Multi-element sensors for monitoring composite structures

Abstract

A sensor for monitoring a composite structure, a manufacturing method thereof, and a method of attaching the same to a composite structure are provided. [Solution] The system of the present invention includes a plurality of sensors coupled to a composite cylinder and configured to detect deformation data relating to the composite cylinder; a control unit communicatively connected to the plurality of sensors and configured to determine a damage value based on the deformation data when the composite cylinder suffers impact damage and to provide notification if the damage value exceeds an impact damage threshold; and a filling control unit communicatively connected to the plurality of sensors and configured to control a valve to fill the composite cylinder with fluid, to detect damage to the composite cylinder based on the deformation data from the plurality of sensors as the composite cylinder is filled with the fluid, and to automatically perform a safety action if damage to the composite cylinder is detected.

Description

Related Applications

[0001] This application claims priority to U.S. patent application Ser. No. 17 / 395,885, entitled "Multi-Element Sensor for Monitoring Composite Structure," filed on August 6, 2021, and U.S. patent application Ser. No. 17 / 223,628, entitled "Composite Cylinder Monitoring System," filed on April 6, 2021, the entire disclosures of which are incorporated herein by reference. [Technical field]

[0002] The present disclosure relates to sensors for monitoring composite laminate structures. [Background technology]

[0003] Vehicles may be used to transport passengers and / or cargo. Some vehicles for transporting cargo are powered by fuel stored in tanks (cylinders). Summary of the Invention [Problem to be solved by the invention]

[0004] Such cylinders can become damaged during operation of the vehicle, and if so, it is important to have the cylinder repaired. [Means for solving the problem]

[0005] Described herein is a sensor for monitoring a composite structure, the sensor comprising a first sensor element of a first size configured to detect data related to a first monitoring task, the sensor further comprising a second sensor element of a second size configured to detect data related to a second monitoring task.

[0006] Also described herein is a method of manufacturing a sensor. The method includes fabricating a first positive electrode having a first size and a second positive electrode having a second size. The method further includes fabricating a ground electrode having a size greater than the first size and the second size combined. The method further includes disposing a piezoelectric material between the layer of the first and second positive electrodes and the ground electrode.

[0007] Also described herein is a method for monitoring a composite structure, the method comprising determining a plurality of monitoring tasks for a sensor having a plurality of sensor elements, the method further comprising determining a plurality of sensor element sizes for the plurality of sensor elements, respectively, based on each of the plurality of monitoring tasks, the method further comprising manufacturing the sensor based on the determined plurality of sensor element sizes, and the method further comprising coupling the sensor to the composite structure.

[0008] Those skilled in the art will recognize additional systems, methods, features, and advantages of the present invention upon examination of the following drawings and detailed description. Components illustrated in the drawings are not necessarily to scale and may be exaggerated to more clearly illustrate the important features of the present invention. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing a vehicle equipped with a composite cylinder that stores fuel for powering the vehicle in accordance with each embodiment. [Figure 2A] FIG. 2 is a diagram showing a composite cylinder in each embodiment. [Figure 2B] FIG. 11 is another diagram showing the composite cylinder in each embodiment. [Figure 3A] FIG. 2 is a block diagram illustrating each monitoring component of the system in accordance with various embodiments. [Figure 3B]FIG. 2 is another block diagram illustrating monitoring components of the system according to embodiments. [Figure 4] FIG. 4 is a diagram showing models of the cylinder, each sensor, and an impact point in each embodiment. [Diagram 5] FIG. 4 is a diagram showing sensor data of the system in each embodiment. [Figure 6] FIG. 11 is another diagram showing sensor data of the system in each embodiment. [Figure 7] 5A to 5C are diagrams showing models of the cylinder, each sensor, and an estimated location of an impact in each embodiment. [Figure 8] FIG. 4 is a diagram showing data of the present system in each embodiment. [Figure 9] FIG. 2 is a block diagram showing components that fill a cylinder in accordance with each embodiment. [Figure 10] FIG. 2 is a block diagram showing components that monitor and fill cylinders in each embodiment. [Figure 11] 5A-5C show data detected during filling of the cylinder in accordance with the various embodiments; [Figure 12] FIG. 11 is another diagram illustrating data detected during filling of the cylinder in accordance with various embodiments. [Figure 13] 11A-11C are further diagrams illustrating data detected during filling of the cylinder in accordance with various embodiments. [Figure 14] FIG. 2 is a block diagram of the system according to each embodiment. [Figure 15A] FIG. 2 is a flow diagram of each process executed by the system in each embodiment of the present invention. [Figure 15B] FIG. 11 is another flow chart of each process executed by the system in each embodiment of the present invention. [Figure 16A] FIG. 2 is a plan view of a sensor in each embodiment of the present invention. [Figure 16B] FIG. 2 is a side cross-sectional view of the sensor in each embodiment of the present invention. [Figure 16C]FIG. 2 is a side view showing the sensor on a flat surface in each embodiment of the present invention. [Figure 16D] FIG. 2 is a side view showing the sensor on a curved surface in accordance with each embodiment of the present invention. [Figure 17] FIG. 2 is a plan view of a sensor having sensor elements of three different sizes in each embodiment of the present invention. [Figure 18] FIG. 2 is a plan view of a sensor having sensor elements of four different sizes in accordance with each embodiment of the present invention. [Figure 19] FIG. 2 is a plan view of a sensor having sensor elements of five different sizes in accordance with each embodiment of the present invention. [Figure 20] FIG. 2 is a schematic diagram of an experimental setup for application of the sensor in accordance with embodiments of the present invention. [Figure 21A] FIG. 11 is a diagram showing detected experimental data in each embodiment of the present invention. [Figure 21B] FIG. 11 is another diagram showing detected experimental data in each embodiment of the present invention. [Figure 22] 11A and 11B are diagrams showing detection data time-shifted to a coherent state and the sum of signals in a time-coherent state in each embodiment of the present invention. [Figure 23A] FIG. 11 is a diagram showing detected experimental data in each embodiment of the present invention. [Figure 23B] FIG. 11 is another diagram showing detected experimental data in each embodiment of the present invention. [Figure 24] FIG. 4 is a diagram showing the frequency-wavelength dispersion relationship in each embodiment of the present invention. [Diagram 25] FIG. 2 is a schematic diagram of an experimental setup for application of the sensor in accordance with embodiments of the present invention. [Figure 26] 11A-11C are diagrams comparing sensing elements of different diameters in accordance with embodiments of the present invention; [Figure 27] FIG. 2 is a flow diagram showing a method for manufacturing a sensor in accordance with each embodiment of the present invention. [Figure 28]FIG. 2 is a flow diagram showing a method of manufacturing and using a sensor in each embodiment of the present invention. [Figure 29A] 3A to 3C are diagrams illustrating a process for producing a piezoelectric element used in the sensor in each embodiment of the present invention. [Figure 29B] 7A to 7C are diagrams illustrating other steps of manufacturing a piezoelectric element used in the sensor in each embodiment of the present invention. [Figure 29C] 7A to 7C are diagrams illustrating still other manufacturing steps of the piezoelectric element used in the sensor in each embodiment of the present invention. [Figure 29D] 7A to 7C are diagrams illustrating still other manufacturing steps of the piezoelectric element used in the sensor in each embodiment of the present invention. [Figure 29E] 7A to 7C are diagrams illustrating still other manufacturing steps of the piezoelectric element used in the sensor in each embodiment of the present invention. [Figure 29F] 7A to 7C are diagrams illustrating still other manufacturing steps of the piezoelectric element used in the sensor in each embodiment of the present invention. [Figure 30A] FIG. 29C is a diagram showing a sensor having the piezoelectric element of FIGS. 29A to 29F in each embodiment of the present invention. [Figure 30B] FIG. 29B is another diagram showing a sensor having the piezoelectric element of FIGS. 29A to 29F in each embodiment of the present invention. [Figure 30C] FIG. 29B is still another diagram showing a sensor having the piezoelectric element of FIGS. 29A to 29F in each embodiment of the present invention. [Figure 30D] FIG. 29B is still another diagram showing a sensor having the piezoelectric element of FIGS. 29A to 29F in each embodiment of the present invention. [Diagram 31] FIG. 2 is a schematic diagram of an experimental setup for application of the sensor in accordance with embodiments of the present invention. [Diagram 32] 13 is a graph of the sources used in the experimental setup applied to the sensor in accordance with the embodiments of the present invention. [Diagram 33] FIG. 11 is a diagram showing detected experimental data in each embodiment of the present invention. [Figure 34A]FIG. 11 is another diagram showing detected experimental data in each embodiment of the present invention. [Figure 34B] FIG. 11 is yet another diagram showing detected experimental data in accordance with each embodiment of the present invention. [Diagram 35] FIG. 11 is yet another diagram showing detected experimental data in accordance with each embodiment of the present invention. [Figure 36A] FIG. 11 is yet another diagram showing detected experimental data in accordance with each embodiment of the present invention. [Figure 36B] FIG. 11 is yet another diagram showing detected experimental data in accordance with each embodiment of the present invention. [Figure 37] FIG. 11 is yet another diagram showing detected experimental data in accordance with each embodiment of the present invention. [Figure 38A] FIG. 11 is yet another diagram showing detected experimental data in accordance with each embodiment of the present invention. [Figure 38B] FIG. 11 is yet another diagram showing detected experimental data in accordance with each embodiment of the present invention. [Figure 39] FIG. 11 is yet another diagram showing detected experimental data in accordance with each embodiment of the present invention. [Figure 40A] FIG. 11 is yet another diagram showing detected experimental data in accordance with each embodiment of the present invention. [Figure 40B] FIG. 11 is yet another diagram showing detected experimental data in accordance with each embodiment of the present invention. [Diagram 41] FIG. 2 is a flow diagram showing a method for manufacturing a sensor in accordance with each embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Disclosed herein are systems, vehicles, and methods for monitoring a composite cylinder in a vehicle that automatically detects damage to the composite cylinder and takes appropriate action. The systems and methods described herein continuously monitor the integrity of the composite cylinder from use through to filling (or refilling), thereby improving the safety of vehicles using the composite cylinder.

[0011] Although the description herein focuses on composite cylinders, the systems and methods may be applied in a variety of applications, such as wind turbines, airframes, wing leading edges, or any composite structure where impact damage is detrimental.

[0012] Also disclosed are sensors for use in monitoring the composite structure. The sensors described herein can be multi-element sensors capable of performing multiple monitoring tasks with a single sensor. The sensors described herein can be easily tunable and redesigned, and can be manufactured in large quantities at low cost. Conventional piezoelectric sensors are not only costly, but also do not support multiple monitoring tasks.

[0013] As used herein, "operator" may refer to a human who drives a vehicle if the vehicle is non-autonomous, and / or as used herein, "driver" may refer to one or more computer processors used to drive the vehicle autonomously or semi-autonomously. "User" may refer to a driver or passenger of a vehicle if the vehicle is non-autonomous, while a passenger of the vehicle if the vehicle is autonomous or semi-autonomous. As used herein, "cylinder" includes storage tanks, pressure vessels, and other vessels that can be used to store gas, and is not necessarily limited to a particular shape, such as a right cylinder and / or a cylinder with a constant or non-changing circular cross-section. As used herein, "fuel" or "gas" refers to any fluid used to power a vehicle, such as gaseous or liquid fuels.

[0014] 1 illustrates a vehicle 102. Specifically, the vehicle 102 is a tractor configured to couple to and tow a trailer 106. The vehicle 102 may be powered by a fuel stored in a composite pressurized cylinder (or "composite cylinder" or "cylinder"). For example, the fuel may be compressed natural gas stored in a composite cylinder.

[0015] The cylinder may be part of a gas cylinder assembly that is in fluid communication with any power generating system, such as an engine, of a vehicle 102 to provide fuel. The vehicle 102 may be a large vehicle, such as an automobile, a stationary vehicle, a van, a bus, a passenger vehicle, a truck, a tractor trailer truck, a garbage truck, or any other vehicle. In some embodiments, the gas cylinder assembly is configured for a marine vehicle, an aircraft, or a mobile or stationary fuel station.

[0016] The fuel canister may be stored, for example, in a compartment or housing 104A on the side of the vehicle 102, in a compartment or housing 104B on the trailer 106, or in a compartment or housing 104C behind the cab of the vehicle 102. In some embodiments, the fuel canister may be stored on the rooftop or mounted on the tailgate of the vehicle.

[0017] In-service failures of composite pressure cylinders arise primarily from three root causes: thermal exposure events, impact damage, and cumulative damage detrimental to the composite laminate. While thermal exposure can be mitigated, there are no systems or methods (commercially available or otherwise) that protect composite pressure cylinders from impact damage (e.g., automobile collisions) or cumulative damage accumulated due to improper operating conditions (e.g., improper installation, debris lodged between the cylinder and the enclosure). Experience has shown that when a cylinder experiences significant levels of impact damage or latent damage accumulates due to improper environmental conditions (e.g., bolts lodged between the cylinder and the enclosure), the stress state within the laminate exceeds a critical level, causing catastrophic failure of the cylinder during a subsequent fill cycle.

[0018] 2A illustrates a cylinder 100 configured to store a fluid such as compressed natural gas or hydrogen. The cylinder 100 may be constructed from a metal such as steel or aluminum, a composite material such as fiberglass, carbon fiber, a polymer, a carbon fiber reinforced polymer, another suitable material, or a combination thereof. For example, the cylinder 100 may be a high pressure carbon fiber reinforced plastic construction on an airtight polyethylene plastic inner liner. In another example, the cylinder 100 may be a metal liner encased in a composite or fiber resin.

[0019] FIG. 2B is a side cross-sectional view of the cylinder 100. The cylinder 100 may be made of multiple layers. For example, the cylinder 100 may have an inner layer 222 and an outer layer 220. The inner layer 222 may be made of metal, plastic or any other highly rigid material. The outer layer 220 may be made of a composite or fiber resin that is placed on the inner layer 222 during a manufacturing process. The outside of the outer layer 220 may form the outer surface 218 of the cylinder 100. The walls of the cylinder 100 may define an interior space 224 for storing the fuel. Although FIG. 2B depicts two layers (e.g., the inner layer 222 and the outer layer 220), any number of layers may be used to construct the cylinder 100.

[0020] Referring again to FIG. 2A, the cylinder 100 has a central portion 216 and two ends 208, 210. The central portion 216 may be cylindrical, but may be any other shape. In some embodiments, the two ends 208, 210 each comprise a dome-like structure, as shown in FIG. 2A. In some embodiments, the two ends are symmetrical to each other. The dome-like structure may be substantially hemispherical at least at the ends. In some embodiments, the two ends 208, 210 are different shapes, resulting in an asymmetric shape of the cylinder 100.

[0021] In some embodiments, the cylinder 100 has at least one neck 212, 214 (e.g., a longitudinal protrusion of a boss, etc.) that provides an inlet and / or outlet to the interior space of the cylinder 100. In some embodiments, the cylinder 100 has necks 212, 214 at both ends 208, 210. In some embodiments, only one of the two ends 208, 210 may have a neck. In some embodiments, the neck 212, 214 may be part of a metal structure (sometimes referred to as a boss) that is formed to penetrate one end of a high-pressure enclosure (sometimes referred to as an inner liner assembly, or simply a liner) inside the cylinder 100.

[0022] The necks 212, 214 can be made of any number of materials, such as metal. In some embodiments, the necks 212, 214 are constructed of one or more materials not used in the inner high pressure enclosure. In some embodiments, the necks 212, 214 are made of the same material as the inner high pressure enclosure.

[0023] The cylinder 100 may have an exterior surface 218 that spans the body of the cylinder 100. In some embodiments, the exterior surface 218 includes necks 212, 214. In other embodiments, the exterior surface 218 does not include necks 212, 214. As described herein, the cylinder 100 may be damaged. The damage may occur when the cylinder 100 is struck by an object such as a rock or another vehicle. The damage may occur when an object such as a bolt becomes caught between the cylinder 100 and the container (e.g., the housing or compartment 104) of the cylinder 100, damaging the cylinder 100 as the cylinder 100 expands based on changes in pressure or temperature. In some cases, the damage may result in a visible dent 204, but in many cases, the damage may not result in a visible dent. This damage, which is not readily visible to the human eye, may be just as detrimental to the cylinder 100 as a visible dent. The systems and methods described herein prevent the reuse of damaged cylinders, such as cylinders that have suffered damage not readily visible to the human eye.

[0024] A number of sensors 202 may be attached to the cylinder 100 at various sensor locations 206. The sensors 202 are configured to detect an impact to the cylinder 100. The sensors 202 may be wideband piezoelectric sensors that sense the out-of-plane displacement component of the laminate of the composite pressure cylinder (e.g., cylinder 100). The sensors 202 may detect and determine the energy level of the impact event. The wideband piezoelectric sensors measure stress waves caused by the impact and progressive damage accumulation within the laminate by interaction between the piezoelectric material and the composite laminate. In some embodiments, a wideband piezoelectric sensor as used herein does not necessarily detect damage to the composite laminate by measuring a shift in resonant or anti-resonant frequency caused by a change in the stress state of the piezoelectric material. In some embodiments, a wideband piezoelectric sensor as used herein detects damage to the composite laminate without relying on measuring a shift in resonant or anti-resonant frequency caused by a change in the stress state of the piezoelectric material.

[0025] Sensor 202 may be considered a passive sensor in that it does not actively generate waves for another sensor to detect, but rather, sensor 202 passively monitors the stack as it is subjected to stress from an external source, as well as determining when, where, and how severe an impact event occurs in the tank.

[0026] In some embodiments, the sensor 202 is removably attached to the cylinder 100. In other embodiments, the sensor 202 is integrally formed and embedded within the cylinder 100. The sensor 202 may be disposed on the exterior surface 218 or within (or between) a layer of the cylinder 100. In some embodiments, the sensor 202 may be disposed on an interior surface within the interior space 224 of the cylinder 100.

[0027] The sensors 202 may be located at known sensor locations 206. The data detected by the sensors, along with the sensor locations 206 on the cylinder 100, may be used to determine the location of any damage, such as a detected dent 204. Although four sensors 202 are depicted in the drawings, any number of sensors may be used. In most cases, the more sensors 202 used, the more accurate the determination of the location of the damage and the extent of the damage will be.

[0028] 3A is a block diagram of components that may be connected to the cylinder 100. As described herein, the system 300 includes the cylinder 100 and a sensor 202. As also described herein, the sensor 202 is physically coupled to the cylinder 100.

[0029] The sensor 202 may be communicatively connected to the control unit 302 (or a "cylinder control unit," "cylinder-side control unit," or "shock monitoring control unit"). The sensor 202 may be configured to detect deformation data relating to an impact received by (or caused on) the cylinder 100. In this specification, "deformation data" may be used as a term referring to deformation of the cylinder 100. In this regard, "disturbance data," "shock data," "cylinder integrity data," and the like may also be used synonymously with "deformation data."

[0030] The deformation data may be provided to a control unit 302. The control unit 302 may be a computer processor, a microprocessor, or a control device, or any device configured to execute instructions stored in a non-transient memory. The control unit 302 may be provided in a housing that is physically connected to the cylinder 100 (e.g., directly on the cylinder 100, in a housing of the cylinder 100, or in a device connected to the cylinder 100). As shown in FIG. 3A, the control unit 302 is configured to monitor only the cylinder 100, and if the vehicle 102 uses multiple cylinders, a set of sensors 202 and control units 302 are associated with each cylinder 100.

[0031] The sensors 202 and the controller 302 may be communicatively coupled by wires or wirelessly using respective transceivers (e.g., a transceiver for each sensor 202 and a transceiver for the controller 302). Although two sensors 202 are depicted in the drawings, the system 300 may include any number of sensors 202, and any one of the sensors 202 may be communicatively coupled to the controller 302.

[0032] The control unit 302 may receive the deformation data detected by the sensor 202, detect whether an impact event has occurred on the cylinder 100, and determine the energy level of the impact event. In some embodiments, the control unit 302 digitizes the deformation data detected by the sensor 202, detects whether an impact event has occurred on the cylinder 100, and determines the energy level of the impact event.

[0033] 3B is a block diagram illustrating components that may be connected to each cylinder 100 (e.g., cylinder 100A and cylinder 100B). As described herein, system 350 includes a plurality of cylinders 100 and sensors 202 (e.g., sensor 202A and sensor 202B). As also described herein, sensor 202 is physically coupled to a corresponding cylinder 100.

[0034] The sensor 202 may be communicatively connected to a controller 352 similar to the controller 302. The sensor 202 may be configured to detect deformation data related to an impact received by (or caused by) the cylinder 100. The deformation data may be provided to the controller 352. The controller 352 may be a computer processor, a microprocessor, or a control device, or any device configured to execute instructions stored in a non-transient memory. The controller 352 may be provided in a housing that is physically connected to the cylinder 100 (e.g., directly on any cylinder 100, in a housing of the cylinder 100, or in a device connected to the cylinder 100). As shown in FIG. 3B, the controller 352 is configured to monitor the cylinder 100A and the cylinder 100B, so that the controller 352 can detect the impact regardless of whether the cylinder 100A or the cylinder 100B has been subjected to the impact.

[0035] The sensors 202 and the control unit 352 may be communicatively connected by wires or wirelessly using their respective transceivers (e.g., a transceiver in each sensor 202 and a transceiver in the control unit 352). Although the drawings depict two sets of sensors 202 and cylinders 100, the system 350 may include any number of sets of sensors 202 and cylinders 100, and any set of sensors 202 may be communicatively connected to the control unit 302.

[0036] The controller 352 may receive the deformation data detected by the sensors 202, detect whether an impact event occurred on the cylinder 100, and determine the energy level of the impact event. The data received from the sensors 202 may include identification information regarding which cylinder 100 the data pertains to. For example, each sensor 202 may be associated with an identifier, which may be communicated by the sensors 202 to the controller 352 along with the deformation data.

[0037] In some embodiments, the controller 302, 352 is a separate controller from the controller of the vehicle 102 (e.g., an electronic control unit) and from the controller of any other subsystems of the vehicle 102. In other embodiments, the controller 302, 352 is a controller of the vehicle 102 that is also configured to control one or more other subsystems of the vehicle 102.

[0038] 4 illustrates a sensor configured to detect deformation data and a model 401 of a cylinder. The model 401 may be constructed by a controller (e.g., controller 302, 352, etc.) communicatively coupled to a sensor (e.g., sensor 202, etc.). The cylinder 400 of the model 401 is equivalent to the real cylinder 100. In some embodiments, the controller may be provided with identification information corresponding to the cylinder 100 and may retrieve dimensions corresponding to the cylinder 100 from a local or remote non-transient memory. In some embodiments, the dimensions of the cylinder 100 are provided to the controller.

[0039] The sensors 402 of the model 401 are equivalent to the real sensors 202. The controller is given the location of the real sensors 202 on the real cylinder 100 and determines the corresponding location of the model sensors 402 on the model cylinder 400. Although four sensors 402 are depicted in the drawings, any number of sensors may be used. In most cases, the more sensors 402 used, the more accurate the determination of the location and extent of damage will be.

[0040] In experiments conducted using the systems and methods described herein, a Type 4 composite pressure cylinder (250 bar) measuring 353 mm diameter by 889 mm long with a wideband piezoelectric sensor coupled to its surface was modeled by cylinder 400 and sensor 402.

[0041] Next, a hemispherical TUP with a diameter of 50 mm was impacted (as shown by the modeled impact point 404) against the instrumented cylinder (energy level: 600 J), and the stress waves of the displacement components propagating in the out-of-plane direction were collected and digitized for quantitative analysis of position and energy.

[0042] FIG. 5 shows graphs 500 of waveforms collected from an example impact event, from which the propagation of guided stress waves resulting from the impact event can be seen.

[0043] Each graph trace corresponds to a respective sensor 202 and represents the amplitude (i.e., out-of-plane displacement) detected by each sensor over time. The propagation of these waves varies with the guided mode of wave propagation: an extensional mode E0 is followed by a flexural mode F0 of larger amplitude. Each mode has a different speed and comprises a wide frequency bandwidth. Therefore, it is clearly not a good proposition to try to identify the frequency components of the same mode common to each sensor channel and determine the arrival time of that wave at each sensor.

[0044] Figure 6 shows a graph 600 in which the direct arrival times (shown as vertical lines) of the 25 kHz component of the fundamental bending vibration wave at each channel have been determined using a threshold-independent arrival time estimation technique. The direct arrival times at each sensor channel are input into a source localization algorithm that finds the geodesic of the surface.

[0045] Specifically, an optimal calculation of the source location on the cylinder surface can be performed by knowledge of the group velocity of the 25 kHz component of the fundamental bending wave mode derived from knowledge of the dispersion relation of the laminate, discretizing the cylinder surface into N points, calculating the geodesic propagation distance from the i-th point on the cylinder to the j-th sensor, and minimizing the sum of squared errors due to the difference between the calculated and measured differences in arrival times between channels.

[0046] Figure 7 shows a model (with geodesic paths superimposed on the cylinder surface) after best guessing the source location of the impulse event identified in Figure 6. Knowing this location allows the determination of the direct wave arrival time from the impulse location to each sensor. This direct arrival time is used to determine the direct waveform energy measurement described below.

[0047] The systems and methods described herein quantify and calculate the direct waveform energy. WAVE ) can be calculated from the collected waveform using the following formula:

[0048]

number

[0049] The systems and methods described herein use direct energy because the quantification of the other energy may include reflected waves and wave energy that may have propagated from the impact in other arrival paths (longer distances) and been amplified by constructive interference with other waves, which may lead to inaccurate quantification of the detected impact. For example, quantification of the energy focusing on the evaluation of the amplitude is not as accurate as the systems and methods described herein because the propagating waves may combine with each other in constructive or destructive interference, leading to inaccurate evaluation of the wave energy. In contrast, the systems and methods described herein use direct wave energy, which suppresses reflected and indirect waves. The loss of energy as a function of the propagation distance due to the geometrical spreading of the wave front as it propagates from the source is addressed by the normalization process described herein.

[0050] From FIG. 8, it can be seen that the measurement of the direct wave energy (caused by an impact event) decays with distance according to a modified inverse square law. Therefore, the magnitude of the impact energy can be quantitatively evaluated from the wave energy measurement. Thus, it is possible to determine the impact energy based on the propagation distance and evaluate it against a threshold for any cylinder configuration. The systems and methods described herein detect events above the threshold and perform normalization for any wave propagation effects that may occur in practice. This normalization reduces the number of false triggers and increases the reliability of the system. As described herein, the normalization also accounts for amplitude and energy loss due to geometric spread in the source-sensor distance, along with other attenuation effects.

[0051] If the quantitative assessment of the magnitude of the impact energy exceeds an impact damage threshold (e.g., a predetermined laminate impact energy threshold), the controller 302, 352 is configured to notify the cylinder 100 that damage has occurred. The notification may be provided to any number of devices, such as the ECU of the vehicle 102, a local non-transient memory, a remote non-transient memory, etc.

[0052] Upon providing the notification to the ECU of the vehicle 102, the ECU of the vehicle 102 may illuminate a light or other notification indicator, such as a light on the dashboard of the vehicle 102 or on the instrument panel of the vehicle 102. The light or other type of notification may serve as a reminder to inspect the cylinder 100 before refilling it.

[0053] When providing the notification to the local non-transient memory, the controller 302, 352 may update the local non-transient memory with a status indicator corresponding to each cylinder 100 in the vehicle 102. The status indicator may change from a first status corresponding to an undamaged cylinder to a second status corresponding to a possibly damaged cylinder. The local non-transient memory may be accessed by another device (e.g., a filling device) to determine whether the cylinder 100 should be inspected before being refilled. If the local non-transient memory indicates that the cylinder is in the second status, the filling device (i.e., another device) may provide a notification to an operator or automatically prevent the filling of the cylinder 100.

[0054] Similarly, when providing the notification to the remote non-transient memory, the controller 302, 352 may update the remote non-transient memory with a status indicator corresponding to each cylinder 100 of the vehicle 102. The status indicator may change from a first status corresponding to an undamaged cylinder to a second status corresponding to a possibly damaged cylinder. The remote non-transient memory may be accessed by another device (e.g., a filling device) to determine whether the cylinder 100 should be inspected before refilling. If the remote non-transient memory indicates that the cylinder is in the second status, the filling device (i.e., another device) may notify an operator or automatically prevent the filling of the cylinder 100. The controller 302, 352 may access the remote non-transient memory using their respective transceivers (e.g., a transceiver connected to the controller 302, 352 and a transceiver connected to the remote non-transient memory).

[0055] When refilling a cylinder 100 that has suffered an impact and become weakened, the sensor 202 used to detect the impact can also perform modal acoustic emission (MAE) testing to detect loss of integrity of the cylinder during refill.

[0056] 9 shows a system 900 including a cylinder 100 connected to a filling device. The filling device may include a valve 902 and a supply tank 904. The valve 902 may be automatically controlled by a controller to control the filling of the cylinder 100 with gas stored in the supply tank 904. The cylinder 100 may also be filled while attached to the vehicle 102.

[0057] During filling of the cylinder 100, the contents of the cylinder 100 exert an outward pressure on the cylinder's shell, generating mechanical stresses within the composite laminate of the cylinder 100. As described herein, damage can cause material degradation of the composite laminate resulting in volumetric failure of the affected area through a number of damage mechanisms associated with composite pressurized cylinders (e.g., fiber breakage, matrix cracking, interfacial failure, etc.). These damage mechanisms cause stress waves to propagate from the origin of the damage mechanism to the wall of the cylinder 100. A sensor (e.g., a wideband piezoelectric sensor) 202 detects deformation data associated with these damage mechanisms by converting the stress waves into voltage and digitally collecting them for analysis.

[0058] If damage is detected during filling, one or more measures may be taken to mitigate the adverse effects of the damaged cylinder. A visual warning, such as a light or message display, may be activated. An audible warning, such as a siren or alarm, may be activated. Valve 902 may be automatically closed to prevent further filling of the cylinder with gas.

[0059] In some embodiments, gas from the supply tank 904 and / or cylinder 100 may be transferred to the surge tank 906 by selectively opening or closing one or more ports between the supply tank 904-cylinder 100-surge tank 906. For example, the valve 902 may be capable of opening and closing a port connected to the supply tank 904, a port connected to the cylinder 100, and a port connected to the surge tank 906. The ports may be selectively opened and closed in any combination. For example, during filling, the ports of the supply tank 904 and cylinder 100 may be opened and the ports of the surge tank 906 may be closed. In another example, if a break in the cylinder 100 is detected, the ports of the cylinder 100 and surge tank 906 may be opened and the ports of the supply tank 904 may be closed.

[0060] In some embodiments, the surge tank 906 is set at a lower pressure than the cylinder 100. This allows gas to be forced to move into the surge tank 906 if a port between the surge tank 906 and the cylinder 100 is opened. In some embodiments, suction or pressure can be applied to the gas to force it from the cylinder 100 to the surge tank 906. A vent stack can also be present to facilitate gas movement.

[0061] Modal acoustic emission analysis algorithms for digitally collected waveforms may focus on one or more of: detection and quantification of fiber tow breaks above a specified threshold; measurement of instabilities above a specified threshold for instabilities within a local material volume; damage mechanisms above a specified threshold for damage mechanisms accumulated in a local material volume; and detection of fretting emissions above a specified threshold as a function of the cylinder stack.

[0062] When a combination of the above is used to detect the presence or absence of a cylinder defect at the time of filling, the coefficients may be weighted based on various characteristics of the cylinder and the fuel system, including the cylinder's dimensions and structure. For example, when fretting emissions and local damage growth are combined to determine the presence or absence of a cylinder defect at the time of filling, the weighting of fretting emissions may be set higher than the weighting of local damage growth.

[0063] 10 is a block diagram of a system 1000. The system 1000 includes a cylinder 100, a sensor 202, and a control unit 302, as described herein.

[0064] The control unit 302 may be communicatively connected to a filling control unit 1002 (or a "filling device control unit" or a "filling side control unit"). The control unit 302 may be communicatively connected to the filling control unit 1002 by wire or wirelessly. The filling control unit 1002 may also be communicatively connected to a valve 902 that controls the flow of fuel when the cylinder 100 is refilled.

[0065] As described herein, the filling control unit 1002 may obtain the status of the cylinder 100 from the control unit 302 and / or the ECU of the vehicle 102 and / or local non-transient memory and / or remote non-transient memory.

[0066] The filling control 1002 may also be communicatively connected to a display 1004 and a speaker 1006. The filling control 1002 may be configured to display a graphical user interface on the display 1004. The graphical user interface may include a notification as to whether or not the cylinder 100 should be inspected before filling. The display 1004 may display the notification. The filling control 1002 may also be configured to provide a notification as to whether or not the cylinder 100 should be inspected before filling using the speaker 1006. The speaker 1006 may issue a notification such as a sound, an alarm, a spoken message (e.g., "Please inspect the cylinder before filling," etc.).

[0067] In some embodiments, the fill control 1002 may be unaware of the state of the cylinder 100 and perform the functions described herein without regard to the current state of the cylinder 100 .

[0068] As the cylinder 100 is filled with fuel, the sensor 202 may detect deformation data and provide the detected deformation data to the filling control 1002. In some embodiments, the sensor 202 is communicatively coupled to the filling control 1002 via the control unit 302. In some embodiments, the sensor 202 and the filling control 1002 are communicatively coupled by wire or directly using their respective transceivers.

[0069] The filling control unit 1002 receives the detected deformation data and detects damage caused to the cylinder 100 by filling the cylinder 100. If the detected damage exceeds a threshold, the filling control unit 1002 may automatically close the valve 902 to prevent further filling of the cylinder 100. In some embodiments, the filling control unit 1002 constantly monitors the cylinder 100 during filling to detect damage to the integrity of the cylinder 100 using the sensor 202. In some embodiments, the filling control unit 1002 monitors the cylinder 100 during filling using the sensor 202 only if the control unit 302, 352 detects damage exceeding an impact damage threshold based on a quantified value of the direct energy of the impact.

[0070] If the filling control unit 1002 receives the detected deformation data and detects damage caused to the cylinder 100 due to filling of the cylinder 100, receipt of fuel by a surge tank (e.g., surge tank 906) may be performed as described herein.

[0071] The control unit 302, 352 and the filling control unit 1002 utilize the same sensor 202, but while the control unit 302, 352 is configured to detect impact caused by an external force on the cylinder 100, the filling control unit 1002 is configured to detect damage to the cylinder 100 that may result in rupture due to previously weakened or deformed parts (e.g., parts where an impact has occurred) caused by the expansion of the cylinder 100 during filling.

[0072] In experiments conducted using the systems and methods described herein, a Type 4 composite pressure cylinder (250 bar) measuring 353 mm diameter by 889 mm long was fitted with a wideband piezoelectric sensor surface coupled to it, modeled by cylinder 400 and sensor 402 in Figure 4. A fill simulation was also performed with the same sensor to demonstrate MAE inspection of an aged cylinder.

[0073] 11 shows a plot 1100 of cumulative event detection by a channel above a first threshold (vertical axis: pressure vs. horizontal axis: test time). That is, plot 1100 shows the cumulative number of events by a first detection channel during a simulated cylinder filling. The dashed line corresponds to the pressure in the cylinder during two filling cycles.

[0074] Figure 12 shows a plot of local instability of a cylinder during a filling simulation. The solid line represents the pressure inside the cylinder. The dashed line is the background energy of instability, which represents the local instability within a given volume of the cylinder. Instability is indicated when the background energy curve undergoes a number of oscillations that exceed a specified threshold for a given cylinder configuration. When an instability analysis was performed, the cylinder in channel 1 exhibited local instability that exceeded a threshold level determined for the cylinder configuration, causing the filling process to be halted.

[0075] As described herein, the instability analysis shown in Figure 12 may be one of several factors used to identify damage during filling of the cylinder 100. Alternatively, a frequency vs. energy quantification algorithm may be used to quantitatively assess the magnitude of fiber damage and evaluate it against a specified threshold.

[0076] FIG. 13 shows time and time-frequency domain plots of an impact fiber tow failure event detected during a simulated filling of an impacted cylinder, occurring in the material volume where the impact damage occurred.

[0077] FIG. 14 illustrates an example of a system 1400 according to embodiments of the present invention. The system 1400 includes a cylinder 100, a sensor 202, and a controller 302, as described herein. As described herein, the sensor 202 is configured to detect deformation data of the cylinder 100 and communicate the deformation data to the controller 302. The sensor 202 may be a piezoelectric sensor (e.g., fiber Bragg grating, non-contact laser, etc.) or any other sensor configured to detect deformation of the cylinder 100. As also described herein, the controller 302 is configured to detect damage to the cylinder 100 based on the deformation data and determine whether the damage exceeds an impact threshold. The damage may be a quantified value determined based on the direct energy of an impact of an object in contact with the cylinder 100.

[0078] The system 1400 further includes a memory 1402 connected to the controller 302. The memory 1402 may be a non-transient memory configured to store instructions executed by the controller 302, which may be a computer processor such as a microprocessor, a microcontroller, etc. The memory 1402 may also store data such as deformation data detected by the sensor 202, the state of the cylinder 100, etc. The state of the cylinder 100 may be expressed by a number of stages (e.g., 2 stages, 3 stages, 4 stages, etc.) each associated with a word (e.g., "normal", "requires inspection", "damaged", etc.) or a number (e.g., 1, 2, 3, 4, etc.).

[0079] The system 1400 further includes a transceiver 1404 coupled to the controller 302. The transceiver 1404 may connect the controller 302 to a network, such as a local area network (LAN), a wide area network (WAN), a cellular network, a digital short range communications (DSRC), the Internet, or a combination thereof.

[0080] The transceiver 1404 may include a communication port or channel, such as one or more of a Wi-Fi unit, a Bluetooth unit, a radio frequency identification (RFID) tag or reader, a DSRC unit, or a cellular network unit for accessing a cellular network (e.g., 3G, 4G, 5G, etc.). The transceiver 1404 may transmit data to or receive data from devices or systems not directly connected to the controller 302. For example, the controller 302 may communicate with a remote data server 1408 and / or a filling device 1416. The transceiver 1404 may also access a network to which the remote data server 1408 and / or the filling device 1416 are connected.

[0081] The controller 302 may also be configured to communicate with one or more computers or electronic control units (ECUs) of a vehicle (e.g., vehicle 102) that uses the cylinder 100 to power it. As described herein, the vehicle's ECU may control one or more aspects of the vehicle, such as indicator lights, a display screen, a speaker, or other notification devices, to alert a driver or user when the controller 302 detects damage to the cylinder 100. The controller 302 may communicate with the vehicle's ECU via wires or through the transceiver 1404, which may be connected to its own transceiver. In this regard, the ECU may also be connected to its own non-transitory memory, similar to the memory 1402.

[0082] The cylinder 100, the sensor 202, the control unit 302, the memory 1402, and the transceiver unit 1404 may be collectively referred to as a cylinder monitoring device 1406. The cylinder monitoring device 1406 may be physically installed in a vehicle (e.g., the vehicle 102). In some embodiments, the "cylinder monitoring device" may refer to the sensor 202 and / or the control unit 302 and / or the memory 1402 and / or the transceiver unit 1404, and the cylinder 100 may not be included in the cylinder monitoring device. Although FIG. 14 illustrates each component being connected to the control unit 302, each component of the cylinder monitoring device 1406 may be connected to each other by a communication bus.

[0083] The controller 302 may communicate deformation data from the sensor 202 and / or updates to the status of the cylinder 100 to a remote data server 1408. The remote data server 1408 may include a processor 1410, a memory 1412, and a transceiver 1414. The processor 1410 may be any computing device configured to execute instructions stored in a non-transitory memory. The memory 1412 may be similar to the memory 1402 and configured to store instructions executed by the processor 1410, as well as deformation data detected by the sensor 202, the status of the cylinder 100, etc.

[0084] The transceiver 1414 is similar to the transceiver 1404 and is configured to transmit and receive data to and from one or more other devices, such as a cylinder monitoring device 1406, a filling device 1416, and the like.

[0085] In some embodiments, instead of the controller 302 making decisions based on deformation data from the sensor 202, the processor 1410 may receive the deformation data and assume one or more of the functions of the controller 302 described herein. In such embodiments, it may be computationally more efficient to communicate the deformation data detected by the sensor 202 to the remote data server 1408 (via their respective transceivers 1404, 1414) for processing by the processor 1410, rather than having the controller 302 perform the processing.

[0086] Although only one remote data server 1408 is depicted in the drawings, there may be multiple remote data servers 1408 configured to distribute the computational load and improve computational efficiency. In some embodiments, the remote data server 1408 may be any device capable of communicating with the cylinder monitoring device 1406 and capable of performing computer processing, such as a vehicle ECU, a mobile device (e.g., a smartphone, laptop, tablet, etc.), etc.

[0087] The controller 302 may also communicate deformation data from the sensor 202 and / or updates on the status of the cylinder 100 to the filling device 1416. The filling device 1416 includes a filling controller 1002 as described herein. The filling controller 1002 is configured to control a valve (e.g., valve 902) for filling the cylinder 100. The filling controller 1002 may receive data from the controller 302 via a transceiver 1418, similar to the transceiver 1404 and transceiver 1414. The filling controller 1002 may be coupled to a memory 1422 (e.g., a non-transient memory, etc.). The memory 1422 may be similar to the memory 1402 and memory 1412 and may be configured to store instructions to be executed by the filling controller 1002, as well as deformation data detected by the sensor 202, the status of the cylinder 100, etc.

[0088] As used herein, a "unit" may refer to hardware components, such as, for example, one or more computer processors, controllers, or computing devices, configured to execute instructions stored in non-transitory memory.

[0089] FIG. 15A is a flow diagram illustrating a method 1500 performed by the system described herein.

[0090] A number of sensors (e.g., sensor 202) detect deformation data (step 1502) on a composite cylinder (e.g., cylinder 100), the composite cylinder being a laminated structure made of multiple layers, and the deformation data detected by the sensors may indicate damage to one or more of the multiple layers. Each sensor may be a piezoelectric sensor located at a different location on the composite cylinder.

[0091] A controller (e.g., controller 302) determines a damage value based on the detected deformation data when the composite cylinder sustains impact damage (step 1504). Each sensor may be connected to the controller by wire or wirelessly. The damage value may be determined based on a direct wave energy measurement as described in detail in connection with FIG. 15B herein.

[0092] Continuing with method 1500 of FIG. 15A, the controller notifies 1506 if the damage value exceeds an impact damage threshold. The impact damage threshold may be predetermined and stored in a memory (e.g., memory 1402). The impact damage threshold may vary between composite cylinder models, each with different constructions, dimensions, and material compositions.

[0093] As described herein, the notifying by the controller when the damage value exceeds the impact damage threshold may include notifying at least one ECU of a vehicle (e.g., vehicle 102) to turn on a light indicating an inspection of the composite cylinder and / or notifying a non-transient memory (e.g., memories 1402, 1412, 1422) to update a stored state for the composite cylinder. The notifying by the controller 302 when the damage value exceeds the impact damage threshold may be performed using a respective transceiver (e.g., transceiver 1404, 1414, 1418).

[0094] The notification alerts a user, operator or technician to inspect the composite cylinder before refilling. Any damage to the composite cylinder caused by an impact with an object may be detected and the composite cylinder may be removed and / or repaired as appropriate. However, there may be situations in which a refill of the composite cylinder is performed despite undetected damage from impact with an object or accumulated damage due to improper operating conditions (e.g., a bolt getting stuck between the cylinder and the housing).

[0095] A fill control (e.g., fill control 1002) controls a valve (e.g., valve 902) to fill the composite cylinder with a fluid (e.g., gas fuel, liquid fuel, etc.) (step 1508). During this filling (or refilling) of the composite cylinder with the fluid, the integrity of the composite cylinder can be monitored using the sensor.

[0096] The filling control receives the deformation data from the sensors and detects damage to the composite cylinder based on the deformation data as the composite cylinder is filled with the fluid (step 1510). The filling control may detect damage to the composite cylinder by modal acoustic emission testing using the plurality of sensors.

[0097] The filling control unit can determine whether at least one indicator exceeds a respective predetermined threshold value through modal testing of the acoustic emissions, and if so, can determine that the integrity of the composite cylinder has been compromised.

[0098] The at least one indicator may comprise one or more of: a fiber tow failure indicator corresponding to a quantification of a detected fiber tow failure event and comparison to a fiber tow failure threshold; an instability indicator corresponding to instability within a local material volume exceeding an instability threshold; accumulated damage within a designated local material volume; a damage mechanism indicator corresponding to damage mechanisms accumulated in the local material volume exceeding a damage mechanism threshold; and a fretting emissions indicator corresponding to fretting emissions exceeding a fretting emissions threshold based on a laminate composition of the composite cylinder.

[0099] The fiber tow failure indicator may be determined based on a frequency and an energy amount of a wave detected by the sensor during modal testing of the acoustic emission and reflected in sensor data. The fiber tow failure indicator may also be determined based on a normalized direct energy determined by the multiple sensors.

[0100] The instability indicator may be a local instability indicator identified based on detected values ​​of vibration and background energy detected by the sensor during modal testing of the acoustic emission and reflected in sensor data.

[0101] The separation event indicator may be determined based on normalized direct energies determined by the multiple sensors, and may be determined based on a sharpness of a frequency spectrum of waves detected by the sensors during modal testing of the acoustic emissions and reflected in sensor data.

[0102] The damage mechanism indicators may be related to damage from local material volumes. The location (clustering) of damage mechanisms may be identified based on threshold-independent measurements of the arrival time of damage detected by the sensors and the shortest propagation distance through the curvilinear space of damage detected by the sensors.

[0103] The above indicators may be considered alone or in combination. When considered in combination, a weight may be assigned to each indicator. For example, when the fiber tow breakage indicator and the instability indicator are considered together, the weight of the fiber tow breakage indicator may be set lower than the weight of the instability indicator, or vice versa. The indicators considered may vary based on any characteristic of the composite cylinder, such as the composition of the composite cylinder, the materials used in the composite cylinder, the dimensions of the composite cylinder, etc. Also, each threshold value for the indicators may vary based on any characteristic of the composite cylinder, such as the composition of the composite cylinder, the materials used in the composite cylinder, the dimensions of the composite cylinder, etc.

[0104] In some embodiments, the filling controller may detect damage to the composite cylinder if any of the indicators exceed a respective threshold value during filling. For example, if the fiber tow failure indicator and the instability indicator are considered, the filling controller may detect damage to the composite cylinder if the fiber tow failure indicator exceeds its threshold value or the instability indicator exceeds its threshold value during filling.

[0105] In some embodiments, the filling control unit determines an integrated damage index based on the number of indicators exceeding each threshold, and detects damage to the composite cylinder when the number (or the percentage) of indicators exceeding each threshold exceeds a threshold during filling. For example, the fiber tow failure indicator, the fretting emission indicator, and the instability indicator are considered. The threshold for the number of indicators exceeding each threshold may be two out of three. In other words, the filling control unit detects damage to the composite cylinder when two or more of the fiber tow failure indicator, the fretting emission indicator, and the instability indicator exceed their respective thresholds during filling.

[0106] In some embodiments, the filling control unit obtains an integrated damage index based on a weighted value of the number of indicators exceeding each threshold, and when the weighted ratio of the indicators exceeds a threshold during filling, the filling control unit detects damage to the composite cylinder. For example, the fiber tow failure indicator, the fretting emission indicator, and the instability indicator are considered. The weight of the fiber tow failure is 5, the weight of the fretting emission indicator is 1 (indicating that the fiber tow failure is 5 times more important than the fretting emission indicator), and the weight of the instability indicator is 2. In other words, when the fiber tow failure indicator, the fretting emission indicator, and the instability indicator all exceed their respective thresholds, a total of 8 points of the indicators can be considered. The threshold of the ratio of the indicators exceeding each threshold is 65%. Thus, if, during filling, the fiber tow failure index exceeds its threshold (5 points), the fretting emission index exceeds its threshold (1 point), and the instability index does not exceed its threshold, the filling control unit detects damage to the composite cylinder because 6 points divided by 8 points exceeds 65%. If, during filling, only the fiber tow failure index exceeds its threshold, the filling control unit does not detect damage to the composite cylinder because 5 points divided by 8 points does not exceed 65%.

[0107] Each of the thresholds described herein may be determined based on testing and calibrated for a composite cylinder. Each of the thresholds may be stored in a non-transient memory (e.g., memories 1402, 1412, 1422) and indexed with an identifier associated with the composite cylinder being monitored, such that the filling controller may look up the corresponding threshold based on the composite cylinder being monitored.

[0108] Both the controller and the fill controller may avoid false triggering by implementing digital signal processing algorithms that reduce external noise sources commonly encountered in normal operation (e.g., electromagnetic interference (EMI), flow noise, mechanical rub, etc.). The digital signal processing algorithms may be applied to deformation data detected by the sensor. The digital signal processing algorithms may make a false trigger determination based on one or more of: the simultaneous arrival of waves at the sensor; the detected energy before trigger; and the ratio of post-trigger energy to pre-trigger energy.

[0109] A safety action may be automatically performed after the filling control detects damage to the composite cylinder as the composite cylinder is filled with fluid (step 1512). The safety action may include the filling control closing the valve to prevent further filling of the composite cylinder. The safety action may include providing notification of the detected damage over a speaker or display screen to allow an operator to stop filling the composite cylinder. The safety action may include the filling control adjusting the valve to direct the fluid to a surge tank.

[0110] The automatic process during filling of the composite cylinder may be performed at all times, regardless of whether the control unit detects impact damage to the composite cylinder. In another embodiment, the automatic process during filling of the composite cylinder may be performed only if the control unit detects impact damage to the composite cylinder.

[0111] 15B is a flow diagram illustrating a method 1520 for measuring the direct wave energy performed by a system described herein, which may be used by the controller to determine the impact value associated with impact damage in step 1504 of method 1500 of FIG.

[0112] The controller (eg, controller 302) receives the deformation data from the sensor (eg, sensor 202) and digitizes the deformation data (step 1522).

[0113] Next, the control unit determines the direct arrival time of each of the specific wave components from the impact location to each of the multiple sensors (step 1524). That is, each of the multiple sensors detects the deformation data (e.g., deformation data represented by waves from four sensors appears in four channels in FIG. 5). A specific wave component common to each wave (e.g., vertical lines attached to each wave from the four sensors in FIG. 6) is identified. For each sensor, the arrival time of the common specific wave is determined. The arrival time represents the travel time of the specific wave component from the impact location to each sensor.

[0114] The controller determines 1526 an estimate of the location of the impact on the composite cylinder. The estimate may be determined based on the determined arrival times, the velocities of the wave components used to estimate the arrival times, the geometry of the cylinder being monitored, and the known locations of the sensors on the cylinder. The geometry of the various cylinders, dispersion relations (wave mode velocities as a function of frequency), and the known locations of the sensors may be stored in a memory (e.g., memories 1402, 1412, 1422) and accessed by the controller. The controller may model the estimated location of the impact on the composite cylinder (e.g., as shown in FIG. 7).

[0115] The controller determines the direct wave energy based on the respective direct arrival times of particular wave components at each sensor and the detected voltages at each sensor (step 1528). In some embodiments, the controller determines the direct waveform energy (U WAVE ) can be obtained.

[0116]

number

[0117] The systems and methods described herein may provide reliable coverage and monitoring using a relatively large number of sensors 202. The relatively high cost of conventional sensors may pose a challenge in providing a robust monitoring system. Thus, novel sensor designs are needed that provide at least comparable performance (e.g., in terms of sensitivity and bandwidth) at an economical cost.

[0118] 16A is a plan view of a sensor 1600 configured for use in the systems and methods described herein, as well as other systems and methods. As described herein, the sensor 1600 is a sensor that can be used as the sensor 202. That is, where the sensor 202 is described herein as having certain characteristics or capabilities, the sensor 1600 can have the same characteristics or capabilities. As described herein, the sensor 1600 is mass-producible and relatively low-cost. Additionally, the sensor 1600 is capable of sensing a number of different applications. Additionally, the sensor 1600 also allows for economical adjustments and changes in design.

[0119] The sensor 1600 is a multi-element piezoelectric sensor configured to detect deformation data of a composite structure, such as the composite cylinder 100 or any other composite structure mentioned herein (e.g., any composite structure where impact damage is detrimental, such as a wind turbine, an airframe, a leading edge of a wing, etc.). The sensor 1600 has a plurality of sensing elements 1602 configured to detect the deformation data. Specifically, the sensor 1600 has a first sensing element 1602A, a second sensing element 1602B, a third sensing element 1602C, a fourth sensing element 1602D, and a fifth sensing element 1602E.

[0120] The sensor 1600 has a number of leads 1616 configured to connect each sensing element 1602 to the connector 1610. Specifically, the first sensing element 1602A is connected to the connector 1610 by a first lead 1616A, the second sensing element 1602B is connected to the connector 1610 by a second lead 1616B, the third sensing element 1602C is connected to the connector 1610 by a third lead 1616C, the fourth sensing element 1602D is connected to the connector 1610 by a fourth lead 1616D, and the fifth sensing element 1602E is connected to the connector 1610 by a fifth lead 1616D. The sensor 1600 is connected to other components in the system (e.g., the controller 302, the controller 352, the fill controller 1002, etc.) via the connector 1610. In most embodiments, the sensing element 1602 is connected to a preamplifier circuit configured to amplify a signal detected by the sensing element 1602. The preamplifier circuit is connected to the controller (e.g., controller 302, controller 352, fill controller 1002, etc.).

[0121] As shown in FIG. 16, the sensing elements 1602 include a first sensing element 1602A, a second sensing element 1602B, a third sensing element 1602C, and a fourth sensing element 1602D having the same sensing area (or aperture or size) 1612, arranged to surround a fifth sensing element 1602E having a larger sensing area 1614. The first sensing element 1602A, the second sensing element 1602B, the third sensing element 1602C, and the fourth sensing element 1602D may have the same diameter 1604, resulting in the same sensing area 1612. The fifth sensing element 1602E may have a larger diameter 1606, resulting in a larger sensing area 1614.

[0122] Larger elements (e.g., sensing element 1602E) have better sensitivity (at a given low frequency range) due to their larger surface area, but perform poorly at higher frequencies due to phase cancellation caused by the so-called aperture effect. Smaller elements (e.g., sensing elements 1602A-1602D) cannot be as sensitive as larger elements (assuming all other structural details are the same) but have better high frequency response because they are not subject to phase cancellation caused by the aperture effect.

[0123] Although the sensing elements 1602 are depicted as being circular in the figures, in other embodiments the sensing elements 1602 are other shapes, for example, hexagonal, pentagonal, decagonal, etc. In other embodiments, the elements may be designed with an elliptical geometry and aligned on an anisotropic structure exhibiting a quasi-elliptical wave mode.

[0124] Also, although a particular number and arrangement of sensing elements 1602 are depicted in Figure 16A, any number of sensing elements may be fabricated and used in any configuration or arrangement. The number of sensing elements, the size of each sensing area, and the arrangement of each sensing element may all be adjusted based on the application of sensor 1600 and / or the location of sensor 1600 on the structure being monitored and / or the composition of the structure being monitored.

[0125] For example, the systems and methods described herein for monitoring a composite structure (e.g., composite cylinder 100) may utilize quantitative impact detection to detect damage to the composite structure due to impact or cumulative damage, and may also utilize MAE testing to detect damage to the composite structure as it is filled with fluids such as compressed natural gas, hydrogen, etc. In this example, one or more relatively small sensing elements (e.g., sensing elements 1602A-1602D) are included in sensor 1600 and may be used to detect damage to the composite structure as it is filled with fluid. Additionally, one or more relatively large sensing elements (e.g., sensing element 1602E) are included in sensor 1600 and may be used to detect impact events.

[0126] For quantitative impact detection, events that are not excited at relatively high frequencies (i.e., short wavelengths) are of interest, so larger diameter elements with high sensitivity are more appropriate. In contrast, when performing MAE inspection of laminated composite structures, higher frequencies must be detected by the sensing element to differentiate between damage mechanisms (e.g., fiber breaks vs. matrix cracks vs. delamination), so smaller diameter sensing elements are more appropriate.

[0127] By integrating both application-specific sized elements into the same sensor 1600, the sensor 1600 can specifically address the sensing requirements of the system depending on the specific scenario. This allows the same sensor 1600 to be used in scenarios where two different sensing technologies or sensing applications are applied. The first sensor element size can be optimized for the first technology or application, and the second sensor element size can be optimized for the second technology or application. This allows the sensor 1600 to be more versatile when connected to various systems (via connector 1610) than other sensors that only have one sensor element size. The sensor 1600 with multiple sensor element sizes is both more computationally and cost-effective than using two separate sensors with two different sizes.

[0128] Figure 16B is a side cross-sectional view taken along line AA in Figure 16A. Although Figure 16B depicts a side cross-sectional view of the first 1602A and fourth 1602D sensing elements, the features described with respect to the first 1602A and fourth 1602D sensing elements may be present in any of the sensing elements 1602.

[0129] The sensor 1600 can include a first polyimide film layer 1624 (e.g., Kapton® by DuPont®, etc.) configured to provide a dielectric layer between the ground electrode and the structure when the sensor is integrated into a stack.

[0130] The sensor 1600 may further include a positive electrode 1626 for each sensing element 1602. The positive electrode 1626 may be made of a conductive material such as copper. As shown in FIG. 16B, there is a first positive electrode 1626A corresponding to the first sensing element 1602A, and a fourth positive electrode 1626D corresponding to the fourth sensing element 1602D. The top surface of each positive electrode 1626 contacts the bottom surface of the polyimide film layer 1624. As shown in FIG. 16B, the positive electrodes 1626 of each sensing element 1602 may be flush with each other if the sensor is flat. If the sensor is not flat but is wrapped around a curved surface, the positive electrodes 1626 of each sensing element 1602 will still be flush with each other on a curved surface parallel to the curved surface on which the sensor is disposed.

[0131] A positive electrode 1626 is located above a first tape layer 1628. The first tape layer 1628 connects the positive electrode 1626 to an active sensing element 1630 located below the first tape layer 1628. The top surface of the first tape layer 1628 contacts the bottom surface of the positive electrode 1626 and the bottom surface of the first tape layer 1628 contacts the top surface of the active sensing element 1630.

[0132] The first tape layer 1628 may be comprised of one or more layers of z-axis anisotropic tape that is conductive only in the z-axis. That is, the first tape layer 1628 may not conduct electricity along the x-axis or y-axis. Additionally, the top surface of the active sensing element 1603 in contact with the first tape layer 1628 does not have a conductive layer and does not form an equipotential surface. This allows the first positive electrode 1626A and the fourth positive electrode 1626D to be both electrically connected to the active sensing element 1630 while being electrically isolated from each other. Although only the first positive electrode 1626A and the fourth positive electrode 1626D are shown in the drawings, each positive electrode is electrically connected to the active sensing element 1630 while being electrically isolated from each other.

[0133] The active sensing body 1630 may be a piezoelectric material with an inherently low quality factor suitable for a broadband response, such as PVDF-TrFE (Polyvinyldifluoride-trifluoroethylene). The active sensing body 1630 is configured to generate a current when subjected to mechanical stress. That is, when mechanical stress is applied to the active sensing body 1630 (e.g., due to the propagation of a transient stress wave caused by an impact on the structure or the breakage of the material of the structure), a voltage is generated between the positive electrode 1626 and the ground electrode 1634, which is detected by the system (at a control unit connected to the connector 1610) as described herein and used to determine deformation of the structure.

[0134] The active sensor 1630 is located above the second tape layer 1632. That is, the bottom surface of the active sensor 1630 contacts the top surface of the second tape layer 1632. In some embodiments, the second tape layer 1632, like the first tape layer 1628, is made of one or more layers of z-axis anisotropic tape that is conductive only in the z-axis. In other embodiments, the second tape layer 1632 is conductive in all directions. In contrast to the top surface of the active sensor 1630, the bottom surface of the active sensor 1630 that contacts the second tape layer 1632 may be provided with a conductive layer, in which case the bottom surface is an equipotential surface.

[0135] 16B, the width (e.g., horizontal width along the y-axis) of the first tape layer 1628, the active sensing element 1630, and the second tape layer 1632 may be greater than the width of each positive electrode (e.g., the first positive electrode 1626A, the fourth positive electrode 1626D, etc.). That is, the size and shape of the first tape layer 1628, the active sensing element 1630, and the second tape layer 1632 do not have to match the size and shape of the positive electrode 1602. This is possible due to the nature of the first tape layer 1628 being conductive only in the z-axis. Because the first tape layer 1628, active sensing element 1630, and second tape layer 1632 do not need to be fabricated to match the size and shape of the positive electrode 1602, but may extend over a portion or the entirety of the positive electrode 1602, the sensor 1600 may be less complex to fabricate than a sensor in which the first tape layer 1628, active sensing element 1630, and second tape layer 1632 are all conformed to the positive electrode. From the outline 1608 in FIG. 16A, it can be seen that the first tape layer 1628, active sensing element 1630, and second tape layer 1632 extend over a wide area across multiple elements. FIG. 16A also shows that the positive electrode 1626 is circular in shape.

[0136] 16B, the second tape layer 1632 is positioned above the ground electrode 1634. The ground electrode 1634 may be made of a conductive material such as copper. The top surface of the ground electrode 1634 may contact the bottom surface of the second tape layer 1632.

[0137] The ground electrode 1634 is located above a second polyimide film layer 1636 (e.g., Kapton® by DuPont®, etc.) which serves a dual purpose of being a dielectric layer between the ground electrode and the structure (when integrated into the laminate) and also providing a compliant substrate well suited for bonding to structures subjected to complex stress conditions (e.g., biaxial tension, etc.).

[0138] In some embodiments, a copper layer 1638 may be provided on top of the sensor 1600 to provide an electromagnetic interference (EMI) shield to protect the sensor 1600 from electromagnetic interference by one or more other devices.

[0139] FIG. 16B also illustrates a cross section of the lead 1616A. The lead 1616 may be made of a conductive material such as copper. Although FIG. 16B illustrates a first polyimide layer 1624 and a copper layer 1638 covering the lead 1616, in some embodiments, the first polyimide layer 1624 and the copper layer 1638 do not extend laterally to cover the lead 1616. In some embodiments, the area 1640 below the lead 1616 consists only of a dielectric material to insulate the lead from underlying objects. In some embodiments, some components, including the active sensor 1630, extend laterally below the lead 1616. However, in these embodiments, a non-conductive layer is provided between the active sensor 1630 and the lead 1616 to insulate the lead from the active sensor 1630.

[0140] The ground electrode layer 1634, the positive electrode 1626, and the lead 1616 may all be fabricated on a highly durable flexible printed circuit board using a flexible substrate so as to be flexible. In addition, the active sensing body 1630 may also be flexible. The first tape layer 1628, the second tape layer 1632, the first polyimide film layer 1624, and the second polyimide film layer 1636 may also be flexible. The flexibility of each component of the sensor 1600 allows the sensor 1600 to be flexible and conform to the mounting surface, improving adhesion and acoustic coupling to curved and / or rough surfaces compared to a rigid sensor.

[0141] The ground electrode layer 1634, the positive electrode 1626, and the leads 1616 can be fabricated on the flexible substrate by any method, including, for example, thermal transfer and resist development, CNC electrode deposition, etc. These methods can facilitate cost-effective manufacturing and mass production.

[0142] 16C is a side cross-sectional view of a sensor 1600 mounted on an exterior surface 1656 of the cylinder 100. The sensor 1600 has an exterior surface 1654 and an interior surface 1652. The interior surface 1652 of the sensor 1600 is in contact with the exterior surface 1656 of the cylinder 100. The sensor 1600 may be attached to the exterior surface of the cylinder 100 in any manner, such as with an adhesive.

[0143] 16D is a side cross-sectional view of a sensor 1600 that conforms to the curved surface of the cylinder 100. The sensor 1600 may be attached to the cylinder 100 with an adhesive or in any other manner. In some embodiments, the sensor 1600 may be manufactured integrally with the cylinder 100. For example, the sensor 1600 may be fabricated directly onto the cylinder 100 or may be disposed between layers of the cylinder 100 if the cylinder 100 is made of multiple layers.

[0144] In some embodiments, during manufacture of the cylinder 100, the exterior surface 1656 (or the portion of the exterior surface 1656 to which the sensor 1600 is attached) may be smoothed to facilitate sealing of the sensor 1600 to the cylinder 100. For example, during manufacture of the cylinder 100, a backing plate may be used that has a curvature that matches the outer diameter of the cylinder. A mold release agent may be applied to the backing plate. A mold-released backing plate is placed on the uncured cylinder 100 at the location where the sensor is to be attached. The cylinder 100 is cured, and the backing plate is removed after curing to provide a smooth surface for sealing of the sensor. This improves the bondline performance (i.e., bondline cycle life) and acoustic coupling (good response) of the sensor 1600.

[0145] Although Figures 16C and 16D depict the sensor 1600 attached to the cylinder 100, the sensor 1600 may be coupled to any monitored structure, such as a wind turbine, an airframe, a wing leading edge, or any other composite structure where impact damage is detrimental or exposed to large stresses.

[0146] 17 illustrates a sensor 1700 that is similar to sensors 1600 and 202, but differs in that it is made up of three different sensor element sizes. Sensor 1700 is assigned the same reference numerals as sensor 1600, and unless otherwise noted, has a similar configuration to sensor 1600. In particular, the cross-sectional structure illustrated in FIG. 16B is the same as the cross-sectional structure of sensor 1700 taken along line AA.

[0147] The sensor 1700 includes a plurality of sensing elements 1702. That is, the sensor 1700 includes a first sensing element 1702A, a second sensing element 1702B, a third sensing element 1702C, a fourth sensing element 1702D, and a fifth sensing element 1702E. The first sensing element 1702A, the second sensing element 1702B, and the fourth sensing element 1702D all have the same diameter 1704, and therefore have the same sensing area (or aperture or size).

[0148] Similar to the sensor 1600, the fifth sensing element 1702E is larger than the first sensing element 1702A, the second sensing element 1702B, and the fourth sensing element 1702D. The diameter 1706 of the fifth sensing element 1702E is larger than the diameter 1704. Thus, the sensing area of ​​the fifth sensing element 1702E is larger than the first sensing element 1702A, the second sensing element 1702B, and the fourth sensing element 1702D.

[0149] Unlike the sensor 1600, the third sensing element 1702C is larger than the first sensing element 1702A, the second sensing element 1702B, and the fourth sensing element 1702D, and smaller than the fifth sensing element 1702E. The diameter 1740 of the third sensing element 1702D is larger than the diameter 1704 and smaller than the diameter 1706. Thus, the sensing area of ​​the third sensing element 1702D is larger than the first sensing element 1702A, the second sensing element 1702B, and the fourth sensing element 1702D, and smaller than the fifth sensing element 1702E.

[0150] While sensor 1600 has two sensor element sizes, sensor 1700 has three sensor element sizes. This allows sensor 1700 to be used in situations where three different sensing technologies or sensing applications are applied. The first sensor element size may be optimized for a first technology or application, the second sensor element size may be optimized for a second technology or application, and the third sensor element size may be optimized for a third technology or application. This allows sensor 1700 to be more versatile when connected to various systems (via connector 1710) than other sensors that have only two or fewer sensor element sizes. Sensor 1700 with multiple sensor element sizes is both more computationally and cost-effective than using multiple separate sensors of different sizes.

[0151] FIG. 18 illustrates a sensor 1800 that is similar to sensors 1600, 1700, and 202, but differs in that it is made up of four different sensor element sizes. Sensor 1800 is assigned the same reference numerals as sensors 1600 and 1700, and has a similar configuration to sensors 1600 and 1700 unless otherwise noted. In particular, the cross-sectional structure illustrated in FIG. 16B also applies to sensor 1800. If line AA of FIG. 16A were present in FIG. 18, the side cross-sectional structure would be similar to that shown in FIG. 16B, except that the horizontal width of the first positive electrode would be wider in sensor 1800 than in sensor 1600, as will be described in more detail below.

[0152] The sensor 1800 includes a plurality of sensing elements 1802. That is, the sensor 1800 includes a first sensing element 1802A, a second sensing element 1802B, a third sensing element 1802C, a fourth sensing element 1802D, and a fifth sensing element 1802E. The second sensing element 1802B and the fourth sensing element 1802D both have the same diameter 1804, and therefore the same sensing area (or aperture or size).

[0153] Similar to sensors 1600 and 1700, the fifth sensing element 1802E is larger than the second sensing element 1802B and the fourth sensing element 1802D. The diameter 1806 of the fifth sensing element 1802E is larger than the diameter 1804. Thus, the sensing area of ​​the fifth sensing element 1802E is larger than the second sensing element 1802B and the fourth sensing element 1802D.

[0154] Unlike sensor 1600 (but similar to sensor 1700), the third sensing element 1802C is larger than the second sensing element 1802B and the fourth sensing element 1802D, and smaller than the fifth sensing element 1802E. The diameter 1840 of the third sensing element 1802D is larger than the diameter 1804 and smaller than the diameter 1806. Thus, the sensing area of ​​the third sensing element 1802D is larger than the second sensing element 1802B and the fourth sensing element 1802D, and smaller than the fifth sensing element 1802E.

[0155] Unlike the sensor 1600 and the sensor 1700, the first sensing element 1802A is larger than the second sensing element 1802B, the third sensing element 1802C, and the fourth sensing element 1802D, and smaller than the fifth sensing element 1802E. The diameter 1842 of the first sensing element 1802A is larger than the diameters 1804 and 1840, and smaller than the diameter 1806. Thus, the sensing area of ​​the first sensing element 1802A is larger than the second sensing element 1802B, the third sensing element 1802C, and the fourth sensing element 1802D, and smaller than the fifth sensing element 1802E.

[0156] While the sensor 1700 has three sensor element sizes, the sensor 1800 has four sensor element sizes. This allows the sensor 1800 to be used in situations where four different sensing technologies or sensing applications are applied. The first sensor element size may be optimized for a first technology or application, the second sensor element size may be optimized for a second technology or application, the third sensor element size may be optimized for a third technology or application, and the fourth sensor element size may be optimized for a fourth technology or application. This allows the sensor 1800 to be more versatile when connected to various systems (via the connector 1810) than other sensors that have only three or fewer sensor element sizes. The sensor 1800 with multiple sensor element sizes is more efficient, both computationally and cost-effectively, than multiple separate sensors of different sizes.

[0157] 19 illustrates sensor 1900, which is similar to sensors 1600, 1700, 1800, and 202, but differs in that it is made up of five different sensor element sizes. Sensor 1900 is assigned the same reference numerals as sensors 1600, 1700, and 1800, and has a similar configuration to sensors 1600, 1700, and 1800, unless otherwise noted. In particular, the cross-sectional structure illustrated in FIG. 16B also applies to sensor 1900.

[0158] The sensor 1900 has a plurality of sensing elements 1902. That is, the sensor 1900 has a first sensing element 1902A, a second sensing element 1902B, a third sensing element 1902C, a fourth sensing element 1902D, and a fifth sensing element 1902E. The second sensing element 1902B has a diameter 1904 and a sensing area (or aperture or size) corresponding thereto.

[0159] Unlike sensors 1600, 1700, and 1800, the fourth sensing element 1902C is larger than the second sensing element 1902B. The diameter 1944 of the fourth sensing element 1902D is larger than the diameter 1904. Thus, the sensing area of ​​the fourth sensing element 1902D is larger than the second sensing element 1902B.

[0160] Unlike sensor 1600 (but similar to sensors 1700 and 1800), the third sensing element 1902C is larger than the second sensing element 1902B and the fourth sensing element 1902D, and smaller than the fifth sensing element 1902E. The diameter 1940 of the third sensing element 1902D is larger than the diameters 1904 and 1944, and smaller than the diameter 1906. Thus, the sensing area of ​​the third sensing element 1902D is larger than the second sensing element 1902B and the fourth sensing element 1902D, and smaller than the fifth sensing element 1902E.

[0161] Unlike sensors 1600 and 1700 (but similar to sensor 1800), the first sensing element 1902A is larger than the second sensing element 1902B, the third sensing element 1902C, and the fourth sensing element 1902D, and smaller than the fifth sensing element 1902E. The diameter 1942 of the first sensing element 1902A is larger than the diameters 1904, 1940, and 1944, and smaller than the diameter 1906. Thus, the sensing area of ​​the first sensing element 1902A is larger than the second sensing element 1902B, the third sensing element 1902C, and the fourth sensing element 1902D, and smaller than the fifth sensing element 1902E.

[0162] Similar to sensors 1600, 1700 and 1800, the fifth sensing element 1902E is larger than any of the other sensing elements. The diameter 1906 of the fifth sensing element 1902E is larger than the diameters 1904, 1940, 1942 and 1944. Thus, the sensing area of ​​the fifth sensing element 1902E is larger than the other sensing elements.

[0163] While the sensor 1800 has four sensor element sizes, the sensor 1900 has five sensor element sizes. This allows the sensor 1900 to be used in situations where five different sensing technologies or sensing applications are applied. The first sensor element size may be optimized for a first technology or application, the second sensor element size may be optimized for a second technology or application, the third sensor element size may be optimized for a third technology or application, the fourth sensor element size may be optimized for a fourth technology or application, and the fifth sensor element size may be optimized for a fifth technology or application. This allows the sensor 1900 to be more versatile when connected to various systems (via the connector 1910) than other sensors that have only four or fewer sensor element sizes. The sensor 1900 with multiple sensor element sizes is more efficient, both computationally and cost-effectively, than using multiple separate sensors of different sizes.

[0164] Although Figures 16A, 17, 18, and 19 depict sensors with varying numbers of sensor elements of varying sizes, the sensors described herein may include any number of sensor elements and may employ any number of different sizes. The use of two, three, four, or five sensor elements and / or sensor element sizes is exemplary only and is not intended to be limiting of the invention.

[0165] As described herein, the sensors (e.g., sensor 1600, sensor 1700, sensor 1800, sensor 1900, etc.) may be considered passive sensors in that they do not actively generate waves for another sensor to detect, but rather, they passively monitor the composite structure as the composite laminate is subjected to stress from an external source, as well as determining when, where, and how severe an impact event occurs in the composite structure.

[0166] To demonstrate the performance of various embodiments of the sensors described herein, which may also be referred to as multi-purpose multi-element grated array (OMEGA) sensors, data collected from examples of OMEGA sensors similar to sensor 1600 are presented and the configuration of each example is described.

[0167] To quantify the sensitivity of the OMEGA sensor relative to a conventional wideband piezoelectric sensor, both an OMEGA sensor as shown in Figures 16A and 16B and a conventional single element B1025 sensor were bonded to a 7075 aluminium plate with lateral dimensions of 1200mm x 1800mm and a thickness of 3.1mm. The left side of Figure 20 shows a schematic diagram with relevant dimensions of the experimental setup used, while the right side of Figure 20 shows the actual experimental setup.

[0168] The time waveform and time-frequency distribution from source 2 (a 0.5 mm 6H pencil lead fracture source) for the B1025 sensor (transducer) are shown in FIG. 21A. The time waveform and time-frequency distribution from source 2 for element 1 (e.g., first element 1602A) of the OMEGA sensor are shown in FIG. 21B. Several important pieces of information can be obtained from FIG. 21A and FIG. 21B. First, the OMEGA sensor is more sensitive to in-plane deformation (S0 mode) than the B1025 sensor, while its sensitivity to out-of-plane deformation (A0 mode) is less than that of the B1025 sensor. Second, the peak response of element 1 (e.g., first element 1602A) of the OMEGA sensor is 10 dB below that of the B1025 sensor.

[0169] If it is desired to obtain a sensitivity response exceeding that of a conventional piezoelectric ceramic sensor consisting of a single element, a method of time-shifting and combining signals into a coherent state can be utilized for the OMEGA sensor. As an example, as shown in Figure 22, the data of each element (diameter 5 mm) in Figures 21A and 21B was time-shifted to a coherent state based on the time base of element 1, and the signals in the time-coherent state were summed.

[0170] The time waveform and time-frequency distribution from source 2 (a 0.5 mm 6H pencil lead fracture source) for the B1025 sensor are shown in Figure 23A. The time waveform and time-frequency distribution from source 2 for the sum of signals time-shifted to a coherent state in the OMEGA sensor are shown in Figure 23B.

[0171] It is known that the diameter of the sensing element of a sensor has a large influence on the sensitivity of the sensor due to the so-called aperture effect. Indeed, if the wavelength of the propagating wave is equal to the diameter of the active sensing body (or an integer multiple thereof), half of the piezoelectric element will be in tension while the other half will be in compression, resulting in a net zero response of the sensor to that wavelength (frequency). In most engineering structures, the thickness of the components is much smaller than the propagating wavelength, so the type of propagated wave is a guided wave (determined by the dispersion relation). Figure 24 shows the frequency-wavelength (λ) dispersion relation of a 3.1 mm thick 7075 Al plate, where the shaded area of ​​the aperture (φ) for each diameter corresponds to the frequency (wavelength) that is not affected by the aperture distortion. From Figure 24, it can be seen that the frequency at which the aperture effect occurs is mode dependent. It can be seen that the larger the aperture diameter, the lower the high frequency sensitivity for all modes of interest.

[0172] To illustrate the effect of aperture size on the acquired signal, a representative example of an OMEGA sensor was bonded to a 7075T6Al plate with lateral dimensions of 1200 mm x 1800 mm and thickness of 3.1 mm. The OMEGA sensor was designed as shown in FIG. 16A, with elements 1-4 (e.g., sensor elements 1602A-1602D) having a diameter of 5 mm and element 5 (e.g., sensor element 1602E) having a diameter of 13 mm. FIG. 25 is a schematic diagram of the experimental setup. As an example, FIG. 25 uses source 1 (a 0.5 mm 6H pencil lead break (PLB) fracture). FIG. 26 shows the time response (top) and normalized frequency response (bottom) for element 1 (e.g., sensor element 1602A) (diameter 5 mm) and element 5 (e.g., sensor element 1602E) (diameter 13 mm). From FIG. 26 it can be seen that while the 13 mm diameter has a much larger amplitude response due to its larger element surface area, the 5 mm diameter active element has a relatively better frequency response above 150 kHz.

[0173] In the data in Figure 26, the damage source is oriented out-of-plane with respect to the plate, so the fundamental bending vibration mode (F0) is preferentially excited. As can be seen in Figure 26, the smaller diameter element has a better high frequency response, as the first aperture effect of the F0 mode occurs at 150 kHz for the 13 mm diameter element, whereas the first aperture effect of the F0 mode does not occur until 550 kHz for the 5 mm diameter element.

[0174] Different measurement scenarios may require different sensitivity or high frequency response. For example, if the passive sensor is to monitor impact events with durations in the millisecond range and do not excite frequencies above about 100 kHz, it is advantageous to choose a large diameter element with high sensitivity. Conversely, if the passive sensor is to monitor frequency content due to material damage (in the nanosecond to microsecond range) up to 1 MHz or higher, a small diameter element without distortion due to aperture effects is the preferred solution.

[0175] In the inspection of composite pressure cylinders, it is beneficial to be able to distinguish between various damage mechanisms and quantify the adverse damage mechanisms in order to provide a better quantitative assessment and reduce false alarms. For example, in the modal acoustic emission (MAE) inspection of composite pressure vessels, frequency components up to 600 kHz (or higher) are used to distinguish between fiber fracture and various other damage mechanisms (e.g., matrix cracks, fiber / matrix disbonds, delamination, etc.). Small diameter active sensors are necessary to detect the frequency components without distortion due to aperture effects.

[0176] FIG. 27 is a flow diagram illustrating a method 2700 of manufacturing a sensor described herein (eg, sensor 1600, sensor 1700, sensor 1800, sensor 1900, etc.).

[0177] Fabrication of a ground electrode (e.g., ground electrode 1634) occurs (step 2702). The ground electrode may be made of a conductive material such as copper and may be fabricated using a flexible substrate as described herein to exhibit flexibility.

[0178] A plurality of positive electrodes (e.g., positive electrode 1626) and respective leads (e.g., lead 1616) are fabricated (step 2704). The positive electrodes and leads may be made of a conductive material such as copper and may be fabricated using a flexible substrate to exhibit flexibility, as described herein.

[0179] A bottom surface of a piezoelectric material (eg, sensing element 1630) is connected to a top surface of the ground electrode using a conductive tape (eg, second tape layer 1632) (step 2706).

[0180] The top surface of the piezoelectric material is connected to the bottom surface of the positive electrode using z-axis anisotropic tape (e.g., first tape layer 1628) (step 2708). As described herein, the piezoelectric material, the conductive tape connecting the piezoelectric material to the ground electrode, and the z-axis anisotropic tape can be shaped and sized independently of the shape and size of the positive electrode. This can lead to more efficient and less costly manufacturing than sensors in which the shape and size of each layer are matched to the shape and size of the positive electrode.

[0181] In some embodiments, the positive electrode is covered with a polyimide film layer (e.g., first polyimide film layer 1624) and the ground electrode is also connected to a polyimide film layer (e.g., second polyimide film layer 1636). In some embodiments, the sensor is covered with a copper layer (e.g., copper layer 1638) configured to provide EMI shielding for the sensor.

[0182] FIG. 28 is a flow diagram illustrating a method 2800 of making and using a sensor described herein (eg, sensor 1600, sensor 1700, sensor 1800, sensor 1900, etc.).

[0183] A number of monitoring tasks for the sensor are determined (step 2802). The number of monitoring tasks may be determined based on the monitored structure and / or the environment in which the monitored structure is installed or is installed. For example, in the case of a composite cylinder configured to store fuel for a vehicle, the monitoring tasks may include monitoring for impact events affecting the integrity of the composite cylinder, as described herein, as well as monitoring for loss of structural integrity of the composite cylinder when refilling the composite cylinder.

[0184] A plurality of sensor element sizes are respectively determined based on the plurality of monitoring tasks (step 2804). In some embodiments, a processor of a computing device may automatically determine the sensor element size and the arrangement and layout of sensor elements of various sizes in the sensor based on the monitoring tasks. The computing device has a non-transient computer readable memory configured to store instructions executed by the processor. The computing device may automatically determine the position of the sensor element on a composite structure and / or the sensor element size and / or the arrangement and layout of sensor elements of various sizes in the sensor based on the plurality of monitoring tasks as well as materials used to fabricate the composite structure. A sensor element size is determined for each monitoring task of the plurality of monitoring tasks. For example, if the sensor is configured to monitor for three different monitoring tasks, three sensor element sizes are determined.

[0185] The computing device can quickly adjust and redesign the layout of each sensing element of the sensor according to any changes in the number of monitoring tasks and / or the type of monitoring tasks and / or the sensor locations and / or the materials of the composite structure. The layout of each sensing element can refer to the layout of the positive electrode, since the layers above and below the positive electrode can remain the same for different sensor designs. Thus, the sensors described herein have lower redesign costs and faster redesign times than conventional sensors where all layers of the sensor can be redesigned and adjusted.

[0186] A sensor is fabricated (step 2806) having a plurality of element sizes corresponding to the plurality of monitoring tasks. The fabrication process of step 2806 may be similar to method 2700 described herein. The fabrication process may be automated by one or more machines configured to automatically fabricate layers of the sensor (e.g., ground electrode layer, positive electrode layer, and lead layer) and / or pick and place layers of the sensor to perform the fabrication steps described herein. Each sensor element may be designed using computer-understandable computer-aided design data corresponding to a dedicated computer-aided design software. A machine that prints a printed circuit board may automatically fabricate each layer of the sensor using the computer-understandable computer-aided design data.

[0187] The fabricated sensor is coupled to the composite structure (step 2808). As described herein, the exterior surface of the composite structure may be smoothed to facilitate sealing of the sensor to the composite structure, improving acoustic coupling and mechanical reliability of the bond line. The fabricated sensor may be automatically coupled to the composite structure by any method or technique, such as by application of an adhesive.

[0188] Advantageously, the piezoelectric elements used in the sensors described herein may be fabricated by a die-and-fill composite (DFC) method. The piezoelectric elements fabricated by the DFC method described herein may also be referred to as DFC piezoelectric elements.

[0189] Figures 29A-29F illustrate a method of making a DFC piezoelectric element 2900. In Figure 29A, a piezoelectric material 2902 is provided. In Figure 29B, the piezoelectric material 2902 is diced (i.e., scored) in a first direction 2906 (e.g., along the x-axis) to create columns 2904 of piezoelectric material 2902. In Figure 29C, the piezoelectric material 2902 is diced (i.e., scored) in a second direction 2910 (e.g., along the y-axis) to create columns 2908 of piezoelectric material 2902.

[0190] In FIG. 29D, epoxy 2912 is applied over the diced piezoelectric material 2902. In FIG. 29E, the epoxy 2912 and diced piezoelectric material 2902 may be heated and / or exposed to a vacuum so that the epoxy 2912 flows into the grooves 2914 between the posts 2908 of the diced piezoelectric material 2902. The epoxy 2912 may be initially liquid, and heating reduces the viscosity and promotes flow. The vacuum promotes degassing and reduces voids. In FIG. 29F, the piezoelectric material 2902 is coated with a conductor 2916. For example, a sputtered film of gold is applied to the piezoelectric material 2902.

[0191] Because the grooves are filled with epoxy, DFC piezo element 2900 can more easily conform to the mounting surface than a piezo element that is continuously solid along its length and / or width. The finished DFC piezo element / DFC sensor 2900 can be made to conform to a particular profile based on the surface of the composite structure being monitored by heating it to a temperature sufficient to soften the epoxy 2912 and cause it to bend.

[0192] Although the first direction 2906 is depicted as being orthogonal to the second direction 2910 in the figures, in some embodiments the first direction 2906 and the second direction 2910 may not be orthogonal. For example, if the surface of the composite structure is made up of multiple contours in various directions, the dicing of the DFC piezoelectric elements 2900 may be performed in a pattern specific to the surface of the composite structure. The closer the shape of the DFC piezoelectric elements 2900 is to the surface of the composite structure, the greater the contact area between the sensor using the DFC piezoelectric elements 2900 and the composite structure. Increasing the contact area between the sensor and the composite structure improves acoustic coupling (i.e., sensor response) and bond line integrity. As shown in Figures 29A-29F, the resulting piezoelectric element 2900 is a 1-3 piezoelectric composite, suggesting that it is conductive in only one direction.

[0193] 30A is a plan view of a sensor 3000 fabricated using a DFC piezoelectric element (e.g., DFC piezoelectric element 2900). Sensor 3000 includes a sensing element 3002 and leads 3016. In most embodiments, sensing element 3002 is connected to a preamplifier circuit configured to amplify a signal detected by sensing element 3002. The preamplifier circuit is connected to the controller (e.g., controller 302, controller 352, fill control 1002, etc.).

[0194] Figure 30B is a side cross-sectional view taken along line AA in Figure 30A. Sensor 3000 is a single element sensor, but otherwise the layer structure of sensor 3000 may be similar to sensor 1600. Similar components / layers are similarly numbered.

[0195] The sensor 3000 may include a first polyimide film layer 3024 (e.g., Kapton® by Dupont®, etc.) configured to provide a dielectric layer between the ground electrode and the structure when the sensor is integrated into a stack.

[0196] The sensor 3000 may further include a positive electrode 3026. The positive electrode 3026 may be made of a conductive material such as copper. The top surface of the positive electrode 3026 contacts the bottom surface of the polyimide film layer 3024.

[0197] The positive electrode 3026 is located above the first conductive layer 3028. The first conductive layer 3028 conductively connects the positive electrode 3026 to the active sensing body 3030 located below the first conductive layer 3028. The first conductive layer 3028 can be made of any conductive material, such as conductive tape, Z-axis conductive tape, solder, etc., configured to connect adjacent components. The top surface of the first conductive layer 3028 contacts the bottom surface of the positive electrode 3026, and the bottom surface of the first conductive layer 3028 contacts the top surface of the active sensing body 3030.

[0198] The active sensing element 3030 may be a piezoelectric element, such as piezoelectric element 2900. The active sensing element 3030 is configured to generate a current when subjected to mechanical stress such that when mechanical stress is applied to the active sensing element 3030 (e.g., due to the propagation of a transient stress wave caused by an impact on the structure or the failure of the material of the structure), a voltage is generated between the positive electrode 3026 and the ground electrode 3034, which is detected by the system (at a controller connected to the lead 3016) as described herein to determine deformation of the structure.

[0199] The active sensing body 3030 is located above the second conductive layer 3032. That is, the bottom surface of the active sensing body 3030 contacts the top surface of the second conductive layer 3032. The second conductive layer 3032 can be made of any conductive material, such as conductive tape, z-axis conductive tape, solder, etc., configured to connect adjacent components. The second conductive layer 3032 is located above the ground electrode 3034. The ground electrode 3034 can be made of a conductive material, such as copper. The top surface of the ground electrode 3034 can contact the bottom surface of the second conductive layer 3032.

[0200] In embodiments in which first conductive layer 3028 and second conductive layer 3032 are solder, manufacturing may be automated in that solid solder is placed between adjacent corresponding layers and the sensor is placed in a reflow oven where the solder melts to conductively connect the adjacent corresponding layers.

[0201] The ground electrode 3034 is located above a second polyimide film layer 3036 (e.g., Kapton® by DuPont®, etc.) which serves a dual purpose of being a dielectric layer between the ground electrode and the structure (when integrated into the laminate) and also providing a compliant substrate well suited for bonding to structures subjected to complex stress conditions (e.g., biaxial tension, etc.).

[0202] In some embodiments, a copper layer 3038 may be provided on top of the sensor 3000 to provide an electromagnetic interference (EMI) shield to protect the sensor 3000 from electromagnetic interference by one or more other devices.

[0203] The leads 3016 may be made of a conductive material such as copper. In some embodiments, the first polyimide layer 3024 and the copper layer 3038 cover the leads 3016. In other embodiments, the first polyimide layer 3024 and the copper layer 3038 do not extend laterally to cover the leads 3016. In some embodiments, the area below the leads 3016 consists only of a dielectric material to insulate the leads from underlying objects. In some embodiments, some components, including the active sensing body 3030, extend laterally to be located below the leads 3016. However, in these embodiments, a non-conductive layer is provided between the active sensing body 3030 and the leads 3016 to insulate the leads from the active sensing body 3030.

[0204] The ground electrode layer 3034, the positive electrode 3026, and the lead 3016 may all be fabricated on a highly durable flexible printed circuit board using a flexible substrate so as to exhibit flexibility. In addition, the active sensing body 3030 may also exhibit flexibility. The first conductive layer 3028, the second conductive layer 3032, the first polyimide film layer 3024, and the second polyimide film layer 3036 may also exhibit flexibility. By having each component of the sensor 3000 exhibit flexibility, the sensor 3000 can also exhibit flexibility and be able to follow the installation surface, and the sensor 3000 can have improved adhesion and acoustic coupling to curved and / or rough surfaces compared to a rigid sensor.

[0205] The ground electrode layer 3034, the positive electrode 3026 and the lead 3016 can be fabricated on the flexible substrate by any method including, for example, thermal transfer and resist development, CNC electrode deposition, etc. These methods can facilitate efficient manufacturing costs and mass production.

[0206] 30C is a side cross-sectional view of a sensor 3000 mounted on an exterior surface 3056 of the cylinder 100. The sensor 3000 has an exterior surface 3054 and an interior surface 3052. The interior surface 3052 of the sensor 3000 is in contact with the exterior surface 3056 of the cylinder 100. The sensor 3000 may be attached to the exterior surface of the cylinder 100 in any manner, such as with an adhesive.

[0207] 30D is a side cross-sectional view of the sensor 3000 conforming to the curved surface of the cylinder 100. The sensor 3000 may be attached to the cylinder 100 with an adhesive or in any other manner. In some embodiments, the sensor 3000 may be manufactured integrally with the cylinder 100. For example, the sensor 3000 may be fabricated directly onto the cylinder 100 or may be disposed between layers of the cylinder 100 if the cylinder 100 is made of multiple layers.

[0208] In some embodiments, during manufacture of the cylinder 100, the exterior surface 3056 (or the portion of the exterior surface 3056 to which the sensor 3000 is attached) may be smoothed to facilitate sealing of the sensor 3000 to the cylinder 100. For example, during manufacture of the cylinder 100, a backing plate may be used having a curvature that matches the outer diameter of the cylinder. A mold release agent may be applied to the backing plate. A mold-released backing plate is placed on the uncured cylinder 100 at the sensor attachment location. The cylinder 100 is cured, and the backing plate is removed after curing to provide a smooth surface for the sensor to seal. This improves the bondline performance (i.e., bondline cycle life) and acoustic coupling (good response) of the sensor 3000.

[0209] In some embodiments, the sensor 3000 may measure the transition temperature at which the resin 2912 of the DFC piezoelectric element 2900 changes from a solid to a malleable state (e.g., the glass transition temperature T g) or above. Heating the sensor 3000 above the transition temperature helps to bend and curve the DFC piezoelectric elements 2900 to conform to the surface of the composite structure being monitored. The selection of the resin (or resin mixture) may depend on a number of factors, including the desired transition temperature. That is, one or more resins may be used to achieve the desired transition temperature.

[0210] In contrast to sensor 1600, which is a multi-element sensor, sensor 3000 is a single-element sensor. As such, multiple sensors 3000 are used in the composite structure monitoring system described herein. Although multiple sensors 3000 are used, the system cost may be significantly lower than other similar sensors, such as multi-element sensor 1600, due to the lower electronic component costs provided by DFC piezoelectric element 2900. Additionally, sensor 3000 may be able to better conform to the surface of a composite structure than other similar sensors due to DFC piezoelectric element 2900.

[0211] Although Figures 30C and 30D depict the sensor 3000 attached to the cylinder 100, the sensor 3000 may be coupled to any monitored structure, such as a wind turbine, an airframe, a wing leading edge, or any other composite structure where impact damage would be adverse or exposed to large stresses.

[0212] To demonstrate the performance of the various embodiments of DFC sensors described herein, data collected from example sensors similar to sensor 3000 are presented and the construction of each example is discussed.

[0213] To quantify the sensitivity of the DFC sensor relative to a conventional broadband piezoelectric sensor, both the DFC sensor and a conventional single-element B1025 sensor were bonded to a 7075 aluminum plate with lateral dimensions of 1200 mm × 1800 mm and a thickness of 3.1 mm. Figure 31 shows a schematic diagram of the experimental setup used with relevant dimensions.

[0214] The source (damage source due to breakage of 0.5 mm 6H pencil lead) is shown in Figure 32. The model of the source shown in Figure 32 is expressed by a cosine bell forcing function (magnitude: 1 N, rise time: 1 μs).

[0215] The time and frequency waveforms from source 1 (damage source due to 0.5 mm 6H pencil lead breakage) for the B1025 sensor and the DFC sensor are shown in FIG.

[0216] The time-frequency distribution from source 1 (a 0.5 mm 6H pencil lead fracture source) for the DFC sensor is shown in Figure 34A. The time-frequency distribution from source 1 for the B1025 sensor is shown in Figure 34B. As can be seen from a comparison of Figures 34A and 34B, the DFC sensor is an order of magnitude more sensitive than the B1025 sensor.

[0217] The time and frequency waveforms from source 2 for the B1025 and DFC sensors are shown in FIG.

[0218] The time-frequency distribution from source 2 for the DFC sensor is shown in Figure 36A. The time-frequency distribution from source 2 for the B1025 sensor is shown in Figure 36B. As can be seen from comparing Figures 36A and 36B, the DFC sensor is an order of magnitude more sensitive than the B1025 sensor.

[0219] The time and frequency waveforms from source 3 for the B1025 and DFC sensors are shown in FIG.

[0220] The time-frequency distribution from source 3 for the DFC sensor is shown in Figure 38A. The time-frequency distribution from source 3 for the B1025 sensor is shown in Figure 38B. As can be seen from comparing Figures 38A and 38B, the DFC sensor is an order of magnitude more sensitive than the B1025 sensor.

[0221] In another experiment, a DFC sensor and a B1025 sensor were bonded in close proximity to each other on a Type 3 Self-Contained Breathing Apparatus (SCBA) cylinder. Source 1 was an out-of-plane failure and Source 2 was an in-plane failure. The following table shows the locations of each source and each sensor:

[0222] [Table 1]

[0223] The time and frequency waveforms from source 1 (out-of-plane fracture) for the B1025 and DFC sensors are shown in FIG.

[0224] The time-frequency distribution from source 1 (out-of-plane fracture) for the DFC sensor is shown in Figure 40A. The time-frequency distribution from source 1 for the B1025 sensor is shown in Figure 40B. As can be seen from comparing Figures 40A and 40B, the DFC sensor is an order of magnitude more sensitive than the B1025 sensor.

[0225] FIG. 41 is a flow diagram illustrating a method 4300 of making and using a sensor described herein (eg, sensor 3000).

[0226] A ground electrode (e.g., ground electrode 3034) is fabricated (step 4302). The ground electrode may be made of a conductive material such as copper and may be fabricated using a flexible substrate as described herein to exhibit flexibility.

[0227] A positive electrode (e.g., positive electrode 3026) and respective leads (e.g., lead 3016) are fabricated (step 4304). The positive electrode and the leads may be made of a conductive material such as copper and may be fabricated using a flexible substrate as described herein to exhibit flexibility.

[0228] A DFC piezoelectric element (e.g., DFC piezoelectric element 2900) is fabricated (step 4306). As described herein, the DFC piezoelectric element may be fabricated by dicing a piezoelectric material in multiple directions as shown in Figures 29A-29F and filling the grooves formed by the dicing with resin.

[0229] A bottom surface of the DFC piezoelectric element (eg, sensing element 3030) is connected to a top surface of the ground electrode (eg, using second conductive layer 3032) (step 4308).

[0230] The top surface of the DFC piezoelectric element is connected to the bottom surface of the positive electrode (eg, using first conductive layer 3028) (step 4310).

[0231] In some embodiments, the positive electrode is covered with a polyimide film layer (e.g., first polyimide film layer 3024) and the ground electrode is also connected to a polyimide film layer (e.g., second polyimide film layer 3036). In some embodiments, the sensor is covered with a copper layer (e.g., copper layer 3038) configured to provide EMI shielding for the sensor.

[0232] The fabricated sensor is coupled to a composite structure (step 4312). As described herein, the outer surface of the composite structure may be smoothed to facilitate bonding of the sensor to the composite structure, improving acoustic coupling and mechanical reliability of the bond line. As also described herein, the sensor is bonded to a composite structure at a transition temperature (e.g., glass transition temperature T g ) or above. When the sensor is heated to or above the transition temperature, it tends to bend and curve the DFC piezoelectric element to conform to the surface of the composite structure being monitored. The fabricated sensor can be automatically coupled to the composite structure by any method or technique, such as by application of an adhesive.

[0233] Exemplary embodiments of the method / system have been disclosed, but are merely illustrative. Thus, the terms used throughout should not be read as limiting the present invention. Although minor modifications to the teachings herein will be apparent to those skilled in the art, it is understood that the scope of the patent, if granted, which would define the scope of the present invention includes any embodiment that would reasonably be considered to be within the scope of the innovation that the patent contributes to the art, and is not limited except by the scope of the appended claims and equivalents. Any configuration described herein and combinations of two or more such configurations are intended to be within the scope of the present invention, unless the configurations included in such combinations are mutually exclusive.

Claims

1. a plurality of sensors coupled to the composite cylinder and configured to detect deformation data relating to the composite cylinder; A control unit communicatively connected to the plurality of sensors, determining a damage value based on the detected deformation data when the composite cylinder is impact damaged; and providing a notification if the damage value exceeds an impact damage threshold; A control unit configured as above; A filling control unit communicatively connected to the plurality of sensors, controlling a valve to fill the composite cylinder with fluid; and detecting damage to the composite cylinder based on the deformation data from the plurality of sensors when the composite cylinder is filled with the fluid; and automatically performing a safety action if damage to the composite cylinder is detected; A filling control unit configured as above; A monitoring system comprising:

2. 10. The system of claim 1, wherein the composite cylinder is a laminated structure made up of multiple layers, and the deformation data detected by the multiple sensors indicates damage to one or more of the multiple layers.

3. 3. The system according to claim 1 or 2, wherein the control unit is further configured to determine direct wave energy from an object when the composite cylinder suffers the impact damage, and the control unit determines the damage value based on the determined direct wave energy.

4. 4. The system according to claim 3, wherein the control unit: digitizing the deformation data from the plurality of sensors; determining a direct arrival time of each of the minimum velocity wave components from the impact position to each of the plurality of sensors; determining an estimate of the impact location on the composite cylinder; The direct wave energy is determined based on the respective direct arrival times of the minimum velocity wave components at each sensor and the detected voltages at each sensor. The system determines the direct wave energy by:

5. 2. The system of claim 1, wherein the filling control is further configured to perform modal acoustic emission testing to detect damage to the composite cylinder as the composite cylinder is filled with the fluid.

6. 2. The system of claim 1, wherein the controller is configured to: provide the notification to a vehicle ECU to turn on a light indicating an inspection of the composite cylinder; and / or provide the notification to a non-transient memory to update a stored status for the composite cylinder.

7. 2. The system of claim 1, wherein the safety action includes closing the valve to prevent filling of the composite cylinder, and / or providing a notification through a speaker or display screen, and / or adjusting the valve to direct the fluid to a surge tank.

8. 2. The system of claim 1, wherein the filling control unit is configured to detect damage to the composite cylinder based on at least one indicator exceeding a respective predetermined threshold when the composite cylinder is filled with the fluid.

9. 10. The system of claim 8, wherein the at least one indicator comprises one or more of: a fiber tow failure indicator corresponding to a quantification of a detected fiber tow failure event and comparison to a fiber tow failure threshold; an instability indicator corresponding to instability in a local material volume exceeding an instability threshold; a delamination event indicator corresponding to delamination of one or more layers of the composite cylinder exceeding a delamination threshold; a damage mechanism indicator corresponding to damage mechanisms accumulated in the local material volume exceeding a damage mechanism threshold; and a fretting emissions indicator corresponding to fretting emissions exceeding a fretting emissions threshold based on a laminate composition of the composite cylinder.

10. 2. The system of claim 1, the plurality of sensors are piezoelectric sensors each having a groove formed by dicing a piezoelectric material in a plurality of directions, the piezoelectric sensors being configured to follow the shape of the composite cylinder; the grooves of the piezoelectric material are filled with a resin configured to change to a plastic state upon reaching a temperature above a threshold temperature; The system wherein the piezoelectric material is located between a positive electrode and a ground electrode.

11. 11. The system of claim 10, wherein each piezoelectric sensor further includes a first polyimide film positioned above the positive electrode and a second polyimide film positioned below the ground electrode.

12. detecting deformation data relating to the composite cylinder with a plurality of sensors coupled to the composite cylinder; a step of calculating a damage value based on the deformation data detected by a control unit communicably connected to the plurality of sensors when the composite cylinder is damaged by impact; a step of notifying, by the control unit, when the damage value exceeds an impact damage threshold; a filling control unit communicatively connected to the plurality of sensors to control a valve to fill the composite cylinder with fluid; detecting damage to the composite cylinder based on the deformation data from the sensors by the filling control unit when the composite cylinder is filled with the fluid; automatically performing a safety action if damage to the composite cylinder is detected; A method comprising:

13. 13. The method of claim 12, wherein the composite cylinder is a laminated structure made up of multiple layers, and the deformation data detected by the multiple sensors indicates damage to one or more of the multiple layers.

14. The method according to claim 12 or 13, further comprising: A step of determining, by the control unit, a direct wave energy from an object when the composite cylinder sustains the impact damage, the control unit determining the damage value based on the determined direct wave energy; A method comprising:

15. 15. The method of claim 14, wherein the step of determining the direct wave energy comprises: a substep of digitizing said deformation data from said plurality of sensors; a sub-step of determining the respective direct arrival times of the lowest velocity wave components from the impact location to each of the plurality of sensors; a sub-step of determining an estimated location of the impact location on the composite cylinder; and determining said direct wave energy based on said respective direct arrival times of said lowest velocity wave components at each sensor and the detected voltages at each sensor. A method comprising:

16. 13. The method of claim 12, wherein the step of detecting damage to the composite cylinder as the composite cylinder is filled with the fluid includes the substep of performing, by the filling control, modal acoustic emission testing using the plurality of sensors.

17. 13. The method of claim 12, wherein the step of notifying by the controller if the damage value exceeds the impact damage threshold includes the substep of notifying an ECU of a vehicle to turn on a light indicating an inspection of the composite cylinder and / or notifying a non-transient memory to update a stored status for the composite cylinder.

18. 13. The method of claim 12, wherein the safety action includes closing the valve to prevent further filling of the composite cylinder, and / or providing a notification over a speaker or display screen, and / or adjusting the valve to direct the fluid to a surge tank.

19. 13. The method of claim 12, wherein the step of detecting damage to the composite cylinder as it is filled with the fluid includes the substep of determining whether at least one indicator exceeds a respective predetermined threshold.

20. 20. The method of claim 19, wherein the at least one indicator comprises one or more of: a fiber tow failure indicator corresponding to a quantification of a detected fiber tow failure event and comparison to a fiber tow failure threshold; an instability indicator corresponding to instability in a local material volume exceeding an instability threshold; a delamination event indicator corresponding to delamination of one or more layers of the composite cylinder exceeding a delamination threshold; a damage mechanism indicator corresponding to damage mechanisms accumulated in the local material volume exceeding a damage mechanism threshold; and a fretting emissions indicator corresponding to fretting emissions exceeding a fretting emissions threshold based on a laminate composition of the composite cylinder.

21. A sensor for monitoring a composite structure, comprising: a first sensor element of a first size configured to detect data related to a first monitoring task; a second sensor element of a second size configured to detect data related to a second monitoring task; and the first sensor element includes a first positive electrode and the second sensor element includes a second positive electrode, the first positive electrode being coplanar with the second positive electrode.

22. 22. The sensor of claim 21, wherein the first positive electrode has the first size and the second positive electrode has the second size, and the first positive electrode and the second positive electrode have a first conductive electrode configured such that a lower surface of each of them is configured to conduct electricity only along a vertical axis. A sensor connected via a tape layer to an active sensing element having a size larger than the sum of the first size and the second size, the active sensing element being configured to generate an electric current when placed under mechanical stress.

23. 23. The sensor of claim 22, wherein the first conductive tape layer has a size greater than the first size and the second size combined.

24. 24. The sensor of claim 22 or 23, wherein a lower surface of the active sensing body is connected via a second conductive tape layer to an upper surface of a ground electrode having a size larger than the sum of the first size and the second size.

25. 25. The sensor of claim 24, wherein the second conductive tape layer has a size greater than the first size and the second size combined.

26. 25. The sensor of claim 24 further comprising: a first polyimide film layer positioned above the first positive electrode and the second positive electrode, and a second polyimide film layer positioned below the ground electrode; A sensor comprising:

27. 27. The sensor of claim 26 further comprising: a copper layer overlying the first polyimide film layer and configured to block electromagnetic interference to the sensor; A sensor comprising:

28. 27. The sensor of claim 26, wherein the first polyimide film layer, the first positive electrode, the second positive electrode, the first conductive tape layer, the active sensor, the second conductive tape layer, the ground electrode, and the second polyimide film layer are each flexible and configured to conform to a surface to which the sensor is coupled.

29. 22. The sensor of claim 21, wherein the composite structure is a composite cylinder configured to store a fluid, and the first monitoring task is to detect direct wave energy from an object when the composite cylinder suffers impact damage from the object, and the second monitoring task is to detect damage to the composite cylinder when the composite structure is filled with the fluid.

30. 30. The sensor of claim 29, wherein the first sensor element is electrically connected to a controller configured to determine a damage value based on the detected direct wave energy, and the second sensor element is electrically connected to a controller configured to perform modal acoustic emission testing to detect damage to the composite cylinder as the composite cylinder is filled with the fluid.

31. 1. A method of manufacturing a sensor, comprising the steps of: fabricating a first positive electrode having a first size and a second positive electrode having a second size; preparing a ground electrode having a size greater than the first size and the second size; disposing a piezoelectric material between the layer of first and second positive electrodes and the ground electrode; A method comprising:

32. 32. The method of claim 31 further comprising: connecting a bottom surface of the piezoelectric material to a top surface of the ground electrode using conductive tape; connecting a top surface of the piezoelectric material to both bottom surfaces of the positive electrodes using z-axis anisotropic tape; A method comprising:

33. 33. The method of claim 31 or 32, further comprising: connecting a first polyimide film layer over the first positive electrode and the second positive electrode; connecting a second polyimide film layer underneath the ground electrode; A method comprising:

34. 32. The method of claim 31 , The step of fabricating the first positive electrode includes a sub-step of using a flexible substrate material so that the first positive electrode has flexibility and is configured to conform to a surface to which the sensor is connected; The step of fabricating the second positive electrode includes a sub-step of using a flexible substrate material so that the second positive electrode has flexibility and is configured to conform to a surface to which the sensor is connected; The method, wherein fabricating the ground electrode includes the substep of using a flexible substrate material such that the ground electrode is flexible and conforms to a surface to which the sensor is coupled.

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