Surface acoustic wave temperature sensor and cable joint temperature monitoring system

Abstract

The application provides a surface acoustic wave temperature sensor and a cable joint temperature monitoring system, the device comprises a reflective grating, a piezoelectric substrate, an interdigital transducer and an acoustic absorption part, the reflective grating, the interdigital transducer and the acoustic absorption part are attached to the piezoelectric substrate, the interdigital transducer is composed of two groups of staggered comb-shaped metal strips, is used for directly exciting and passively detecting a surface acoustic wave on a piezoelectric substrate material, the material of the piezoelectric substrate is EVA-PZT-metal nanoparticles, the piezoelectric substrate is used for realizing mutual conversion between an electric signal and a surface acoustic wave signal, a first sub-grating structure and a second sub-grating structure of the reflective grating are respectively arranged on the two sides of the interdigital transducer, are used for reflecting and superimposing a sound signal to form resonance, and the acoustic absorption part is arranged outside the reflective grating. The surface acoustic wave temperature sensor made of a flexible material can be placed in the cable joint, and the problem that the distributed optical fiber temperature measurement in the prior art cannot realize accurate monitoring of the temperature in the cable joint is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of temperature measurement, in particular to a surface acoustic wave temperature sensor and a cable joint temperature monitoring system. BACKGROUND

[0002] At present, the application of Internet of Things can greatly broaden the business scope of the existing power network, improve the safety and fault resistance of the power system, so the power department is committed to building an intelligent power system based on Internet of Things technology. However, the power Internet of Things is still in its early stages of development, and there are many deficiencies, especially the special high-voltage, strong electromagnetic field environment and structural characteristics of the power system equipment put forward strict requirements for monitoring equipment. For high-voltage cables, the joint is a key point of heat and fault hidden danger, so it is necessary to monitor the temperature of the cable joint in real time.

[0003] The traditional temperature measurement optical fiber is arranged outside the cable skin or shielding layer, cannot directly contact the conductor, cannot directly monitor the operating temperature state of the conductor core of the cable joint, can only monitor the temperature of the cable surface or the outside of the insulation layer, and cannot respond in time to the sharp change of the internal temperature of the cable joint, and the internal space of the cable joint is extremely small, which has strict requirements for the size of the sensor. In addition, the internal space of the cable joint is a strong electromagnetic field environment, the stability of the sensor cannot be guaranteed, and the electrical performance and operation reliability of the cable joint itself will also be affected. SUMMARY

[0004] The main purpose of the present application is to provide a surface acoustic wave temperature sensor and a cable joint temperature monitoring system to solve the problem that the distributed optical fiber temperature measurement in the prior art cannot realize real-time monitoring of the internal temperature of the cable joint.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a surface acoustic wave temperature sensor is provided, the surface acoustic wave temperature sensor comprises a reflective grating, a piezoelectric substrate, an interdigital transducer and an acoustic absorption part, the reflective grating has a first sub-grating structure and a second sub-grating structure, the reflective grating, the interdigital transducer and the acoustic absorption part are attached to the piezoelectric substrate, the first sub-grating structure and the second sub-grating structure are respectively arranged on both sides of the interdigital transducer, and the acoustic absorption part is arranged outside the reflective grating; wherein the material for preparing the piezoelectric substrate is ethylene-vinyl acetate copolymer added with PZT piezoelectric ceramic powder and nano-sized metal particles, and the surface acoustic wave temperature sensor is used for monitoring the temperature inside the cable joint.

[0006] Further, the surface acoustic wave temperature sensor is arranged outside the conductor connecting pipe of the cable joint, and the surface acoustic wave temperature sensor is clamped between the inner insulation layer of the cable joint and the conductor connecting pipe.

[0007] Further, the interdigital transducer is composed of two groups of staggered comb-shaped metal strips, the plurality of bars of the reflection grating are parallel, and the bars of the reflection grating are parallel to the comb-shaped metal strips of the interdigital transducer.

[0008] According to another aspect of the present application, a cable joint temperature monitoring system is also provided, which comprises any one of the surface acoustic wave temperature sensors, the surface acoustic wave temperature sensor is installed in the cable joint; the cable joint temperature monitoring system comprises a signal transmitting and receiving device and a signal processor, the signal transmitting and receiving device is installed in the surrounding area of the surface acoustic wave temperature sensor, and is used for transmitting a radio frequency signal and collecting an echo signal of the surface acoustic wave temperature sensor; the signal processor is electrically connected with the signal transmitting and receiving device, and is used for determining the temperature in the cable joint according to the echo signal.

[0009] Further, the signal processor comprises: a sweep signal generator, which is used for generating a sweep signal; a signal modulator, which is electrically connected with the sweep signal generator, and is used for modulating the sweep signal to obtain a modulated sweep signal; a first signal filter, which is electrically connected with the signal modulator, and is used for filtering the modulated sweep signal; and a first signal amplifier, which is electrically connected with the first signal filter and the signal transmitting and receiving device respectively, and is used for amplifying the filtered modulated sweep signal.

[0010] Further, the signal processor comprises: a second signal amplifier, which is electrically connected with the signal transmitting and receiving device, and is used for amplifying the echo signal received by the signal transmitting and receiving device; a second signal filter, which is electrically connected with the second signal amplifier, and is used for filtering the amplified echo signal to obtain a filtered echo signal; and a signal demodulator, which is electrically connected with the second signal filter, and is used for demodulating the filtered echo signal.

[0011] Further, the signal processor further comprises: a power divider, which is electrically connected with the signal demodulator.

[0012] Further, the cable joint temperature monitoring system comprises: a positioner, which is in communication with the signal processor, and is installed on the cable joint, and is used for acquiring position information of the cable joint.

[0013] Further, the positioner comprises a Bluetooth positioning module and a UWB positioning module.

[0014] Further, the cable joint temperature monitoring system further comprises: a host computer, which is in communication with the signal processor, and is used for monitoring the temperature in the cable joint in real time.

[0015] The technical scheme of the application is applied to directly stimulate and passively detect the acoustic surface wave on the piezoelectric substrate material through the interdigital transducer, reflect and stack the acoustic signals to form resonance through the reflection grating, return the attenuation oscillation signal with the resonance frequency as the main frequency, and output the signal through the interdigital transducer, and use the EVA-PZT-metal nanoparticle as the base material of the piezoelectric substrate. The large piezoelectric coefficient of the PZT can ensure that the material has both flexibility and piezoelectric performance. When the surrounding environment of the sensor changes, the resonance frequency of the sensor also changes, and the echo signal of the sensor also changes accordingly. Therefore, the change of the monitored parameter can be accurately obtained by analyzing the frequency, amplitude and other information of the echo signal, thereby solving the problem that the distributed optical fiber temperature measurement in the prior art cannot monitor the temperature inside the cable joint. BRIEF DESCRIPTION OF DRAWINGS

[0016] The accompanying drawings, which form a part of the present description, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the present application, and their

[0017] Figure 1 A structure schematic diagram of a surface acoustic wave sensor according to an embodiment of the present application is shown.

[0018] Figure 2 A structure schematic diagram of an interdigital transducer according to an embodiment of the present application is shown.

[0019] Figure 3 A structure schematic diagram of an EVA-PZT-metal nanoparticle according to an embodiment of the present application is shown.

[0020] Figure 4 A schematic diagram of a cable joint monitoring system according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0021] It should be noted that the following detailed description is illustrative only, and is intended to provide further description in order to provide a further understanding of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0022] It should be noted that the terms used herein are only intended to describe specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in the specification, they refer to the presence of a feature, step, operation, device, component and / or combination thereof.

[0023] It will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements can also be present. In addition, it will be understood that when an element is referred to as being "connected" to another element, it can be "directly connected" to the other element or "connected" to the other element through a third element.

[0024] For the convenience of description, part of the nouns or terms related to the embodiments of the present application are described as follows:

[0025] PZT: PbZrO3 and PbTiO3 solid solution.

[0026] IDT (Interdigital transducer): refers to a metal pattern formed on a piezoelectric substrate in the shape of a finger cross like two hands.

[0027] As mentioned in the background, the temperature measuring optical fiber in the prior art can only be arranged outside the cable skin or shielding layer, cannot directly contact the conductor, cannot directly monitor the operating temperature state of the conductor core of the cable joint, can only monitor the temperature condition outside the cable surface or the insulation layer, and cannot make a timely response to the sharp change of the internal temperature of the cable joint. In order to solve the problem that the real-time monitoring of the internal temperature of the cable joint cannot be realized by the distributed optical fiber temperature measurement in the prior art, in a typical embodiment of the present application, a surface acoustic wave temperature sensor and a cable joint temperature monitoring system are provided.

[0028] According to the embodiments of the present application, a surface acoustic wave temperature sensor is provided. As shown in Figure 1 The surface acoustic wave temperature sensor includes a reflective grating, a piezoelectric substrate, an interdigital transducer, and an acoustic absorption part. The reflective grating has a first sub-grating structure and a second sub-grating structure. The reflective grating, the interdigital transducer, and the acoustic absorption part are attached to the piezoelectric substrate. The first sub-grating structure and the second sub-grating structure are respectively arranged on both sides of the interdigital transducer. The acoustic absorption part is arranged outside the reflective grating. The material for preparing the piezoelectric substrate is ethylene-vinyl acetate copolymer added with PZT piezoelectric ceramic powder and nano metal particles. The surface acoustic wave temperature sensor is used for monitoring the temperature inside the cable joint.

[0029] As shown in Figure 2 The temperature measuring principle of the surface acoustic wave temperature sensor is that when the resonant type surface acoustic wave sensor is affected by temperature, the piezoelectric substrate expands and contracts with heat and causes deformation, which changes the propagation speed of the surface acoustic wave and the pitch p of the reflective grating, thereby changing the resonant frequency. The specific formula is as follows:

[0030]

[0031]

[0032] Since the temperature change has little effect on the reflection grating pitch, formula 2 can be simplified as:

[0033]

[0034] The relationship between the surface acoustic wave propagation rate and temperature is as follows:

[0035] ν(T) = ν(T0) + α(T - T0) (formula 4)

[0036] By combining formula 3 and formula 4, the relationship between frequency and temperature is as follows:

[0037]

[0038] In the formula, TCF represents the frequency temperature coefficient of the sensor.

[0039] Specifically, an intermittent sinusoidal pulse signal is currently commonly used as an excitation signal for a resonant surface acoustic wave sensor, because the echo signal is an intermittent sinusoidal signal obtained by long-time action of the reflection grating. When the transmission frequency is close to the natural resonance frequency, the superposition of multiple echo signals can make the energy of the output signal much stronger than that of the output signal when the impact pulse input is used. Therefore, under the same transmission and reception conditions, this method can achieve a longer wireless sensing distance. The signal can be represented as:

[0040] x(t) = A0cos(2πf0) (formula 6)

[0041] In the formula, A0 is the amplitude of the sinusoidal wave, and f0 is the frequency of the sinusoidal wave.

[0042] Specifically, within a period of an intermittent sinusoidal signal, when the frequency of the transmitted sinusoidal signal is equal to the resonance frequency of the sensor, the transient output signal of the sensor will be a decaying oscillation signal with the same oscillation frequency f0 and the decay time constant τ. The transient output signal can be represented as:

[0043]

[0044] Specifically, when the ambient temperature changes, the resonance frequency of the sensor will also change accordingly. Let the resonance frequency of the sensor deviate from the frequency of the transmitted excitation signal be f = |f1-f0|, and the transient signal output at this time is:

[0045]

[0046] y'(t) is the output signal after the high-frequency carrier signal is amplitude modulated by the baseband modulation signal, B(t) is a low-frequency baseband modulation signal, that is, the envelope waveform of the output signal, and the frequency thereof reflects the difference (frequency difference) between the excitation signal frequency and the current resonant frequency of the sensor. Only the frequency of the envelope signal of the output signal needs to be measured, and then the resonant frequency under the current temperature condition can be calculated through the above formula, and then the measured temperature information can be obtained by using formula 5, so as to achieve the purpose of temperature measurement.

[0047] Specifically, the above-mentioned reflective grating is an array of reflective elements on the surface of the surface acoustic wave sensor. The above-mentioned reflective grating is composed of a plurality of grating strips arranged on both sides of the above-mentioned interdigital transducer and parallel to the transducer. Although each reflective grating strip has only a small reflectivity, a large number of equidistantly arranged reflective grating strips will confine the surface acoustic wave therein and reflect it back and forth. The reflective effect of the reflective grating composed of a plurality of reflective grating strips will also be superimposed. The reflective grating strip mainly has the following two classification methods. According to the different structures, the reflective grating strip can be divided into short-circuit grating strip and open-circuit grating strip. The short-circuit grating strip is connected in structure, and the open-circuit grating strip is isolated in structure. According to the different materials, the reflective grating strip can be divided into reflective metal strip and reflective groove. Among them, the groove reflective grating has good performance, but the metal reflective grating is easy to realize.

[0048] Specifically, the piezoelectric substrate material in the surface acoustic wave device plays two main roles: one is to complete the mutual conversion between the electrical signal and the surface acoustic wave signal by realizing the mutual coupling between the electrical energy and the mechanical energy in the form of surface acoustic wave; the other is to serve as a carrier for the propagation of surface acoustic wave. If the piezoelectric substrate material of the surface acoustic wave has excellent electromechanical conversion efficiency, it is beneficial for the surface acoustic wave mode to have good stability in different application environments. The performance of the finally prepared surface acoustic wave device is directly affected by the quality and performance of the piezoelectric substrate material. Temperature coefficient, electromechanical coupling coefficient (K2), propagation loss and surface acoustic wave propagation speed are very important physical parameters of the piezoelectric substrate material of the surface acoustic wave in the application of the surface acoustic wave device.

[0049] Specifically, the reasons why the above-mentioned EVA-PZT-metal nanoparticles are used as the base material of the piezoelectric substrate are as follows: (1) EVA is a high polymer material, which is acceptable in cost as an industrialized raw material; (2) it has sufficient flexibility, and its Young's modulus is 42 MPa (for comparison, the Young's modulus of the commonly used polyimide Pi material is 2.5 GPa, and the Young's modulus of aluminum is 70 Gpa), so it is soft enough to be used as a flexible substrate material; (3) it can be used as an adhesive, so it can be well bonded with the outer packaging material and the interdigital transducer (IDT), improving the mechanical reliability of the whole device.

[0050] Specifically, as shown in FIG. 6, the surface acoustic wave sensor is composed of a piezoelectric substrate 1, an interdigital transducer (IDT) 2, an outer packaging material 3 and a reflective grating 4. Figure 3As shown, the reason for selecting PZT ceramic is that PZT ceramic is a material with a large piezoelectric coefficient, which can increase the piezoelectric coefficient of the PZT-EVA composite material. The piezoelectric effect of PZT piezoelectric ceramic is used to generate the separation of electric charges. After the separation of electric charges, the electric field is localized and amplified under the quantum (nano) effect of metal nanoparticles. The surface acoustic wave temperature sensor measures the temperature based on the piezoelectric effect.

[0051] By applying the technical solution of the present application, the surface acoustic wave is directly excited on the piezoelectric substrate material by the interdigital transducer and is passively monitored, then the acoustic signal is reflected and superimposed by the reflection grating to form resonance, the return signal with the resonance frequency as the main frequency is output by the IDT, and the EVA-PZT-metal nanoparticle is used as the base material of the piezoelectric substrate. The large piezoelectric coefficient of PZT can ensure that the material has both flexibility and piezoelectric performance. When the surrounding environment of the sensor changes, the resonance frequency of the sensor also changes, and at the same time, the echo signal of the sensor also changes accordingly. Therefore, the change of the monitored parameter can be accurately obtained by analyzing the frequency, amplitude and other information of the echo signal, thereby solving the problem that the distributed optical fiber temperature measurement cannot accurately monitor the temperature inside the cable joint in the prior art. In the embodiment, the surface acoustic wave temperature sensor is arranged outside the conductor connecting pipe of the cable joint, and the surface acoustic wave temperature sensor is clamped between the inner insulating layer and the conductor connecting pipe of the cable joint. The surface of the surface acoustic wave temperature sensor is also covered with a protective layer.

[0052] By applying the technical solution of the present application, the conductor temperature inside the contact cable joint can be directly measured. Moreover, since the material is flexible, the internal space of the surface wave temperature sensor is small, which ensures complete sealing and excellent composite interface electrical performance. The internal structure of the cable intermediate joint is compact, and electromagnetic interference is avoided due to the thick insulating layer and the inner and outer shielding structures.

[0053] In an embodiment of the present application, the interdigital transducer is composed of two groups of staggered comb-shaped metal strips, the multiple strips of the reflection grating are parallel, and the strips of the reflection grating are parallel to the comb-shaped metal strips of the interdigital transducer.

[0054] Specifically, as shown in Figure 2 two groups of interdigital transducer electrodes are connected to bus bars (buses), where a is the interdigital width, p is the pitch, and the ratio of a to p η=a / p is called the metallization rate W is the aperture of the transducer. The aperture W, the interdigital width a and the finger pitch p are all constants. The uniform transducer refers to an IDT with constant metallization rate η, which has constant interdigital width a and finger pitch p. The weighted transducer refers to an IDT in which the geometric parameters a, p or W change with the coordinates. Among them, the uniform transducer is the most basic and simplest IDT.

[0055] Specifically, when an alternating voltage Vt is applied to the above-mentioned interdigital transducer, an electric field distribution generated around the interdigital transducer is constituted in a period of the interdigital transducer interval (2p). The newly generated electric field distribution causes the surface of the piezoelectric substrate material to deform elastically accordingly, and the solid particles begin to vibrate. The inverse piezoelectric effect occurs in the interdigital transducer, and the mechanical energy is converted into an electric signal. Finally, the elastic wave in the form of a surface acoustic wave is transmitted from the end of the transducer. When the surface acoustic wave reaches the other end of the piezoelectric substrate material, the piezoelectric effect occurs in the interdigital transducer, and the electric charge is induced between the two metal electrodes. The conversion from the surface acoustic wave signal to the electric signal occurs and is outputted to the outside through the output interdigital transducer. When the interdigital transducer excites the acoustic wave, it presents a column of ultrasonic wave sources. The surface acoustic wave excited by each pair of fingers will be superimposed according to the wave interference principle. Finally, the ideal surface acoustic wave excited by the two electrodes of the interdigital transducer will present the phenomenon of in-phase superposition enhancement. This can only be obtained when the interdigital transducer finger interval p is equal to an integer multiple of the half wavelength (λ0 / 2) of the surface acoustic wave. At this time, the following relationship exists:

[0056]

[0057] Specifically, when K = 1, the natural frequency of the resonator itself is equal to or close to the frequency of the external excitation signal, and the emitted acoustic wave is the strongest. At this time, the following relationship exists:

[0058] f0 = v s / 2p (Formula 10)

[0059] wherein vs is the wave velocity of the surface acoustic wave on the piezoelectric material, and f0 is the acoustic synchronization frequency or the resonant frequency of the interdigital transducer. In the above-mentioned scheme, the two groups of interlaced distribution of the comb-shaped metal strips in the interdigital transducer make it have the frequency selection characteristic. When the surface acoustic wave velocity vs is constant, the IDT finger interval is reduced, and then the acoustic wave frequency determined by the IDT structure will increase. Conversely, when the frequency of the surface acoustic wave received by the output interdigital transducer is equal to the acoustic synchronization frequency of the interdigital transducer, the effect of the converted electric signal is also the most ideal.

[0060] The embodiments of the present application also provide a cable joint temperature monitoring system, as shown in Figure 4 FIG. 1, the system comprises any one of the above-mentioned surface acoustic wave temperature sensors, the above-mentioned surface acoustic wave temperature sensor is installed in the inside of the cable joint; a signal transmitting and receiving device is installed in the surrounding area of the above-mentioned surface acoustic wave temperature sensor, for emitting a radio frequency signal and collecting a return wave signal of the above-mentioned surface acoustic wave temperature sensor; a signal processor is electrically connected with the above-mentioned signal transmitting and receiving device, for determining the temperature in the inside of the cable joint according to the above-mentioned return wave signal.

[0061] Specifically, the signal transmitting and receiving device includes a transmitter and a receiver.

[0062] Specifically, the signal transmitting and receiving device includes a SAW tag installed in a high-voltage cable intermediate joint as a monitoring node, used to complete extraction of environmental characteristic parameter information of the high-voltage cable intermediate joint, and realize data interaction with the sweep signal generator through wireless radio frequency communication. The sweep signal generator transmitting link transmits an electromagnetic signal of a specific frequency and amplitude as the SAW tag challenge signal source within a certain time, the sweep signal generator receiving link receives an electromagnetic feedback signal with characteristic parameter information reflected from the SAW tag, and simultaneously interconnects with a data processing module to complete signal demodulation and temperature information extraction, thereby realizing real-time monitoring of the temperature of the high-voltage cable intermediate joint. The model of the interactive host computer software is built based on PYQT, and the functions are realized by python programs. The temperature of the cable intermediate joint can be seen above. In the above scheme, by installing the surface wave temperature sensor inside the cable joint, the temperature inside the cable joint can be well monitored, and the signal processor and the signal transmitting and receiving device are electrically connected to accurately determine the temperature inside the cable joint.

[0063] In an embodiment of the present application, as shown in Figure 4 The signal processor includes a sweep signal generator, a signal modulator, a first signal filter, and a first signal amplifier. The sweep signal generator is used to generate a sweep signal; the signal modulator is electrically connected to the sweep signal generator and is used to modulate the sweep signal to obtain a modulated sweep signal; the first signal filter is electrically connected to the signal modulator and is used to filter the modulated sweep signal; and the first signal amplifier is electrically connected to the first signal filter and the signal transmitting and receiving device respectively and is used to amplify the filtered modulated sweep signal. Specifically, the first signal filter is a band-pass filter.

[0064] Specifically, the sweep signal generator can select a step frequency continuous wave (SFCW) as the sweep signal generator challenge signal. Compared with the common linear frequency continuous wave (LFCW), the SFCW has lower linearity requirement and overcomes the disadvantage of being unable to realize multi-target monitoring. Compared with the common frequency shift keying (FSK) signal generation, the SFCW has faster response speed and thus improves the real-time performance.

[0065] Specifically, the above-mentioned sweep signal generator can also use AD9850 as a sweep signal generator chip, directly outputting 10MHz-12MHz step frequency modulation signals, wherein the step frequency is 500k Hz, according to the Nyquist sampling theorem. The reference signal obtains the discrete digital sequence of the synthesized signal through the data input register and the frequency / phase register in the chip, and the analog output and square wave output of the synthesized signal can be obtained by using the self-provided high-performance DAC and high-speed comparator. Specifically, the above-mentioned sweep signal generator can also use MSP430G2211 chip as the main control chip (MCU) of AD9850 for serial input tuning word, and the integrated development environment is CCS. The 40-bit control word data is stored in the D39-D0 register, wherein D39-D35 is the phase control word register, D34 is the power control word register, D33-D32 is the control word input mode register, and D31-D0 is the frequency control word register. In the design, only four general digital I / O pins of the MCU are connected with the WCLK, RESET, FQUD and D7 pins of the AD9850 respectively.

[0066] Specifically, the above-mentioned sweep signal generator can generate SFCW software to first initialize the system, reset all I / O ports, and determine the rationality of the input control word data. Secondly, the data conversion is carried out according to the frequency and phase parameters input by the user, the address chip selection signal is sent out and written into the corresponding register address, and finally the data of the specified number of bits is written to generate the analog sinusoidal signal corresponding to the parameters.

[0067] Specifically, ADF4350 is used as a PLL chip, and AMS1117-3.3 is used as a power supply chip. The PLL chip integrates PD and low phase noise VCO internally, the internal register is controlled through a three-wire interface, combined with an external loop filter and a reference crystal oscillator, a fractional N frequency divider or an integer N frequency divider frequency synthesizer can be realized, and a 305MHz single-frequency sinusoidal signal can be directly output. Among them, the reference signal is input by INREF, enters the 2-time frequency multiplier, 10-bit R frequency divider and 2-time frequency divider, and then enters the PD, and after the phase comparison with the VCO output signal, an error voltage signal is generated. The error voltage signal is output from the charge pump port pin CPOUT and introduced into the external loop filter port VTUNE to become a tuning voltage to control the VCO output frequency. The output signal of the VCO is fed back to the PD and repeatedly compared with the reference signal to make the difference tend to a constant value, forcing the VCO output signal to change to the corresponding frequency, and using this closed-loop feedback system to achieve the purpose of stable signal frequency.

[0068] In a specific embodiment, as Figure 4As shown in the figure, the signal processor comprises: a second signal amplifier electrically connected with the signal transmitter-receiver, for amplifying the echo signal received by the signal transmitter-receiver; a second signal filter electrically connected with the second signal amplifier, for filtering the amplified echo signal to obtain a filtered echo signal; and a signal demodulator electrically connected with the second signal filter, for demodulating the filtered echo signal. Specifically, the second signal filter is a band-pass filter.

[0069] In some specific embodiments, as shown in the figure, the signal after demodulation by the signal demodulator is filtered by a low-pass filter, and then used for subsequent data sampling and uploaded to the host computer. Figure 4

[0070] In some specific embodiments, as shown in the figure, the signal after demodulation by the signal demodulator is filtered by a low-pass filter, and then used for subsequent data sampling and uploaded to the host computer. Figure 4

[0071] Specifically, the cable joint monitoring system comprises a locator in communication with the signal processor, installed on the cable joint, for obtaining position information of the cable joint.

[0072] Specifically, the locator comprises a Bluetooth positioning module and a UWB positioning module. In the receiving end, the signal received by the UWB antenna is amplified by a low-noise amplifier and then sent to one input end of a correlator, and a locally generated pulse sequence modulated by a user pseudo-random code synchronized with the transmitting end is added to the other input end of the correlator. The received signal and the locally synchronized pseudo-random code modulated pulse sequence are subjected to multiplication, integration and sample-and-hold operations in the correlator to generate a signal separated from the user address information, which only contains user transmission information and other interference. Then, the signal is subjected to demodulation operation.

[0073] Specifically, the locator can be composed of a workbench and a cable monitoring device built-in Bluetooth and uwb modules. Bluetooth technology is actually a short-range wireless communication technology. In simple terms, Bluetooth technology enables modern mobile communication devices and computer devices that are easy to carry to be connected without the aid of cables, and can realize wireless Internet access. Its actual application range can also be extended to various information home appliances, consumer electronics products and automobiles, etc. to form a huge wireless communication network.

[0074] ​​Specifically, Ultra-Wide Broadband (UWB) technology is a wireless carrier communication technology that uses frequency bandwidths above 1 GHz. It does not employ sinusoidal carriers but instead uses nanosecond-level non-sinusoidal narrow pulses to transmit data, thus occupying a large spectrum. Although it uses wireless communication, its data transmission rate can reach hundreds of megabits per second or more. UWB technology can transmit signals over a very wide bandwidth; the US Federal Communications Commission (FCC) stipulates that UWB technology should occupy a bandwidth of at least 500 MHz in the 3.1–10.6 GHz band. UWB is essentially a carrierless spread spectrum technology that uses impulse pulses with very low duty cycles as information carriers. It achieves this by directly modulating impulse pulses with very steep rise and fall times. Typical UWB directly transmits impulse pulse trains, eliminating the traditional concepts of intermediate frequency (IF) and radio frequency (RF). The transmitted signal can be considered both a baseband signal (in conventional radio terms) and an RF signal (considering the spectral components of the transmitted signal). The impulse pulses are typically single-cycle Gaussian pulses, and one information bit can be mapped to hundreds of such pulses. A single-cycle pulse has a width on the nanosecond scale and a wide spectrum. UWB has developed a new wireless channel with gigahertz capacity and the highest spatial capacity. A CDMA-based UWB pulse transceiver generates a pulse sequence with a certain repetition period at the transmitting end. The information to be transmitted by the user and a pseudo-random code representing the user's address are modulated in a certain way, either separately or by combining them. The modulated pulse sequence drives a pulse generation circuit to form a pulse sequence with a certain pulse shape and pattern, which is then amplified to the required power and coupled to the UWB antenna for transmission. At the receiving end, the signal received by the UWB antenna is amplified by a low-noise amplifier and sent to one input of a correlator. A locally generated pulse sequence modulated by the user's pseudo-random code, synchronized with the transmitting end, is added to the other input of the correlator. The received signal and the locally synchronized pseudo-random code-modulated pulse sequence undergo multiplication, integration, and sample-and-hold operations in the correlator to generate a signal that separates the user address information, containing only the user's transmitted information and other interference. This signal is then demodulated.

[0075] Specifically, the aforementioned locator utilizes these two technologies to integrate a Bluetooth + UWB module into the work radio and cable monitoring device. The UWB end of the monitoring device is normally in sleep mode. Once the Bluetooth connection between the radio and the monitoring device is established, the real-time ranging and search function can be activated by operation. The UWB then starts ranging, and the radio displays the real-time distance to the corresponding monitoring device and provides simple directional guidance.

[0076] In one embodiment of this application, such as Figure 4 As shown, the cable joint monitoring system also includes a host computer that communicates with the signal processor to monitor the temperature inside the cable joint in real time.

[0077] It is to be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, components, and / or groups thereof, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof.

[0078] From the above description, it can be seen that the above-mentioned embodiments of the present application achieve the following technical effects:

[0079] 1) The acoustic surface wave temperature sensor of the present application directly excites and passively monitors the acoustic surface wave on the piezoelectric substrate material through the interdigital transducer, then reflects and superimposes the acoustic signal through the reflection grating to form resonance, returns the decay oscillation signal with the resonance frequency as the main frequency, and outputs by the IDT, and uses EVA-PZT-metal nanoparticles as the base material of the piezoelectric substrate. The large piezoelectric coefficient of PZT can ensure that the material has both flexibility and piezoelectric performance. When the surrounding environment of the sensor changes, the resonance frequency of the sensor also changes, and at the same time, the echo signal of the sensor also changes accordingly. Therefore, the change of the monitored parameter can be accurately obtained by analyzing the frequency, amplitude, etc. of the echo signal, thereby solving the problem that the distributed optical fiber temperature measurement in the prior art cannot accurately monitor the temperature inside the cable joint.

[0080] 2) The cable joint monitoring system of the present application has the following technical effects by using the acoustic surface wave temperature sensor: directly measuring the temperature of the conductor inside the contact cable joint; the internal space is small, which ensures complete sealing and excellent composite interface electrical performance, the internal structure of the cable intermediate joint is compact; it has a relatively thick insulation layer and an inner and outer shielding structure; it ensures complete sealing and excellent composite interface electrical performance, and is installed in a fully sealed manner; the service life is up to 30 years, it works normally during the whole service life of the cable system, and the change of the monitored parameter can be accurately obtained by analyzing the frequency, amplitude, etc. of the echo signal, thereby solving the problem that the distributed optical fiber temperature measurement in the prior art cannot accurately monitor the temperature inside the cable joint.

[0081] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various changes and modifications to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A surface acoustic wave temperature sensor, characterized by, The acoustic surface wave temperature sensor comprises a reflective grating, a piezoelectric substrate, an interdigital transducer and a sound absorption part, the reflective grating has a first sub-grating structure and a second sub-grating structure, the reflective grating, the interdigital transducer and the sound absorption part are attached to the piezoelectric substrate, the first sub-grating structure and the second sub-grating structure are arranged on the two sides of the interdigital transducer respectively, and the sound absorption part is arranged on the outer side of the reflective grating. The material for preparing the piezoelectric substrate is ethylene-vinyl acetate copolymer added with PZT piezoelectric ceramic powder and nano metal particles, and the acoustic surface wave temperature sensor is used for monitoring the temperature inside the cable joint. The acoustic surface wave temperature sensor is arranged outside the conductor connecting pipe of the cable joint, and the acoustic surface wave temperature sensor is clamped between the inner insulation layer of the cable joint and the conductor connecting pipe.

2. The surface acoustic wave temperature sensor of claim 1, wherein, The interdigital transducer is composed of two groups of staggered comb-shaped metal strips, the plurality of grating bars of the reflective grating are parallel, and the grating bars of the reflective grating are parallel to the comb-shaped metal strips of the interdigital transducer.

3. The surface acoustic wave temperature sensor according to claim 1 or 2, characterized in that, The acoustic surface wave temperature sensor comprises a reflective grating, a piezoelectric substrate, an interdigital transducer and a sound absorption part, the reflective grating has a first sub-grating structure and a second sub-grating structure, the reflective grating, the interdigital transducer and the sound absorption part are attached to the piezoelectric substrate, the first sub-grating structure and the second sub-grating structure are arranged on the two sides of the interdigital transducer respectively, and the sound absorption part is arranged on the outer side of the reflective grating.

4. A cable joint temperature monitoring system characterised in that, The acoustic surface wave temperature sensor is arranged outside the conductor connecting pipe of the cable joint, and the acoustic surface wave temperature sensor is clamped between the inner insulation layer of the cable joint and the conductor connecting pipe. The interdigital transducer is composed of two groups of staggered comb-shaped metal strips, the plurality of grating bars of the reflective grating are parallel, and the grating bars of the reflective grating are parallel to the comb-shaped metal strips of the interdigital transducer. The acoustic surface wave temperature sensor comprises a reflective grating, a piezoelectric substrate, an interdigital transducer and a sound absorption part, the reflective grating has a first sub-grating structure and a second sub-grating structure, the reflective grating, the interdigital transducer and the sound absorption part are attached to the piezoelectric substrate, the first sub-grating structure and the second sub-grating structure are arranged on the two sides of the interdigital transducer respectively, and the sound absorption part is arranged on the outer side of the reflective grating. The signal processor comprises:

5. The cable joint temperature monitoring system of claim 4, wherein, The signal processor comprises: The signal processor comprises: The signal processor further comprises: The cable joint temperature monitoring system comprises: The cable joint temperature monitoring system further comprises:

6. The cable joint temperature monitoring system of claim 4, wherein, The cable joint temperature monitoring system further comprises: ​ ​ ​ 7. The cable joint temperature monitoring system of claim 6, wherein, ​ ​ 8. The cable joint temperature monitoring system of any one of claims 4 to 7, wherein, ​ ​ 9. The cable joint temperature monitoring system of claim 8, wherein, ​ 10. The electrical cable joint temperature monitoring system of any one of claims 4 to 7, wherein, ​ ​

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