Wireless integrity sensing acquisition module

Abstract

Aspects of the present disclosure relate to a measurement module for measuring a multi-electrode resistance sensing element with improved noise performance and accuracy. In some embodiments, stimulation of the sensing element is provided by a current path that originates from a signal source, passes through a switch block, through a pair of terminals, and terminates at a reference node such as ground. An analog-to-digital converter (ADC) is directly coupled to one or both terminals to digitize the voltage. The ADC is coupled to the terminals on the sensing element to measure the sensing voltage signal before the sensing signal passes through the switch block. As a result, the measured voltage signal can be free of noise that can be picked up by the switch block, and the accuracy of the resistance measurement on the sensing element can be improved.

Description

[0001] Cross-references to related applications

[0002] This application claims the benefit of U.S. Provisional Application Serial No. 63 / 106,346, filed on October 27, 2020, Agent's File No. G0766.70330US00, entitled "Wireless Integrity Sensing Acquisition Module", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to sensors. Background Technology

[0004] When a target material is exposed to certain environmental conditions, one or more states of the material may change. For example, when exposed to specific temperatures, mechanical vibrations, humidity, or moisture conditions over a period of time, the target material may be corroded, causing its physical and chemical properties to change within the same timeframe. Sensor devices can be used to monitor the state of the target material.

[0005] Sensors are devices sometimes used to sense various environmental or structural health conditions. Environmental or structural sensors sense the conditions of interest and communicate with a reader device 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.

[0006] 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

[0007] This disclosure relates to a measurement module for measuring a multi-electrode resistance sensing element with improved noise performance and accuracy. In some embodiments, stimulation of the sensing element is provided by a current path originating from a signal source, passing through a switching block, through a pair of terminals, and terminating at a reference node such as ground. An analog-to-digital converter (ADC) is directly coupled to one or both terminals to digitize the voltage. The ADC is coupled to the terminals on the sensing element to measure the sensed voltage signal before the sensed signal passes through the switching block. As a result, the measured voltage signal may be free of noise that can be picked up by the switching block, and the accuracy of the resistance measurement on the sensing element can be improved.

[0008] According to some embodiments, an apparatus for measuring the resistance of a variable resistance sensor is provided. The variable resistance sensor has a plurality of terminals. The apparatus includes a switching block configured to selectively couple a reference signal source to a first terminal among the plurality of terminals of the variable resistance sensor; and an analog-to-digital converter (ADC) coupled to the first terminal among the plurality of terminals and configured to digitize the voltage present at the first terminal among the plurality of terminals.

[0009] According to some embodiments, a sensing device is provided for measuring parameters of a variable resistance sensor. The variable resistance sensor has multiple terminals. The sensing device includes an analog-to-digital converter (ADC); a switching block; a reference signal source; and a current path via the switching block between the reference signal source and a first terminal of the multiple terminals of the sensor. The current path continues via the switching block to a reference voltage node. The ADC is coupled to the first terminal and configured to digitize the voltage present at the first terminal.

[0010] According to some embodiments, a method for measuring parameters of a sensor is provided. The sensor has multiple terminals. The method includes closing a first switch in a switching block such that a reference signal source is coupled to a first terminal of the plurality of terminals of the sensor; and digitizing a voltage present at the first terminal using an analog-to-digital converter (ADC) in response to a reference voltage signal at the reference signal source. Attached Figure Description

[0011] 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:

[0012] Figure 1 This is a schematic diagram of an exemplary sensor according to some embodiments;

[0013] Figure 2A This is a schematic top view of an exemplary sensing element according to some embodiments;

[0014] Figure 2B It is shown that... Figure 2A A schematic circuit diagram of the equivalent circuit of the sensing element shown.

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

[0016] Figure 3A This is a schematic top view of an exemplary sensing element according to some embodiments;

[0017] Figure 3B It is shown that... Figure 3AA schematic circuit diagram of the equivalent circuit of the sensing element shown.

[0018] Figure 4A This is a schematic top view of an exemplary PNC sensing element and several measurement configurations according to some embodiments;

[0019] 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;

[0020] Figure 5A yes Figure 4A A schematic top view of an exemplary PNC sensing element, in which the measurement configuration shows nine possible arrangements of electrode pairs;

[0021] 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;

[0022] 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;

[0023] 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).

[0024] Figure 7 This is a schematic diagram of an exemplary sensor according to some embodiments;

[0025] Figure 8 This is a schematic diagram of an exemplary sensor according to some embodiments;

[0026] Figure 9 This is a schematic diagram of an exemplary sensor according to some embodiments;

[0027] Figure 10 This is a schematic diagram illustrating an exemplary implementation of a wireless integrity sensing and acquisition module with environmental compensation capability according to some embodiments. Detailed Implementation

[0028] In passive resistive sensors, the resistance of a passive resistive sensing element, such as a resistive film, can be monitored to represent a parameter of interest in a target material. To measure the resistance of the resistive film, terminals can be formed to make electrical contact with the resistive film, for example, by depositing conductive electrodes. The resistance between two terminals can be measured between each pair of terminals.

[0029] The resistance at the two terminals of the resistive film is contributed non-zero by the two series contact resistances at the terminal-to-film contact point, causing the measured resistance to be greater than the actual resistance of the resistive film portion between the two terminals. Furthermore, the resistance of resistive films containing composite polymers can be affected by undesirable drift from temperature or other environmental variations. It has been recognized that contact with the resistive film can be made at multiple contact points via multiple electrodes, and calibration schemes can be performed based on the combination of resistances measured at multiple electrode pairs to compensate for sensor background drift and eliminate contact resistance. Some aspects of self-calibrating or self-compensating sensing elements are described in: U.S. Patent Application Serial No. 63 / 038,551, filed June 12, 2020, Attorney General's File No. G0766.70312US00, entitled "Self-calibrating Polymer Nanocomposite (PNC) Sensing Element"; and U.S. Patent Application Serial No. 17 / 346,049, filed June 11, 2021, Attorney General's File No. G0766.70312US01, entitled "Self-calibrating Polymer Nanocomposite (PNC) Sensing Element", the entire disclosure of which is incorporated herein by reference.

[0030] This disclosure relates to a measurement module for measuring a multi-electrode resistance sensing element with improved noise performance and accuracy. In some embodiments, the stimulation of the resistance sensor is provided by a current path originating from a signal source, passing through a switching block, through a pair of terminals, and terminating at a reference node such as ground. An analog-to-digital converter (ADC) is directly coupled to one or both terminals to digitize the voltage. Because the ADC directly measures the voltage at the terminals and outside the switching block, the digitized voltage is a more accurate representation of the voltage sensed on the resistance sensor, which is unaffected by noise and resistance voltage drop within the switching block. As a result, more accurate resistance measurements can be achieved on the resistance sensor.

[0031] Some measurement modules include circuitry that applies an excitation signal to a resistive sensor and measures the electrical characteristics of the resistive sensor in response to the excitation signal. The measurement module may include a multiplexed switch block (or switch matrix, switch bar) controlled to selectively couple one or more stimulus sources within the measurement module to one or more selected terminals of the resistive sensor. In this way, a one-to-one correspondence is not required for a given number of terminals of stimulus sources.

[0032] Some measurement modules may also include an ADC that converts one or more analog electrical signals into digital signals, which can be transmitted to a reader, for example, via the sensor’s communication module.

[0033] In some embodiments, the switches in the switching block are selectively controlled to close, such that a reference signal source is coupled to a first terminal on a variable resistance sensor, thereby forming a current path that supplies current from the reference signal source to the first terminal via the switching block, flows out from the second terminal through a portion of the variable resistance sensor that is in contact with the first and second terminals, and ultimately sinks at a reference node such as ground. The reference node can be selectively coupled to the second terminal via the switches in the switching block.

[0034] In such an embodiment, the ADC is coupled to the first terminal to digitize the voltage present at the first terminal. The digitized voltage can be combined with the current in the current path to determine the resistance value of the variable resistance sensor portion between the first and second terminals. By directly measuring the voltage at the first terminal and the voltage outside the current path through the switching block, more accurate voltage measurement can be achieved without the contribution from the switching block.

[0035] In some embodiments, the ADC can also digitize the voltage at the second terminal. The voltages at the first and second terminals can form a differential measurement to represent the voltage difference between the first and second terminals.

[0036] In some embodiments, the reference signal source is the voltage output of the ADC, although this is not required and any suitable voltage or current source can be used as the reference signal source.

[0037] In some embodiments, a reference resistor is provided between the reference signal source and the switching block. The voltage drop across the reference resistor can be measured, for example, by coupling the ADC to the reference resistor, to represent the current in the current path.

[0038] 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.

[0039] Figure 1 This is a schematic diagram of an exemplary sensor according to some embodiments. Figure 1A sensor 10 is shown, comprising a measurement module 16, a sensing element 100, a connector 18, and the sensing element 10. 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 capable of providing 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).

[0040] 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 breaks disposed on the sensing element 100 and interfacing with 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.

[0041] 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.

[0042] Although Figure 1 Not 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.

[0043] 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 a WISP is found in U.S. Patent Application Serial No. 16 / 268,437, filed February 5, 2019, Attorney General’s File No. G0766.70274US00, entitled “Integrated RF Powered Platform for Aircraft Structural Health Monitoring (SHM) Using Nanostructured Sensing Materials,” and published as U.S. Patent Publication No. 2020 / 0247562A1, the entire disclosure of which is incorporated herein by reference.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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 of region C (hereinafter referred to as R) is measured. CSimilarly, the resistance of other regions labeled alphabetically can be related to the degree to which region C is exposed to a corrosive environment.

[0048] 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 performance of the resistive film 210 is non-uniform in the XY plane, region B may be more preferably chosen as the reference portion than, for example, region A, because region B is arranged closer to the sensing portion at region C, and therefore more accurately reflects the resistance of the underlying film material at region C.

[0049] 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 in the left and right ranges 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.

[0050] The inventors fully recognize and understand 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 on several selected electrode pairs to extract calibration or compensation resistance values ​​that are independent of contact resistance, i.e., unaffected by contact resistance.

[0051] 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 2AThis 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, SA).

[0052] 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 similar in many respects to... Figure 2A The sensing element 200 is configured such that electrode Z is removed, resulting in only five electrodes being used on the resistive film 210. In some embodiments, region C of the sensing element 2001 can be used as a sensing portion, while region B can be 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.

[0053] Figure 4A This is a schematic top view of an exemplary PNC sensing element 400 and several measurement configurations according to some embodiments. Figure 4A The 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.

[0054] Any suitable measuring device can be used (e.g.) Figure 1 The measurement module 16) measures the resistance between the two terminals of 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, Pair1, Pair2, Pair3, and Pair4, are shown.

[0055] 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 between any electrode and the resistive film.

[0056] 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 is the value that 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 it with the baseline resistance of the region.

[0057] According to one aspect of this application, the baseline resistance Ro of region C can be determined by using Ro = R B *AF to R B It is created by averaging and normalizing, where AF is the area factor or geometric factor representing the geometric ratio between region C and region B.

[0058] 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.

[0059] Figure 5A yes Figure 4A A schematic top view of an exemplary PNC sensing element, wherein the measurement configuration illustrates nine possible arrangements of electrode pairs 1-9 for two-terminal resistance measurement, and 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.

[0060] 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.

[0061] 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 resistance R, which is independent of contact resistance... C The target is a test resistor R, whose value will change based on the sensed conditions. However, R C This will also change due to the inherent background drift of the PNC film in the sensing element 400. (For R calibration) C To remove the background drift effect, R from regions B and D can be used. B and R D As compensation R C The reference resistance value, R B and R D It does not change based on sensing conditions.

[0062] According to one aspect of this application, Ro = (R) can be used... B +R D The baseline resistance Ro is created by averaging and normalizing RB and RD using AF / 2, 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 CIf 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 manufacturing 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 the average or average value of two or more reference resistors.

[0063] 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 Ro = (R B *AF B +R D *AF D ) / 2.

[0064] In a non-limiting example, the baseline resistance Ro and test resistance R of region C have been obtained. In one example, the calibration resistance can be obtained as R / Ro = 2R. C / AF*(R B +R D In this example, the calibrated or compensated resistor is a scaling value, which is 100% if R is the same as the baseline Ro. Changes in R due to sensing conditions will cause changes in R / Ro to represent these changes. On the other hand, any background drift in the resistor will completely cancel out in R and Ro and will not affect R / Ro.

[0065] Figure 5B An exemplary calculation is also shown for an application of using a calibration resistor to monitor cracks when structural changes in region C of the PNC film 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 )-1)=sqrt(R / Ro-1).

[0066] 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.

[0067] 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 OR / R, 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 OR / R from resistance to crack length. For example, crack length...

[0068] 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 in the sensor measurement versus the measurement noise (expressed as a percentage). Measurement noise, or OR / R, can represent the relative uncertainty in the measured resistance, which introduces 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.

[0069] 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 follows: 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 D0 This is the baseline resistance of the corresponding 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, the 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.

[0070] Figure 7 This is a schematic diagram of an exemplary sensor according to some embodiments. Figure 7A sensor 70 is shown, having a measurement module 720 coupled to a sensing element 710 having multiple terminals 1, 2, ... 8. The measurement module 720 includes an ADC 724, a reference signal source 726, and a switching block 722. A current path 728 originates from the reference signal source 726, passes through a closed switch 7321 within the switching block 722, and reaches the first terminal 1. A portion of the current path flows through the sensing element 710, through terminal 2, through the closed switch 7322, and terminates at a groundable reference voltage node 730. The input terminal 734 of the ADC 724 is directly coupled to terminal 1 to digitize the voltage signal at terminal 1. Through direct coupling to terminal 1, the input terminal 734 is coupled to a point outside the switching block 728 on the current path 728, or to a point between the switching block 728 and terminal 1 of the sensing element 710.

[0071] Figure 8 This is a schematic diagram of an exemplary sensor according to some embodiments. Figure 8 A sensor 80 including a switch block 823 is shown. When switches 8321 and 8322 within the switch block 823 are closed, a current is generated from the ADC REF through R... ref A first current path, via terminals S2 and D2 to terminal 2, applies stimulation to electrode X on sensing element 810. The first current path continues through electrode Z, terminal 1 to terminals S1 and D1 of switching block 822, and flows to ground. The first current path supplies resistance R between electrodes X and Z of the sensing element. xz Apply a current. R can be measured, for example, using the input on an ADC. ref The voltage V across the terminals is used to calculate the current I1 in the first current path, which is I1 = V / R. ref In this example, the voltage V at terminal 2 CH2+ Directly coupled to ADC (e.g.) Figure 7 The input of the ADC734 is digitized. CH2+ Relative to the ground, and can be used in conjunction with h to calculate R. xz .

[0072] In some embodiments, a single-ended voltage V is not used. CH2+ As R xz Instead of the voltage at terminal 1, it uses another voltage V. CH2- Directly coupled to the input of the ADC for digitization. Differential voltage V CH2+ -V CH2- It can be used with I1 to calculate R more accurately. xz Because V CH2+ and V CH2- These represent the voltages at electrodes Z and X, which do not have the voltage drop from the first current path flowing through the parasitic resistance in switch block 822.

[0073] To avoid being bound by a specific theory, the parasitic resistance in switch block 822 may be caused by voltage drops across one or more switches in the switch block. In some embodiments, the switch can be implemented as an analog switch with on-state resistance, which can be the drain-source voltage V. DS and / or power supply voltage V DD The function of V. In such an embodiment, the on-state resistance in the switch not only contributes non-zero to the parasitic resistance, but the resistance value in the on-state can also be determined according to V. DS V DD The value fluctuates, further introducing noise or uncertainty into the voltage drop across the switching block.

[0074] Still referencing Figure 8 When switches 8323 and 8324 are closed within switch block 822, the same ADC REF can also be used to apply current to measure the resistance R between electrodes X and L of the sensing element. XL The second current path is from ADC R. EF Through R ref The current flows through terminals S2 and D2 to terminal 2 to apply stimulation at electrode X, then continues through electrode L, terminal 5, through terminals S5 and D5 of switch block 822, and to ground. The second current path leads to the resistance R between electrodes X and Z of the sensing element. xz Apply current. The current I2 in the second current path can be monitored by R. ref The voltage across the terminals is determined in the same way as I1. In this example, the voltage V at terminal 5 is... CH3+ It is directly coupled to the input of the ADC to be digitized. V CH3+ It is relative to ground and can be used in conjunction with the amplitude of I2 to calculate R. XL .

[0075] Switch block 822 may, and indeed in a preferred embodiment, include two or more switches that can be controlled to switchably multiplex the ADC REF to measure any combination of two-terminal resistances on sensing element 810.

[0076] Figure 9 This is a schematic diagram of an exemplary sensor according to some embodiments. Figure 9 Sensor 90 is shown, in which a reference signal source ADC-REF is coupled to the output 925 of ADC 924. Sensor 90 also includes a processing unit 940 and an antenna 950. A communication link SPI couples the processing unit 940 to a switch bar 922, sending control signals that selectively close or open switches within the switch bar 922, thereby enabling multiplexing measurements at the selected terminals of the sensing element 910.

[0077] Figure 10 This is a schematic diagram illustrating an exemplary implementation of a wireless integrity sensing and acquisition module with environmental compensation capabilities according to some embodiments. Figure 10 In the diagram, sensor 1000 is shown as including a patch antenna 1130, impedance matching circuit 1134, energy storage unit 1120, power management unit (PMU) and load switch 1122, controller 1124, ADC 1112, switch bar 1132, memory 1134, and sensing element 1110. Sensing element 1110 can sense conditions representing permanent changes in the structural state, such as corrosion or cracking. Figure 10 Some aspects of the wireless integrity sensing acquisition module of the type shown and the reader for wirelessly reading from the sensing acquisition module are described in U.S. Patent Application Serial No. 16 / 840,274 (U.S. Patent Publication No. 2021 / 0314871), filed April 3, 2020, Attorney General’s File No. G0766.70307US00, entitled “Wireless Sensor Reader with Soft Controlled Power Exciter and Method of Operation Thereof,” the entire disclosure of which is incorporated herein by reference.

[0078] In addition to the above, some novel aspects of this application are summarized below.

[0079] In some embodiments, a wireless integrity sensing acquisition module is provided. This wireless integrity sensing acquisition module has an improved noise floor, which can be achieved through multiple unbiased resistance measurements using a combination of various electrical breakpoint pairs of sensing elements to account for material and / or manufacturing variability as well as due to mechanical and / or environmental factors such as strain or temperature changes or aging.

[0080] In some embodiments, a wireless integrity sensing acquisition module is provided. This wireless integrity sensing acquisition module has precise compensation capabilities, which can be achieved through multiple unbiased resistance measurements using combinations of various electrical breakpoint pairs of the sensing element, to account for variability in materials and / or manufacturing processes, as well as changes due to mechanical causes and / or environmental factors such as strain, temperature variations, or aging.

[0081] In some embodiments, the wireless integrity sensing acquisition module may have an ADC with signal conditioning circuitry; a switch bar located outside the ADC measurement path to enable unbiased measurement of various combinations of resistance at the sensor electrical branch points; and a core with a transceiver for implementing wireless data links and compensation algorithms based on the collected measurements.

[0082] In some embodiments, a passive version of the wireless integrity sensing acquisition module with accurate compensation capabilities is provided. In such embodiments, the wireless integrity sensing acquisition module further includes an energy harvester to power the module.

[0083] In some embodiments, the switch bar is located outside the ADC measurement path to eliminate switch bar resistance matching between various resistance data paths, thereby optimizing measurement errors.

[0084] In some embodiments, the switch bar is located outside the ADC measurement path to eliminate the switch bar resistance survivability due to ambient temperature variations, and the on-resistance flatness is matched across various resistance data paths to optimize measurement error.

[0085] The terms "approximately" and "about" can be used to indicate within ±20% of the target value in some embodiments, within ±10% of the target value in some embodiments, within ±5% of the target value in some embodiments, but within ±2% of the target value in some embodiments. The terms "approximately" and "about" may include the target value.

Claims

1. An apparatus for measuring the resistance of a variable resistance sensor having multiple terminals, the apparatus comprising: The switch block is configured as follows: The reference signal source is selectively coupled to the first terminal of the plurality of terminals of the variable resistance sensor; as well as The second terminal of the plurality of terminals of the variable resistance sensor is selectively coupled to the reference voltage node, such that a current path exists between the reference signal source and the first terminal via the switching block, and continues between the second terminal and the reference voltage node via the switching block; and An analog-to-digital converter (ADC) is coupled to the first terminal of the plurality of terminals and is configured to digitize the voltage present at the first terminal of the plurality of terminals.

2. The device according to claim 1, wherein the reference signal source is the output of the ADC.

3. The device of claim 1, wherein the ADC is coupled to the second terminal and configured to digitize the voltage present at the second terminal.

4. The device of claim 3, wherein the current path is configured to pass through a portion of the variable resistance sensor between the first terminal and the second terminal.

5. The device of claim 1, further comprising a reference resistor in the current path, the reference resistor being connected between the reference signal source and the first terminal.

6. The device of claim 5, wherein the ADC is coupled to the reference resistor and configured to digitize the voltage across the reference resistor.

7. A sensing device for measuring parameters of a variable resistance sensor having multiple terminals, the sensing device comprising: Analog-to-digital converter (ADC); Switch block; Reference signal source; and The current path between the first terminal of the plurality of terminals of the reference signal source and the sensor via the switching block, wherein the current path continues to the reference voltage node via the switching block, wherein The ADC is coupled to the first terminal and configured to digitize the voltage present at the first terminal. The switch block is located outside the measurement path, and The switch block is configured to selectively couple a second terminal of the plurality of terminals of the variable resistance sensor to the reference voltage node.

8. The sensing device according to claim 7, wherein the reference signal source is the output of the ADC.

9. The sensing device of claim 7, wherein the ADC is coupled to the second terminal and configured to digitize the voltage present at the second terminal.

10. The sensing device of claim 9, wherein the current path is configured to pass through a portion of the variable resistance sensor between the first terminal and the second terminal.

11. The sensing device of claim 7, further comprising a reference resistor in the current path, the reference resistor being connected between the reference signal source and the first terminal.

12. The sensing device of claim 11, wherein the ADC is coupled to the reference resistor and configured to digitize the voltage across the reference resistor.

13. A method for measuring parameters of a sensor having multiple terminals, the method comprising: The first switch in the closed switch block is closed, causing the reference signal source to couple with the first terminal of the plurality of terminals of the sensor; and In response to the reference voltage signal at the reference signal source, the voltage present at the first terminal is digitized by the analog-to-digital converter (ADC) by directly coupling the voltage present at the first terminal to the ADC. as well as Closing the second switch in the switch block couples the second terminal of the sensor with the reference voltage node, thereby creating a current path between the reference signal source and the first terminal via the switch block, and continuing via the switch block between the second terminal and the reference voltage node.

14. The method of claim 13, wherein the reference signal source is the output of the ADC.

15. The method of claim 13, further comprising: The current is allowed to pass along the current path through a portion of the sensor between the first terminal and the second terminal.

16. The method of claim 15, wherein the parameter of the sensor is a portion of the resistance of the sensor between the first terminal and the second terminal, and the method further comprises: The parameters of the sensor are calculated using one or more processors based on the digital voltage and the magnitude of the current present at the first terminal.

17. The method of claim 16, further comprising: The voltage present at the second terminal is digitized using the ADC, and the parameters of the sensor are calculated based on the digitized voltage present at the second terminal.

18. A method for measuring the resistance of a sensor having multiple terminals, the method comprising: The reference signal source is coupled to the first terminal of the plurality of terminals via a switching block; The grounding node is coupled to the second terminal of the plurality of terminals via the switch block; The current is directed along a current path from the reference signal source through the switch block, through a portion of the sensor between the first and second terminals, and to the ground node; The analog-to-digital converter (ADC) is coupled to the first terminal via a measurement path that bypasses the switch block; In response to the bias voltage at the reference signal source, the first voltage present at the first terminal and the second voltage present at the second terminal are digitized using an ADC; and The resistance of the sensor is calculated using one or more processors based on the difference between the first voltage and the second voltage and the magnitude of the current.

19. A wireless integrity sensing and acquisition module, comprising: A resistance sensing element is attached to the structure, the resistance sensing unit having a resistor and including multiple terminals; A measurement module, coupled to the plurality of terminals and configured to calculate structural integrity parameters of the structure; and The wireless communication module is configured to send a signal representing the structural integrity parameters to the wireless reader, wherein... The measurement module includes: Analog-to-digital converter (ADC); Switch block; Reference signal source; The current path between the first terminal of the plurality of terminals of the reference signal source and the resistive sensing element via the switching block, wherein the current path continues to the reference voltage node via the switching block, wherein The ADC is coupled to the first terminal and configured to digitize the voltage present at the first terminal; and The processor is configured to calculate the target resistance of the resistance sensing element based on the digitized voltage and the current in the current path, and to calculate the structural integrity parameter based on the target resistance.

20. The wireless integrity sensing and acquisition module of claim 19, wherein the structural integrity parameter is a crack length, and wherein the structure is part of an aircraft.

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