Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
1 Field of the Invention
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This invention relates generally to the measurement of distance by
means of an electromagnetic radiation field and more particularly to the meas-
urement of distance by means of a component oE a vector potential magnetic field
A for which the CURL A = O.
2. Description of the Prior Art
It is known in the prior art to provide a distance measurement system
by generating an electromagnetic radiation field from a transmitter and meas-
uring the time for the radiation field to reach the target object and return to
a receiver. Because electromagnetic radiation travels with the speed of light,the time between transmission of the radiation and the detection of the reflec-
ted radiation by the receiver, ~the receiver havillg a known spatial relationship
with the transmitter) defines the distance. Familiar examples include micro-
wave band ranging and optical ~i.e., laser) reflection techniques. This tech-
nique for measuring distance is limited by the opacity of the intervening media
to the transmitted electromagnetic radiation.
The Maxwell equations, which govern the prior art distance measuring
techniques by electromagnetic fields can be written:
1. CURL E ~ ~ ~
2. CURL H ~
~t
3. DIV B = O
4. DIV D = p
where E is the electric field density, H is the magnetic field intensity B is
the magnetic flux density, D is the electric displacement, J is the current
density and p is the change density. In this notation the bar over a quantity
,~
. :
" . , .:
1 727~1D
indicates that this is a vector quantity, i.e., a quantity for which a spatial
orientation is required for complete specification. The terms CURL and DIV
refer to the CURL and DIVERGENCE mathematical operations. Furthermore, the
magnetic field intensity and the magnetic flux density are related by the equa-
tionsl~ while the electric field density and the electric displacement
are related by the equation D = ~ H. These equations can be used to describe
the transmission of electromagnetic radiation through a vacuum or through vari-
ous media.
It is known in the prior art that solutions to Maxwell's equations
can be obtained through the use of electric scalar potential functions and mag-
netic vector potential f~mctions. The electric scalar potential field is given
by the expression:
5- ~(1) = ~ ~d~
where 0(1) is the scalar potential field at point 1, p(2) is the charge den-
sity at point 2, ~12 is the distance between point 1 and 2, and the integral is
taken over all differential volumes dv(2). T'he magnetic vector potential is
given by the expression
6. A(l) = ~ ~ c~
where A(l) is the vector potential at point l,~o is the permittivity of ~ree
space, C is the velocity of light, J(2) is the (vector) current density at point
2, rl2 is the distance between point 1 and point 2 and the integral is taken
over all differential volume. '~le potential functions are related to Maxwell's
equations in the following manner.
7. E = -GRAD ~ - ~ A
where GRAD is the GRADIENl' mathematical operation.
8. B = CURL A
~ 1 ~2~0
where A can contain, for completeness a term which is the gradient of a scalar
function. In the remaining discussion, the scalar function and the electric sca-lar field will be taken to be substantially zero. Therefore, attention will be
focused on the magnetic vector potential A.
In the prior art literature, consideration has been given to the phys-
ical significance of the magnetic vector potential field A. The magnetic vector
potential field was, in some instances, believed to be a mathematical artifice,
useful in solving probîems, but devoid of independent physical significance.
~ore recently, however, the magnetic vector potential has been shown
to be a quantity of independent physical significance. For example, in quantum
mechanics, the Schroedinger equation for a (non-relativistic, spinless) particlewith charge 2 and mass m moving in an electromagnetic field is given by
9 ~ Rfl~ G/~flD- ~ A )~
where t~ is Planl;~s constant divided l-y 2~,r, i is the imaginary number ~ is
the electric scalar potential experienced by the particle, A is the magnetic
scalar potential ex~erienced by the particle and ~ is the wave function of the
particle. 'rhe ability of quantum mechanical systems to be influenced by the mag-
netic vector potential field has resulted in dcvices which can be used to detectthe magnetic vector potential field.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to provide an im-
proved system for the measurement of distance by means of an electromagnetic ra-diation field.
Itis afurther object of the present invention to provide a system for
measurement of distance that can operate through media opaque to more usual el-
ectromagnetic radiation fields.
It is yet another object of the present invention to provide a system
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for measurement of clistance by means of a curl-free magnetic vector potential
field.
Itis amore particular object of the present invention to provide appar-
atus for generation o~ a curl-free magnetic vector po~ential field and apparatus
for detection of curl-free magnetic vector potential fields, the strength of the
field at the detection apparatus being a measure of the distance.
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RELATED APPLICATIONS
Apparatus and Method for Transfer of Information by
Means of a Curl-Free Magnetic Vector Potential Field, invented
by Raymond C. Gelinas, Application No. 390,420, and assigned to
the same assignee as named herein.
Apparatus and Method for Direction Determination by
Means of a Curl-Free Magnetic Vector Potential Field, invented
by Raymond C. Gelinas, Application No. 390,282, and assigned to
the same assignee as named herein.
Apparatus and Method for Demodulation of a Modulated
Curl-Free Magnetic Vector Potential Field, invented by Raymond
C. Gelinas, Application No. 390,669, and assigned to the same
assignee as named herein.
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SUMMARY OF THE INVENTION
The aforementioned and other objects are accomplished,
according to the present invention, by apparatus for generating a
magnetic vector potential field A having a substantial component
subject to the condition CURL A = O (i.e., a curl-free magnetic
vector potential field component), and by apparatus for detecting
the curl-free magnetic vector potential field. The magnetic vector
potential field generating apparatus generates a field having
predetermined components. The detection apparatus determines the
magnitude of the components. secause the steady-state curl-free
component of the magnetic vector potential field has limited
interaction with the intervening media, the magnitude of the
detected curl-free magnetic vector potential is determined by the
magnitude of curl-free magnetic vector pGtential field produced by
the generating apparatus and the distance between generating
apparatus and detection apparatus. Because the media does interact
with a changing curl-free vector potential field, an upper limit to
the frequency components of the applied field is imposed.
Examples of the apparatus generating magnetic vector
potential fields with substantial curl-free components include
solenoid configurations and toroidal configurations. The Josephson
junction device is an example of a device which can detect a curl-
free magnetic vector potential field. secause the generating
apparatus and detecting apparatus have directional characteristics,
the generating and detecting apparatus must be aligned.
In accordance with the present invention, there is
provided a method for determining distance between a radiation
transmitting apparatus and a radiation receiving apparatus compris-
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t 1 72~160
ing the steps of: (a) generating a curl-free magnetic vector
potential field having predetermined characteristics b~ said trans-
mitting apparatus; (b) measuring an output signal of said curl-free
magnetic vector potential field by said receiving apparatus as a
function of distance from said transmitting apparatus and as a
function of said predetermined characteristics of said generating
means; and (c) measuring an output signalof said receiving
apparatus when said transmitter means is generating a magnetic
vector potential field with said predetermined characteristics at
an unknown distance.
In accordance with another aspect of the invention, there
is provided apparatus for determining a distance between a first
location and a second location comprising: .means for ge.nerating a
radiation field having a substantial curl-free magnetic vector
potential field component with predetermined characteristics, said
field generating means located at said first location; means for
determining a magnitude of a curl-free magnetic vector potential
field component, said field magnitude determining means located at
said second location said field determining means responsive to
said predetermined characterist.ics for determining said magnitude
wherein said field magnitude determining means has been previously
calibrated as a function of distance from said field generating
means and as a function of said predetermined field charac.teristics
generated by said field generating means.
These and other features of the present invention will be
understood upon reading of the following description along with the
drawings.
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BRIEF DESCRIrTIO;`~ OF TIIE DRA~`~INGS
Figure 1 is a schematic diagram illustrating the procedure for deter-
mining a magnetic vector potential at a point.
Figure 2 is a schematic diagram illustrating the generation of a curl-
free magnetic vector potential field using an infinite solenoid.
Figure 3 is a schematic diagram illustrating the generation of a curl-
free magnetic vector potential field using a toroidal configuration.
Figure 4A is a cross-sectional diagram o a Josephson junction.
Figure 4B is a perspective diagram of a Josephson junction.
Figure 5 is a diagram of the current flowing in a Josephson junction as
a function of the magnetic vector potential field perpendicular to the plane of
the junction.
Figure 6 is a schematic diagram of a system for using a curl-free vec-
tor potential radiation field for transmissions of information.
Figure 7 shows a schematic diagram for apparatus for determining the
magnitude o the curl-free magnetic vector potential field for weak fields.
Figure 8 shows a schematic diagram for apparatus for determining the
magnitude o.E the curl-free magnetic vector potential field Eor strong fields.
Figure 9 illustrates the operation of the apparatus determining the
0 magnitude of strong curl-free magnetic vector potential fields.
OPERATION OF THE PREFERRED EMBODIMENT
1. Detailed Description of the Figures
Referring to Figure 1, the method of determining the magnetic vector
potential field A(l) 12 ~i.e., at point 1) is illustrated. Referring to equation
6, the contribution by the differential volume element at point 2, dv(2) 11 hav-
ing a current density J~2) 13 associated therewith is given by
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~r~"c ~1~
To obtain equation 6, equation 10 must be integrated. Equations 6 and 10 are
valid where J is not a function of time.
Referring to Figure 2, an example of current configuration producing a
substantial component of curl-free magnetic vector potential fields is shown.
Conductors carrying a current I are wrapped in a solenoidal configuration 21 ex-
tending a relatively great distance in both directions along the z-axis. With
the solenoid 21 the magnetic flux density B = Cl]RL A, is a constant directed a-
long the z-axis with a value
11. B = B =
~0 C
where n is the number of conductor turns per unit length. Outside of the sole-
noid, it can be shown that the components of A in the x-y plane are~
13 A
Y ~O c-.
14. Az = 0
where a is the radius of the solenoid. It can be shown that CURL A = 0 for the
magnetic vector potential field outside of the solenoid 21~ To the extent that
the solenoid is not infinite along the z-axis, dipole terms ~i.e., CURL A = 0)
will be introduced in the magnetic vector potential field.
Referring to Figure 3, another example of a current geometry generating
magnetic vector potential field with a substantial curl-free component is shown.
In this geometry~ the current carry conductors are l~Tapped uniformly in toroidal
configuration 31. Within the toroidal configuration, the magnetic flux B = CURL A
and the magnetic flux is contained substantially within the torus. In the re-
gion external to the tor-us, B = CURL A = 0 and the orientation of the magnetic
vector potential field in the plane of the torus is parallel to the axis of the
torus.
~"~
~ 1 ~2~60
Referring to Figure 4a and Figure 4b, the sc~lematic diagram, a detector
capable of detecting the curl-free component of the magnetic vector potential isshown. This detector is referred to as a Josephson junction device. The Joseph-
son junction consists of a first superconducting material 41 and a second super-conducting material 42. These two superconducting materials are separated by a
thin insulating material 43. According to classical electromagnetic theory, the
insulating material 43 will prevent any substantial conduction of electrons be-
tween the two su?erconducting regions. Howeverj quantum theory predicts, and
experiments verify that conduction can take place through the insulating material.
The result of this conduction is a net current
15- IJJ = k sin i dD ~ cl3 ~ t~ J
where the magnitude of the current K and the phase ~O are determined by intrinsic
properties of the junction device e is the charge of the electron, A is an ex-
ternally applied magnetic vector potential, ds is a differential element extend-ing from one superconducting element to the other superconducting element, t is
time, and V is an externally applied voltage. I'his conduction takes place when
leads 44 and 45 are coupled with very low impedance to the current flow. The
component of the magnetic vector potential field perpendicular to the plane of
the junction determines the current IJJ.
Referring to Figure 5, the relationship of the Josephson junction device
current as a function of externally applied magnetic vector potential field is
shown. Referring to Equation 15, the integral ~ A-ds, as A is increased, resultsin a change of phase for IJJ. This change in phase produces the oscillating be-
havior for IJJ as a function of magnetic vector potential field perpendicular tothe Josephson junction. This relationship will hold as there is no externally
applied voltage to the Josephson junction (i.e., V = 0).
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Referring next to Figure 6, a system for the determination of distance
using a curl-free vector potential field is shown. Apparatus 60 is comprised of
a current source 6~ and apparatus 65 configured to generate a magnetic vector
potential field having a substantial curl-free component using the current from
the current source. The magnetic vector potential field is established in the
intervening media 61 and impinges upon a magnetic vector potential field detector
66. The property of detector 66 indicating the presence of a magnetic vector
potential field is analyzed in apparatus 67 to determine the magnitude of the
field .
Referring next to Figure 7, a method of determining the strength of the
magnetic vector potential field applied to the Josephson junction is shown. As
the magnetic vector potential field A changes, the phase of the Josephson junction
current IJJ in conductor 73 will change causing the voltage applied to the analog-
to-digital converter 79 to change.
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The analog-to-digital converter provides a digital representation
of I which is convenient for storage and for analysis. The output
of the analog-to-digital converter 79 is applied to storage,
analyzer and display device 78. Thus any change in IJJ will be
recorded in device 78.
Referring next to Figure 8, when a magnetic vector
potential field A 71 of sufficient strength is applied to the
Josephson junction 66, the Josephson junction current will
experience a multiple of oscillations. In this situation, it can
be more convenient to use digital techniques. The signal from
transEer means 74 is applied to amplifier 91. The overdriven
amplifier 91 converts the oscillating signal to a series of square
waves. The square wave signal is applied to differentiating
circuit 920 The output signal of the differentiating circuit
comprising a series of pulses is applied to counter 93, and the
output signal oE counter 93 is applied to storage, analyzer and
display device 88.
Referring to Figure 9, the oukput signals of the various
components of the apparatus illustrated in Figure 8 are shown for
a period of change of the curl-free magnetic field component
perpendicular to the plane of the Josephson junction. Components
f ~1 field generated by a source of magnetic vector potential
field generator 65 are shown by functions 111, 112 and 113. Each
generated field has a Al component 115 which is a function of time.
This period of time 114 is expanded for the remainder of the
indicated time periods. For ease of illustration, changing Al
component 115 is shown to be linear over time period 114. There-
fore, during time period 114, IJJ will have a component with
-- 11 --
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sinusoidal periodity, this sinusoidal component will be transferred
via apparatus 74 to amplifier 91. Overdrive amplifier 91 will have
a periodic square-wave output signal. The square-wave will be
applied to the differentiating circuit 93 and the output signal of
the differentiating circuit shown in Figure 9 will be a series of
pulses during time period 114. While the change in Al has been
assumed to be linear with time, non-linear changes will also
produce a pulse train, but as will be clear, this pulse train is no
longer periodic. Counter circuit 93 will count the pulses and
storage analyzer and display circuit will determine what counts to
display. It will be clear in the example shown in Figure 9 that the
count will be displayed during a period of a relativel~ constant A
component and will recycle when a series of counts is being
generated by counter 93. It will be clear that the number of
counts in device 88 will depend, for a given change in the field
only, on the magnitude of the change.
2. Operation of the Preferred Embodiment
In order to determine a distance, i-t is necessary in
general to provide a predetermined change in the curl-free vector
potential field. No mention has been made in the previous
discussion of the effect of varying the current source. It will
be clear that the finite field
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propagation velocity will cause a delay between a change in the curl-free mag-
netic vector potential field produced by the generator of the field and the de-
tection of that change by the detector located at a distance from the generator.
However, these delay effects are not important for practicing this invention and
will be ignored in this discussion. With respect to curl-free vector potential
field generating apparatus, any limitation on the upper limit of generated fre-
quency components imposed will be the result of parameters impacting ra~id
changes in the current. I`hus, parameters such as inductance can provide a limit
to ability to impose high frequency modulation on the vector potential field.
With respect to the media between the field generating apparatus and
the field detecting apparatus, two effects are import-ant. First as implied by
equation (1)
16. CURL E ~ ~B = CURL E t CURL d3 A = CURL ~E ~A~ = o
or
17. ~ = -F.
Therefore,as modulation is imposed on the vector potential field, the change in
the vector potential field will produce an electric field intensity. The elec-
tric field intensity will produce a flow of current in conducting material or a
temporary polarization in polarizable material. With respect to materials demon-
strating magnetic properties, the bulk magnetic properties are responsive to themagnetic flux density B. However, B = CURL A = 0 for the curl-free vector poten-
tial field component. Therefore,the interaction of the curl-free magnetic vector
potential field is weaker in magnetic materials than is true for the general mag-
netic vector potential field. Media effects and especially the conductivity of
the intervening media will provide a mechanism delaying the achievement of steady
state condition for the curl-free magnetic vector potential field (ie., because
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~ 1 7~7~0
-
~ ~ = -E) thus causing a media limitation on frequency. A curl-free magnetic
vector potential field can be established in materials that are not capable of
transmitting normal electromagnetic radiation. The media delay problem can be
compensated or by lowering the frequency spectrum of the modulation on the curl-
free magnetic vector potential field.
With respect to the detectorJ the Josephson junction can be constructed
to provide responses of sufficiently high frequency so that this element of the
system is not typically a factor limiting frequency of information.
As indicated in equation lS, the effect of the application of a vector
potential field to a Josephson jumction, in the absence of a voltage applied to
the junction, is to change the phase of the sine function determining the value
of the junction current IJJ. The excursions from zero magnetic vector potential
field can be analyzed and a determination made of the modulation applied to the
field. When a voltage is applied to the Josephson jumction, oscillation occurs in
the IJJ as will be seen from the Vdt term of equation 12. The application of an
external vector potential field causes the phase of oscillation to change. By
monitoring the phase change in the Josephson jlmction oscillations, the modulation
of the vector potential field can be inferred.
Another method of detection of a magnetic vector potential field util-
izes the property that ~A = -E. Thus, for example, by measuring the changes in
a material resulting from the application of the electric field, the magnetic vec-
tor potential field causing the electric field can be inferred.
In order to determine distance using the present invention, it is nec-
cessary to calibrate the output signal of the detecting apparatus as a function of
distance and as a fumction of field magnitude for field produced by magnetic vec-
tor potential field generating apparatus. Although the calibration can be done
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tileoretically, it is generally more convenient to calibrate the detecting appa-ratus experimentally. I-lowever, two related problems can arise. First, the appa-
ratus generating the curl-free magnetic vector potential field is highly direc-
tional, e.g., the field resulting from the finite solenoid has a maximum value in
the plane through the center of the solenoid. In addition, the Josephson junction
is also directional. Thus it is necessary to orient the generating apparatus andJosephson junction apparatus during a distance measurement. A plurality of
Josephson junctions can be used in the detecting apparatus and the detecting appa-
ratus output signal can be the vector sum of the individual output signal of appa-
ratus associated with the plurality of Josephson junction. This procedure elimi-nates the requirement of the rotation of the Josephson junction device, but ori-entation of the generating apparatus can still be required. After the detecting
apparatus is calibrated with predetermined generating apparatus signals the de-
tecting apparatus can be placed at an unknown distance, ~i.e., in sea water)
from the generating apparatus. The generating apparatus can be rotated slowly
emitting a predetermined signal and the detecting apparatus can use the optimum
signals for the actual measurement of the distance. Because oE the directional-
ity of the curl-free magnetic field, it will be clear that rotating the field
generating apparatus can result in modulation which can be used in the measurement.
Many changes and modifications in the above-described embodiment of the
invention can, of course, be carried out without departing from the scope thereof.
Accordingly, the scope of the invention is intended to be limited only by the
scope of the accompanying claims.
