Abstract:
A module includes a flexible support member, a first piezoelectric element, a second piezoelectric element, an energy harvesting circuit, and a circuit element. The energy harvesting circuit includes a first rectifying device, a second rectifying device, a common output, and an energy storage device. The flexible support member includes an insulator having a pattern of wiring traces. The first piezoelectric element, the second piezoelectric element, the first rectifying device, and the second rectifying device are all mounted on and electrically connected to the flexible support member. The first rectifying device is electrically connected to the first piezoelectric element. The second rectifying device is electrically connected to the second piezoelectric element. The first rectifying device is electrically connected to the second rectifying device to provide the common output. The common output is connected for providing electrical energy harvested from at least one from the group consisting of the first piezoelectric element and the second piezoelectric element to the energy storage device. The energy storage device is connected for providing electricity for powering the circuit element.

Description:
RELATED APPLICATIONS AND PRIORITY 
       [0001]    This application claims priority of Provisional Patent Application 60/753,679, filed Dec. 22, 2005 and Provisional Patent Application 60/762,632, filed Jan. 26, 2006, both of which are incorporated herein by reference. 
         [0002]    This application is related to the following commonly assigned patent applications: 
         [0003]    “Energy Harvesting for Wireless Sensor Operation and Data Transmission,” U.S. Pat. No. 7,081,693 to M. Hamel et al., filed Mar. 5, 2003 (“the &#39;693 patent”), docket number 115-008. 
         [0004]    “Shaft Mounted Energy Harvesting for Wireless Sensor Operation and Data Transmission,” U.S. patent application Ser. No. 10/769,642 to S. W. Arms et al., filed Jan. 31, 2004 (“the &#39;642 application”), docket number 115-014. 
         [0005]    “Robotic system for powering and interrogating sensors,” U.S. patent application Ser. No. 10/379,224 to S. W. Arms et al, filed Mar. 5, 2003 (“the &#39;224 application”), docket number 115-004. 
         [0006]    “Miniature Acoustic Stimulating and Sensing System,” U.S. patent application Ser. No. 11/368,731 to J. Robb et al, filed Mar. 6, 2006 (“the &#39;731 application”), docket number 115-028. 
         [0007]    “Energy Harvesting, Wireless Structural Health Monitoring System,” U.S. patent application Ser. No. 11/518,777, to S. W. Arms et al, filed Sep. 11, 2006 (“the &#39;777 application”), docket number 115-030. 
         [0008]    “Structural Damage Detection and Analysis System,” U.S. Provisional Patent Application No. 60/729,166 to M. Hamel, filed Oct. 21, 2005, (“the &#39;166 application”) docket number 115-036. 
         [0009]    “Sensor Powered Event Logger,” U.S. Provisional Patent Application No. 60/753,481 to D. L. Churchill et al, filed Dec. 22, 2005, (“the &#39;481 application”) docket number 115-034. 
         [0010]    “Strain Gauge with Moisture Barrier and Self-Testing Circuit,” U.S. patent application Ser. No. 11/091,244 to S. W. Arms et al, filed Mar. 28, 2005, (“the &#39;244 application”) docket number 115-017. 
         [0011]    All of the above listed patents and patent applications are incorporated herein by reference. 
     
    
       [0012]    This invention was made with Government support under contract number N6833506C0218, awarded by the US Department of the Navy. The Government has certain rights in the invention. 
     
    
     FIELD 
       [0013]    This patent application generally relates to a system for integrating a piezoelectric composite and support devices. 
       BACKGROUND 
       [0014]    Piezoelectric elements are used as sensors, actuators, and energy harvesting devices. Vibration or strain in a workpiece can be sensed from the electricity the piezoelectric element produces. That electricity can also be harvested to provide power for such things as charging a capacitor, recharging a battery, powering an electronic circuit, logging data from a sensor, or transmitting that data. 
         [0015]    Alternatively, electricity from an external source can be provided to the piezoelectric element causing it to strain or vibrate. If mounted on a substrate this strain or vibration can be transferred to the substrate. The external source can include a power supply and function generator. A pulse of electricity having a particular amplitude variation or that includes a particular set of frequencies can be provided from the function generator to the piezoelectric element to impart a desired vibration to the substrate. 
         [0016]    Thus, piezoelectric elements have been combined with support circuits including signal conditioning, energy harvesting, and signal generator circuits. Each of these support circuits includes a variety of electronic components, such as capacitors, resistors, inductors, transistors, memories, integrated circuits, batteries, transmitters, and the like. These components have typically been mounted and wired together on a printed circuit board. The piezoelectric elements and the printed circuit board have been separately mounted on the substrate and wiring provided there between. 
         [0017]    Commercially available piezoelectric composites have been constructed from a piezoelectric element composed of an array of parallel fibers of a piezoelectric material. The piezoelectric element has been sandwiched between two sheets of metalized polyimide, as described in U.S. Pat. No. 6,629,341 to Wilkie, et al. (“the &#39;341 patent”), incorporated herein by reference. One of the sheets of polyimide has a pair of metal pads on a top surface in electrical contact with metalization layers on inner surfaces of the polyimide sheets contacting each surface of the piezoelectric element. Wiring has been connected to the pair of contact pads extending to the printed circuit board carrying the support circuits. 
         [0018]    Providing piezoelectric composites and circuit boards with support circuits, mounting them on a substrate, and connecting the piezoelectric composites to their support circuits has posed difficulties, and a system has not yet been optimized for this purpose. Thus, an improved system is needed, and this system is provided in the present patent application. 
       SUMMARY 
       [0019]    One aspect of the present patent application is a module including a flexible support member, a first piezoelectric element, a second piezoelectric element, an energy harvesting circuit, and a circuit element. The energy harvesting circuit includes a first rectifying device, a second rectifying device, a common output, and an energy storage device. The flexible support member includes an insulator having a pattern of wiring traces. The first piezoelectric element, the second piezoelectric element, the first rectifying device, and the second rectifying device are all mounted on and electrically connected to the flexible support member. The first rectifying device is electrically connected to the first piezoelectric element. The second rectifying device is electrically connected to the second piezoelectric element. The first rectifying device is electrically connected to the second rectifying device to provide the common output. The common output is connected for providing electrical energy harvested from at least one from the group consisting of the first piezoelectric element and the second piezoelectric element to the energy storage device. The energy storage device is connected for providing electricity for powering the circuit element. 
         [0020]    Another aspect of the present patent application is a smart system that includes a structure, an energy harvesting circuit, a first insulating layer, and a circuit element. The energy harvesting circuit includes a first piezoelectric element and an energy storage device. The first insulating layer includes a pattern of wiring traces. The first insulating layer is mounted on the first piezoelectric element. The first piezoelectric element is electrically connected to the first insulating layer. The first piezoelectric element is mounted to the structure to receive mechanical energy from the structure and convert the mechanical energy into electrical energy. The first piezoelectric element is electrically connected for providing the electrical energy to the energy storage device. And the energy storage device is connected for providing electricity for powering the circuit element. 
         [0021]    Another aspect of the present patent application is a method of fabricating a module, comprising providing a flexible support member, a first piezoelectric element, a second piezoelectric element, a first rectifying device, a second rectifying device, and a common output. The method includes mounting the first piezoelectric element, the second piezoelectric element, the first rectifying device, and the second rectifying device on the flexible support member. The flexible support member includes an insulator having a pattern of wiring traces. The method includes electrically connecting the first rectifying device to the first piezoelectric element, electrically connecting the second rectifying device to the second piezoelectric element, and electrically connecting the first rectifying device to the second rectifying device to provide the common output. 
         [0022]    Another aspect of the present patent application is a module that includes a first piezoelectric element, an energy harvesting circuit, and a circuit element. The piezoelectric element provides physical support for the energy harvesting circuit. The energy harvesting circuit includes an energy storage device. The piezoelectric element converts mechanical energy into electrical energy and is connected to provide the electrical energy to the energy storage device for powering the circuit element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The foregoing will be apparent from the following detailed description as illustrated in the accompanying drawings, for clarity not drawn to scale, in which: 
           [0024]      FIG. 1   a  is a three dimensional view of one embodiment of piezoelectric composites with an integrated diode bridge connected to an energy harvesting, processing and sensing module; 
           [0025]      FIG. 1   b  is a cross sectional view of one of the piezoelectric composites of  FIG. 1   a  with an insulating layer having metalization on both sides and vias there between, and showing the diode bridge mounted on a top surface; 
           [0026]      FIG. 2  is a three dimensional view of another embodiment of a large piezoelectric composite with smaller regions each having an integrated diode bridge, and in which all the diode bridges are connected in parallel to common electrodes and support circuitry; 
           [0027]      FIGS. 3   a  and  3   b  are block diagrams showing components that may be integrated on the piezoelectric composites of the various embodiments or that may be connected thereto; 
           [0028]      FIG. 4  is a cross sectional view of another embodiment including a flex layer bonded to a standard piezoelectric composite with support circuits mounted on the flex layer; 
           [0029]      FIG. 5  is a cross sectional view of a stacked embodiment in which a standard piezoelectric composite is bonded to both sides of the flex layer of  FIG. 4  and support circuits are mounted on a portion of the flex layer that extends beyond the standard piezoelectric composites; 
           [0030]      FIG. 6   a  is a cross sectional view of a large stack of the two layer stacks of  FIG. 5  with support circuits mounted to a flex layer that extends on a top surface of the large stack; 
           [0031]      FIG. 6   b  is a cross sectional view of another embodiment of a large stack including flexes for each piezoelectric composite and in which the flexes are interconnected to each other and to support circuits; 
           [0032]      FIG. 6   c  is a cross sectional view and  FIG. 6   c ′ is a top view of another embodiment of a large stack in which an insulating layer of each piezoelectric composite extends beyond its piezoelectric element and metalization extending on each of these insulating layers are interconnected to each other and to support circuits; 
           [0033]      FIG. 7   a  is a cross sectional view of another embodiment of the piezoelectric composite of  FIG. 1   a ,  1   b  having one of its insulating layers including a strain gauge and support circuits; 
           [0034]      FIG. 7   b  is a cross sectional view of another embodiment including a flex bonded to a standard piezoelectric composite in which a strain gauge and support circuits are mounted on the flex; and 
           [0035]      FIG. 8  is a three dimensional view of a leaf spring with the integrated piezoelectric composite mounted thereto; 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    In one embodiment electrical traces and contact pads for support circuits are formed on the same insulator layer and using the same photolithographic process presently used just to provide the two piezoelectric contact pads. Electronic components are mounted to the support circuit contact pads so formed on this insulator. Thus, contact pads and wiring traces for support circuits are integrated in the manufacture of the piezoelectric composites. In this scheme the piezoelectric composite and its insulator become the carrier for the support circuits. The separate printed circuit board and the wiring connecting the piezoelectric composite with the printed circuit board are eliminated. 
         [0037]    In another embodiment, a flex is provided and mounted on a standard piezoelectric composite that has the standard pair of contact pads. Flex is a free standing layer of an insulator, such as polyimide, that has conductive traces and pads patterned on one or both sides with vias there between. Flex can be multilayered with vias providing electrical connection from one layer to the next. In this embodiment, pads and wiring traces are provided on the flex for mounting support circuits. This embodiment avoids redesign of metalization on the piezoelectric composite itself. 
         [0038]    In the first embodiment, integrated piezoelectric composite  18  has area of insulator  20   a  that has normally been used just for a pair of piezoelectric contact pads enlarged so it can also be used for support circuits, such as diode bridge  22  including diodes  22 ′, as shown in  FIGS. 1   a ,  1   b.    
         [0039]    Electrical pads  24 , for mounting components and making external contact, traces  25 , for interconnecting components, and vias  26 , for connecting between metalization layers on both sides of insulator  20   a , are formed by photolithography during manufacture of piezoelectric composite  18 . Electrodes  27   a ,  27   b  are formed on insulators  20   a ,  20   b  and mounted to piezoelectric fibers  28  of integrated piezoelectric composite  18 , as described in the &#39;341 patent. Electronic components, such as diodes  22 ′, are then soldered, wire bonded, or conductive epoxy bonded to electrical pads  24 . 
         [0040]    Several such integrated piezoelectric composites  18  can be mounted to substrate  29 , as shown in  FIG. 1   a . Diode bridges  22  are integrated on insulator  20   a  on each integrated piezoelectric composite  18 . Outputs of each diode bridge  22  are connected to wires  31  extending to single energy harvesting, processing, and sensing module  32  which is further illustrated in  FIGS. 3   a ,  3   b.    
         [0041]    In another embodiment, single large area layer of piezoelectric fiber material  33  is electrically segregated into smaller areas  33 ′, each of which has its own electrodes  27   a ′,  27   b ′ connected to its own smaller area  33 ′ of single large area layer of piezoelectric fiber material  33 , as shown in  FIG. 2 . Electrodes  27   a ′,  27   b ′ are also connected to individual rectifier bridges  35  mounted on insulator  20   a ′ for each small area  33 ′. Under conditions where single large area layer of piezoelectric fiber material  33  is exposed to a varying strain field this arrangement is advantageous, as current generated in a high strain region would be blocked by rectifier bridges  35  from being dissipated in a lower strain region, thereby increasing the electrical output of single large area layer of piezoelectric fiber material  33  as a whole. 
         [0042]    The outputs of all rectifier bridges  35  on large area layer of piezoelectric fiber material  33  can be connected to traces  38   a ,  38   b , delivered to pads  40   a ,  40   b  and to storage capacitor  42 , which may also be located on insulator  20   a ′. Integrating rectifier bridge  35  on insulator  20   a ′ for each smaller area  33 ′ provides a way to easily implement a large number of such rectifier bridges  35  for different regions of large area layer of piezoelectric fiber material  33  without the need to provide a large number of pairs of external wires. 
         [0043]    Wire crossings that may be needed for this arrangement can be provided on insulator  20   a ,  20   a ′, as shown in  FIG. 1   a ,  1   b  and in  FIG. 2 . Two-sided metalization on insulator  20   a ,  20   a ′ and via  44  there between provides a way for trace  25  to cross under trace  46 , as shown in  FIG. 1   b.    
         [0044]    Energy harvesting circuit  50 , sensor  52   a , signal conditioning circuit  54 , transmitter  56 , and a signal generator circuit (not shown) could also be mounted on insulator  20   a  of  FIGS. 1   a ,  1   b  or insulator  20   a ′ of  FIG. 2 , as shown in  FIG. 3   a . Signal conditioning circuit  54  can include an A/D converter and a microprocessor. Energy harvesting circuit  50  can include a control switch, such as the nanoamp comparator described in the &#39;693 patent, an energy storage device, and a voltage converter, such as a buck converter, to convert raw output of integrated piezoelectric composite  18  from a high voltage and a high impedance to a low voltage and low impedance. The energy storage device can include a capacitor and a battery, such as a thin film battery. Larger energy storage devices (not shown) can also be mounted separately from integrated piezoelectric composite  18  and connected to pads on integrated piezoelectric composite  18  with wires. Certain elements, such as sensor  52   b  can be located off insulator  20   a . Wiring can be provided for connection there between, as shown in  FIG. 3   b . Sensor  52   a ,  52   b  can be a strain sensor mounted directly to substrate  29 . As shown in  FIGS. 3   a  and  3   b , conditioning power is provided from energy harvester and storage  50  to power elements such as signal conditioner, processor, and memory  54 . As described in the &#39;642 application, all power for communications interface  56  can be provided by energy harvesting and storage  50  as well. 
         [0045]    In another embodiment, standard off the shelf piezoelectric composites can be used. Additional circuit elements  70  are mounted to their own flex  72  that is mounted to make contact with standard contact pads  74  of standard piezoelectric composite  76 , as shown in  FIG. 4 . Flex  72  may be adhesively attached to standard piezoelectric composite  76 . Flex  72  includes all the pads  78  and interconnect wiring  80  for additional circuit elements  70 , such as diode bridge  82  and integrated circuit  84 . 
         [0046]    Providing additional layer of flex  90  also advantageously facilitates stacking of standard piezoelectric composites  76   a ,  76   b , as shown in  FIG. 5  for improving the amount of energy harvested in an available area of substrate  29 . Wiring traces  92  and pads  94  are provided on both surfaces  96   a ,  96   b  of flex  90 . Metal studs  98   a ,  98   b  are provided through flex  90  to provide contact between support circuits  100  and to provide ground connection between stacked standard piezoelectric composites  76   a ,  76   b . This arrangement retains the advantages of reduced cost and simplified mounting to substrate  29  while providing integration of support circuits  100  on stacked piezeoelectrics  102 . Adhesive layers  103  are provided connecting bottom insulator to substrate  29  and connecting between flex  90  and standard piezoelectric composites  76   a ,  76   b.    
         [0047]    With standard piezoelectric composites  76   a ,  76   b  and flex  90  having thicknesses on the order of mils (0.025 mm), energy from vibration of substrate  29  is transmitted throughout stacked piezoelectrics  102  and harvested by support circuits  100  on one or both sides of flex  90  that are connected to both standard piezoelectric composites  76   a ,  76   b . Support circuits  100  can include diode bridges. Support circuits  100  can also include components, such as an energy harvesting circuit, a capacitor, a battery, a sensor, a signal conditioning circuit, a processor, a transmitter, a receiver, and a transceiver, as shown in  FIG. 3   a . Only one such support circuit  100  may be required on one side of flex  90  for stacked standard piezoelectric composites  76   a ,  76   b  to serve both standard piezoelectric composites  76   a ,  76   b . Since both standard piezoelectric composites  76   a ,  76   b  in stack  102  experience approximately the same level of strain and generate about the same amount of electricity at about the same time, separate diode bridges for each piezoelectric composite  76   a ,  76   b  may not be needed. 
         [0048]    Because piezoelectric composite  76   a  is oppositely oriented compared to piezoelectric composite  76   b  in  FIG. 5 , these two piezoelectric composites  76   a ,  76   b  may generate electricity oppositely phased. Opposite output pads can be connected or outputs can be combined after rectifier bridge  22  to avoid output of one interfering with the other. 
         [0049]    Stacked piezoelectrics  102  can themselves be stacked to provide large stack  104  that includes more energy harvesting layers on the same area of substrate  29 , as shown in  FIG. 6   a . In one embodiment, stacked piezoelectrics  102 , each including a pair of standard piezoelectric composites  76   a ,  76   b  mounted on opposite sides of flex  90 , as shown in  FIG. 5 , are stacked on each other with adhesive  103  as shown in  FIG. 6   a . In this case flex  90  between each pair of the stacked piezolectrics  102  extends sufficiently beyond standard piezoelectric composites  76   a ,  76   b  so pads  106  on each flex  90  can be connected with solder or conductive epoxy connectors  108 . Since standard piezoelectric composites  76   a ,  76   b  in large stack  104  are all mounted on the same area of substrate  29  they are all expected to experience approximately the same level of strain and generate about the same amount of electricity at about the same time, so separate diode bridges for each standard piezoelectric composite  76   a ,  76   b  in larger stack  104  may not be needed. Alternatively, if desired, diode bridges  110  for each standard piezoelectric composite  76   a ,  76   b  in larger stack  104  can be provided, along with other support circuitry, on top surface  111  of flex  112  on large stack  104 . In this case a pair of wires extending from each standard piezoelectric composite  76   a ,  76   b  to flex  112  can be provided extending to diode bridge  110  for that particular standard piezoelectric composite  76  on flex  112 . 
         [0050]    Alternatively, a stack of standard piezoelectric composites  76   a ,  76   b  each with its own flex  113  bonded and similarly interconnected can also be provided, as shown in  FIG. 6   b.    
         [0051]    Integrated piezoelectric stack  114  of individual layers  115  can be mounted on substrate  29 , each individual layer  115  including integrated insulator  116  that extends beyond piezoelectric element  117  to provide connection from each electrode  118  through each overlying integrated insulator  116  to a diode bridge  119  on top insulator  120 , as shown in  FIG. 6   c ,  6   c ′. Electrodes  118  of each layer  115  can have a separate path to top insulator  120  where a separate diode bridge is provided for each pair of electrodes. Alternatively, positive electrodes and negative electrodes of each layer  115  can be joined in common and connected to a single diode bridge on top surface  120 . 
         [0052]    In another embodiment, piezoelectric composite  121  can be integrated with a sensor, such as strain gauge  122 , and support circuit  123  to provide integrated sensor and piezoelectric energy harvester  124 , as shown in  FIG. 7   a . In one approach, strain gauge  122  is adhesively mounted to lower surface  125  of lower insulator  20   b ″, and both are then adhesively mounted to substrate  29 . Insulator  20   b ″ can include portion  126  that extends beyond piezoelectric element  127 . Portion  126  of insulator  20   b ″ includes pad  128  on its lower surface  125  and via  129  that provides contact between pad  128  and pad  130  on its upper surface  131 . Pad  132  of strain gauge  122  is aligned with pad  128  on lower surface  125  of insulator  20   b ″ and connected with solder or conductive epoxy  133 . Upper surface  131  of portion  126  provides contact pads for the two electrodes of piezoelectric composite  121  and is also a carrier for diode bridge  132  and for other support circuitry, such as support circuit  123 . 
         [0053]    In another approach, pad  138  on top surface  140  of flex  142  contacts pad  144  of standard piezoelectric composite  76 , as shown in  FIG. 7   b . Bottom surface  146  of flex  142  includes piezoresistive strain gauge  148  and adhesive layer  150  for mounting to substrate  29 . Top surface  140  of flex  142  provides contact to the two electrodes of standard piezoelectric composite  76  and is also a carrier for additional support circuitry, such as diode bridge  152  and support circuit  154  for strain gauge  148 . 
         [0054]    Strain gauges  122  and  148  can have two pads. They can also include two gauges perpendicular to each other with a shared pad, as shown in  FIGS. 7   a ,  7   b . They can be rosettes which can have 3 strain gauges, each with two pads, angled to one another to obtain strain information from different directions. 
         [0055]    An integrated piezoelectric composite and support circuit of one of the embodiments of the present patent application could be provided on a ship bulkhead or on a vibrating machine to generate electricity from vibration of the ship or the machine as described in US publication patent application number 20050146220. It can also be provided on structures subject to impact, such as landing gear, to generate electricity from the impact of landing. It can also be provided on a weapon to generate electricity from the impact of firing the weapon. It can also be provided on a rotating part, such as a helicopter rotor blades or to a part, such as a helicopter pitch link to generate electricity from strains or vibration induced in those parts. It can also be provided on suspension systems, such as on a truck&#39;s composite leaf springs to generate electricity from strains from flexing of the spring. It can also be provided as part of an energy harvesting system within a car tire to generate electricity from flexing of the tire as it rotates, as described in US publication patent application number 20050146220. Many other components on vehicles and structures, such as fixed and rotary wing aircraft, trucks, tanks, earth moving machines, mining machines, buildings, bridges, pipes, and wind turbines could be instrumented with an integrated piezoelectric composite and support circuit of this patent application, providing a smart, energy harvesting sensor and/or actuating component. 
         [0056]    Structures with integrated piezoelectric composites and support circuits that harvest energy, provide and analyze sensor data, and transmit data would be able to provide health management functions, including embedded test &amp; evaluation (ET &amp;E), health usage monitoring (HUMS), and structural health monitoring (SHM). The use of the piezoelectric composite as an actuator to provide signals to the component adds further test and evaluation capability, as described in the &#39;731 application. This smart component could compute its usage profile and estimate remaining life span without the need for a battery maintenance schedule. Each smart component could include a unique identification code, such as the 92 bit electronic product code which would allow its usage data to be recorded in a data base that would allow for improved condition based maintenance of each component and of the equipment that includes each component. 
         [0057]    Use of integrated piezoelectric composites and support circuits on a leaf spring is shown in  FIG. 8  as an illustrative example. In addition to piezoelectric composite  160  and piezoresistive strain gauge  162 , support circuit  164  is integrated on piezoelectric energy harvesting element  160  includes rectifier bridges serving different portions of piezoelectric energy harvesting element  160 , a storage capacitor, microprocessor, signal conditioning circuit, RF transceiver, RF antenna  166  and battery  167 . Support circuit  164  can also include a signal generator to provide signal to leaf spring  168  for crack detection, as described in the commonly assigned 115-028 patent application, incorporated herein by reference. Insulation, electromagnetic interference shielding, a protective overcoat, and encapsulation (not shown for clarity) are also provided. 
         [0058]    Negative effect of non-uniform strains in leaf spring  168  are mitigated by segmenting piezoelectric composite  160  into portions, each with its own rectifier bridge, and by integrating these rectifiers on insulator of piezoelectric composite  160 , as described herein above. By also integrating other support circuit elements, shown on flex  170 , on piezoelectric composite  160  further advantage in cost reduction, size, and ease of assembly on a structure are obtained. 
         [0059]    In addition to processing data for fatigue analysis, the strain data from strain gauge  160  on leaf springs  168  located near all four corners can be used to determine the operating loads borne by the leaf spring and by the vehicle. Knowledge of the operating loads can be used to classify and analyze vehicle operations and vehicle operating regimes. The amount of time that a vehicle is used in various operating regimes can be logged in a non-volatile memory by the on board embedded processors located permanently on the vehicle&#39;s structural elements. The method of classifying operation of a structure on a vehicle, the time spent in that operation, calculating fatigue of the structure from strain gauges bonded to that structure, and transmitting the data, is described in the &#39;777 application. The classification can distinguish rough or smooth road conditions, for example and the time spent on each. This information is useful to the owners and operators of the vehicles in order to facilitate condition based maintenance of the structure monitored and adjacent vehicle components since accumulated damage estimation is facilitated by a historic knowledge of a vehicle&#39;s particular operating regimes. This historic record could be sent to a remote location in real time via cellular telephone or satellite uplink to allow the owners of the vehicle to better maintain various components or to take action to prevent conditions that could lead to early failure. 
         [0060]    In addition, the loads borne by suspension elements may be useful to aid in balancing the weight carried by the vehicle and to estimate the weight of the material carried by the vehicle. The smart composite leaf springs as described in this patent application could provide an output estimate of the vertical static load borne by the springs by using strain data combined with a calibration record. The calibration record could be stored in the embedded processor&#39;s non volatile memory. For a given strain reading, the processor can relate that strain reading to a corresponding load. This relationship could be linear or non linear, and may include temperature compensation routines, and may use look up methods, or direct computational means. Calibration can be accomplished by providing known loads to the vehicle and recording the response from the known loads in the strain gauges and creating a data file of known loads vs. response. Alternatively, load vs. strain response data can be provided for each instrumented leaf spring or other structural component, such as a helicopter pitch link, from measurements at the factory. 
         [0061]    With smart leaf springs located near each supporting corner of a wheeled vehicle, the sum of loads provided from each corner could be used to estimate the payload carried by the vehicle and its center of gravity location relative to the vehicle&#39;s four leaf spring locations. The weight of the load can be determined from the sum of the strain responses at each corner. The weight can be determined from a table that provides a relationship between the measured total strain and the known loads applied. If the strains measured at the four corners varies significantly then this would indicate an unbalanced load, and corrective action could be taken to prevent excess wear and tear on the suspension element subject to the greatest load. 
         [0062]    Furthermore, should the vehicle be operated in a manner which may place the vehicle&#39;s structure, components, or its operators at risk, the embedded monitoring system could provide a warning in real time to a display in clear view of the operator. Alternatively, this warning could be sent to a remote location via cellular telephone or satellite uplink. 
         [0063]    Layers of encapsulation, shielding, and a protective cover can be provided for the integrated piezoelectric composite and support circuit, as described in the &#39;244 application. 
         [0064]    While the disclosed methods and systems have been shown and described in connection with illustrated embodiments, various changes may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.