CN103884447A - SAW sensing method based on combination of code division multiple access and OFC coding - Google Patents
SAW sensing method based on combination of code division multiple access and OFC coding Download PDFInfo
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- CN103884447A CN103884447A CN201410073651.3A CN201410073651A CN103884447A CN 103884447 A CN103884447 A CN 103884447A CN 201410073651 A CN201410073651 A CN 201410073651A CN 103884447 A CN103884447 A CN 103884447A
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Abstract
The invention provides an SAW sensing method based on the combination of code division multiple access and OFC coding. The method includes the steps that a reader transmits an inquiry signal to an acoustic surface wave sensor through a broadband antenna, the acoustic surface wave sensor receives an OFC signal by means of a single interdigital transducer according to triggering of the inquiry signal and converts the OFC signal into an acoustic surface wave signal, the acoustic surface wave signal is reflected by a frequency orthogonal reflecting grating chip set and forms an echo signal through the single interdigital transducer, the reader receives the echo signal through the broadband antenna, the reader carries out lower linear frequency modulation on the echo signal, and the reader carries out temperature monitoring according to the echo signal after lower linear frequency modulation. According to the long-distance, multi-point-connection and anti-interference acoustic surface wave wireless sensor method based on the combination of orthogonal frequency and code division multiplexing coding, the near-far effect of a passive sensor system of code division multiplexing coding is eliminated, and requirements of an intelligent power grid for power equipment temperature wireless monitoring can be met.
Description
Technical field
The present invention relates to the temperature monitoring field of power equipment, particularly, relate to the SAW method for sensing combining of encoding based on CDMA and OFC.
Background technology
In the numerous monitoring variables of power equipment state monitoring, temperature is one of the most key detection limit.By temperature monitoring, can understand timely and accurately running status and the failure message of power equipment.The running temperature of monitoring power equipment, as the oil temperature of transformer, the conductor temperature of transmission line of electricity (pole line and power cable) can be calculated its load limit capacity and ageing equipment degree, thereby upgrades foundation is provided for power equipment dynamic compatibilization or maintenance.The temperature that the rotor, high-tension switch cabinet, busbar joint, outdoor chopper switch, contact of breaker, capacitor, reactor, high-tension cable, transformer etc. of monitoring generator are located, can find in time that local or the overall overheated or Temperature Distribution of following is relatively abnormal in the time that it occurs abnormal conditions or fault, also can be fault analysis historical summary is provided.
The existing technical schemes such as infrared measurement of temperature, active radio thermometric and distributed optical fiber temperature measurement that mainly contain for power equipment temperature monitoring.It is larger that infrared measurement of temperature is affected by environmental baseline factor, and scheme cost is also high; Active radio thermometric scheme, generally taking now after battery or current transformer (CT) power taking is thermometric chip power supply, distance sensing is very far away.But under the rugged surroundings such as high temperature, ultralow temperature, strong-electromagnetic field, the life-span of battery and electronic component all has problems.Take the active sensor of CT way to take power, because the coil of CT power taking has installation site requirement, under circuit malfunction, also cannot power, its application has significant limitation equally.Optical fiber temperature-measurement belongs to wired thermometric mode, and optical fiber or its sheath of measuring high voltage primary side exist insulation against ground problem.Optical fiber has characteristic easy to break, easily broken simultaneously.Fibre Optical Sensor equipment manufacturing cost is higher in addition.
Radio temperature sensor utilization based on surface acoustic wave (surface acoustic wave, is abbreviated as SAW) technology be piezoelectric, there is pure passive, radio characteristics, need not consider the problems such as sensor power supply, High-Voltage Insulation, equipment rotation; Can withstand high temperatures and low temperature (～-200～1000 DEG C); It does not involve the transition process of electronics in semiconductor material, and the interference performances such as life-span length, anti-discharge impact and anti-electric field, magnetic field are strong; Size sensor little (centimetre-sized), lightweight, be easy to structural design and installation.As can be seen here, the temperature monitoring that SAW wireless sensor technology is power equipment provides a desirable technique platform with broad prospect of application.
But the SAW wireless sensing array of development can't meet the demand to temperature monitoring in intelligent grid and extra-high voltage application completely at present, and the problem showing mainly comprises:
Problem 1: operating distance is inadequate.Taking the temperature monitoring of overhead transmission line dynamic compatibilization as example, if consider as the centre of sphere taking the SAW reader of installing, radius of action is at least 30 meters of left and right.The SAW wireless senser thermometric operating distance for switch cabinet temperature monitor of Sengenuity company of U.S. development is only within 2 meters.Germany Brunsb ü ttel, Preussen Elektra company and Darmstadt polytechnical university can reach 10 meters in the SAW wireless temperature measuring system operating distance for application such as whether power transmission line, conductor oxidate lightning arrester and disconnector combined floodgate put in place of development at the end of the nineties in last century, but in power equipment monitoring, apply, its operating distance still needs further raising.
Problem 2: the temperature spot quantity simultaneously detecting is inadequate.In transmission line of electricity monitoring, consider the three-phase of an AC high-voltage electric transmission line on same shaft tower, if connect on power transmission line and install in tower both sides, the situations such as the environment temperature monitoring that consideration multi circuit transmission lines need to carry out with bar situation and the reckoning of conductor temperature model, the quantity of sensor is at least more than 7.The temperature monitoring of temperature of oil in transformer, switch cabinet temperature and other power equipments requires number of sensors to require similar.The SAW wireless sensing array number of sensors for switch cabinet temperature monitor of Sengenuity company of U.S. development can reach 6 and (adopt 3 antennas, implement can reach 18 after space division multiplexing), but occupy 20MHz bandwidth, the 1.87MHz bandwidth requirement allowing considerably beyond 433MHz frequency range.The SAW wireless senser of the electric power thermometric of the domestic Central China University of Science and Technology, Shanghai Communications University, University Of Chongqing and the development of acoustics Suo Deng unit of the Chinese Academy of Sciences also belongs to this working method.
Problem 3: sensor interference free performance has much room for improvement.Along with the widespread use of wireless senser in " intelligent grid ", sensor array is subject to, and possibility sudden, in-band on-channel disturbing effect increases greatly; Under the various application scenarios of " intelligent grid ", the impacts such as the frequency selective fading of different scenes, multipath effect, climatic environment are also different, may cause passive sensor wireless link to interrupt, echo data is lost or is caused because signal to noise ratio (S/N ratio) is very poor and measure wild value.These factors all seriously have influence on the reliability of sensor array, may cause even protective relaying maloperation work of false alarm.
In recent years, there is scholar to propose to adopt the SAW radio-frequency (RF) tag sensing technology scheme of orthogonal frequency coding (OFC).This scheme has been used for reference the thought of OFDM (OFDM) in wireless telecommunications, can effectively overcome the frequency selective fading of channel, is conducive to improve the reliability of SAW sensor.Meanwhile, every reflecting grating of SAW wireless senser of OFC is all arrowband, does not substantially reflect other orthogonal frequencies.With respect to reflection delay line style SAW sensor, the reflectivity of every reflecting grating is no longer only 10% left and right (otherwise subsequent reflection grid will not receive inquiry pulse energy), but can reach 40～50%.Only one of reflecting grating reflection loss, adopts the SAW sensor of OFC just can reduce Insertion Loss 12-13dB.Orthogonal frequency coding is a kind of spread spectrum coding, is similar to intrapulse information modulation radar, and sensor is being separated timing, can, according to the number of chips N comprising in every, increase 20log
10the signal to noise ratio (S/N ratio) of N, is conducive to the raising of operating distance.According to the literature, SAW radio-frequency (RF) tag (RFID) reading distance of OFC coding can reach 60 meters.But this coded system also exists some difficulties to overcome while being used for temperature sensor:
Difficulty 1: because will be to responsive to temperature, therefore the piezoelectric that can not choose low-temperature coefficient as OFC-RFID is as substrate material.But due to temperature variation, be similar to OFDM in communication system and produce Doppler shift, the condition of mutually orthogonal frequency is destroyed originally.When reader demodulation sensor information, relevant peaks performance varies with temperature scope and increases and sharply decline.The temperature-measuring range of bibliographical information only has 55 degree.
Difficulty 2:OFC itself does not have multiple access ability.SAW device is again pure passive, can only reflect passively request signal, when sends or stops transmission information and can not control on one's own initiative.If when multiple OFC-SAW sensor be inquired about and be read to reader will simultaneously, existing scheme is to adopt time division multiplex to combine with OFC coding.But owing to being limited to applicable wireless bandwidth and SAW substrate material length, on the piezoelectric substrate of 10 millimeters long (be the limit, longer SAW propagation loss and diffraction loss will be greatly cannot accept) be difficult to realize 8 kinds of above sensor types.
Summary of the invention
For defect of the prior art, the object of this invention is to provide a kind of based on CDMA and the OFC SAW method for sensing combining of encoding.
, comprise the steps: based on CDMA and the OFC SAW method for sensing combining of encoding according to provided by the invention
Step 1: reader is launched request signal to surface acoustic wave sensor by broad-band antenna; Wherein, described surface acoustic wave sensor, comprising: unidirectional interdigital transducer, frequency orthogonal reflecting grating chip set;
Step 2: surface acoustic wave sensor is received orthogonal frequency coded signal and is converted into surface acoustic wave signal according to the triggering of request signal by single tine finger transducer;
Step 3: make surface acoustic wave signal reflect and pass through unidirectional interdigital transducer through frequency orthogonal reflecting grating chip set and form echoed signal;
Step 4: reader receives echoed signal by broad-band antenna;
Step 5: reader carries out lower linear frequency modulation to echoed signal;
Step 6: reader carries out temperature monitoring according to the echoed signal after lower linear frequency modulation.
Preferably, described step 6 comprise following any or appoint multiple steps:
Step 6A: the first coded signal according to sensor coding identifies the surface acoustic wave sensor that sends echoed signal, wherein, the sub-frequency that the corresponding first chip of described the first coded signal forms;
Step 6a: obtain temperature information according to echoed signal, particularly, step 6a comprises the steps:
Step 6a1: according to the surface acoustic wave sensor identifying, adaptive generation and this surface acoustic wave sensor reflecting grating frequency are from closing matched signal g[(f-△ f
i), (t-τ
i), s
i], g (f, t, s
i) be adaptive matched filter function, △ f
ifor frequency shift (FS), τ
ifor time delay, s
ifor the function of power match coefficient, optimum matching coefficient (△ f
m, τ
m, s
m) be relevant peaks corresponding matching factor value when maximum;
Step 6a2: carry out temperature search, calculate the matched signal g[(f-△ f at each temperature in n temperature
i), (t-τ
i), s
i], and by matched signal g[(f-△ f
i), (t-τ
i), s
i] carry out related calculation with echoed signal, obtain correlation peak;
Step 6a3: maximal value (the △ f of all correlation peaks
m, τ
m, s
m) corresponding temperature is the temperature information that this surface acoustic wave sensor is corresponding;
Step 6a4: if the first coded signal has multiple sensor signals, obtain successively temperature information according to above-mentioned steps 6a1,6a2,6a3.
Preferably, described surface acoustic wave sensor is the sensor after optimizing as follows:
-by Green function in conjunction with finite element tool, optimize SAW sensor transducer and reflecting grating structure, reduce insertion loss, be specially: according to different orientation, transducer and open circuit on lithium niobate substrate, short circuit, float finger formula reflecting grating under fundamental frequency and secondary harmonics: amplitude and the Phase Changing of finger number, metallization thickness, degree of metalization and the weighting of unsteady finger topology, position weighting and reflection, transmission coefficient, calculate different finger numbers, reflection coefficient and the transmission coefficient of reflecting grating under the conditions such as thickness, degree of metalization that metallize; Utilize its regularity, design the identical SAW sensor of each orthogonal frequency component reflection coefficient; Utilize the temperature coefficient under Lagrangian description, bring Green function into, optimization, to the minimum reflecting grating topological structure of the temperature variation slope of each orthogonal frequency reflection characteristic, reduces the impact of temperature on reflectivity, ensures that sensor reading distance is along with temperature raises and significantly decline.
Preferably, described frequency orthogonal reflecting grating chip set, comprising: n the chip being arranged in order;
A described n chip forms a kind of sensor coding; The sensor coding that the contained frequency orthogonal reflecting grating of different surface acoustic wave sensors chip set forms is different;
Each chip is made up of the certain reflecting grating electrode of a kind of centre frequency, forms the reflection to a positive jiao zi frequency;
The sub-frequency forming between described multiple chip is mutually orthogonal;
The time length of field of each chip reflected signal is consistent, and meets orthogonality condition.
Preferably, in each frequency orthogonal reflecting grating chip set, an equal fixed delay τ is all set between adjacent chip
das protection fill, with time domain space to the stack of different frequency signals with influence each other form cut off, suppress the interference between each sub-frequency.
Preferably, in the array of saw sensors forming at multiple surface acoustic wave sensors, the sub-frequency that first chip corresponding to each sensor coding forms is different, and the arrangement employing random code of the sub-frequency of n-1 chip formation, precoding or the Turbo code based on Carrier interference ratio maximum are encoded below.
Compared with prior art, the present invention has following beneficial effect:
Remote, multiple spot that the present invention proposes to combine with code division multiplexing coding based on orthogonal frequency are connected and jamproof surface acoustic wave wireless sensor, method, it is innovation, because this technology path can be by means of orthogonal frequency technology, solve preferably " near-far interference " of the passive sensor system of code division multiplexing coding, can read multiple passive SAW sensor operating distance system farthest simultaneously, meet the requirement of intelligent grid to the monitoring of power equipment temperature wireless.Aspect concrete technology path, there are two place's research characteristics.The first can produce non-orthogonal problem after for orthogonal frequency coding temperature influence; the present invention proposes and fill and can ensure between each chip, can not form phase mutual interference to the reflection of each sub-frequency signal on SAW sensor increasing this protection between reflecting grating; even if each chip is subject to the impact of temperature; reflection frequency is offset; this section of time slot also can time domain space the stack of different frequency signals is cut off with influencing each other to form, suppress the interference between each sub-frequency.It two is to represent orthogonal frequency when coding at the reflecting grating that utilizes SAW (Surface Acoustic Wave) device, the present invention utilizes generalized green function in conjunction with finite element theory, the physical problems such as reflection, transmission and the scattering of the Rayleigh ripple of the reflecting grating of the sparse electrode composition of Accurate Analysis under fundamental frequency and harmonics, have solved and have utilized in the world the shortcomings such as in fourier transform method, computing velocity is slow, bulk wave scattering computational accuracy is low.
Brief description of the drawings
By reading the detailed description of non-limiting example being done with reference to the following drawings, it is more obvious that other features, objects and advantages of the present invention will become:
Fig. 1 is the power equipment temperature monitoring scheme general frame based on OFC surface acoustic wave sensor;
Fig. 2 is time-frequency characteristic of multisensor code division multiplexing coding;
Fig. 3 is the adaptive matched filter schematic diagram based on CDMA;
Fig. 4 is transmission line-oriented temperature monitoring sensor structure.
In figure:
101 is counterpart bolt;
102 is the core of power transmission line;
103 is screw;
104 is microstrip antenna;
105 is surface acoustic wave sensor;
106 is the metal shell of power transmission line.
Embodiment
Below in conjunction with specific embodiment, the present invention is described in detail.Following examples will contribute to those skilled in the art further to understand the present invention, but not limit in any form the present invention.It should be pointed out that to those skilled in the art, without departing from the inventive concept of the premise, can also make some distortion and improvement.These all belong to protection scope of the present invention.
The invention provides a kind of CDMA (CDMA) and the OFC SAW(passive and wireless combining of encoding) sensor technology.CDMA is the good method that solves multiple access in mobile communication.But passive SAW sensor can not carry out on one's own initiative power equalization as communication facilities, in the time there is " near-far interference " in multiple sensors and reader, echo amplitude differs greatly, cannot isolate by related operation the information of each sensor, therefore adopt separately the SAW sensor array of CDMA coding also impracticable.If but orthogonal frequency coding is combined with CDMA, can, first by estimating the frequency spectrum size of each orthogonal frequency, realize power equalization, then can realize multi-sensor information and separate and solve one by one.Because all reflection echo signals of the SAW sensor of this mode allow to overlap in time domain, but can well separate at time-frequency two-dimensional space, in addition, the sensor echoed signal of designing can realize again the relevant treatment gain of code division multiplexing, can realize easily more than 8 kinds different sensors.
Orthogonal frequency combine with CDMA coding SAW sensor in the time carrying out thermometric, can adopt the demodulation method that is different from current OFC-SAW temperature sensor.On the one hand, can vary with temperature relation to each orthogonal frequency reflection characteristic by accurate Calculation SAW reflecting grating, therefrom optimization to each orthogonal frequency reflection characteristic to the minimum reflecting grating topological structure of temperature variation slope, reduce the impact of temperature on reflectivity, ensure that sensor reading distance is along with temperature raises and significantly decline; On the other hand, can adopt a kind ofly according to the demodulation method of measuring temperature self-adaptation search, matched filtering, in obtaining coupling output, also obtain dut temperature value.
For solving " intelligent grid " power equipment, the particularly demand of extra-high voltage electric power equipment to temperature monitoring, the present invention proposes based on the orthogonal frequency passive wireless acoustic surface wave method for sensing combining with CDMA of encode, the temperature monitoring of, multiple spot connection measurement remote to realize and high reliability.
Below the general frame of system of the present invention is described.
As shown in Figure 1, in the constructed power equipment temperature monitoring model space, comprising: reader, broad-band antenna, multiple surface acoustic wave sensor.Wherein, surface acoustic wave sensor comprises: unidirectional interdigital transducer, frequency orthogonal reflecting grating chip set; Surface acoustic wave sensor 1～N distribute arbitrarily (according to power equipment monitoring actual demand, N value can meet the demands between 8 to 10).
Temperature monitoring signal processing flow is as follows:
Step 1: reader is launched Linear frequency modulation (upchirp) request signal by broad-band antenna, and Linear frequency modulation request signal is transmitted to surface acoustic wave sensor in strong electromagnetic channel A;
Step 2: surface acoustic wave sensor is received OFC signal and is converted into surface acoustic wave signal according to Linear frequency modulation request signal by unidirectional interdigital transducer;
Step 3: make surface acoustic wave signal reflect and pass through unidirectional interdigital transducer through frequency orthogonal reflecting grating chip set and form echoed signal;
Step 4: echoed signal is transmitted to reader in strong electromagnetic channel A, reader is received echoed signal and is carried out lower linear frequency modulation (downchirp) by broad-band antenna;
Step 5: reader carries out the signal processings such as demodulation to the echoed signal after lower linear frequency modulation, carries out multisensor identification and extracts with temperature information.
Wherein, upper and lower linear frequency modulation can increase the processing gain of 20～50 left and right, is conducive to improve surface acoustic wave sensor operating distance.
Below OFC is described in conjunction with the technology path of CDMA coding.
As shown in Fig. 1 lower right corner, surface acoustic wave sensor contains f
0～f
78 chips also form a kind of coding, and wherein, chip refers to chip.The electrode that wherein each chip is fixed by centre frequency again forms, and forms the reflection to a positive jiao zi frequency; The sub-frequency forming between multiple is mutually orthogonal.Should design according to orthogonal frequency coding theory the quantity of electrode in each chip, to guarantee the time length of field of each chip reflected signal (the time delay τ on time response in corresponding diagram 1 that is consistent
c), meet orthogonality condition.The difference that puts in order of each chip, forms other codings.For example: f in Fig. 1
6, f
4, f
0, f
7, f
1, f
2, f
5, f
3put in order and form a kind of coding; If press f
4, f
7, f
6, f
0, f
1, f
2, f
3, f
5put in order and form another sensor.According to orthogonal coding theory, in the time that response device carries out auto-correlation computation, can there is very high relevant peaks (to there is in theory the surface acoustic wave sensor of N position orthogonal frequency coding, process echoed signal by the mode of compression pulse, can form N
2times processing gain, in conjunction with upper and lower chirped processing gain 50, therefore can, under emissive power and receiving sensitivity same case, improve sensor wireless operating distance greatly).And the device of two kinds of different codings is while carrying out computing cross-correlation, but has very low simple crosscorrelation peak.The present invention studies emulation and selects the sensor array of coding composition that those cross correlation peaks are very low, even if these sensors respond the request signal of reader simultaneously, echo is all aliasing in together in time domain, still can distinguish by code division multiplexing method.
In Fig. 1, also can see: between each chip, increased an equal fixed delay τ
d(protection is filled).Increasing this protection filling can ensure between each chip, can not form phase mutual interference to the reflection of each sub-frequency signal on SAW sensor; even if each chip is subject to the impact of temperature; reflection frequency is offset; this section of time slot also can time domain space the stack of different frequency signals is cut off with influencing each other to form, suppress the interference between each sub-frequency.
Below FUSION WITH MULTISENSOR DETECTION identification, frequency deviation estimation and the temperature detection based on adaptive matched filter are described.
In order to realize the identification of multiple surface acoustic wave sensors, in complex electromagnetic environment, improve the discrimination of coding, for take related operation raising signal processing gain and personal identification method in echo signal processing for, need to reduce the cross correlation between each coded signal, just need to optimize the space sequence of corresponding each sub-frequency chip.Possible aligning method can be used for reference random code, precoding based on Carrier interference ratio maximum or Turbo code coding all can reduce intersymbol interference, ensures the raising of signal processing gain.Said method is also the multiple access principle of code division multiplexing.But in distance between multisensor and reader not etc. in the situation that, the power of each sensor echoed signal and noise level are not etc., only have " near-far interference " eliminated between reader and sensor, could be in multisensor time domain response each other in aliasing situation, the response of effectively isolating each sensor.
The present invention makes the sub-frequency difference of first chip of the each sensor coding in array of saw sensors, and the arrangement of n-1 frequency below adopts random code, precoding or Turbo code based on Carrier interference ratio maximum to encode.The time slot increasing in the time solving intersymbol interference on sensor substrate equally to sensor identification work.If time delay τ
dbe greater than modulation signal and the travel-time sum in channel through the echoed signal after sensor response, if radius is the ball domain space of 30 meters, this time delay is less than 200ns, this time delay can ensure that reader is in the time receiving multisensor echoed signal, the second coded signal of any sensor echo time can not enter the first coded signal time slot in domain space.As shown in Figure 3, f (t) is the stack of all the sensors time domain response signal, g[(f-△ f
i), (t-τ
i), s
i] be adaptive matched filter function, be frequency shift (FS), time delay, the function of power match coefficient, optimum matching coefficient (△ f
m, τ
m, s
m) be relevant peaks corresponding matching factor value when maximum.Echoed signal first paragraph (τ after demodulation
c+ τ
d) in time slot, the corresponding different sensors of the signal of contained different frequency composition.Can tentatively identify according to the signal of the first coding the coding that contains several sensor informations and these sensors in aliasing signal like this.The present invention, according to the assessment of each echoed signal power spectrum, carries out power equalization to different coding sensor.Now the size accuracy of every sub-frequency frequency deviation is not high, can not be used for temperature detection, but can greatly dwindle the temperature hunting zone of follow-up matched filtering process, improves search efficiency.
Then can be according to the method shown in Fig. 3, successively carry out adaptive matched filter, when generating the matched signal g (f of a certain specific coding, s, t), while reaching maximal value with the auto-correlation computation relevant peaks of the multiple sensor signals f (t) of time domain aliasing, can determine the temperature value that this code sensor is corresponding.And then the another one existing in replacing array echo signal coding is searched for by Fig. 3 again.It should be noted that, the matched signal g (f, s, t) of generation appears to be a 2D signal, but two functions that independent variable is all temperature wherein, according to the temperature of search, can be determined value separately.Therefore wholely search plain speed and can ensure.
Below the optimization response of sensor is described.
For ensureing that the low-loss that orthogonal frequency is coded on SAW sensor characterizes, primary study interdigital transducer Frequency Response of the present invention, the reflection characteristic of conversion efficiency and reflecting grating and Frequency Response, and its parameter is optimized to design.The reflecting grating metallization thickness of encoding because of orthogonal frequency is identical, but reflecting grating periodicity, reflecting electrode radical differ greatly, can be according to different orientation, transducer and open circuit on lithium niobate substrate, short circuit, float finger formula reflecting grating under fundamental frequency and secondary harmonics: amplitude and the Phase Changing of finger number, metallization thickness, degree of metalization and the weighting of unsteady finger topology, position weighting and reflection, transmission coefficient, calculate different finger numbers, reflection coefficient and the transmission coefficient of reflecting grating under the conditions such as thickness, degree of metalization that metallize.Obtain its regularity, to guarantee to design the identical SAW sensor of each orthogonal frequency component reflection coefficient.Utilize the temperature coefficient under Lagrangian description, bring Green function into, optimization, to the minimum reflecting grating topological structure of the temperature variation slope of each orthogonal frequency reflection characteristic, reduces the impact of temperature on reflectivity, ensures that sensor reading distance is along with temperature raises and significantly decline.
Aspect sensor construction, should consider installation of sensors, sensor accuracy and dynamic and eliminate the problems such as disturbing factor such as stress, reader crystal oscillator temperature float of installing.Fig. 4 is the transmission line-oriented temperature detection sensor structure that the present invention takes.The position of installation of sensors as shown in Figure 4, can contact by metal and core are fine, separate by partiting thermal insulation material and outer cover metal, guarantee temperature can be followed the variation of heart yearn temperature well simultaneously, the precision that simultaneously can not measure because of the heat radiation impact of outer cover metal again.Between microstrip antenna and Shell Plate, separate with insulating material, fix by screw.Utilize the instruments such as finite element software to optimize thermal capacity and the conductive structure of sensor construction size and encapsulation.Improve sensor dynamic index.The encapsulation of sensor and lead-in wire are the key factors that affects sensor stability, and because SAW is very responsive to quality loading, the factors such as dust, oil stain, humidity may make sensor complete failure.How both to ensure by reasonable encapsulation that substrate surface and the external world isolated completely, ensure again measured can being efficiently loaded on substrate after installation of sensors, reach mechanically firm, anti-vibration, shock resistance, avoid the impact on sensitive element and high frequency surface wave of thermal stress and package parasitics, the problem that must consider and solve while being surface wave sensor encapsulation simultaneously.
Aspect Antenna Design, adopt microstrip line antenna form.Adopt full-wave simulation software Ansoft HFSS to carry out modeling, the parameters such as reflection coefficient, gain, directional diagram and the impedance curve of simulation calculation antenna.The correct design of feed system is for improving aerial radiation, and receiving efficiency is very important.The impedance of SAW (Surface Acoustic Wave) device itself can be realized and being mated by microstrip feed line network structure with the impedance of emitting antenna.According to the impedance characteristic of antenna, design microstrip balun feeder line, makes antenna at design frequency band internal impedance gradual change to 50 Ω.The 890MHz-940MHz that the frequency band of antenna is 915MHz according to the characteristic initial option of the on-the-spot electromagnetic interference signal of electric apparatus monitoring in centre frequency.
That realizes according to the present invention realizes the noiseless synchronous read in 30 meters of 8-10 sensors, and temperature detection scope-50 DEG C～+ 150 DEG C, in detection error ± 1 DEG C.The operating distance of 915MHz wireless SAW sensor wherein can reach 5 meters.By reducing sensor reflection loss 12-13dB, upper and lower linear frequency modulation brings processing gain 50 to be multiplied by 64, two of code division multiplexing demodulation process gains to amount to altogether 30dB, and therefore, the operating distance of sensor is brought up to 30 meters can be achieved.
Above specific embodiments of the invention are described.It will be appreciated that, the present invention is not limited to above-mentioned specific implementations, and those skilled in the art can make various distortion or amendment within the scope of the claims, and this does not affect flesh and blood of the present invention.
Claims (3)
1. based on CDMA and the OFC SAW method for sensing combining of encoding, it is characterized in that, comprise the steps:
Step 1: reader is launched request signal to surface acoustic wave sensor by broad-band antenna; Wherein, described surface acoustic wave sensor, comprising: unidirectional interdigital transducer, frequency orthogonal reflecting grating chip set;
Step 2: surface acoustic wave sensor is received orthogonal frequency coded signal and is converted into surface acoustic wave signal according to the triggering of request signal by single tine finger transducer;
Step 3: make surface acoustic wave signal reflect and pass through unidirectional interdigital transducer through frequency orthogonal reflecting grating chip set and form echoed signal;
Step 4: reader receives echoed signal by broad-band antenna;
Step 5: reader carries out lower linear frequency modulation to echoed signal;
Step 6: reader carries out temperature monitoring according to the echoed signal after lower linear frequency modulation;
Correspondingly, in step 1, described request signal is Linear frequency modulation request signal.
2. according to claim 1ly it is characterized in that based on CDMA and the OFC SAW method for sensing combining of encoding, described step 6 comprise following any or appoint multiple steps:
Step 6A: the first coded signal according to sensor coding identifies the surface acoustic wave sensor that sends echoed signal, wherein, the sub-frequency that the corresponding first chip of described the first coded signal forms;
Step 6a: obtain temperature information according to echoed signal, particularly, step 6a comprises the steps:
Step 6a1: according to the surface acoustic wave sensor identifying, adaptive generation and this surface acoustic wave sensor reflecting grating frequency are from closing matched signal g[(f-△ f
i), (t-τ
i), s
i], g (f, t, s
i) be adaptive matched filter function, △ f
ifor frequency shift (FS), τ
ifor time delay, s
ifor the function of power match coefficient, optimum matching coefficient (△ f
m, τ
m, s
m) be relevant peaks corresponding matching factor value when maximum;
Step 6a2: carry out temperature search, calculate the matched signal g[(f-△ f at each temperature in n temperature
i), (t-τ
i), s
i], and by matched signal g[(f-△ f
i), (t-τ
i), s
i] carry out related calculation with echoed signal, obtain correlation peak;
Step 6a3: maximal value (the △ f of all correlation peaks
m, τ
m, s
m) corresponding temperature is the temperature information that this surface acoustic wave sensor is corresponding;
Step 6a4: if the first coded signal has multiple sensor signals, obtain successively temperature information according to above-mentioned steps 6a1,6a2,6a3.
3. according to claim 1ly it is characterized in that based on CDMA and the OFC SAW method for sensing combining of encoding, described surface acoustic wave sensor is the sensor after optimizing as follows:
-by Green function in conjunction with finite element tool, optimize SAW sensor transducer and reflecting grating structure, reduce insertion loss, be specially: according to different orientation, transducer and open circuit on lithium niobate substrate, short circuit, float finger formula reflecting grating under fundamental frequency and secondary harmonics: amplitude and the Phase Changing of finger number, metallization thickness, degree of metalization and the weighting of unsteady finger topology, position weighting and reflection, transmission coefficient, calculate different finger numbers, reflection coefficient and the transmission coefficient of reflecting grating under the conditions such as thickness, degree of metalization that metallize; Utilize its regularity, design the identical SAW sensor of each orthogonal frequency component reflection coefficient; Utilize the temperature coefficient under Lagrangian description, bring Green function into, optimization, to the minimum reflecting grating topological structure of the temperature variation slope of each orthogonal frequency reflection characteristic, reduces the impact of temperature on reflectivity, ensures that sensor reading distance is along with temperature raises and significantly decline.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201410073651.3A CN103884447B (en) | 2014-03-03 | 2014-03-03 | Encode, with OFC, the SAW method for sensing combined based on CDMA |
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| CN201410073651.3A CN103884447B (en) | 2014-03-03 | 2014-03-03 | Encode, with OFC, the SAW method for sensing combined based on CDMA |
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| CN105043584A (en) * | 2015-07-10 | 2015-11-11 | 北京中讯四方科技股份有限公司 | Wireless temperature measurement system |
| CN105547203A (en) * | 2015-12-04 | 2016-05-04 | 中国人民解放军理工大学 | SAW sensor multipath asynchronous reflection signal reading method |
| CN110455423A (en) * | 2019-08-20 | 2019-11-15 | 武汉科瑞新电气自动化有限公司 | A kind of overlength distance low-power consumption temperature monitoring sensor |
| CN112182833A (en) * | 2020-08-03 | 2021-01-05 | 天津大学 | Method for determining frequency spacing factor of surface acoustic wave pseudo-orthogonal frequency coding system |
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| CN203039924U (en) * | 2012-12-14 | 2013-07-03 | 桂林电子科技大学 | Network-node coding structure for passive wireless sensor |
| CN103471631A (en) * | 2013-04-22 | 2013-12-25 | 江苏声立传感技术有限公司 | Multi-target anti-collision coding method of delay line type SAW (surface acoustic wave) sensor |
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| CN105547203A (en) * | 2015-12-04 | 2016-05-04 | 中国人民解放军理工大学 | SAW sensor multipath asynchronous reflection signal reading method |
| CN110455423A (en) * | 2019-08-20 | 2019-11-15 | 武汉科瑞新电气自动化有限公司 | A kind of overlength distance low-power consumption temperature monitoring sensor |
| CN112182833A (en) * | 2020-08-03 | 2021-01-05 | 天津大学 | Method for determining frequency spacing factor of surface acoustic wave pseudo-orthogonal frequency coding system |
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