Abstract:
A method of using a superconductor to generate energy. The superconductor is alternated between a temperature above and below a critical temperature defined by a transition between the superconducting and non-superconducting state. The superconductor interacts with a magnetic field as the superconductor changes states. Energy is harnessed by coupling with the magnetic field as its strength fluctuates. The method would be particularly suitable for harnessing solar energy in space.

Description:
FIELD OF THE INVENTION 
   The invention pertains to generating energy using a superconductor, and in particular to generating energy by interacting the superconductor with a magnetic field and cycling the superconductor through its transition temperature. 
   BACKGROUND OF THE INVENTION 
   Since the discovery in 1911 that mercury is electrically superconductive when cooled to 4° K, many materials have been shown to become superconductive below some critical temperature or transition temperature T c . 
   Superconductors are divided into type 1 and type 2. Type 1 superconductors tend to have a low T c  and the transition between the non-superconducting and superconducting state typically occurs over a temperature span of less than 1° K. Type 1 superconductors are mainly pure metals that conduct electricity at room temperature. All type 1 superconductors only become superconducting at temperatures within less than 20 degrees K of absolute zero. Examples are tungsten (T c =0.15° K), titanium (T c =0.40° K), aluminum (T c =1.175° K), tin (T c =3.72° K) and lead (T c =7.2° K). All these values are at normal pressures. The type 1 material with the highest known T c  is sulfur, for which T c  is about 17° K; however, sulfur needs to be compressed to 930,000 atmospheres to become superconducting and 1.6 million atmospheres to achieve a T c  of 17° K. 
   In type 2 superconductors, the transition between states usually extends over a broader range of temperature, typically 5° K. While type 1 and type 2 T c  values overlap, the majority of type 2 materials superconduct at much higher temperatures than any type 1 material and include the so-called “high-T c ” superconductors, which are typically ceramic materials. Examples of type 2 superconductors are the elements vanadium (T c =5.4° K), technetium (T c =7.8° K) and niobium (T c =9.25° K). These and all further values of T c  will be understood to be at atmospheric pressure. 
   The first superconductive wire was composed of Nb 0.6 Ti 0.4 . The first ceramic superconductor discovered, in 1986, was La 0.85 Ba 0.15 CuO 4 , with a T c  of 35° K). A common high-T c  material is the compound YBa 2 Cu 3 O 7 , often referred to as “YBCO” or “123”. YBCO has a T c  of 93° K. The highest T c  currently known is 138° K for the compound Hg 0.8 Tl 0.2 Ba 2 Ca 2 Cu 3 O 8.33 . Practical applications have been sought for superconductive materials. One use is in power transmission, in which the absence of electrical resistance would significantly reduce power losses. Power transmission over long distances is precluded by the requirement to maintain low temperatures by some means such as using liquid nitrogen. There have been specialized commercial applications; for example, power transmission over relatively short distances through limited spaces such as tunnels is greatly increased by using superconductors, to a degree not achievable by using conventional power cables. 
   Other behaviors are associated with superconductivity, in particular the Meissner effect, whereby an article in a superconductive state can strongly deflect a magnetic field; the superconductor and a magnet will produce a mutually repulsive force. This effect is used in magnetic levitation (maglev) transportation systems that are in development. 
   SUMMARY OF THE INVENTION 
   Hitherto, superconductors have been applied for practical use substantially under steady state conditions; that is, they are maintained in a superconducting state. The present invention discloses engines for producing usable energy by cycling a superconductor repeatedly through a transition region between a superconducting and a non-superconducting state, by alternately cooling and heating the article through T c . In the presence of a magnetic field, this causes the strength of the field to vary at a given point. Coupling an energy conversion means with the magnetic field provides a way of generating usable energy. Embodiments are disclosed in which mechanical and electrical energy are generated. 
   It will be understood that the term “generating” is used in an accepted sense of producing energy in a usable form, which strictly refers to harnessing one form of energy and converting it to another form which is more appropriate for a contemplated use. For example, chemical or nuclear energy can be released from an appropriate fuel as thermal energy. Thermal energy can be harnessed as mechanical energy to drive a vehicle or an electrical generator. Electrical energy can be transmitted over long distances, then reconverted to other forms of energy such as mechanical or thermal energy as required. Each step in a chain of energy conversion involves some inefficiency with a consequent loss of energy. 
   In the present invention a superconductor is heated and cooled through T c  so that it cycles between the superconducting and a non-superconducting state, in the presence of a magnetic field produced by a magnet. The magnetic field strength at a given point consequently fluctuates. This fluctuation can be translated into mechanical energy by allowing the superconductor and magnet to repel each other. A movable arm is attached to either the superconductor or the magnet. 
   The fluctuation also be translated into electrical energy. An electrical current can be induced in a conductor such as a wire or coil directly exposed to the fluctuating magnetic field strength. Alternatively, a piezoelectric body can be coupled with either the superconductor or the magnet, so that it responds to a fluctuating force therefrom; the electrical conductor can be connected to the piezoelectric body to accept the electrical current therefrom. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram showing the levitation of a magnet by an article in a superconducting state. 
     FIGS.  2 ( a ),  2 ( b ) and  2 ( c ) are schematics of an engine for generating mechanical energy from the transition of a superconducting article between a non-superconducting and a superconducting state, the engine being shown in different operating positions. 
       FIG. 3  is a resistivity-temperature curve showing a transition of a superconductor through a transition temperature. 
       FIG. 4  is a diagram of the engine of  FIG. 2  in accordance with a second embodiment of the invention, the engine configured also to generate electrical energy. 
     FIGS.  5 ( a ) and  5 ( b ) are diagrams of an engine in accordance with a third embodiment in which the electrical energy is generated by alternately exposing the superconducting article to and shielding it from thermal radiation. 
       FIG. 6  shows the engine of  FIG. 5  with a mask intended to alternately expose the superconducting article to and shield it from radiation. 
       FIG. 7  shows the mask of  FIG. 6  configured to have alternate heat absorbing and heat reflecting segments. 
     FIGS.  8 ( a ) and  8 ( b ) are diagrams of a portion of the engine of  FIG. 5  showing an electrically conductive coil embedded in the superconducting article in the non-superconductive and the superconductive state respectively. 
       FIG. 9  is a diagram of a portion of the engine of  FIG. 5  wherein a grid of conductive wires is disposed into a surface of the superconductive article. 
     FIGS.  10 ( a ) and  10 ( b ) are diagrams of an engine in accordance with a fourth embodiment having a liquid crystal shutter controlled by feedback from the released electrical energy, the shutter alternately intercepting and passing radiation. 
       FIG. 11  is a diagram of an engine in accordance with a fifth embodiment having a piezoelectric element for releasing the electrical energy. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   In the following description, terms such as “superconductor” or “superconducting article” are understood to refer to an article having a superconducting and a non-superconducting state. The terms are not intended to define whether or not the article is currently in the superconducting state. 
   This invention relates to generating energy using a superconducting article  100  by coupling with a magnetic field  102  that changes as a result a transition of the article between the states, such that the magnetic field strength at some given point fluctuates. 
   Superconductors when in a superconducting state will strongly interact with a proximate magnetic field  102 . This phenomenon is manifested by the well-known Meissner effect, in which a magnet  104  is levitated by the repulsion from the superconducting article  100  below T c , as illustrated in FIG.  1 . Above T c , interaction between the superconductor and the magnetic field is no stronger than with other comparable materials. For example, a ceramic superconductor in the non-superconducting state will behave like a conventional ceramic material. 
   Therefore, during the transition of the superconducting article  100  between states, the strength of the magnetic field at a given location will change. It is possible by coupling with the changing magnetic field to extract usable energy. In all embodiments of the invention, the transition is caused by cooling or heating the superconducting article  100  through T c . 
   A first embodiment of the invention generates mechanical energy. An engine  110 , shown schematically in  FIG. 2 , includes a movable mechanical member such as a beam  114  supported by a fulcrum  112 . The superconducting article  100  is attached to one end of the beam  114  and a counterweight  116  is attached to the opposite end. 
   The article  100  is suspended directly above the magnet  104  contained in a liquid-nitrogen cooling bath  118 , the magnet  104  being oriented vertically, that is, with its poles aligned up and down. The beam  114  is free to swing about the fulcrum  112  between first and second positions. In the first position, the article  100  is spaced well apart from the magnet  104  and also well clear of the cooling bath  118 . In the second position, the article  100  is in close proximity with the magnet  104  and is placed in the cooling bath  118 , or close enough to be cooled thereby. 
   The superconducting article  100  is selected to have a T c  higher than the temperature of the cooling bath, which in the present case is defined by the boiling point of liquid nitrogen, 77° K. In other words, the bath  118  can cool the article to below T c . In the engine  110 , the material selected for the superconducting article is YBa 2 Cu 3 O 7 , (YBCO) which has a T c  of 93° K, although it could be any superconducting material with a sufficiently high T c . Other possibilities include YBa 4 Cu 7 O 15  (T c =93° K) Bi 2 Sr 2 CaCu 7 O 9  (T c 110° K) and HgBa 2 Ca2Cu 3 O 8  (T c =123-124° K). The resistivity-temperature curve for YBCO is shown in FIG.  3 . The YBCO composition is typical of ceramic superconductors in that it is an insulator above T c . Whatever cooling means is used, it must correspond with a superconducting material having an appropriate T c . At present, the upper temperature limit of potential coolants must be below 138° K, the highest T c  currently known (for Hg 0.8 Tl 0.2 Ba 2 Ca 2 Cu 3 O 8.33 ). 
   The engine  110  works as follows. With the superconducting article  100  above its transition temperature, the beam  114  is balanced so that gravity is just sufficient to bring the article  100  into the cooling bath  118  and into close proximity with the magnet  104 . Once the article  100  has cooled below the transition temperature, it reflects the magnetic field of the magnet  104  as a mirror image. This produces a repulsive force, so that the superconducting article  100  moves away from the magnet  104  and out of the cooling bath  118 . The ambient temperature being higher than the transition temperature, the article  100  warms up sufficiently to lose its superconductivity. It no longer reflects the magnetic field of the magnet  104 , and the repulsive force decays. Gravity brings the article  100  back into the cooling bath  118  and into close proximity with the magnet  104 , for the cycle to be repeated. The beam  114  can continue to oscillate indefinitely as long as the cooling bath is maintained below T c . In effect, energy originally consumed in liquefying the nitrogen is released as mechanical energy. 
   In a second embodiment shown in  FIG. 4 , the counterweight  116  is a second magnet  120  next to which is disposed an electrically conductive wire  122 , which could be a coil. With oscillation of the beam  114 , the second magnet  120  moves relative to the wire  122 , and a resulting variation in magnetic flux  121  at the wire  122  induces an alternating electrical current therein detectable with a meter  124 . 
   In a third embodiment, an assembly  126  is constructed wherein the superconducting article  100  and a magnet  104  are fixedly spaced by a distance within which the undeviated magnetic field of the magnet  104  extends to the superconducting article  100 . The conductive wire or coil  122  is disposed in the undeviated magnetic field, as illustrated in FIG.  5 ( a ). When the article  100  is cooled to below T c , it becomes superconducting and reflects the magnetic field of the magnet  104 , thus setting up a mutual repulsion. The resultant deviated magnetic field between the article  100  and the magnet  104  is illustrated in FIG.  5 ( b ). 
   Thus, an alternating current is induced in the wire  122  as it is exposed to a varying magnetic field when the article  100  goes through the transition between states. 
   This effect could be executed by intermittent thermal irradiation of the article  100 , such that it would be above T c  when irradiated and below T c  when not irradiated. This would be particularly achievable in a space environment, as illustrated in FIG.  5 . The assembly  126  would be allowed to spin so that the superconducting article  100  alternately faced towards and away from the sun  150 . 
   The third embodiment could be modified to provide for the superconducting article  100  to face the sun at all times, being alternately exposed to solar radiation and shielded by a movable mask  140 . This could for example be a disc rotating about an axis perpendicular to the exposed face of the article, the disc having alternate open and solid segments as in  FIG. 6 , or it could be a slat (not illustrated) rotating about an axis generally parallel to the exposed face of the article. The rotating disc might also be entirely solid with alternating heat reflective segments  142  and heat absorbing segments  144 , as in FIG.  7 . This could provide an advantage compared with an array of conventional solar cells, for example since the solid disc would provide protection from damage by foreign particles of space debris. 
   A modified structure of the third embodiment is illustrated in FIG.  8 . Here, the wire or coil  122  is embedded inside the article  100 , as can be done in the case of a ceramic superconductor by conventional ceramic forming techniques. In FIG.  8 ( a ), the article is in the non-superconducting state, with the magnetic field  102  passing through the article undeviated. In FIG.  8 ( b ) the article is in the superconducting state and the magnetic field  102  is deviated around the article. In another modification shown in  FIG. 9  a series of fine conductive wires in the form of a grid  128  could be pressed into the surface of the superconducting article  100  which could be in the form of a thin layer. 
   The generation of alternating electrical current in the coil  122  by cycling the article  100  between the superconducting and non-superconducting states is analogous to what occurs in a conventional electric generator, whereby a current is generated in electrically conductive windings which move relartive to a magnetic field. A given portion of the windings “sees” a varying magnetic field strength as the windings move. 
   In a fourth embodiment, illustrated in  FIG. 10 , part of the current generated in the wire or coil  122  could be used in a feedback mode to actuate a liquid crystal shutter  130  which alternately intercepts and passes solar radiation directed towards the superconducting article. The shutter  130  could be controlled by a conventional rectifying circuit  132  that would deliver a unidirectional current varying between zero and some upper limit. With the current at the upper limit, as in FIG.  10 ( a ), the shutter  130  would be dark, therefore intercepting radiation and allowing the article to cool below T c . With the current at zero, as in FIG.  10 ( b ) the shutter  130  would be clear, thus passing radiation to the article so that it would heat to above T c . 
   In a fifth embodiment shown in  FIG. 11 , electrical power is generated by via a piezoelectric body  134 . The superconducting article  100  and the magnet  104  are spaced within interactive range of each other, and either of them connected to the piezoelectric body so that it can exert a varying pressure thereon in response to article  100  going in and out of the superconducting state. The wire  122  is connected to the piezoelectric body  134  and the electrical current generated therein can be registered on the meter  124 . 
   The various embodiments and modifications describe above are not intended to be exhaustive. For example, any embodiment could be used in combination with any appropriate masking or shuttering device. While the invention has been shown and described with particularity, it will be appreciated that various changes and modifications may suggest themselves to one having ordinary skill in the art upon being apprised of the present invention. It is intended to encompass all such changes and modifications as fall within the scope and spirit of the appended claims.