CN101644608B - An Integrated Surface Acoustic Wave Wireless Temperature Sensor - Google Patents

Abstract

The invention relates to an integrated SAW wireless temperature sensor, which comprises an interdigital transducer with an EWC/SPUDT structure and 11 reflectors with a short-circuit grid structure on a piezoelectric substrate, and is received by the EWC/SPUDT through a wireless antenna. The electromagnetic wave signal emitted by the wireless reading unit is converted into a surface acoustic wave, propagates along the direction of the reflectors on the surface of the piezoelectric substrate, and is reflected by the reflectors respectively, and the reflected sound waves pass through the EWC/ SPUDT2 is re-converted into an electromagnetic wave signal, which is sent back to the wireless reading unit by the wireless antenna, and through signal processing methods, the phase change of the time domain response is evaluated to realize the detection of temperature. In order to reduce multiple reflections between reflectors, the 11 reflectors of the SAW reflective delay line are divided into two channels, one channel with 8 devices for 8-bit electronic tags, and the other channel with 3 reflectors for temperature detection ; And by adjusting the number of reflector electrodes to obtain a uniform response time domain S11 reflection peak.

Description

An Integrated Surface Acoustic Wave Wireless Temperature Sensor

technical field

The present invention relates to a surface acoustic wave (surface acoustic wave: SAW) temperature sensor with an integrated electronic label, in particular to a SAW reflective delay using a single-phase unidirectional transducer with a controlled electrode width and a short-circuit grid reflector structure line of wireless temperature sensors.

Background technique

The propagation speed of SAW has a linear relationship with temperature, that is, Δv=v ₀ ×TCD×(TT _ref ), where TCD is the first-order delay temperature coefficient of the piezoelectric substrate (depending on the crystal structure of the piezoelectric substrate material and Tangential), Δv is the speed change, v ₀ is the SAW speed, and T _ref is the reference temperature. In this way, the detection of temperature can be realized by using some piezoelectric substrates with higher temperature coefficient, ie high TCD value, such as LiNbO ₃ , LiTaO ₃ and La ₃ Ga ₅ SiO ₄ . In recent years, with the help of wireless identification technology, a SAW reflective delay line has been applied to SAW wireless temperature sensor applications. This SAW reflective delay line consists of a piezoelectric substrate, an interdigital transducer and several reflectors arranged along the sound wave propagation direction (the number of reflectors depends on the actual application). The antenna receives the electromagnetic wave signal emitted by the wireless reading unit (Reader unit), and converts it into SAW that propagates along the surface of the piezoelectric substrate, and is reflected by the reflector, and the reflected SAW is converted into electromagnetic wave again through the interdigital transducer The signal is sent back to the wireless reading unit through the wireless antenna. Due to the linear correlation between the SAW speed and temperature, the linear response of the time-domain phase of the SAW reflection delay line is achieved, so as to realize the wireless detection of temperature.

As an example, a SAW reflective delay line 1 with a conventional structure applied to a wireless temperature sensor includes a piezoelectric substrate, and an interdigital transducer fabricated by a semiconductor planar process on the piezoelectric substrate and arranged along the sound wave propagation direction , as shown in Figure 1, wherein 9 is a piezoelectric substrate, 2 is an interdigital transducer, 3, 4 and 5 are three reflectors, reflector 3 and interdigital transducer 2 and The distance between the reflectors is determined according to the delay requirement. 6, 7 and 8 are the first, second and third reflected echo signals reflected from the reflectors 3, 4 and 5, respectively. The piezoelectric substrate 9 is usually made of materials such as LiNbO ₃ and LiTaO ₃ with a high temperature coefficient. Taking advantage of its high sensitivity to temperature, the speed of sound waves changes linearly with changes in the ambient temperature, thereby causing SAW reflection-type delay line reflection The time domain delay/phase response of coefficient S ₁₁ is used to realize the detection of temperature.

The detection range of the prototype SAW wireless temperature sensor based on this SAW reflective delay line with a working frequency of 2.4GHz in the prior art is (room temperature to 200°C), and its sensitivity has reached 34°/°C, and a temperature of less than 0.1K has been obtained. Temperature detection resolution. Since this SAW temperature sensor is composed of a single device and has a simple structure, three sensors as described in Document 1: L.M.Reindl: Wireless measurement of temperature using surface acoustic wavesensors, IEEE Trans.UFFC, 51, 1457-1463 (2004) are used. The structure of the reflector and the corresponding signal processing method can effectively eliminate the signal ambiguity caused by the phase detection exceeding 360 degrees, and it is possible to obtain a good temperature sensitivity improvement; in addition, the phase is used as the sensor output signal, which has a higher sensitivity resolution, And the device itself can be absolutely passive, suitable for working under high temperature conditions, so this kind of SAW wireless temperature sensor has a good application prospect and arouses great interest of people. For this wireless SAW temperature sensor, the design of the SAW reflective delay line directly determines the performance indicators of the sensor, especially the detection range, because as the temperature increases, the sound wave propagation attenuation also increases correspondingly, which is directly expressed as SAW The time-domain response of the reflective delay line, the loss of S11 increases with the increase of temperature (Document 2: R.S.Hauser, et al: A wirelessSAW-based temperature sensor for harsh environment, Proceeding of IEEE Sensors, Vol.2pp: 860-863 , 2004), which requires a SAW reflection delay line with low loss, high signal-to-noise ratio and uniform, steep and sharp time-domain reflection peaks. However, the SAW reflective delay line currently used in wireless temperature sensors has major problems due to device structure design, such as:

1. The interdigital transducer 2 used in the above conventional SAW reflective delay line 1 adopts a bidirectional transducer structure, which causes sound waves to propagate in both directions, thus increasing the sound propagation loss (generally 50-60dB); The signal-to-noise ratio is low, which seriously affects the temperature detection range and wireless reading distance (inversely proportional to device loss, document 3: CECook, M.Bernfeld: Radar signals, Norwood, MA, Artech House, 1993), more It directly affects the temperature detection range of the sensor. In addition, the reflective delay line in the prior art fails to realize the steep and sharp time-domain reflection peak of the reflection coefficient S ₁₁ , which is not conducive to the accurate extraction of the time-delayed signal, thus causing a large deviation of the detection signal.

2. The above-mentioned conventional SAW reflective delay line 1 applied to the SAW wireless temperature sensor usually adopts a single-finger type or an interdigital transducer type as the reflector of the delay line. The interdigitated reflector has a large reflection coefficient, so it can better improve the device loss and signal-to-noise ratio, but due to the reflection between the interdigitated electrodes and the acoustic-electric regeneration, it causes relatively large time-domain noise. The single-finger reflector can reduce the time-domain noise of the device, but the small reflection coefficient leads to large device loss and low signal-to-noise ratio.

3. Due to the attenuation of sound wave propagation, usually the long propagation path of the delay line leads to poor uniformity of the reflection peaks from each reflector. The farther away from the transducer, the greater the loss and the lower the signal-to-noise ratio, which directly affects the time domain Extraction of delayed signals.

4. At present, an important development trend of the sensor system is the integration of functions, which is conducive to the real-time detection of multiple parameters, and is also conducive to the realization of system miniaturization and portability; and the existing wireless sensors using SAW reflective delay lines The temperature sensor has a single function; therefore, it directly hinders some performance improvements and practical applications of the SAW wireless temperature sensor.

Contents of the invention

The purpose of the present invention is to solve the existing problems of the above-mentioned SAW wireless temperature sensor; in order to realize that the SAW reflective delay line has the characteristics of low loss, high signal-to-noise ratio, low time-domain noise and uniform time-domain response, thereby providing a method using 41°YXLiNbO ₃ piezoelectric substrate, with aluminum as the interdigitated electrode, a SAW reflective delay line for temperature detection using a controlled electrode width single-phase unidirectional transducer (EWC/SPUDT) and a short-circuit grid reflector; 11 A short-circuit grid reflector is divided into two sets, one with 8 reflectors for 8-bit electronic tags, and the other 3 reflectors for temperature detection, realizing a portable integrated electronic tag SAW wireless temperature for real-time detection of multiple parameters sensor.

The purpose of the present invention is achieved like this:

An integrated surface acoustic wave wireless temperature sensor provided by the present invention, as shown in Figure 2a, includes a SAW reflective delay line 11; the SAW reflective delay line 11 consists of a piezoelectric substrate 9, and The above-mentioned piezoelectric substrate 9 is composed of two conductive films 10 coated on the upper and lower sides along the sound wave propagation direction, and a transducer 2 and a reflector provided; it is characterized in that it also includes surface mount components (surface mount device: SMD) 12, sound-absorbing glue, impedance matching network 13, wireless antenna 14 and reading unit 17, and the number of reflectors arranged on the piezoelectric substrate 9 is 11;

The piezoelectric substrate 9 is a lithium niobate (LiNbO ₃ ) substrate that rotates 41° in the Y direction and propagates along the X direction, and is selected at one end of the long side of the piezoelectric substrate 9, along the upper surface up and down Two conductive films 10 are coated on both sides, and the first sound-absorbing glue 18 is coated in the middle of the two conductive films 10, and the EWC/SPUDT2 is arranged along the sides of the conductive films 10; The other end of the long side of the substrate 9 is coated with a second sound-absorbing glue 18;

The surface mount component 12 is used to seal and package the SAW reflective delay line 11 to form protection for the EWC/SPUDT2, 11 reflectors 19-29 and the surface of the piezoelectric substrate 9, and to complete the SAW reflective delay line The electrical connection between the line 11 and the peripheral impedance matching network 13;

Described transducer 2 is control electrode width single-phase unidirectional transducer (EWC/SPUDT), and this control electrode width single-phase unidirectional transducer uses aluminum as electrode, and specific structure is as shown in Figure 3a; The electrode width single-phase unidirectional transducer is composed of more than 2 interdigital electrode pairs 31, and a reflective electrode 30 with an electrode width of 1λ/4 is arranged between each 2 interdigital electrode pairs 31, where λ: acoustic wave wavelength The distance between the reflective electrode 30 and the interdigital electrode pair 31 is 3λ/16, and the interdigital electrode pair 31 is composed of two 1λ/8 electrodes; wherein the position of the reflective electrode 30 depends on the base The material of sheet and reflective electrode 30, for example, use 41 ° YX LiNbO ₃ piezoelectric substrate and aluminum electrode, reflective electrode 30 is placed on the left side of interdigitated electrode pair 31, that is, the direction opposite to the unidirectional radiated sound wave to obtain unidirectional Propagation of sound waves towards radiation;

A series inductance 32 is connected in the connection circuit between the input end N1 of the transducer of the SAW reflective delay line 11 and the signal end N3 of the wireless antenna 14, and the series inductance 32 is connected to the A grounded inductance 33 is connected in the connection circuit between the signal terminals N3 of the wireless antenna 14; the ground terminal N4 of the wireless antenna 14 is electrically connected with the ground terminal N2 of the transducer 2, so as to realize the SAW reflection delay Impedance matching between the wire 11 and the wireless antenna 14;

The electromagnetic wave signal 15 emitted from the reading unit 17 is received by the wireless antenna 14, converted into SAW by the single-phase unidirectional transducer 2 with the width of the control electrode, and sent along the surface of the piezoelectric substrate 9 propagated and partly reflected by 11 reflectors back to the control electrode width single-phase unidirectional transducer, re-converted into electromagnetic wave signal 16, and transmitted back to the reading unit 17 through the wireless antenna 14, the sound wave velocity is also caused by the change of the peripheral temperature , resulting in the time-domain phase response of the SAW reflective delay line 11, which is evaluated by the reading unit to realize real-time detection of temperature.

In the above technical solution, the coupling coefficient of the lithium niobate (LiNbO ₃ ) substrate is 17.2%, the sound propagation velocity is 4750m/s, and the first-order retardation temperature coefficient is 85ppm/°C.

In the above-mentioned technical scheme, the position of the reflective electrode 30 depends on the reflection phase of the reflective electrode 30, and it is related to the material of the piezoelectric substrate 9 and the reflective electrode 30; Caused by the piezoelectric short-circuit and mechanical load effect of the grid bar to the substrate surface, in the single-phase unidirectional transducer structure of the control electrode width shown in Figure 3a, the acoustic wave unidirectional radiation in the direction of 11 reflectors in Figure 2b is obtained The condition is that the reflective electrode 30 is placed on the left side of the interdigital electrode pair 31, that is, the direction opposite to the unidirectionally radiated sound wave.

In the above technical solution, the logarithm of the EWC/SPUDT 2 index is 10-20 to obtain a relatively steep and sharp time-domain reflection peak.

In the above technical solution, in order to reduce the multiple reflections between reflectors and the peak-to-peak noise of time-domain reflections, the 11 reflectors are divided into two sets, and the A-th reflector 19 to the H-th reflector 26 are set In one path, it is used for 8 electronic tags; the I-th reflector 27～K-th reflector 29 is set in another path for temperature detection; in addition, in order to compensate the influence of sound wave propagation attenuation, the 11 reflectors The number of electrodes is set according to a certain rule, that is, the A-C reflectors 19-21 closest to EWC/SPUDT2 have the least number of electrodes (for example, 5 electrodes with a width of λ/4), and as the distance between the reflector and EWC/SPUDT The number of reflector electrodes increases correspondingly, the Dth reflector 22 to the Fth reflector 24 have 6 electrodes, the Gth reflector 25 to the Hth reflector 26 have 7 electrodes, and the Ith reflector 25 to the Hth reflector 26 have 7 electrodes. The number of electrodes of the first reflector 27 to the Jth reflector 28 is 8, and the Kth reflector 29 farthest from the EWC/SPUDT has the largest number of electrodes (nine electrodes are used in the present invention).

In the above-mentioned technical solution, the A-th reflector 27 to the K-th reflector 29 used for temperature detection are set according to certain rules to obtain higher detection accuracy and eliminate the occurrence of over 360 degrees in phase detection. Signal ambiguity, that is, the distance between the Kth reflector 28 and the Jth reflector 29 needs to be much greater than the distance between the Ith reflector 27 and the Jth reflector 28, but as the sound wave propagation distance increases , the sound wave propagation loss also increases accordingly. Therefore, considering comprehensively, the distance between the J-th reflector 28 and the K-th reflector 29 is three times the distance between the I-th reflector 27 and the J-th reflector 28.

In the above technical solution, the distance between the A-th reflector 19 and the EWC/SPUDT2 is 3272.4 μm, so as to provide a sufficient time delay of more than 1.2 μs to separate the environmental noise echo from the sensor reflection signal.

The advantages of the present invention are:

The SAW temperature sensor of the present invention is integrated, and its basic structure is to make a reflector of EWC/SPUDT2 and 11 short-circuit grid structures on the piezoelectric substrate, and the EWC/SPUDT receives the data from the wireless reading through the wireless antenna. The electromagnetic wave signal emitted by the unit is converted into a surface acoustic wave, propagates along the direction of the reflectors on the surface of the piezoelectric substrate, and is reflected by the reflectors respectively, and the reflected sound waves are reconverted into electromagnetic waves by EWC/SPUDT2 The signal is transmitted back to the wireless reading unit by the wireless antenna, and the temperature is detected by evaluating the phase change of the time domain response through a signal processing method.

Due to the SAW reflective delay line 11 of the present invention, a structure of a control electrode width unidirectional single-phase transducer has been designed, which utilizes the phase superposition of the forward and reverse propagating acoustic waves caused by the reflective electrode reflection of the distribution, effectively Improve the forward sound wave, and suppress or even cancel the propagation of the reverse sound wave, so that the device loss can be effectively improved, and the signal-to-noise ratio performance of the reflective delay line can be improved.

In the SAW reflective delay line 11, a short-circuit grid reflector structure is designed. Because the reflector has a high reflection coefficient and zero acoustic-electric regenerative reflection, the SAW reflective delay line has a good signal-to-noise ratio, and at the same time Reduce reflection peak-to-peak noise.

The present invention adopts 41°YX LiNbO ₃ 2 with high piezoelectric coefficient (17.2%), sound propagation velocity (4750m/s) and higher first-order delay temperature coefficient (85ppm/°C) as the piezoelectric substrate. And adopt the EWC/SPUDT of aluminum electrode and the structure of short grid reflector, reduce device loss (in the utility model, reflection peak loss is about 40dB in the time domain S ₁₁ signal), improve the signal-to-noise ratio of the sensor; By optimizing the design of SAW The reflector electrode index, reflector acoustic aperture, propagation path, etc. of the reflective delay line are used to obtain the time-domain reflector reflection peak with uniform loss and signal-to-noise ratio. The position of the reflector is configured through an optimized design to obtain temperature compensation and sensitivity improvement of the sensor.

The 11 reflectors using the short-circuit grid structure provided by the present invention are divided into two paths, 8 reflectors are used as one path for 8-bit electronic tags, and the other 3 reflectors are arranged on the other path to realize temperature detection .

The present invention adopts the coating of sound-absorbing glue 18 on both ends of the piezoelectric substrate 9, which is mainly used to eliminate the edge reflection of the sound wave, so as to reduce the time-domain noise caused by the edge reflection of the device.

In order to obtain relatively steep and sharp time-domain reflection peaks, the present invention adopts limited reduction of the index logarithm (10 to 20 pairs) of EWC/SPUDT 2, which is a relatively effective way compared to the prior art.

Description of drawings

FIG. 1 is a schematic diagram of the structure of a conventional SAW reflective delay line;

Figure 2a is a schematic diagram of the composition of the integrated SAW wireless temperature sensor of the present invention;

Fig. 2b is the SAW reflective delay line used for the integrated wireless temperature sensor of the present invention;

Fig. 3a is a schematic structural diagram of the (EWC/SPUDT) used in the SAW reflective delay line of the present invention;

Fig. 3b is a structural schematic diagram of a short-circuit grid reflector used in the SAW reflective delay line of the present invention;

Fig. 4 is a structural design diagram of the SAW reflective delay line of the present invention;

Fig. 5 is the impedance matching network between the integrated SAW wireless temperature sensor and the wireless antenna in the scheme of the present invention;

Fig. 6 is a test time-domain response curve diagram of the SAW reflective delay line of the present invention.

The illustrations are as follows:

1. Conventional SAW reflective delay line 2. Transducer 3. First reflector

4. The second reflector 5. The third reflector 6. The first echo signal

7. Second echo signal 8. Third echo signal 9. Piezoelectric substrate

10. Conductive film 11. SAW reflective delay line

12. Surface mount components (SMD) 13. Impedance matching network 14. Wireless antenna

15. Electromagnetic wave signal 16. Sensor signal 17. Wireless reading unit

18. The first and second sound-absorbing glue 19. The first reflector 20. The B-th reflector

21. Cth reflector 22. Dth reflector 23. Eth reflector

24. F-th reflector 25. G-th reflector 26. H-th reflector

27. The I-th reflector 28. The J-th reflector 29. The K-th reflector

30. Reflective electrode 31. Interdigitated electrode pair 32. Series inductance

33. Parallel inductor

Detailed ways

In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Referring to FIG. 2 a , an integrated SAW temperature sensor is manufactured, including: a SAW reflective delay line 11 , surface mount components 12 , and an impedance matching network 13 between the SAW reflective delay line 11 and the wireless antenna 14 .

With reference to Fig. 2 b, the SAW reflective delay line 11 of the embodiment of the present invention consists of a piezoelectric substrate 9, and a transducer made on the piezoelectric substrate 9 (the transducer of this embodiment adopts a control electrode Wide single-phase unidirectional transducer, ie EWC/SPUDT)2 with eleven short-circuit grid reflectors. The SAW reflective delay line 11 is hermetically packaged with a surface mount component 12 to protect the piezoelectric substrate 9, EWC/SPUDT 2 and eleven short-circuit grid reflectors; Package components with 10 pins.

The piezoelectric substrate 9 of this embodiment adopts a niobium acid (LiNbO ₃ ) substrate that rotates 41° along the Y direction and propagates in the X direction as a vibrating film; the piezoelectric substrate 9 has a size of (a×b, a: 6mm, b: 18mm), that is, 41°YXLiNbO ₃ with a length of 18mm, a width of 6mm, and a thickness of 350μm; the piezoelectric substrate has a high acoustic wave velocity (4750m/s), a piezoelectric coupling coefficient (17.2%) and a Order delay temperature coefficient (85ppm/℃). And select one end of the long side of the piezoelectric substrate 9, coat two conductive films 10 along the upper and lower sides of the upper surface, and coat the first sound-absorbing glue 18 in the middle of the two conductive films 10, The EWC/SPUDT2 is arranged along one side of the conductive film 10; the other end of the long side of the piezoelectric substrate 9 is also coated with a second sound-absorbing glue 18 (implemented by this professional conventional technology). It is mainly used to eliminate the edge reflection of the sound wave to reduce the time domain noise caused by the edge reflection of the device.

铝膜制作；该单相单向换能器由6个叉指电极对31，和在6个叉指电极对31之间设置的5个电极宽度为1λ/4的反射电极30组成，当然叉指电极对31还可以是10-20之间的任何数；反射电极30与叉指电极对31(由两个1λ/8的电极组成)之间的距离为3λ/16。反射电极30的位置决定于压电基片9以及反射电极30材料。在本发明实施例中采用41°YXLiNbO₃基片与铝电极材料，图3a所示的控制电极宽度单相单向换能器获得如图2a中三个反射器方向的声波单向辐射的条件是反射电极30置于叉指电极对31的左侧，即与单向辐射的声波相反的方向。With reference to Fig. 3 a, the transducer 2 of the present embodiment is a control electrode width single-phase unidirectional transducer (EWC/SPUDT) using aluminum as an electrode, wherein the interdigital electrode pair 31 and the reflective electrode 30 are composed of

Made of aluminum film; the single-phase unidirectional transducer is composed of 6 interdigital electrode pairs 31, and 5 reflective electrodes 30 with an electrode width of 1λ/4 arranged between the 6 interdigital electrode pairs 31. Of course, the fork The number of finger electrode pairs 31 can also be any number between 10-20; the distance between the reflective electrode 30 and the interdigital electrode pair 31 (composed of two 1λ/8 electrodes) is 3λ/16. The position of the reflective electrode 30 is determined by the piezoelectric substrate 9 and the material of the reflective electrode 30 . Adopt 41 ° YXLiNbO ₃ substrates and in the embodiment of the present invention Aluminum electrode material, the control electrode width shown in Figure 3a. The single-phase unidirectional transducer obtains the acoustic wave unidirectional radiation in the direction of the three reflectors in Figure 2a. The condition is that the reflective electrode 30 is placed on the left side of the interdigitated electrode pair 31 , that is, in the opposite direction to the unidirectionally radiated sound waves.

The 11 reflectors (the A-th reflector 19 to the K-th reflector 29) all adopt a short-circuit grid reflector structure (the specific structure is shown in Figure 3b), and the minimum is 2 to obtain 3 to 10 1λ/4 widths The electrodes are short-circuited. In order to reduce the sound wave attenuation caused by multiple reflectors between reflectors, 11 reflectors are placed in two paths, and the Ath reflector 19 to the Hth reflector 26 are placed in one path for 8-bit electronic tags , the I-th reflector 27 to the K-th reflector 29 are arranged on another path for temperature detection. Since the peripheral temperature change is based on the linear correlation between the sound wave speed and temperature, the sound wave propagation speed changes linearly, thus causing the time-domain reflection peak time of the I-th reflector 27 to the K-th reflector 29 used for temperature (T) detection delay changes, its temperature phase sensitivity ΔΦ can be evaluated by the formula ΔΦ=l ₂ /l ₁ ×2πf ₀ l ₁ /v ₀ ×TCD×(TT _ref )=l ₂ /l ₁ ×2πf ₀ ×Δτ (Reference 5 : LMReindl, et al, Wireless measurement of temperature using surface acoustic waves sensors, IEEE, Trans.UFFC, Vol.51, No.11, 2004, pp.1457-1463), where l ₁ and l ₂ are respectively J The distance between the first reflector 28 and the K reflector 29 and the I reflector 27 and the J reflector 28, f ₀ is the sensor operating frequency, and v ₀ is the sound wave velocity under the reference temperature (usually room temperature) condition , TCD is the first-order temperature coefficient of the substrate material, and T _ref is the reference temperature (ie room temperature). The larger the l ₂ /l ₁ value, the higher the detection sensitivity is likely to be obtained. However, considering the propagation attenuation of sound wave propagation, that is, the longer the propagation distance will result in a greater propagation loss, so the sound wave propagation distance needs to be controlled within a certain range In order to reduce the sound propagation loss, in the solution of the present invention, the value of l ₂ /l ₁ is about 3 after comprehensive consideration.

The basic structure of the integrated SAW temperature sensor of the present embodiment is: make an EWC/SPUDT2 and the reflector of above-mentioned 11 short-circuit grid structures on the piezoelectric substrate 9, by EWC/SPUDT 2 receive by wireless antenna 14 from The electromagnetic wave signal 15 emitted by the wireless reading unit 17 is converted into a surface acoustic wave, propagates along the direction of 11 reflectors on the surface of the piezoelectric substrate 9, and is reflected by the 11 reflectors respectively. The sound wave is re-converted into an electromagnetic wave signal 16 by the EWC/SPUDT2, and is transmitted back to the wireless reading unit 17 by the wireless antenna 14, and passes through a signal processing method (which is competent for those skilled in the art) to evaluate the phase change of the time domain response To realize the detection of temperature.

In addition, due to the influence of sound wave propagation attenuation, in order to maintain a uniform time-domain response, the electrode structure of the 11 reflectors of the SAW reflective delay line 11 needs to be optimally designed to compensate for the time-domain loss caused by sound propagation attenuation. The nearest A-th reflector 19 to C-th reflector 21 of EWC/SPUDT 2 adopts the least number of electrodes (5 electrodes in the embodiment of the present invention), the farther away from EWC/SPUDT 2, the more the number of reflector electrodes (D-F reflector 22～24 adopts 6 electrodes in the embodiment of the present invention, G reflector 25～H reflector 26 adopts 7 electrodes, I reflector 22～J reflector 28 adopts 8 electrodes, and the Kth reflector 29 farthest from EWC/SPUDT 2 adopts 9 electrodes).

In the embodiment of the present invention, the connection relationship between the matching network 13 between the SAW reflective delay line 11 and the wireless antenna 14, as shown in Figure 5, the input end N1 of the transducer 2 of the SAW reflective delay line 11, and the The signal terminal N3 of the antenna 14 is connected to an inductance 32 in series in the circuit, and an inductance 33 in parallel; the ground terminal N2 of the E transducer 2 is directly connected to the ground terminal N4 of the wireless antenna; through the matching network 13, the encapsulated SAW reflection The impedance matching state is achieved between the type delay line 11 and the wireless antenna 14, so as to obtain lower loss and improve the signal-to-noise ratio performance of the sensor.

In this embodiment, in order to obtain relatively steep and sharp time-domain reflection peaks, the number of finger pairs of EWC/SPUDT 2 is 15, that is, it includes 15 interdigital electrode pairs 31 as shown in Figure 3a, and is distributed on the electrode pairs. 14 reflective electrodes 30 between them.

In this embodiment, the distance between the A-th reflector 19 of the SAW reflective delay line 11 and the EWC/SPUDT 2 is 3272.4 μm, so as to provide the necessary distance between the environmental noise echo and the sensor signal Sufficient latency of at least 1.2 μs.

The concrete structure of the SAW reflective delay line 11 is shown in Figure 4, and the relevant structural parameters in the figure are as follows:

The working frequency of the SAW reflective delay line 11: 434MHz; the wavelength of the sound wave λ: 10.9μm;

The width of a=piezoelectric substrate 9: 6mm;

The length of b=piezoelectric substrate 9: 18mm;

A=EWC/SPUDT 2 length: 15×λ=163.5μm;

B＝Acoustic aperture of EWC/SPUDT 2: 110×λ＝1199μm;

C=the width of the bus bar of the A-th reflector 19 to the K-th reflector 29: 5×λ=54.5 μm;

D = Acoustic aperture of reflector A 19 to reflector K 29: 50×λ=545 μm; H ₁ =length of reflector 19: 9×(1/4λ)=24.5 μm;

H ₂ =length of the Bth reflector 20: 9×(1/4λ)=24.5 μm; H ₃ =length of the reflector 21: 9×(1/4λ)=24.5 μm;

H ₄ =length of the Dth reflector 22: 11×(1/4λ)=30 μm; H ₅ =length of the reflector 23: 11×(1/4λ)=30 μm;

H ₆ =length of the Fth reflector 24: 11×(1/4λ)=30 μm; H ₇ =length of the reflector 25: 13×(1/4λ)=35.4 μm;

H ₈ =length of the Hth reflector 26: 13×(1/4λ)=35.4 μm; H ₉ =length of the reflector 27: 15×(1/4λ)=40.9 μm;

H ₁₀ = length of the J-th reflector 28: 15×(1/4λ)=40.9 μm; H ₁₁ = length of the reflector 29: 17×(1/4λ)=46.3 μm;

l ₁ = the distance between the A-th reflector 19 and EWC/SPUDT 2: 3272.4 μm;

l ₂ = the distance between the Bth reflector 20 and the reflector 19: 383.4 μm;

l ₃ = the distance between the Cth reflector 21 and the reflector 20: 386.1 μm;

l ₄ = the distance between the Dth reflector 22 and the reflector 21: 388.8 μm;

l ₅ = the distance between the Eth reflector 23 and the reflector 22: 391.5 μm;

l ₆ = the distance between the Fth reflector 24 and the reflector 23: 394.2 μm;

l ₇ = the distance between the Gth reflector 25 and the reflector 24: 396.9 μm;

l ₈ = the distance between the Hth reflector 26 and the reflector 25: 399.6 μm;

l ₉ = the distance between the first reflector 27 and the reflector 26: 437.4 μm;

l ₁₀ = the distance between the Jth reflector 28 and the reflector 27: 442.8 μm;

l ₁₁ = the distance between the Kth reflector 29 and the reflector 28: 1309.5 μm;

With this reflector design, the SAW reflective delay line 11 will obtain a uniform reflection peak in the time domain of the reflector, and have a consistent loss and signal-to-noise ratio. Fig. 6 shows the response curve of the typical time-domain reflection coefficient S ₁₁ of the 434MHz SAW reflective delay line 11 before packaging observed from the HP8510 network analyzer. The 11 reflection peaks come from the 11 reflectors of the SAW reflective delay line, which have relatively uniform loss and signal-to-noise ratio performance, and the corresponding time domain S ₁₁ loss is 39-43dB; the 1st to 8th reflection peaks come from The A-th reflector 19 to the H-th reflector 26 are applied to 8-bit electronic tags, and the time delay corresponding to the first reflection peak is 1.4 μs. The ninth to eleventh reflection peaks come from the first reflector 27 to the J reflector 29, and are used for temperature detection. The time delay corresponding to the ninth reflection peak is 2.81 μs, the time delay corresponding to the tenth reflection peak is 3 μs, and the time delay corresponding to the eleventh reflection peak 11 is 3.54 μs. The time delay difference between the 10th and 11th reflection peaks is about 3 times the time delay difference corresponding to the 9th and 10th reflection peaks. Judging from the above test results, lower loss, good signal-to-noise ratio, sharper reflection peak and lower peak-to-peak noise are achieved.

The embodiments described above are only one of the more preferred specific implementation modes of the present invention, and the usual changes and replacements performed by those skilled in the art within the technical solution of the present invention shall be included in the protection scope of the present invention.

Claims (7)

1. the surface acoustic wave wireless temperature sensor of an integrated form, comprise SAW reflective delay line (11); Described SAW reflective delay line (11) is by a piezoelectric substrate (9), with upper along the Acoustic Wave Propagation direction at described piezoelectric substrate (9), two conducting films (10) that apply out on the both sides, up and down, and a set transducer (2) forms with reverberator; It is characterized in that: also comprise element pasted on surface (12), sound absorption glue, impedance matching network (13), wireless antenna (14) and reading unit (17), and the reverberator that arranges at this piezoelectric substrate (9) is 11;

Described piezoelectric substrate (9) is 41 ° of lithium niobate substrates of propagating along directions X of a Y-direction rotation; And be chosen in an end on the long limit of described piezoelectric substrate (9), both sides up and down along the surface apply out two conducting films (10), the first sound absorption glue (18) is set in the middle of described two conducting films (10), and described transducer (2) is along the end setting of conducting film (10); Also the other end at described piezoelectric substrate (9) arranges the second sound absorption glue;

Described transducer (2) is control electrode width single phase unidirectional transducer; This transducer (2), is reached the reflecting electrode that an electrode width is 1 λ/4 (30) composition is set between every 2 interdigital electrodes are to (31) (31) by 2 above interdigital electrodes, and wherein λ is wave length of sound; Described reflecting electrode (30) and described interdigital electrode are 3 λ/16 to the distance between (31), described interdigital electrode forms (31) electrode by two 1 λ/8 width, and described interdigital electrode is done by aluminum (31) and described reflecting electrode (30);

Described 11 reverberators are the short-circuit gate reverberator, and wherein, described each short-circuit gate reverberator is comprised of the electrode of 21 λ/4 width at least; Described 11 reverberators are divided into the two-way setting, and one the tunnel is used for electronic tag, and the short-circuit gate reverberator word order that is equated by 8 sizes, spacing forms; An other paths is used for temperature detection, is comprised of 3 short-circuit gate reverberators, and setting position word order below last reverberator of continuing to use in 8 short-circuit gate reverberators of electronic tag forms;

Be connected a series inductance (32) in connecting circuit between the input end N1 of the transducer (2) of described SAW reflective delay line (11) and the signal end N3 of described wireless antenna (14), be connected the inductance (33) of a ground connection in the connecting circuit between the signal end N3 of described series inductance (32) and described wireless antenna (14); The earth terminal N4 of this wireless antenna (14) is electrically connected to the earth terminal N2 of described control electrode width single phase unidirectional transducer (2), realizes impedance matching between SAW reflective delay line (11) and wireless antenna (14) with this;

Described element pasted on surface (12) has 10 pins, the sealed package that is used for the SAW radio temperature sensor, the protection of formation to the electrode of the transducer (2) of SAW reflective delay line (11), 11 reverberators and piezoelectric substrate (9) surface, and complete being electrically connected to of SAW reflective delay line (11) and impedance matching network (13);

receive the electromagnetic wave signal (15) that comes from described reading unit (17) emission by described wireless antenna (14), convert SAW to by described control electrode width single phase unidirectional transducer (2), and propagate and be reflected back this control electrode width single phase unidirectional transducer (2) by 11 reflector sections along piezoelectric substrate (9) is surperficial, again convert electromagnetic wave signal (16) to, and pass reading unit (17) back by wireless antenna (14), also cause the variation of acoustic velocity due to the variation of peripheral temperature, thereby the time domain phase response that causes SAW reflective delay line (11), estimated to realize real-time detection to temperature by reading unit (17).

2. by the surface acoustic wave wireless temperature sensor of integrated form claimed in claim 1, it is characterized in that, the electromechanical coupling factor of described lithium niobate substrate is 17.2%, and acoustic propagation velocity is 4750m/s, 85ppm/ ℃ of first-order lag temperature coefficient.

3. by the surface acoustic wave wireless temperature sensor of integrated form claimed in claim 1, it is characterized in that, described transducer (2) refers to that logarithm is 10-20.

4. press the surface acoustic wave wireless temperature sensor of integrated form claimed in claim 1, it is characterized in that, the number of electrodes of described 11 reverberators arranges according to following rule: be that the A-C reverberator has minimum number of electrodes from 3 nearest reverberators of control electrode width single phase unidirectional transducer (2), along with the increase of distance, the number of electrodes of all the other reverberators increases progressively successively; The D-F reverberator adopts 6 electrodes, and the G-H reverberator adopts 7 electrodes, and the I-J reverberator adopts 8 electrodes, and K reverberator adopts 9 electrodes.

5. press the surface acoustic wave wireless temperature sensor of integrated form claimed in claim 1, it is characterized in that, the distance of described control electrode width single phase unidirectional transducer and A reverberator (19) is 3272.4 μ m, distance between B reverberator (20) and A reverberator (19) is 383.4 μ m, distance between C reverberator (21) and B reverberator (20) is 386.1 μ m, distance between D reverberator (22) and C reverberator (21) is 388.8 μ m, distance between E reverberator (23) and D reverberator (22) is 391.5 μ m, distance between F reverberator (24) and E reverberator (23) is 394.2 μ m, distance between G reverberator (25) and F reverberator (24) is 396.9 μ m, distance between H reverberator (26) and G reverberator (25) is 399.6 μ m, distance between I reverberator (27) and H reverberator (26) is 437.4 μ m, distance between J reverberator (28) and I reverberator (27) is 442.8 μ m, distance between K reverberator (29) and J reverberator (28) is 1309.5 μ m.

6. press the surface acoustic wave wireless temperature sensor of integrated form claimed in claim 5, it is characterized in that, the distance between described J reverberator (28) and K reverberator (29) is 3 times of distance between I reverberator (27) and J reverberator (28).

7. by the surface acoustic wave wireless temperature sensor of integrated form claimed in claim 1, it is characterized in that, the material of piezoelectric substrate (9) and reflecting electrode (30) is depended in the position of described reflecting electrode (30).

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