recognized in the art. Having explained the 
quantitative considerations of the present invention, the apparatus of the 
present invention will be explained. 
Apparatus of the Present Invention 
The apparatus of the present invention efficiently separates electrically 
conductive, nonmagnetic particles based upon the particle's size and the 
particle's specific electrical resistivity. Thus, one type of desired 
electrically conductive, nonmagnetic particle can be readily separated 
from other undesired electrically conductive, nonmagnetic particles in 
accordance with the present invention. Thus, even if the desired and 
undesired particles are of substantially the same particle size, but the 
particles have different specific electrical resistivities, the particles 
can be separated from one another using the present invention. From 
Expression (10) it will be appreciated that the desired particle is pushed 
out from the oscillating magnetic field, i.e., its trajectory is altered, 
and the undesired particles are substantially unaffected by the 
oscillating magnetic field and thus pass through without substantial 
alteration of their trajectories. 
The present invention can be carried out so that particles can be separated 
from each other in a batch-by-batch fashion or in a continuous flow 
process. The continuous flow process is presently preferred and more 
efficient. Thus, the apparatus described herein are all of the continuous 
flow type. The present invention can, however, be adapted to batch 
processing. As explained earlier, gold particles will be described herein 
as exemplary desired particles. It is to be understood that the present 
invention has equal applicability with other suitable materials. 
The magnitude of the separation effect on a particle is represented by 
Expression (13). Expression (13) shows an exemplary numeric value of the 
velocity which a desired particle acquires as it is moved out of the 
locality of the oscillating magnetic field having a strength equal to 
B.sub.0. PG,21 
##EQU10## 
From Expression (13), it will be appreciated that a particle subjected to 
an oscillating magnetic field having a strength of about 1 kGs acquires a 
velocity of about 0.5 m/sec. Moreover, this velocity will be in one or 
more predetermined directions in relation to the oscillating magnetic 
field. Thus, as will be explained in greater detail shortly, separation of 
the desired particles from the undesired particles can occur by changing 
the trajectory of the desired particles when they pass through the 
locality of the oscillating magnetic field, whereas the trajectory of 
undesired particles doesn't substantially change and the particles will 
pass through as if the oscillating magnetic field didn't exist. 
As will now be appreciated, the present invention requires the creation of 
an oscillating, also referred to herein as an alternating, magnetic field 
of the proper frequency and of sufficient strength. Those skilled in the 
art will readily appreciate which of the components available in the art 
can be used to generate an oscillating signal of sufficient strength and 
of high enough frequency to move the desired particles. 
FIGS. 2-4 illustrate preferred structures used for carrying out the present 
invention. FIG. 2 is a diagrammatic representation of a first presently 
preferred embodiment for carrying out the present invention. 
Represented generally at 100 in FIG. 2 is a magnetic field localizer. The 
magnetic filed localizer 100 functions to focus and localize the magnetic 
field at a gap generally represented at 103. 
The magnetic field localizer 100 includes a core 102 whose preferred 
triangular cross sectional shape can be seen at the cross sectional view 
provided at the gap 103. The core 102 is shaped similarly to a torus and 
is closed except for the gap 103. The closed shape more efficiently 
localizes the magnetic field at the gap 103. Other shapes which are now 
known or which may be devised in the future can also be used. For example, 
the cross sectional shape of the core 102 can also preferably be 
rectangular. 
Ferrite is the preferred material for the core 102. As is known in the art, 
the term ferrite refers to a group of materials which provide good 
magnetic properties but which are relatively poor conductors of electrical 
current. Thus, any number of materials which share this characteristic 
should be considered as preferred candidates for the material from which 
the core 102 is fabricated. It is also preferred to laminate the core 102 
as is known in the art to reduce electrical loses. 
A coil 104 is wrapped around the core 102. The representation of the coil 
104 in the figures provided herein is diagrammatic only and is not 
intended to limit the type of coil-like structure which is provided about 
the core. It will be appreciated that many different structures can be 
used as the coil 104. Any structure which allows an oscillating electrical 
current passing therethrough to induce a corresponding flux in the gap 103 
can function as the coil 104. 
A frequency generator 106 provides alternating or oscillating electrical 
current to the coil 104. The frequency generator 106 should be able to 
provide sufficient current to induce a magnetic field of substantial 
strength at the gap 103. For example, field strengths of about 1 kGs to 
about 10 kGs are preferred. Greater or smaller field strengths may also be 
used. Those skilled in the art can readily obtain commercially available 
generators capable of providing sufficient currents to carry out the 
present invention in a frequency range of from about 10 kHz to about 10 
mHz. Such frequency generators are widely used for induction heating 
applications. 
From the foregoing discussion, when gold particles having a radius of about 
1 mm and larger are to be separated, the frequency generator 106 must 
provide a signal at least as great as about 20 kHz. As the size of 
particles decreases the frequency output from the frequency generator 106 
must increase in order to maintain the efficiency of the separation 
operation. A ten fold decrease in the size of the particles requires that 
the frequency of the frequency generator 106 must be increased 100 times 
to maintain the efficacy of the separation. The minimum size of particles 
which can be separated by the present invention is limited by the highest 
frequency that can be produced and should satisfy the condition: 
-.alpha..sub.1 &gt;.alpha..sub.2 or .delta.&lt;d. 
It is to be understood that the signal which is output from the frequency 
generator 106 need not be stabilized and that the wave form of the 
alternating signal which is output need not be strictly sinusoidal. 
The apparatus represented in FIG. 2 also includes a particle conditioning 
unit 108. The particle conditioning unit 108 carries out such tasks as 
providing properly and relatively uniformly sized particles. Particle 
conditioning can include, for example, adjusting the size of particles, 
determining the size of the particles, and sorting the particles according 
to size using various means known in the art for carrying out that 
purpose. Since the size of the particles determines the separation 
results, the particle conditioning unit 108 preferably regulates the size 
of the particles passing into the gap 103. The particle conditioning unit 
108 can also carry out whatever other tasks which will improve the 
efficiency of the separation. 
A particle director 110 receives the particles from the particle 
conditioning unit 108 and directs them to the gap 103 in an orderly 
fashion. It will be appreciated that the dimensions of the stream of 
particles entering the gap 103 will influence the efficiency of the 
separation. Moreover, the velocity of the particles as they enter the gap 
103 will also influence the efficiency of the separation. Thus, the 
particle director 110 desirably includes structures to monitor the 
dimensions of the particles in the stream and to control the velocity of 
the particles as they enter the gap 103. 
FIG. 2A is a cross sectional view of the core 102 with the particles which 
emerge from the particle director 110 being represented by a solid line P. 
FIG. 2A diagrammatically represents the action of the present invention as 
the particle stream P enters the location of the magnetic field in the gap 
103. The particle stream can include desired gold particles and any number 
of different undesired particles. As the particle stream falls under the 
force of gravity into the location of the magnetic field, the desired gold 
particles are moved out of the particle stream P by acquiring a new 
trajectory indicated by dots P.sub.1. The undesired remaining particles, 
represented by dashes P.sub.2, from the particle stream P, continue in 
substantially the same downward trajectory. 
While the presently preferred arrangements for carrying out the present 
invention utilize gravity to move the desired particles out of the 
particle stream P, it will be appreciated that a force other than gravity 
could be used to move the particle stream P into the location of the 
magnetic field. Moreover, it will be appreciated that the magnetic field 
localizer 100 must be properly oriented in relation to the particle stream 
P for efficient separation. The trajectory of gold particles P.sub.1 is 
similar to that of a light ray passing through an optical prism. Thus, the 
operation of the apparatus represented in FIGS. 2 and 2A can be described 
as a "magnetic prism." 
As diagrammatically shown in FIG. 2, after the trajectories of the desired 
gold particles P.sub.1 has been sufficiently altered, a separation plate 
112 gathers the gold particles P.sub.1 into a first collection area 114 
while the remaining particles are allowed to fall into a second collection 
area 116. 
FIG. 3 represents another example of a magnetic field localizer. The 
magnetic field localizer illustrated in FIG. 3 includes four core and coil 
sections 130A-D and four gaps 132A-D. The four core and coil sections 
130A-D may all be driven from same frequency generator such as frequency 
generator 106 in FIG. 2. Moreover, each gap 132A-D can be provided with 
corresponding particle directors, such as particle director 110 in FIG. 2, 
and separation plates, such as separation plate 112 in FIG. 2. In this 
way, the efficiency of the separation system can be increased. 
After consideration of the information set forth herein, those skilled in 
the art will appreciate that a magnetic field localizer can include tens, 
or even hundreds, of structures which function as the gaps 132A-D. 
Moreover, it is possible to omit a core from the coil structure. As is 
known in the art, as the frequency of an alternating magnetic field is 
increased, the inclusion of a core will result in greater loses and lower 
electrical efficiency. All of the arrangements described herein are 
intended to come within the scope of the means for localizing a magnetic 
field in accordance with the present invention. 
FIG. 4 illustrates another arrangement of the present invention wherein one 
frequency generator 154 supplies current to a plurality of cores 150A-F 
and their corresponding coils 152A-D. Six gaps 156A-F are provided whereat 
the magnetic field is concentrated. Each gap 156A-F can be provided with 
corresponding particle directors, such as particle director 110 in FIG. 2, 
and separation plates, such as separation plate 112 in FIG. 2. It is to be 
appreciated that the representation provided in FIG. 4 is merely 
diagrammatic and is intended to indicate the benefits of coupling a 
plurality of cores, coils, and gaps together. 
In addition to the embodiments represented in FIGS. 2-4, further 
embodiments of the present invention can be devised by those skilled in 
the art using the information contained herein. For example, it is within 
the scope of the present invention to arrange a number of the 
above-described embodiments in a serial arrangement to allow the particles 
which are output from a first magnetic prism to further separation by 
subsequent magnetic prism structures. 
In view of the foregoing, it will be appreciated that the present invention 
provides a system and method for separating electrically conductive 
nonmagnetic materials which does not rely on moving mechanical parts to 
achieve a separation of the particles. The present invention also provides 
a system and method for separating electrically conductive, nonmagnetic 
particles wherein the magnetic field which induces eddy currents in the 
particles also causes movement of the particles which are to be separated 
and wherein both the electrical conductivity and the size of the particle 
determine the separation of one type of particle from other types of 
particles. 
The present invention may be embodied in other specific forms without 
departing from its spirit or essential characteristics. The described 
embodiments are to be considered in all respects only as illustrative and 
not restrictive. The scope of the invention is, therefore, indicated by 
the appended claims rather than by the foregoing description. All changes 
which come within the meaning and range of equivalency of the claims are 
to be embraced within their scope.