Abstract:
An energy harvesting system and method. An array of cantilevers with PZT films is electrically connected to an energy harvesting device that converts vibration energy to electrical energy. An AC output signal provided by the cantilevers can be rectified to a DC output, thereby avoiding impairment in total electrical output. The DC output terminals can be connected in parallel and/or in series in order to achieve a higher voltage and/or a higher current that prevents the output from different cantilevers from counteracting one another. The connection circuitry includes one or more rectifying components integrated with one or more micro-cantilevers into a single integrated circuit chip. An oscillograph can be utilized to monitor the DC output voltage signal from an associated testing circuit.

Description:
TECHNICAL FIELD 
   Embodiments are generally related to electrical power harvesting systems and methods. Embodiments are also related to piezoelectric energy harvesting devices. Embodiments are additionally related to connection circuitry for energy harvesting. 
   BACKGROUND OF THE INVENTION 
   Power conservation is an important factor in many electrical systems, such as but not limited to, wireless sensor networks (WSNs) that operate according to low power requirements and low data rates. Long battery life (e.g., up to 10 years) is essential in such systems where line power is not available or if the system is mobile in nature. In many applications, however, utilizing and replacing batteries, even long-lived battery types, is impractical due to factors such as, but not limited to, hard-to-access locations, and labor and replacement battery costs. Accordingly, solutions have been sought for harvesting or extracting electrical power from the environment. 
   Energy harvesting devices can be utilized to collect and convert environmental energy into electric energy for supporting electrical components, devices and/or systems, thereby eliminating the need for batteries. One example of an energy harvesting device or system is a cantilever(s) with Lead-Zirconate-Titanate (PZT) film(s), which can convert vibration energy in an environment into electrical energy. Piezoelectric materials can be utilized as a means for transforming ambient vibrations into electrical energy, which can be stored and used to power other devices. With the recent surge of microscale devices, piezoelectric power generation can provide convenient alternative to traditional power sources used to operate certain types of sensors/actuators, telemetry and MEMS devices. The energy produced by these materials in many cases, however, is much too small to directly power an electrical device. Therefore, the majority of research into power harvesting has focused on techniques for accumulating the energy until a sufficient amount is present, thereby allowing the intended electronics to be powered. 
   One single cantilever can only function in a single frequency and produces a very limited power output. The cantilevers must be connected to a cantilever array to overcome these problems. When the cantilevers are electrically connected directly, however, the AC electrical power from different cantilevers can be counteracted as they have different phases. The connection method thus cannot achieve ideal results. 
   A prior art representation of a connection configuration currently used in electrical connection circuitry of an energy harvesting system  100  is illustrated in  FIG. 1A . The block diagram depicted in  FIG. 1A  shows a capacitor  101  connected in series with one or more other capacitors  107 ,  109  and so forth. A signal can be provided to an AC/DC converter  102  to attain a high voltage output  103 . In the prior art configuration depicted in  FIG. 1A , the output from different cantilevers counteract. 
   Another prior art connection configuration currently utilized in the electrical connection circuitry of an energy harvesting system  100  is illustrated in  FIG. 1B . Note that in  FIGS. 1A-1B , similar or identical parts are generally indicated by identical reference numerals. Thus, a block diagram depicted in  FIG. 1B  illustrates capacitor  101  connected in parallel with capacitors  107 ,  109  and so forth. A signal can be provided to the AC/DC converter  102  to attain a high voltage output  103 . In the configuration of system  100  depicted in  FIG. 1B , the output from different cantilevers can also counteract. 
   Based on the foregoing, it is believed that a need exists for an energy harvesting device that overcomes such problems. It is believed that the system and method disclosed herein provides a solution to these problems by offering a configuration in which a DC output can be attained by rectifying an AC output from a cantilever array and DC output terminals are connected in parallel or in series to achieve a higher voltage or current output such that the output from different cantilevers cannot be counteracted. 
   BRIEF SUMMARY 
   The following summary is provided to facilitate an understanding of some of the innovative features unique to the embodiments disclosed and is not intended to be a full description. A full appreciation of the various aspects of the embodiments can be gained by taking the entire specification, claims, drawings, and abstract as a whole. 
   It is, therefore, one aspect of the present invention to provide for an improved system and method for electrical power harvesting. 
   It is another aspect of the present invention to provide for an improved energy harvesting device incorporating a piezoelectric material. 
   It is a further aspect of the present invention to provide for connection circuitry for integrating rectifying components and micro-cantilevers into a single IC (Integrated Circuit) chip. 
   The aforementioned aspects and other objectives and advantages can now be achieved as described herein. An energy harvesting method and system is disclosed, which includes the use of a waveform generator for generating a signal, and a vibrator for providing mechanical vibrations in order to characterize the performance of an Energy Harvesting (EH) device. The vibrator can be program-controlled by the waveform generator. An accelerator can also be attached to the vibrator, wherein the accelerator measures the vibration strength of mechanical vibrations and an amplitude or velocity of the signal, thereby permitting a clamped component subject to the accelerator and the vibrator to provide converted vibration energy in the form of an AC signal that is rectified to a DC voltage output in order to achieve an electrical energy in the form of a higher voltage or a current output that is harvested and utilized to characterize the electrical functioning of an associated electrical system or device. 
   A power amplifier can also be integrated with the waveform generator to drive the vibrator and regulate vibration strength of the mechanical vibrations. Additionally, an accelerator monitor can be associated with the accelerator, wherein the accelerator monitor delivers a signal strength associated with the signal. The clamped sample or clamped component can be implemented in one embodiment as cantilever array. In another embodiment, the clamped sample may be provided as a cantilever array with nickel mass. A testing circuit can also be provided, which includes a bridge rectifier and a capacitor. The testing circuit detects the electrical energy harvested and is generally utilized to support the electrical functioning of the associated electrical system or device. 
   An oscillograph can also be connected to the testing circuit, wherein the oscillograph monitors a DC output voltage signal generated by the testing circuit. The bridge rectifier associated with the testing circuit generally comprises at least four diodes connected electrically in series with one another. A laser displacement sensor can also be provided for tip displacement testing, wherein the laser displacement sensor is connected to the clamped component. Such a laser displacement sensor can include a laser source and a signal controller in association with the laser source. The laser displacement sensor further includes an optical tuner setup module associated with the laser source and the signal controller; and a data-processing apparatus for data storage and processing. Such a data-processing apparatus is associated with the laser source, the signal controller and the optical tuner setup module. 
   The use of a cantilever array (i.e., clamped component) can overcome issues of frequency and power output encountered with the case of a single cantilever. When the cantilevers are electrically connected directly, the AC electrical power from different cantilever can be counteracted due to their different phases. Instead of electrically connecting the cantilevers of an energy harvesting device directly, the AC output can be rectified to a DC output. The DC output terminals can be connected in parallel or in series to achieve a higher voltage or output current. The connection circuitry, including the rectifying components, can be integrated with one or more micro cantilevers into a single IC chip. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the embodiments and, together with the detailed description, serve to explain the embodiments disclosed herein. 
       FIG. 1A  illustrates a prior art representation of a connection method used in the electrical connection circuitry of an energy harvesting system, which can be implemented in accordance with an alternative embodiment; and 
       FIG. 1B  illustrates another prior art representation of a connection method used in the electrical connection circuitry of an energy harvesting system, which can be implemented in accordance with an alternative embodiment. 
       FIG. 2  illustrates a process flow diagram depicting a method for fabricating a cantilever, in accordance with a preferred embodiment; 
       FIG. 3  illustrates a pictorial view of a SEM of a cantilever micromachined on a PCB (Printed Circuit Board), in accordance with an alternative embodiment; 
       FIG. 4  illustrates a block diagram of an electrical energy harvesting system, which can be implemented in accordance with a preferred embodiment; 
       FIG. 5  illustrates a block diagram indicating the architecture of a power management module, which can be implemented in accordance with an alternative embodiment; 
       FIG. 6  illustrates a schematic view of a circuit diagram of a testing system, which can be implemented in accordance with an alternative embodiment; and 
       FIG. 7  illustrates a block diagram indicating the electrical connection circuitry  700  of an energy harvesting system  400  in which the DC output terminals are connected in series in accordance with a preferred embodiment. 
       FIG. 8  illustrates a block diagram indicating the electrical connection circuitry  700  of an energy harvesting system  400  in which the DC output terminals are connected in parallel in accordance with a preferred embodiment. 
       FIG. 9A  illustrates a block diagram indicating the electrical connection circuitry  800  of an energy harvesting system  400  in which parallel and series connection of the DC output terminals  702 ,  707 ,  705  and  713  can be employed at the same time to improve the voltage and current output connected in parallel and in series in accordance with an alternative embodiment. 
       FIG. 9B  illustrates a block diagram indicating the electrical connection circuitry  800  of an energy harvesting system  400  in which parallel and series connection of the DC output terminals  702  and  707  can be employed at the same time to improve the voltage and current output connected in parallel and in series in accordance with an alternative embodiment. 
       FIG. 10  illustrates a high-level flow chart of operations depicting logical operational steps of a method for electrical power harvesting, which can be implemented in accordance with a preferred embodiment. 
   

   DETAILED DESCRIPTION 
   The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof. 
     FIG. 2  illustrates a process flow diagram depicting a method  200  for fabricating a cantilever, in accordance with a preferred embodiment. A general flow process is depicted in  FIG. 2  with respect to illustrative steps [ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], and [ 6 ]. As indicated at step [ 1 ], a (100) oriented silicon substrate  201  of 500 μm thickness, can be wet-oxidized. Note that the value of 500 μm is merely an illustrative and suggested value only and is not considered a limiting feature of the embodiments. The same is also true for other parameters and values discussed herein. A layer of 2 μm thick silicon oxide  202  serves to improve the adhesion of a functional layer to the silicon substrate  201  surface and can act as a mask during a later-implemented wet etching operation. 
   Thereafter, a Pt/Ti bottom electrode  205 , (e.g., of 30 nm thick Ti and (111) oriented 300 nm thick Pt successively) can be sputtered on the layer of silicon oxide  202 . Next, one or more lead-zirconate-titanate (PZT) films  203  can be deposited according to a sol-gel operations to achieve a crackless PZT film  203  layer. One or more, Ti/Pt top electrodes  204  can then be sputtered upon the PZT film layer  203 . Thereafter, as indicated at step [ 2 ], the silicon substrate  201  with the prepared PZT film layer  203  can be patterned utilizing a standard photolithography technique. 
   As indicated at step [ 3 ], a black-oxide window with align-marks can be created through the use of HF solution etching and front electrodes and the PZT film layer  203  can then be patterned in an orderly manner, by employing reactive ion etching (RIE) and wet etching respectively, through a double-side alignment process. Next, KOH chemical etching can be utilized for bulk silicon substrate  201  micromachining as indicated at step [ 4 ]. In order to prevent the KOH solution from eroding the PZT film layer  203 , a delicate jig can be employed to protect the PZT film layer  203  and the wet etching process can be halted. Thereafter, as depicted at step [ 5 ], a silicon RIE processing operation can then be utilized to release the formed composite cantilever  206 . 
   Next, as indicated at step [ 6 ], a well-chosen nickel mass  207  can be fabricated utilizing, for example, an UV-LIGA SU-8 technique and affixed to the composite cantilever  206  utilizing a glue. Following completion of the wire bonding process, the PZT film layer  203  can be poled by applying, for example, a 160 V/cm DC voltage for five minutes. The resulting cantilevers  206  composed of, for example, Pt/Ti/PZT/Pt/Ti/SiO2/Si/SiO2 multilayered structures, are found to be flat. An arrow  208  indicates a section of cantilever  206  depicted in  FIG. 2  illustrating a dielectric  209 , a Pt/Ti top electrode  204 , the PZT film layer  203 , nickel mass  207  and a silicon base  210 . 
     FIG. 3  illustrates a pictorial view of a screen shot of a view provided an SEM (Scanning Electron Microscope) of a configuration  300  that includes a cantilever  206  micromachined on a PCB  301 , in accordance with an alternative embodiment. Note that an SEM is a type of electron microscope capable of producing high-resolution images of a sample surface. Due to the manner in which the image is created, SEM images have a characteristic three-dimensional appearance and are useful for judging the surface structure of the sample. Note that in  FIGS. 2-8  herein, identical or similar parts or elements are generally indicated by identical reference numerals. As indicated in  FIG. 3 , the composite cantilever  206  can be mounted on the PCB  301 . The cantilever  106  generally contains a nickel mass  207  and a silicon base  210 . The cantilever  206  additionally includes one or more shortened Pt/Ti top electrodes  204  and the PZT film layer  203  discussed earlier. A bonding wire  302  generally ties the cantilever  206  to the PCB  301 . 
     FIG. 4  illustrates a block diagram of an electrical energy harvesting system  400 , which can be implemented in accordance with a preferred embodiment. The electrical energy harvesting system  400  generally includes a vibrator  403 , which can be utilized to supply reliable mechanical vibrations to a clamped sample  406 . The vibrations can be program controlled by an arbitrary waveform generator  401 . Additionally, the electrical energy harvesting system  400  includes a power amplifier  402  that can be incorporated into and associated with the waveform generator  401  to drive the vibrator  403  and regulate vibration strength. The electrical energy harvesting system  400  further includes an accelerator  404  that can be attached to the spindle of the vibrator  403 , such that a resulting vibration strength, an acceleration, an amplitude and/or a velocity can be measured and a signal strength thereof delivered to an accelerator monitor  405 . 
   The electrical energy harvesting system  400  further includes an oscillograph  408  that can be utilized to monitor one or more voltage signals from the clamped sample  406 . For power generation, a testing circuit  407  can also be employed by system  400 , which includes a bridge rectifier  601  circuit and an electrical storage capacitor  602  utilized for harvesting the electrical energy. A common four-germanium-diodes bridge rectifier  601  circuit, with a diode forward bias voltage of, for example, 0.18V at steady state, can be introduced for rectification purposes. A varying resistor (not shown in figure) connected to the power generator  501  can be monitored utilizing the oscillograph  408  in order to measure and calculate the power output. The system  400  can also include the use of a laser displacement sensor  409 , which can be introduced for tip displacement testing. The laser displacement sensor  409  includes a laser source  310 , a signal controller  311 , an optical tunable setup module  312 , and a data-processing apparatus or computer  313  for data storage and processing. 
     FIG. 5  illustrates a block diagram depicting the architecture of a power management module  500 , in accordance with an alternative embodiment. Again, as a reminder, in  FIGS. 2-8  discussed and illustrated herein, identical or similar parts or elements are generally indicated by identical reference numerals. The power management module  500  includes a micro-power generator  501  that is composed of a nickel mass  207  connected to the silicon substrate  201  by the flexure cantilever  206  discussed earlier. When the structure composed of the cantilever  206  and the nickel mass  207  is excited by vibrations, the structure can oscillate within its respective frequency mode shapes. During the movement, the cantilever  206  can be stressed in compression and elongation on the upper and bottom surfaces. The PZT film layer  203  placed on the top of the cantilever  206  can be stressed and by consequence, some electrical energy charges can appear on the surface of the PZT film layer  203 . 
   These charges can be collected by metallic electrodes and transmitted to an energy harvesting circuit  502 . The signal provided by the generator  501  is generally an AC (Alternating Current) signal and the voltage is typically very low. By consequence, some operations of voltage rectification and elevation are required. These operations can be configured with the best efficiency such that the circuit  502  possesses very low power consumption. The energy harvesting circuit  502  can be composed of an AC/DC circuit  503  for rectification, and a DC/DC circuit  504  for elevation of the voltage. The DC/DC circuit  504  can be managed by a digital controller  505 , since it is an active circuit that can adapt depending on the incoming electrical signal to maximize the energy transfer. The output DC voltage can be measured by the oscillograph  408 . Because of the phase differences of each cantilever  206 , the parallel/serial connection impairs the total electrical output before rectification. After rectification, the DC electrical energy can be accumulated. Therefore, voltage increases under a serial connection and the voltage difference is split with respect to a parallel connection thereof. 
     FIG. 6  illustrates a circuit diagram depicting a testing circuit  600 , which can be implemented in accordance with a preferred embodiment. The circuit  600  comprises a bridge rectifier  601 , a capacitor  602  and an oscillograph  408  for measuring the voltage output. The voltage produced by PZT film layer  203  can be first fully wave rectified and then accumulated in a large capacitor  602  such that the DC voltage across the capacitor  602  can be thereafter measured by the oscilloscope  408  described earlier. The simplicity of circuit  600  allows circuit  600  to be constructed very compactly and without additional components, which may result in increased power dissipation. 
     FIG. 7  illustrates a block diagram illustrating the electrical connection circuitry  700  of the energy harvesting system  400  described earlier in accordance with a preferred embodiment. The electrical connection circuitry  700  depicted in  FIG. 7  generally includes one or more DC output terminals  702  and  705 , which can be respectively connected in a series configuration. The DC output terminal  702 , for example, is connected to the AC/DC circuit  503  in order to provide a higher voltage output  703 . The DC output terminal  705  can, for example, be output from the AC/DC circuit  511  to provide the higher voltage output  703 . A capacitor  701  is generally connected to the AC/DC circuit  503 . Similarly, in the configuration depicted in  FIG. 7 , a capacitor  709  is connected to an AC/DC circuit  509 , and a capacitor  711  is connected to an AC/DC circuit  511 , and so forth. The AC output can be rectified firstly to DC output by one or more of the AC/DC circuits  503 ,  509 ,  511  and so forth. The DC output terminals  702  can be connected in series to obtain the higher voltage output  703 . 
     FIG. 8  illustrates a block diagram indicating the electrical connection circuitry  700  of the energy harvesting system  400  in which the DC output terminals  702 ,  705  are connected in a parallel arrangement in accordance with an alternative embodiment. Note that in  FIGS. 7-8 , identical or similar parts or elements are generally indicated by identical reference numerals. The AC output can be rectified firstly to DC output by an AC/DC circuit  503 . The DC output terminals  702  can be connected in parallel to obtain a higher current output  703 . 
     FIG. 9A  illustrates a block diagram indicating the electrical connection circuitry  800  of an energy harvesting system  400  in which parallel and series connection of the DC output terminals  702 ,  707 ,  705  and  713  can be employed at the same time to improve the voltage and current output connected in parallel or in series in accordance with an alternative embodiment. The electrical connection circuitry  800  depicted in  FIG. 9A  generally includes one or more DC output terminals  702 , and  707 , which can be respectively connected in a series configuration. The DC output terminals  702  and  707 , for example, are connected to the AC/DC circuits  503  and  513  in order to provide a higher voltage output  703 . The DC output terminal  705  and  713  can, for example, be output from the AC/DC circuit  511  and  517  to provide the higher voltage output  703 . 
   The capacitors  701  and  715  are generally connected to the AC/DC circuits  503  and  513 . Similarly, in the configuration depicted in  FIG. 9A , capacitors  709 ,  717  are connected to AC/DC circuits  509  and  515 , and capacitors  711 ,  719  are connected to an AC/DC circuits  511  and  517 , and so forth. The AC output can be rectified firstly to DC output by one or more of the AC/DC circuits  503 ,  509 ,  511  and so forth. The DC output terminals  702  can be connected in series to obtain the higher voltage output  703 . Similarly the DC output terminals  707  can be connected in series to obtain the higher voltage  703 . The DC output terminals  702 ,  707 ,  705  and  713  can be connected in parallel to obtain higher current output  703 . Two methods can thus be utilized in single circuit at the same time. 
     FIG. 9B  illustrates a block diagram indicating the electrical connection circuitry  800  of an energy harvesting system  400  in which parallel and series connection of the DC output terminals  702 ,  705 ,  707  and  713  can be employed at the same time to improve the voltage and current output connected in parallel or in series in accordance with an alternative embodiment. A block diagram depicted in  FIG. 9B  includes a capacitor  701  connected in parallel with one or more other capacitors  709 ,  711  and a capacitor  715  connected in parallel with capacitors  717 ,  719  and so forth. The electrical connection circuitry  800  depicted in  FIG. 9B  generally includes one or more DC output terminals  702 ,  705 ,  707 , and  713  which can be respectively connected in a parallel configuration. The AC output can be rectified to DC output by AC/DC circuits  503 ,  513  and so forth. The DC output terminals  702 ,  705 ,  707  and  713  can be connected in parallel to obtain a higher current output  703 .The DC output terminals  702  and  707  can be connected in series to obtain a higher voltage output  703 . Two methods can thus be simultaneously or alternatively utilized in a single circuit. Note that in  FIGS. 7-9B , identical or similar parts or elements are generally indicated by identical reference numerals. 
     FIG. 10  illustrates a flow chart of operations depicting logical operational steps of a method  900  for electrical power harvesting, which can be implemented in accordance with a preferred embodiment. The process begins as depicted at block  901 . Thereafter, as depicted at block  902 , an alternative input signal can be generated by the waveform generator  401 . Next, as indicated at block  903 , the input signal can be amplified and applied to the vibrator  403 . As illustrated next at block  904 , the clamped sample  406  can be excited by vibrations and as a result of this operation, electrical charges are generated. Thereafter, as indicated at block  905 , the electrical charge generated by the piezoelectric layer in the clamped sample  906  can be employed to the testing circuit. The natural frequency and AC output voltage can then be measured by the oscillograph  408  as depicted at block  906 . 
   Next, as depicted at block  907 , maximum power output can be measured by calculating the voltage drop across a load resistor (not shown in figure). Thereafter, the AC voltage signal can be converted to DC voltage utilizing an A/D converter and a full wave rectification operation can be performed as indicated at block  908 . Next, as illustrated at block  909 , the DC voltage after rectification can be measured employing the oscillograph  408 . The DC electricity can be accumulated and measured across a capacitor utilizing the oscillograph  408  as indicated at block  910 . Next, as depicted at block  911 , the tip displacement of the clamped sample  406  can be monitored by employing the laser displacement sensor  409 . The process can then terminate as depicted at block  912 . 
   The invention can be utilized in cases where AC sources have phase-difference problem and can be counteractive when connected. The method finds application with micro-machined beams with PZT films and also macro PZT vibrating devices. 
   It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.