Abstract:
An energy harvesting device is provided that may include any of a number of features. One feature of the energy harvesting device is that it is adapted for insertion into a human blood vessel for converting pulsatile pressure in the blood vessel into electrical energy. The energy harvesting device can provide electrical energy to another electronic or electromechanical on or in the human body. The energy harvesting device can include an electrostatic generator. Methods associated with use of the energy harvesting device are also covered.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. 119 of U.S. Provisional Patent Application No. 61/090,700, filed Aug. 21, 2008, titled “DEVICE FOR ENERGY HARVESTING WITHIN A VESSEL.” This application is herein incorporated by reference in its entirety. 
     
    
     INCORPORATION BY REFERENCE 
       [0002]    All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
       FIELD OF THE INVENTION 
       [0003]    This invention relates generally to the power generation field, and more specifically to new and useful devices, methods, and systems for harvesting energy. 
       BACKGROUND OF THE INVENTION 
       [0004]    Implantable medical devices, such as implantable pulse generators like neurostimulators, spinal cord stimulators, or pacemakers, require a power supply to generate a pulse or stimulation. Conventional stimulators typically have either large batteries that are uncomfortable for the patient, or smaller batteries that require frequent recharging. Additionally, for example, conventional Cardiac Resynchronization Therapy (CRT) Implantable Cardioverter Defibrillators (ICDs) stimulate the heart frequently and as a result have a high current drain from the battery and typically only last a few years before they need to be replaced due to battery depletion. 
         [0005]    Thus there is a need in the implantable medical devices field for an alternative source of power for these devices, allowing these devices to be smaller and/or not require recharging or frequent recharging. Such improvements might significantly increase the longevity of these implantable medical devices resulting in improved patient care and reduced cost. 
         [0006]    The various illustrative embodiments described herein provide an alternative source of power for these devices or other suitable devices or machines. Described herein are new and useful devices, methods, and systems for harvesting energy. 
       SUMMARY OF THE INVENTION 
       [0007]    One aspect of the invention includes an energy harvesting device, comprising a body adapted to be inserted into a blood vessel, a central lumen configured allow for a largely unimpeded flow of blood, and an energy harvesting generator disposed in the body, the energy harvesting generator adapted to convert pressure variations in the central lumen into electrical energy. 
         [0008]    In some embodiments, the energy harvesting generator is an electrostatic generator. The electrostatic generator can comprise a capacitor having a high pressure state and a low pressure state. In some aspects of the invention, electrical energy can be harvested from the capacitor upon a change from the high pressure state to the low pressure state. In other embodiments, electrical energy can be harvested from the capacitor upon a change from the low pressure state to the high pressure state. 
         [0009]    In some aspects of the invention, the energy harvesting generator can further comprise a membrane in fluid communication with the blood, an outer wall not in fluid communication with the blood, a first electrical conductor disposed between the membrane and the outer wall, a second electrical conductor disposed between the first electrical conductor and the outer wall, and a fluid disposed between the first and second electrical conductors. 
         [0010]    In some embodiments, the energy harvesting generator includes a high pressure state and a low pressure state, wherein electrical energy is harvested from the energy harvesting generator upon a change from the high pressure state to the low pressure state. In other embodiments, electrical energy is harvested from the energy harvesting generator upon a change from the low pressure state to the high pressure state. 
         [0011]    In some embodiments, the fluid disposed between the first and second electrical conductors can have a low dielectric constant. The fluid can be an oil, for example. In some embodiments, the first electrical conductor can be a conductive film disposed on the membrane and the second electrical conductor can be a metallic foil. The metallic foil can comprise titanium or stainless steel, for example. In additional embodiments, an insulator can be disposed on an outer surface of the metallic foil. The insulator can comprise barium titanate, for example. In even additional embodiments, the energy harvesting device can further comprise a gas filled expansion space disposed between the second electrical conductor and the outer wall. 
         [0012]    In one aspect of the invention, the energy harvesting device is configured to be inserted into a human vessel. The body can have an outer diameter of approximately 10 to 50 mm and a length of approximately 10 to 100 mm, for example. 
         [0013]    Another aspect of the invention is a method of harvesting energy from a blood vessel, comprising inserting an elongate body into a blood vessel, allowing blood to flow largely unimpeded through the elongate body, and generating electrical energy from the pressure variations caused by blood flow through the elongate body. In some embodiments, the electrical energy is generated by an energy harvesting generator. The energy harvesting generator can comprise a capacitor having a high pressure state and a low pressure state. In some embodiments, electrical energy can be harvested from the capacitor upon a change from the high pressure state to the low pressure state. In another embodiment, electrical energy can be harvested from the capacitor upon a change from the low pressure state to the high pressure state. The energy harvesting generator can form a high value capacitor during the high pressure state and a low value capacitor during the low pressure state. 
         [0014]    Another aspect of the invention provides a method of harvesting energy from a blood vessel, comprising inserting an energy harvesting device into a blood vessel, and generating electrical energy with the energy harvesting device from pulsatile pressure in the blood vessel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which. 
           [0016]      FIG. 1  shows a radial cross section of a stent or stent-like device incorporating an energy harvesting circuit. 
           [0017]      FIG. 2  shows a longitudinal cross section of a stent or stent-like device incorporating an energy harvesting circuit. 
           [0018]      FIG. 3  shows a cross section of an electrostatic generator adapted for use in a stent or stent-like device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]      FIG. 1  shows a radial cross section of a stent or stent-like device incorporating an energy harvesting circuit. The device has an outer structure  110  that is like a stent and intended to locate on the inner lumen of a naturally occurring body vessel such as an artery. The outer structure  110  is sized to fit in the major blood vessels of the body and is preferably on the order of 0.25 to 4.0 centimeters in diameter. The central lumen  140  allows largely unimpeded flow of arterial blood. There are several compartments  100  that can be used to house electronic devices such as stimulators for stimulating nerves or tissue such as cardiac or pulmonary tissue. Such compartments  100  would be on the order of  100  cubic millimeters in volume to accommodate the electronic devices. Electrodes  120  are disposed on the surface to contact tissue for the purposes of electrical stimulation. The electrical stimulation may be of the sympathetic or parasympathetic system to treat hypertension, pain, headache, inflammation, diabetes, and metabolic and gastric disorders or other disorders susceptible to neural stimulation. The compartments  100  may also be used to house energy harvesting generators such as the one shown in  FIG. 3  adapted to convert naturally occurring pressure variations in the central lumen  140  into electrical energy. 
         [0020]      FIG. 2  shows a longitudinal cross section of a representative embodiment. The outer wall  210  is a stent or stent-like structure intended to locate on the inner surface of a naturally occurring body vessel such as an artery. Depending on the vessel into which the device is deployed, the length may be of the order of one to ten centimeters. A central lumen  240  allows for the largely unimpeded flow of arterial blood. Compartments  200  are shown in cross section, some of which may be used to house electronics to implement nerve or cardiac stimulators (for example) and some of which may be used to house an energy harvesting generator as depicted in  FIG. 3 . 
         [0021]      FIG. 3  shows a cross section of an embodiment of an electrostatic generator suitable for use in a stent or stent-like device inserted into the arterial system of a patient (or other animal). A membrane  300  preferably fabricated of a thin polymer is in contact with a patient&#39;s blood, and receives pressure variations from the patient&#39;s blood. Such pressure variations are typically on the order of 40 millimeters of mercury each cardiac cycle. On the side of the membrane  300  not in contact with the patient&#39;s blood is an electrically conducting film  320 . The film  320  is typically deposited on the membrane  300 . A pierced metal foil  310  has apertures  305  that are filled with a fluid having a low dielectric constant such as an oil. The metal foil  310  may be made of titanium, stainless steel or any other suitable conductor. On the surface of the metal foil  310  is a thin coating of an insulator  315 . The insulator  315  is preferably made from a material having a high dielectric constant such as barium titanate. On the other side of the foil  310  from the membrane  300  is a compliant separator  350  backed by a gas filled expansion space  345  that is further contained by a comparatively rigid wall  340 . The gas may be any suitable gas such as air, nitrogen or argon. The space between the separator  350  and the membrane  300  is sealed at edges with an adhesive  335  or equivalent. Two electrically conducting wires  330  and  325  connect to the conductive film  320  and the foil  310 . 
         [0022]    In operation, when the pressure in the arterial vessel increases, the membrane  300  with its conductive foil backing  320  displaces the dielectric fluid and is pressed up against the insulating coating  315  of the foil  310 . Under these circumstances (the high pressure state), a comparatively high value capacitor is formed having the foil  310  and the conductive membrane  320  as its electrodes, and the high dielectric constant insulator  315  as the dielectric. During the high pressure state, a force is transmitted to the separator  350  by the dielectric fluid causing it to bulge into the compliance space  345  compressing the gas within. When the arterial pressure subsides (the low pressure state), the spring force of the compressed gas in the compliance space  345  and the distended separator  350  puts a force on the dielectric fluid that pushes the membrane  300  and the foil layer  320  away from metal foil  310  and the insulating layer  315 . During the low pressure state, a comparatively low value capacitor is formed not only because the plates of the capacitor ( 320  and  310 ) are further apart, but also because the low dielectric fluid is now between the plates ( 320  and  310 ) dropping the capacitance dramatically. 
         [0023]    The electrical cycle to harvest energy from an electrostatic generator is well known and is briefly reviewed here. During the high pressure state the capacitance is high and a low voltage (the “seed” voltage) is imposed on the capacitor. During the low pressure state the capacitance drops and the voltage on the capacitor increases allowing energy to be harvested. With this device energy may be harvested in amounts suitable to power a low-powered stimulator which may require on the order of 100 microwatts to function. 
         [0024]    In this embodiment the foil  310  is one plate of the capacitor and the conductive film  325  on the membrane  300  is the other plate. An alternative configuration that may be preferred is to have the conductive film  320  on the separator  350 . A further configuration would be to have conductive film  320  on both the separator  350  and the membrane  300  allowing energy harvesting both on transition from the low pressure state to the high pressure state and the high pressure state to the low pressure state. 
         [0025]    In operation an energy harvester (an embodiment of which is shown in  FIG. 3 ) is used to power circuits contained in housings ( 100  and  200 ) of the device that is placed in a naturally occurring body lumen such as an artery. The device may further include communications circuits for the implanted device to communicate with an external clinical controller for setting operating parameters and transmitting data such as the pressure in the lumen. The energy harvester in the device provides power (at least in part) for the electronic or electromechanical device in the stent or stent-like structure. The electronic or electromechanical device may be, without limitation, a neurostimulator, a pacemaker, drug pump, or a sensor such as a pressure, flow, temperature, optical, glucose, genetic or cellular sensor. The device may be implanted in a range of vessels including (without limitation) the aorta, the pulmonary vessels, the carotid, and the hepatic and renal artery to treat hypertension, asthma, COPD, and to improve cardiac contractility and diabetes. 
         [0026]    As for additional details pertinent to the present invention, materials and manufacturing techniques may be employed as within the level of those with skill in the relevant art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts commonly or logically employed. Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein. Likewise, reference to a singular item, includes the possibility that there are plural of the same items present. More specifically, as used herein and in the appended claims, the singular forms “a,” “and,” “said,” and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. Unless defined otherwise herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The breadth of the present invention is not to be limited by the subject specification, but rather only by the plain meaning of the claim terms employed.