Abstract:
An apparatus for perpetually harvesting ambient near ultraviolet to far infrared radiation to provide continual power regardless of the environment, incorporating a system for the harvesting electronics governing power management, storage control, and output regulation. The harvesting electronics address issues of efficiently matching the voltage and current characteristics of the different harvested energy levels, low power consumption, and matching the power output demand. The device seeks to harvest the largely overlooked blackbody radiation through use of a thermal harvester, providing a continuous source of power, coupled with a solar harvester to provide increased power output.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     This invention was made in part with Government support under contract no. W31P4Q10C0034 awarded by US Army Aviation and Missile Command. The Government has certain rights in the invention. 
    
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     Not Applicable 
     CROSS REFERENCE TO RELATED APPLICATIONS 
     None. 
     FIELD OF INVENTION 
     This invention pertains to the harvesting of ambient energy in the surrounding environment. More particularly this invention is related to a semiconductor perpetual energy harvesting and storage device and the harvesting electronics that control energy storage and output allowing the device to continually harvest and provide continuous power during both day and night in any environment. 
     BACKGROUND OF INVENTION 
     There are many sources of energy that can be converted into electrical energy. Sources that have been explored for harvesting are wind, temperature differences, motion, light energy and radio frequency energy. In all these energy situations, a specific situation must be present, such as air flow, temperature gradient, movement, sunlight, or transmitted RF, before energy can be harvested. When these situations do not occur, there is no source for energy to be harvested. 
     Harvesting ambient thermal energy has not been widely explored. The characteristic of thermal energy having a peak at long infrared wavelengths poses a significant challenge for harvesting. Additionally, power management, storage control, and regulation electronics must be developed to operate efficiently and respond to the power output demand. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A  and B depicts a high level structural representation of an energy harvesting system. 
         FIG. 2  depicts power available from blackbody radiation at various temperatures 
         FIG. 3  depicts the discharge characteristics of a lithium ion battery. 
         FIG. 4  depicts a block diagram of the harvester electronics utilizing a dual circuit design. 
         FIG. 5  depicts an alternate embodiment of a block diagram of the harvester electronics utilizing a dual circuit design. 
         FIG. 6  depicts a block diagram of the harvester electronics utilizing a single circuit design. 
         FIG. 7  depicts an alternate embodiment of a block diagram of the harvester electronics utilizing a single circuit design. 
     
    
    
     DETAILED DESCRIPTION 
     Reference is made in detail to the preferred embodiments of the invention. While the invention is described in conjunction with the preferred embodiments, the invention is not intended to be limited by these preferred embodiments. The contemplated embodiments for carrying out the present invention are described in turn with reference to the accompanying figures. 
     For purposes of the invention, radiation is defined to be the electromagnetic spectrum, particularly the near ultraviolet, visible, near infrared, short-wave infrared, mid-wave infrared, long-wave infrared and far infrared bands. The near ultraviolet band is comprised of wavelengths from about 300 to 400 nm. The visible light band is comprised of wavelengths from about 400 to 780 nm. The near infrared band is comprised of wavelengths from about 0.78 to 1 μm. The short-wave infrared band is comprised of wavelengths from about 1 to 3 μm. The mid-wave infrared band is comprised of wavelengths from about 3 to 6 μm. The long-wave infrared band is comprised of wavelengths from about 6 to 14 μm. The far infrared band is comprised of wavelengths from about 14 to 40 μm. However, the boundary between near ultraviolet radiation and visible light along with the boundary between visible light and infrared radiation is not precisely defined, resulting in overlap between the bands. 
     The term electrically connected is defined to encompass an electrical current flow, including bidirectional, unidirectional, or any hybrid current flow, such as an uneven current. 
       FIG. 1  depicts a high level structural configuration for an energy harvesting system.  FIG. 1A  illustrates a cross section of the structural configuration.  FIG. 1B  shows an exploded three dimensional view. The interconnects and electrodes in the structural configurations depicted in  FIGS. 1A  and B are not shown. 
     The energy harvesting system comprises a solar harvester  105 , a thermal harvester  110 , a battery  115 , and harvester electronics  120 . The thermal harvester  110  is located between the solar harvester  105  and the battery  115 . The harvester electronics  120  is attached to the thermal harvester  110  on the same side as the battery  115 . The solar harvester  105  and thermal harvester  110  are electrically isolated from each other and individually electrically connected to the harvester electronics  120 . The battery  115  is electrically connected to the harvester electronics  120 . 
     The solar harvester  105  and the thermal harvester  110  may be comprised of a photovoltaic or photoelectrochemical system. The solar harvester  105  may include any photovoltaic system which absorbs radiation within the near ultraviolet, visible, or near infrared bands to generate power. The solar harvester  105  may be comprised of any type of solar cell, including traditional crystallized silicon solar cells, thin film solar cells, multi-layered solar cells, dye sensitized solar cells, or organic polymer solar cells. The material comprising the solar harvester may include, but is not limited to, amorphous silicon, polysilicon, crystalline silicon, Ge, SiGe, CdTe, ZnO, CdZnTe, HgCdTe, HgZnTe, GaAs, GaN, InP, GaSb, InSb, other semiconductors, light sensitive dyes, or polymers. A photovoltaic thermal harvester  105  may be comprised of a single junction or multiple junctions. The material comprising the thermal harvester  105  may include HgCdTe, HgZnTe, InSb, InAs, GaSb, GaAs, InP, PbTe, or polymers. 
     The battery  115  may be any type of rechargeable battery. One embodiment of the invention contemplates the use of solid state thin film battery may be comprised of lithium-ion polymer, lithium, semiconductor, polymer, or flexible batteries. Optionally, the solid state thin film battery may be discretely or monolithically integrated with the harvester. Optionally, in a separate embodiment, bulk batteries may be used. For example, rechargeable lithium air, nickel-cadmium, or nickel metal-hydride batteries. Optionally, a single or multiple battery cells may be used. Optionally, in the case of multiple battery cells, the cells may be arranged in various configurations, e.g. series, parallel, etc. The battery  115  may be flexible, semi-flexible, or rigid. The battery  115  is electrically connected to the harvester electronics  120 . 
     The harvester electronics  120  may be comprised of circuitry which regulates the rate of charge and voltage level of the battery along with regulating the output of power to a load. In one embodiment of the invention, the harvester electronics may be comprised of a single chip integrated circuit. Optionally, the integrated circuits may be a CMOS circuit. Alternatively, an FPGA may be used for harvester electronics  120  to be configurable in the field. Optionally, the harvester electronics may be discretely integrated with the battery  115 . The harvester electronics may be flexible, semi-flexible, or rigid. The harvester electronics  120  may be powered by the battery  115 , energy from the solar harvester  105  or thermal harvester  110 , or a combination of energy sources. 
     The system is oriented to absorb radiation  100  arriving from the indicated direction, passing through the solar harvester  105  before reaching the thermal harvester  110 . The radiation  100  is comprised of the near ultraviolet, visible, near infrared, short-wave infrared, mid-wave infrared, long-wave infrared, and far infrared bands. 
       FIG. 2  illustrates the blackbody power as a function of wavelength at various temperatures. The blackbody radiation spectrum ranges from near ultraviolet to the infrared spectrum. Blackbody radiation has been largely overlooked as a potential energy source. 
     Blackbody radiation is a physical effect in which all objects at temperatures above 0 K emit electromagnetic power. The spectral radiance of an object is described through Planck&#39;s Law, which is presented as, 
                 I   ⁡     (   λ   )       =       2   ⁢     hc   2           λ   5     (       e     hc     λ   ⁢           ⁢   k   ⁢           ⁢   T         -   1     )         ,         
where c is the speed of light, k is Boltzmann&#39;s constant, h is Planck&#39;s constant, λ is wavelength, and T is temperature in Kelvin of the object. By applying Lambert&#39;s cosine law to a hemispherical flux density from a flat surface, the maximum amount of incident radiation is equal to πI. This yields a maximum spectral radiance of
 
                 I   ⁡     (   λ   )       =       2   ⁢           ⁢   π   ⁢           ⁢     hc   2           λ   5     (       e     hc     λ   ⁢           ⁢   k   ⁢           ⁢   T         -   1     )         ,         
which best models the intensity of radiation from a planar source. As temperature increases, power (in watts per meters squared) increases at lower wavelengths. This results in the peak shifting towards lower wavelengths at higher temperatures.
 
     As shown in  FIG. 2 , at the temperatures ranging from −40° C. (233 K to +60° C., the peak power is at about 9 μm wavelength. Using Stefan-Boltzmann&#39;s law, 5.67×10 −8 ×T 4 , the total available blackbody radiation at a given temperature can be calculated. At room temperature, about 293 Kelvin, the total available blackbody radiation is estimated to be 413 W/m 2  with a peak between 7 to 10 μm. 
       FIG. 3  illustrates the discharge characteristics of a lithium-ion polymer cell at various currents. The figure shows that the cell maintains a relatively constant voltage, which drops sharply as the current decreases due to the battery&#39;s inherent resistance increasing. Given this characteristic of lithium-ion polymer cells, completely discharging cells, otherwise known as deep discharge, results in damage to the cells, which may include the inability to hold a charge and sustain a voltage across a load. To guard against this damage, low voltage protection is required. While the figure illustrates the characteristics for a 1.0 mAh grade lithium-ion polymer cell, the characteristics are similar for other lithium-ion polymer cells. 
       FIG. 4  illustrates a block diagram of the harvester electronics  120  utilizing a two circuit configuration. The harvester electronics  120  are comprised of a thermal harvester interface  400 , a solar harvester interface  405 , a battery manager  410 , and a voltage regulator  415 . Each component comprising the harvester electronics  120  may be electrically connected to and powered by the battery  115 . Optionally, the components of the harvester electronics  120  may be powered by the energy from the solar or thermal harvesters. Optionally, a combination of energy sources may be used to power the harvester electronics  120 . For example, the harvester electronics  120  may be powered by energy from the solar harvester  105  and the battery  115 . 
     The solar harvester  105  is electrically connected to the solar harvester interface  405 . The solar energy harvested by the solar harvester  105  is transferred to the solar harvester interface  405 . Optionally, the solar harvester interface may comprise a voltage boost to allow harvesting of solar energy at low voltages. Optionally, the voltage boost may be dynamically triggered below a certain threshold. The solar harvester interface is electrically connected to the battery manager  410 . 
     The thermal harvester  110  is electrically connected to the thermal harvester interface  400 . The thermal energy harvested by the thermal harvester  110  is transferred through the thermal harvester interface  400 . Due to the low voltage output of thermal energy, the thermal harvester interface  400  comprises a voltage boost. For example, the voltage boost may boost voltages from as low as 20 mV. The thermal harvester interface  400  is electrically connected to the battery manager  410 . 
     The solar harvester interface  405  and the thermal harvester interface  400  transfer the harvested energy to the battery manager  410 . The battery manager  410  merges the harvested energy from the solar harvester interface  405  and the thermal harvester interface  400 . This merged energy may be used to charge the battery  115  and/or be supplied to the electrically connected voltage regulator  415 . The battery manager  410  controls the rate of charge for the battery  115 . The rate of charge varies depending on the battery requirements. The battery manager  410  may be configured to disconnect the battery  115  from the output load when the battery discharge reaches a voltage threshold where further discharge would be harmful to the battery. The voltage at which the battery manager  410  disconnects the battery varies depending on the battery specifications and configuration. For example, if the battery  115  is a lithium-ion polymer with discharge characteristics shown in  FIG. 3 , the battery manager  410  will disconnect the battery from the load when the sharp voltage drop occurs. For example, but not to serve as a limitation, if the battery  115  is a 3.3 V lithium polymer battery, the battery manager  410  may be disconnect the battery from the load when the battery output voltage reaches 2.1 V. While the battery  115  is disconnected from the load, the battery manager  410  may continue to charge the battery  115  while providing power to the voltage regulator  415 . 
     Optionally, the battery manager  410  may include cell balancing capability when multiple battery cells are used. In the case where the battery cells have the same capacity, the battery manager  410  may differentially charge each cell to maximum capacity. In the case where the battery cells have varying capacities, the battery manager  410  may differentially charge each cell to maintain the same state of charge. 
     The battery manager  410  may be configured to disconnect the battery  115  when the battery is fully charged to prevent overcharging. In the situation where the battery  115  is fully charged and disconnected from further charging, the battery manager  410  will direct all the harvested energy to the voltage regulator  415 . In the absence of adequate power from the solar harvester  105 , the battery manager  410  may utilize the battery  115  to supplement power from the thermal harvester  110  to the voltage regulator  415 . 
     The voltage regulator  415  maintains a constant voltage level output, which enables the harvester electronics  120  to produce a regulated power output  420 . The voltage regulator  415  may be comprised of a Low Drop Out (LDO) DC-DC voltage regulator. Optionally, other linear voltage regulators or switching regulators may be used. For example, but not to serve as a limitation, other linear voltage regulators may comprise zener regulators, series regulators, transistor regulators, or regulators comprising an op-amp. The voltage regulator  415  may be modular and configured to match a specific range of output loads or increase power output drive capability. 
     Optionally, the components of the harvesting electronics may be specifically configured to efficiently supply adequate power depending on the specific applications. While the embodiment of the invention contemplates the harvester electronics  120  comprised on a single chip, alternate embodiments may comprise each block or a combination of two or more blocks as discrete circuits. 
       FIG. 5  illustrates an alternate embodiment of the harvester electronics utilizing a two circuit configuration. The solar harvester  105 , thermal harvester  110 , battery  115 , thermal harvester interface  400 , solar harvester interface  405 , battery manager  410 , and voltage regulator  415  are as described above in  FIG. 1  and  FIG. 4 . 
     The harvester electronics comprises a bandgap reference  500 . The bandgap reference  500  is electrically connected to and powered by the battery  115 . Optionally, the bandgap reference may be powered separately by the battery manager, not shown. The bandgap reference  500  provides a temperature independent voltage reference (REF)  505 . The bandgap reference is electrically connected to the battery manager  410  and voltage regulator  415 , along with the MPPT controls and charge pump controls comprising the thermal harvester interface  400  and solar harvester interface  405  and outputs the REF  505  to each of the components. 
     The solar harvester interface  405  and thermal harvester interface  400  may be further comprised of individual maximum power point tracking (MPPT) inputs  510 , MPPT controls  515 , charge pumps  520 , and charge pump controls  525 . The different harvesting conditions for solar and thermal harvesters may result in different circuitry comprising the aforementioned components. The aforementioned components comprising the individual harvester interfaces may be powered by the battery  115 . Optionally, the components may be powered by the battery manager  410  or the solar or thermal harvester. 
     The MPPT input  510  is electrically connected to and receives input from the solar or thermal harvester and MPPT control  515 . The MPPT input  510  may track to match the input impedance to the maximum harvesting input impedance to achieve the greatest possible power harvest, during moment to moment variations of light level, shading, temperature, and photovoltaic module characteristics based on the input from the MPPT control  515 . 
     The MPPT control  515  is electrically connected to and receives input from the solar or thermal harvester and bandgap reference  500 . The input from the bandgap reference  500  comprises the REF  505 . The MPPT control  515  indicates to the MPPT input  510  whether the operating voltage of the harvesting input has changed in a given direction and to adjust the impedance accordingly. Optionally, the MPPT control  515  may determine the disturbance of the operating voltage of the harvesting input through a logic algorithm utilizing the REF  505  and harvester inputs. The MPPT input  510  is electrically connected to and provides an output to the battery manager  410 . 
     Optionally, the MPPT input  510  may be electrically connected to the charge pump  520 . The charge pump  520  is electrically connected to and receives input from the MPPT input  510  and the charge pump control  525 . The charge pump  520  may be comprised of a capacitive charge pump. Alternatively, the charge pump  520  may be comprised of a step-up converter, boost converter, boost converter, another type of DC-DC converter, or a DC-AC converter coupled to a voltage multiplier. Optionally, the charge pump  520  may be comprised of multiple stages. For example, the charge pump  520  may pump from a voltage as low as 20 mV to over 4 V, using multiple stages to achieve the result. 
     The charge pump control  525  is electrically connected to and receives input from the bandgap reference  500  in the form of REF  505 . Based on the REF  505 , the charge pump control  525  may adjust the oscillator frequency and the number of charge pump stages used by the charge pump  520 , which may be none, one, or multiple stages. 
     In an embodiment where the components of the harvester electronics  120  is powered by the battery  115 , the output from the MPPT input  510  to the battery manager  410  may serve as a bypass in the situation where the battery  115  goes below the harvester electronics  120  operating voltage. If the battery  115  goes below the harvester electronics  120  operating voltage, the components may fail to function. This bypass may allow the battery manager to recover the device with a voltage input that could drive the harvest electronics  120  and charge the battery  115  above the minimum operating voltage. 
     While the embodiment of the invention contemplates the harvester electronics  120  comprised on a single chip, alternate embodiments may comprise each block or a combination of two or more blocks as discrete circuits. 
       FIG. 6  illustrates a block diagram embodiment of the harvester electronics  120  in a single circuit configuration. The thermal harvester  110  is electrically connected to a voltage boost  600 . The voltage boost  600  may be comprised of a capacitive charge pump. Alternatively, the voltage boost  600  may be comprised of a step-up converter, boost converter, boost converter, another type of DC-DC converter, or a DC-AC converter coupled to a voltage multiplier. The voltage boost increases the low voltage input from the thermal harvester. The voltage boost  600  is electrically connected to the charge control  605 . The charge control  605  controls the energy storage for a first battery  610 . The boosted energy from the thermal harvester  110  is used to charge the first battery  610 . The charge control  605  controls the rate of charge and the battery voltage level of the first battery  610 . When the first battery  610  is fully charged, the charge control  605  disconnects the battery to prevent overcharging. 
     The first battery  610  may be comprised of any type of rechargeable battery. One embodiment of the invention contemplates the use of solid state thin film battery may be comprised of lithium-ion polymer, lithium, semiconductor, polymer, or flexible batteries. Optionally, the solid state thin film battery may be discretely or monolithically integrated with the harvester. Optionally, in a separate embodiment, bulk batteries may be used. For example, rechargeable lithium air, nickel-cadmium, or nickel metal-hydride batteries. Optionally, the first battery  610  may be comprised of single or multiple battery cells. 
     The first battery  610  is electrically connected to the power management block  615 . The power management block disconnects the first battery  610  from the output load when the battery when the battery discharge reaches a voltage threshold where further discharge would be harmful to the battery. For example, if the first battery  610  comprises a lithium-ion polymer battery with discharge characteristics similar to the depiction in  FIG. 3 , the power management block  615  will disconnect the battery from the load when the sharp voltage drop occurs. Additionally, the power management  615  is electrically connected to a second battery  620 . The power management block  615  regulates the output voltage of the first battery  610  to charge the second battery  620 . Optionally, the charge control  605  and the power management block  615  may be combined into a single block to regulate the storage and output of the first battery  610 . 
     The second battery  620  may be comprised of any type of rechargeable battery. One embodiment of the invention contemplates the use of a solid state thin film battery comprised of lithium-ion polymer, lithium, semiconductor, polymer, or flexible batteries. Optionally, the solid state thin film battery may be discretely or monolithically integrated with the harvester. Optionally, in a separate embodiment, bulk batteries may be used. For example, rechargeable lithium air, nickel-cadmium, or nickel metal-hydride batteries. Optionally, the second battery  620  may be comprised of single or multiple battery cells. The second battery  620  is electrically connected to and receives solar energy input from the solar harvest regulator  625 . 
     The solar harvest regulator  625  is electrically connected to and receives input from the solar harvester  105 . Optionally, a zener protection diode may be used between the solar harvester  105  and solar harvest regulator  625  to protect the entire circuit. The solar harvest regulator  625  may comprise a mechanism to disconnect the second battery  620  once the battery reaches a full charge to prevent overcharging. Optionally, the solar harvest regulator  625  may be electrically connected to the voltage boost  600  and receives harvested thermal energy. Additionally, the solar harvest regulator  625  may comprise a voltage output regulator to disconnect the output when the battery discharge reaches a voltage threshold where further discharge would be harmful to the battery. Optionally, the solar harvest regulator may comprise a LDO regulator, another type of linear voltage regulator, or a switching regulator to control the output to a load. For example, but not to serve as a limitation, other linear voltage regulators may comprise zener regulators, series regulators, transistor regulators, or regulators comprising an op-amp. Optionally the solar harvest regulator  625  may protect the second battery  620  from unintended discharge when the input is lower than the battery voltage. For example, a zener protection diode may be used as a mechanism, where the voltage of the solar input must match the voltage of the battery plus the zener diode voltage. 
     While the embodiment of the invention contemplates the harvester electronics  120  comprised on a single chip, alternate embodiments may comprise each block or a combination of two or more blocks as discrete circuits. 
       FIG. 7  illustrates an alternate block diagram embodiment of the harvester electronics  120  in a single circuit configuration. The harvester electronics comprises a bandgap reference  700 . The bandgap reference  700  is electrically connected to and powered by the second battery  620 . Optionally, the bandgap reference may be powered separately by the solar harvest regulator  625 , not shown. The bandgap reference  700  provides a temperature independent voltage reference (REF)  705  output. The bandgap reference is electrically connected to the solar harvest regulator  625  and the MPPT control  715  for the thermal and solar harvester inputs and outputs the REF  505  to each of the components. 
     The MPPT input  710  is electrically connected to and receives input from the solar or thermal harvester and MPPT control  715 . The MPPT input  710  may track to match the input impedance to the maximum harvesting input impedance to achieve the greatest possible power harvest, during moment to moment variations of light level, shading, temperature, and photovoltaic module characteristics based on the input from the MPPT control  715 . 
     The MPPT control  715  is electrically connected to and receives input from the solar or thermal harvester and bandgap reference  700 . The input from the bandgap reference  700  comprises the REF  705 . The MPPT control  715  indicates to the MPPT input  710  whether the operating voltage of the harvesting input has changed in a given direction and to adjust the impedance accordingly. Optionally, the MPPT control  715  may determine the disturbance of the operating voltage of the harvesting input through a logic algorithm utilizing the REF  705  and harvester inputs. 
     Optionally, in another embodiment of the invention, a second bandgap reference, not shown, may be connected to the charge control  605  and the first battery  610 . The second bandgap reference is electrically connected to and provides a reference output to the MPPT control  715  connected to the thermal harvester  110 . This embodiment allows for individual MPPT tracking for different sources of harvested energy. 
     While the embodiment of the invention contemplates the harvester electronics  120  comprised on a single chip, alternate embodiments may comprise each block or a combination of two or more blocks as discrete circuits. 
     While the aforementioned embodiments depict harvesting electronics which control the storage of energy and regulate output to a load for solar and thermal harvesters, the harvesting electronics may be configured to receive input from multiple sources of energy harvesting. Examples of other sources may include, but are not limited to, air flow, temperature gradient, movement and transmitted radio frequencies. 
     Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that the particular embodiments shown and described by way of illustration are in no way intended to be considered limiting. Therefore, reference to the details of the preferred embodiments is not intended to limit their scope. 
     The embodiments were chosen and described in order to explain the principles and applications of the invention, thereby allowing others skilled in the art to utilize the invention in its various embodiments and modifications according to the particular purpose contemplated. The scope of the invention is intended to be defined by the claims appended hereto and their equivalents. 
     The expected practical use of the present invention is the novel integrated perpetual energy harvester with energy storage and harvesting electronics. The proposed invention may be used as a one chip solution to store power from multiple sources of energy harvesting and regulate the output to a load.