Structural Health Monitoring Sensors and Systems

Abstract

The structural health monitoring system consists of a frequency sweep generator circuit that generates an alternating current that is simultaneously fed to multiple impedance measurement circuit modules. Each impedance measurement circuit module is connected to a piezoelectric transducer (PZT) placed on or embedded in the structure being monitored. Each impedance measurement circuit module is configured to generate two output signals: the first signal is a voltage proportional to the phase difference between the input sweep signal and the PZT current signal, and the second signal is a voltage proportional to the current through the PZT. The data acquisition module digitizes the signals and generates an estimate of the real component of the PZT's (complex) impedance at the sweep frequency. The sweep generator is configured to generate multiple sweep signals, each at a different frequency across the sweep frequency range, generating an impedance spectrum that can be used to detect structural changes such as cracks.

Description

[Technical Field]

[0001] Related literature This application claims priority to Australian Provisional Patent Application No. 2022901989 entitled "Structural Health Monitoring Sensor and System" filed on July 15, 2022, the contents of which are incorporated herein by reference in their entirety.

[0002] The present disclosure relates to a structure and material monitoring system. In certain aspects, the present disclosure relates to a monitoring system for monitoring structural health and material condition (including soil condition), and integrity, damage, including environmental, crack and fracture development, in infrastructure including various materials, machinery, pressure vessels, mining and civil structures. [Background technology]

[0003] In mining, oil and gas, geotechnical, mechanical, civil engineering, and infrastructure industries, structures and materials must be regularly inspected for crack initiation, crack progression, and damage for a variety of safety and economic reasons. Traditionally, inspections have been performed manually, with inspectors visually inspecting structures. This manual approach is time-consuming and prone to human error and inaccuracy. In some situations, visual inspection is simply not possible. Therefore, in recent years, various technological solutions have been explored for structural health monitoring using radiography, fiber optics, ultrasound, and vibration-based systems. However, these systems have many drawbacks, including high cost, large size and weight, limited applicability to a wide range of structures, and the need for skilled operators.

[0004] One approach has been proposed: installing or embedding piezoelectric transducers (also known as piezoelectric sensors) in structures to enable continuous or periodic monitoring over long periods of time. A piezoelectric transducer (PZT) consists of a small patch or wafer of piezoelectric material, such as a piezoelectric ceramic, connected to two wires. Piezoelectric materials generate an electric charge when mechanical stress is applied, and the electrical impedance of a PZT has been shown to be directly related to the mechanical impedance of the substrate in which it is mounted. Measuring the electrical impedance of a PZT at various frequencies (typically in the 30-400 kHz range) allows for continuous monitoring of the mechanical properties of the substrate over long periods of time. Detecting changes in electrical impedance can be an indicator of changes in structural integrity, such as cracks, damage, or deterioration of structural components such as bolts. However, because impedance is a complex quantity, measurement requires specialized circuitry. One approach involves directly measuring the complex impedance of a PZT using an impedance analyzer, such as the HP4194A. However, these impedance analyzers are large, which increases the size of the monitoring system, and because they are designed for laboratory use, they are not rugged and are not suitable for permanent field installation.

[0005] Some researchers have proposed alternatives to expensive impedance analyzers. One approach involves placing a PZT in series with a resistor and measuring the voltage across the resistor (e.g., based on a voltage-divider configuration). The impedance of the PZT is approximated as the voltage across the resistor divided by the current through the resistor. The problem with this approach is that it only approximates the impedance across the PZT and can result in significant error. Therefore, an alternative method using a calibrated resistor with a precisely known resistance has been proposed, allowing for more accurate impedance measurements. This method requires measuring the voltage across the PZT and the voltage across the calibrated resistor. However, to avoid the need for expensive differential probes, the voltage across the PZT is measured indirectly by subtracting the voltage across the calibrated resistor from the input voltage signal from a frequency generator (an alternating current (AC) power source). Furthermore, to avoid the need to actually measure the phase angle, an FFT-based method has been employed, performing an FFT to analyze the signal between the input and the calibrated resistor to obtain estimates of the magnitude and phase of the PZT's impedance. The impedance spectrum obtained with this system can be compared to a reference spectrum to detect changes indicative of damage or cracks. Another method suggested that the AC signal be a linear chirp signal. Another method involves measuring the RMS current of the resistor along with the average power consumed by the PZT. While average power depends on the phase angle, direct measurement of the phase angle is not necessary. Instead, a high-precision, high-speed analog multiplier is used to obtain power as a function of time, and this signal is then fed into a low-pass filter to provide a direct current (DC) value representing average power. The RMS current is obtained by measuring the shunt voltage across the resistor and converting it to a DC value using an RMS-to-DC converter, using the known resistor voltage. From these measurements, a microcontroller is used to determine the resistance, which is the average power over the square of the RMS current. This process is repeated for multiple frequencies. However, none of these proposed approaches achieved commercial success or widespread adoption.This is likely due to limitations that hinder large-scale deployment and scale-up, such as a lack of robustness and the need for sequential or dedicated measurements of each PZT, as well as the large size and cost of the equipment and the inability to read from many sensors simultaneously.

[0006] Another approach proposes using two PZTs. One acts as an actuator (stimulus source) and the other as a sensor (receiver) to detect Lamb waves (or Rayleigh-Lamb waves), which are elastic waves propagating along the surface of a structure. A stimulus signal transmitter sends a waveform signal to the stimulus PZT, generating an acoustic signal on the substrate to which it is attached. A second PZT, positioned at a distance from the stimulus PZT, is then used as a receiver. The two outputs of the receiver PZT are fed into a differential amplifier to generate an amplified version of the signal across the PZT. A second amplifier stage with controllable gain is used to generate a signal ranging from 0 to 3 V, which is fed into an ADC to measure the signal magnitude. This process can be repeated for multiple receivers at different locations and at multiple frequencies. The digital signal is then analyzed by a computer program to detect changes in the structure. This device can also perform electrochemical impedance spectroscopy to obtain impedance as a function of frequency, and the observed spectral curve can be compared to a reference curve. However, a limitation of this system is that it uses Lamb wave-based measurements, which, while useful for monitoring surface conditions, are unreliable for detecting cracks or damage to the body. Further readings from multiple sensors using this approach are complex and require extensive data analysis. Summary of the Invention [Problem to be solved by the invention]

[0007] Currently, there are few commercial systems for structural health monitoring, and those that do exist generally require expensive and complex equipment or suffer from other application limitations (e.g., specific structures). While PZT-based systems have great potential, prior art systems remain expensive and are not currently applicable to many real-world structures, such as bridges, which are often large, comprised of many components and sections, and subject to a complex variety of forces. Therefore, there is a need to provide improved structural health monitoring systems and circuits suitable for large-scale deployment, or at the very least, to provide a useful alternative to existing structural health monitoring systems. [Means for solving the problem]

[0008] In the first form, a buffer configured to receive an alternating current (AC) sweep signal from a frequency sweep generator, the buffer configured to provide the buffered sweep signal to an input of the piezoelectric sensor; a current-to-voltage converter connected in parallel with a feedback resistor, the current-to-voltage converter and feedback resistor receiving the piezoelectric output signal from the piezoelectric sensor and generating a piezoelectric current signal, the AC voltage in the piezoelectric current signal being proportional to both the phase angle and the current at the piezoelectric sensor; a phase comparison circuit configured to receive the buffered sweep signal at a first input and the piezoelectric current signal at a second input, compare the piezoelectric current signal with the buffered sweep signal, and generate an output piezoelectric phase signal having a direct current (DC) voltage proportional to a phase difference between the buffered sweep signal and the piezoelectric current signal; a rectifier circuit adapted to receive the piezoelectric current signal at a first input and to generate an output piezoelectric current signal having a DC voltage proportional to the current through the piezoelectric sensor; An impedance measurement circuit is provided, comprising:

[0009] In one embodiment, the phase comparator circuit comprises: a digital phase detector configured to receive the buffered sweep signal at a first input, receive the piezoelectric current signal from the current-to-voltage converter at a second input, and compare the piezoelectric current signal with the buffered sweep signal to generate a first piezoelectric phase signal; a first low pass filter configured to receive the first piezoelectric phase signal and to generate an output piezoelectric phase signal having a DC voltage proportional to a phase difference between the buffered sweep signal and the piezoelectric current signal; Including, The rectifier circuit is a rectifier configured to receive a piezoelectric current signal at a first input and to rectify the piezoelectric current signal to generate a first piezoelectric current signal; a second low pass filter configured to receive the first piezoelectric current signal and generate an output piezoelectric current signal having a DC voltage proportional to the current through the piezoelectric sensor; Includes:

[0010] In one form, the AC sweep signal has a frequency in the range of 5 kHz to 1 MHz, and the components of the impedance measurement circuit are configured to operate in the frequency range of 5 kHz to 1 MHz.

[0011] In one form, the output piezoelectric phase signal and the output piezoelectric current signal are DC signals having a voltage in the range of 0 to 5 V. In one embodiment, a phase signal of 4.2 V represents a 90° phase shift.

[0012] In one form, the impedance measurement circuit consumes less than 5 watts of power.

[0013] In the second form, a sweep signal input connector configured to receive an input AC sweep signal or a sweep generation circuit configured to generate an AC sweep signal; a voltage conversion circuit configured to generate a plurality of regulated power supply voltages from the input supply voltage connector; a plurality of impedance measurement circuit modules according to the first aspect, each of the impedance measurement circuit modules providing a sweep signal as an input to the impedance measurement circuit; a plurality of paired input connectors for connecting to the inputs and outputs of the piezoelectric sensors, each paired input connector being connected to one of a plurality of impedance measurement circuit modules; a plurality of paired output connectors, each paired output connector connected to one output of an impedance measurement circuit module, the paired outputs having an output piezoelectric phase signal and an output piezoelectric current signal from each impedance measurement circuit module; A multi-sensor impedance measurement circuit module is provided, comprising:

[0014] In one form, the voltage converter circuit is configured to generate regulated +5V, -5V, and +3V power supplies.

[0015] In a further aspect, the impedance measurement circuit further comprises a compact, miniature housing that houses a circuit board having a plurality of surface mount components that mount one or more components of the multi-sensor impedance measurement circuit module. In a further aspect, the circuit board has a first dimension that is 38 mm or less and a second dimension that is 55 mm or less.

[0016] In a third form, there is provided a structural health monitoring circuit module for use in a structural health monitoring system. In one form, the structural health monitoring circuit comprises: One or more multi-sensor impedance measurement circuit modules according to a second aspect, including a power supply circuit and a sweep signal generator, the power supply circuit including a voltage regulator configured to receive an unregulated voltage supply in the range of 9V to 18V (nominal 12V) and regulated +5V, +3V, and -5V power supplies; and one or more multi-sensor impedance measurement circuits; a user interface, at least one processor, and at least one memory; Equipped with The user interface is configured to receive one or more user input signals, the one or more user input signals being provided to at least one of the at least one processor for configuring the structural health monitoring circuit module, including configuring the sweep generation circuit, the one or more user input signals being received using the input device and / or from a remote device. In an alternative, a structural health monitoring circuit module for use in a structural health monitoring system and for connection to one or more multi-sensor impedance measurement circuit modules according to any one of claims 6 to 8, the one or more multi-sensor impedance measurement circuit modules having an input supply voltage connector and a sweep signal input connector; The structural health monitoring circuit module comprises: a power supply circuit including a voltage regulator configured to receive an unregulated voltage supply in the range of 9V to 18V (12V nominal) and regulated +5V, +3V, and -5V supplies; a power output connector for supplying an unregulated voltage power supply to the input supply voltage connector of one or more multi-sensor impedance measurement circuit modules via a wired connector; a sweep generator circuit configured to generate an AC sweep signal; a sweep signal output connector for supplying an AC sweep signal to a sweep signal input connector of one or more multi-sensor impedance measurement circuit modules via a wired connector; a user interface, at least one processor, and at least one memory; Equipped with The user interface is configured to receive user input signals, which are provided to the at least one processor for configuring the structural health monitoring circuit module, including configuring the sweep generation circuit, and the one or more user input signals are received using an input device or from a remote device. In some embodiments, the user interface can be a touch screen.

[0017] In one embodiment, the AC sweep signal has a frequency in the range of 5 kHz to 1 MHz.

[0018] In one form, the AC sweep signal has an RMS voltage of (nominal) 200mV or less. In one form, the sweep generating circuitry can further include a sweep trigger signal.

[0019] In one form, the system further comprises an analog-to-digital conversion circuit adapted to convert each output piezoelectric phase signal and each output piezoelectric current signal from each of the one or more multi-sensor impedance measurement circuit modules into a digital representation comprising a digital phase signal and a digital current signal; one or more processors adapted to analyze the digital representation and estimate the real impedance as a function of frequency for each sensor and generate and store in at least one memory a monitoring report; It further comprises a communication module that allows for transmitting or downloading the stored monitoring reports.

[0020] In one form, the at least one memory is configured to store a recipient address and one or more alert trigger conditions for generating an alert, the one or more processors are configured to analyze the digital phase signal and the digital current signal for each of the one or more multi-sensor impedance measurement circuit modules to determine whether one or more of the one or more alert trigger conditions are met, and the communication module is configured to send a monitoring report to the recipient address and / or send an alert to the recipient when one or more of the one or more alert trigger conditions are met. The recipient address may be a cloud data storage location, a server address, an email address, a mobile phone number, or other electronic address.

[0021] In one embodiment, one or more user input signals are received from a remote device via a communications module or from a user interface, the one or more user input signals including one or more frequency ranges of the sweep generating circuits, signal levels, one or more monitoring parameters, one or more alert trigger conditions, and / or one or more recipient addresses. In one embodiment, the input device includes a touchscreen and is configured to allow a user to input one or more monitoring parameters, such as the frequency ranges, signal levels, and scan rates of the one or more sweep generating circuits. The user interface may allow a user to input or set one or more alert trigger conditions and / or one or more recipient addresses. In one embodiment, the one or more monitoring parameters configure the microprocessor to monitor predefined groups of one or more impedance measurement circuits. In some embodiments, each group includes two or more impedance measurement circuits located in a portion of the structure being monitored. In some embodiments, the impedance measurement circuits in a group are proximate (or near) each other to enable cross-sectional or spatial monitoring of the structure.

[0022] In one form, analyzing the digital phase signal and the digital current signal for each of the one or more multi-sensor impedance measurement circuit modules includes determining a real impedance Z real = Vcos(θ) / I, where θ is the respective digital phase signal, I is the respective digital current signal, and V is a predetermined constant obtained from calibration measurements that include measuring the input voltage across each piezoelectric sensor.

[0023] In the fourth form, a structural health monitoring circuit module according to a third form; one or more multi-sensor impedance measurement circuit modules according to the second aspect; a data collection module comprising an analog-to-digital conversion circuit, at least one processor, at least one memory, and a communications module, wherein the analog-to-digital conversion circuit is configured to convert each output piezoelectric phase signal and each output piezoelectric current signal from each of the one or more multi-sensor impedance measurement circuit modules into a digital representation consisting of a digital phase signal and a digital current signal, the at least one processor is configured to analyze the digital representation and estimate the real impedance as a function of frequency for each sensor, and generate and store a monitoring report in the at least one memory, and the communications module is configured to enable transmission or download of the stored monitoring report; A structural health monitoring system is provided.

[0024] In one form, the at least one memory is configured to store a recipient address and one or more alert trigger conditions for generating an alert, the one or more processors are configured to analyze the digital phase signal and the digital current signal for each of the one or more multi-sensor impedance measurement circuit modules to determine whether one or more of the one or more alert trigger conditions are met, and the communication module is configured to send a monitoring report to the recipient address and / or send an alert to the recipient when one or more of the one or more alert trigger conditions are met.

[0025] In one form, one or more user input signals are received from a remote device or from a user interface via the communications module, the one or more user input signals including one or more frequency ranges of the sweep generator circuit, a signal level, one or more monitoring parameters, one or more alert trigger conditions, and / or one or more recipient addresses. In a further form, the one or more monitoring parameters are used to configure the one or more processors to monitor a predefined group of the one or more impedance measurement circuits.

[0026] In one form, analyzing the digital phase signal and the digital current signal for each of the one or more multi-sensor impedance measurement circuit modules determines a real impedance Z real = Vcos(θ) / I, where θ is each digital phase signal, I is each digital current signal, and V is a predetermined constant obtained from calibration measurements that include measuring the input voltage across each piezoelectric sensor.

[0027] In the fifth form, 1. A method for measuring impedance of a piezoelectric sensor, comprising: buffering an alternating current (AC) sweep signal received from a frequency sweep generator and providing the buffered sweep signal to an input of a piezoelectric sensor; generating a piezoelectric current signal using a current-to-voltage converter in parallel with a feedback resistor adapted to receive a piezoelectric output signal from the piezoelectric sensor, wherein the AC voltage in the piezoelectric current signal is proportional to both the phase angle and the current in the piezoelectric sensor; generating an output piezoelectric phase signal having a direct current (DC) voltage proportional to a phase difference between the buffered sweep signal and the piezoelectric current signal using a phase comparator circuit, the phase comparator circuit configured to receive the buffered sweep signal at a first input and the piezoelectric current signal at a second input, and to compare the piezoelectric current signal with the buffered sweep signal; generating an output piezoelectric current signal having a DC voltage proportional to the current through the piezoelectric sensor using a rectifier circuit that receives the piezoelectric current signal at a first input; The present invention provides a method comprising:

[0028] In one form, the method further includes digitizing the output piezoelectric phase signal to obtain a digital phase signal θ; digitizing the output piezoelectric current signal to obtain a digital current signal I; and digitizing the real impedance Z real = Vcos(θ) / I, where V is a predetermined constant obtained from a calibration measurement that includes measuring an input voltage across the piezoelectric sensor. [Brief explanation of the drawings]

[0029] Embodiments of the present disclosure will be described with reference to the accompanying drawings.

[0030] [Figure 1A] FIG. 1 is a schematic diagram of a structural health monitoring system according to one embodiment.

[0031] [Figure 1B] FIG. 1 is a schematic diagram of an impedance measurement circuit module of a structural health monitoring system according to one embodiment.

[0032] [Figure 2] FIG. 1 is a schematic diagram of a modularized distributed structural health monitoring system according to one embodiment.

[0033] [Figure 3A] FIG. 1 is a wiring diagram of a structural health monitoring system including a sweep generator and a first multi-sensor module according to one embodiment.

[0034] [Figure 3B] 3B is a circuit diagram of a first portion of the first impedance measurement module of the first multi-sensor module of FIG. 3A.

[0035] [Figure 3C] 3B is a circuit diagram of a first portion of the second impedance measurement module of the first multi-sensor module of FIG. 3A.

[0036] [Figure 3D] 3B is a circuit diagram of a first portion of the third impedance measurement module of the first multi-sensor module of FIG. 3A.

[0037] [Figure 3E] 3B is a circuit diagram of a first portion of the fourth impedance measurement module of the first multi-sensor module of FIG. 3A.

[0038] [Figure 3F] 3B is a circuit diagram of a second portion of the first and second impedance measuring modules of the first multi-sensor module of FIG. 3A.

[0039] [Figure 3G] 3B is a circuit diagram of a second portion of the third and fourth impedance measurement modules of the first multi-sensor module of FIG. 3A.

[0040] [Figure 3H] 1 is a wiring diagram of a structural health monitoring system including a sweep generator, a first multi-sensor module, and a second multi-sensor module according to one embodiment.

[0041] [Figure 4A] 1 is a plot of real impedance as a function of frequency of a piezoelectric sensor embedded in a mortar joint at a first location under various loads produced by a structural health monitoring system according to one embodiment.

[0042] [Figure 4B] 10 is a plot of real impedance as a function of frequency for a second piezoelectric sensor embedded in a mortar joint at a second location under various loads produced by a structural health monitoring system according to one embodiment.

[0043] [Figure 5A] 1 is a schematic diagram of a brick wall formed with brick and mortar joints, showing the approximate locations of five piezoelectric sensors, according to one embodiment.

[0044] [Figure 5B] 5B is a bar graph of damage index as a function of increasing load for five piezoelectric sensors placed on brick surfaces of the wall shown in FIG. 5A according to one embodiment.

[0045] [Figure 5C] 5B is a bar graph of damage index as a function of increasing load for five piezoelectric sensors embedded in the mortar joints of the wall shown in FIG. 5A according to one embodiment.

[0046] [Figure 5D] 5B is a bar graph of damage index as a function of increasing load for five piezoelectric sensors placed on the mortar joint surfaces of the wall shown in FIG. 5A according to one embodiment.

[0047] [Figure 6]1 is a plot of real impedance as a function of frequency from a structural health monitoring system according to one embodiment for two piezoelectric sensors placed on a steel plate with a bolt loosely fastened through the steel plate to a steel beam (first plot) and with the bolt tightly fastened through the steel plate to a steel beam (second plot).

[0048] In the following description, reference characters designate like or corresponding parts throughout the figures. DETAILED DESCRIPTION OF THE INVENTION

[0049] Referring to FIG. 1A, a structural health monitoring system 1 according to one embodiment is shown. The system includes a frequency sweep generator circuit 110 that generates an alternating current (AC) sweep signal 112 and a sweep trigger signal 114. The sweep signal is an AC signal at a specific sweep frequency and is fed simultaneously to multiple (N) impedance measurement circuit modules 120. Each impedance measurement circuit module 120 is connected to a piezoelectric sensor 122, also known as a piezoelectric transducer or PZT, that is disposed on or embedded within the structure being monitored (each PZT is located at a different location). While some embodiments of the system consist of a single impedance measurement circuit module 120, in most typical structural monitoring applications, a structure is monitored at multiple locations by multiple impedance measurement circuit modules 120 and associated PZTs, each at a different location on the structure. The sweep signal 112 is applied as an input to each impedance measurement circuit module 120 and associated PZT 122 to generate two output measurements: a phase signal 136 as a first output and a current signal 139 as a second output. The phase signal 136 is a direct current (DC) signal having a voltage proportional to or representative of the phase difference between the PZTs, and the current signal 139 is a DC signal having a voltage proportional to or representative of the current through the PZTs.

[0050] 1A, the sweep signal 112 is simultaneously fed to N impedance measurement modules (120a, 120b, ... 120n), which generate N phase signals (136a, 136b, ... 136n) and N current signals (139a, 139b, ... 139n), which are provided as inputs to a data acquisition system (DAQ) 150. The DAQ consists of one or more analog-to-digital conversion (ADC) circuits 152, which convert each of the phase 136 and current 139 signals associated with a particular PZT into a digital representation of the real component (Zreal) of the (complex) impedance across the PZT. f ) are analyzed by a processor 154 and memory 156 configured to estimate the (complex) impedance signals 136 and 139. As shown in FIG. 1A, the DAQ may be configured with N ADC circuits (152a, 152b, ... 152n), i.e., one ADC dedicated to each impedance measurement module and PZT (e.g., a 1:1 relationship), to generate N estimates of the real component of the (complex) impedance at each of the N PZTs (159a, 159b, ... 159n). However, it will be appreciated that other ADC circuit configurations may be used in other embodiments, e.g., using digital multiplexing to digitize all N phase signals 136 and current signals 139. Analysis by the DAQ may be used to generate monitoring reports and / or alerts to recipients. In some embodiments, the DAQ may include a wireless communication module.

[0051] The sweep generator is configured to generate multiple sweep signals at different frequencies (f) over a sweep frequency range (e.g., from 5 kHz to 1 MHz or higher). At each sweep frequency, the sweep signal is simultaneously fed to each impedance measurement module 120 and associated PZT 122, and the output phase 136 and current 139 measure the real component (Zreal) of the impedance of the PZT 159 at that sweep frequency. f) is used to generate an estimate of the impedance. By generating multiple sweep signals (each at a different frequency) over a swept frequency range, an impedance spectrum can be generated, which is shown in FIG. 1A as a plot of real impedance as a function of (swept) frequency 153.

[0052] In this embodiment, a sweep trigger signal 114 is also provided from the frequency sweep generator 110 to the DAQ 150 and is used to initiate processing of the received signals, for example, by triggering the ADC 152 to digitize the received phase 136 and current 139 signals. The frequency sweep generator generates multiple sweep signals, each with a different frequency, across a sweep frequency range. The sweep trigger may generate a trigger signal at the start of each different sweep signal (e.g., frequency) within the sweep frequency range. In other embodiments, the sweep frequency generator may sweep through the sweep frequency range with a predetermined sampling pattern known (e.g., stored) by the DAQ, such that only a single sweep trigger is generated at the start of the sweep (or sweep pattern). The predetermined pattern may be, for example, a sampling frequency of 1 kHz (i.e., one sample interval per millisecond), increasing from the start frequency in 1 kHz, 5 kHz, or 10 kHz increments, at a predetermined interval, until the stop frequency is reached. In other embodiments, the predetermined pattern may be a predetermined set of frequencies between the start frequency and the stop frequency, with each frequency varying according to the sampling frequency. The sweep trigger signal 114 is a signal used by the data acquisition system (DAQ) 150 to initiate processing of the received signal. In another embodiment, such as that shown in FIG. 2, digitization of the received phase 136 and current 139 signals is performed by one or more ADC circuits operatively connected to the frequency sweep generator, and the trigger signal is used to activate the ADC circuits. Alternatively, the ADC circuits can monitor the input signals and generate digital signals when they detect an input signal, thereby eliminating the need for the trigger signal 114. Alternatively, a microprocessor can control the frequency sweep generator circuitry and the ADC circuits, eliminating the need for a sweep trigger signal. Thus, the sweep trigger signal is optional, depending on the specifics of the implementation.

[0053] FIG. 1B shows a schematic diagram of one embodiment of the impedance measurement circuit module 120, which includes a buffer 121, a current-to-voltage conversion module 124, a phase comparison circuit 130, and a rectifier circuit 135. The buffer 121 is configured to receive the AC sweep signal 112 from the frequency sweep generator 110 and provide the buffered sweep signal to the input of the piezoelectric sensor / transducer PZT 122. The current-to-voltage conversion module 124 is disposed at the output of the PZT 122 and includes a current-to-voltage converter 126 connected in parallel with a feedback resistor 125, such that the current-to-voltage converter 126 and the feedback resistor 125 receive the piezoelectric output signal from the PZT 122 and generate a piezoelectric current signal. In this piezoelectric current signal, the AC voltage is proportional to both the phase angle and the current in the piezoelectric sensor 122. Because the piezoelectric current signal is the output of the current-to-voltage converter, it is also referred to as a piezoelectric voltage signal. However, in the following description, the term piezoelectric current signal is used because the voltage is proportional to the current generated by the piezoelectric sensor. In one embodiment, the output signal of PZT 122 (or the signal across the PZT) is provided to the negative input of current-to-voltage (IV) converter 126, whose output is regulated to a voltage that maintains a current equal to but opposite to the current through feedback resistor 125 to balance the PZT current. Phase comparison circuit 130 is configured to receive buffered sweep signal 123 at a first input and piezoelectric current signal 127 at a second input, compare the piezoelectric current signal to the buffered sweep signal, and generate output piezoelectric phase signal 134 having a DC voltage proportional to the phase difference between the buffered sweep signal and the piezoelectric current signal. Rectification circuit 130 receives piezoelectric current signal 127 at a first input and generates output piezoelectric phase signal 139 having a DC voltage proportional to the current through PZT 122.

[0054] In one embodiment, the phase comparison circuit 130 includes a digital phase detector 131 configured to receive the buffered sweep signal 123 at a first input and the piezoelectric current signal 127 from the current-to-voltage converter at a second input, and to compare the piezoelectric current signal with the buffered sweep signal to generate a first piezoelectric phase signal 132. A first low-pass filter 133 is configured to receive the first piezoelectric phase signal 132 and generate an output piezoelectric phase signal 134 having a DC voltage proportional to the phase difference between the buffered sweep signal and the piezoelectric current signal. In one embodiment, the rectification circuit includes a rectifier 136 configured to receive the piezoelectric current signal 127 at a first input and rectify the piezoelectric current signal to generate a first piezoelectric current signal 137. A second low-pass filter 138 is configured to receive the first piezoelectric current signal 137 and generate an output piezoelectric current signal 139 having a DC voltage proportional to the current through the piezoelectric sensor. The first and second low-pass filters can be single-pole low-pass filters, although other multi-pole filters can also be used. These low-pass filters can be active or passive filters.

[0055] As previously mentioned, the AC sweep signal has a frequency ranging from 5 kHz to 1 MHz, and the circuit components are configured to operate within that frequency range. That is, they are designed to operate with consistent performance (e.g., linear or at least stable response) within that frequency range. In some embodiments, the piezoelectric phase output signal and the piezoelectric current output signal are DC signals having voltages ranging from 0 to 5 V. In one embodiment, a 4.2 V phase signal represents a 90-degree phase shift. In one embodiment, the impedance measurement circuit consumes less than 5 watts of power (or less than 5 watts per four PZT sensor modules).

[0056] The use of a buffer (or buffer amplifier) ​​121 at the input isolates each impedance measurement circuit 120 from the other impedance measurement circuits, allowing all PZTs (and impedance measurement circuits) to receive the sample amplitude sweep signal without interfering with each other. This allows all N impedance measurement circuits 120 in the system 100 to be operated (excited) simultaneously from a single sweep signal. That is, at a particular sweep frequency, all N impedance measurement circuits 120 operate in parallel. This allows the entire structure to be monitored simultaneously. This parallel operation speeds up the monitoring process when the limiting factor is the time required to sweep across the sweep frequency range. As previously mentioned, the sampling frequency can be on the order of 1 kHz (i.e., 1 sample per millisecond), allowing the entire structure to be monitored across its frequency range in less than 1 second (depending on the number of distinct sweep frequencies generated).

[0057] 2 is a schematic diagram of a modularized, distributed structural health monitoring system 200 according to one embodiment. In this embodiment, the system 200 comprises a structural health monitoring (SHM) circuit module 210 for monitoring a structure 202 and a data acquisition module (DAQ) 250 for digitizing and analyzing data generated by the structural health monitoring circuit module 210 and transmitting reports or alerts to a user computing device 270.

[0058] The structural health monitoring system 200 can be provided as a single integrated module in a single housing having both the structural health monitoring circuit module 210 and the DAQ 250. Alternatively, the system may be comprised of multiple modules, each in its own housing, connected by a wired or wireless link. That is, in some embodiments, the structural health monitoring circuit module 210 is provided in a first housing and the DAQ 250 is provided in a second housing (i.e., two separate physical modules), with the two modules / housings connected by one or more cables that provide output phase 134 and current 139 signals from the impedance measurement module 220 to the DAQ 250 for processing and storage. In one embodiment, the structural health monitoring circuit module 210 is an integrated module and includes one or more multi-sensor impedance measurement circuit modules 220 that make up the multiple impedance measurement circuit modules 120 as shown in FIG. 1B. The structural health monitoring circuit module 210 further includes a frequency sweep generator 230 and a power supply circuit 240. The structural health monitoring circuit module 210 comprises a processor device, such as a microprocessor unit (MPU) or microcontroller, having a CPU 212 and memory 214, and further comprises a user interface 254 configured to receive user input signals for configuring the structural health monitoring circuit module 210, including configuring the sweep generation circuit 210. The structural health monitoring circuit module 210 is connected to a DAQ (data acquisition module) 250, which comprises an ADC 256 that receives the output phase 136 and current 139 signals from the impedance measurement circuit module 220 via cable 222 and digitizes the input signals. The DAQ 250 further comprises a processor device, such as a microprocessor unit (MPU) or microcontroller, having a CPU 252 and memory 254.The microprocessor may include on-board memory (e.g., RAM 254) and / or may be connected to additional memory, including removable memory 258, such as an SD card used for program storage and data storage. A trigger signal 114 is provided to the processor unit (e.g., CPU 252) via cable 224 to initiate digitization of the output signal of the impedance measurement circuit module 220 by the ADC 256. The digitized signal is stored in memory 254 and can be written to removable memory 258 as a data file, along with additional data such as a timestamp and metadata related to the measurement, such as frequency sweep generator settings and ADC settings. The removable memory 258 can also be used to store software modules for generating the data file, such as file formatting and capturing date, time, and configuration parameters for the structural health monitoring circuit 210 (e.g., frequency range) and ADC 256 (sampling rate, etc.). A communications module 260 is also provided for transmitting data to a user computing device 270 for further analysis and display. In some embodiments, the communications module is a wireless communications module. The user computing device 270 is configured to analyze and / or display the data collected by the structural health monitoring circuit module 210 and processed by the DAQ 250, and includes one or more CPUs 272 and memory 274, and stores results (e.g., Z. realThe system 200 also includes a display 276 for displaying a plot of the signal strength (or signal strength) versus frequency, and a communication interface 278 configured to receive data from the DAQ 250. The two communication interfaces 260 and 278 can communicate via a wireless link 262 or a wired link 262'. In some embodiments, the system 200 may be provided as a fully integrated system 280 including the structural health monitoring circuit module 210, the DAQ 250, and a user computing device 270. The user computing device 270 may be a general-purpose computing device, such as a mobile phone, tablet, laptop, or desktop computer, running software for analyzing and / or displaying data received from the DAQ 250. In the case of an integrated system (e.g., combining the structural health monitoring circuit module 210 and the DAQ 250), a single microprocessor may be used to provide processing and memory for both the structural health monitoring module 210 and the DAQ 250. That is, the CPU 252 and memory 254 of the DAQ may be provided by the CPU 212 and memory 214 of the structural health monitoring module. Additionally, multiple microprocessors may be used in both the structural health monitoring module and the DAQ to control different functions (ADC control, user interface, data storage, data transmission).

[0059] The multi-sensor impedance measurement circuit modules 220 may be provided in separate housings and wired to a central housing, or may be integrated into a single housing (an integrated module) with other components of the structural health monitoring circuit module 210. FIG. 2 illustrates an embodiment in which the multi-sensor impedance measurement circuit modules 220 are integrated into a single housing, while FIG. 3A is a wiring diagram illustrating a distributed embodiment in which a central housing houses central components and is wired to a single multi-sensor impedance measurement circuit module 220 in another housing. FIG. 3H is a wiring diagram illustrating a distributed embodiment in which a central housing houses central components and is wired to two single multi-sensor impedance measurement circuit modules 220 housed in separate housings and connected via wires. That is, in one embodiment, the structural health monitoring circuit module 210 includes one or more multi-sensor impedance measurement circuit modules 220, a power supply circuit 240, and a sweep signal generator 230. In another embodiment, the structural health monitoring circuit module 210 is for connection to one or more multi-sensor impedance measurement circuit modules 220. In this embodiment, the one or more multi-sensor impedance measurement circuit modules include an input supply voltage connector and a sweep signal input connector, and the structural health monitoring circuit module includes a power supply circuit 240 and a power supply output connector for supplying a power supply voltage via a wired connector to the input supply voltage connector of the one or more multi-sensor impedance measurement circuit modules, and a sweep signal generator 230 and a sweep signal output connector for supplying an AC sweep signal via a wired connector to the sweep signal input connector of the one or more multi-sensor impedance measurement circuit modules 220. The structural health monitoring circuit module 210 may further include a user interface 216 and a microprocessor including a CPU 212 and memory 214. The microprocessor may be integrated into the user interface or may be connected to the user interface 216.The user interface 216 is configured to receive one or more user input signals that are provided to the microprocessor for configuring the structural health monitoring circuit module (including configuring the sweep generation circuit), where the one or more user input signals are received using an input device and / or a remote device. The user interface 216 may be a touchscreen device or a plurality of push buttons and a digital display, and may be configured to allow a user to access menus and select values ​​(e.g., frequency intervals) to configure the device.

[0060] The power supply circuit 240 includes a voltage regulator configured to receive an unregulated voltage source in the range of 9V to 18V (12V nominal) and a regulated voltage source of +5V, +3V, or −5V. The unregulated voltage source 342 may be a battery, such as a lithium battery, although other battery technologies are possible, such as using a solar panel to provide power or recharge the battery. A small 12V lithium battery (e.g., 80mm x 30mm - 15mm) weighing 110g can provide enough power for 24 hours of monitoring. Using a larger battery or charging it with a solar panel allows for even longer use. In some embodiments, mains power may be used if available. In other embodiments, the power supply circuit 240 may be configured to accept a wider / larger input range, such as 5V to 18V, 5V to 24V, 9V to 24V, or 24V or more.

[0061] FIG. 3A shows a circuit embodiment in which a rectifier diode IN4007 is located downstream of a connector for an unregulated voltage supply 342. In this embodiment, the voltage supply is between 9V and 18V and provides a nominal 12V signal via wires to the multi-sensor impedance measurement circuit module 320. An LM1084 linear voltage regulator accepts a nominal 12V input and outputs +5V, +3V, and −5V signals, which are provided to a sweep generation circuit 310 configured to generate an AC sweep signal and a trigger signal. The sweep generation circuit 310 includes a sweep signal output connector 355 that provides the AC sweep signal via a wired connector to the multi-sensor impedance measurement circuit module 320 (or each of multiple modules, as shown in FIG. 3H). A user interface 216, such as a touchscreen or input buttons, may also be provided to allow a user to input one or more frequency ranges for the sweep generation circuit and one or more monitoring parameters, such as scan rate and signal level. The user interface may allow a user to input (or configure) one or more alert trigger conditions and one or more recipient addresses. In some embodiments, the user interface is configured to receive user input signals from the DAQ 250, for example, via a wired interface with the DAQ 250. In some embodiments, the structural health monitoring circuit module 210 may include a communications module or interface that provides a wired or wireless interface with the DAQ's communications interface 260. In some embodiments, the communications module 260 is used to communicate with a remote computing device 270 to enable remote configuration of the system (e.g., entry of these inputs / parameters). A combination of the two may be used to enable both local and remote configuration of the structural health monitoring circuit module 210. The microprocessor (e.g., CPU 212, RAM 214) is configured to receive user input signals for configuration of the structural health monitoring circuit module, including configuration of the sweep generation circuit 230.In one embodiment, the user input signal comprises one or more frequency ranges of the sweep generation circuit, a signal level, one or more monitoring parameters, one or more alert trigger conditions, and / or one or more recipient addresses. In embodiments in which a remote device 270 is used (e.g., the user interface is a remote user interface), the remote device may include an additional local user interface that allows a user to input configuration parameters on the remote computing device 270, which sends the input signals (or commands based on those input signals) to the structural health monitoring circuit module 210 (via the DAQ 250) and processes or executes them to configure the structural health monitoring circuit module 210. The user interface 216 or the DAQ CPU 252 may also be configured to send alerts and results to the remote computing device 270, which may display the results on a local user interface, such as a display 276 on the remote computing device 270. In some embodiments, the user interface 212 is configured to receive user input commands to configure monitoring of one or more impedance measurement circuits that comprise each of one or more predefined groups. In some embodiments, each group consists of two or more impedance measurement circuits located on a portion of the structure being monitored. In some embodiments, each impedance measurement circuit in a group is located in close proximity (or near) each other to enable monitoring of a cross section or volume of the structure, i.e., a cluster of impedance measurement circuits / sensors. That is, monitoring can be performed on selected individual sensors (a group), or multiple groups or clusters of sensors. Groups can be configured using the user interface 216 (local or remote). The user interface can also be configured to enable monitoring schedules.For example, certain groups can be monitored more frequently than other groups (or all sensors). The user interface 216 provides information to the DAQ, which can then store the monitoring configuration in and execute it via the removable memory 258 of the DAQ 250.

[0062] In this embodiment, the frequency sweep generator is a compact circuit measuring 85 mm x 50 mm x 10 mm and weighing less than 60 g. The frequency sweep generator is configured to generate an AC sweep signal with a nominal RMS voltage of 200 mV or less at a frequency ranging from 5 kHz to 1 MHz. With a touchscreen user interface, the dimensions are 85 mm x 50 mm x 30 mm and the weight is 150 g. The integrated sweep generator and touchscreen module facilitate all adjustments required for monitoring a given structure, such as adjusting the operating sweep frequency, signal amplitude / voltage, scan rate, etc. A memory 214 is provided to save the last settings displayed on the screen when the unit is rebooted. This allows for a sleep mode, improving power efficiency and enhancing monitoring safety against power failures. Additionally, the integrated sweep generator and touchscreen module includes a microprocessor unit that allows a program to be written for the operation of the sweep generator. In one embodiment, the program allows for sweeping at 1000 frequency steps per second. The program allows targeted display on demand and supports new features.

[0063] In one embodiment, the DAQ 250 further comprises a communications module 260 configured to transmit data to a remote unit 270 (or a communications interface 278 within the remote unit). This data includes representations of the output piezoelectric phase signal 136 and output piezoelectric current signal 139 associated with each PZT 122. The communications module may be a wired module, e.g., one using a wired, Ethernet, or fiber optic link, or a wireless communications module implementing one or more wireless communications protocols, such as Bluetooth, Wi-Fi, or 4G / 5G cellular protocols. The communications module may be used to send data files and alerts to an email address or may use an email-to-SMS gateway to send SMS alerts. The data may be transmitted to a user computing device 270, such as a PC, mobile device, or tablet, or to a cloud server that stores the data and provides a monitoring interface for multiple users. The communications module 260 may also be used to receive configuration commands for configuring the structural health monitoring module 210, including the frequency sweep generator, report format, frequency, and alert trigger conditions. The microprocessor 252 and memories 254, 258 are used to configure the operation of the structural health monitoring module 210 and can be used to enable user-defined activation of user-defined sensors from the overall monitoring system, user-defined pre-programmed and pre-scheduled monitoring, and user-defined and pre-scheduled partial or spatial monitoring of a structure. Wireless sensors can be programmed to enter a sleep mode to reduce power consumption and data communication, enabling a cost-effective monitoring solution. The use of wireless communication modules enables remote control and interrogation, including on-demand sensing and result requests. Sensors periodically send summary data to a cloud server, enabling continuous, automated monitoring and data display.

[0064] In one embodiment, the communications module 260 in the DAQ 250 is a wireless communications module. An analog-to-digital converter (ADC) circuit 256 in the DAQ is configured to convert each output piezoelectric phase signal and each output piezoelectric current signal into a digital representation, which is provided to the wireless communications module 260 for transmission to a user-defined destination, such as an email address or server. The DAQ 250 includes a processor 252 and a memory 254, both of which may be located on a microprocessor board (e.g., an MPU). The microprocessor board is used to estimate real impedance as a function of frequency, which can be displayed on user equipment (e.g., a display 276 of the user computing device 270). Alternatively, a report or alert can be generated to the user when an alert trigger condition is met, including, for example, cracks or damage to the structure and / or material. In some embodiments, a removable memory 258, such as an SD card, is included in the DAQ module 250 and is used to store digital representations of each output piezoelectric phase signal and each output piezoelectric current signal, which are stored as files that can be transmitted to the user computing device 270. The removable memory can also be used as backup storage of measurements for later download or transfer to the user computing device 270 by the communications module 260. The communications module can transfer data directly to the remote computing device 270 via a wired or wireless link, or can transfer the data using an intermediary. For example, the communications module can establish a wireless link to an access point and transmit the data to the user computing device over a network such as the Internet. In some embodiments, the memory is used to store the most recent N measurements, where N is a predefined amount based on available storage capacity (e.g., a rolling window) or corresponding to a time window.That is, a certain amount of storage is allocated for storing measurement data, and when the allocated storage is full, the oldest records are overwritten to make room for recording new measurements.

[0065] In some embodiments, the structural health monitoring module is integrated with a DAQ and includes an analog-to-digital converter circuit 254 to provide data acquisition system functionality and is also configured to perform data analysis and generate alerts and reports. In this embodiment, the analog-to-digital converter circuit 256 is configured to convert each output piezoelectric phase signal and each output piezoelectric current signal into a digital representation, and the microprocessor 252 is configured to analyze the digital representation to estimate the real impedance as a function of frequency for each sensor and transmit monitoring reports and / or alerts to recipients using the wireless communication module 260. The memory 212 and / or 254 (if present) can be configured to store recipient addresses, report formats for generating alerts, and one or more alert trigger conditions. A user interface 216, such as a touchscreen, a screen and buttons, or other interface, allows a user to input one or more frequency ranges for the sweep generation circuit, one or more monitoring parameters, one or more alert trigger conditions, and one or more recipient addresses. As mentioned above, DAQ 250 may include or use removable memory, such as an SD card, to store digital representations of each output piezoelectric phase signal and each output piezoelectric current signal, which may allow for removal and transfer to user computing device 270 or serve as backup storage. In some embodiments, a software application running on user computing device 270 may be used to remotely configure structural health monitoring module 210 and DAQ 250 modules via communications module 260.

[0066] As mentioned above, one or more multi-sensor impedance measurement circuit modules 220 are provided that include multiple impedance measurement circuit modules 120. As mentioned above, this may be integrated into a structural health monitoring module, as shown in Figure 2, where four impedance measurement circuit modules 120 in the multi-sensor impedance measurement circuit module 220 are connected to four PZTs (221, 222b, 222c, 222d) disposed on or embedded in the structure 202.

[0067] In another embodiment, one or more multi-sensor impedance measurement circuit modules 220 are provided as distributed forward-deployed modules, each contained in a compact, weatherproof housing, located adjacent to or on the structure to be monitored, and locally wired to PZTs integrated into or located on the structure. These forward-deployed multi-sensor impedance measurement circuit modules 220 can be wired to a central module of the structural health monitoring module 210, which can include a frequency sweep generator 230 and a power supply 240 with or connected to a DAQ 250.

[0068] 3A shows a wiring diagram of one embodiment of a multi-sensor impedance measurement circuit module 320 comprising four impedance measurement circuit modules. In one embodiment, the multi-sensor impedance measurement circuit module 320 comprises a sweep signal input connector 312 configured to receive an input AC sweep signal 355 and a voltage conversion circuit configured to generate multiple regulated voltages from the voltage from the input supply voltage connector 344. In one embodiment, a nominal 12V input voltage is provided and the voltage conversion circuit is configured to generate regulated +5V, −5V, and +3V supplies.

[0069] The sweep signal 312 is provided as an input to each impedance measurement circuit. A plurality of paired input connectors 321 are provided for connecting to the inputs and outputs of the piezoelectric sensors 322, each paired input connector being connected to one of the impedance measurement circuit modules. A plurality of paired output connectors 329 are also provided, each paired output connector being connected to the output of one of the impedance measurement circuit modules. The paired outputs 329 carry output piezoelectric phase signals 136 and output piezoelectric current signals 139 from the respective impedance measurement circuit modules 120. These may be connected directly to the data acquisition system 351 or to a central module of the structural health monitoring module 210 that is connected to the DAQ 250 or includes the DAQ 250. The microprocessor within the DAQ 250 may be configured to generate monitoring reports or alerts, which may be transmitted to a user computing device 270 via the communication module 260, for example, via a wireless link 262.

[0070] It should be noted that the PZTs 222, 322 are not contained within the housing of the multi-sensor impedance measurement circuit module 220, but the housing is provided with connectors that allow wiring to be connected to PZTs located on or embedded in the structure being monitored.

[0071] Figures 3B, 3C, 3D, and 3E are circuit diagrams of the first portions of the first, second, third, and fourth impedance measurement modules of the first multi-sensor module of Figure 3A, Figure 3F is a circuit diagram of the second portions of the first and second impedance measurement modules of the first multi-sensor module of Figure 3A, and Figure 3G is a circuit diagram of the second portions of the third and fourth impedance measurement modules of the first multi-sensor module of Figure 3A.

[0072] Take Figure 3B as an example, which is a more detailed circuit diagram of the embodiment shown in Figure 1A, showing the main components as well as additional components (e.g., capacitors, resistors, diodes) for filtering, pulling up, or pulling down the signal / input. Sweep signal 312 is provided as an input to buffer 321a (LTI 362). Sweep signal 312a is also branched to buffers 321b, 321c, and 321d in the second, third, and fourth circuits of Figures 3C through 3E.

[0073] Current-to-voltage converter 326a (LTI1252) is connected in parallel with a 470 Ω feedback resistor. The current-to-voltage converter and feedback resistor are configured to receive the piezoelectric output signal from piezoelectric sensor 322a and generate piezoelectric current signal 328a, whose AC voltage is proportional to both the phase angle and the current in the piezoelectric sensor. Because the piezoelectric current signal is the output of the current-to-voltage converter, it may also be referred to as a piezoelectric voltage signal. However, in the following discussion, the piezoelectric current signal is used because it is a voltage proportional to the current generated by the piezoelectric sensor. The piezoelectric output signal is fed to the negative input of an LT1252 I-V converter, which adjusts the voltage to maintain a current equal to but opposite to the current through resistor 325a to balance the PZT current. The output is split, with one branch connected to a digital phase detector (AD8302) configured to receive a buffered sweep signal 323a at a first input and a piezoelectric current signal 327a from a current-to-voltage converter 326a at a second input, compare the piezoelectric current signal with the buffered sweep signal, and generate a first piezoelectric phase signal (PH1). The piezoelectric current signal 328a is fed to an LT1364 operational amplifier (with the piezoelectric current signal 328a fed to its negative input) and a precision rectifier 336a comprised of an MM4148 diode and resistors, which are configured to rectify the piezoelectric current signal to generate a first piezoelectric current signal I1 337a. Similar circuits are shown in Figures 3C-3E.

[0074] Figure 3F shows an embodiment of a first low-pass filter 333a that receives the first piezoelectric phase signal PH1 332a and generates an output piezoelectric phase signal 334a having a DC voltage proportional to the phase difference between the buffered sweep signal and the piezoelectric current signal. The first low-pass filter 333a is configured with a 22 kΩ resistor (R18) and a 68 nF capacitor (C19) to provide a cutoff frequency of 106 Hz, and uses a TLC2272 op amp (with R19 and R20) as its gain stage. The second low-pass filter 338a, shown in Figures 3A and 3E, includes the RC components of Figure 3A (22 kΩ resistor R37 and 68 nF capacitor C33) to provide a cutoff frequency of 106 Hz, and the op amp gain stage (TLC2272 and resistors R22 and R23) of Figure 3E. Figure 3E shows the equivalent first and second low pass filters 333b, 338b for the second circuit, and Figure 3F shows the equivalent first and second low pass filters (333c, 338c, 333d, 338d) for the third and fourth circuits.

[0075] FIG. 3F shows a voltage conversion circuit 346 comprising a TMR3-1221 DC / DC converter that receives a nominal 12V supply and produces regulated +5V and −5V supply voltages 347, and an LP2950 voltage regulator 348 that produces a regulated +3V 349 from a 5V input.

[0076] The circuits are mounted on a circuit board with a first dimension of 38 mm and a second dimension of 55 mm, and the impedance measurement circuit consumes less than 5 watts of power per four PZT sensor modules. Surface mount components may be used, and the circuit may be housed in a weatherproof housing.

[0077] In another aspect, the impedance measurement circuit includes a compact, miniature housing that houses a circuit board having a plurality of surface mount components that implement one or more components of the multi-sensor impedance measurement circuit module. In one embodiment, the circuit board has a first dimension of 38 mm or less and a second dimension of 55 mm or less.

[0078] The DAQ250 analyzes the piezoelectric phase and current output signals to estimate the real component of the impedance through the PZT. real =Vcos(θ) / I, where θ is the digitized phase signal 136, I is the digitized current signal 139, and V is a constant based on the input voltage across the PZT, which may be predetermined, such as by taking measurements during calibration of the circuit. In one embodiment, the components (and gain) are selected to produce an output DC voltage between 0 and 5V.

[0079] The estimates of the real component of the impedance can be saved along with the corresponding swept frequency, and these data pairs can be saved for every swept frequency within the swept frequency range so that they can be plotted or analyzed using LabVIEW, MATLAB, R, or an equivalent suitable graphing or analysis package. The data can be saved to a file, such as a spreadsheet, on removable memory 258.

[0080] FIG. 4A shows a plot 400 of real impedance 402 as a function of frequency 404 for a piezoelectric sensor 416 embedded in a first location in a mortar joint 413 between two bricks 412, 414, under applied loads 422 of 0, 44, 45, 48, and 50 kN. This data was generated by the structural health monitoring system embodiment described above. In this embodiment, the impedance for loads above 45 kN, near 100-125 kHz, increases significantly compared to lower loads, indicating the presence of a crack. FIG. 4B shows a plot 400 of real impedance 402 as a function of frequency 404 for a second piezoelectric sensor embedded in a second location in a mortar joint between two bricks 412, 414, under loads of 0, 10, 20, 35, 40, 45, and 50 kN. Compared to the lower load signals, the presence of a crack 440 is indicated at higher loads of 40 kN or greater at approximately 90 Hz to 110 Hz.

[0081] These plots demonstrate that cracks can be identified by sudden changes, such as an increase in impedance at a specific frequency, compared to previously recorded plots. Therefore, cracks can be detected by setting an alert when deviations from the average or reference curve occur. The analysis module of the DAQ or remote computing device can be configured to analyze the estimates of the real component of impedance over the swept frequency range to detect structural changes, such as cracks. This analysis may include detecting significant deviations at a specific frequency or a band of frequencies within the swept frequency range. One or more trigger alert conditions may be stored in memory, which may include one or more predetermined thresholds, and an alert may be generated if the real component of impedance exceeds the predetermined threshold. Other analysis methods and alert conditions may be based on signal analysis of the components of impedance over the swept frequency range, including Fourier analysis-based methods, change detection, and statistical techniques that detect increased deviations compared to past values. The triggering of an alert condition may be determined based on the particular signal analysis method used.

[0082] FIG. 5A is a schematic diagram of a brick wall formed of bricks and mortar joints, showing the approximate locations of five piezoelectric sensors (PZT1-PZT5) in one embodiment. FIG. 5B is a bar graph of the damage index as a function of increasing load for five piezoelectric sensors located on the brick surfaces of the wall shown in FIG. 5A. FIG. 5C is a bar graph of the damage index as a function of increasing load for five piezoelectric sensors embedded in the mortar joints of the wall shown in FIG. 5A. FIG. 5D is a bar graph of the damage index as a function of increasing load for five piezoelectric sensors located on the mortar joint surfaces of the wall shown in FIG. 5A.

[0083] These plots show that the closer the transducer is to the crack, the higher the damage index recorded, with the damage index increasing with increasing load. A higher average damage index was observed for PZTs embedded in mortar joints. Crack initiation was detected earliest with PZTs embedded in mortar joints. Therefore, it was concluded that PZTs embedded within mortar joints are best for new buildings, while PZTs embedded on the surface of mortar joints are best for existing buildings.

[0084] FIG. 6 is a plot 600 of the real impedance 602 of a piezoelectric sensor placed on the head of a bolt as a function of frequency 604. The plot is generated by the structural health monitoring system 200 in accordance with one embodiment and is shown for a bolt 610 loosely threaded into a steel beam and for the same bolt tightly threaded into a steel beam 610′. A schematic diagram of setup 606 is also shown inset in FIG. 6. Two beam sections 607 and 608 are fastened together via a flat plate 609 into which bolts 610 and 612 are threaded. Piezoelectric sensors 614 and 616 are attached to the heads of the bolts 610 and 612 and wired to the structural health monitoring circuit module 210. The signal for the loose bolt 610 is shown in black, and the signal for the tight bolt is shown as a dashed black line 610′. In FIG. 6, it can be seen that the loose bolt has a large peak 620 around 120 kHz compared to a similar peak 622 for the tight bolt 610' configuration.

[0085] In one embodiment, the module operates in a frequency range of 5 kHz to 1 MHz. This is a suitable frequency range for SHM (structural health monitoring) applications, although narrower or wider frequency ranges can be used, such as a lower limit of 1 kHz, 10 kHz, or 20 kHz, or an upper limit of 200 kHz, 500 kHz, or 2 MHz. This frequency range can be used to perform active SHM on a wide range of materials and structures, monitor with different sized PZTs, or vary the size of the monitored area.

[0086] The operating range between the start and stop frequencies can be determined by examining the response from the attached PZT before each test. In some embodiments, the frequency range is between 20 kHz and 400 kHz, depending on the size and material of the PZT. The module can operate at frequencies up to 1 MHz.

[0087] Calibration of the real impedance value of each module is performed by replacing the PZT with a 100 ohm resistor, then varying either the signal generator output or the constants in the real impedance equation (or both) to obtain a straight 100 ohm line across the frequency sweep.

[0088] The phase angle vs. voltage transfer function has a nonlinear portion approaching 0 degrees. However, this is insignificant because the cosine function at angles less than 5 degrees is within 0.5 percent. Therefore, at these low angles, the real part of the impedance will be within 0.5 percent of the impedance magnitude, and after calibration, the error in the displayed real part of the impedance will not exceed 0.5 percent.

[0089] Calibration of the phase angle voltage can be performed by placing a 10 nF capacitor in place of the PZT and measuring the output voltage of the digital phase detector with a digital voltmeter. This value was chosen to be close to the inherent capacitance of the PZT, but is not an exact value. After the voltage is measured, it is multiplied by four and used as the denominator in the cosine calculation for that module. Theoretically, the real impedance value of the capacitor should be zero. Because capacitors are not ideal, observed values ​​of less than a few ohms do not affect the overall results.

[0090] Embodiments of this system are compact, cost-effective, and can be deployed across a wide range of structures, making them a useful alternative to existing systems.

[0091] Embodiments of the system can be used to monitor: Typical steel structural connections used in bridges and various civil and industrial structures Typical scale model 3D galvanized steel truss structures used in industrial engineering, civil engineering, roofs, bridges, frames, warehouses, various steel and metal structures (e.g. silos, submarines, ships, trains, etc.) Typical scaled-down steel and timber joints used in a variety of structures such as houses, bridges, roofs, and all other civil, mining, petroleum (e.g. drilling rigs), machinery (machines and trains), geotechnical, and railroad track structures Individual bolt health monitoring Monitoring of tightening torque for individual bolts or bolt groups as required Rock bolting and reinforced ground support structures Reinforced concrete structures, e.g. rebar Rock condition Soil condition -Concrete condition Pressure vessels, submarines, etc. Stone structures · Machinery and equipment parts and condition

[0092] Embodiments of the system can provide a compact, portable module that uses an internal battery and solar panel to provide power and a wireless communication link to transmit data to the user. The structural health monitoring module, consisting of a frequency generator, is lightweight and can also include a touchscreen interface. A compact multi-sensor impedance measurement circuit module can be forward-deployed from the central module and wired to the central module, providing power and the sweep signal. The output signal is sent to the DAQ 250 and transmitted to a user-specified destination via the communication module 260 for further analysis, processing, and display on the user's computing device 270. Communication can be via a wireless link, e.g., via a 4G / 5G or Wi-Fi network, or a wired link. The DAQ can also perform analysis of the output signal, and data can be stored locally on removable storage, such as an SD card.

[0093] The processing unit or computing device in the structural health monitoring module 210, DAQ, and user computing device 270 may be configured to analyze sensor data, estimate real impedance, detect changes, generate reports and alerts, and plot results. The computing device may include a central processing unit (CPU), memory, and input / output (or communication) interfaces, and may further include a graphics processing unit (GPU), input devices, and output devices. The CPU may include an arithmetic logic unit (ALU), a control unit, and a program counter element. The memory may include solid-state memory and secondary storage such as a hard disk or SD card. The input / output interface may include a network interface and / or communication module for communicating with an equivalent communication module in another device using a predetermined communication protocol (e.g., Bluetooth, Zigbee, IEEE 802.15, IEEE 802.11, TCP / IP, UDP, etc.). The input / output device may be connected via a wired or wireless connection. The input / output interface may communicate with a storage device and save the analysis results in external storage. Input / output devices may include a keyboard, a mouse, and a display device such as a flat screen display (e.g., LCD, LED, plasma, touch screen, etc.), a projector, etc. The computing devices in the structural health monitoring module 210 and DAQ 250 may be microprocessor boards or microprocessor units (MPUs) consisting of one or more processors and memory on a PCB board with an integrated interface, and may include additional modules such as wireless communication modules providing Wi-Fi and Bluetooth connectivity.

[0094] One embodiment of the structural health monitoring module 210 was constructed in which the user interface 216 is a touchscreen interface for the TFT display module ILI9341, and the frequency sweep generator 230 is a DDS function generator module based on the Analog Devices AD9833 chip. The microprocessor may be an Espressif Systems ESP32 DevKitC 32UE development module, which may be assembled on a PCB. Software was developed to control the operation of the touchscreen using the open-source Arduino IDE software with the help of several open-source libraries, including the TFT_eSPI library by Bodner, the Arduino SPI library, and the Preferences library by Volodymyr Shymanskyy.

[0095] A DAQ250 embodiment was constructed in which the ADC256 was configured using two AD7606 modules, providing 16-bit resolution and a maximum sampling rate of 200ksps. These ADC modules configured a total of 16 channels corresponding to eight PZT sensors, controlled by an Arduino Mega 2560 R3 microcontroller. The DAQ microprocessor was provided by a DFRobot FireBettle eESP32 module (DFR0478), which also provides the wireless communication module 260. A real-time clock module, the RTC module SD2405, was incorporated to provide accurate real-time timekeeping and date stamping functionality.

[0096] The computer program developed for the DAQ250 was designed to perform several tasks using the ESP32 and ATMEGA2560 microcontrollers and various libraries. In one embodiment, the program code was configured to provide the following functionality: 1) The code connects the ESP32 to a Wi-Fi network and establishes an Internet connection; 2) The code connects to a time server (ntp.org) and retrieves the current date and time adjusted for a specified time zone; 3) The code stores the retrieved date and time in the real-time clock module; 4) The code waits for a trigger signal (e.g., via cable 224) from the structural health monitoring (SHM) module 210; 5) Upon receiving the trigger signal, the code sends a trigger to the ATmega2560 microcontroller to control the ADC; 6) The ATmega2560 retrieves measurements from the ADC254 and sends the data to the ESP32; 7) The ESP32 receives the digitized piezoelectric phase and current signals from the ATmega2560; and 8) The code converts the measured signals into real impedance values ​​(Z real = Vcos(θ) / I). 9) The data is saved to a text file with a filename in a user-defined format. 10) The data file contains a header with column descriptions for date, time, sample number, phase, current, and impedance values. 11) The code uses the SMTP client library to send the data file as an email attachment to the specified recipient. 12) The code also includes the necessary library imports, pin assignments, and global variables used throughout the program. There are two separate sets of program code uploaded to the ESP32 and ATMEGA2560, respectively.

[0097] The processing units or computing devices in the structural health monitoring module 210, DAQ, and user computing device 270 may have a single CPU (core) or multiple CPUs (multi-core), or multiple processors. The computing devices may be servers, desktops, portable computers (including tablets), smartphones, smartwatches, or microprocessor devices incorporating a processor and on-board memory and interfaces. The processor may use parallel processors, vector processors, or be part of a distributed (cloud) computing device. Memory is operatively connected to the processor and may include RAM and ROM components, as well as secondary storage components such as solid-state disks and hard disks, which may be internal or external to the device. External storage may be a directly connected external device or a network storage device external to the computing device (i.e., connected via a network interface), including cloud-based storage. The memory may include instructions for causing the processor to perform the methods described herein. The memory may be used to store an operating system and additional software modules or instructions. The processor may be configured to load and execute software modules or instructions stored in the memory. The computing device may be configured to continuously analyze the input sensor signal and generate a report or alarm if a change is detected. For example, the computing device may store a set of rules or thresholds that indicate a change that can be compared to the analysis results (e.g., deviation from a reference curve or spectrum). The microprocessor used in the module may be a microcontroller, such as an Arduino microcontroller, and may include on-board memory.

[0098] Those skilled in the art will appreciate that information and signals may be represented using any of a variety of technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips may be referenced throughout the above description and may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0099] Those skilled in the art will appreciate that the various illustrative logic blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein can be implemented as electronic hardware, computer software, or instructions, or a combination of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled engineers may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

[0100] The steps of a method or algorithm described in connection with the embodiments disclosed herein may be implemented directly in hardware, in a software module executed by a processor, or a combination of both. In a hardware implementation, processing may be performed within one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, or other electronic units designed to perform the functions described herein, or any combination thereof. Software modules, also known as computer programs, computer code, or instructions, may include multiple source or object code segments or instructions and may be stored in any computer-readable medium, such as RAM memory, flash memory, ROM memory, EPROM memory, registers, hard disk, removable disk, CD-ROM, DVD-ROM, Blu-ray disc, or other computer-readable medium. In some aspects, the computer-readable medium may include a non-transitory computer-readable medium (e.g., a physical medium). Furthermore, in another aspect, the computer-readable medium may include a transitory computer-readable medium (e.g., a signal). Combinations of the above should also be included within the scope of computer-readable media. In another aspect, the computer-readable medium may be integral to the processor. The processor and the computer-readable medium may reside in an ASIC or related device. The software codes may be stored in a memory unit, and the processor may be configured to execute them. The memory unit may be implemented within the processor or external to the processor, in which case it may be communicatively coupled to the processor via various means known in the art.

[0101] Furthermore, it should be understood that modules and / or other suitable means for performing the methods and techniques described herein can be downloaded and / or otherwise obtained by a computing device. For example, such a device can be connected to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, the various methods described herein can be provided via storage means (e.g., RAM, ROM, physical storage media such as a compact disc (CD) or USB storage drive, etc.), and a computing device can obtain the various methods by connecting or providing the storage means to the device. Furthermore, other suitable techniques for providing the methods and techniques described herein to a device can be utilized.

[0102] In one form, the present invention may comprise a computer program product for performing the methods or operations presented herein. For example, such a computer program product may comprise a computer (or processor) readable medium having instructions stored (and / or encoded) thereon, which instructions are executable by one or more processors to perform the operations described herein. In certain aspects, the computer program product may include packaging materials.

[0103] The methods disclosed herein include one or more steps or actions for achieving the described method. The steps and / or actions of the methods may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and / or use of specific steps and / or actions may be changed without departing from the scope of the claims.

[0104] As used herein, the terms "determining," "obtaining," and "estimating" encompass a wide range of actions. For example, "determining," "obtaining," and "estimating" can include calculating, computing, processing, deriving, examining, referencing (e.g., referencing in a table, database, or other data structure), ascertaining, and the like. Also, "determining" and "obtaining" can include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), and the like. Also, "determining," "obtaining," and "estimating" can include resolving, selecting, choosing, establishing, and the like.

[0105] The reference herein to prior art is not an acknowledgement that such prior art is part of the common general knowledge, nor should it be taken as such an indication.

[0106] As used in this specification and the appended claims, the terms "comprises", "includes", and their derivatives (e.g., comprises, consisting of, includes, includes) should be interpreted to inclusively include the features referred to by the terms and do not exclude the presence of additional features, unless otherwise stated or implied.

[0107] In some cases, multiple features may be combined in a single embodiment for brevity or to facilitate understanding of the scope of the disclosure. In such cases, it should be understood that these multiple features may be provided separately (in separate embodiments) or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined in a single embodiment unless otherwise stated or implied. This also applies to claims that may be recombined in any combination. That is, a claim may be amended to include features defined in another claim. Furthermore, the phrase "at least one" in a list of items refers to any combination of those items, including single members. For example, "at least one of a, b, or c" is intended to cover a, b, c, ab, ac, bc, and abc.

[0108] Those skilled in the art will understand that the disclosed subject matter is not limited to the particular application or applications described. Nor is the disclosure limited to preferred embodiments with respect to the specific elements and / or functions described or depicted herein. It should be understood that the disclosure is not limited to the disclosed embodiment or embodiments, but rather is capable of numerous rearrangements, modifications, and substitutions without departing from the scope defined by the appended claims.

Claims

1. A buffer for receiving an AC sweep signal from a frequency sweep generator, configured to supply the buffered sweep signal to the input of a piezoelectric sensor, A current-voltage converter connected in parallel with a feedback resistor, wherein the current-voltage converter and the feedback resistor receive a piezoelectric output signal from the piezoelectric sensor and generate a piezoelectric current signal, and the AC voltage in the piezoelectric current signal is proportional to both the phase angle and the current at the piezoelectric sensor, A phase comparison circuit is provided which receives the buffered sweep signal at a first input unit, receives the piezoelectric current signal at a second input unit, compares the piezoelectric current signal with the buffered sweep signal, and generates an output piezoelectric phase signal having a DC voltage proportional to the phase difference between the buffered sweep signal and the piezoelectric current signal. A rectifier circuit that receives the piezoelectric current signal at a first input unit and generates an output piezoelectric current signal having a DC voltage proportional to the current flowing through the piezoelectric sensor, An impedance measurement circuit module equipped with the following features.

2. The aforementioned phase comparison circuit is A digital phase detector is configured to receive the buffered sweep signal at a first input unit, receive the piezoelectric current signal from the current-voltage converter at a second input unit, and generate a first piezoelectric phase signal by comparing the piezoelectric current signal with the buffered sweep signal. A first low-pass filter configured to receive the first piezoelectric phase signal and generate the output piezoelectric phase signal having a DC voltage proportional to the phase difference between the buffered sweep signal and the piezoelectric current signal, Includes, The rectifier circuit described above is A rectifier configured to receive the piezoelectric current signal at a first input unit and rectify the piezoelectric current signal to generate a first piezoelectric current signal, A second low-pass filter configured to receive the first piezoelectric current signal and generate the output piezoelectric current signal having a DC voltage proportional to the current flowing through the piezoelectric sensor, An impedance measurement circuit module according to claim 1, including the above.

3. The impedance measurement circuit module according to claim 1, wherein the AC sweep signal has a frequency in the range of 5 kHz to 1 MHz, and the components of the impedance measurement circuit module are configured to operate in the frequency range of 5 kHz to 1 MHz.

4. The impedance measurement circuit module according to claim 1, wherein the output piezoelectric phase signal and the output piezoelectric current signal are DC signals having a voltage in the range of 0 to 5V.

5. The impedance measurement circuit module according to claim 1, wherein the power consumption is less than 5 watts.

6. A sweep signal input connector configured to receive an input AC sweep signal, or a sweep generation circuit configured to generate an AC sweep signal, A voltage conversion circuit configured to generate multiple stabilized power supply voltages from an input supply voltage connector or power supply circuit, A plurality of impedance measurement circuit modules according to any one of claims 1 to 5, wherein the sweep signal is provided as an input to each of the impedance measurement circuit modules, A plurality of paired input connectors for connecting to the input and output sections of a piezoelectric sensor, wherein each paired input connector is connected to one of the plurality of impedance measurement circuit modules, A plurality of paired output connectors, each paired output connector connected to one of the output sections of the impedance measurement circuit module, and the paired output having the output piezoelectric phase signal and the output piezoelectric current signal from each impedance measurement circuit module, A multi-sensor impedance measurement circuit module equipped with the following features.

7. The multi-sensor impedance measurement circuit module according to claim 6, wherein the voltage conversion circuit is configured to generate stabilized +5V power supplies, -5V power supplies, and +3V power supplies.

8. The multi-sensor impedance measurement circuit module according to claim 6, further comprising a compact, integrated housing for a circuit board having multiple surface-mount components on which one or more components of the multi-sensor impedance measurement circuit module are mounted.

9. A structural integrity monitoring circuit module for use in a structural integrity monitoring system, One or more multisensor impedance measurement circuit modules according to claim 6, comprising a power supply circuit and a sweep signal generator, wherein the power supply circuit includes a voltage regulator configured to receive an unregulated voltage power supply in the range of 9V to 18V and a regulated +5V, -5V, +3V power supply, A user interface, at least one processor, and at least one memory, Equipped with, The user interface is configured to receive the one or more user input signals, the one or more user input signals being supplied to at least one of the at least one processors for configuring the structural health monitoring circuit module, which includes configuring the sweep generation circuit, the one or more user input signals being received by the structural health monitoring circuit module using an input device and / or from a remote device.

10. A structural health monitoring circuit module for use in a structural health monitoring system, for connection to one or more multisensor impedance measurement circuit modules according to claim 6, wherein the one or more multisensor impedance measurement circuit modules each have the input supply voltage connector and the sweep signal input connector. The structural integrity monitoring circuit module is, A power supply circuit including a voltage regulator configured to receive an unregulated voltage power supply in the range of 9V to 18V and regulated +5V, -5V, and +3V power supplies, A power output connector for supplying the aforementioned unstabilized voltage power supply to the input supply voltage connector of the one or more multi-sensor impedance measurement circuit modules via a wired connector, A sweep generation circuit configured to generate the aforementioned AC sweep signal, A sweep signal output connector for supplying the AC sweep signal to the sweep signal input connector of the one or more multi-sensor impedance measurement circuit modules via a wired connector, A user interface, at least one processor, and at least one memory, Equipped with, The user interface is configured to receive one or more user input signals, the one or more user input signals being supplied to at least one of the at least one processors to configure the structural health monitoring circuit module, which includes configuring the sweep generation circuit, and the one or more user input signals being received using an input device and / or a remote device.

11. The structural integrity monitoring circuit module according to claim 9, wherein the AC sweep signal has a frequency in the range of 5 kHz to 1 MHz.

12. The structural integrity monitoring circuit module according to claim 9, wherein the AC sweep signal has an RMS voltage of 200 mV or less.

13. The structural integrity monitoring circuit module according to claim 9, wherein the sweep generation circuit further has a sweep trigger signal.

14. The system further comprises an analog-to-digital conversion circuit configured to convert each output piezoelectric phase signal and each output piezoelectric current signal from each of the one or more multi-sensor impedance measurement circuit modules into a digital representation consisting of a digital phase signal and a digital current signal. The one or more processors are configured to analyze the digital representation, estimate the actual impedance as a function of frequency for each sensor, generate a monitoring report, and store it in the at least one memory. The structural health monitoring circuit module according to claim 13, further comprising a communication module that enables the transmission or download of the stored monitoring report.

15. The structural health monitoring circuit module according to claim 14, wherein the at least one memory is configured to store a receiver address and one or more alert trigger conditions for generating an alert, the one or more processors are configured to analyze the digital phase signal and the digital current signal for each of the one or more multisensor impedance measurement circuit modules to determine whether one or more of the one or more alert trigger conditions are met, and the communication module is configured to send the monitoring report to the receiver address and / or send an alert to the receiver when one or more of the one or more alert trigger conditions are met.

16. The structural health monitoring circuit module according to claim 14, wherein one or more user input signals are received from the remote device or the user interface via the communication module, the one or more user input signals include one or more frequency ranges of the sweep generation circuit, signal levels, one or more monitoring parameters, one or more alert trigger conditions, and / or one or more recipient addresses.

17. The structural health monitoring circuit module according to claim 16, wherein the one or more monitoring parameters are used to configure the one or more processors to monitor a predefined group of one or more impedance measurement circuit modules.

18. The structural integrity monitoring circuit module according to claim 14, wherein for each of the one or more multi-sensor impedance measurement circuit modules, the analysis of the digital phase signal and the digital current signal includes estimating the real impedance Zreal = Vcos(θ) / I, where θ is the respective digital phase signal, I is the respective digital current signal, and V is a predetermined constant obtained from calibration measurements including measuring the input voltage applied to each of the piezoelectric sensors.

19. A structural integrity monitoring circuit module according to claim 10, One or more multi-sensor impedance measurement circuit modules according to claim 6, A data acquisition module comprising an analog-to-digital conversion circuit, at least one processor, at least one memory, and a communication module, wherein the analog-to-digital conversion circuit is configured to convert each output piezoelectric phase signal and each output piezoelectric current signal from each of the one or more multi-sensor impedance measurement circuit modules into a digital representation consisting of a digital phase signal and a digital current signal, the at least one processor is configured to analyze the digital representation, estimate the actual impedance as a frequency function for each sensor, generate a monitoring report and store it in at least one memory, and the communication module is configured to enable transmission or download of the stored monitoring report. A structural integrity monitoring system equipped with [specific features / features].

20. The system according to claim 19, wherein the at least one memory is configured to store a recipient address and one or more alert trigger conditions for generating an alert, the one or more processors are configured to analyze the digital phase signal and the digital current signal for each of the one or more multisensor impedance measurement circuit modules to determine whether one or more of the one or more alert trigger conditions are met, and the communication module is configured to send the monitoring report to the recipient address and / or send an alert to the recipient when one or more of the one or more alert trigger conditions are met.

21. The system according to claim 19, wherein one or more user input signals are received from the remote device via the communication module or from the user interface, and the one or more user input signals include one or more frequency ranges of the sweep generation circuit, signal levels, one or more monitoring parameters, one or more alert trigger conditions, and / or one or more recipient addresses.

22. The system according to claim 21, wherein the one or more monitoring parameters are used to configure the one or more processors and to monitor a predefined group of one or more impedance measurement circuit modules.

23. The system according to claim 20, wherein for each of the one or more multisensor impedance measurement circuit modules, the analysis of the digital phase signal and the digital current signal includes estimating the real impedance Zreal = Vcos(θ) / I, where θ is the respective digital phase signal, I is the respective digital current signal, and V is a predetermined constant obtained from calibration measurements including measuring the input voltage applied to each piezoelectric sensor.

24. A method for measuring the impedance of a piezoelectric sensor, The steps include buffering the AC sweep signal received from the frequency sweep generator and supplying the buffered sweep signal to the input section of the piezoelectric sensor, A step of generating a piezoelectric current signal using a current-voltage converter in parallel with a feedback register, which is configured to receive a piezoelectric output signal from the piezoelectric sensor, wherein the AC voltage in the piezoelectric current signal is proportional to both the phase angle and the current at the piezoelectric sensor. A step of generating an output piezoelectric phase signal having a DC voltage proportional to the phase difference between the buffered sweep signal and the piezoelectric current signal, using a phase comparison circuit, wherein the phase comparison circuit is configured to receive the buffered sweep signal at a first input, receive the piezoelectric current signal at a second input, and compare the piezoelectric current signal with the buffered sweep signal. The steps include generating an output piezoelectric current signal having a DC voltage proportional to the current flowing through the piezoelectric sensor using a rectifier circuit that receives the piezoelectric current signal at the first input unit, A method that includes this.

25. The method according to claim 24, further comprising the steps of: digitizing the output piezoelectric phase signal to obtain a digital phase signal θ; digitizing the output piezoelectric current signal to obtain a digital current signal I; and estimating the actual impedance Zreal = Vcos(θ) / I, where V is a predetermined constant obtained from a calibration measurement which includes measuring the input voltage applied to the piezoelectric sensor.

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