Abstract:
An implantable assembly is disclosed comprising a diode device charging assembly having the means for transferring thermal energy from a living organism to a diode device, means for creating electrical energy from said thermal energy, and means for charging an implantable device with said electrical current. The diode device of this invention is a thermotunneling or thermionic converter. In a preferred embodiment the electrodes of the diode device have been modified to reduce their work function by through the addition a periodically repeating structure comprised of one or more indentations of the dimensions so as to create de Broglie wave interference, leading to a change in electron work function. The implantable assembly utilizes a temperature difference in a body to efficiently generate energy to be harnessed by a wide range of devices.

Description:
This application claims the benefit of U.K. Patent Application No. GB0617934.5, filed Sep. 12, 2006, said document incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     This present invention relates to a device for providing a permanent source of energy through a temperature gradient in a living body, comprising a diode device. 
     The mammalian body is a natural producer of thermal energy. In recent years, researchers have looked towards the body as a potential source of usable energy. The conversion of a body&#39;s thermal energy into electric energy creates a potential for medical devices and wearable devices that are powered by body heat. 
     For example, U.S. Pat. No. 5,889,735 discloses a thermoelectrically powered wristwatch that utilizes a temperature difference between a human body and its surroundings to generate a voltage to power a device such as a wristwatch. Similar to the concept that a temperature difference exists between the body and its surroundings is the concept that there exists differences in temperature within one body. Further, U.S. Pat. No. 6,640,137 discloses a biothermal power source for a device implanted within the human body that is comprised of a thermoelectric module for converting thermal energy to electrical energy. This device is said to produce a power output of 100 microwatts from a temperature differential of between 1 to 5 degrees Celsius. 
     However, because thermoelectric devices are only 5-8% efficient, the low power output of such devices requires that thousands of thermocouples be built into one device in order to generate the energy necessary to power the device (or to continuously trickle-charge the batteries). This would be difficult to manufacture, and as of yet, only tens of thermocouples have been arrayed. Thus there is a need to provide a biothermal power source that has a higher percentage of practical efficiency 
     Recent technology has been developed to provide such a power source.  FIGS. 1-5  illustrate some embodiments of such power sources having a higher percentage of practical efficiency. 
     U.S. Patent App. Pub. No. 2007/0013055 discloses a thermotunneling/thermionic converter. A preferred embodiment of this diode device is shown in  FIG. 1  in which silicon wafers  100  and  102  have their inner surfaces substantially facing one another, and a spacer or plurality of spacers  104  positioned between them. Preferably, silicon wafers  100  and  102  have matching surfaces, that where one has an indentation the other has a protrusion. Thus when matched, the two surfaces are substantially equidistant from each other. In a preferred embodiment, a vacuum  106  is introduced. In this design, active piezo control is not required to maintain the gap, making the device inexpensive. The use of active elements is not required due to the mechanical properties of silicon, such that if a small particle is trapped in between two silicon wafers, a non-bonded area of 5000 times the size (height) of the particle is created. Therefore the spacers consisting of a dot of silicon oxide topped by a protective layer will have the effect of keeping the two silicon wafers at a desired distance. 
     U.S. Pat. No. 6,720,704 discloses a thermionic vacuum diode device with adjustable electrodes. A preferred embodiment of this diode device is depicted in  FIG. 2 , in which a first electrode  202 , disposed on substrate  204 , is attached to the end of actuator tube  90 , and a second electrode  206 , disposed on substrate  208 , is attached to the other end of tube  90 . The two electrodes are also connected to an electrical load or power supply  210  by means of wires  212 . Actuator tube  90  has electrodes  92  disposed on its surface which are connected to controller  214  via wires  216 . This controller sets the separation of electrodes  202  and  206 . Electrodes  202  and  206  may also be connected to capacitance controller  218  which is able to assess the separation of the electrodes, and the separation of the electrodes may be accurately controlled via a feedback loop  220  to controller  214 . Typically, the electrode separation is of the order of 0.1 to 100 nm. In a preferred embodiment, electrodes  202  and  206  may be formed as depicted in  FIG. 3 . 
     Referring now to  FIG. 3 , composite  80  is any material which has a similar thermal expansion coefficient to quartz and can be bonded to quartz. Preferably, composite  80  is a molybdenum disc. Electrically conducting paste  94 , preferably silver paste, lies upon the upper surface of the molybdenum disc and is in contact with a composite  78 . Composite  78  is preferably a matching electrode pair precursor, such as shown in step 130 of WO99/13562 or U.S. Pat. No. 6,417,060, or is more preferably a layer of titanium  72  deposited on substrate  70 , and a layer of silver  74  further deposited on the layer of titanium. A further layer of copper  76  is grown electrochemically on the layer of silver. Ideally, substrate  70  is a silicon wafer, and is polished at least around its periphery where it is in contact with tube  90 . Alternatively, composite  78  is composite  79  depicted in  FIG. 4 . Though upon formation and at first contact with paste  94 , composite  78  is a single unit, high pressure followed by heat causes the composite to open, as depicted in  FIG. 3 , forming a pair of matching electrodes  72  and  74 . 
     In a further embodiment, depicted in  FIG. 4 , substrate/composite  80  has a depression  82  across part of its surface. Substrate/composite  80  also has a locating hole  84  in its surface. An additional feature of this embodiment is alignment pin  86 , which is premachined, and is attached to the composite  79  at the layer of copper  76 . The diameter of the alignment pin is the same as the diameter of the locating hole which results in a tight fit between the alignment pin  86  and the locating hole  84  when the pin seats in the locating hole. The tight fit ensures that electrodes  72  and  74  do not slide relative to one another. 
     U.S. Patent App. Pub. No. 2005/0147841, as seen in  FIG. 5 , discloses an electrode for a diode device having an indented surface. The indents are formed on wafer  442  by means of laser, chemical or other means for etching a geometric pattern on the surface of solid materials such as silicon, metal, and the like. Preferably, the one or more indents should have a depth approximately 5 to 20 times a roughness of the material&#39;s surface and a width approximately 5-15 times the material&#39;s depth. It is also preferable that the indents be substantially sharp and substantially perpendicular to one another. Such indents alter the distribution of quantum states within a volume limited by a potential energy barrier and promote the transfer of elementary particles across a potential energy barrier. In one embodiment, the electrode is consists of a layer of silver  444  upon indented wafer  442 , followed by a layer of titanium  446 , upon which a layer of copper  448  is grown electrochemically to form a composite  450 . When the composite  450  is opened, as shown in  FIG. 5 , it forms a pair of matching electrodes that can be utilized to make diode devices. 
     U.S. Pat. Nos. 6,281,514, 6,495,843, and 6,531,703 disclose methods for promoting the passage of electrons at or through a potential barrier comprising providing a potential barrier having a geometrical shape for causing de Broglie interference between electrons. In another embodiment, the invention provides an electron-emitting surface having a series of indents. The depth of the indents is chosen so that the probability wave of the electron reflected from the bottom of the indent interferes destructively with the probability wave of the electron reflected from the surface. This results in the increase of tunneling through the potential barrier. In further embodiments, the invention provides vacuum diode devices, including a vacuum diode heat pump, a thermionic converter and a photoelectric converter, in which either or both of the electrodes in these devices utilize said electron-emitting surface. In yet further embodiments, the invention provides devices in which the separation of the surfaces in such devices is controlled by piezo-electric positioning elements. A further embodiment provides a method for making an electron-emitting surface having a series of indents. 
     U.S. Pat. No. 6,680,214 and U.S. Pat. App. Pub. No. 2004/0206881 disclose methods for the induction of a suitable band gap and electron emissive properties into a substance, in which the substrate is provided with a surface structure corresponding to the interference of electron waves. Lithographic or similar techniques are used, either directly onto a metal mounted on the substrate, or onto a mold which then is used to impress the metal. In a preferred embodiment, a trench or series of nano-sized trenches are formed in the metal. 
     U.S. Pat. No. 6,117,344 discloses methods for fabricating nano-structured surfaces having geometries in which the passage of electrons through a potential barrier is enhanced. The methods use combinations of electron beam lithography, lift-off, and rolling, imprinting or stamping processes. 
     WO9964642 discloses a method for fabricating nanostructures directly in a material film, preferably a metal film, deposited on a substrate. In a preferred embodiment a mold or stamp having a surface which is the topological opposite of the nanostructure to be created is pressed into a heated metal coated on a substrate. The film is cooled and the mold is removed. In another embodiment, the thin layer of metal remaining attached to the substrate is removed by bombarding with a charged particle beam. 
     WO04040617 offers a method which blocks movement of low energy electrons through a thermoelectric material. This is achieved using a filter which is more transparent to high energy electrons than to low energy ones. A tunnel barrier on the path of the electrons is used as filter. The filter works on the basis of the wave properties of the electrons. The geometry of the tunnel barrier is such that the barrier becomes transparent for electrons having certain de Broglie wavelength. If the geometry of the barrier is such that its transparency wavelength matches the wavelength of high energy electrons it will be transparent for high energy electrons and will block low energy ones by means of tunnel barrier. 
     In WO03/083177, the use of electrodes having a modified shape and a method of etching a patterned indent onto the surface of a modified electrode are disclosed. The patterned indent increases the Fermi energy level inside the modified electrode, leading to a decrease in electron work function.  FIG. 6  shows the shape and dimensions of a modified thin metal film  600 . Indent  640  on metal substrate  600  has a width b and a depth a, and the separation between the indents is c. Preferably distances b and c are substantially equal. Preferably distance b is of the order of 2 μm or less. Experimental observations using a Kelvin probe indicate that the magnitude of a reduction in apparent work function increases as distance a is reduced. Utilization of e-beam lithography to create structures of the kind shown in  FIG. 6  may allow indents to be formed in which distance b is 200 nm or less. Distance a is of the order of 20 nm or less, and is preferably of the order of 5 nm. Metal film  600  is given sharply defined geometric patterns or indents  640  of a dimension that creates a De Broglie wave interference pattern that leads to a decrease in the electron work function, thus facilitating the emissions of electrons from the surface and promoting the transfer of elementary particles across a potential barrier. The surface configuration of film  600  may resemble a corrugated pattern of squared-off, “u”-shaped ridges and/or valleys. Alternatively, the pattern may be a regular pattern of rectangular “plateaus” or “holes,” where the pattern resembles a checkerboard. The walls of indent  640  should be substantially perpendicular to one another, and its edges should be substantially sharp. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a biothermal power generator comprised of a diode device, which utilizes a temperature differential in the body for converting thermal energy to electric energy. The device thus comprises a heat source in contact with a first surface of the diode device; a heat sink in contact with a second surface of the diode device; and means for transferring thermal energy from the heat source through the diode device to the heat sink. The heat source is a living organism. 
     In one embodiment the power generating assembly comprises a diode device which is a thermionic diode device having adjustable electrode. 
     In a further embodiment the power generating assembly comprises a diode device comprising a plurality of electrodes having surfaces substantially facing one another, and a respective spacer or plurality of spacers disposed between said electrodes to allow gaps between said electrodes, and where the surface area of the spacer or plurality of spacers in contact with said surface is less than the surface are of said surfaces. 
     In a further embodiment the power generating assembly comprises a diode device having one or more electrodes comprising a substantially plane slab of a metal having on one surface one of more indents of a depth approximately 5-20 times a roughness of said surface and a width approximately 5-15 times said depth. In a further embodiment, the one or more electrodes have a periodically repeating structure comprised of said indents such that the work function of said diode device is substantially lower than a diode device that does not comprise said periodically repeating surface structure. 
     The present invention further contemplates a method for generating electricity comprising the steps of: disposing a diode device at a location within a living organism, wherein said location comprises a temperature differential; generating an electrical current from the temperature differential; charging the electrical circuit with the electrical current. 
     A technical advantage of the present invention is its ability to provide continuous power. 
     Another advantage of the present invention is its compatibility with the use of magnetic resonance imaging. 
     A further advantage of the present invention is to provide possible automatic recharging of medical implants, thereby providing continuous treatment of chronic disease. 
     Another advantage of the present invention is that the generator does not require surgical removal in order to be recharged. This results in improved quality of life for a patient by minimizing the time spent in the hospital and the risks involved in surgery. 
     A further technical advantage of the present invention is its efficiency. Such a device has been projected to achieve 70-80% of Carnot efficiency, meaning that with a temperature differential of only 2 degrees Celsius across the device, it could produce a power output of at least 0.005 watts per watt of heat. As the temperature difference between a hot and cold side grows larger, more power can be extracted, and thus with a differential of 5 degrees Celsius, an electrical output of 0.011 watts per watt of heat could be achieved. 
     Further objects and advantages will become apparent from a consideration of the ensuing description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       For a more complete understanding of the present invention and the technical advantages thereof, reference is made to the following description taken with the accompanying drawings, in which: 
         FIGS. 1-5  refer to prior art inventions, and: 
         FIG. 1  is a diagrammatic representation of a thermotunneling or thermionic converter. 
         FIG. 2  is a diagrammatic representation of a thermionic vacuum diode device with adjustable electrodes. 
         FIG. 3  is a diode device having a tubular housing/actuator. 
         FIG. 4  shows one preferred embodiment of a diode device. 
         FIG. 5  shows a diode device having an indented surface. 
         FIG. 6  is a cross sectional view of a modified electrode. 
         FIG. 7  is a block diagram displaying the basic elements of this invention. 
         FIG. 8  is a block diagram of a preferred embodiment of this invention. 
         FIG. 9  is a schematic of one preferred device of this invention with its placement near the skin surface. 
         FIG. 10  is a schematic of one preferred device of this invention with a further preferred placement near the skin surface. 
         FIG. 11  is a schematic of a further preferred embodiment of this invention in which the diode device is at a distance from the implantable device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to  FIG. 7 , a block diagram is depicted, displaying the basic elements of one preferred embodiment of the present invention. Enclosed within case  42  are implantable device  20 , which may further include pacing leads  24  or conduit  26 , battery  18 , and diode device  10 . The depicted assembly is implanted within a patient and utilizes a difference in temperature to generate power that can be harnessed for a wide range of devices and functions. Among its many possible functions, this biothermally powered diode device can power a medical device that responds to various medical needs by providing drug delivery, electrical stimulation, or other forms of assistance. Alternatively, nonmedical devices and other devices, could be provided with electrical energy. 
     Since the present invention utilizes a temperature differential to generate energy, it must be positioned at a location in the body where such a differential is available. A temperature gradient of up to 5 degrees C. can be found between the skin surface and the body core, and thus, placing the present invention beneath the skin and extending towards the body core is preferred. Another possible configuration would be to have diode device  10  at a distance from case  42  and all it contains, but connected by means of a lead. 
     As previously discussed, diode device  10  consists of a thermionic or themotunneling converter having two matching electrodes facing one another. Voltage is created when there is a difference in temperature between the two surfaces of the device. It is preferred that diode device  10  be a thermionic or thermotunneling converter consisting of two silicon electrodes maintained at a desired distance from one another by means of spacers, as can be seen in  FIGS. 1 . Alternatively, a further preferred form of diode device  10  would be the thermionic vacuum diode device with adjustable electrodes in which the separation between the electrodes is set and controlled through the use of piezo-electric positioning elements that is depicted in  FIGS. 2 through 4 , and as is disclosed in U.S. Pat. No. 6,720,704. An even further preferred form of diode device  10  would be to utilize the method described in U.S. Patent App. No. 2005/0147841 for creating the electrodes in which indents and/or protrusions are etched into the wafer surface by means of laser, chemical, or other etching methods, as seen in  FIGS. 5 and 6 . 
     Battery  18  functions as a storage element wherein voltage produced by the diode device can be stored. In times when leads  100  and  102  do not maintain a temperature difference and therefore do not produce any electrical current, the electrical energy stored within battery  18  can supply power to implantable device  20 . 
       FIG. 8  is a block diagram displaying the power generator of  FIG. 7  with the addition of elements that may be added, either independently or in combination, to enhance the functioning of the biothermal power generator. In the preferred embodiment depicted in  FIG. 8 , diode device  10  is connected to and provides electrical current to control circuit  14  through lead  12 . Control circuit  14 , in turn, is operatively connected to voltage regulator  16 , which provides direct current to battery  18 . Battery  18 , in turn, provides power to the implantable device  20 . Alternatively, voltage regulator  16  could provide electrical current directly to implantable device  20 . 
     If the temperature on a first surface of diode device  10  is higher than the temperature on the second surface of diode device  10 , then the polarity of the produced electric current produced will be the opposite of the situation than when the temperature of the first surface is lower than the temperature of the second surface. Therefore, leads  12  may first communicate with polarity reverser  30  before they are connected with control circuit  14 . Through the use of a polarity reversal device  30 , electrical current will effectively flow into control circuit  14  under all conditions of temperature. 
       FIG. 9  is a schematic of one preferred device of this invention in which some unnecessary details have been omitted for simplicity of illustration. In the preferred embodiment depicted in  FIG. 9 , the assembly  50  utilizes the diode device  10 , which may be any of the devices described in  FIGS. 1-6 , generating electrical current from the temperature gradient between the internal body core  60  and the skin surface  62 . Usually the body core temperature is greater than the skin surface temperature, but even in cases where this relationship is reversed, a control circuit  14  (not shown, see  FIG. 8 ) will reverse the polarity of its voltage regulator so the battery can continue to be recharged. 
     Referring again to  FIG. 9 , the implant comprises a primary device  64  and a diode device  10 . Primary device  64  is comprised of the implantable device  20  and all elements enhancing the implantable device such as those depicted in  FIG. 8 , with the exception of the diode device  10 . Encompassing primary device  64  is a case  42 , which provides a hermetic seal around all the entire apparatus while allowing for the passage of wires without breaching the hermetic seal, and has specialized thermal properties that can be achieved by the usage of precise combinations of a variety of materials and fabrication methods. Depending on the desired result, properties such as strength, durability, high thermal conductivity, biocompatibility, magnetic impermeability, and flexibility can be built into the case. Preferably, the diode device  10  is situated immediately against the case  42  and is in thermal contact therewith. The entire assembly is disposed close to the skin surface, and the case  42  may or may not be in direct contact with the skin. In a preferred embodiment, a layer of gel or polymer  68  is planted directly above the device case  42  and is contained within a conductive sealing membrane  70 . Both gel  68  and membrane  70  provide a highly thermally conductive path from the device case  42  to the skin surface  62  as well as creating a greater degree of comfort for the patient. 
     Another feature that may be added to assembly  50  to thermally isolate it from the surrounding environment is an insulating sheath. In  FIG. 9 , and the preferred embodiment depicted therein, insulating sheath  72  surrounds primary device  64  and is made preferably of a flexible polymeric insulating material. 
     One benefit of assembly  50  being disposed immediately below the skin surface is the capacity for heat to be added or removed from one side of the diode device through the use of an external hot (or cold) source. By way of example, a patient could apply an ice pack or a warming apparatus to the skin surface directly above the implanted medical device, creating a greater temperature differential between the two surfaces of the diode device, and thus providing increased electrical current to the implantable device. In this way, a patient could ensure a plentiful supply of electrical current to the implanted device regardless of the ambient temperature. 
       FIG. 10  is a schematic of another preferred design of assembly  50 . Like  FIG. 9 , it generates electrical current through the temperature differential between the body core and the skin surface. Many of the components are similar in design and function to the corresponding components described in  FIG. 9 . However, in this preferred embodiment, gel/polymer  68  and its membrane  70  have been removed, and device case  42  is now in direct contact with the skin. Furthermore, an inward facing portion of the device  50  has been extended towards the body core  60  to enhance current generation by contacting a region with a greater average temperature. A conductive rod  74 , which may be a rod or heat pipe, extends from the diode device  10  towards the body&#39;s center and ends in a thermal contact  76 . The insulating sheath  72  of  FIG. 8  has been extended along the length of rod  74 , maintaining thermal isolation from the surrounding body tissue. The design depicted in  FIG. 9  is meant to provide for a greater temperature differential, and thus a greater current generation. 
     There exist a multiplicity of variations for the positioning, size, and comfort of the implant that may or may not make use of design features such as a conformable gel or polymer between the device and the skin, insulating sheath, conductive plates and other electrical features that will be obvious to those skilled in the art. 
       FIG. 11  is a further preferred embodiment of the present invention in which the diode device is placed at a distance from the implantable circuitry to which it provides power. An advantage of such a configuration is that the diode device could be positioned at a location that provides the greatest possible temperature gradient while the circuitry it powers could be positioned at a second location that provides for greater comfort, ease of installation, repair, and monitoring, or other advantages. In  FIG. 11 , diode device  10  is connected to primary device  64  via electrically conducting lead  104 . 
     While this invention has been described with reference to numerous embodiments, it is to be understood that this description is not intended to be construed in a limiting sense. It will be obvious to persons skilled in the art that the biothermal power generation process described herein encompasses numerous embodiments in which there are changes in the details of the present invention and additional embodiments of the present invention will be apparent to, and may be made by, persons of ordinary skill in the art having reference to this description. It is to be understood that all the embodiments described above can be utilized in any possible combination. It is contemplated that all such changes and additional embodiments are within the spirit and true scope of the invention as claimed below.