Structural health monitoring sensor and system

Abstract

A structural health monitoring system includes a sweep signal generator that generates alternating current signals that are simultaneously provided to a plurality of impedance measurement circuit modules. Each impedance measurement circuit module is connected to a piezoelectric sensor (PZT) that is placed on or embedded within the structure to be monitored. Each impedance measurement circuit module is used for generating two output signals. The first signal is a voltage proportional to a phase difference between an input scan signal and a PZT current signal, and the second signal is a voltage proportional to a current through the PZT. A data acquisition module digitizes these signals and generates an estimate of the real part of the (complex) impedance across the PZT at the scanning frequency. The scan signal generator is used to generate a plurality of scan signals within a scan frequency range, each scan signal corresponding to a different frequency to generate an impedance spectrum that can be used to detect structural changes such as cracks.

Description

Priority Document

[0001] This application claims priority to Australian Provisional Patent Application No. 2022901989, filed on July 15, 2022, entitled “Structural Health Monitoring Sensors and Systems”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present invention relates to systems for monitoring structures and materials. In a particular form, the present invention relates to a monitoring system for monitoring structural health and material condition (including soil condition) integrity, damage (including environmental damage), crack and fracture progression, etc. in various materials, machinery, pressure vessels, infrastructure (including mining and civil structures). Background Art

[0003] In the mining, oil and gas, geotechnical, mechanical, civil engineering and infrastructure sectors, structures and materials need to be regularly inspected for crack initiation, crack activation and damage for various safety and economic reasons. Traditionally, inspections are performed manually by inspectors through visual inspection of the structure. This manual method is very time-consuming and prone to human error and inaccuracy. In some cases, visual inspection is simply not possible. Therefore, various technical solutions have been investigated in recent years for structural health monitoring using systems based on X-ray, fiber optics, ultrasound and vibration. However, these systems have many drawbacks, such as high cost, large size, heavy weight, limited availability on a wide range of structures and / or the need for skilled operators.

[0004] One approach proposed is to use piezoelectric transducers (also known as piezoelectric sensors) placed on or embedded in a structure for long-term continuous or periodic / repeated monitoring. A piezoelectric transducer (PZT) consists of a small piece or sheet of piezoelectric material (e.g., piezoelectric ceramic) to which two wires are connected. Piezoelectric materials have the property of generating an electrical charge when subjected to mechanical stress, and it has been shown that the electrical impedance of a PZT is directly related to the mechanical impedance of the host structure in which it is placed. They can be used to achieve long-term continuous monitoring of the mechanical properties of the host structure by measuring the electrical impedance of the PZT over a certain frequency range (usually in the range of 30 to 400kHz). Detecting changes in the electrical impedance signature can be considered an indication of changes in the integrity of the structure, such as signs of cracks, damage, or deterioration in structural components such as bolts. However, impedance is a complex quantity and therefore requires specialized circuitry to measure it. One approach is to use an impedance analyzer (e.g., the HP4194A) to directly measure the complex impedance across the PZT. However, these impedance analyzers are bulky, making any monitoring system cumbersome. Furthermore, the analyzer was designed for laboratory use and therefore not rugged enough or suitable for permanent deployment in the field.

[0005] Some researchers have proposed alternatives to using expensive impedance analyzers. One approach is to connect the PZT in series with a resistor and then measure the voltage across the resistor (e.g., modeled in a voltage divider configuration). The impedance in the PZT is then approximated as the ratio of the voltage across the resistor to the current flowing through the resistor. The problem with this approach is that it only approximates the impedance across the PZT and can therefore produce large errors. Therefore, an alternative approach has been proposed that uses calibrated resistors whose resistance values ​​have high precision, allowing for more accurate impedance measurements. This requires measuring the voltage across the PZT and the voltage across the calibrated resistor. However, to avoid the use of expensive differential probes, the voltage across the PZT is measured indirectly by subtracting the voltage across the calibrated resistor from the input voltage signal of a frequency generator (alternating current (AC) source). In addition, to avoid actually measuring the phase angle, an FFT-based approach is used, where the input and signal on the calibrated resistor are FFTed to obtain estimates of the amplitude and phase of the impedance across the PZT. The impedance spectrum obtained using this system can be compared to a reference spectrum to detect changes that indicate damage or cracks. Another variation suggests that the source AC signal is a linear frequency modulated signal. Yet another variation measures the RMS current in the resistor as well as the average power consumed by the PZT. Although the average power depends on the phase angle, the phase angle does not need to be measured directly. Instead, a precision high-speed analog multiplier is used to obtain the power as a function of time, and this signal is then fed to a low-pass filter that provides a direct current (DC) value representing the average power. The RMS current is obtained by measuring the shunt voltage across the resistor and, using the known voltage across the resistor, converting it to a DC value using an RMS-DC converter. From these measurements, a microcontroller can be used to determine the resistance, which is the ratio of the average power to the square of the RMS current. This process is repeated for multiple frequencies. However, none of these proposed methods have achieved much commercial success and have not been widely adopted. This may be due to a lack of robustness or due to limitations such as the need to perform sequential or dedicated measurements on each PZT, which prevents large-scale deployment or scaling up, and the large size and high cost of the equipment, which prevents data from a large number of sensors being read simultaneously.

[0006] Another approach proposes the detection of Lamb waves (or Rayleigh-Lamb waves, i.e. elastic waves propagating on the surface of a structure) using two PZTs, with the first PZT acting as an actuator (stimulus source) and the second PZT acting as a sensor (receiver). A stimulus signal transmission device transmits a waveform signal to the stimulator PZT to generate an acoustic signal in the substrate on which it is mounted. Then, a second PZT at a certain distance from the stimulator PZT is used as a receiver. The two outputs of the receiver PZT are provided to a differential amplifier, which generates an amplified version of the signal on the PZT. A second amplifier stage with controllable gain is used to generate a signal in the range of 0 to 3V, which is provided to an ADC to measure the signal strength. This process can be repeated for multiple receivers at different locations and multiple frequencies. A program on a computer can then analyze the digitized signal to detect changes in the structure. The device can also be used to perform electrochemical impedance spectroscopy to obtain the impedance as a function of frequency, and the observed spectral curve can be compared with a reference curve. However, the limitation of this system is that by using Lamb wave-based measurements, it is only suitable for monitoring surface conditions and is not very reliable for detecting internal cracks and damage. Moreover, reading data from multiple sensors using this method is very complex and requires extensive data analysis.

[0007] To date, there are few commercially available systems for structural health monitoring, and existing systems are often expensive, require complex equipment, or are subject to other application limitations (e.g., specific structures). Although PZT-based systems have great potential, prior art systems remain expensive and are currently not applicable to many practical structures, such as bridges, which are often large, contain many components or parts, and are often subject to a complex range of forces. Therefore, there is a need to provide improved structural health monitoring systems and circuits suitable for large-scale deployment, or at least to provide useful alternatives to existing structural health monitoring systems. Summary of the invention

[0008] According to a first aspect, there is provided an impedance measurement circuit, comprising: a buffer for receiving an AC sweep signal from a sweep signal generator and providing the buffered sweep signal to an input of the piezoelectric sensor; a current-to-voltage converter connected in parallel with a feedback resistor and configured such that the current-to-voltage converter and the feedback resistor receive a piezoelectric output signal from the piezoelectric sensor and generate a piezoelectric current signal in which an AC voltage is proportional to both a phase angle and a current flowing through the piezoelectric sensor; a phase comparison circuit receiving the buffered scanning signal on a first input and the piezoelectric current signal on a second input and configured to compare the piezoelectric current signal with the buffered scanning signal to generate an output piezoelectric phase signal having a DC voltage proportional to a phase difference between the buffered scanning signal and the piezoelectric current signal; A rectifier circuit receives the piezoelectric current signal at a first input and is configured to generate an output piezoelectric current signal having a DC voltage proportional to a current flowing through the piezoelectric sensor.

[0009] In one form, the phase comparison circuit comprises: a digital phase detector receiving the buffered scan signal on a first input and the piezoelectric current signal from the current-to-voltage converter on a second input, and for comparing the piezoelectric current signal with the buffered scan signal to generate a first piezoelectric phase signal; and a first low pass filter for receiving the first piezoelectric phase signal and generating an output piezoelectric phase signal having a DC voltage proportional to a phase difference between the buffered scanning signal and the piezoelectric current signal; The rectifier circuit comprises: a rectifier for receiving the piezoelectric current signal on a first input and rectifying the piezoelectric current signal to generate a first piezoelectric current signal; and A second low-pass filter is used to receive the first piezoelectric current signal and generate an output piezoelectric current signal having a DC voltage proportional to the current flowing through the piezoelectric sensor.

[0010] In one form, the AC sweep signal has a frequency in the range of 5 kHz to 1 MHz, and components of the circuit are configured to operate within 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 with a voltage range of 0 to 5 V. In one embodiment, a 4.2 V phase signal represents a 90 degree phase shift.

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

[0013] According to a second aspect, a multi-sensor impedance measurement circuit module is provided, comprising: a scanning signal input connector for receiving an input AC scanning signal, or a scanning signal generator circuit for generating an AC scanning signal; a voltage converter circuit for generating a plurality of regulated supply voltages from an input power connector or a power supply circuit; a plurality of impedance measurement circuit modules according to the first aspect, wherein a scan signal input is provided as an input to each impedance measurement circuit; a plurality of pairs of input connectors for connecting to inputs and outputs of the piezoelectric sensor, wherein each pair of input connectors is connected to one impedance measurement circuit module among the plurality of impedance measurement circuit modules; and A plurality of pairs of output connectors, each pair connected to the output of one of the impedance measurement circuit modules, wherein the paired outputs include an output piezoelectric phase signal and an output piezoelectric current signal from the corresponding impedance measurement circuit module.

[0014] In one form, the voltage conversion circuit is used to generate regulated +5V, -5V and +3V supply voltages.

[0015] In another form, the impedance measurement circuit further comprises a compact unitary housing housing a circuit board comprising a plurality of surface mount components that implement one or more components of the multi-sensor impedance measurement circuit module. In a further form, the circuit board has a first dimension of 38 mm or less and a second dimension of 55 mm or less.

[0016] According to a third aspect, a structural health monitoring circuit module for a structural health monitoring system is provided. In one form, the structural health monitoring circuit comprises: One or more multi-sensor impedance measurement circuit modules according to the second aspect, wherein the one or more multi-sensor impedance measurement circuit modules include a power supply circuit and a scanning signal generator, wherein the power supply circuit includes a voltage regulator, the voltage regulator is used to receive an unregulated supply voltage in the range of 9V to 18V (nominal 12V) and regulated +5V, -5V and +3V supply voltages; and a user interface, at least one processor, and at least one memory, wherein 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, the processor being configured to configure the structural health monitoring circuit module, including configuring the scanning signal generator circuit, wherein the one or more user input signals are received using an input device and / or from a remote device. In an alternative form, the structural health monitoring circuit is adapted to be connected to one or more multi-sensor impedance measurement circuit modules according to the second aspect, wherein the one or more multi-sensor impedance measurement circuit modules include an input power connector and a scanning signal input connector, and the structural health monitoring circuit modules include: A power supply circuit including a voltage regulator for receiving an unregulated supply voltage in the range of 9V to 18V (nominal 12V) and regulated supply voltages of +5V, -5V and +3V; a power output connector for providing an unregulated power supply voltage to the input power connector of the one or more multi-sensor impedance measurement circuit modules via a wired connector; A scanning signal generator circuit for generating an AC scanning signal; and a scanning signal output connector, for providing an AC scanning signal to the scanning signal input connector of one or more multi-sensor impedance measurement circuit modules through a wired connector; and a user interface, at least one processor, and at least one memory, wherein 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, the processor being configured to configure the structural health monitoring circuit module, including configuring the scanning signal generator circuit, wherein the one or more user input signals are received using an input device and / or a remote device. In some embodiments, the user interface may be a touch screen.

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

[0018] In one form, the RMS voltage (nominal value) of the AC scanning signal is 200mV or less. In one form, the scanning signal generator circuit may also generate a trigger signal.

[0019] In one form, the structural health monitoring module further comprises: an analog-to-digital conversion circuit for converting 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 digitized phase signal and a digitized current signal, wherein the one or more processors are used to analyze the digital representation and estimate a real impedance as a function of frequency for each sensor, generate a monitoring report and store it in the at least one memory; and A communication module is used to allow the stored monitoring reports to be sent or downloaded.

[0020] In one form, the at least one memory is used to store a recipient address and one or more alarm triggering conditions for generating an alarm, the one or more processors are used to analyze the digitized phase signal and the digitized current signal of each of the one or more multi-sensor impedance measurement circuit modules to determine whether one or more of the one or more alarm triggering conditions are met, and the communication module is a wireless communication module, which is used to send a monitoring report to a recipient address and / or send an alarm to a recipient when one or more of the one or more alarm triggering 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 form, one or more user input signals are received from the remote device via the communication module, or one or more user input signals are received from the user interface, and the one or more user input signals include one or more of the frequency range, signal level, one or more monitoring parameters, one or more alarm trigger conditions and / or one or more recipient addresses of the scanning signal generator circuit. In one form, the input device includes a touch screen and is configured to allow a user to input one or more frequency ranges, signal levels and one or more monitoring parameters (e.g., scanning rate) of the scanning signal generator circuit. The user interface can also allow the user to input or configure one or more alarm trigger conditions and / or one or more recipient addresses. In one form, one or more monitoring parameters configure the microprocessor to monitor a predefined group of one or more impedance measurement circuits. In some embodiments, each group includes two or more impedance measurement circuits located on a portion of the structure to be monitored. In some embodiments, each impedance measurement circuit in the group is adjacent (or close) to each other to achieve cross-sectional or spatial monitoring of the structure.

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

[0023] According to a fourth aspect, there is provided a structural health monitoring system, comprising: The structural health monitoring circuit module according to the third aspect; One or more multi-sensor impedance measurement circuit modules according to the second aspect; 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 used 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 digitized phase signal and a digitized current signal, the at least one processor is used to analyze the digital representation to estimate the real impedance of each sensor as a function of frequency, generate a monitoring report and store it in the at least one memory, and the communication module is used to allow the stored monitoring report to be sent or downloaded.

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

[0025] In one form, one or more user input signals are received from a remote device via a communication module or from a user interface, and the one or more user input signals include one or more of a frequency range of a scanning signal generator circuit, a signal level, one or more monitoring parameters, one or more alarm trigger conditions, and / or one or more recipient addresses. In another form, 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 circuits.

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

[0027] According to a fifth aspect, there is provided a method for measuring impedance of a piezoelectric sensor, comprising: buffering an AC sweep signal received from a sweep signal 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 which an AC voltage is proportional to both a phase angle and a current flowing through the piezoelectric sensor, the current-to-voltage converter being connected in parallel with a feedback resistor and configured so that the current-to-voltage converter and the feedback resistor receive a piezoelectric output signal from the piezoelectric sensor; generating an output piezoelectric phase signal having a DC voltage proportional to a phase difference between the buffered scan signal and the piezoelectric current signal using a phase comparison circuit, the phase comparison circuit receiving the buffered scan signal on a first input and the piezoelectric current signal on a second input and being configured to compare the piezoelectric current signal with the buffered scan signal; and An output piezoelectric current signal having a DC voltage proportional to the current flowing through the piezoelectric sensor is generated using a rectifier circuit that receives the piezoelectric current signal on a first input.

[0028] In one form, the method further comprises: digitizing the output piezoelectric phase signal to obtain a digitized phase signal θ, digitizing the output piezoelectric current signal to obtain a digitized current signal I, and estimating the real impedance, Z real =Vcos(θ) / I, where V is a predetermined constant obtained from calibration measurements, which include measuring the input voltage across the corresponding piezoelectric sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Embodiments of the present invention will be discussed with reference to the accompanying drawings, in which:

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

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

[0032] Figure 2 is a schematic diagram of a modular distributed structural health monitoring system according to one embodiment;

[0033] Figure 3A is a wiring diagram of a structural health monitoring system including a scanning signal generator and a first multi-sensor module according to one embodiment;

[0034] Figure 3B yes Figure 3A A circuit diagram of a first part of a first impedance measurement module of a first multi-sensor module;

[0035] Figure 3C yes Figure 3AA circuit diagram of a first portion of a second impedance measurement module of a first multi-sensor module;

[0036] Figure 3D yes Figure 3A A circuit diagram of a first part of a third impedance measurement module of a first multi-sensor module;

[0037] Figure 3E yes Figure 3A A circuit diagram of a first part of a fourth impedance measurement module of a first multi-sensor module;

[0038] Figure 3F yes Figure 3A A circuit diagram of a second portion of the first and second impedance measurement modules of the first multi-sensor module;

[0039] Figure 3G yes Figure 3A A circuit diagram of a second portion of a third and fourth impedance measurement module of a first multi-sensor module;

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

[0041] Figure 4A is a graph of real impedance of a piezoelectric sensor embedded in a first location in a mortar joint over a range of loads, the real impedance being a function of frequency, generated by a structural health monitoring system according to one embodiment;

[0042] Figure 4B is a graph of real impedance versus frequency for a second piezoelectric sensor embedded in a second location in a mortar joint under a range of loads, the real impedance being a function of frequency, generated by a structural health monitoring system according to one embodiment;

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

[0044] Figure 5B According to one embodiment, Figure 5A Bar graph showing the variation of damage index with increasing load for five piezoelectric sensors located on the surface of wall tiles;

[0045] Figure 5C According to one embodiment, Figure 5A Bar graph showing the variation of damage index with increasing load for five piezoelectric sensors embedded in mortar joints in a wall;

[0046] Figure 5D According to one embodiment, Figure 5A Bar graph showing the variation of damage index with increasing load for five piezoelectric sensors located on the surface of wall mortar joints;

[0047] Figure 6 Graphs of real impedance as a function of frequency for two piezoelectric sensors located on a steel plate with bolts loosely screwed into a steel beam through the steel plate in the first graph and tightly screwed into the steel beam through the steel plate in the second graph generated by a structural health monitoring system according to one embodiment.

[0048] In the following description, the same reference numerals throughout the drawings denote the same or corresponding parts. DETAILED DESCRIPTION

[0049] Reference now Figure 1A , shows a structural health monitoring system 1 according to an embodiment. The system includes a sweep signal generator 110, which generates an alternating current (AC) sweep signal 112 and a sweep trigger signal 114. The sweep signal is an AC signal of a specific sweep frequency, which is simultaneously provided to a plurality of (N) impedance measurement circuit modules 120. Each impedance measurement circuit module 120 is connected to a piezoelectric sensor (also called a piezoelectric transducer or PZT) 122, which is placed on or embedded in the structure to be monitored (each PZT is located at a different location). In some embodiments, the system may include a single impedance measurement circuit module 120, but in most typical structural monitoring applications, the structure will be monitored at multiple locations by multiple impedance measurement circuit modules 120 and associated PZTs, each PZT being located at a different location on the structure. The sweep signal 112 is applied as an input to each impedance measurement circuit module 120 and the associated PZT 122, and produces two output measurement results, wherein the first output is a phase signal 136 and the second output is a current signal 139. Phase signal 136 is a direct current (DC) signal whose voltage is proportional to or represents the phase difference across the PZT, while current signal 139 is a DC signal whose voltage is proportional to or represents the current across the PZT.

[0050] like Figure 1AAs shown, the scanning signal 112 is simultaneously provided to N impedance measurement modules (120a, 120b, ..., 120n), and the N impedance measurement modules generate N phase signals (136a, 136b, ..., 136n) and N current signals (139a, 139b, ..., 139n), and the N current signals are provided as inputs to a data acquisition system (DAQ) 150. The DAQ includes one or more analog-to-digital converter (ADC) circuits 152, which are used to convert each phase signal 136 and current signal 139 associated with a particular PZT into a digital representation, which is then analyzed by a processor 154 and a memory 156, which are used to generate a scanning frequency (Zreal f ) is an estimate of the real part of the (complex) impedance across the PZT. Figure 1A As shown, the DAQ may include N ADC circuits (152a, 152b, ..., 152n), i.e., each impedance measurement module and PZT has a dedicated ADC (e.g., 1:1 relationship) for generating N estimates of the real part of the (complex) impedance across each of the N PZTs (159a, 159b, ..., 159n). However, it should be understood that in other embodiments, other ADC circuit configurations may be used, such as using digital multiplexing to achieve digitization of all N phase signals 136 and current signals 139. The analysis performed by the DAQ can be used to generate monitoring reports and / or issue alerts to recipients. In some embodiments, the DAQ may include a wireless communication module.

[0051] The scanning signal generator is used to generate multiple scanning signals within a scanning frequency range, such as from 5kHz to 1MHz or higher, each scanning signal corresponding to a different frequency (f). At each scanning frequency, the scanning signal is simultaneously provided to each impedance measurement module 120 and the associated PZT 122, and the output phase 136 and current 139 are used to generate the scanning frequency Zreal f ) is an estimate of the real part of the impedance in the PZT 159 at . By generating multiple sweep signals (each sweep signal corresponds to a different frequency) within the sweep frequency range, an impedance spectrum can be generated, such as Figure 1A As shown, the impedance spectrum is a graph of real impedance varying with (sweeping) frequency 153 , where real impedance is a function of (sweeping) frequency 153 .

[0052] In this embodiment, the sweep signal generator 110 also provides a sweep trigger signal 114 to the DAQ 150, and the sweep trigger signal 114 is used to trigger the processing of the received signal, such as triggering the ADC 152 to digitize the received phase signal 136 and current signal 139. The sweep signal generator generates multiple sweep signals within the sweep frequency range, each sweep signal corresponding to a different frequency. The sweep trigger can generate a trigger signal at the beginning of each different sweep signal (e.g., frequency) within the sweep frequency range. In other embodiments, the sweep frequency generator can be used to sweep across the entire sweep frequency range according to a predetermined sampling pattern, which is also known (e.g., stored) by the DAQ, so that only a single sweep trigger signal is generated at the beginning of the sweep (or sweep pattern). The predetermined pattern can be a predetermined interval at a predetermined sampling frequency, for example, at a sampling frequency of 1 kHz (i.e., one sampling interval every millisecond), starting from the start frequency in increments of 1 kHz, 5 kHz, or 10 kHz until the stop frequency is reached. In other embodiments, the predetermined pattern can be a set of predefined frequencies between the start frequency and the stop frequency, where each frequency changes according to the sampling frequency. The scan trigger signal 114 is a signal used by the data acquisition system (DAQ) 150 to trigger the processing of the received signal. Figure 2 In other embodiments shown, digitization of the received phase signal 136 and current signal 139 is performed by one or more ADC circuits co-located with or operably connected to the swept frequency signal generator, and the trigger signal is used to trigger the ADC circuit. Alternatively, the ADC circuit can monitor its input and generate a digitized signal when the input signal is detected, thereby eliminating the need for the trigger signal 114, or the microprocessor can control the swept frequency signal generator and the ADC circuit, thereby eliminating the need for a sweep trigger signal. That is, depending on the specific circumstances of the implementation, the sweep trigger signal is optional.

[0053] Figure 1BA schematic diagram of an embodiment of an impedance measurement circuit module 120 is shown, which includes a buffer 121, a current-to-voltage converter module 124, a phase comparison circuit 130, and a rectifier circuit 134. The buffer 121 is used to receive the AC sweep signal 112 from the sweep signal generator 110 and provide the buffered sweep signal to the input of the piezoelectric sensor / transducer PZT 122. The current-to-voltage converter module 124 is located at the output side of the PZT 122, includes a current-to-voltage converter 126 connected in parallel with a feedback resistor 125, and is configured so that the current-to-voltage converter 126 and the feedback resistor 122 receive the piezoelectric output signal from the PZT 122 and generate a piezoelectric current signal in which the AC voltage is proportional to both the phase angle and the current flowing through the piezoelectric sensor 127. The piezoelectric current signal can also be called a piezoelectric voltage signal because it is the output of the current-to-voltage converter. However, in the following discussion, the piezoelectric current signal will be used herein because its voltage is proportional to the current generated by the piezoelectric sensor. In one embodiment, the output signal of PZT 122 (or the signal on PZT) is provided to the negative input of current-to-voltage (IV) converter 126, and the output of IV converter 126 is adjusted to a voltage that maintains equal but opposite currents through feedback resistor 125 to balance the PZT current. Phase comparison circuit 130 receives buffered scanning signal 123 at a first input terminal and piezoelectric current signal 127 at a second input terminal, and is used to compare the piezoelectric current signal with the buffered scanning signal to generate an output piezoelectric phase signal 134, which has a DC voltage proportional to the phase difference between the buffered scanning signal and the piezoelectric current signal. The rectifier circuit receives the piezoelectric current signal 127 at a first input and is used to generate an output piezoelectric phase signal 139, which has a DC voltage proportional to the current flowing through PZT 122.

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

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

[0056] A buffer (or buffer amplifier) ​​121 is used at the input to isolate each impedance measurement circuit 120 from the other impedance measurement circuits and to ensure that all PZTs (and impedance measurement circuits) receive the sampled amplitude sweep signal without interfering with each other. This enables all N impedance measurement circuits 120 in the system 100 to be operated (stimulated) simultaneously by a 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 because the limiting factor is the time required to sweep the entire sweep frequency range. As described above, the sampling frequency may be on the order of 1 kHz (i.e., one sample per millisecond), allowing the entire structure to be monitored over the frequency range in about 1 second or less (depending on the number of separate sweep frequencies generated).

[0057] Figure 2is a schematic diagram of a modular distributed structural health monitoring system 200 according to one embodiment. In this embodiment, the system 200 includes a structural health monitoring 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 sending reports or alerts to a user computing device 270.

[0058] The structural health monitoring system 200 may be provided as a single integrated module in a single housing, including the structural health monitoring circuit module 210 and the DAQ 250, or the system may be composed of multiple modules, each of which is located in its own housing and connected by a wired or wireless link. That is, in some embodiments, the structural health monitoring circuit module 210 is disposed in a first housing and the DAQ 250 is disposed in a second housing (i.e., two separate physical modules), and the two modules / housings are connected by one or more cables that provide the output phase signal 134 and the current signal 139 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 that includes one or more multi-sensor impedance measurement circuit modules 220, such as the impedance measurement circuit module 120. Figure 1BAs shown. The structural health monitoring circuit module 210 also includes a sweep signal generator 230 and a power supply circuit 240. The structural health monitoring circuit module 210 may also include a processor device, which includes a CPU 212 and a memory 214, such as a microprocessor unit (MPU) or a microcontroller, and a user interface 254, which is used to receive user input signals to configure the structural health monitoring circuit module 210, including configuring the sweep signal generator circuit 210. The structural health monitoring circuit module 210 is connected to a data acquisition module (DAQ) 250, which includes an ADC 256, which receives the output phase signal 136 and the current signal 139 from the impedance measurement circuit module 220 through a cable 222 and digitizes the input signals. The DAQ 250 also includes a processor device, which includes a CPU 252 and a memory 254, such as a microprocessor unit (MPU) or a microcontroller. The microprocessor may include onboard memory (e.g., RAM 254) and / or it may be connected to additional memory, including removable memory 258, such as an SD card for storing programs and / or storing data. The trigger signal 114 is provided to the processor device (e.g., CPU 252) via the cable 224 to trigger the ADC 256 to digitize the output signal of the impedance measurement circuit module 220. The digitized signal is stored in the memory 254 and may be written to a data file in the removable memory 258 along with additional data (e.g., timestamp, metadata related to the measurement such as the configuration of the swept signal generator and the configuration of the ADC). The removable memory 258 may also be used to store software modules for generating data files, such as formatting of files, capturing of date, time, and configuration parameters of the structural health monitoring circuit 210 (e.g., frequency range) and configuration parameters of the ADC 256 (sampling rate, etc.). A communication module 260 is also provided to send data to a user computing device 270 for further analysis and display. In some embodiments, the communication module is a wireless communication module. The user computing device 270 is used 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 a memory 274, and a computer for displaying the results (e.g., Z realThe system 200 may include a display device 276 for displaying a graph of the relationship between the structural health monitoring circuit module 210 and the frequency, and a communication interface 278 for receiving data from the DAQ 250. The two corresponding communication interfaces 260 and 278 may 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 that includes the structural health monitoring circuit module 210, the DAQ 250, and the user computing device 270. The user computing device 270 may be a general-purpose computing device, such as a mobile phone, tablet computer, laptop computer, or desktop computer, which runs software to analyze and / or display data received from the DAQ 250. In the case of an integrated system (e.g., a combined structural health monitoring circuit module 210 and DAQ 250), a single microprocessor may be used to provide processing and storage for both the structural health monitoring module 210 and the DAQ 250. That is, the DAQ CPU 252 and the memory 254 may be provided by the CPU 212 and the memory 214 of the structural health monitoring module. Multiple microprocessors can also be used in the structural health monitoring module and DAQ to control different functions (ADC control, user interface, data storage, data transmission).

[0059] The multi-sensor impedance measurement circuit modules 220 may be disposed in separate housings and wired to the central housing, or they may be integrated with the other components of the structural health monitoring circuit module 210 in a single housing (an integrated module). Figure 2 2 shows an embodiment in which a multi-sensor impedance measurement circuit module 220 is integrated in a single housing. Figure 3A is a wiring diagram illustrating a distributed embodiment where a central housing houses the central components and makes wire connections to a single multi-sensor impedance measurement circuit module 220 in a separate housing. Figure 3H2 is a wiring diagram showing a distributed embodiment, wherein a central housing houses a central component and is wired to two individual multi-sensor impedance measurement circuit modules 220, each of which is located in a separate housing and connected by 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 scanning signal generator 230. In another embodiment, the structural health monitoring circuit module 210 is used to connect to one or more multi-sensor impedance measurement circuit modules 220. In this embodiment, one or more multi-sensor impedance measurement circuit modules include an input power connector and a scanning signal input connector, the structural health monitoring circuit module provides a power supply circuit 240 and a power output connector for providing a power supply voltage to the input power connector of one or more multi-sensor impedance measurement circuit modules through a wired connector, and the scanning signal generator 230 and the scanning signal output connector are used to provide an AC scanning signal to the scanning signal input connector of one or more multi-sensor impedance measurement circuit modules 220 through a wired connector. The structural health monitoring circuit module 210 may also include a user interface 216 and a microprocessor including a CPU 212 and a memory 214. The microprocessor may be integrated into or connected to a user interface 216. The user interface 216 is used to receive one or more user input signals, which are provided to the microprocessor for configuring the structural health monitoring circuit module, including configuring the scanning signal generator circuit, wherein one or more user input signals are received using an input device and / or a remote device. The user interface 216 may be a touch screen device or a plurality of buttons and a digital display screen, which is used to allow a user to access a menu and select a value (e.g., a frequency interval) to configure the device.

[0060] The power supply circuit 240 includes a voltage regulator that is used to receive an unregulated supply voltage in the range of 9V to 18V (nominal value is 12V) and regulated +5V, +3V and -5V supply voltages. The unregulated power supply 342 can be a battery, such as a lithium battery, but other battery technologies can also be used, including using solar panels to provide power or recharge the battery. A compact 12V lithium battery (e.g., 80mm×30mm-15mm) weighs 110 grams and can provide enough power for 24 hours of monitoring. The charging time can be extended by using a larger battery or solar panel. In some embodiments, the main power supply (if available) can be used. In other embodiments, the power supply circuit 240 can be used to accept a wider / larger input range, such as 5V to 18V, or 5 to 24V, 9 to 24V, or more than 24V.

[0061] Figure 3AAn embodiment of the circuit is shown in which a rectifier diode IN4007 is located downstream of an unregulated power supply 342 connector 342, which in this embodiment has a voltage between 9V and 18V and provides a nominal 12V signal that is provided via wires to a multi-sensor impedance measurement circuit module 320. The LM1084 linear voltage regulator accepts a nominal 12V input and outputs +5V, +3V, and -5V signals that are provided to a scan signal generator circuit 310 that is used to generate an AC scan signal and a trigger signal. The scan signal generator circuit 310 includes a scan signal output connector 355 that is used to provide an AC scan signal to the multi-sensor impedance measurement circuit module 320 (or a trigger signal) via a wired connector. Figure 3HEach of the multiple modules shown). A user interface 216 (e.g., a touch screen and / or input buttons) may also be provided to allow a user to input one or more frequency ranges and one or more monitoring parameters (e.g., scanning rate and signal level) for the scanning signal generator circuit. The user interface may also allow a user to input (or configure) one or more alarm trigger conditions and one or more recipient addresses. In some embodiments, the user interface is used 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 communication module or interface that provides a wired or wireless interface with a communication interface 260 in the DAQ. In some embodiments, the communication module 260 is used to communicate with a remote computing device 270 to allow remote configuration of the system (e.g., input these inputs / parameters). A combination of the two may be used to allow local and remote configuration of the structural health monitoring circuit module 210. A microprocessor (e.g., CPU 212, RAM 214) is used to receive user input signals for configuring the structural health monitoring circuit module (including configuring the scanning signal generator circuit 230). In one embodiment, the user input signal includes one or more of a frequency range of the sweep signal generator circuit, a signal level, one or more monitoring parameters, one or more alarm trigger conditions, and / or one or more recipient addresses. In embodiments where a remote device 270 is used (e.g., the user interface is a remote user interface), the remote device may also include a local user interface to allow a user to enter configuration parameters on the remote computing device 270, which then sends the input signals (or commands based on these input signals) to the structural health monitoring circuit module 210 (via the DAQ 250) and processes or implements them to configure the structural health monitoring circuit module 210. The user interface 216 or DAQ CPU 252 may also be used to send alarms and results to the remote computing device 270, which may be displayed by a local user interface (e.g., a display 276 on the remote computing device 270). In some embodiments, the user interface 212 is used to receive user input commands to configure monitoring of one or more predefined groups, each predefined group including one or more impedance measurement circuits. In some embodiments, each group includes two or more impedance measurement circuits located on a portion of the structure to be monitored. In some embodiments, each impedance measurement circuit in the group is adjacent (or close) to each other to enable cross-sectional or spatial monitoring of the structure, that is, to form a cluster of impedance measurement circuits / sensors. That is, monitoring can be based on a selected plurality of individual sensors (groups of 1), or based on groups of sensors or clusters of sensors. The group can be configured using a user interface 216 (locally or remotely). The user interface can also be used to allow monitoring planning.For example, certain groups may be monitored more frequently than other groups (or all sensors).The user interface 216 may provide information to the DAQ, which stores and implements the monitoring configuration via the removable memory 258 of the DAQ 250.

[0062] The sweep signal generator in this embodiment is a compact circuit with dimensions of 85mm×50mm×10mm and a weight of less than 60 grams. The sweep signal generator is used to generate an AC sweep signal with a frequency range of 5kHz to 1MHz and a nominal RMS voltage of 200mV or less. With a touch screen user interface 216, the dimensions are 85mm×50mm×30mm and the weight is 150 grams. An integrated sweep signal generator and touch screen module are provided, and all adjustments required for monitoring a given structure can be easily applied, such as adjusting the operating sweep frequency, the strength / voltage of the signal, the sweep rate, etc. A memory 214 is provided to store the last settings displayed on the screen once the device is restarted. This can implement a sleep mode, making it more energy-efficient, and the monitoring will not be affected by power interruptions. In addition, the integrated sweep signal generator and touch screen module includes a microprocessor unit that can program the operation of the sweep signal generator. In one embodiment, the program provides a sweep of 1000 frequency steps per second. The program can be targeted and accommodate new functions according to needs.

[0063] In one embodiment, the DAQ 250 also includes a communication module 260 that is used to transmit data to a remote unit 270 (or a communication interface 278 in the remote unit). The data includes a representation of the output piezoelectric phase signal 136 and the output piezoelectric current signal 139 associated with each PZT 122. The communication module can be a wired module, such as using a wired, Ethernet, or fiber optic link, or a wireless communication module that implements one or more wireless communication protocols, such as Bluetooth, Wi-Fi, or 4G / 5G cellular protocols. The communication module can be used to send data files and alarms to an email address, and can use an email SMS gateway to send SMS alarms. The data can be sent to a user computing device 270 such as a PC, mobile phone, tablet, or to a cloud server that stores data and provides a monitoring interface for multiple users. The communication module 260 can also be used to receive configuration commands to configure the structural health monitoring module 210, including the sweep signal generator, report format, frequency, and alarm trigger conditions. The microprocessor 252 and the memories 254, 258 may be used to configure the operation of the structural health monitoring module 210 and support user-defined activation of user-defined sensors in the overall monitoring system, user-defined pre-programmed and pre-planned monitoring, and user-defined and pre-planned cross-sectional or spatial monitoring of the structure. The wireless sensors may be programmed to enter a sleep mode to reduce power consumption and data traffic and enable a cost-effective monitoring solution. Remote control and interrogation may be enabled using the wireless communication module, including requesting on-demand sensing and results. The sensors may periodically send aggregated data to a cloud server, enabling continuous automatic monitoring and display of data.

[0064] In one embodiment, the communication module 260 in the DAQ 250 is a wireless communication module. The analog-to-digital converter (ADC) circuit 256 in the DAQ is used to convert each output piezoelectric phase signal and each output piezoelectric current signal into a digital representation, each of which is provided to the wireless communication module 260 for transmission to a user-defined destination, such as an email address or a server. The DAQ 250 includes a processor 252 and a memory 254, both of which can be provided on a microprocessor board (e.g., an MPU), for estimating the real impedance as a function of frequency, which can then be displayed on a user device (e.g., a display 276 of a user computing device 270), or a report or alarm is generated to the user when an alarm trigger condition is met (e.g., indicating that a crack or damage occurs in the structure and / or material). In some embodiments, the DAQ module 250 includes a removable memory 258 (e.g., an SD card) for storing the digital representation of each output piezoelectric phase signal and each output piezoelectric current signal. It can then be stored as a file that can be sent to the user computing device 270. The removable memory can also be used as a backup storage of the measurement results so that they can be downloaded or transmitted to the user computing device 270 later by the communication module 260. The communication module can transmit the data to the remote computing device 270 via a direct wired or wireless link, or it can also use an intermediate device to transmit the data. For example, the communication module can establish a wireless link to an access point and then send the data to the user computing device via a network such as the Internet. In some embodiments, the memory is used to store the last N measurement results, where N is an amount based on the available storage capacity (e.g., a rolling window) or a predefined amount corresponding to a time window. That is, a fixed amount of storage space is allocated to store the measurement results, and when the allocated storage space is full, the oldest record will be overwritten to provide space for recording new measurement results.

[0065] In some embodiments, the structural health monitoring module, integrated with the DAQ, includes an analog-to-digital converter circuit 254 to provide data acquisition system functions, and can also be used to analyze data and generate alarms and reports. In this embodiment, the analog-to-digital converter circuit 256 is used to convert each output piezoelectric phase signal and each output piezoelectric current signal into a digital representation, and the microprocessor 252 is used to analyze the digital representation and estimate the real impedance of each sensor as a function of frequency, and use the wireless communication module 260 to send monitoring reports and / or alarms to the recipient. The memory 212 and / or 254 (if any) can be used to store the recipient address, the report format, and one or more alarm trigger conditions for generating an alarm. The user interface 216 (such as a touch screen, screen and buttons or other interface) allows the user to enter one or more frequency ranges of the scanning signal generator circuit, one or more monitoring parameters, one or more alarm trigger conditions, and one or more recipient addresses. As described above, the DAQ 250 may include a removable memory, such as an SD card, which can also be used to store the digital representation of each output piezoelectric phase signal and each output piezoelectric current signal to either allow removal and transfer to the user computing device 270, or as a backup storage. In some embodiments, a software application running on the user computing device 270 may be used to remotely configure the structural health monitoring module 210 and the DAQ 250 module via the communication module 260 .

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

[0067] In another embodiment, one or more multi-sensor impedance measurement circuit modules 220 are arranged as distributed front-end deployment modules, each module is arranged in a compact weatherproof housing that can be located near or on the structure to be monitored and locally connected to the PZT located on or embedded in the structure. These front-end deployed multi-sensor impedance measurement circuit modules 220 can be wired back to a central module of the structural health monitoring module 210, which includes a swept frequency signal generator 230 and a power supply 240, which is either integrated with or connected to the DAQ 250.

[0068] Figure 3AAlso shown is a wiring diagram of an embodiment of a multi-sensor impedance measurement circuit module 320 including four impedance measurement circuit modules. In one embodiment, the multi-sensor impedance measurement circuit module 320 includes a scan signal input connector 312 for receiving an input AC scan signal 355 and a voltage converter circuit for generating a plurality of regulated supply voltages from an input power connector 344. In one embodiment, a nominal 12V input voltage is supplied and the voltage converter circuit is used to generate regulated +5V, -5V, and +3V supply voltages.

[0069] A sweep signal input 312 is provided as an input to each impedance measurement circuit. Multiple sets of paired input connectors 321 are used to connect the input and output of the piezoelectric sensor 322, and each paired input connector is connected to one of the (multiple) impedance measurement circuit modules. Multiple sets of paired output connectors 329 are also provided, each connected to the output of one impedance measurement circuit module. The paired outputs 329 include the output piezoelectric phase signal 136 and the output piezoelectric current signal 139 from the corresponding impedance measurement circuit module 120. They can be directly connected to the data acquisition system 351, or connected back to the central module of the structural health monitoring module 210, which is connected to or includes the DAQ 250. The microprocessor in the DAQ 250 can be used to generate a monitoring report or alarm, which can be sent to the user computing device 270 via the communication module 260 (for example, via the wireless link 262).

[0070] Notably, the PZTs 222, 322 are not contained within the housing of the multi-sensor impedance measurement circuit module 220, but the housing provides connectors so that wires can be extended to the PZTs placed on or embedded in the structure to be monitored.

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

[0072] by Figure 3B For example, this is Figure 1AA more detailed circuit diagram of the illustrated embodiment shows the main components as well as additional components (e.g., capacitors, resistors, and diodes) used to filter, pull up, or pull down the signal / input. The scan signal 312 is provided to the buffer 312a (LTI 362) as an input. The scan signal 312a is also split into Figures 3C to 3E Buffers 312b, 312c, 312d in the second, third and fourth circuits.

[0073] The current-to-voltage converter 326a (LTI1252) is connected in parallel with the feedback resistor 470Ω, which is configured so that the current-to-voltage converter and the feedback resistor receive the piezoelectric output signal from the piezoelectric sensor 322a and generate a piezoelectric current signal 328a in which the AC voltage is proportional to both the phase angle and the current flowing through the piezoelectric sensor. The piezoelectric current signal can also be called a piezoelectric voltage signal because it is the output of the current-to-voltage converter. However, in the following discussion, the piezoelectric current signal will be used because its voltage is proportional to the current generated by the piezoelectric sensor. The piezoelectric output signal is provided on the negative input of the LT1252 IV converter, which is adjusted to a voltage that maintains equal but opposite currents flowing through the resistor 325a to balance the PZT current. The output is split, with one branch being directed to a digital phase detector (AD8302) which receives the buffered scan signal 323a on a first input and the piezoelectric current signal 327a from the current-to-voltage converter 326a on a second input and is used to compare the piezoelectric current signal with the buffered scan signal and generate a first piezoelectric phase signal (PH1). The piezoelectric current signal 328a is provided to a precision rectifier 336a which consists of an LT1364 operational amplifier (piezoelectric current signal 328a is provided to the negative input), an MM4148 diode and a resistor arranged to rectify the piezoelectric current signal to generate a first piezoelectric current signal I1 337A. Figures 3C to 3E A similar circuit is shown in .

[0074] Figure 3F An embodiment of a first low pass filter 333a is shown which 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 scanning signal and the piezoelectric current signal. The first low pass filter 333 comprises a 22k resistor (R18) and a 68nF capacitor (C19), has a cut-off frequency of 106Hz, and uses a TLC2272 operational amplifier as a gain stage (with R19 and R20). The second low pass filter 338a is divided into Figure 3A and 3E , Figure 3AThe RC components (22k ​​resistor R37 and 68nF capacitor C33) provide a cutoff frequency of 106Hz. Figure 3E There is an op amp gain stage (TLC2272 and resistors R22 and R23) on top. Figure 3E Equivalent first and second low pass filters 333b 338b of the second circuit are shown. Figure 3F The equivalent first and second low pass filters (333c, 338c, 333d, 338d) of the third and fourth circuits are shown.

[0075] Figure 3E Also shown is a voltage converter circuit 346 which includes a TMR 3-1221 DC / DC converter which takes a nominal 12V supply and generates regulated +5V and -5V supply voltages 347, and a LP2950 voltage regulator 348 which generates a regulated +3V supply voltage 349 from a 5V input.

[0076] The circuits are implemented on a circuit board having 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 can be used, and the circuit can be housed in a weatherproof enclosure.

[0077] In another form, the impedance measurement circuit further comprises a compact, low-profile housing housing a circuit board comprising 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 DAQ 250 analyzes the output piezoelectric phase signal and the output piezoelectric current signal to estimate the real part of the impedance through the PZT. This can be calculated based on the equation Z 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 can be predetermined, such as by measuring during circuit calibration. In one embodiment, the components (and gain) are selected to generate an output DC voltage between 0 and 5V.

[0079] The estimate of the real part of the impedance can be saved with the associated sweep frequency, and these data pairs can be saved for all sweep frequencies within the sweep frequency range and then plotted or analyzed using a suitable graphics or analysis package (e.g., LabVIEW, MATLAB, R, or equivalent software). The data can be saved in a file (e.g., a spreadsheet) in the removable memory 258.

[0080] Figure 4A4 is a graph 400 of the real impedance 402 of a first position piezoelectric sensor 416 embedded in a mortar joint 413 between two bricks 412, 414 as a function of frequency 404 for a range of applied loads 422 starting at 0, 44, 45, 48, and 50 kN. The data was generated by one embodiment of the structural health monitoring system described above. In this embodiment, the impedance increases significantly at loads above 45 kN around 100-125 kHz compared to lower loads where crack initiation 420 is shown. Figure 4B is Figure 4B 400 shows a graph 402 of a second piezoelectric sensor at a second location embedded in a mortar joint between two bricks 412, 414 as a function of frequency 404 at loads of 0, 10, 20, 35, 40, 45 and 50 kN. At higher loads above 40 kN, crack presence 440 is shown around 90 Hz to 110 Hz compared to the lower load signals.

[0081] These graphs show that cracks can be identified by sudden changes (e.g., an increase in impedance at a specific frequency) compared to previously recorded graphs. Therefore, cracks can be detected by setting an alarm when there is a deviation from an average curve or a reference curve. An analysis module in a DAQ or remote computing device can be used to analyze the estimated value of the real part of the impedance within the scanning frequency range to detect structural changes, such as cracks. The analysis may include detecting significant deviations at a specific frequency or over a frequency band within the scanning frequency range. One or more triggering alarm conditions may be stored in a memory and may include one or more predetermined thresholds, wherein an alarm is generated if the real part of the impedance exceeds a predetermined threshold. Other analysis methods and alarm conditions can be developed based on signal analysis of the impedance component within the scanning frequency range, including Fourier-based methods, change detection, and statistical methods for detecting increased deviations compared to historical values. The alarm condition trigger can be determined based on the specific signal analysis method used.

[0082] Figure 5A is a schematic diagram of a brick wall formed of bricks and mortar joints, showing the approximate locations of five piezoelectric sensors (PZT 1 to PZT 5) according to one embodiment. Figure 5B is located in Figure 5A Bar graph showing the variation of damage index with increasing load for five piezoelectric sensors on the brick surface of the wall shown in . Figure 5C is embedded Figure 5A Bar graph of the damage index of five piezoelectric sensors in a wall mortar joint as the load increases. Figure 5D is located in Figure 5ABar graph showing the damage index of five piezoelectric sensors on the mortar joint surface of the wall as the load increases.

[0083] The figures show that the damage index increases with increasing load, with higher damage indices recorded when the transducer is closer to the crack. Higher average damage indices were observed for the PZT embedded in the mortar joint. The initiation of cracks was first detected by the PZT embedded in the mortar joint, leading to the conclusion that for new buildings, PZT embedded in the mortar joint is the best option, while for existing buildings, it is best to place it on the surface of the mortar joint.

[0084] Figure 6 is a graph 600 of the real impedance 602 of a piezoelectric sensor located on a bolt head as a function of frequency 604. These graphs show when a bolt 610 is loosely screwed into a steel beam and when the same bolt 610' is tightly screwed into the steel beam, as generated by the structural health monitoring system 200 according to one embodiment. Figure 6 A schematic diagram of the setup 606 is also shown as an inset in FIG. The two beam sections 607 and 608 are fastened together by a plate 609 into which bolts 610 and 612 are screwed. Piezoelectric sensors 614 and 616 are attached to the heads of the bolts 610 and 612 and wired back to the structural health monitoring circuit module 210. The signal in the loose bolt 610 is shown in black, while the signal in the tight bolt is shown as a black dashed line 610'. Figure 6 As can be seen, the loose bolt configuration 610' has a significant large peak 620 at around 120 kHz compared to the equivalent peak 622 of the tightened bolt configuration 610'.

[0085] In one embodiment, the module operates in a frequency range of 5kHz to 1MHz, which is a suitable frequency range for SHM applications, although smaller or larger frequency ranges can be used, for example, a lower limit of 1, 10 or 20kHz can be used, while an upper limit of 200kHz, 500kHz or 2MHz can be used. This frequency range can be used to perform active SHM on a variety of materials and structures, using different sized PZTs for monitoring and varying the size of the monitored area.

[0086] Before starting each test, the operating range between the start and end frequencies can be selected after checking the response from the installed PZT. In some embodiments, the frequency range is between 20kHz and 400kHz. This is related to the PZT size and material. The module can operate at frequencies up to 1MHz.

[0087] The value of the real impedance of each module is calibrated by replacing the PZT with a 100 ohm resistor. Once this is done, either or both of the signal generator output or the constant in the real impedance calculation formula can be changed to obtain a 100 ohm straight line across the frequency sweep.

[0088] The transfer function of phase angle to voltage has a nonlinear portion close to zero degrees. This is not critical, however, because the cosine function for angles less than 5 degrees is within 0.5% of 1. Therefore, at these low angles, the real part of the impedance will be within 0.5% of the magnitude of the impedance, making the displayed real part of the impedance, after such calibration, no more than 0.5% error.

[0089] When a 10nF capacitor is substituted for the PZT, the phase angle voltage can be calibrated by measuring the voltage at the output of the digital phase detector with a digital voltmeter. This value is chosen because it is close to the inherent capacitance of the PZT, but is not critical. After the voltage is measured, it is multiplied by 4 and used as the denominator for the cosine calculation of this module. From a theoretical perspective, the real impedance value of the capacitor should be zero. Since capacitors are not perfect, observed values ​​less than a few ohms will not affect the overall result.

[0090] Embodiments of the system are compact and cost-effective, suitable for widespread deployment on a variety of structures, thereby providing a more useful alternative to existing systems.

[0091] Embodiments of the system may be used to monitor: Typical steel connections in bridges and various civil and industrial engineering structures; · Scaled 3D typical galvanized steel truss structures used in industrial engineering, civil engineering, truss structure types such as roofs, bridges, frames, warehouses, various steel and metal structures (e.g., silos, submarines, ships, trains...), etc.; Typical proportional steel and timber connections used in a variety of structures such as homes, bridges, roofs and all other civil engineering, mining, petroleum (e.g. drilling rigs), mechanical (machinery and trains) and geotechnical, railway line structures, Monitor the integrity of individual bolts; Monitor the torque tightness of individual bolts or groups of bolts as needed; Anchor bolts and reinforced geotechnical supports; Reinforced concrete structures, such as steel bars; Rock conditions; Soil conditions; Concrete condition; Pressure vessels, submarines, etc. Masonry; and / or ·Parts and conditions of machinery and equipment.

[0092] Embodiments of the system may be provided as a compact and mobile module that uses internal batteries and solar panels to provide power and uses a wireless communication link to send data back to the user. The structural health monitoring module including the frequency generator is lightweight and may include a touch screen interface. The compact multi-sensor impedance measurement circuit module may be forward deployed from the central module and wired back to the central module that provides power and scanning signals. The output signal is sent to the DAQ 250 and reaches the user-specified destination via the communication module 260 for further analysis, processing and display on the user computing device 270. Communication may be performed over a wireless link, such as over a 4G / 5G or Wi-Fi network, or over a wired link. The DAQ may also analyze the output signal and the data may be stored locally, such as on a removable memory device such as an SD card.

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

[0094] An embodiment of the structural health monitoring module 210 is constructed, wherein the user interface 216 is a touch screen interface in the form of a TFT display module ILI9341, and the sweep signal generator 230 is a DDS function generator module based on the AD9833 chip from Analog Devices. The microprocessor can be an ESP32DevKitC 32UE development module from Espressif Systems. They can be assembled on a PCB. The software is written using the open source Arduino IDE software and with the help of multiple open source libraries to control the operation of the touch screen. They include Bodner's TFT_eSPI library, the Arduino SPI library, and Volodymyr Shymanskyy's Preferences library.

[0095] An embodiment of the DAQ 250 was constructed in which the ADC 256 is provided by two AD7606 modules, providing 16-bit resolution and sampling rates up to 200ksps. These ADC modules have a total of 16 channels for 8 PZT sensors and are controlled by an Arduino Mega 2560R3 microcontroller. The DAQ microprocessor is provided by a DFRobot FireBettle eESP32 module (DFR0478), which also provides the wireless communication module 260. A real-time clock module in the form of an RTC module SD2405 is also included to provide accurate real-time timing and date stamping capabilities.

[0096] A computer program was developed for the DAQ 250 to perform multiple tasks using the ESP32 and ATMEGA2560 microcontrollers and various libraries. In one embodiment, the program code is used to provide the following functionality: 1) The code connects the ESP32 to a Wi-Fi network and establishes an internet connection. 2) It connects to a time server (ntp.org) to retrieve the current date and time and adjusts it according to the specified time zone. 3) The acquired date and time are saved in the real-time clock module. 4) The code waits for a trigger signal from the structural health monitoring (SHM) module 210 (eg, via cable 224). 5) After receiving the trigger signal, it sends a trigger to the ATmega2560 microcontroller to control the ADC. 6) The ATmega2560 will take the readings from the ADC 254 and send the data to the ESP32. 7) The ESP32 receives the digitized piezo phase and current signals from the ATmega2560. 8) The measured signal is converted into a real impedance value (Zreal =Vcos(θ) / I). 9) The data is then saved to a text file with a file name format defined by the user. 10) The data file includes a header with columns describing the 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 recipients. 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 or computing device in the structural health monitoring module 210, DAQ and user computing device 270 may include a single CPU (core) or multiple CPUs (multiple cores) or multiple processors. The computing device may be a server, a desktop, a portable computer (including a tablet), a smart phone, a smart watch, or a microprocessor device including a processor and onboard memory and an interface. The processor may use a parallel processor, a vector processor, or may be part of a distributed (cloud) computing device. The memory is operably connected to the processor and may include RAM and ROM components and auxiliary storage components such as solid-state drives and hard disks, which may be located inside or outside the device. The external storage device 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 a cloud-based storage device. The memory may include instructions that cause 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 used to load and execute software modules or instructions stored in the memory. The computing device may be used to continuously analyze input sensor signals and may be used to generate reports or alarms when changes are detected. For example, the computing device may store a set of rules or thresholds that indicate changes (e.g., deviations from a reference curve or spectrum) that can be compared to the analysis results. The microprocessor used in the module may be a microcontroller such as an Arduino microcontroller and may include onboard memory.

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

[0099] Those skilled in the art will further appreciate that the various illustrative logic blocks, modules, circuits and algorithm steps described in conjunction with the embodiments disclosed herein can be implemented as electronic hardware, computer software or instructions, middleware, platform or a combination of the two. In order to clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits and steps have been described above generally according to their functions. Whether this functionality is implemented as hardware or software depends on specific applications and the design constraints imposed on the entire system. Those skilled in the art can implement the described functions in various ways for each specific application, but these determined implementations should not be interpreted as causing departure from the scope of the present invention.

[0100] The steps of the method or algorithm described in conjunction with the embodiments disclosed herein may be directly embodied in hardware, a software module executed by a processor, or a combination of the two. For hardware implementation, processing may be implemented in 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, other electronic units designed to perform the functions described herein, or a combination thereof. A software module, also referred to as a computer program, computer code, or instruction, may include multiple source code or target code segments or instructions, and may be located in any computer-readable medium, such as RAM memory, flash memory, ROM memory, EPROM memory, registers, hard disks, removable disks, CD-ROMs, DVD-ROMs, Blu-ray discs, or any other form of computer-readable medium. In some aspects, a computer-readable medium may include a non-temporary computer-readable medium (e.g., a tangible medium). In addition, for other aspects, a computer-readable medium may include a temporary computer-readable medium (e.g., a signal). The above combination should also be included in the scope of a computer-readable medium. In another aspect, a computer-readable medium may be integrated with a processor. The processor and computer readable medium may reside in an ASIC or related device. The software code may be stored in a memory unit and the processor may be used to execute them. The memory unit may be implemented inside the processor or outside the processor, in which case it may be communicatively connected to the processor by various means known in the art.

[0101] In addition, it should be understood that the modules and / or other suitable devices for performing the methods and techniques described herein can be downloaded and / or otherwise obtained by the computing device. For example, such a device can be connected to a server to facilitate the transmission of the device for performing the methods described herein. Alternatively, the various methods described herein can be provided via a storage device (e.g., RAM, ROM, physical storage media such as a compact disc (CD) or a USB storage drive, etc.), so that the computing device can obtain various methods when the storage device is connected or provided to the computing device. Moreover, any other suitable technology for providing the methods and techniques described herein to a device can be used.

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

[0103] The method disclosed herein includes one or more steps or actions for implementing the described method. The method steps and / or actions can be interchanged with each other 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 can be modified without departing from the scope of the claims.

[0104] As used herein, the terms "determine", "obtain", and "estimate" encompass a wide variety of actions. For example, "determine", "obtain", and "estimate" may include calculating, computing, processing, deriving, investigating, searching (e.g., searching in a table, database, or other data structure), ascertaining, etc. In addition, "determine" and "obtain" may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), etc. In addition, "determine", "obtain", and "estimate" may include solving, selecting, choosing, establishing, etc.

[0105] The reference to any prior art in this specification is not, and should not be taken as, any form of admission that such prior art forms part of the common general knowledge.

[0106] It should be understood that the terms "comprises" and "comprising" and any variations thereof used in this specification and the following claims should be construed as including the features referred to by the terms and are not meant to exclude the existence of any additional features unless otherwise stated or implied.

[0107] In some cases, for the sake of brevity and / or to help understand the scope of the present invention, multiple features can be combined in one embodiment. It should be understood that in this case, these multiple features can be provided separately (in each separate embodiment) or in any other suitable combination. Alternatively, when separate features are described in separate embodiments, unless otherwise specified or implied, these separate features can be combined into one embodiment. This also applies to claims that can be recombined in any combination. That is, a claim can be amended to include features defined in any other claim. In addition, the phrase "at least one" in the list of items refers to any combination of these 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 appreciate that the use of the present invention is not limited to the specific applications described. The present invention is not limited to its preferred embodiments with respect to the specific elements and / or features described or depicted herein. It should be understood that the present invention is not limited to the disclosed one or more embodiments, but can be variously rearranged, modified and replaced without departing from the scope set forth and defined by the appended claims.

Claims

1. An impedance measurement circuit, comprising: a buffer for receiving an AC sweep signal from a sweep signal generator and providing the buffered sweep signal to an input of the piezoelectric sensor; a current-to-voltage converter connected in parallel with a feedback resistor and configured such that the current-to-voltage converter and the feedback resistor receive a piezoelectric output signal from the piezoelectric sensor and generate a piezoelectric current signal in which an AC voltage is proportional to both a phase angle and a current flowing through the piezoelectric sensor; a phase comparison circuit receiving the buffered scanning signal on a first input and the piezoelectric current signal on a second input and configured to compare the piezoelectric current signal with the buffered scanning signal to generate an output piezoelectric phase signal having a DC voltage proportional to a phase difference between the buffered scanning signal and the piezoelectric current signal; A rectifier circuit receives the piezoelectric current signal at a first input and is configured to generate an output piezoelectric current signal having a DC voltage proportional to a current flowing through the piezoelectric sensor.

2. The impedance measurement circuit of claim 1, wherein: The phase comparison circuit comprises: a digital phase detector receiving the buffered scan signal on a first input and the piezoelectric current signal from the current-to-voltage converter on a second input, and for comparing the piezoelectric current signal with the buffered scan signal to generate a first piezoelectric phase signal; and a first low pass filter for receiving the first piezoelectric phase signal and generating an output piezoelectric phase signal having a DC voltage proportional to a phase difference between the buffered scanning signal and the piezoelectric current signal; and The rectifier circuit comprises: a rectifier for receiving the piezoelectric current signal on a first input and rectifying the piezoelectric current signal to generate a first piezoelectric current signal; and A second low-pass filter is used to receive the first piezoelectric current signal and generate an output piezoelectric current signal having a DC voltage proportional to the current flowing through the piezoelectric sensor.

3. The impedance measurement circuit according to claim 1 or 2, wherein: The frequency range of the AC scanning signal is 5 kHz to 1 MHz, and the components of the circuit are configured to operate within the frequency range of 5 kHz to 1 MHz.

4. The impedance measurement circuit according to claim 1, 2 or 3, wherein: The output piezoelectric phase signal and the output piezoelectric current signal are direct current signals with a voltage range of 0 to 5V.

5. The impedance measurement circuit according to any one of claims 1 to 4, wherein: The impedance measurement circuit consumes less than 5 watts of power.

6. A multi-sensor impedance measurement circuit module, comprising: a scanning signal input connector for receiving an input AC scanning signal, or a scanning signal generator circuit for generating an AC scanning signal; a voltage converter circuit for generating a plurality of regulated supply voltages from an input power connector or a power supply circuit; A plurality of impedance measurement circuit modules as claimed in any one of claims 1 to 5, wherein a scan signal input is provided as an input to each impedance measurement circuit; a plurality of pairs of input connectors for connecting to inputs and outputs of the piezoelectric sensor, wherein each pair of input connectors is connected to one impedance measurement circuit module among the plurality of impedance measurement circuit modules; as well as A plurality of pairs of output connectors, each pair connected to the output of one of the impedance measurement circuit modules, wherein the paired outputs include an output piezoelectric phase signal and an output piezoelectric current signal from the corresponding impedance measurement circuit module.

7. The impedance measurement circuit according to claim 6, wherein: The voltage conversion circuit is used to generate regulated +5V, -5V and +3V supply voltages.

8. The impedance measurement circuit of claim 6 or 7, further comprising a compact unitary housing housing a circuit board including a plurality of surface mount components implementing one or more components of the multi-sensor impedance measurement circuit module.

9. A structural health monitoring circuit module for a structural health monitoring system, comprising: One or more multi-sensor impedance measurement circuit modules according to any one of claims 6 to 8, wherein the one or more multi-sensor impedance measurement circuit modules include a power supply circuit and a scanning signal generator, wherein the power supply circuit includes a voltage regulator, and the voltage regulator is used to receive an unregulated power supply voltage in the range of 9V to 18V and regulated +5V, -5V and +3V power supply voltages; as well as a user interface, at least one processor, and at least one memory, wherein 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, the processor being configured to configure the structural health monitoring circuit module, including configuring the scanning signal generator circuit, wherein the one or more user input signals are received using an input device and / or from a remote device.

10. A structural health monitoring circuit module, used in a structural health monitoring system and used to be connected to one or more multi-sensor impedance measurement circuit modules according to any one of claims 6 to 8, wherein the one or more multi-sensor impedance measurement circuit modules include an input power connector and a scanning signal input connector, and the structural health monitoring circuit module includes: A power supply circuit including a voltage regulator for receiving an unregulated supply voltage in the range of 9V to 18V and regulated supply voltages of +5V, -5V and +3V; a power output connector for providing an unregulated power supply voltage to the input power connector of the one or more multi-sensor impedance measurement circuit modules via a wired connector; A scanning signal generator circuit, which is used to generate an AC scanning signal; as well as a scanning signal output connector, for providing an AC scanning signal to the scanning signal input connector of one or more multi-sensor impedance measurement circuit modules via a wired connector; as well as a user interface, at least one processor, and at least one memory, wherein 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, the processor being configured to configure the structural health monitoring circuit module, including configuring the scanning signal generator circuit, wherein the one or more user input signals are received using an input device and / or a remote device.

11. The structural health monitoring circuit module according to claim 9 or 10, wherein: The frequency range of the AC scanning signal is 5 kHz to 1 MHz.

12. The structural health monitoring circuit module according to claim 9, 10 or 11, wherein: The RMS voltage of the AC scanning signal is 200 mV or less.

13. The structural health monitoring circuit module according to any one of claims 9 to 12, wherein: The scan signal generator circuit also includes a scan trigger signal.

14. The structural health monitoring module of claim 13, further comprising: an analog-to-digital conversion circuit for converting 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 digitized phase signal and a digitized current signal, wherein the one or more processors are used to analyze the digital representation and estimate a real impedance as a function of frequency for each sensor, generate a monitoring report and store it in the at least one memory; and A communication module is used to allow the stored monitoring reports to be sent or downloaded.

15. The structural health monitoring module of claim 14, wherein: The at least one memory is used to store a recipient address and one or more alarm triggering conditions for generating an alarm, The one or more processors are used to analyze the digitized phase signal and the digitized current signal of each of the one or more multi-sensor impedance measurement circuit modules to determine whether one or more of the one or more alarm triggering conditions are met, and The communication module is a wireless communication module, which is used to send a monitoring report to a recipient address and / or send an alarm to the recipient when one or more of one or more alarm triggering conditions are met.

16. The structural health monitoring module according to claim 14 or 15, wherein: One or more user input signals are received from the remote device via the communication module, or one or more user input signals are received from the user interface, wherein the one or more user input signals include one or more of a frequency range of a scanning signal generator circuit, a signal level, one or more monitoring parameters, one or more alarm trigger conditions and / or one or more recipient addresses.

17. The structural health monitoring module of claim 16, wherein: The one or more monitoring parameters are used to configure the one or more processors to monitor a predefined set of one or more impedance measurement circuits.

18. The structural health monitoring module according to any one of claims 14 to 17, wherein: Analyzing the digitized phase signal and the digitized current signal for each of the one or more multi-sensor impedance measurement circuit modules includes: estimating the real impedance, Z real =Vcos(θ) / I, where θ is the corresponding digitized phase signal, I is the corresponding digitized current signal, and V is a predetermined constant obtained from calibration measurements, which include measuring the input voltage across the corresponding piezoelectric sensor.

19. A structural health monitoring system comprising: The structural health monitoring circuit module according to any one of claims 10 to 13; One or more multi-sensor impedance measurement circuit modules as claimed in any one of claims 6 to 8; 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 used 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 digitized phase signal and a digitized current signal, the at least one processor is used to analyze the digital representation to estimate the real impedance of each sensor as a function of frequency, generate a monitoring report and store it in the at least one memory, and the communication module is used to allow the stored monitoring report to be sent or downloaded.

20. The system of claim 19, wherein: The at least one memory is used to store a recipient address and one or more alarm triggering conditions for generating an alarm, The one or more processors are used to analyze the digitized phase signal and the digitized current signal of each of the one or more multi-sensor impedance measurement circuit modules to determine whether one or more of the one or more alarm triggering conditions are met, and The communication module is a wireless communication module, which is used to send a monitoring report to a recipient address and / or send an alarm to the recipient when one or more of one or more alarm triggering conditions are met.

21. The system of claim 19 or 20, wherein: One or more user input signals are received from a remote device via a communication module or from a user interface, and the one or more user input signals include one or more of a frequency range of a scanning signal generator circuit, a signal level, one or more monitoring parameters, one or more alarm trigger conditions and / or one or more recipient addresses.

22. The system of claim 21, wherein: The one or more monitoring parameters are used to configure the one or more processors to monitor a predefined set of one or more impedance measurement circuits.

23. The system of any one of claims 20 to 22, wherein: Analyzing the digitized phase signal and the digitized current signal for each of the one or more multi-sensor impedance measurement circuit modules includes: estimating the real impedance, Z real =Vcos(θ) / I, where θ is the corresponding digitized phase signal, I is the corresponding digitized current signal, and V is a predetermined constant obtained from calibration measurements, which include measuring the input voltage across the corresponding piezoelectric sensor.

24. A method for measuring the impedance of a piezoelectric sensor, comprising: buffering an AC sweep signal received from a sweep signal 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 which an AC voltage is proportional to both a phase angle and a current flowing through the piezoelectric sensor, the current-to-voltage converter being connected in parallel with a feedback resistor and configured so that the current-to-voltage converter and the feedback resistor receive a piezoelectric output signal from the piezoelectric sensor; generating an output piezoelectric phase signal having a DC voltage proportional to a phase difference between the buffered scan signal and the piezoelectric current signal using a phase comparison circuit, the phase comparison circuit receiving the buffered scan signal on a first input and the piezoelectric current signal on a second input and being configured to compare the piezoelectric current signal with the buffered scan signal; as well as An output piezoelectric current signal having a DC voltage proportional to the current flowing through the piezoelectric sensor is generated using a rectifier circuit that receives the piezoelectric current signal on a first input.

25. The method of claim 24, further comprising: The output piezoelectric phase signal is digitized to obtain a digitized phase signal θ, the output piezoelectric current signal is digitized to obtain a digitized current signal I, and the real impedance, Z, is estimated. real =Vcos(θ) / I, where V is a predetermined constant obtained from calibration measurements, which include measuring the input voltage across the corresponding piezoelectric sensor.

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