Abstract:
A method and apparatus are provided for converting electromagnetic radiation directly into electricity. The method aligns a plurality of ferromagnetic nanocrystals to produce an aggregate magnetic field; utilizes an electrical coil in the aggregate magnetic field; and alternately directs and removes radiant energy from the ferromagnetic nanocrystals such that the aggregate magnetic field decays and regenerates to produce a current in the electrical coil. The apparatus includes either a distribution or a stackup of ferro-magnetic nanocrystals and an electrical coil, the combination of the nanocrystals and the electrical coil operating with energy derived from the source of radiant energy.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a continuation of application Ser. No. 10/784,086 filed on Feb. 20, 2004 now U.S. Pat. No. 7,098,547 issued on Aug. 29, 2006. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to the direct conversion of radiant energy into electricity, and more particularly, to a method and apparatus for producing electricity by causing a magnetic field to alternatingly decay and regenerate. 
   2. Description of the Prior Art 
   Historically, electricity has been produced by using a generator device to move an electrical coil and a magnetic field relative to one another. Such methods require mechanical moving parts which can wear out or break down and create an interruption in providing electrical power to components. 
   Various methods have been proposed to directly convert an energy source directly into electricity. U.S. Pat. No. 5,714,829 issued to Gurusprasad, for example, discloses a magnetic mechanical heat engine for converting heat into electricity using electromotive force induced by demagnetization. The heat engine utilizes a magnetic medium which is magnetized by means of a magnetic field produced by an external electrical coil. However, operation of the apparatus disclosed in Gurusprasad &#39;829 requires that the magnetic medium be brought into and out of thermal contact with a heat source, which thus necessitates moving parts and reduces the efficiency of the apparatus. 
   What is needed is an apparatus for efficiently converting energy directly into electricity. 
   SUMMARY OF THE INVENTION 
   The present invention provides a method and an energy conversion device for efficiently converting radiant energy directly into electricity. 
   In one general aspect of the present invention, a first embodiment comprises a distribution of ferro-magnetic nanocrystals and an electrical coil, the combination operating with energy directed from a radiation source. 
   In another general aspect of the present invention, a second embodiment comprises two distributions of ferromagnetic nanocrystals, a pair of electrical coils enclosing the ferromagnetic nanocrystals, and a controllable radiation source. 
   In yet another general aspect of the present invention, a third embodiment comprises a controllable radiation source, a plurality of transparent annular disks alternatingly stacked with a plurality of soft magnetic disks coated with ferromagnetic nanocrystals embedded in a matrix layer, a transparent cylindrical core, and an electrical coil enclosing the stacked annular disks and cylindrical core. 
   In a further general aspect of the present invention, a method is provided for converting energy from a radiant source into electricity. Initially, a plurality of ferromagnetic nanocrystals are aligned so as to produce an aggregate magnetic field; an electrical conductor is placed into the aggregate magnetic field; and radiant energy is directed onto the plurality of ferromagnetic nanocrystals such that the aggregate magnetic field begins to decay. The radiant energy is then attenuated, allowing the aggregate magnetic field to regenerate, and the process is repeated inducing electric current in the electrical conductor in response to the changing magnetic field. 
   These and other aspects, features, and advantages of the present invention will become more readily apparent from the attached drawings and the detailed description of the preferred embodiments, which follow. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The preferred embodiments of the invention will hereinafter be described in conjunction with the appended drawings provided to illustrate and not to limit the invention, where like designations denote like elements, and in which: 
       FIG. 1  is a diagrammatical representation of an energy conversion system, in accordance with the present invention, including a source of radiant energy irradiating a magnetic dipole module enclosed in an electrical coil which is connected to a load; 
       FIG. 2  is a perspective pictorial view of the magnetic dipole module and the electrical coil of  FIG. 1 ; 
       FIG. 3  is a perspective view of an energy conversion system having a radiant energy source transmitting radiant energy via optical fibers into two magnetic dipole modules, each magnetic dipole module enclosed in an electrical coil; 
       FIG. 4  is an exploded perspective pictorial view of a portion of the energy conversion device of  FIG. 3  showing a ferromagnetic nanocrystal distribution provided as part of the magnetic dipole module of  FIG. 3 ; 
       FIG. 5  is a pictorial view of a portion of the ferromagnetic nanocrystal distribution of  FIG. 4 ; 
       FIG. 6  is a pictorial view of a portion of an alternative ferromagnetic nanocrystal distribution of  FIG. 4  including dopant elements; 
       FIG. 7  is an exploded perspective pictorial view of an alternative embodiment of the energy conversion device of  FIG. 4  showing a ferromagnetic stackup provided as part of the magnetic dipole module; 
       FIG. 8  is an alternative embodiment of the energy conversion system of  FIG. 3  including the energy conversion device of  FIG. 7 ; 
       FIG. 9  is a pictorial perspective view of the magnetic dipole module of  FIG. 7 ; and 
       FIG. 10  is a side pictorial view of the magnetic dipole module of  FIG. 9 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Shown throughout the figures, the present invention is generally directed to a method and device for producing electricity. In comparison to other methods known in the art, the method of the present invention provides an elegant and efficient process for directly converting energy into electricity. 
   Referring initially to  FIGS. 1-2 , an energy conversion device, shown generally as reference numeral  10 , includes a magnetic dipole module  11  enclosed by an electrical coil  13  having a plurality of ‘N’ turns or windings. The electrical coil  13  is thus immersed in a magnetic field produced by the magnetic dipole module  11 . For clarity of illustration, only a first turn  15 , a second turn  17 , and a third turn  19  are shown in the diagrammatical representation of  FIG. 1 , but it should be understood that the number of turns or windings is much greater than three turns. 
   The magnetic dipole module  11  may be generally cylindrical in shape having a module longitudinal axis  21  and comprising a plurality of ferromagnetic nanocrystals  23  distributed within a matrix  25 . The ferromagnetic nanocrystals  23  are preferably single-domain particles or smaller, and each ferromagnetic nanocrystal  23  comprises a material having a Curie temperature denoted by T C . 
   Each ferromagnetic nanocrystal  23  has an associated nanocrystal magnetic dipole moment  27  generally aligned along the module longitudinal axis  21 . In this aligned configuration, each nanocrystal magnetic dipole moment  27  contributes to a module aggregate magnetic field  29 , designated by the vector symbol {right arrow over (B)} and defined in accordance with a vector coordinate system  31 . 
   The magnetic dipole module  11  may also include a rod-shaped core magnet  33  having a core magnetic dipole moment  35  aligned along, and preferably coincident with, the longitudinal axis  21 . This aligned configuration serves to ensure that the contribution of the core magnetic dipole moment  35  to the strength of the module aggregate magnetic field  29  is optimal. 
   The core magnet  33  may comprise a permanent magnet, for example, or an electromagnet to provide a greater core magnetic dipole moment  35  than may be possible with a permanent magnet of similar size. A stronger core magnetic dipole moment  35  can, in turn, increase the magnetic strength of the ferromagnetic nanocrystals  23  which can, accordingly, subject the turns or windings of the electrical coil  13  to a greater magnetic flux produced by the magnetic dipole module  11 . 
   Because of extremely small physical size, the ferromagnetic nanocrystals  23  may, under certain conditions, become superparamagnetic. The core magnet  33  serves to offset this potential occurrence by maintaining the magnetic moment orientation of the ferromagnetic nanocrystals  23  at temperatures below the Curie temperature until incident radiation decouples the magnetic moments. 
   The operation of the energy conversion device  10  follows from Faraday&#39;s observation that a transient electrical current can be induced in the electrical coil  13  if the magnetic field {right arrow over (B)} is changed as a function of time. This changing magnetic field produces a corresponding change in the magnetic flux across the electrical coil  13 . An electromotive force can be induced in an electrical circuit  37  comprising the electrical coil  13  and an external electrical load  39  in response to this change in the magnetic field {right arrow over (B)}. In accordance with Faraday&#39;s Law, the electromotive force is proportional to the time rate of change of the magnetic flux linking the electrical coil  13 , 
           E   =       -   k     ⁢       ⅆ   F       ⅆ   t               
where
         E is the electromotive force around the electrical coil  13 ;   k is a constant of proportionality dependent on the choice of units for the electric and magnetic field quantities; and   F is the magnetic flux linking the electrical circuit  37  which includes turns  15 ,  17 , and  19 .
 
The negative value of k indicates that the induced current (and accompanying magnetic flux) is in such a direction as to oppose the change of flux through the windings of the electrical coil  13  (exemplified by the turns  15 ,  17 , and  19 ). As can be appreciated by one skilled in the relevant art, the resulting current can be increased by increasing the number of turns ‘N’ in the electrical coil  13 .
       
   In accordance with the present invention, the magnitude of the magnetic field {right arrow over (B)} can decay and regenerate as a function of radiant energy incident on the energy conversion device  10 . The radiant energy may be provided in the form of a radiation beam  41  emitted from a radiation source  43 , as described in greater detail below. 
   The matrix  25  is highly transparent to the wavelength λ of the radiation beam  41  such that the radiation source  43  transmits the radiation beam  41  through an enclosure  49  and through the matrix  25  with minimal attenuation to irradiate the ferromagnetic nanocrystals  23 . Preferably, the wavelength λ of the radiation beam  41  is also selected so as to effectively impart thermal energy to irradiated ferromagnetic nanocrystals  23 . In an alternative embodiment, the enclosure  49  comprises a “soft” magnetic material. 
   At the start of operation, that is, before the radiation source  43  is powered to direct the radiation beam onto the magnetic dipole module  11 , the ferromagnetic nanocrystals  23  are initially at an ambient temperature T a , where T a  is less than the Curie temperature T C  of the ferromagnetic nanocrystals  23 . When the energy conversion device  10  is irradiated by the radiation beam  41  for a predetermined amount of time, the ferromagnetic nanocrystals  23  are heated to a temperature of T 1  or greater, where T 1  is greater than the Curie temperature T C . 
   As the respective temperatures of the ferromagnetic nanocrystals  23  rise above the Curie temperature T C , the magnetic dipole moments  27  decouple out of alignment with the module longitudinal axis  21 . The module magnetic field  29  begins to decay and may decrease to a value approximately that of the core magnetic dipole moment  35 . This results in a decrease in magnetic flux across the electrical coil  13 . 
   After a predetermined period of time, the irradiation of the magnetic dipole module  11  is reduced or terminated so as to allow heat to flow from the ferromagnetic nanocrystals  23  into the matrix  25 . This action can be accomplished by, for example, attenuating the output of the radiation source  43  or by blocking the radiation beam  41 . In one embodiment, the radiation source comprises a pulsed laser device (not shown) which functions to output a radiation beam  41 , which controllably varies between full power and an attenuated power level. 
   In an alternative embodiment, the radiation beam can be blocked by closing a shutter  45 , such as an optical Kerr cell or similar device, interposed between the radiation source  43  and the magnetic dipole module  11 . As the nanocrystals  23  lose heat to the relatively cooler matrix  25 , the temperatures of the nanocrystals  23  drop to a value of T 2  or lower, where T 2  lies below the Curie temperature. That is, T 2 &lt;T C &lt;T 1 . This drop in temperature allows the magnetic flux to regenerate and to reappear across the electrical coil  13 . 
   Operation of the energy conversion device  10  thus comprises repetitive cycles of alternatingly causing the magnetic flux to decay across the electrical coil  13  and then enabling the magnetic flux to regenerate. These cycles of decay and regeneration are achieved by alternating the steps of: (1) irradiating the ferromagnetic nanocrystals  23  to a temperature of T 1  or higher to cause the magnetic flux to decay, and (2) reducing or terminating the irradiation for a predetermined amount of time to allow the temperatures of the ferromagnetic nanocrystals  23  to fall below T 2  so as to enable the magnetic flux to regenerate across the electrical coil  13 . 
   In accordance with Faraday&#39;s Law, a corresponding electrical current i, indicated by an arrow  47 , is produced in the electrical coil  13  with the decay and regeneration of the magnetic flux produced by the ferromagnetic nanocrystals  23 . The high output frequency of the electrical current i, may be converted to a DC signal, and then to a lower-frequency AC signal, such as a 60 Hz output signal, for example. The energy conversion device  10  thus functions to directly convert a portion of the energy in the incident radiation beam  41  into the electrical current i provided to the external electrical load  39 . 
   As understood by one skilled in the relevant art, a single domain may be approximately 10 −6  to 10 −2  cm 3  in size, for example, and may contain 10 15  to 10 21  atoms. The small physical sizes of the nanocrystals  23  thus allow the magnetic flux to be cycled at high frequencies. For example, single-domain particles having temperatures above the Curie temperature T C  can be demagnetized in time intervals as small as one femtosecond. Changing the magnetic field at a high frequency can thus provide a relatively large electrical current even if the magnetic field is relatively small. 
   The radiation source  43  can be, for example, a narrowband source such as a laser, or a broadband source such as sunlight. The radiation beam  41  can thus comprise a range of frequencies best suited to induce heating of the ferromagnetic nanocrystals  23 . As can be appreciated by one skilled in the art, the broadband sunlight source may be more practical than a narrowband laser source for providing, or boosting, an external electrical current source. In other applications, the best source to provide electricity, e.g., to a subcutaneous cardiac pacemaker or insulin pump, may be a pulsed radio-frequency source. 
   Referring now to  FIGS. 3-4 , an energy conversion device, shown generally as reference numeral  50 , comprises a first ferromagnetic suspension chamber  51  at least partially enclosed in a first electrical coil  53 , and a second ferromagnetic suspension chamber  55  at least partially enclosed in a second electrical coil  57 . The energy conversion device  50  further includes a disk-shaped core magnet  59  disposed between the first ferromagnetic suspension chamber  51  and the second ferromagnetic suspension chamber  55 . 
   The first ferromagnetic suspension chamber  51  includes a first cylindrical shell  61  and a first endcap  63 , and the second ferromagnetic suspension chamber  55  includes a second cylindrical shell  65  and a second endcap  67 . The first cylindrical shell  61 , the first endcap  63 , the second cylindrical shell  65 , and the second endcap  67  can be fabricated from: (1) aluminum; (2) a nonmagnetic material or soft metal such does not hold a magnetic force when not in a magnetic field; or (3) a “soft” magnetic material. The first ferromagnetic suspension chamber  51  houses a first ferromagnetic suspension  71  comprising a distribution of the aligned ferromagnetic nanocrystals  23  in the matrix  25 . Likewise, the second ferromagnetic suspension chamber  55  also houses a second ferromagnetic suspension  73  comprising a plurality of the ferromagnetic nanocrystals  23  disposed in the matrix  25 . 
   Radiant energy is provided to the energy conversion device  50  by a radiation source  81 , such as a pulsed laser source. When operating in accordance with the present invention, the radiation source  81  provides pulsed radiation (not shown) to the first ferromagnetic suspension  71  via a first optical fiber  83 , and pulsed radiation to the second ferromagnetic suspension  73  via a second optical fiber  85 . The energy conversion device  50 , the radiation source  81 , the first optical fiber  83 , and second optical fiber  83  form an energy conversion system  20 . The radiation pulses may be provided to the two ferromagnetic suspensions  71  and  73  either simultaneously or alternately. 
   Referring now to  FIG. 5 , in which the first ferromagnetic suspension  71  is shown in greater detail, the nanocrystals  23  comprise nickel having a Curie temperature of about 627° K., and the matrix  25  comprises aluminum oxide. In an alternative embodiment, the nanocrystals  23  comprise iron having a Curie temperature of about 1043° K. In other alternative embodiments, the nanocrystals  23  may be formed from: (1) “hard” ferromagnetic crystals comprising metal ions such as cobalt, neodymium, or gadolinium; (2) ferrite crystals comprising metal ions such as cobalt, neodymium, or gadolinium; or (3) ferrites such as yttrium-iron-garnet. When utilized in the first ferromagnetic suspension  71 , a ferrite crystal may produce a weaker magnetic field than when utilizing a nanocrystal, but the frequency of operation may be greater than that for nonocrystals. 
   Referring now to  FIG. 6 , a doped ferromagnetic suspension  75  is shown comprising a distribution of nanocrystals  23  in the matrix  25 . The doped ferromagnetic suspension  75  further comprises a distribution of dopant particles  77  comprised of a material such as titanium, copper, yttrium, or other such transition metal. The dopant particles  77  may serve to scatter the radiation from the radiation source  81  throughout the first ferromagnetic suspension chamber  51  or the second ferromagnetic suspension chamber  55 . In addition, as titanium has a relatively high thermal conductivity, the dopant particles would also serve to absorb heat from the nanocrystals  23 . In yet another alternative embodiment, the dopant particles  77  comprise a material such as Ti:Sapphire-titanium-doped sapphire (Ti 3+ :Al 2 O 3 ). 
   Referring now to  FIG. 7 , an energy conversion device, shown generally as reference numeral  90 , comprises a first layered ferromagnetic chamber  91  at least partially enclosed in the first electrical coil  53 , and a second layered ferromagnetic chamber  93  at least partially enclosed in the second electrical coil  57 . In an alternative embodiment, the energy conversion device  90  may include the disk-shaped core magnet  59  disposed between the first layered ferromagnetic chamber  91  and the second layered ferromagnetic chamber  93 . 
   The first layered ferromagnetic chamber  91  includes the first cylindrical shell  61 , a first layered ferromagnet  95 , and the first endcap  63 . The second layered ferromagnetic chamber  93  includes the second cylindrical shell  65 , a second layered ferromagnet  97 , and the second endcap  67 . The energy conversion device  90  can be used with the radiation source  81 , the first optical fiber  83 , and the second optical fiber  85  to form an energy conversion system  100 , shown in  FIG. 8 . In an alternative embodiment, the energy conversion system  100  may comprise the first layered ferromagnetic chamber  91 , the first electrical coil  53 , the first optical fiber  83 , and the radiation source  81 . 
   Referring now to  FIGS. 9-10 , the first layered ferromagnet  95  comprises a plurality of “soft” ferromagnetic annular disks  101  alternately stacked with a plurality of inner Ti:Sapphire annular disks  103 . An outer Ti:Sapphire annular disk  105  is provided at both ends of the first layered ferromagnet  95 . The outer Ti:Sapphire annular disk  105  may also include a coating  113  which is highly reflective to the wavelength λ of the radiation beam  41 . The configuration of the second layered ferromagnet  97  is similar to that of the first layered ferromagnet  95 . 
   For clarity of illustration, the perspective view of  FIG. 9  shows a stack of four soft ferromagnetic annular disks  101  and three inner Ti:Sapphire annular disks  103  but it should be understood that fewer or more soft ferromagnetic annular disks  101  and Ti:Sapphire annular disks  103  can be used in the first layered ferromagnet  95  and in the second layered ferromagnet  97 . 
   The first layered ferromagnet  95  also includes a cylindrical Ti:Sapphire core  107  extending through the inside of the stack comprising the soft ferromagnetic annular disks  101 , the inner Ti:Sapphire annular disks  103 , and the outer Ti:Sapphire annular disks  105 . Preferably, the Ti:Sapphire core  107  is disposed along a layered ferromagnet axis  109  of the first layered ferromagnet  95 . 
   Each of the soft ferromagnetic annular disks  101  includes a ferromagnetic nanocrystal coating  111  on a first disk face  115  and on a second disk face  117 , as best seen in  FIG. 10 . Each soft ferromagnetic annular disk  101  also includes a central opening  119 , each inner Ti:Sapphire annular disks  103  includes a central opening  121 , and each outer Ti:Sapphire annular disk  105  includes a central opening  123 . Each of the central openings  119 , the central openings  121 , and the central openings  123  is preferably sized to allow insertion of the Ti:Sapphire core  107 . This configuration provides for the placement of the cylindrical Ti:Sapphire core  107  into the stack comprising the soft ferromagnetic annular disks  101 , the inner Ti:Sapphire annular disks  103 , and the outer Ti:Sapphire annular disks  105  as shown. 
   The ferromagnetic nanocrystal coating  111  comprises a layer of the matrix  25  having embedded therein a plurality of “hard” ferromagnetic nanocrystals  23  (not shown) with respective nanocrystal magnetic dipole moments (not shown) aligned with the layered ferromagnet axis  109 . The soft ferromagnetic annular disks  101  comprise a magnetic material having a Curie temperature T Csoft  where T Csoft &gt;T C , the Curie temperature of the ferromagnetic nanocrystals  23 . The ferromagnetic nanocrystals  23  may comprise nickel or iron, as described above, or may comprise iron-nickel-titanium alloy particles of sufficiently large size that the ferromagnetic nanocrystals  23  are not superparamagnetic. The magnetic dipole moments  27  produce the module aggregate magnetic field  29 , shown in  FIG. 9 . 
   Operation of the energy conversion system  100  includes irradiating the first layered ferromagnet  95  and the second layered ferromagnet  97  with the radiation beam  41 , as described above for the energy conversion system  20 . The radiation beam  41  is transmitted to the first layered ferromagnet  95 , for example, via the first optical fiber  83 . From the first optical fiber  83 , the radiation beam  41  is directed into the Ti:Sapphire core  107 , as indicated by arrow  114 . As the Ti:Sapphire core  107  is transparent to the radiation beam  41 , the radiation beam  41  is internally scattered into the plurality of inner Ti:Sapphire annular disks  103 , such as indicated by arrows  116  and  118 , and into the two outer Ti:Sapphire annular disks  105 . 
   The scattered radiation beam  41  irradiates the ferromagnetic nanocrystals  23  embedded in the plurality of ferromagnetic nanocrystal coatings  111  on the soft ferromagnetic disks  101 . The nanocrystal magnetic dipole moments  27  are uncoupled by the incident radiation and begin to decay. This action causes the soft ferromagnetic annular disks  101  to demagnetize, causes the module aggregate magnetic field  29  to collapse, and results in the generation of an electrical current in the first electrical coil  53  as described in greater detail above. 
   In an alternative embodiment, discs comprising yttrium aluminum garnet (YAG) are used in place of the Ti:Sapphire annular disks  103  and  105 , and a core comprising yttrium aluminum garnet is used in place of the Ti:Sapphire core  107 . Additionally, the yttrium aluminum garnet discs comprise coatings of yttrium-iron-garnet (YIG) nanocrystal particles. 
   Since many modifications, variations, and changes in detail can be made to the described preferred embodiments of the invention, it is intended that all matters in the foregoing description and shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. Thus, the scope of the invention should be determined by the appended claims and their legal equivalence.