Nano-energetic applications for aircraft

A non-destructive examination (NDE) system for use on a structural element comprises nano-energetic actuators configured for creating a controlled combustion in response to thermal energy, thereby inducing vibrations in a surface of the structural element. The NDE system further comprises sensors configured for measuring the vibrations induced in the surface of the structural element and generating vibration data. An applique comprises a planar substrate, nano-energetic actuators affixed to the planar substrate, each configured for creating controlled combustions in response to thermal energy, and an adhesive affixed to the planar substrate, such that the applique can be adhered to a structural element. A means of transportation having an accumulation of ice comprises a structural element, and nano-energetic actuators, each configured for creating a controlled combustion in response to thermal energy, thereby inducing vibrations in a surface of the structural element great enough to generate cracks in the ice.

FIELD

The present disclosure generally relates to techniques for monitoring and/or facilitating the safety of vehicles, and more particularly, to non-destructive examination (NDE) and de-icing techniques used on structural bodies, such as those found in aircraft.

BACKGROUND

Currently, inspection for damage or deterioration to structural bodies (e.g., aircraft composite structures) due to fatigue or impacts must be performed on a fixed schedule. These inspections are done to assess the integrity of the structure in question. Each inspection is time-consuming and is costly, not only in terms of time and skill needed to perform a thorough job, but also in terms of lost revenue from the structural bodies (e.g., aircraft) being out-of-service. Inspection of structural bodies is typically performed using what is referred to as “Non-Destructive Evaluation (NDE),” which requires careful location of multiple transducers (both actuating and sensing) on the structural body to provide for a fairly high energy path during transducer-to-transducer energy transfer.

In the case of aircraft, an automated on-board system may be designed to perform NDE, thereby eliminating the cost of potentially lost revenue from out-of-service aircraft, except when significant damage has actually occurred. In addition, because the damage has been located and/or characterized (e.g., determination of damage size, depth, etc.), repairs can be performed more quickly by using appropriate repair kits. Such an on-board system may include actuators and sensors in the form of transducers that are typically large, expensive, and require individual wiring. In certain applications, the additional weight of the wiring and/or the transducers may be prohibitive, especially for aircraft. Conventional wiring is also very heavy and requires a large amount of manual labor to install. In addition, the cost of a large number of transducers applied over a large area may be prohibitive. Another drawback to the use of large known transducers is that the signal-to-noise ratio for the long paths between the actuators and sensor is much lower than that of shorter paths. Long paths make it difficult to localize and determine the shape of a damage site.

To address these concerns, a lightweight scalable transducer system that allows the assessment of the integrity of a structural body in real-time or near real-time has been developed, as described in U.S. Pat. No. 8,447,530, which is expressly incorporated herein by reference. This lightweight scalable transducer system uses actuators, e.g., in the form of relatively inexpensive piezoelectric transducers (PZTs). The advent of direct write electronics and other additive manufacturing processes make the approach described in U.S. Pat. No. 8,447,530 more economically viable and brings possibilities of Active Damage Interrogation (ADI) during flight or ground operations. However, even with direct write of the transducers and electronics, this requires the part surface to be available for application of the wiring and materials and is best suited for investment in this at the time of manufacture of the structure.

Furthermore, it is desirable to maximize the sensitivity of an NDE system to damage or degradation of a structure by generating as much energy from the actuators in an NDE system as possible in order to provide a “clean” signal that will traverse all discontinuities in the structure. The use of relatively small and inexpensive PZT actuators in an NDE system may be fine up to a point, but these PZT actuators might not always generate enough energy to provide the desired signals. The relatively low energy signals may be integrated over time; however, this technique may extend the time to interrogate the structure longer than desired. In some scenarios, such as when the aircraft is on the ground, the structure may be hit with a rubber mallet in order to generate a relatively high energy signal that can then be sensed by the sensors of the NDE system. However, this technique cannot be performed in-flight, and cannot be routinely performed at inaccessible locations of the structure without disassembling the structure.

There, thus, remains a need for a relatively inexpensive, light-weight, and high energy transducer for use in an NDE system for monitoring of damage or deterioration in structures, such as aircraft structures.

Another issue that arises in the context of airplane flight is the accumulation of ice on leading edges of the wings and flight control surfaces, which may ultimately lead to loss of control or insufficient lift to keep the aircraft airborne, as well as the accumulation of ice on sensors, transducers, and probes, which may lead to erroneous data readings, and therefore, a potentially deleterious effect on the functioning of the aircraft. Electric deicing heaters, may be used to melt, and therefore prevent dangerous build up, of ice, on the critical components exposed to the external environment. However, this may take an extended period of time, causing scheduling delays in flights, especially if the ice is relatively thick.

There, thus, remains a need for a more efficient means to remove ice from aircraft.

SUMMARY

In accordance with one aspect of the present inventions, a non-destructive examination (NDE) system for use on a structural element comprises is provided. The NDE system comprise at least one nano-energetic actuator, each configured for creating a controlled combustion in response to thermal energy, thereby inducing vibrations in a surface of the structural element. The NDE system may optionally comprises at least one ignition element configured for generating the thermal energy in response to at least one electrical pulse, and at least one energy source configured for generating at least one electrical pulse. In one embodiment, each of the nano-energetic actuator(s) comprises copper oxide, and each of the ignition element(s) comprises platinum. Each of the nano-energetic actuator(s) may comprise nano-energetic material having a particle size less than 100 nanometers, and may have a size in the range of 1 micrometer to four millimeters.

The NDE system further comprises at least one sensor configured for measuring the vibrations induced in the surface of the structural element and generating vibration data. In one embodiment, the NDE system further comprises a data collection device configured for collecting and storing the vibration data, and at least one processor configured for determining a condition of the structural element based on the collected and stored vibration data. If multiple nano-energetic actuators are provided, the NDE system may further comprise a processor programmed to control delivery of a plurality of electrical pulses from the at least one electrical source to cause the plurality of nano-energetic actuators to generate a plurality of controlled combustions in a time-phased manner. The NDE system optionally comprises at least one electro-mechanical transducer, each configured for vibrating in response to at least one electrical pulse, thereby inducing vibrations in the surface of the structural element.

In accordance with a second aspect of the present inventions, a means of transportation is provided. The means of transportation comprises a structural element (e.g., a bridge, railroad, or vehicular structural element, such as the structural element of an aircraft).

In accordance with a third aspect of the present inventions, a method of performing a non-destructive examination (NDE) on a structural element (e.g., a bridge, railroad, or vehicular structural element, such as the structural element of an aircraft) is provided. The method comprises applying at least one controlled combustion to the structural element, thereby inducing vibrations in the structural element. In one method, the controlled combustion(s) does not damage the structural element. If the structural element is a structural element of an aircraft, the controlled combustion(s) can be applied to the aircraft structural element in-flight. In one method, a plurality of controlled combustions is applied to the structural element in a time-phased manner to preferentially induce the vibrations along a particular direction in the structural element.

The method further comprises measuring the vibrations induced in the surface of the structural element, generating vibration data corresponding the measured vibrations, collecting and storing the vibration data, and determining a condition of the structural element based on the collected and stored vibration data.

In accordance with a fourth aspect of the present inventions, an applique comprises a planar substrate (e.g., one composed of a polymeric material, metallic foil, a metalized polymeric material, or a multilayer substrate of polymeric and metallic films), and a plurality of nano-energetic actuators affixed to the planar substrate, each configured for creating a plurality of controlled combustions in response to thermal energy. Each of the nano-energetic actuators may comprise nano-energetic material (e.g., copper oxide) having, e.g., a particle size less than one hundred nanometers, and may have a size, e.g., in the range of one micrometer to four millimeters.

The applique further comprises an adhesive affixed to the planar substrate, such that the applique can be adhered to a structural element. The applique may optionally comprise a plurality of ignition elements (e.g., platinum), at least one inductive coil, and a plurality of electrically conductive interconnections affixed to the planar substrate. The ignition elements are thermally coupled to the nano-energetic actuators, and the electrically conductive connections electrically couple the inductive coil(s) to the ignition elements.

In one embodiment, the applique further comprises a plurality of sensors, at least one data collection device, and at least one processor affixed to the planar substrate. The sensors are configured for measuring vibrations induced in the surface of the structural element by the plurality of controlled combustions, and generating vibration data, the data collection device(s) is configured for collecting and storing the vibration data, and the processor(s) is programmed to control delivery of a plurality of electrical pulses from an electrical source to the plurality of ignition elements to cause the plurality of nano-energetic actuators to generate the plurality of controlled combustions in a time-phased manner.

In accordance with a fifth aspect of the present invention, a method of manufacturing an applique is provided. The method comprises providing a planar substrate (e.g., one composed of a polymeric material, metallic foil, a metalized polymeric material, or a multilayer substrate of polymeric and metallic films). The method further comprises depositing a plurality of nano-energetic actuators on the planar substrate, each configured for creating a plurality of controlled combustions in response to thermal energy. Each of the nano-energetic actuators may comprise nano-energetic material (e.g., copper oxide) having, e.g., a particle size less than one hundred nanometers, and may have a size, e.g., in the range of one micrometer to four millimeters. The method further comprises affixing an adhesive to the planar substrate, such that the applique can be adhered to a structural element.

One method further comprises depositing a plurality of ignition elements (e.g., platinum) on the planar substrate, such that the plurality of ignition elements is thermally coupled to the plurality of nano-energetic actuators, depositing at least one inductive coil disposed on the planar substrate, such that the at least one inductive coil is electrically coupled to the plurality of ignition elements, and depositing a plurality of electrically conductive interconnections on the planar substrate, such that the plurality of electrically conductive interconnections electrically couple the at least one inductive coil to the nano-energetic actuators.

Another method further comprises depositing a plurality of sensors, at least one data collection device, and at least one processor on the planar substrate. The plurality of sensors are configured for measuring vibrations induced in the surface of the structural element by the plurality of controlled combustions, and generating vibration data, the data collection device(s) is configured for collecting and storing the vibration data, and the processor(s) is programmed to control delivery of a plurality of electrical pulses from an electrical source to the plurality of ignition elements to cause the plurality of nano-energetic actuators to generate the plurality of controlled combustions in a time-phased manner.

In accordance with a sixth aspect of the present inventions, a method of removing ice from a structural element (e.g., a bridge, railroad, or vehicular structural element, such as the structural element (e.g., a wing or flight control surface) of an aircraft) is provided. The method comprises applying at least one controlled combustion to the structural element adjacent the ice, thereby inducing vibrations in a surface of the structural element, such that cracks are formed in the ice, and optionally applying vibrations to the cracked ice via electro-mechanical actuators, thereby removing the cracked ice from the structural element. The controlled combustion(s) preferably does not damage the structural element. In one method, controlled combustions may be generated in a time-phased manner to induce the vibrations in the surface of the structural element.

In accordance with a seventh aspect of the present inventions, a means of transportation having an accumulation of ice is provided. The means of transportation comprises a structural element (e.g., a bridge, railroad, or vehicular structural element, such as the structural element (e.g., a wing or flight control surface) of an aircraft), and at least one nano-energetic actuator, each configured for creating a controlled combustion in response to thermal energy, thereby inducing vibrations in a surface of the structural element great enough to generate cracks in the ice. The means of transportation may optionally comprise at least one electro-mechanical transducer, each configured for vibrating in response to the at least one electrical pulse, thereby inducing vibrations in the surface of the structural element great enough to remove the cracked ice from the structural element.

The means of transportation may optionally comprises at least one ignition element configured for generating the thermal energy in response to at least one electrical pulse, and at least one energy source configured for generating at least one electrical pulse. In one embodiment, each of the nano-energetic actuator(s) comprises copper oxide, and each of the ignition element(s) comprises platinum. Each of the nano-energetic actuator(s) may comprise nano-energetic material having a particle size less than 100 nanometers, and may have a size in the range of 1 micrometer to four millimeters. If multiple nano-energetic actuators are provided, the means of transportation may further comprise a processor programmed to control delivery of a plurality of electrical pulses from the at least one electrical source to cause the plurality of nano-energetic actuators to generate a plurality of controlled combustions in a time-phased manner.

DETAILED DESCRIPTION

Referring toFIG. 1, a vehicle10constructed in accordance with one embodiment of the present inventions will now be described. The vehicle10may be an aircraft, a ground vehicle, a naval vessel or any other vehicle or structure requiring structural health monitoring. The vehicle10comprises structural elements12, which may include, but is not limited to, a fuselage, door, panel, wing, engine component, or any other component that is susceptible to damage or deterioration. The structural elements12may include any material or combination of materials typically present in a conventional vehicle10or structure construction. For example, the structural elements12may include metal, composite, polymer, ceramic or any other material typically utilized for construction of vehicles10or other structures. AlthoughFIG. 1illustrates a vehicular structure element, and in particular an aircraft structural element, the present disclosure is not limited to vehicular structural elements and may include any other structural element associated with a means of transportation, e.g., bridges or railroads, or any structural element associated with other fixed structures, such as buildings, architectural elements, and other structures.

The vehicle10comprises a Non-Destructive Evaluation (NDE) system14configured for monitoring the health of the structural elements12of the vehicle10. “Health monitoring”, “structural health” and other uses of the term “health”, as used herein include the structural integrity of a structure, component or equipment element. For example, damage to a surface or structure may include indentation, delamination (localized or otherwise), scratches, cracks, water soaking into material, or any other damage caused by impact or other contact. In addition, damage may include a reduction in the integrity of the structure that may require analysis and/or potential repair.

The NDE system14monitors the health of the structural elements12of the vehicle10by obtaining acoustic signatures between transmit and receive transducers affixed to each structural element12. Such an acoustic signature provides a lot of information about the structural elements12, which may be quite useful when using the structural elements12of the vehicle10beyond their designed life or designed performance. Presently acquired acoustic signatures can be compared to a baseline acoustic signature to ascertain whether the characteristics of the respective structural element12have changed in a manner that indicates damage or deterioration of the structural element12.

To this end, the NDE system14generally comprises a plurality of damage monitoring units16respectively associated with the structural elements12, a central processing device (CPD)18(which may be contained in an single integrated device or may be distributed amongst several components) in communication with each of the damage monitoring units16for determining and localizing any damage to deterioration in one of the structural elements12, and a power source20configured for providing electrical power and signals to the damage monitoring units16and central processing device (CPD)18. WhileFIG. 1is shown as including four damage monitoring units16, more or less than four damage monitoring units16may be present on the vehicle10.

Significantly, the NDE system14is capable of injecting relatively high energy acoustic signals into each structural element12compared to prior art NDE systems without an increase in cost or weight. The NDE system14accomplishes this feat by utilizing nano-energetic material, instead of piezoelectric material, to generate the vibrational signal within each structural element12.

To this end, and with reference toFIG. 2, each damage monitoring unit16comprises one or more nano-energetic actuators22(only one in the embodiment illustrated inFIG. 2), each of which is configured for creating a controlled combustion in response to thermal energy, thereby inducing vibrations in a surface of the respective structural element12. Nano-energetic material can be defined as a metastable intermolecular composite (MIC) characterized by a particle size of its main constituents (a metal and a metal oxide) under one micron, and typically under one hundred nanometers. Nano-energetic material allows for high volumetric energy density, is capable of producing controlled combustion, may be environmentally benign, and allows for high and customizable reaction rates. In the illustrated embodiment, the nano-energetic material comprises an aluminum-copper (II) oxide, although the nano-energetic material may comprise, e.g., aluminum-molybdenum (VI) oxide, aluminum-iron (II, III) oxide, antimony-potassium permanganate, aluminum-potassium permanganate, aluminum-bismuth (III) oxide, aluminum-tungsten (VI) oxide hydrae, aluminum-fluoropolymer, or titanium-boron. Each nano-energetic actuator22may have a suitable size that induces the necessary vibrational energy in the surface of the structural element12without causing damage to the structural element12, e.g., in the range of one micrometer to four millimeters.

Advantageously, the vibrational energy induced into the surface of the respective structural element12by the controlled combustion of the nano-energetic actuator22is substantially greater than the energy or energy per unit time that would otherwise be induced into the surface of the structural element12by a conventional piezoelectric transducer (PZT). However, such vibrational energy generated by the nano-energetic actuator22is substantially small enough, such that the structural element12is not damaged. Thus, the composition of the structural element12will preferably be taken into account when considering the size and composition of the nano-energetic actuator22. For example, if the structural element12is composed of metal, the nano-energetic actuator22may be designed to generate a larger energy controlled combustion, and if the structural element12is composed of a ceramic or polymer material, the nano-energetic actuator22may be designed to generate a smaller energy controlled combustion.

It is preferable that the energy released by the nano-energetic actuator22be matched to the composition of the structural element12that is intended to interact with. In particular, it is desirable that the propagation of the vibration energy resulting from the controlled combustion of the nano-energetic actuator22be maximized within the structural element12. Although the controlled combustion will generally produce a vibrational spike having broadband frequencies, not all of these frequencies will propagate through the structural element12, especially one with discontinuities that will serve as a filter, allowing some frequencies to pass through, while preventing other frequencies from passing through. As such, the controlled combustion of the nano-energetic actuator22is preferably tuned to a natural resonant frequency of the structural element12to ensure that the vibrational energy propagates across these discontinuities. The natural resonant frequency to which the controlled combustion of the nano-energetic actuator22is tuned is preferably one that provides good transmission along the entire path and is within the frequency range of the sensors (described below).

Each damage monitoring unit16may additionally comprise one or more electro-mechanical actuators24(only one in the embodiment illustrated inFIG. 2) in the form of a PZT that, like the nano-energetic actuator22, induces vibrations into the structural element12. However, the vibrational energy provided by the electro-mechanical actuator24is substantially less than the vibration energy or energy per unit time provided by the nano-energetic actuator22.

Each damage monitoring unit16optionally comprises one or more ignition elements26(only one in the embodiment illustrated inFIG. 2) configured for generating the thermal energy necessary for the nano-energetic actuator22to generate the controlled combustion. In the illustrated embodiment, the ignition element26takes the form of a thermoelectric transducer that is in physical contact with the nano-energetic actuator22and that generates the thermal energy in response to an electrical signal (e.g., a 5V pulse). The ignition element26may, e.g., be composed of well-known material used in conventional low-resistance electric igniters, e.g., platinum wire, to generate the thermal energy necessary to initiate the reaction in the nano-energetic actuator22. Alternatively, the ignition elements may be electromagnetic energy—based, e.g., using a laser or flash light or radio frequency source, or friction-based, e.g., by impacting the nano-energetic actuator22. In alternative embodiments, the simple application of a voltage may generate the thermal energy necessary for the nano-energetic actuator22to generate the controlled combustion, in which case, a separate ignition element may not be required.

Each damage monitoring unit16further comprises a plurality of sensors28that are configured for measuring the vibrations induced in the surface of the structural element12by the nano-energetic actuator22and optional electro-mechanical actuator24, and generating electrical vibration data in response thereto. The sensors28may be any device capable of measuring vibration or other vibratory motion, such as, but not limited to, a transducer. Devices suitable for use as sensors28may include piezoelectric transducers (PZTs), accelerometers, strain gages, fiber optic sensors, and/or any other device that responds to a high frequency vibration. For example, a PZT may generate a measurable voltage in response to a sensed vibration. By “vibration,” “vibratory motion,” and grammatical variations thereof, as used herein, it is meant to include reciprocal or non-reciprocal motions and/or strain within a material that are capable of being sensed and/or measured at a distance across a material. Optical measurements of small distance measurement may also be used to sense vibration including those based on interferometry- or Moiré-based techniques.

Each damage monitoring unit16further comprises a data collection device30configured for collecting and storing the vibration data generated by the sensors28of the respective damage monitoring unit16. The data collection device30, may, e.g., be a microprocessor, integrated circuit or other device capable of collecting and/or analyzing data provided by the sensors28. For example, while not being limited to particular parameters, the data collection device30may be a microprocessor or integrated circuit having the following parameters: at least about eight analog-to-digital (ND) conversion channels at 3 MHz each, about at least 1024 data points per channel; at least about 1 Kb memory storage per channel temporary, at least about 1 Kb memory storage per channel permanent, and sufficient memory to perform a calculation between two 1024 vectors.

Each damage monitoring unit16further comprises electrically conductive interconnections32that interconnect the electro-mechanical actuator24, ignition element26, sensors28, and data collection device30. AlthoughFIG. 2illustrates each damage monitoring unit16as including eight sensors28, any number of sensors28may be utilized, including less than eight or greater than eight sensors28. Likewise, additional nano-energetic actuators22and/or electro-mechanical actuators24may be utilized in the damage monitoring unit16.

As one example, because each nano-energetic actuator22can only be used one time (i.e., once a nano-energetic actuator22is used to generate a controlled combustion, it cannot be used to generate another controlled combustion), multiple nano-energetic actuators22may be provided for each damage monitoring unit16, so subsets of the nano-energetic actuators22can be activated over several NDEs. Preferably, the centroids of the subsets of the nano-energetic actuators22are at identical locations in order to mimic the same location from which the controlled combustion originates. As such, the acoustic signature generated by each subset from the perspective of the surrounding sensors28will be identical or near identical. If individual nano-energetic actuators22are activated or the centroids of sets of nano-energetic actuators are not the same, the different locations of the controlled combustions will have to be accounted for when comparing to a baseline.

For example, with reference toFIG. 3, a “corral” of nano-energetic actuators22from which a subset of nano-energetic actuators22can be selected for activation for a particular NDE. As there shown, ten pairs of nano-energetic actuators22a,22b,22c,22d,22e,22f,22g,22h,22i,and22jcan be respectively used for ten NDEs. Thus, actuators22acan be activated for a first NDE, actuators22bcan be activated for a second NDE, actuators22ccan be activated for a third NDE, and so on. The centroid of each of these pairs of nano-energetic actuators22are located at the point “x,” so that the actuators pairs have identical acoustic signatures relative to the sensors28. It should be appreciated that the particular geometric arrangement of nano-energetic actuators22illustrated inFIG. 3does not preclude other geometric arrangements of nano-energetic actuators22with uniform or non-uniform spacing or a totally random distribution of nano-energetic actuators22. Furthermore, although the nano-energetic actuators22are illustrated inFIG. 3as being of uniform size, the sizes of the nano-energetic actuators22may differ from each other to meet variable energy requirements for a given application.

Regardless of the number of nano-energetic actuators22contained in each damage monitoring unit16, The CPD18is configuring for delivering trigger signals (e.g., electrical pulses or other signals (either directly or from a power source20)) that activate the damage monitoring units16to generate vibrations in the respective structural elements12, and for collecting data from the damage monitoring units16. Thus, the CPD18controls the timing and performs data analysis to determine damage location and characteristics in each structural element14. In order to activate a selected nano-energetic actuator22in one of the damage monitoring units16, the CPD18sends a signal (e.g., a 5V pulse) via a trigger line34to the corresponding ignition element26. In order to activate a selected electro-mechanical actuator24, the CPD18may also send a signal via a trigger line36to electro-mechanical actuator24. In one embodiment, the CPD18may also send a signal to the corresponding data collection device30for purposes of timing and to facilitate data collection. Further, the CPD18receives data from the data collection device30via the data line38. WhileFIG. 2shows the trigger lines34,36and data line38as wired connections, the communications may be provided via wireless or other data transfer method. In addition, the trigger lines34,36and the data line38may be a single wired connection or multiple wire connections.

Referring further toFIG. 4, a single path arrangement between a nano-energetic actuator22(or optionally an electro-mechanical actuator24) will now be described. The nano-energetic actuator22is activated (i.e., it creates a controlled combustion), such as by providing an electrical pulse to the corresponding ignition element26. In response to the applied voltage, the controlled combustion generated by the nano-energetic actuator22induces a vibration in the surface of the structural element12. The vibration propagates across the substrate50(representing the structural element12) forming a vibratory path52. The sensor28senses and measures vibration and/or movement corresponding to the vibration propagating along vibratory path52. The sensor28generate a voltage in response to vibration. The voltage or a signal corresponding to the voltage can be transmitted to the data collection device30for collection and analyzing. Although the vibratory path52is illustrated as a single straight line, it is noted that the vibration generated by the nano-energetic actuator22propagates in all directions from the nano-energetic actuator22along the substrate50, and thus, a plurality of vibratory paths52are present originating at the activated nano-energetic actuator22.

In an alternative embodiment, multiple nano-energetic actuators22may be sequentially actuated, such that the controlled combustions are generated in a time-phased manner, thereby causing the vibrational energy to preferentially travel in a particular direction. In this case, the CPD18may transmit the trigger signals to the respective ignition elements26in a time-phased manner, or alternatively, differing signal delay elements (not shown) can be coupled to the ignition elements26via the respective electrically conductive interconnections32, in which case, the CPD18may simultaneously transmit the trigger signals to the intervening signal delay elements.

In an optional embodiment, the vibration energy can be directed, focused reflected, filtered in frequency, or dispersed horizontally along the plane of the structural element12using surface acoustic wave structures. For example, raised lines can be printed on the structural element12to direct or reflect the vibrational energy. For example, such a surface acoustic wave structure may be placed in front of a component (e.g., a bolt) to prevent the vibrational energy from adversely affecting that component (e.g., loosening the bolt). As another example, a surface acoustic wave structure can be used to pass or reflect vibrational energy in a narrow frequency band towards a portion of the structural element12to be examined. Thus, surface acoustic wave structures can be used as a reflector or a filter to tune the direction and spectral content of energy entered in an area to be examined. As still another example, three surface acoustic wave structures can be constructed to reflect vibrational energy from a single controlled combustion from a nano-energetic actuator22into a “hidden” area (e.g., around a corner) of the structural element12, thereby emulating three separate but simultaneous controlled combustions.

Regardless of the nature of the vibrational energy, each data collection device30receives the data from the sensors28and calculates a damage index (DI) value corresponding to the data obtained. In particular, the data collection device30compares data obtained from sensors28to data previously collected from sensors28on the undamaged structural element12. Specifically, while not so limited, the data collection device30may perform the following calculation to determine a root mean square value damage index (DI) value, as follows:

D⁢⁢I=RMS⁡(Datacur-Dataref)RMS⁡(Dataref),
where Datacurcorresponds to current data (e.g., a vector of 1024 elements corresponding to measured voltages) obtained from sensors28; and Datarefcorresponds to previous (baseline) data obtained from the sensors28when the respective structural element12is known to be in an undamaged condition. The DI value computed by the data collection device30may be transmitted to and used by the CPD18to determine the location and/or nature of any damage that is present in the respective structural element12.

In one embodiment, DI includes eight scalar answers or responses (one per channel or one per sensor28) that are returned to the corresponding data collection device30, which are then transmitted to and used by the CPD18to determine the location and/or nature of any damage that is present in the corresponding structural element12. While the calculation shown above is a root mean square calculation, other data manipulation, algorithms or calculations may be utilized, as desired, to obtain DI values that are able to determine the location and character of damage on the structural element12.

In the embodiments including adjacent damage monitoring units16, the nano-energetic actuators22and/or optional electro-mechanical actuators24are activated in a manner that minimizes vibration interference at the individual sensors28. In other words, for any particular damage monitoring unit16, the lengths of the vibratory paths52between the actuators22/24generating the vibration and the sensors28measuring the vibrations are maintained, such that the vibrations at sensors28are substantially free of vibrations (i.e., amplitude at the vibration is sufficiently small) generated by actuators22/24in other damage monitoring units16.

Furthermore, although only one damage monitoring unit16is illustrated inFIG. 1as being associated with each structural element12, multiple damage monitoring units16may be arranged over a large area of the respective structural element12in order to obtain high resolution health monitoring, as illustrated inFIG. 5. In this case, for each structural element12to be examined, the damage monitoring units16are arranged and preferably activated at periodic intervals to monitor the health of the respective structural element12. Alternatively, the damage monitoring units16may be activated at the same time, provided that the activated damage monitoring units16are sufficiently spaced to permit the vibration amplitude to sufficiently decay to reduce or eliminate undesired noise at the sensors28of activated adjacent damage monitoring units16.

As shown inFIG. 5, an area of damage54is present on the structural element12, which may have been caused by impact, contact, abrasion or any other type of contact that may result in scratching, delamination or other damage that may affect the mechanical or other properties of the structural element12. One of the damage monitoring units16spans this damaged area54. AlthoughFIG. 5illustrates he damaged area54as being spanned by only one damage monitoring unit16, it should be appreciated that the damaged area54may coincide with several damage monitoring units16.

As shown inFIG. 6, this damage monitoring unit16during the process of monitoring the health of the structural element12taken from damaged area54ofFIG. 5will now be described. A signal from the CPD18(not shown inFIG. 6) is provided to the ignition element26of the nano-energetic actuator22and the data collection device30(not shown inFIG. 6) to activate the nano-energetic actuator22and to optionally prepare the data collection device30(not shown inFIG. 6) to receive data. In response, the nano-energetic actuator22generates a controlled combustion that induces a vibration that propagates across the surface of the structural element12and along vibratory paths52. The vibratory paths52travel across the structural element12and may be measured by the sensors28. The sensors28transmit the measured vibration to the data collection device30, which obtains and analyzes the data.

In one embodiment, the data collection device30compares the voltages transmitted by the sensors28to a stored set of data corresponding to an undamaged structural element12. If the structural element12is substantially undamaged, the voltages measured and the voltages stored are substantially the same and the resultant DI is zero or about zero. However, if damage is present as represented by the damaged area54, the sensors28within the damaged area54will measure a level of vibration different than the vibration measured on an undamaged structural element12, and therefore can characterize and locate the damaged area54. In the example shown inFIG. 5, the three sensors28within the damaged area54will return a value of DI that is non-zero, while the remaining five sensors28outside of the damaged area will return a DI of substantially zero. Additional factors such as magnitude of the DI may also be utilized to characterize the damaged area54. The DIs calculated by the data collection device30are transmitted to the CPD18, wherein a plurality of damage monitoring units16also transmit the DIs in order to provide data that can determine the location and characterization of the damaged area54. The characterization of damage may include the size, depth type or other feature of the damage.

The nano-energetic actuators22, optional electro-mechanical actuators24, ignition elements26, sensors28, and data collection device30may be affixed to the structural element12in any suitable manner that permits the generation of vibration in the structural element12by the nano-energetic actuators22and optional electro-mechanical actuators24and the measurement of vibration of the sensors28.

For example, the nano-energetic actuators22, ignition elements26, and associated electrically conductive interconnections32may be directly deposited on an exterior surface of the structural element12using any suitable printing or lithography technique. The optional electro-mechanical actuators24and sensors28may be deposited on an interior surface of the structural element12(e.g., the interior surfaces of the fuselage of an aircraft) using any suitable printing or lithography technique, wherein the exposure to damage to these components would otherwise be on an exterior surface. As one example, components that take the form of PZTs (e.g., the electro-mechanical actuators24and sensors28) can be deposited directly onto a structural element12by a method such as, but not limited to fused deposition of ceramics, robocasting, micropen application, sintering onto the surface using light energy from a high energy source, such as a laser or a xenon flash lamp, or any other suitable PZT deposition process. One suitable method includes the direct sintering and using laser based sintering techniques recited in U.S. Pat. No. 6,531,191, which is expressly incorporated herein by reference.

The data collection device30may be soldered, attached, formed or otherwise disposed on the structural element12and interconnected to the electro-mechanical actuators24and sensors28via the electrically conductive interconnections32, which may be applied using any known application and/or conductive trace printing technique, including, but not limited to direct printing or lithographic methods. The CPD18may be incorporated into any region of the vehicle10and wired to the damage monitoring units16.

In one particularly advantageous embodiment, the nano-energetic actuators22, ignition elements26, and associated electrically conductive interconnections32may be provided in sheet form as an applique100that can be semi-permanently or temporarily affixed to the external surface of the structural element12, as illustrated inFIGS. 7 and 8. In the illustrated embodiment, the applique100is supplied in the form of a roll (shown inFIG. 7) from which adjustable lengths of the applique100can be ripped or cut. Thus, the applique100may permit reusability and/or portability of the actuation portion of the NDE system14. For example, the applique100can be designed for being single-use only, such that after the NDE is performed, the used applique100can be removed, and replaced with an identical applique100for immediate or subsequent use.

To this end, the applique100comprises a flexible planar substrate102(such as a polymeric material, e.g., polyimide film (e.g., Kapton®), metallic foil, a metalized polymeric material, or a multilayer substrate of polymeric and metallic films) on which the plurality of the nano-energetic actuators22, ignition elements26, and electrically conductive interconnections32are affixed to one side using a suitable process, e.g., printing or lithography. The ignition elements26are thermally coupled to the nano-energetic actuators22, and in the illustrated embodiment, are disposed between the planar substrate102and nano-energetic actuators22. The electrically conductive interconnections32are electrically coupled to the ignition elements26. Thus, triggering signals may be input onto the ignition elements26via the electrically conductive interconnections32, thereby activating the nano-energetic actuators22to generate controlled combustions. If multiple nano-energetic actuators22are activated in a time-phased manner to control the direction of the vibrational energy along the structural element12, delay elements (not shown) may be incorporated into the electrically conductive interconnections32and affixed to the planar substrate102.

It should be appreciated that, in addition to providing a means for integrating the applique100, the planar substrate102provides a protective barrier between the controlled combustions generated by the nano-energetic actuators22and the structural element12. In a contrasting embodiment, the planar substrate102may serve as a stiff backing plate (instead of a protective barrier) to vertically direct the vibrational energy into the structural element12. As will be described in further detail below, the applique100may be used in de-icing procedures, in which case, the planar substrate102may be used to vertically direct the energy outward. In any event, the applique100may further comprise a conformal polymer coating (not shown) disposed over the components to protect them from environmental conditions. Further, this protective coating would be designed to address any barrier requirements related to moisture, oxygen, etc. As such, this protective coating may, e.g., take the form of a multi-layer barrier film. In the extreme, this protective material could be sufficient to add its own mechanical properties to the structure to require consideration in the analysis of the data produced, e.g., one or more layers of fiberglass or carbon fiber based polymer composites.

To provide a communication/power means for the applique100, the applique100further comprises at least one inductive coil104(only one shown) affixed to the substrate102. The inductive coil104is configured for receiving trigger signals from a corresponding inductive coil (not shown) associated with the CPD18. The inductive coil104is electrically coupled to the ignition elements26via the electrically conductive interconnections32, such that trigger signals received by the inductive coil104actuate the nano-energetic actuators22. As such, the applique100, when applied to the structural element12, need not be hardwired to the CPD18. Alternatively, the applique100may be hardwired to the CPD18, such that the inductive coil104is not needed. In this case, the applique100may have exterior wires or electrical pads that can be used to electrically connect its components to remaining circuitry of the NDE system14. In another alternative embodiment, a photo cell may be provided on the applique100, and an optical source (e.g., a lase or even the Sun) may emit light onto the photocell, which can be used as power/communication after conversion to electricity. In still another embodiment, an energy storage device, such as a battery, may be provided on the applique100for providing power/communication to the applique100.

In one embodiment, the nano-energetic actuators22are registered to the centers of the damage monitoring units16, with the sensors28(shown in phantom), and the other componentry being affixed directly to the surface element12underneath the applique100. For example, if the damage monitoring units16are spaced six inches apart, the nano-energetic actuators22may be likewise spaced six inches apart. Thus, when adhering the applique100to the structural element12, the nano-energetic actuators22may be aligned with the centers of the damage monitoring units16.

Although the electro-mechanical actuators24, sensors28, and data collection devices30have been described as being directly affixed to or in the structural element12separately from the applique100, it should be appreciated that the electro-mechanical actuators24, sensors28, and/or data collection devices30may be affixed to the planar substrate102using any suitable means. However, because the electro-mechanical actuators24, sensors28, and/or data collection devices30are generally reusable, they can easily be incorporated into the structural element12, and thus, for purposes of efficiency in manufacture and associated cost, these devices may advantageously be incorporated into the structural element12.

The applique100further comprises an adhesive106affixed to the planar substrate102, such that the applique100can be adhered to the structural element12. In one preferred embodiment, the adhesive106is such that the applique100can be easily removed from the structural element10after a single use. Such an applique100is quite useful when used on structural elements12that are easily accessible. The side of the planar substrate102on which the adhesive106is applied may depend on the particular use of the applique100. For NDE, the adhesive106may be applied to the same side of the planar substrate102on which the nano-energetic actuators22are disposed. In this case, when the applique100is adhered to the structural element12, the nano-energetic actuators22will be facing the structural element12, such that the planar substrate102directs the energy from the controlled combustions towards the structural element12. For de-icing procedures if the vehicle10is an aircraft, as will be described in further detail below, the adhesive106may be applied to the side of the planar substrate102opposite to the side on which the nano-energetic actuators22are disposed. In this case, when the applique100is adhered to the wings or flight control surfaces (e.g., flaps, ailerons, elevators, rudders of the aircraft10, the nano-energetic actuators22will be facing outward away from the wings or flight control surfaces, such that the planar substrate102, while also creating a barrier between the energy created by the controlled combustions, directs such controlled combustions outwards towards the ice.

In an alternative embodiment, the adhesive106is such that the applique100is semi-permanently affixed to the structural element10for multiple uses. In this case, multiple nano-energetic actuators22are provided for each damage monitoring unit16. For each NDE performed, one set of nano-energetic actuators22will be activated and therefore used up. Preferably, the applique100in this case will have enough nano-energetic actuators22to support several NDEs performed over a period of time, e.g., as shown inFIG. 3. Such a reusable applique100can be applied to a structural element12in an inaccessible location of the vehicle10, e.g., during manufacture of the vehicle10. As one example, if such structural element12will not be accessed for a period of time (e.g., 10 years), the reusable applique100may have enough nano-energetic actuators22for each damage monitoring unit12to last for all anticipated NDEs during this period of time.

Referring toFIG. 9, one method200of manufacturing the applique100will now be discussed. First, the flexible planar substrate102(e.g., polyimide) is provided (step202). The electrically conductive interconnections32(step204) and ignition elements26(step206) are deposited on the planar substrate102, e.g., via printing or lithography, such that the electrically conductive interconnections32and ignition elements26are electrically coupled together. Next, the nano-energetic actuators22are deposited on the planar substrate102, so that they are thermally coupled to the ignition elements26, and in the illustrated embodiment, respectively on the ignition elements26(step208).

Next, the inductive coil(s)104are deposited on the planar substrate102, such that they are electrically coupled to the ignition elements26, and in the illustrated embodiment, on the electrically conductive interconnections32(step210). Optionally, a conformal coating may be applied over the components (step212).

Lastly, an adhesive is applied to the planar substrate102(step214). In one embodiment, the adhesive is applied to the same side of the planar substrate102as the nano-energetic actuators22, so that the energy from the subsequent controlled combustions is directed away from the planar substrate102toward structural element12. The characteristics of the adhesive may be selected, not just for addressing adhesion requirements, but also to address any impedance matching requirements. This may be useful, e.g., when performing NDE on the structural element12. In another embodiment, the adhesive is applied to the opposite side of the planar substrate102as the nano-energetic actuators22, so that the energy from the subsequent controlled combustions is directed outward away from the planar substrate102. This may be useful, e.g., when performing a de-icing procedure.

Having described the function and arrangement of the NDE system14, one method250of operating the NDE system14to perform an NDE on a structural element12of the vehicle10will now be described with respect toFIG. 10. In this example, the NDE system14utilizes one or more appliques100that complement the sensors28, data collection devices30, and associated circuitry of one or more damage monitoring units12that have been previously integrated with the structural element12. Performance of the NDE on the structural element12can be performed using a single damage monitoring unit16or multiple damage monitoring units16.

First, one or more appliques100are adhered to the structural element12, such that the nano-energetic actuators22of the applique(s)100are in registration with the portions of the damage monitoring units16(e.g., the sensors28and data collection devices30) that have been directly incorporated into the structural element12, itself (step252). Combustion induced energy is then delivered to the structural element12via the applique(s)100, thereby inducting vibrations in the structural element12(step254). In the illustrated embodiment, this is accomplished by sending at least one trigger signal from the CPD18to the ignition element(s)26to activate the respective nano-energetic actuators22carried by the applique100. Multiple controlled combustions may be applied to the structural element12in a time-phased manner to preferentially induce the vibrations along a particular direction in the structural element12.

In an alternative embodiment, vibrations are induced in the structural element12via actuation of the electro-mechanical actuators24if a relatively large amount of vibrational energy is not needed to perform the NDE of the structural element12. In this manner, unnecessary use of the nano-energetic actuators22may be avoided, thereby increasing the useful life of the applique100. Thus, the nano-energetic actuators22will only be actuated if the NDE of the structural element12cannot be accurately performed using the electro-mechanical actuators24, alone. Next, the vibrations induced in the structural element12are sensed (step256), and vibration data corresponding to the measured vibrations is generated by the sensors28integrated into the structural element12(step258). Then, the vibration data is collected from the individual sensors28and stored by the data collection device30(step260).

Then, the condition of the structural element12is determined based on the collected and stored vibration data (step262). In the illustrated embodiment, the data collection device(s)30integrated into the structural element12compares vibration data collected from each sensor28and compares it to reference vibration data, e.g., to obtain a DI for each sensor28. It may be determined that the structural element12has damage or deterioration in any region adjacent any sensors28returning a non-zero DI. If all sensors28return a DI that is substantially non-zero, the structural element12will be deemed to be free from damage or deterioration. Then, the determined condition of the structural element12is returned to the CPD18(step264). Lastly, the structural element12is repaired or replaced if it is determined that the structural element12has been damaged or has deteriorated (step266).

Although the applique100has been described as being used to facilitate NDE of a vehicle, it should be appreciated that the use of an applique100lends itself well to the performance of NDEs on fixed structures, such as bridges, railways, and buildings. In a conventional scenario, a huge amount of time is typically expended in the setting up and tearing down of NDE equipment in the inspection of these structures. Appliques100may be conveniently affixed to these structures (e.g., at every major intersection of metal where rust may form), which may substantially reduce the set up and tear down time.

Although the nano-energetic actuators22have been described as being used in the context of performing NDEs on structural elements12, nano-energetic actuators22may be used in the context of a de-icing system as briefly discussed above. In this case, nano-energetic actuators22and associated ignition elements26, as well as electro-mechanical actuators24, may be incorporated into the vehicle10, in this case an aircraft, for example, on the wings or flight control surfaces of aircraft10. Notably, the sensors28and data collection devices30are not required in this de-icing system. The CPD18transmits trigger signals to the ignition elements26associated with the nano-energetic actuators22and the electro-mechanical actuators24in a manner that effectively and efficiently removes the build-up of ice on the wings or flight control surfaces of the aircraft10, even if such ice is too thick to be quickly removed using conventional means. In particular, the CPD18may transmit trigger signals to the ignition elements26, thereby activating the corresponding the nano-energetic actuators22to generate controlled combustions that induce vibrations in the ice great enough to generate cracks in the ice. The CPD18may also transmit trigger signals to the electro-mechanical actuators24, thereby activating the electro-mechanical actuators24to generate vibrations in the ice great enough to remove the cracked ice from the wings or flight control surfaces of the aircraft10.

Referring now toFIG. 11, one method300of using an applique100in a de-icing procedure performed on a structure, such as a vehicle10, will now be described. In this example, the appliques100complement the electro-mechanical actuators24that have previously integrated with the vehicle10. In an alternative embodiment, the applique100can be used in the de-icing procedure without electro-mechanical actuators24.

First, appliques100are adhered to the wings or flight control surfaces of the aircraft10over the electro-mechanical actuators24that have been directly incorporated into the wings or flight control surfaces of the aircraft10(step302). Combustion induced energy is then delivered to the ice on the wings or flight control surfaces of the aircraft10via appliques100, thereby inducing vibrations that crack the ice (step304). In the illustrated embodiment, this is accomplished by sending at least one trigger signal from the CPD18to the ignition elements26to activate the respective nano-energetic actuators22carried by the applique100. Multiple controlled combustions may be applied to the structural element12in a time-phased manner to preferentially induce the vibrations along a particular direction. Then, additional vibrational energy is applied to the cracked ice, thereby removing the cracked ice from the wings or flight control surfaces of the aircraft10(step306). In the illustrated embodiment, this is accomplished by sending at least one trigger signal from the CPD18to the electro-mechanical actuators24. In an alternative embodiment, the vibrational energy may be applied to the ice via the electro-mechanical actuators24prior to activation of the nano-energy actuators22in an attempt to remove the ice from the wings or flight control surfaces of the aircraft10using the electro-mechanical actuators24, alone. In this manner, unnecessary use of the nano-energetic actuators22may be avoided, thereby increasing the useful life of the applique100. Thus, the nano-energetic actuators22will only be actuated if the ice cannot be removed from the wings or flight control surfaces using the electro-mechanical actuators24, alone.

Although certain illustrative embodiments and methods have been disclosed herein, it can be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods can be made without departing from the true spirit and scope of the art disclosed. Many other examples of the art disclosed exist, each differing from others in matters of detail only. Accordingly, it is intended that the art disclosed shall be limited only to the extent required by the appended claims and the rules and principles of applicable law.