Self-calibrating polymer nanocomposite (PNC) sensing elements

Abstract

Aspects of the present application allow for the measurement of a calibration resistance of a resistive film in a sensing element, such that the effects of contact resistance and background resistance drift due to factors such as temperature, strain, or aging can be reduced or eliminated. In some embodiments, a contact resistance independent resistance of a reference portion of a resistive film can be determined by taking a plurality of two-terminal resistance measurements between a plurality of electrode pairs on the resistive film. Furthermore, a contact resistance independent resistance of a sensing portion of the resistive film can be determined based on the plurality of two-terminal resistance measurements between the electrode pairs. The resistance of the reference portion can be removed from the measured resistance of the sensing portion, such that changes in the reference portion resistance that are not caused by sensing environmental conditions can be compensated for.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 038,551, filed June 12, 2020, Agent's File No. G0766.70312US00, entitled "Self-calibrating Polymer Nanocomposite (PNC) Sensing Element", the entire contents of which are incorporated herein by reference.

[0003] Federally funded research or development

[0004] This invention was completed with government support under a contract granted by the U.S. Air Force, number FA8649-20-9-9068. The government has certain rights to this invention. Technical Field

[0005] This application generally relates to sensors, and more particularly to the measurement of resistance sensors. Background Technology

[0006] Sensors are devices sometimes used to sense various environmental or structural health conditions. Environmental or structural sensors sense states of interest and communicate with reader devices via wired or wireless means. Multiple sensors can be deployed to monitor multiple spatial locations of a structure or environment, and these sensors can also be referred to as sensor nodes.

[0007] When a target material is exposed to certain environmental conditions, one or more states of the target material within a sensor can change. For example, when exposed to specific temperatures, mechanical vibrations, humidity, or moisture conditions over a period of time, the target material can corrode, causing its physical and chemical properties to change within the same timeframe. As another example, the target material in a crack sensor can be subjected to mechanical stresses reflecting those of structural components within a vehicle (e.g., an aircraft), causing one or more physical properties of the target material to change in response to changes in the structural health of the monitored component. Sensor devices can be used to monitor the state of target materials.

[0008] Sometimes, sensors use a wireless transceiver and an antenna included within the sensor to communicate with a reader. Sensors may use an external or battery-powered energy source to operate the transceiver and / or other components of the sensor. Summary of the Invention

[0009] Various aspects of this application allow for the measurement of the calibration resistance of a resistive film in a sensing element, thereby reducing or eliminating the effects of contact resistance and background resistance drift caused by factors such as temperature, strain, or aging. In some embodiments, the contact resistance-independent resistance of a reference portion of the resistive film can be determined by performing multiple two-terminal resistance measurements between multiple electrode pairs on the resistive film. Furthermore, the contact resistance-independent resistance of the sensing portion of the resistive film can be determined based on multiple two-terminal resistance measurements between electrode pairs. The resistance of the reference portion can be removed from the measured resistance of the sensing portion, thereby compensating for variations in the resistance of the reference portion not caused by sensing environmental conditions.

[0010] According to some embodiments, a self-compensating sensor is provided. The self-compensating sensor includes a sensing element. The sensing element includes a polymer nanocomposite (PNC) film. The self-compensating sensor further includes: a plurality of electrical branch points disposed on the sensing element; and measurement circuitry coupled to the plurality of electrical branch points. The measurement circuitry is configured to: measure a plurality of resistance values ​​between multiple pairs of electrical branch points selected from the plurality of electrical branch points; calculate a second resistance of a reference portion of the PNC film adjacent to the sensing portion based on the plurality of resistance values; calculate the second resistance of the reference portion of the PNC film adjacent to the sensing portion based on the plurality of resistance values; and determine a compensation resistance by comparing a first resistance of the sensing portion and the second resistance of the reference portion. The compensation resistance indicates sensing environmental conditions.

[0011] According to some embodiments, a method is provided for sensing the structural health of a structure using a sensing element. The sensing element includes a resistive film and a plurality of linearly arranged electrodes in electrical contact with the resistive film. The method includes: measuring a plurality of resistance values ​​between a plurality of pairs of electrodes selected from the plurality of linearly arranged electrodes; calculating a contact resistance-independent resistance value of a sensing portion of the resistive film based on the plurality of resistance values; calculating a contact resistance-independent resistance value of a reference portion of the resistive film based on the plurality of measured resistance values; and determining a compensation resistance value by combining the resistance values ​​of the sensing portion and the resistance values ​​of the reference portion, such that the compensation resistance indicates the structural health.

[0012] According to some embodiments, a sensor is provided. The sensor includes: a resistive film having a sensing portion and a reference portion adjacent to the sensing portion; a plurality of linearly arranged electrodes, including a first pair of electrodes contacting the sensing portion and a second pair of electrodes contacting the reference portion; and a measurement circuit coupled to the plurality of linearly arranged electrodes. The measurement circuit is configured to: measure a plurality of resistance values ​​between a plurality of pairs of electrodes selected from the plurality of electrodes; calculate a contact resistance-independent resistance value of the sensing portion based on the plurality of resistance values; calculate a contact resistance-independent resistance value of the reference portion based on the plurality of measured resistance values; and determine a compensation resistance value by combining the resistance values ​​of the sensing portion and the resistance values ​​of the reference portion. Attached Figure Description

[0013] Various aspects and embodiments of this application will be described with reference to the following accompanying drawings. It should be understood that these figures are not necessarily drawn to scale. Items appearing in multiple figures are denoted by the same reference numerals in all figures in which they appear. In the drawings:

[0014] Figure 1 This is a schematic diagram of an exemplary sensor according to some embodiments;

[0015] Figure 2A This is a schematic top view of an exemplary sensing element according to some embodiments;

[0016] Figure 2B It is shown that... Figure 2A A schematic circuit diagram of the equivalent circuit of the sensing element shown.

[0017] Figure 2C This is a schematic top view of an exemplary sensing element having five electrodes according to some embodiments;

[0018] Figure 3A This is a schematic top view of an exemplary sensing element according to some embodiments;

[0019] Figure 3B It is shown that... Figure 3A A schematic circuit diagram of the equivalent circuit of the sensing element shown.

[0020] Figure 4A This is a schematic top view of an exemplary PNC sensing element and several measurement configurations according to some embodiments;

[0021] Figure 4B This is a table illustrating an exemplary method for obtaining contact resistance-independent resistance of a resistive film region using four two-terminal resistance measurements according to some embodiments;

[0022] Figure 5A yes Figure 4AA schematic top view of an exemplary PNC sensing element, in which the measurement configuration shows nine possible arrangements of electrode pairs;

[0023] Figure 5B This is a table illustrating an exemplary method for obtaining contact resistance-independent resistance of several regions of a resistive film using four two-terminal resistance measurements according to some embodiments;

[0024] Figure 6A This is a table showing the error in predicting the crack length as a function of the test resistance R for four different given actual crack sizes;

[0025] Figure 6B Is for Figure 6A The table summarizes the four actual crack sizes, and the data graph of the noise floor of the predicted crack length measured by the sensor versus the measurement noise (expressed as a percentage).

[0026] Figure 7A and 7B An exemplary application of the sensors described herein for aircraft sensing is illustrated;

[0027] Figure 8 This is a schematic top view of an exemplary PNC sensing element based on a non-limiting example. Detailed Implementation

[0028] This invention relates to a self-compensating sensor based on a resistance sensing element having a polymer nanocomposite (PNC) film and a plurality of electrodes in contact with various points on the PNC film. One object of this application relates to two factors that can affect the accurate measurement of resistance in a resistive environmental sensor. The inventors have recognized and realized that when using a resistive film to sense environmental conditions (e.g., corrosion or structural crack length), the measured resistance value can be affected by the material properties of the resistor itself, regardless of the environmental conditions. Furthermore, the measured resistance value can be significantly affected by the contact resistance between the PNC film and the corresponding electrodes.

[0029] Embodiments of this application provide solutions to address these two effects on measured resistance values. In some embodiments, the contact resistance-independent resistance of the reference portion of the PNC film can be determined by performing multiple two-terminal resistance measurements between various electrode pairs on the resistance strip. Furthermore, the contact resistance-independent resistance of the sensing portion of the PNC film can be determined based on multiple two-terminal resistance measurements between electrode pairs. The resistance of the reference portion can be removed from the measured resistance of the sensing portion, allowing compensation for variations in the reference portion resistance not caused by sensing environmental conditions.

[0030] Some aspects of this application allow for the measurement of the calibration resistance of the resistive film in a sensing element, thereby reducing or eliminating the effects of contact resistance and background resistance drift caused by factors such as temperature, strain, or aging.

[0031] According to some aspects of this application, the sensing element in the sensor has a resistive film, wherein the resistance value of at least a portion of the resistive film can indicate the sensing state. For example, a portion of the resistive film may be exposed to mechanical stress or a corrosive environment, and its resistance value may represent the structural health state, corrosion state, or erosion state. The inventors have recognized and are aware that the resistance of the resistive film in a sensor device can be affected by background drift over a period of time, and the total measured signal may include a sensor signal superimposed on the background drift. Background drift can be caused, for example, by internal temperature and humidity variations independent of the environment in which the target material is located. Furthermore, in resistive sensors, the resistance from the resistive film to the contact junction increases the bias error in two-terminal resistance measurements, making it difficult to accurately measure the resistance of the resistive film itself and the changes in the resistance of the resistive film due to variations in sensing conditions.

[0032] Calibration of resistive film sensors can correct for sensor background drift. One approach is to provide two separate resistive arms within the same sensor device, with one arm serving as a reference resistor. Both arms are subjected to the same background drift to effectively subtract the common background drift, while emphasizing the desired sensor signal from one of the two resistors exposed to the sensing environment, thereby increasing the signal-to-background ratio without requiring the sensor device to be offline for calibration. An example of this method is described in U.S. Patent No. 10,502,676, Attorney General's File No. G0766.70124US00, the disclosure of which is incorporated herein by reference.

[0033] The inventors of this application have recognized and realized that a sensing element having a monolithic resistive film can be provided, wherein the monolithic resistive film is electrically contacted via multiple electrodes at multiple contact points on the resistive film. The resistive film has multiple regions defined between adjacent contact points, and the sensing element can be operated to accurately obtain the resistance value of one or more regions of the resistive film by removing the contribution of contact resistance. One region may have a resistance variation representing the sensing condition, while another region may be a reference resistor to calibrate or compensate for the effects of background drift, without necessarily relying on a reference resistor as a separate component. Therefore, the sensing element as described herein can be referred to as a self-calibrating or self-compensating sensing element.

[0034] According to one aspect of this application, a method for performing multiple measurements using various combinations of contact point pairs is used to achieve accurate resistance measurement. In some embodiments, the method includes measuring the resistance value between electrode pairs selected from at least four electrodes of a plurality of electrodes, and calculating a calibration resistance of a resistive film representing a sensing condition based on the measured resistance value.

[0035] The above aspects and embodiments, as well as additional aspects and implementation methods, are further described below. These aspects and / or embodiments may be used alone, in combination, or in any combination of two or more, as this application is not limited in this respect.

[0036] Figure 1 This is a schematic diagram of an exemplary sensor according to some embodiments. Figure 1 A sensor 10 is shown, comprising a measurement module 16, a sensing element 100, and a connector 18. The measurement module 16 is coupled to the sensing element 100 via the connector 18, which can be a cable, such as a flexible ribbon cable, or other suitable connectors that provide electrical communication. The sensor 10 may also have one or more antennas 12 for transmitting and receiving power and data signals from an external device, such as a reader. The measurement module 16 may include a housing, and an indicator 14 may be disposed externally to provide visual feedback to the operator. The indicator 14 may include, for example, one or more light-emitting diodes (LEDs).

[0037] The sensing element 100 includes a resistive film 110 and a plurality of electrodes 120 in contact with the resistive film 110. The plurality of electrodes 120 form a plurality of electrical branch points disposed on the sensing element 100 and connected to a connector 18. The electrodes 120 can be formed, for example, by depositing metal strips such as Au or Cu on the surface of the resistive film 110. In some embodiments, the resistive film may include a polymer nanocomposite (PNC) and may be referred to as a PNC film. In a non-limiting example, the PNC film may include carbon nanotubes (CNTs). In an exemplary PNC film, CNTs may be uniformly dispersed through a volume of polymer and disposed in a sheet or film; other forms of mixed CNTs within the PNC film may also be used.

[0038] like Figure 1 As shown, electrodes 120 are arranged in a linear array on resistive film 110 and have six electrodes. However, it should be understood that... Figure 1 Only illustrative examples are shown, and in some embodiments, there may be fewer than 6 electrodes, such as 5 electrodes. In some embodiments, more than 6 electrodes may be used.

[0039] Although Figure 1Not shown, but a non-conductive layer may be disposed on the bottom surface of the sensor, such as on the surface of the measurement module 16, and / or the bottom surface of the sensing element 100, to provide improved electrical isolation and improved adhesion to the host material or structure being monitored by the sensor. A non-conductive layer may additionally or optionally be disposed on the top surface of the sensor to provide improved electrical isolation and contamination isolation from the surrounding environment.

[0040] Sensor 10 can be wirelessly powered and interrogated, and used to sense the structural health of a structure as part of a Wireless Integrity Sensing Platform (WISP). An example of WISP is described in U.S. Patent Application Serial No. 16 / 268,437 (published as U.S. Patent Publication No. 2020 / 0247562A1), filed February 5, 2019, Attorney General's File No. G0766.70274US00, entitled "Integrated RF Power Supply Platform for Aircraft Structural Health Monitoring (SHM) Using Nanostructured Sensing Materials," the entire disclosure of which is incorporated herein by reference.

[0041] Figure 2A This is a schematic top view of an exemplary sensing element 200 according to some embodiments. Figure 2A As shown, the electrical contacts of the resistive film 210 are formed by six electrodes 220, each labeled L, M, N, X, Y, and Z. Figure 2A In this process, electrode 220 is formed into a thin strip that defines a region of resistive film 210 between adjacent electrodes labeled A, B, C, D and E.

[0042] Figure 2B It is shown that... Figure 2A The diagram shows a schematic circuit of the equivalent circuit of the sensing element. It can measure the resistance of a region and correlate it with the physical properties of the host material or structure, or the environment of the host material or tissue. For example, sensing element 200 can be a structural health monitor, and as... Figure 2A Region C of the sensing element shown can be a sensing portion attached to and subject to the same physical constraints of the structure, such that changes in resistance in region C can be used to calculate changes in structural properties, such as strain or cracking. In some embodiments, the resistance measurement of a region of the sensing element 200 can be correlated with the degree of damage, defect, or remaining useful life (RUL) of the host material or structure. In a non-limiting example, the resistance measurement of a region can be correlated with the length of a crack growing in the material.

[0043] Figure 3A This is a schematic top view of an exemplary sensing element 300 according to some embodiments. The sensing element 300 is in many ways similar to... Figure 2A The sensing element 200 is similar to that in the figure, and has similar parts marked with the same reference numerals.

[0044] Figure 3B It is shown that... Figure 3A A schematic circuit diagram of the equivalent circuit of the sensing element is shown. Sensing element 300 can be a witness corrosion sensing element, wherein region C is coated with a corrosion-sensitive material such as electroplated Cu. In this embodiment, the resistance measurement of region C (hereinafter referred to as Rc, and similarly, the resistance of other regions labeled alphabetically) can be correlated with the degree to which region C is exposed to a corrosive environment.

[0045] Return to reference Figure 2A In embodiments where region C is the sensing portion having resistance representing the sensing conditions of the host material, another region unaffected by the sensing conditions can be a reference portion or reference region whose resistance can be used to compensate for background drift in the resistive film. For example, since regions B and C are part of the same resistive film, their resistance values ​​are affected by the same material and / or manufacturing variability, and vary proportionally due to mechanical and / or environmental factors (e.g., strain or temperature changes or aging of the entire resistive film). In some embodiments where the characteristics of the resistive film 210 are not uniform in the XY plane, region B may be more preferably selected as the reference portion than, for example, region A, because region B is positioned closer to the sensing portion at region C, and therefore more accurately reflects the resistance of the underlying film material at region C.

[0046] The resistance value of a region can be defined and measured in any suitable manner. For example, the resistance value of region C can be the resistance in ohms measured along the x-direction on both the left and right sides between electrodes N and X. If the thickness and resistivity of the resistive film 210 are substantially uniform in region C, its resistance value can also be characterized as a square resistance in Ohm / sq. Furthermore, the calculated resistivity of region C can be used.

[0047] The inventors have recognized and realized that when attempting to measure the resistance value of region C, the conventional method of measuring the resistance between electrodes N and X in Figure 2 will produce an exaggerated R. NX =R N +R C +R X , where R C R is the actual resistance of the resistive film at region C. N and R X These are the contact resistances at the two contact points between electrode N and the resistive film, and between electrode X and the resistive film, respectively. R N and R C These are unknown values ​​that are not necessarily equal to each other. One aspect of this application relates to a method that uses multiple two-terminal resistance measurements at multiple selected electrode pairs to extract calibration or compensation resistance values ​​that are independent of contact resistance, i.e., without any contribution from contact resistance.

[0048] exist Figure 2A In this context, the dimensions of the components can be selected in any suitable manner, such as the width of the region AE of electrode 220 and resistive film 210 in the X and Y directions. Figure 2A This illustrates that during sensing operation using the sensing element 200, each region AE has a respective width W along the X direction or along the current flow direction within the resistive film 210. A W B W C W D and W E In some embodiments, a sensor is provided, and the width of the compensation region is greater than the width of the side region. For example, in some embodiments, region C is used as a sensing portion, region B is used as a reference portion or compensation region, and its width W B The side region W adjacent to the outer boundary of the resistive film 210 is larger than A In the non-restricted example, W C It is 12.5mm, W B It is 2.5mm, W A It is 1.5mm, and W D and W E Each of these dimensions is 1.5 mm, but other sizes may also be used. It should be understood that the same dimensional considerations can be applied to other figures showing the electrode layout. Figure 2C , 3A (4A, 5A).

[0049] Figure 2C This is a schematic top view of an exemplary sensing element 2001 having five electrodes according to some embodiments. The sensing element 2001 is in many ways similar to... Figure 2A Similar to sensing element 200, except that electrode Z is removed, resulting in only five electrodes used on resistive film 210. In some embodiments, region C of sensing element 2001 can be used as a sensing portion, while region B is used as a reference portion, as described above. Figure 2A The discussion is as follows. It should be understood that although other figures in this disclosure show six electrodes on a resistive film, aspects of this application do not require six electrodes, and the examples shown throughout the application can be implemented in alternative embodiments with only five electrodes.

[0050] Figure 4A This is a schematic top view of an exemplary PNC sensing element 400 and several measurement configurations according to some embodiments. Figure 4AThe inset shows two scanning electron microscope (SEM) images of the PNC film surface at region D, revealing an inhomogeneous surface morphology with peaks and valleys. Specifically, the left panel of the SEM images shows CNT aggregation in a certain area, resulting in surface inhomogeneity. The right panel of the SEM images shows the peaks and valleys on the imaged surface. This inhomogeneous surface morphology can generate non-negligible contact resistance between electrodes L, M, N, X, Y, Z and the PNC film, which can be compensated for using the methods described herein.

[0051] Any suitable measuring device can be used (e.g.) Figure 1 The measurement module 16) measures the two-terminal resistance between any combination of the two electrodes. The measurement can be based on Ohm's law, for example, by measuring the ratio of the static voltage applied to the two electrodes to the current flowing through one of the electrodes. Figure 4A Four possible arrangements of electrode pairs for two-terminal resistance measurements are shown: pair 1, pair 2, pair 3, and pair 4.

[0052] Figure 4B This is a table illustrating an exemplary method for obtaining contact resistance-independent resistance of a resistive film region using four two-terminal resistance measurements according to some embodiments. Figure 4B It shows in Figure 4A The resistance measured at point 1 will be R1 = R L +R A +R M The method continues by measuring three more pairs of resistors to obtain R2 = R L +R A +R B +R N R3 = R M +R B +R C +R X ;'R4=R N +R C +R X Using four formulas and by eliminating variables, R can be found. B = (R2 + R3 - R1 - R4) / 2. Therefore, the contact resistance of the reference resistor region B can be obtained without knowing the exact contact resistance of any electrode to the resistive film.

[0053] exist Figure 4A In the illustrated embodiment, region C of the PNC sensing element 400 is exposed to the body material or structure. Therefore, the resistance R, which is independent of contact resistance... C The test resistance R of the target will change based on the sensed conditions. The contact resistance-independent resistance of region C can be obtained after performing four two-terminal resistance measurements, combining the results to eliminate contact resistance, and comparing them with the baseline resistance of the region.

[0054] According to one aspect of this application, the baseline resistance Ro of region C can be determined by using R o =R B ×AF is created by averaging and normalizing RB, where AF is an area factor or geometric factor representing the geometric ratio between region C and region B.

[0055] Furthermore, according to one aspect, the contact resistance of region C can be obtained after performing four two-terminal resistance measurements, and the results can be combined to eliminate the contact resistance.

[0056] Figure 5A yes Figure 4A A schematic top view of an exemplary PNC sensing element, showing nine possible arrangement measurements of electrode pairs 1-9 for two-terminal resistance measurements. Figure 5B This is a table illustrating an exemplary method for obtaining contact resistance-independent resistance of several regions of a resistive film using four two-terminal resistance measurements according to some embodiments.

[0057] Figure 5B The contact resistance of region B is shown to be independent of the resistance, which can be obtained through R. B = (R2 + R4 - R1 - R5) / 2, the contact resistance of region C is independent of the resistance, which can be obtained through R C = (R6 + R8 - R5 - R9) / 2, and the contact resistance of region D is independent of the resistance through R. D = (R4 + R6 - R3 - R7) / 2 to obtain.

[0058] exist Figure 5A In the specific example shown, region C of the PNC sensing element 400 is exposed to the host material or structure. Therefore, the contact resistance is independent of the resistance R. C The test resistance R is the target resistance, which will change based on the sensed conditions. However, Rc will also change due to the inherent background drift of the PNC film in the sensing element 400. To calibrate Rc to eliminate the background drift effect, Rc from regions B and D can be used. B RD serves as the reference resistance value for compensating Rc, and regions B and D do not change based on sensing conditions.

[0059] According to one aspect of this application, it is possible to use R O =(R B +R DThe baseline resistance Ro is created by averaging and normalizing RB and RD by 1 / 2 × AF, where AF is an area factor or geometric factor representing the geometric ratio between region C and region B or D. For example, if the length of B in the x-direction is twice that of C, the baseline resistance of C is expected to be twice that of B, and the area factor will be 2.0 to reduce R. B Convert to R C If factors such as width, thickness, and / or resistivity are not the same for regions B and C, but can be determined before measurement, these factors can be determined during the fabrication of the sensing element and incorporated into AF as a scaling factor. The average resistance R of the two reference resistors... B and R D This will reduce the impact of manufacturing variability of the PNC film in the x-direction, and also eliminate the need to use averaging or equalization of two or more reference resistors.

[0060] It should be understood that regions B and D do not need to be the same size, and a unique area factor AF can be used for each region. B and AF D To obtain the averaged and normalized baseline R O =(R B ×AF B +R D ×AF D ) / 2.

[0061] In a non-limiting example, the baseline resistance R of region C has been obtained. O And the test resistor R, in one example, the calibration resistor can be obtained as R / R O =2R C / AF×(R B +R D In this example, the calibrated or compensated resistor is the calibrated value, and if R is equal to the baseline R... O If they are the same, then it is 100%. Changes in R due to the detected conditions will cause changes in R / Ro to represent the change in the detected condition. On the other hand, any background drift in the resistor will completely cancel out in R and Ro and will not affect R / Ro.

[0062] Figure 5B An exemplary calculation for an application of monitoring cracks using a calibration resistor is also shown, where structural changes in region C of the PNC membrane reflect cracks in the host material to which the sensor is attached. In this example, the crack length parameter a can be calculated as a = sqrt(2R) C / AF×(R B +R D )-l)=sqrt(R / R O -l).

[0063] Figure 6A The data shows that for a given actual crack size, the higher the percentage error in R, the greater the deviation between the actual crack size and the predicted crack length. It can be seen that for 1% Rs, there is almost no deviation, but the deviation starts to increase at 10%, and the predicted crack length no longer accurately reflects the actual crack length. For first-order cracks, the relative error between the predicted and actual crack lengths is proportional to half of Rs / Ro; therefore, if the parasitic resistance is 10% of the total resistance, the predicted crack length will have a 5% error.

[0064] Figure 6A The predicted crack length value is calculated using an assumption of a 1 kOhm gauge and a 20 mm gain factor (GF), although this sensor configuration is merely an example and the scope of this application is not limited thereto. The GF can be obtained from... Defined as follows: where GF is the sensor geometry factor, and ΔR is the difference or change in resistance between the measured resistance and the baseline resistance. This equation can be used to map ΔR / R from resistance to crack length. For example, crack length...

[0065] Figure 6B Is for Figure 6A The table summarizes four actual crack sizes, and the data graph shows the noise floor of the predicted crack length measured by the sensor versus the measurement noise (expressed as a percentage). The measurement noise, or ΔR / R, may represent the relative uncertainty of the measured resistance, which can introduce system noise or uncertainty in the predicted crack length. Figure 6B This correspondence is illustrated, and it shows that for a given actual crack size, such as 1 mm, higher measurement noise leads to higher noise or uncertainty in the predicted crack length. Crack length noise can be referred to as the noise floor because the predicted crack length will only be accurate to the noise floor range around the baseline.

[0066] It should be understood that other forms for determining a and R can also be used. Figure 4A In some embodiments where region C is used as the sensing part and region D is used as the reference part, the normalized test resistance R can also be calculated as... Where R C and R D These are the contact resistances of regions C and D, respectively, and R is an independent resistance. C0 and R D0This is the baseline resistance of each region. Aspects of this application can also be applied in other suitable forms to calculate the crack length parameter 'a' based on R. For example, in some embodiments, an equation for 'a' is determined empirically. In some embodiments, the equation for 'a' includes one or more polynomials of the normalized test resistance R. For example, empirical analysis of the crack length as a function of R can lead to the identification of a polynomial relationship between the two. The determined relationship can be used for subsequent crack length calculations as a function of R.

[0067] Figure 8 This is a schematic top view of an exemplary PNC sensing element 800 according to a non-limiting example. The sensing element 800 includes five electrodes m, n, x, y, z disposed on a resistive film 810 having regions A, C, D, and E, and pins P1, P2, ... P7. Pins P1-P5 are electrically connected to the respective electrodes m, n, x, y, z for connection to a measurement module (e.g., for measuring the resistance between electrode pairs). Figure 1 The measurement module 16 shown is an interface. For example, additional pins such as, but not limited to, P6 and P7 can be used to interconnect power, ground, and / or I / O data between the sensing element 800 and the measurement module 16. Figure 8 In the example, region C of the resistive film 810 is used as the sensing portion, while region D is used as the reference portion. The method discussed in this application can be used to measure the calibration resistance of the sensing portion.

[0068] Figure 7A and 7B An exemplary application of the sensor described herein for aircraft sensing is shown. Figure 7A The aircraft 700 and multiple sensors 702 are shown. Figure 7A It is a perspective view. Figure 7B This is a bottom view of the aircraft.

[0069] In this non-limiting embodiment, the illustrated aircraft 700 is an airplane. However, other aircraft may use sensors of the type described herein for structural health monitoring. For example, rockets, space shuttles, unmanned aerial vehicles, gliders, satellites, or other aircraft may use the sensors and sensing technologies described herein. Therefore, the nature of the aircraft is not limiting.

[0070] Sensor 702 may be a nanostructure sensor. These may include smart sensing materials, such as a nanostructure sensing layer. The nanostructure sensing layer may include nanostructure materials, such as carbon nanotubes (CNTs). In some embodiments, the nanostructure sensing element may include CNTs embedded in a polymer matrix. The smart sensing material may change in response to changes in the state of the sensed structure (e.g., an aircraft).

[0071] Sensor 702 can sense conditions that represent permanent changes in the state of an aircraft. For example, sensor 702 can be a corrosion sensor configured to sense the corrosive state of the aircraft. Sensor 702 can be a fatigue crack sensor configured to sense cracks in the aircraft. Aircraft 700 can have various types of sensors, such as corrosion sensors and fatigue crack sensors, or other sensors that can operate by experiencing permanent changes in state to simulate changes in the state of the monitored aircraft.

[0072] The aircraft 700 may include any suitable number of sensors 702. In some embodiments, one or more sensors 702 may be included.

[0073] In addition to the above, some novel aspects of this application are summarized below.

[0074] In some embodiments, a sensor is provided that includes a polymer nanocomposite (PNC) sensing element and more than two electrically disconnected points. Sensor measurements are correlated with changes in the resistance of the PNC sensing element and are self-compensated by performing multiple measurements through various combinations of electrical disconnected point pairs to account for material and / or manufacturing variability and variations due to mechanical and / or environmental factors such as strain, temperature changes, or aging.

[0075] In some embodiments, a non-conductive layer is disposed on the bottom surface of the sensor to provide improved electrical isolation and improved adhesion to the host material or structure. In some embodiments, a non-conductive layer is disposed on the top surface of the sensor to provide improved electrical isolation and contamination isolation from the surrounding environment.

[0076] In some embodiments, the resistance measurement is related to the physical properties of the host material or structure. In some embodiments, the resistance measurement is related to the environment of the host material or structure. In some embodiments, the resistance measurement is related to the degree of damage, defect, or remaining useful life (RUL) of the host material or structure. In some embodiments, the resistance measurement is related to the degree of exposure to a corrosive environment. In some embodiments, the resistance measurement value is related to the length of cracks growing in the material.

[0077] In some embodiments, a self-compensating polymer nanocomposite (PNC) sensing element is provided, comprising a plurality of contacts and a plurality of PNC regions. The multiple contacts and PNC regions are used to collect various combinations of resistance measurements to achieve self-compensation.

[0078] In some embodiments, self-compensation is performed to account for manufacturing variability and changes due to mechanical and / or environmental factors. Such changes may be caused by mechanical and / or environmental factors, such as any one of temperature, strain, and / or aging.

[0079] In some embodiments, some PNC regions are used to estimate the resistance in contact with the PNC, while others are used for sensing. In some embodiments, polymer nanocomposite regions may be functionalized for different structural health monitoring (SHM) sensing tasks. In some embodiments, sensing regions may be copper-plated to create witnessed corrosion sensing elements. In some embodiments, sensing regions may remain pristine or as exposed PNC material to create crack sensing elements.

[0080] In some embodiments, a method for a self-compensating sensor is provided. The sensor includes a polymer nanocomposite (PNC) sensing element and more than two electrical branch points. Sensor measurements are correlated with changes in the resistance of the PNC sensing element, and self-compensation can be achieved by performing multiple measurements through combinations of various electrical branch point pairs to account for material and / or manufacturing variability and variations due to mechanical and / or environmental factors such as strain, temperature changes, or aging.

[0081] In some embodiments, resistance measurements are related to the physical properties of the host material or structure. Resistance measurements may be related to the degree of damage, the degree of defect, or the remaining useful life (RUL) of the host material or structure, or the degree of exposure to a corrosive environment.

[0082] The terms "approximately" and "about" can be used to indicate that in some embodiments the value is within ±20% of the target value, in some embodiments it is within ±10% of the target value, in some embodiments it is within ±5% of the target value, but in some embodiments it is within ±2% of the target value. The terms "approximately" and "about" may include the target value.

Claims

1. A self-compensating sensor, comprising: Sensing elements including polymer nanocomposite PNC films; Multiple electrical branch points are disposed on the sensing element; The measurement circuit, coupled to the plurality of electrical branch points, is configured as follows: Measure multiple resistance values ​​between multiple pairs of electrical branch points selected from the plurality of electrical branch points; Calculate the first resistance of the sensing portion of the PNC film exposed to the environment based on the plurality of resistance values; Calculate the second resistance of the reference portion of the PNC film adjacent to the sensing portion based on the plurality of resistance values; and The compensation resistor is determined by comparing a first resistance of the sensing portion with a second resistance of the reference portion, wherein the compensation resistor indicates the sensing conditions of the environment. Each of the first resistor and the second resistor is a contact resistance-independent resistor. The plurality of electrical branch points comprises a plurality of linearly arranged electrodes, wherein the plurality of linearly arranged electrodes comprises at least five consecutive electrodes. The sensing portion is disposed between a first pair of consecutive electrodes among the plurality of electrodes, and the reference portion is disposed between a second pair of consecutive electrodes among the plurality of electrodes. The first pair of continuous electrodes is a pair of internal electrodes among four of the at least five continuous electrodes, and the contact resistance of the sensing portion is calculated based on at least four resistance values ​​measured between at least four pairs of electrodes selected from the four continuous electrodes.

2. The self-compensating sensor according to claim 1, wherein changes in the contact resistance of the reference portion are compensated in the compensation resistance.

3. The self-compensating sensor of claim 1, wherein the measurement circuit is further configured to calculate the compensation resistance value based on the ratio between the contact resistance-independent resistance of the sensing portion and the contact resistance-independent resistance of the reference portion.

4. The self-compensating sensor according to claim 1, wherein the PNC comprises carbon nanotubes.

5. The self-compensating sensor of claim 1, wherein the sensing element is attached to a structural component, and the sensing condition is the amount of cracks, corrosion state, or erosion state of the structural component.

6. A method for measuring environmental sensing conditions using a sensing element, the sensing element comprising a resistive film and a plurality of linearly arranged electrodes in electrical contact with the resistive film, the method comprising: Measure multiple resistance values ​​between multiple pairs of electrodes selected from the plurality of linearly arranged electrodes; Based on the plurality of resistance values, calculate the contact resistance-independent resistance value of the sensing portion of the resistive film; Based on the measured multiple resistance values, the contact resistance-independent resistance value of the reference portion of the resistive film is calculated; and The compensation resistance value is determined by combining the resistance value of the sensing part and the resistance value of the reference part. Measuring the plurality of resistance values ​​includes measuring the resistance between multiple pairs of electrodes selected from at least five consecutive electrodes of the plurality of linearly arranged electrodes, and The sensing portion of the resistive film is disposed between the first pair of inner electrodes of four of the at least five consecutive electrodes, and the resistance value of the sensing portion is calculated based on at least four resistance values ​​measured between at least four pairs of electrodes selected from the four consecutive electrodes.

7. The method of claim 6, wherein the compensation resistance value indicates the structural health condition of the structure, the structural health condition being the degree of damage to the structure.

8. The method according to claim 7, further comprising determining the remaining service life of the structure based on the compensation resistance value.

9. The method of claim 6, wherein determining the compensation resistance value comprises calculating the ratio between the resistance value of the sensing portion and the resistance value of the reference portion.

10. The method of claim 6, wherein the compensation resistance value is independent of the size of the sensing portion, and determining the compensation resistance value includes normalizing the resistance value of the sensing portion over the size of the reference portion.

11. The method of claim 6, wherein the resistive film comprises a polymer nanocomposite PNC.

12. The method of claim 6, further comprising exposing the sensing portion of the resistive film to the environment, wherein the compensation resistance value indicates the sensing conditions of the environment.

13. The method of claim 12, wherein the environment is a corrosive environment.

14. A sensor, comprising: A resistive film having a sensing portion and a reference portion adjacent to the sensing portion; Multiple linearly arranged electrodes, including a first pair of electrodes in contact with the sensing portion and a second pair of electrodes in contact with the reference portion; The measurement circuit, coupled to the plurality of linearly arranged electrodes, is configured as follows: Measure multiple resistance values ​​between multiple pairs of electrodes selected from the plurality of electrodes; Based on the plurality of resistance values, calculate the contact resistance-independent resistance value of the sensing part; Based on the measured multiple resistance values, calculate the contact resistance-independent resistance value of the reference portion; and The compensation resistance value is determined by combining the resistance value of the sensing part and the resistance value of the reference part. The plurality of linearly arranged electrodes includes at least five consecutive electrodes, and The first pair of electrodes is an inner pair of four consecutive electrodes among the at least five consecutive electrodes, and the resistance value of the sensing portion is calculated based on at least four resistance values ​​measured between at least four pairs of electrodes selected from the four consecutive electrodes.

15. The sensor of claim 14, wherein the measurement circuit is further configured to calculate the compensation resistance value based on the ratio between the resistance value of the sensing portion and the resistance value of the reference portion.

16. The sensor of claim 14, wherein the compensation resistance value is independent of the size of the sensing portion, and the measurement circuit is further configured to calculate the compensation resistance value by normalizing the resistance value of the sensing portion over the size of the reference portion.

17. The sensor of claim 14, wherein the resistive film comprises a polymer nanocomposite PNC.

18. The sensor of claim 17, wherein the PNC comprises carbon nanotubes.

19. The sensor of claim 14, wherein the sensing portion of the resistive film is exposed to the environment, and the compensation resistance value indicates the sensing conditions of the environment.

20. The sensor of claim 19, wherein the resistive film is attached to the structural component, and the sensing condition is the amount of cracks, corrosion state, or erosion state of the structural component.

Images