CA1172757A - Apparatus and method for demodulation of a modulated curl-free magnetic vector potential field - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A system for determining the modulation imposed on a curl-free magnetic vector potential field. The system includes apparatus for detecting the curl-free magnetic vector potential field component by means of a Josephson junction.
The magnetic vector potential field interacts with the Josephson junction by var-ying the phase of the argument of the sine function which determines the Josephson junction current. The output signals of the Josephson junction are coupled to apparatus that can determine the modulation of the detected field. Because the magnitude of the change in the detected curl-free vector potential field causes a proportional change in the phase of the Josephson junction current, the modu-lation of the field can be established.

Description

~ ~ 72757 `

BACKGROUND OF THE INVENTION
1. Field of the Invention This invention relates generally to the transfer of information by means of an electromagnetic field, and more particularly to the apparatus for demodula-tion of the curl-free magnetic vector potential field.

2. Description of the Prior Art It is knol~n in the prior art to provide systems for the transfer oE
information utili~ing electromagnetic fields which are solutions to Maxwell's equations. The information transfer systems include apparatus for generating modu-lated electromagnetic fields and apparatus for detecting and demodulating thegenerated electromagnetic field. Examples of the prior type information transfer systems include radio and television band-based systems, microwave band-based systems and optical band-based systems.
The Maxwell equations, which govern the prior art transfer of informa-tion by electromagnetic fields can be written:
1. CURL E ~
._ 2. CURL H - ~ :

3. DIV B = O
~. DIV D = p where ~ is the electric field density, H is the magnetic field intensity, ~ 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 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 inten-sity and the magnetic flux density are related by the equations B=~l, while the * and are denoted s~nbolically by the ~X and ~-mathematical operators respec-tively.

~ 172~57 electric field density and the electric displacement are related by the equation B = ~E. These equations can be used to describe the transmission of electromag-netic radiation through a vacuum or through various media.
It is known in the prior art that solutions to Maxwell's equations can be obtained through the use of electric scalar potential func~ions and magnetic vector potential functions. The electric scalar potential is given by the expression:
5- ~ )d ~
where ~1) is the scalar potential at point 1, p(2) is the charge density at point 2, ~12 is the distance between point 1 and 2, and the integral is taken over all differential volumes. The magnetic vector potential is given by the expression 6- A~ r~ C ~ ~
where A(l) is the vector potential at point 1, is the permittivity of free space, C is the velocity of light, J(2) is the (vector) current density at point 2, ~12 is the distance between point 1 and point 2 and the integral is taken over all differential volumes. The potential functions are related to Maxwell's equations in the following manner.
7. E=~-GRAD- ~ ~
where GRAD is the gradient mathematical operation and is denoted symbolically by the V mathematical operator.
8. B= CURL A
where A can contain, for completeness, a term which is the gradient of a scalar function. In the remaining discussion, the scalar function will be taken to be substantially zero. Therefore, attention will be focused on the magnetic vector potential A.

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In the prior art literatureJ consideration has been given to the physical significance of the magnetic vector potential field A. The magnetic vec-tor potential field was, in some instances, believed to be a mathematical artifice, useful in solving problems, but devoid of independent physical significance.
More 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) particle with charge ~ and mass ~moving in an electromagnetic field is given by 9. ~ c~ D~ (;RA~
where~ is Planch's constant divided by 2~Y, i is the imaginary number ~r, 0 is the electric scalar potential experienced by the particle, A is the magnetic scalar potential experienced by the particle and ~ is the wave function of the particle. Thus, devices such as the Josephson junction device quantum mechanical effects can be used to detect the presence of curl-free magnetic vector poten-tial. In order to provide a system for transfer of information using the curl-free magnetic vector potential, apparatus for demodulating the modulated curl-free vector potential field must be designed to provide for the physical differ-ences between the typical electromagnetic fielcl generally used in dommunications and the curl-free magnetic vector potential field ~ 1 7~7$7 Obj cts of the Invention It i8 therefore an object of the present invention to provide an improv-ed system for transfer of information.
It is a further object of the present invention to provide apparatus de-modulation of a modulated curl-free vector potential field.
It is a more particular object of the present invention to provide ap-paratus for detection of the curl-free vector potential field and apparatus for analyzing output signals of the detection apparatus.
It is another particular object of the present invention to provide ap-paratus for demodulating the output signals of a Josephson junction, the Josephson junction used to detect the curl-free magnetic vector potential field.
Related Applications Apparatus and Method for Transfer of Information by Means of a Curl-Free Magnetic Vector Potential Field, invented by Raymond C. Gelinas, Serial Number 390,~20, and assigned to the same assignee as named herein.
Apparatus and Method for Distance Determination Between A Receiving Device and A Transmitting Device Utili~ing a Curl-Free Magnetic Vector Potential Field invented by Raymond C. Gelinas, Serial Number 390,701, filed November 23, 1981, and assigned to the same assignee as named herein.
Apparatus and ~ethod for Direction Determination by Means of a Curl-Free Magnetic ~ector Potential Field invented by Raymond C. Gelinas, Serial Number 390,282, filed November 17, 1981, and assigned to the same assignee as named herein.
Summary of the Invention The aEorementioned and other objects are accomplished, according to the present invention, by apparatus for detecting a magnetic vector potential field having a substantial curl-free component (i~e., CURL A = 0) and by apparatus coupled to the detection apparatus for demodulation of signals produced by the .

~ 1 ~2757 detection apparatus. An example of a detector of curl-free magnetic vector poten-tial fields is the Josephson junction. The intention of the curl-free magnetic vector potential field on the Josephson junction results in a change in the phase of the current, IJJ, flowing through the junction. The demodulation system con-verts the Josephson junction current phase changes into quantities directly relat-ed to the modulation of the field.
In accordance with the present invention, there is provided apparatus for demodulating a modulated curl-free magnetic vector potential field comprising:
means for detecting said curl-free magnetic vector potential field,- said detecting means having an observable property determined by a magnitude of said curl-free magnetic vector potential field, and means coupled to said detecting means for determining variations in magnitude of said field from said observable property.
In accordance with the present invention, there is further provided a method for demodulating a modulated curl-free magnetic vector potential field comprising the steps of: (a) detecting a change in said curl-free magnetic vec-tor potential field by a means responsive to said vector field, (b) generating a change in an observable quantity related to a magnitude of said vector field by said responsive means; and (c) determining said vector field change from said observable quantity change.
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 DESCRIPTlON OF THE DRAWINGS
Figure 1 is a schematic diagram illustrating tlle procedure for deter-mining a magnetic vector potential at a point.
Figure ~ 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 of a Josephson junction.
Figure 4b is a perspective drawing of a Josephson junction.
Figure 5 is a diagram of the current flowing in a Josephson junction as a function of field perpendicular to the junction surface.
Figure 6 is a schematic diagram of a system for using a magnetic curl-free vector potential field for transmisslon of information.
Figure 7 is a schematic diagram of apparatus for demodulating a weak curl-free magnetic vector potential field.
Figure 8 illustrates the method of operation of apparatus for demodu-lating a weak curl-free magnetic vector potential field.
Figure 9 is a schematic diagram of apparatus for demodulating a strong curl-free magnetic vector potential field.
Figure 10 illustrates the method of operation for demodulating a strong amplitude-modulated curl-free magnetic vector potential field.
Figure 11 illustrates the method of operation for demodulating a strong curl-free magnetic vector potential field with arbitrary modulation.
DESCRIPTION OF THE PREFERRED EMBODIMENT
1. Detailed Description _ the Figures Referring to Figure 1, the method of determining the magnetic vector -! 172757 potential field A(l) ~i.e., at point 1~ is illustrated. Referring to equation 6, the contribution by the differential volume element at point 2J dv(23, having a current density J(2) associated therewith is given by 10. dA(l) = ~ cc~ ~
To obtain equation 6, equation 10 must be integrated. Equations 6 and 10 are valid where J is not a fur.ction of time.
Referring to Figure 2, an example of current configuration producing a substantial component of curl-free magnetic vector potential field 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. Within solenoid 21, the magnetic flux density ~CURL A is a constant directed along the z-axis with a value 11. E = Bz = n I
where n is the number of conductors per unit lengtll. Outside of the solenoid, it can be shown that the components of A 23 are x l ~ c~ X ty 13, A = ~ ~ x _ 1~. A~ = O
where a is the radius of the solenoid. It can- be shown that CURL A = O for the 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 carrying conductors are ~rapped uniformly in toroidal configuration 31. Within the toroidal configuration, the magnetic flux lg = CURL
and the magnetic flux is contained substantially within the torus. In the region external to the torus, B = CURL A = O and the orientation of the magnetic vector ' I '~ 2 '7 5 '7 potential field is parallel the axis of the torus.
Referring to Figure 4a and Figure 4b, a detector capable of detecting the curl-free component of the magnetic vector potential field is shown. This detector is referred to as a Josephson junction device. Ihe Josephson iunction consists of a first superconducting material 41 and a second superconducting mate-rial 42. These two superconducting materials are separated by a thin insulating material 43. Superconducting material 41 and super conducting material 42 are electrically coupled to other apparatus by conductor 44 and conductor 45 respec-tively. In the simplest configuration, conductor 44 and conductor 45 are super-conduction materials and are coupled together as shown in Figure 7, element 73.According to classical electromagnetic theory, the insulating material 43 will prevent any substantial conduction of electrons between the two superconducting regions. However, quantum theory predicts, and experiments verify that conduction can take place through the insulating material. 'I`he result of this conduction is a net current.
15. IJJ = k sin t ~O ~ ~ rA ds -I ~ Vt) where the magnitude of the current ~ and the phase ~O are determined by intrinsic properties of tlle junction device, e is the charge of the electron,A is an exter-nally applied magnetic vector potential, ds- is a differential element extending from one superconducting element to the other superconducting element and V is an externally applied voltage.
Referring to Figure 5, the relationship of the Josephson junction device current IJJ as a function of externally applied magnetic vector potential field component Al (i.e., the component perpendicular to the plane of the Josephson junc-tion) is shown. The integral rA.ds as A is increased results in a change of phase for IJJ. This change in phase produces the oscillating behavior for IJJ as a function of magnetic vector potential field perpendicular to the Josephson ;

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junction. This relationship will hold as long as tllere is no externally applied voltage to the Josephson junction (i.e., V = O).
Referring next to Figure 6, a system for the transfer of information using a curl-free vector potential field is sho~n. Apparatus 60 is comprised of a current source 64 and apparatus 65 configurecl 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 for information content.
Referring to Figure 7 and Figure 8, apparatus for demodulating a wea~
curl-free magnetic vector potential field is illustrated. A weak curl-free mag-netic vector potential field is one for which the maxium amplitude of the field results in a relatively minor change in phase. The component perpendicular to Josephson junction 72 of curl-free vector potential field 71 Al causes a change in the phase of Josephson junction current, IJJ flowing in conductor 73. The change in current IJJ is applied through transEer means 74 to analog-to-digital converter 79. The resulting digitalized signal is applied to storage analyzer and display device 78. Device 78 has stored therein calibration data which re-2Q lates the perpendicular component of appliance vector potential field A to theresulting Josephson junction current IJJ, (i.e., A = f(IJJ)). In essence, the relationship illustrated by Figure 5 is available to convert the resulting Josephson junction current IJJ to a quantity related to A. Thus it is possible to reconstruct the magnitude of the impinging magnetic vector field potential and the modulation can be extracted therefrom.
Referring next to Figure 9, the schematic diagram of apparatus for _, ~

~ 172757 demodulation strong curl-free vector potential fields is shown. The strong field apparatus is used when the impinging magnetic vector potential field results in multiple phase changes for the Josephson junction current. The weak field ap-paratus has response too slow to determine effectively the magnitude of the vec-tor potential field. The change in component perpendicular to the Josephson junction 72 of the curl-free vector potential field causes a change in the Josephson junction current IJJ flowing in conductor 73. Transfer means 74 causes a signal related to IJJ to be applied to overdriven amplifier 91. The output sig-nal from amplifier 91, essentially a series of square waves, is applied to differ-ential circuit 92. The output signal from circuit 92 is applied to counter 93 and the resulting counts are stored in storage, analyzer and display circuit 94. The result of using this apparatus on an amplitude modulated sinewave signal is shown in Figure 10. In Figure 11, the result of using this apparatus to analyze a general curl-free vector potential field signal is shown.
2. Operation of the Preferred Embo.liment When the curl-free magnetic vector potential carries information the field must vary in a manner so that the information is transmitted therewith. No mention has been made in the previous discussion of the effect of varying the current source. It will be clear, however, that the finite field propagation ue-locity will cause a delay between a change in the curl-free magnetic vector poten-tial field produced by the generator of the field and the detection of that change by the detector located at a distance from the generator. However, these delay effects are not important for the practice of this invention and will be ignored in this discussion. With respect to curl-free vector potential field generating apparatus, any limitation on the up~er limit of generated frequency components imposed will be the result of parameters impacting rapid changes in the current. Thus parameters such as inductance can provide a limit to ability ~ 172757 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 important. First as implied by equation (1) 16. CURL E-~ ~ ~ Cu~L ~ ~ ~u~L ~ = C~L (E~
or 17. ~_-E
Therefore, as modulation is imposed on the vector potential field, the change inthe vector potential field will produce an electric field intensity. The elec-tric field intensity will produce a flow of current in conducting material or atemporary polarization in polarizable material. With respect to materials demon-strating magnetic properties, the bulk magnetic properties are responsive to the magnetic flux density ~. However, B = ~URL A = 0 for the curl-free vector poten-tial field component. Therefore, the interaction of the curl-free magnetic vec-tor potential field is weaker in magnetic materials than is true for the general magnetic vector potential field. Media effects and especially the conductivity of the intervening media will provide amechanism delaying the achievement of steady state condition for the curl-free magnetic vector potential field (i.e., because ~ = -E) and thus causing a media limitation of 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 prob-lem can be compensated for by lowering the frequency spectr~m of the modulation on the curl-free magnetic vector potential field.
With respect to the detector, 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 transfer.

! 1 72 75 7 As indicated in equation 12, the effect of the application of a vector potential field to a Josephson junction, 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 junction, oscillation occurs in the IJJ as will be seen from the Vdt term of equation 12. The application of an external vector potential field causing the phase of the oscillation to change.
By monitoring the pilase change in the Josephson junction oscillations from the modulation of the vector potential field can be inferred.
When a Josephson junction is used in the detection apparatus, the mod-ulated curl-free magnetic vector potential field results in changes in phase forthe current which can be analyzed in a manner depending on whether the field influencing the detecting apparatus is a strong field or a weak field.
Considering first the weak curl-free magnetic vector potential field, the modulation for this field can be accomplished by calibrating the detecting apparatus using the relationship of Figure 5 so that a given current from the Josepilson junction can be interpreted in terms of the detected vector potentialfield.
Considering next the demodulation of a strong curl-free magnetic vector potential field, the use of digital techniques provides a convenient method for analysis. In essence, four pulses are generated for each change of phase of 360~.
Pulses will ~except for noise signals) be generated only when the magnetic fieldis varying. Thus, several forms of modulation can be utilized. The length of time a vector field varies, the relative slope of the changing vector field, andthe relative height of the vector potential field can all be used as modulating methods.

~ 172757 The presence of pulses can indicate that the vector field is changing, the relative number of pulses during a period of vector field can indicate the relative magnitude of the change, and the relative density of pulse ~ùring a vec-tor field change can indicate the relative vector field slope.
In addition, an amplitude modulated signal can be similarly demodulated.
In the case of amplitude modulation, however, there can be little reason to use the carrier frequency. To demodulate an amplitude-modulated signal, the time intervals of a high ~or low) density of pulses can indicate the frequency of the carrier. The number of pulses between the high (or density) pulse density re-gion can indicate the relative modulation imposed on the signal.
Another method of detection of a magnetic vector potential field util-izes the property that ~t = -E. Thus, for example, by measuring the changes in a material resulting from the application of the electric field, the magnetic vector potential field causing the electric field can be inferred.
Many changes and modifications in the above-described embodiment of the invention can, of course, be carried out without departing from the scope thereof.
~ccordingly, the scope of the invention is intended to be limited only by the scope of the accompanying claims.

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. Apparatus for demodulating a modulated curl-free magnetic vector poten-tial field comprising:
means for detecting said curl-free magnetic vector potential field, said detecting means having an observable property determined by a magnitude of said curl-free magnetic vector potential field; and means coupled to said detecting means for determining variations in magnitude of said field from said observable property.

2. The demodulating apparatus of Claim 1, wherein said detecting means includes a Josephson junction and wherein said observable property is a change of phase of current through said Josephson junction.

3. The demodulation apparatus of Claim 1 wherein said magnitude determina-tion means includes means for relating said observable property and said field magnitude.

4. The demodulation apparatus of Claim 1 wherein said magnitude determina-tion means includes apparatus for providing pulse signals, wherein a magnitude of change in said vector field is related to a number of pulse signals.

5. A method for demodulating a modulated curl-free magnetic vector poten-tial field comprising the steps of:
(a) detecting a change in said curl-free magnetic vector potential field by a means responsive to said vector field, (b) generating a change in an observable quantity related to a magnit-ude of said vector field by said responsive means; and (c) determining said vector field change from said observable quantity change.

6. The method of demodulation of a curl-free magnetic vector potential field of Claim 5 wherein step (c) of determining includes the step of generating pulse signals, the number of pulse signals related to said observable quantity change.