CN116642443A - Passive wireless strain detection system and method for nonmetallic pipeline - Google Patents
Passive wireless strain detection system and method for nonmetallic pipeline Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
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- G01B17/00—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations
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Abstract
The invention discloses a passive wireless strain detection system and a passive wireless strain detection method for a nonmetallic pipeline, which relate to the technical field of sensors, wherein the passive wireless strain detection system comprises a sensor, a transmitter and a controller; the transmitter is used for transmitting excitation electromagnetic waves with preset resonant frequency, receiving measurement signals reflected by the sensor and transmitting the measurement signals to the controller; the sensor is attached to the outer surface of the nonmetal pipeline to be tested; the sensor is used for receiving the excitation electromagnetic wave, obtaining energy according to the excitation electromagnetic wave, generating corresponding deformation when the nonmetal pipeline to be tested is deformed, and reflecting the excitation electromagnetic wave based on the deformation to obtain a measurement signal; the controller is used for determining the strain quantity of the nonmetal pipeline to be tested according to the resonance frequency of the exciting electromagnetic wave and the resonance frequency of the measuring signal. The invention can reduce the cost of strain detection of the nonmetal pipeline when a large number of nonmetal long-distance pipelines are arranged.
Description
Technical Field
The invention relates to the technical field of sensors, in particular to a passive wireless strain detection system and method for a nonmetallic pipeline.
Background
Along with the technical development of the chemical industry field, the nonmetallic pipeline is widely applied to urban tap water pipe network systems, natural gas conveying systems and conveying systems in the chemical petroleum field. Compared with the traditional metal pipeline, the nonmetal pipeline comprises Polybutene (PB) and Polyethylene (PE) plastic pipelines, and has the advantages of low price, strong corrosion resistance and simple construction. However, the nonmetallic pipeline has low strength compared with the metal, and can cause the pipeline to be greatly deformed and blocked or even cracked due to the reasons of abnormal formation pressure, thermal stress caused by temperature change, accidental damage caused by construction and the like. Therefore, the detection and monitoring of nonmetallic pipelines is of great significance.
The traditional nonmetal detection method mainly comprises a ground penetrating radar, an ultrasonic detector, an identification method and the like. The ground penetrating radar detects the conductivity and dielectric constant distribution of underground medium by emitting electromagnetic wave in ultra-high frequency range. The method mainly identifies the deformation of the pipeline by analyzing the reflected waveform, but the signal difference caused by the pipeline deformation is extremely weak and the resolution is lower because the non-metallic pipeline and soil are not obvious in dielectric constant and are both between 2.5 and 4.0. The ultrasonic detection method relies on the oscillation of ultrasonic in the medium in the pipeline to judge the structural health condition of the pipeline, but the detector needs to be in contact with the pipeline as much as possible, if the distance is far, the attenuation of sound waves is serious, and the detection difficulty is increased. The marking method is characterized in that a metal marker is buried above a key part of an underground pipeline, electromagnetic waves can be emitted through an electromagnetic wave detector in the later detection process, and the position of the marker is detected by means of echo, so that the positioning before subsequent maintenance and overhaul is facilitated. However, such a marker itself cannot be used as a detection method of deformation. Based on the disadvantages of the conventional detection methods described above, relying on strain sensors to monitor the deformation of nonmetallic pipelines has also become an alternative. However, conventional strain sensors are wired strain gages that require a cable connection to a data acquisition unit to acquire a signal. For buried pipelines, cement wall interior pipelines, thick insulation pipelines, the construction difficulty of the pipelines is increased due to the problems of cable redundancy caused by the construction steps of soil landfill, cement sealing, insulation wrapping and the like required for the construction of the inaccessible/invisible pipelines. In addition, if a wireless communication node for installing a battery is used, the battery replacement problem is faced, and the battery cannot be used stably for a long time.
As an alternative to wired and active wireless sensors, passive wireless sensors aim to solve the problem of cable redundancy during sensor installation and use. When detection is needed, the external radio transmitter can generate electromagnetic waves to provide energy for passive devices or rectifying circuits of the sensor, and then the sensor can reflect or actively send signals to the transmitter through the sensing antenna. Since electromagnetic waves can penetrate the soil, this method provides the possibility for detection of non-contact buried pipelines. The patent reviews of existing passive wireless sensors for buried pipeline detection are as follows:
a passive wireless damage leakage monitoring system and a control method thereof (application number: 202110293500.9) introduce a passive wireless sensing method consisting of a passive sensor consisting of a flexible piezoelectric sensing unit, a conditioning circuit, a passive RFID tag and an RFID antenna, a radio frequency reading module, a display module and the like. The passive tag inside the sensor receives electromagnetic waves and supplies power to the built-in circuit of the sensor when the reader generates an excitation signal, and collects signals of the piezoelectric sensor and returns to the reader.
"internet of things (IoT) supporting wireless sensor systems that can enable process control, predictive maintenance of power distribution networks, liquid and gas pipelines, and monitoring of air pollutants (including nuclear, chemical and biological agents) using attached and/or embedded passive electromagnetic sensors" (application number 201880077911.0), a wireless sensor consisting of a passive acoustic wave sensor and a passive microprocessor is described. The circuit is characterized in that a plurality of induction coils are used for collecting electromagnetic fields emitted by a remote antenna to provide energy for the circuit.
The method relies on an RFID coil antenna in the sensor, acquires alternating current signals from an external electromagnetic field through a circuit, converts the alternating current signals into direct current through a rectifying circuit, supplies power for a microprocessor and various sensors, and finally feeds collected information back to a transmitter through the RFID antenna. In principle, such sensors belong to semi-active wireless sensors, which have the disadvantage that the cost of a single sensor is high and are not suitable for a large number of arrangements on long-distance pipelines.
Disclosure of Invention
The invention aims to provide a passive wireless strain detection system and a passive wireless strain detection method for a nonmetal pipeline, which can reduce the cost of strain detection of the nonmetal pipeline when a large number of nonmetal long-distance pipelines are arranged.
In order to achieve the above object, the present invention provides the following solutions:
a passive wireless strain detection system for a non-metallic pipe, the passive wireless strain sensing system comprising a sensor, a transmitter, and a controller;
the transmitter is used for transmitting excitation electromagnetic waves with preset resonant frequency, receiving measurement signals reflected by the sensor and transmitting the measurement signals to the controller;
the sensor is attached to the outer surface of the nonmetal pipeline to be tested; the sensor is used for receiving the excitation electromagnetic wave, obtaining energy according to the excitation electromagnetic wave, generating corresponding deformation when the nonmetal pipeline to be measured is deformed, and reflecting the excitation electromagnetic wave based on the deformation to obtain the measurement signal;
the controller is used for determining the installation position of the sensor on the outer surface of the nonmetal pipeline to be measured according to the resonance frequency of the measurement signal and the initial resonance frequency calibrated by the sensor, and calculating the strain quantity of the nonmetal pipeline to be measured according to the frequency offset of the measurement signal emitted by the sensor at the installation position and the strain value corresponding to the initial resonance frequency calibrated by the sensor.
Optionally, the transmitter includes a signal transceiver and a transmitting antenna;
the signal transceiver is used for generating excitation electromagnetic waves and receiving the measurement signals, and transmitting the measurement signals to the controller;
the transmitting antenna is connected with the signal transceiver; the transmitting antenna is used for transmitting the excitation electromagnetic wave.
Optionally, the transmitter further comprises a matching circuit;
the matching circuit is connected with the transmitting antenna; the matching circuit is used for adjusting the resonant frequency of the transmitting antenna so that the resonant frequency of the transmitting antenna is consistent with the resonant frequency of the sensor.
Optionally, the transmitting antenna is a directional antenna or an omni-directional antenna.
Optionally, the sensor is a planar antenna type passive wireless strain sensor or an external surface acoustic wave type passive wireless strain sensor.
Optionally, the planar antenna passive wireless strain sensor comprises a substrate, a base plate, a reflecting surface, a matching wire and an electronic tag chip;
the substrate is arranged on the upper surface of the base; the reflecting surface, the matching wire and the electronic tag chip are arranged on the upper surface of the substrate; the matching line is connected with the reflecting surface; the electronic tag chip is arranged at the joint of the matching line and the reflecting surface;
The reflection surface is used for receiving the excitation electromagnetic wave, obtaining energy according to the excitation electromagnetic wave, generating corresponding deformation when the nonmetal pipeline to be measured is deformed, and reflecting the excitation electromagnetic wave based on the deformation to obtain the measurement signal;
the matching line is used for adjusting the resonant frequency of the reflecting surface and the return loss of the measuring signal;
the electronic tag chip is configured to store the number of the sensor and send the sensor number to the transmitter when the energy is greater than an electronic tag activation threshold.
Optionally, the sensor is attached to the outer surface of the nonmetallic pipeline to be tested by using an epoxy resin adhesive.
Optionally, the sensor comprises a substrate; the substrate is a flexible substrate.
The passive wireless strain detection method for the nonmetallic pipeline is applied to the passive wireless strain detection system for the nonmetallic pipeline, and the passive wireless strain sensing method comprises the following steps:
acquiring an initial resonance frequency calibrated by a sensor and a strain value corresponding to the initial resonance frequency;
acquiring a reflected measurement signal of a sensor, and determining the installation position of the sensor on the outer surface of a nonmetal pipeline to be measured according to the measurement signal and the initial resonant frequency;
And calculating the strain value of the outer surface of the measured nonmetallic pipeline at the installation position according to the frequency offset of the measuring signal transmitted by the sensor at the installation position and the strain value corresponding to the initial resonant frequency.
Optionally, the passive wireless strain sensing method further comprises:
calibrating the sensor to obtain the relation between the resonant frequency of the sensor and the temperature and distance; the temperature is the temperature of the working environment of the sensor; the distance is a distance between the emitter and the sensor.
According to the specific embodiment provided by the invention, the invention discloses the following technical effects:
the invention discloses a method for detecting strain of an unreachable nonmetallic pipeline by using a resonant passive wireless strain sensor. The sensor does not contain a battery, does not contain a complex circuit and does not need external cable connection, and the state of the sensor is fed back by completely receiving and reflecting the sweep frequency signal generated by the radio transmitter. Non-contact strain measurement can be achieved. The invention uses the sensor to display the deformation as a characteristic peak value on the reflection coefficient curve of the wireless signal transmitter; the amount of deformation to which the sensor is subjected can be determined by identifying the frequency of the peak. The sensors can be attached to the outer surface of an invisible and inaccessible nonmetal pipe wall in the underground or cement wall, and the sensors can receive signals generated by an external wireless signal transmitter through a sensor antenna to detect, so that the ground surface is not required to be excavated or the wall is not required to be damaged, a wire interface is not required to be reserved on the ground surface, and convenience is brought to safety maintenance and supervision. Based on the characteristics of the resonance type passive wireless sensor, the sensor has higher compatibility with intelligent detection platforms such as unmanned aerial vehicles, robots and the like, can replace manual completion of detection of nonmetal pipeline deformation, and promotes the development of structural health detection to unmanned and intelligent directions.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a planar antenna passive wireless strain sensor and transmitter;
FIG. 2 is a schematic diagram of a surface acoustic wave passive wireless strain sensor and transmitter;
FIG. 3 is a block diagram of a planar antenna passive wireless strain sensor;
FIG. 4 is a block diagram of a surface acoustic wave passive wireless strain sensor;
FIG. 5 is a plan view of a planar antenna passive wireless strain sensor;
FIG. 6 is a schematic diagram of a planar antenna passive wireless strain sensor;
FIG. 7 is an impedance plot of a planar antenna passive wireless strain sensor;
FIG. 8 antenna directivity of a planar antenna passive wireless strain sensor;
FIG. 9 is a schematic diagram showing the evolution rule of the planar antenna type passive wireless strain sensor along with the deformation of the pipeline;
FIG. 10 is a schematic diagram of the positioning principle of a planar antenna type passive wireless strain sensor;
FIG. 11 is a signal diagram of a planar antenna passive wireless strain sensor;
FIG. 12 is a design drawing of a surface acoustic wave passive wireless strain sensor;
fig. 13 is a flow chart of a passive wireless strain detection method for nonmetallic pipelines provided by the invention.
Reference numerals illustrate:
the device comprises a transmitter-1, a plane antenna type passive wireless strain sensor-2, a reflecting surface-3, a substrate-4 of the plane antenna type passive wireless strain sensor, a substrate-5, a dipole antenna-6, a shell-7, a substrate-8 of the surface acoustic wave type passive wireless strain sensor, a piezoelectric sheet-9, a cross transducer-10, a reflecting grating-11, an electronic tag-12, a matching line-13, a coaxial line port-14 and a surface acoustic wave type passive wireless strain sensor-15.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention aims to provide a passive wireless strain detection system and a passive wireless strain detection method for a nonmetal pipeline, which can reduce the cost of strain detection of the nonmetal pipeline when a large number of nonmetal long-distance pipelines are arranged.
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
Example 1
As shown in fig. 1 and 2, the present invention provides a passive wireless strain sensing system for non-metallic pipes, comprising a sensor, a transmitter 1 and a controller. Wherein the controller is not shown in the figures.
The transmitter 1 is used for transmitting excitation electromagnetic waves with preset resonance frequency, receiving measurement signals reflected by the sensor and sending the measurement signals to the controller; the sensor is attached to the outer surface of the nonmetal pipeline to be tested; the sensor is used for receiving the excitation electromagnetic wave, obtaining energy according to the excitation electromagnetic wave, generating corresponding deformation when the nonmetal pipeline to be measured is deformed, and reflecting the excitation electromagnetic wave based on the deformation to obtain the measurement signal; the controller is used for determining the installation position of the sensor on the outer surface of the nonmetal pipeline to be measured according to the resonance frequency of the measurement signal and the initial resonance frequency calibrated by the sensor, and calculating the strain quantity of the nonmetal pipeline to be measured according to the frequency offset of the measurement signal emitted by the sensor at the installation position and the strain value corresponding to the initial resonance frequency calibrated by the sensor. The preset resonant frequency is a frequency value in a set range of the resonant frequency of the sensor; the sensor deforms, so that a characteristic peak value signal appears in a measuring signal at the excitation frequency of the sensor, and a reflection signal containing the characteristic peak value signal is a return loss coefficient of the transmitter or an energy transfer coefficient between the transmitter and the sensor.
In practical use, the passive wireless strain detection system comprises a sensor and a transmitter 1. Wherein the sensor is attached to the surface of the pipe to be measured to measure the deformation of the pipe to be measured, and the transmitter 1 transmits excitation electromagnetic waves to the sensor from outside the surface and receives reflected signals. Specifically, the sensor is composed of a match line 13 for generating a peak signal on the reflected signal and a sensing antenna for receiving external energy.
As a specific embodiment, the transmitter 1 includes a signal transceiver and a transmitting antenna; the signal transceiver is used for generating excitation electromagnetic waves and receiving the measurement signals, and transmitting the measurement signals to the controller; the transmitting antenna is connected with the signal transceiver; the transmitting antenna is used for transmitting the excitation electromagnetic wave.
Further, the transmitter 1 further comprises a matching circuit; the matching circuit is connected with the transmitting antenna; the matching circuit is used for adjusting the resonant frequency of the transmitting antenna so that the resonant frequency of the transmitting antenna is consistent with the resonant frequency of the sensor.
In practical application, the transmitter 1 consists of a transmitting antenna for radiating excitation electromagnetic waves and a signal transceiver for generating excitation signals; in order to adjust the resonant frequency of the transmitter 1 to be equal to the resonant frequency of the sensor, a compensation circuit consisting of passive devices is sometimes also required in series to the transmitting antenna.
Specifically, the sensor is a planar antenna type passive wireless strain sensor 2 or an external surface acoustic wave type passive wireless strain sensor 15.
As shown in fig. 3, the planar antenna passive wireless strain sensor 2 is a planar reflection antenna, the upper and lower surfaces of which are both metal foils, respectively referred to as a reflection surface 3 and a substrate 5, and the middle interlayer is a flexible non-metal plate, referred to as a substrate 4 of the planar antenna passive wireless strain sensor 2. The planar antenna type passive wireless strain sensor 2 has a resonant frequency, and when the frequency of the excitation source is equal to the excitation frequency, the intensity of electromagnetic waves received and reflected by the planar antenna type passive wireless strain sensor 2 reaches the maximum value, so that the structure is the matching line 13 and the sensing antenna of the planar antenna type passive wireless strain sensor 2. The plane antenna type passive wireless strain sensor 2 can be directly attached to the outer surface of a nonmetal pipeline, and is adaptive to pipelines with different outer diameters.
When the pipeline is deformed due to external force, the deformation of the whole structure of the planar antenna type passive wireless strain sensor 2 is caused, so that the resonant frequency of the planar antenna type passive wireless strain sensor 2 is changed, and finally, the peak value of the characteristic signal of the planar antenna type passive wireless strain sensor 2 received by the transmitter 1 is translated in the frequency domain.
The planar antenna type passive wireless strain sensor 2 has the advantages of simple manufacturing process and strong self-adaption, and can realize non-contact strain measurement with the furthest wireless transmission distance reaching more than 1 m. The planar antenna type passive wireless strain sensor 2 is similar to the identification method used in the traditional nonmetal pipeline detection, but the difference is that the metal identification in the identification method also depends on reflected electromagnetic waves to determine the position of the metal identification, but the metal identification does not deform along with the pipeline, so the resonance frequency of the metal identification is a fixed value, and the detection frequency of the metal identification does not need to be close to the resonance frequency of the identification.
As shown in fig. 4, the surface acoustic wave passive wireless strain sensor 15 includes a cross transducer 10, a reflective grating 11, a piezoelectric sheet 9, a substrate 8 of the surface acoustic wave passive wireless strain sensor 15, a dipole antenna 6, and a housing 7. The cross transducer 10 and the reflecting grating 11 are metal coatings on the surface of the piezoelectric sheet 9, and the piezoelectric sheet 9 is attached to the upper surface of the substrate 8 of the surface acoustic wave passive wireless strain sensor 15. The dipole antenna 6 is connected to the coaxial line port 14. For the piezoelectric sheet 9 with high material rigidity, the lower surface of the substrate 8 of the surface acoustic wave passive wireless strain sensor 15 needs to be processed into an inner arc so as to adapt to the outer arc surface of the pipeline; for the flexible piezoelectric sheet 9 with smaller material rigidity and thinner thickness, the flexible piezoelectric sheet can be directly attached to the outer surface of the pipeline. In order to prevent the saw passive wireless strain sensor 15 buried in the soil from being worn and corroded, a housing 7 must be installed outside the substrate 8 of the saw passive wireless strain sensor 15, and the inside of the housing may be sealed, so that the aging of the saw passive wireless strain sensor 15 is further reduced.
When the dipole antenna 6 receives the excitation voltage transmitted by the transmitting antenna, the alternating signal passes through the two crossed electrodes of the crossed transducer 10, and due to the coupling effect of the piezoelectric material, a surface acoustic wave transmitted along the transverse direction is generated on the surface of the piezoelectric sheet 9, and after being reflected by the reflecting grating 11, the reflected acoustic wave and the incident acoustic wave generate a superposition effect on the surface, so that the crossed transducer 10 generates resonance. When the piezoelectric sheet 9 is deformed, the transmission distance of the acoustic wave between the cross transducer 10 and the reflecting grating 11 is changed, thereby causing a change in the resonance frequency.
The advantage of the surface acoustic wave passive wireless strain sensor 15 is that the surface acoustic wave generates a high quality factor (Q > 10000) after resonating, which makes the characteristic signal received by the transmitter 1 appear sharp peak signals, and greatly improves the resolution of strain detection. In addition, the high quality factor of the surface acoustic wave passive wireless strain sensor 15 allows the characteristic signal to be detected over a longer distance, so that the sensing distance of this method can reach about 2 m.
Further, the transmitting antenna is a directional antenna or an omni-directional antenna.
The planar antenna type passive wireless strain sensor 2 and the external surface acoustic wave type passive wireless strain sensor 15 have the common feature that the impedance is reduced by relying on resonance caused by special structures and materials in the sensor, so that the intensity of reflected waves at the resonance frequency is changed, and the return loss of the transmitter 1 is changed. In addition, the receiving range of the sensor depends on the gains and directivities of the sensing antenna and the receiving antenna in addition to the impedance characteristics of the sensor itself. For antennas with better directivity, the sensor distance will be further; for the omnidirectional antenna, the distance of the sensor is reduced, but the sensor can be used as a marker to position the pipeline, and signal receiving can be completed without accurately aligning the direction, so that the use difficulty is reduced.
As a connection mode between the receiving antenna and the sensor, the plane antenna type passive wireless strain sensor 2 is a receiving antenna and does not need additional connection; as shown in fig. 4, the external surface acoustic wave passive wireless strain sensor 15 is connected in such a manner that the positive and negative electrodes of the receiving antenna are respectively connected with two electrodes of the cross transducer 10, which are mutually crossed.
As a specific embodiment, the sensor is attached to the outer surface of the nonmetallic pipeline to be tested by using an epoxy resin adhesive. Specifically, the passive wireless strain sensing system further comprises a non-metallic strap; the nonmetal binding band is used for binding and fixing the sensor after the epoxy resin adhesive is applied to the outer surface of the nonmetal pipeline to be tested and the outer surface of the nonmetal pipeline to be tested. Further, the width of the nonmetallic binding strip is consistent with the width of the sensor.
The invention provides a passive wireless strain detection system for a nonmetallic pipeline, which utilizes a resonance passive wireless strain sensor which does not contain a battery, a complex circuit and a wire connection to check the strain of a invisible and inaccessible nonmetallic pipeline. The sensor has a flexible substrate that can be attached to a nonmetallic tubing surface with a curvature. The sensor has a resonant frequency at which the conductivity of the sensor itself is maximized. The transmitter 1 of the wireless signal is located outside and provides energy to the sensor by generating a swept excitation signal around the resonant frequency of the sensor. The sensor reflects the signal back to the transmitter 1 such that the return loss coefficient or energy transfer coefficient measured by the transmitter 1 exhibits a characteristic peak signal at the excitation frequency of the sensor. The resonant frequency of the sensor changes with the deformation of the pipe, and the strain of the metal pipe can be identified according to the shift of the peak value of the resonant frequency.
The following describes a specific implementation of strain detection for nonmetallic pipelines using a planar antenna passive wireless strain sensor 2.
As shown in fig. 5, the planar antenna passive wireless strain sensor includes a base, a substrate, a reflecting surface, a matching line and an electronic tag chip; the substrate is arranged on the upper surface of the base; the reflecting surface, the matching wire and the electronic tag chip are arranged on the upper surface of the substrate; the matching line is connected with the reflecting surface; the electronic tag chip is arranged at the joint of the matching line and the reflecting surface; the reflection surface is used for receiving the excitation electromagnetic wave, obtaining energy according to the excitation electromagnetic wave, generating corresponding deformation when the nonmetal pipeline to be measured is deformed, and reflecting the excitation electromagnetic wave based on the deformation to obtain the measurement signal; the matching line is used for adjusting the resonant frequency of the reflecting surface and the return loss of the measuring signal; the electronic tag chip is configured to store the number of the sensor and send the sensor number to the transmitter when the energy is greater than an electronic tag activation threshold.
Firstly, the design of the planar antenna type passive wireless strain sensor 2 is carried out, the dimension design of the planar antenna type passive wireless strain sensor 2 is shown in fig. 5, and the resonance frequency is 1.2GHz. The substrate 5 is made of Low Density Polyethylene (LDPE), has high flexibility and can adapt to the curvature of various pipelines. The reflective surfaces 3 and the base on the upper and lower surfaces are made of gold, and are attached to both sides of the substrate 5 by surface deposition and etching. In order to ensure that the electrodes on two sides are prevented from being corroded by electrolyte in soil and worn by sand and stone, a protective coating layer is sprayed on the upper surface, the thickness is more than 50 microns, and the material is various polymer resins. The matching line 13 is added to adjust the resonant frequency and return loss of the planar antenna type passive wireless strain sensor 2. The match line 13 is a length of "L" shaped wire, the dimensions of which are varied to shift the resonant frequency. In particular, the resonant frequency of a planar antenna sensor is determined by all components on the sensor in common. In general, this resonance frequency is basically determined by determining the length and width of the square piece, but fine tuning is required to perform impedance matching, and the energy transfer efficiency is improved, so that the matching line 13 is increased. The electronic tag 12 is a generic RFID tag chip at the selected operating frequency, and is a small chip that can be viewed as a consumer with an impedance at its input and output. Which when connected to the sensor antenna will become part of the circuit and can be seen as a series element like a resistor and a capacitor. The portions other than the electronic tag can be regarded as a power source. When the impedance is matched, the port impedance (without the electronic tag) at the two ends of the electronic tag in the sensor is required to be the same as the real part and the imaginary part of the internal impedance of the electronic tag, so that the energy obtained by the electronic tag is maximized. The reflecting surface, the base 4, the substrate 5 and the matching line together act as a receiving antenna.
When the sensor antenna receives energy exceeding its lowest activation power, it returns information, such as the sensor number, etc., to the transmitter 1 for storage. Specifically explained below, the transmitter 2 sequentially transmits electromagnetic waves at different transmission powers at respective frequencies within the operating frequency band of the sensor 1, and if the energy received by the sensor 2 is sufficient to activate the electronic tag 12, the transmitter 2 will receive the modulated reflected waves; the controller marks the corresponding points of the frequency and the power as '1', otherwise marks as '0', scans in sequence to obtain a second-order matrix, and then extracts the envelope curve marked with '1', so as to obtain an energy transmission coefficient curve; the resonant frequency of the sensor 1 can be determined based on the peak position of the curve, as shown in fig. 6. The impedance of the tag is determined by the chip, and matching of the impedance needs to be completed by matching the matching line 13, so that the imaginary part of the planar antenna passive wireless strain sensor 2 approaches 0 at the working frequency, as shown in fig. 7. The specific method is that the model of the antenna is built by numerical simulation software, a voltage port is built at the electronic tag 12 and the port impedance is designated as its own impedance, and then the resonant frequency is adjusted to the target value by changing the length and width of the long and short arms of the matching line 13. Although theoretically, the electronic tag 12 is an unnecessary component, and in the absence of the component, the transmitter 2 can determine the change of the resonant frequency according to the measured change of the return loss coefficient curve of the transmitter, but the quality factor of the planar antenna passive wireless strain sensor 2 is low, and the dielectric property of the soil will promote the loss of the electromagnetic wave transmission process, so that the change of the return loss of the transmitter caused by the change of the resonant frequency of the sensor is very weak. The method for setting up the threshold power through the electronic tag can be matched with a high-power signal transceiver to directly find the frequency with highest energy acquisition efficiency of the buried sensor, namely the resonant frequency.
As shown in fig. 8, the antenna directivity of the planar antenna type passive wireless strain sensor 2 is such that the maximum gain in the +z direction is 5dBi when the antenna plane is in the XY plane. This shows that the signal strength is maximized when the transmitting antenna is located directly above the plane of the planar antenna type passive wireless strain sensor 2. Because the quality factor of the planar antenna type passive wireless strain sensor 2 is low, in order to improve the recognition distance of the characteristic signals, a high-directivity antenna such as a horn antenna, a yagi antenna and the like is adopted as the transmitting antenna.
Specifically, a PE pipeline with the diameter of 315mm which is common in natural gas transportation is taken as an application object, and the burial depth is 1 meter from the upper surface to the ground surface.
After the planar antenna type passive wireless strain sensor 2 is manufactured, the temperature and distance calibration is carried out. The temperature is the quantity that needs to be measured synchronously by the controller during the measurement process, and then the deformation of the sensor is estimated together according to the measured temperature and the resonance frequency. This is because the temperature will cause thermal expansion of the substrate 5, thereby changing the resonance frequency. In addition, due to the energy transmission law of the coupling system, when the planar antenna type passive wireless strain sensor 2 is close to the sensor, the wireless sensing distance will cause the change of the resonant frequency. Therefore, the influence of the calibrated temperature and distance on the resonant frequency of the planar antenna type passive wireless strain sensor 2 is required. The approximate rule is that the higher the temperature, the higher the resonant frequency; the closer the distance, the lower the resonant frequency.
Further, the calibration method of the planar antenna type passive wireless strain sensor 2 is that the planar antenna type passive wireless strain sensor 2 is attached to the surface of a sample of a detected pipeline, the sample is one end of the detected pipeline, the sample can be embedded into a test box filled with experimental soil, and the shell of the test box is made of a nonmetallic material to avoid electromagnetic wave reflection. The transmitting antenna is arranged outside the test box, is a certain distance away from the plane antenna type passive wireless strain sensor 2 and points to the sensor. When in calibration, the temperature is used as a first variable, the antenna distance is used as a second variable, the resonant frequency of the characteristic signal of the planar antenna type passive wireless strain sensor 2 is used as output, and the first variable or the second variable is sequentially changed to draw a three-dimensional calibration curved surface. Specifically, when the temperature variable is changed, the temperature variable can be realized by heating the experiment box in a laboratory environment or can be realized by naturally changing the air temperature in different time periods when the experiment box is placed in an open air environment.
Before installing the planar antenna passive wireless strain sensor 2, firstly removing impurities such as broken stone, dust and the like on the surface of the PE pipe; and then polishing the safety part on the surface right above the pipeline by using sand paper, and respectively polishing the safety part by using coarse sand paper and fine sand paper along an included angle of plus or minus 45 degrees with the trend of the pipeline so as to improve the connection between the curing agent and the pipeline.
When the planar antenna type passive wireless strain sensor 2 is installed, after an epoxy resin adhesive is coated on an installation position, the lower surface of the planar antenna type passive wireless strain sensor 2 is pressed on the surface of a pipeline, so that the whole structure of the sensor is bent and attached to the surface of the pipeline. The planar antenna passive wireless strain sensor 2 is then pressed against the pipe surface using a flexible nonmetallic strap having a width approximately equal to the width of the planar antenna passive wireless strain sensor 2, thereby curing the adhesive. If the construction side has no special requirement, the binding band does not need to be removed.
The change of the return loss of the sensor along with the deformation of the pipeline according to the numerical simulation result is shown in fig. 9. The solid line in the figure is S in the initial condition 11 Coefficient, peak at excitation frequency of 1.21GHz, ofI.e. the resonant frequency of the sensor. When the pipeline is subjected to 1% tensile deformation along the axial direction, the resonant frequency of the pipeline is reduced to 1.205GHz, and the resolution is 5 Hz/mu epsilon; when 1% compression set occurs, it rises to 1.218GHz.
During the inspection, the transmitter 1 may be carried by an inspection person or a ground inspection robot. When in use, the transmitter 1 is required to be close to the ground for sensor signal detection; if carried by the robot, the transmitter 1 is mounted at the bottom of the robot to maintain a distance from the ground. Specifically, the transmitting antenna adopts a directional antenna.
As shown in fig. 10, when the transmitting antenna enters the approximate sensing range of the signal of the planar antenna passive wireless strain sensor 2 and points to the approximate position, the transmitter 1 can receive the characteristic signal of the characteristic frequency band of the planar antenna passive wireless strain sensor 2, namely, the tag threshold curve representing the energy transmission between the transmitter 2 and the sensor 1. The sweep frequency range of the signal transceiver is more than 3 times of the characteristic signal bandwidth of the planar antenna type passive wireless strain sensor 2 by taking the characteristic frequency of the planar antenna type passive wireless strain sensor 2 as the center. The amplitude of the characteristic signal of the planar antenna type passive wireless strain sensor 2 can be changed by adjusting the direction of the transmitting antenna, and when the minimum activation power of the sensor reaches the minimum value, the direction of the planar antenna type passive wireless strain sensor 2 is the direction. The transmitter 1 is then translated in the determined direction and the amplitude of the characteristic signal of the planar antenna passive wireless strain sensor 2 will increase due to the decrease of the antenna spacing. At this time, the direction of the antenna needs to be determined again, and the global minimum of the characteristic peak value is found by the method repeatedly, and at this time, the plane antenna type passive wireless strain sensor 2 should be located right below the position pointed by the antenna, namely, the positions of the plane antenna type passive wireless strain sensor 2 and the pipeline.
Since the resonant frequency is affected by the sensor distance, the resonant frequency should be read after the characteristic signal reaches a maximum value and converted into a strain value according to calibration data. To read the strain value, it is necessary to measure the initial resonant frequency of the planar antenna-type passive wireless strain sensor 2 after the planar antenna-type passive wireless strain sensor 2 is installed and the planar antenna-type passive wireless strain sensor 2 is buried, and record the resonant frequency as strain equal to 0.
As shown in fig. 11, in the process of detecting a nonmetallic pipeline to be detected by using a passive wireless strain detection system for nonmetallic pipelines, a history log should be formed, the change of the resonant frequency at each detection is recorded, and the strain of the pipeline is calculated by the shift of the characteristic frequency. Specifically, when the strain change of the sensor is calculated from the resonance frequency, the following steps are divided. Firstly, a temperature sensor inside the controller is used for measuring the air temperature and presuming the temperature of the sensor buried depth in the soil, and an additional sensor can be added for temperature calibration, wherein the sensor structure is completely consistent with the strain sensor, but a buffer structure with thicker thickness and higher flexibility exists between the substrate 5 and the pipe wall, so that the strain and the temperature are decoupled. And secondly, according to a calibration result between the resonant frequency and the temperature, obtaining the offset of the resonant frequency at the temperature, wherein the higher the offset frequency is, the larger the deformation is. Finally, according to the geometric relation between the resonant frequency and the sensor, the deformation of the structure to be measured in the current thermal expansion is reversely pushed; more specifically, the resonance frequency of the sensor under the conditions of different deformation of the measured surface at each temperature can be obtained through finite element simulation. Further, at least two plane antenna type passive wireless strain sensors with electronic tags are used for detecting the nonmetallic pipelines to be detected; at least one plane antenna type passive wireless strain sensor with an electronic tag is attached to the outer surface of a nonmetallic pipeline to be detected, and the at least one plane antenna type passive wireless strain sensor with the electronic tag is not directly contacted with the nonmetallic pipeline to be detected; when the excitation electromagnetic wave emitted by the emitter enables the energy generated by the sensor to be larger than the activation threshold value of the electronic tag, the electronic tag in the plane antenna type passive wireless strain sensor with the electronic tag sends a sensor number to the emitter; the transmitter receives the measuring signals reflected by at least two plane antenna type passive wireless strain sensors with electronic labels and corresponding sensor numbers, and determines which sensor is used for measuring deformation and which sensor is used for eliminating errors according to the sensor numbers; because the sensor also generates deformation under a certain temperature condition, the measuring signals reflected by the sensor for measuring the nonmetallic pipeline to be detected comprise deformation generated by temperature and deformation of the nonmetallic pipeline to be detected, and the measuring signals reflected by the sensor which is not contacted with the nonmetallic pipeline to be detected are only deformation caused by temperature, so that data caused by temperature transformation in the measuring signals reflected by the sensor for measuring the nonmetallic pipeline to be detected can be eliminated, and more accurate deformation data of the nonmetallic pipeline to be detected can be obtained.
A specific implementation of strain detection for nonmetallic pipelines using the surface acoustic wave passive wireless strain sensor 15 is described below.
The resonance frequency of the surface acoustic wave passive wireless strain sensor 15 is 1.5GHz, and the piezoelectric sheet 9 is LiNbO 3 A film. The cross transducer 10 and the reflective grating 11 are gold electrodes. The detection object is a PE tube with the diameter of 315 mm. The design of the surface acoustic wave passive wireless strain sensor 15 is shown in fig. 12, which comprises a piezoelectric sheet 9 and a substrate 8 of the flexible surface acoustic wave passive wireless strain sensor 15, and two electrodes of the cross transducer 10 extend from the piezoelectric sheet 9 to a point on the substrate 8 of the surface acoustic wave passive wireless strain sensor 15 for connecting a sensing antenna; the hatched area is the housing 7 protecting the inner sensitive element. LiNbO 3 The wavelength at the resonance frequency of 1.5GHz is 2.7 μm. To excite the surface acoustic wave that propagates bi-directionally along the surface of the piezoelectric sheet 9, the following two conditions need to be satisfied. First, the adjacent electrode spacing is one quarter of the vibration wavelength, namely 67.5nm; second, the thickness of the piezoelectric sheet 9 is 3 times or more the wavelength, that is, more than 8.1 μm. The width of the cross transducer 10 is about 80 times the wavelength, i.e. 216 μm; the spacing between the cross transducer 10 and the reflective grating 11 is 100 times the wavelength, i.e. 270 μm. The number of electrodes of the cross transducer 10 and the reflective grating 11 is 3, for improving the resolution of the characteristic signal.
In particular, the sensing antenna is typically an omni-directional dipole antenna 6 to increase the direction of coverage of the signal, facilitating positioning of the surface acoustic wave passive wireless strain sensor 15. However, if the surface acoustic wave passive wireless strain sensor 15 can be accurately positioned, the antenna is replaced with a highly directional antenna, such as a horn antenna or the like. If the transmitting antenna is directional, the positioning flow of the plane antenna type passive wireless strain sensor 2 and the positioning flow of the surface acoustic wave type passive wireless strain sensor 15 are consistent; if the transmitting antenna is an omni-directional antenna, the step of adjusting the antenna direction is omitted in the positioning process, and the position is moved only.
In the processing process of the surface acoustic wave type passive wireless strain sensor 15, firstly, the shell 7 of the surface acoustic wave type passive wireless strain sensor 15 is processed by a laser etching method, the material of the shell is PMMA plastic, the maximum dimension of three sides is 30mm multiplied by 15mm multiplied by 1.5mm, and the radius of the intrados at the bottom is approximately equal to the curvature of the outer wall of the pipe wall by 3.2mm -1 . Thereafter, liNbO having a thickness of about 40 μm was obtained by polishing 3 The film is attached to the surface of a substrate 8 of a surface acoustic wave passive wireless strain sensor 15 made of PET plastic, wherein the surface acoustic wave passive wireless strain sensor is 30mm multiplied by 15mm multiplied by 500 mu m in size, and then the steps of spraying, photoetching, etching and the like are sequentially carried out through a microelectronic processing technology to process the lines of the electrode. The housing 7 not only serves as a seal, but also fixes the antenna, extending the service life of the surface acoustic wave passive wireless strain sensor 15.
When the surface acoustic wave passive wireless strain sensor 15 is mounted on the surface of a nonmetallic pipeline, the surface of the pipeline is firstly ground and sprayed with an adhesive. Thereafter, the substrate 8 with the surface acoustic wave sensor is attached to the pipe surface, and the flexible substrate 8 is bent. The rigid, concave-lower-surface housing 7 is then bonded to the curved substrate 8 by adhesive and the seam is sealed.
The positioning and signal acquisition procedure of the surface acoustic wave passive wireless strain sensor 15 is similar to that of the planar antenna type passive wireless strain sensor 2. If both the sensing antenna and the transmitting antenna are directional antennas, the method is the same as that of the planar antenna type passive wireless strain sensor 2. If the sensing antenna and the transmitting antenna are all omni-directional antennas, the procedure of adjusting the direction of the transmitting antenna can be omitted in the positioning process, and the operation procedure is simpler although the receiving distance is reduced. In addition, because such sensors have a high quality factor, the return loss coefficient curve of the transmitter can be measured directly at the transmitter end, which curve will produce sharp characteristic peaks at the resonant frequency after receiving the back-wave of the sensor.
Example two
In order to implement a system corresponding to the above embodiment to achieve the corresponding functions and technical effects, a passive wireless strain detection method for a nonmetallic pipeline is provided below, as shown in fig. 13, where the passive wireless strain sensing method includes:
Step S1: and acquiring an initial resonant frequency calibrated by the sensor and a strain value corresponding to the initial resonant frequency. In practical applications, the strain value corresponding to the initial resonance frequency is set to 0.
Step S2: and obtaining a reflection coefficient characteristic curve of the sensor, and determining the installation position of the sensor on the outer surface of the nonmetal pipeline to be measured according to the measurement signal and the initial resonant frequency. Specifically, the signal corresponding to the surface acoustic wave passive wireless strain sensor 15 is a return loss coefficient curve of the transmitter; the planar antenna passive wireless strain sensor 2 corresponds to the threshold curve required for sensor activation and also represents the energy transfer curve.
Step S3: and calculating the strain value of the outer surface of the measured nonmetallic pipeline at the installation position according to the frequency offset of the measuring signal transmitted by the sensor at the installation position and the strain value corresponding to the initial resonant frequency.
In addition, the passive wireless strain sensing method further comprises the following steps:
calibrating the sensor to obtain the relation between the resonant frequency of the sensor and the temperature and distance; the temperature is the temperature of the working environment of the sensor; the distance is a distance between the emitter and the sensor.
In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.
The principles and embodiments of the present invention have been described herein with reference to specific examples, the description of which is intended only to assist in understanding the methods of the present invention and the core ideas thereof; also, it is within the scope of the present invention to be modified by those of ordinary skill in the art in light of the present teachings. In view of the foregoing, this description should not be construed as limiting the invention.
Claims (10)
1. A passive wireless strain sensing system for a nonmetallic pipeline, characterized in that the passive wireless strain sensing system comprises a sensor, a transmitter, and a controller;
the transmitter is used for transmitting excitation electromagnetic waves with preset resonant frequency, receiving measurement signals reflected by the sensor and transmitting the measurement signals to the controller;
the sensor is attached to the outer surface of the nonmetal pipeline to be tested; the sensor is used for receiving the excitation electromagnetic wave, obtaining energy according to the excitation electromagnetic wave, generating corresponding deformation when the nonmetal pipeline to be measured is deformed, and reflecting the excitation electromagnetic wave based on the deformation to obtain the measurement signal;
The controller is used for determining the installation position of the sensor on the outer surface of the nonmetal pipeline to be measured according to the resonance frequency of the measurement signal and the initial resonance frequency calibrated by the sensor, and calculating the strain quantity of the nonmetal pipeline to be measured according to the frequency offset of the measurement signal emitted by the sensor at the installation position and the strain value corresponding to the initial resonance frequency calibrated by the sensor.
2. The passive wireless strain detection system for a non-metallic conduit of claim 1, wherein the transmitter comprises a signal transceiver and a transmit antenna;
the signal transceiver is used for generating excitation electromagnetic waves and receiving the measurement signals, and transmitting the measurement signals to the controller;
the transmitting antenna is connected with the signal transceiver; the transmitting antenna is used for transmitting the excitation electromagnetic wave.
3. The passive wireless strain detection system for non-metallic tubing of claim 2, wherein the transmitter further comprises a matching circuit;
the matching circuit is connected with the transmitting antenna; the matching circuit is used for adjusting the resonant frequency of the transmitting antenna so that the resonant frequency of the transmitting antenna is consistent with the resonant frequency of the sensor.
4. The passive wireless strain detection system for non-metallic pipes of claim 2, wherein the transmitting antenna is a directional antenna or an omni-directional antenna.
5. The passive wireless strain detection system for non-metallic conduit of claim 1, wherein the sensor is a planar antenna type passive wireless strain sensor or an external surface acoustic wave passive wireless strain sensor.
6. The passive wireless strain detection system for non-metallic conduit of claim 5, wherein the planar antenna passive wireless strain sensor comprises a base, a substrate, a reflective surface, a match line, and an electronic tag chip;
the substrate is arranged on the upper surface of the base; the reflecting surface, the matching wire and the electronic tag chip are arranged on the upper surface of the substrate; the matching line is connected with the reflecting surface; the electronic tag chip is arranged at the joint of the matching line and the reflecting surface;
the reflection surface is used for receiving the excitation electromagnetic wave, obtaining energy according to the excitation electromagnetic wave, generating corresponding deformation when the nonmetal pipeline to be measured is deformed, and reflecting the excitation electromagnetic wave based on the deformation to obtain the measurement signal;
The matching line is used for adjusting the resonant frequency of the reflecting surface and the return loss of the measuring signal;
the electronic tag chip is configured to store the number of the sensor and send the sensor number to the transmitter when the energy is greater than an electronic tag activation threshold.
7. The passive wireless strain detection system for non-metallic tubing as recited in claim 1, wherein the sensor is attached to the outer surface of the non-metallic tubing being tested using an epoxy adhesive.
8. The passive wireless strain detection system for a non-metallic conduit of claim 1, wherein the sensor comprises a substrate; the substrate is a flexible substrate.
9. A passive wireless strain detection method for a non-metallic pipe, applied to the passive wireless strain detection system for a non-metallic pipe of any one of claims 1 to 8, the passive wireless strain sensing method comprising:
acquiring an initial resonance frequency calibrated by a sensor and a strain value corresponding to the initial resonance frequency;
acquiring a reflected measurement signal of a sensor, and determining the installation position of the sensor on the outer surface of a nonmetal pipeline to be measured according to the measurement signal and the initial resonant frequency;
And calculating the strain value of the outer surface of the measured nonmetallic pipeline at the installation position according to the frequency offset of the measuring signal transmitted by the sensor at the installation position and the strain value corresponding to the initial resonant frequency.
10. The passive wireless strain detection method for a non-metallic conduit of claim 9, wherein the passive wireless strain sensing method further comprises:
calibrating the sensor to obtain the relation between the resonant frequency of the sensor and the temperature and distance; the temperature is the temperature of the working environment of the sensor; the distance is a distance between the emitter and the sensor.
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