Structure and method of surface acoustic wave tag with radio frequency identification and temperature measurement functions

Abstract

This invention discloses a surface acoustic wave (SAW) tag structure and method with radio frequency identification (RFID) and temperature measurement functions. All coded SAW tags are fabricated using four photomasks, dividing the tag into four sub-regions. The center frequencies of the first and second sub-regions are 922.5 MHz, and those of the third and fourth sub-regions are 842.5 MHz. The coded reflective grating is located in one time slot of the corresponding coded data area. The last coded reflective grating in each sub-region is an interdigitated structure with an external load capacitor. The coding capacity is expanded based on the characteristic that the reflectivity of the interdigitated reflective grating changes with the external capacitor. The advantages of this invention are that it fully utilizes the reusable nature of the photomasks, meeting the requirements of large-scale applications with large coding capacity and a small number of photomasks, and allowing for dynamic expansion of the coding capacity. Not only are the identification results unaffected by temperature, but the temperature measurement accuracy is also further improved.

Description

Technical fields:

[0001] This invention relates to a surface acoustic wave tag structure and method with radio frequency identification and temperature measurement functions, belonging to the fields of radio frequency identification and wireless sensing. Background technology:

[0002] In the field of food safety, information traceability and temperature monitoring of food are extremely important. In recent years, the demand for cold chain food and fresh food delivery has exploded. At the same time, many food safety incidents have occurred during the production, storage, transportation, and distribution of cold chain food. The reasons can be summarized as follows:

[0003] (1) Many food safety incidents cannot be traced back to their source. The lack of full-process tracking of production, logistics and other aspects leads to unclear responsibility.

[0004] (2) Cold chain foods and other foods with specific temperature requirements are not monitored in real time during production and distribution, so that corresponding measures cannot be taken in time when unexpected situations such as abnormal temperature occur.

[0005] To address the issue of food safety incidents where the source cannot be traced, data on food from production to the table can be aggregated by assigning unique codes and using radio frequency identification (RFID) to ensure reliable traceability of food information. At the same time, by monitoring food temperature and issuing warnings when temperatures are abnormal, it is possible to ensure that cold chain foods are produced and distributed at specified temperatures.

[0006] Surface acoustic wave (SAW) tags can be encoded using information such as the number of reflective gratings and the distance between them to achieve radio frequency identification (RFID) functionality. Simultaneously, the propagation characteristics of SAW waves are temperature-sensitive, thus SAW tags can also perform temperature measurement. The invention patent "Surface Acoustic Wave Device with Integrated Radio Frequency Identification and Wireless Sensing Functions and its Working Method" (Application No.: 202010855130.9, Application Date: 2020.08.24) introduces a dual-frequency, four-channel, single-ended delay linear structure, which integrates RFID and temperature sensing functions through two channels (single frequency). However, this patent has the following problems:

[0007] (1) Although the combination of time slot coding and phase slot coding can theoretically increase the coding capacity, different coding surface acoustic wave tags must use different masks, which is extremely expensive and makes it almost impossible to realize large-scale food safety applications with large-capacity coding. This is the bottleneck that surface acoustic wave radio frequency identification and wireless sensing integrated tags currently face.

[0008] (2) The coding capacity is determined by the design rules. Once the design and production work is completed, the coding capacity cannot be changed. When the food safety application scenario is upgraded and the coding capacity is insufficient, it is usually necessary to change the design rules and remake the surface acoustic wave labels. All the original labels will be unusable, and dynamic expansion of the coding capacity cannot be achieved.

[0009] (3) The phase gap coding is significantly affected by temperature. During identification, it is necessary to deduce the initial phase of the coding reflective grating at the reference temperature based on the positional relationship between the reflective gratings, so as to solve the phase gap coding, which makes the tag design and identification algorithm more complicated. Summary of the Invention:

[0010] This invention addresses the problems existing in current surface acoustic wave (SAW) tags that integrate radio frequency identification (RFID) and temperature measurement functions. It proposes a SAW tag structure and method with RFID and temperature measurement functions, which can not only overcome the current bottlenecks faced by SAW RFID and wireless sensing integrated tags to a certain extent, but also has an open expansion function for encoding capacity, as well as a relatively simple identification algorithm and high temperature measurement accuracy.

[0011] The present invention adopts the following technical solution: a surface acoustic wave tag structure with radio frequency identification and temperature measurement functions, wherein all coded surface acoustic wave tags are made by splicing four mask plates and externally connected to capacitors of different capacitance values;

[0012] The surface acoustic wave (SAW) tag structure includes a piezoelectric substrate, a first interdigital transducer, a second interdigital transducer, a third interdigital transducer, a fourth interdigital transducer, a first reference reflector, a second reference reflector, a first temperature-compensated reflector, a second temperature-compensated reflector, a third temperature-compensated reflector, a fourth temperature-compensated reflector, a first coded reflector, a second coded reflector, a third coded reflector, a fourth coded reflector, a fifth coded reflector, a sixth coded reflector, a seventh coded reflector, an eighth coded reflector, a ninth coded reflector, a tenth coded reflector, a first load capacitor, a second load capacitor, a third load capacitor, a fourth load capacitor, and an antenna; wherein, the fourth coded reflector, the fifth coded reflector, the ninth coded reflector, and the tenth coded reflector are interdigital grid structures, respectively externally connected to the first load capacitor, the second load capacitor, the third load capacitor, and the fourth load capacitor, while the other reflector grids are open-circuit grid structures;

[0013] The surface acoustic wave (SAW) tag is divided into four sub-regions, namely the first sub-region, the second sub-region, the third sub-region, and the fourth sub-region, from the top to the bottom of the piezoelectric substrate. The four sub-regions correspond one-to-one with the four masks used in the fabrication of the SAW tag, that is, the first sub-region corresponds to the first mask, the second sub-region corresponds to the second mask, the third sub-region corresponds to the third mask, and the fourth sub-region corresponds to the fourth mask.

[0014] The first interdigital transducer, the first reference reflector, the second temperature-compensated reflector, the second coded reflector, and the fourth coded reflector constitute the first sub-region of the surface acoustic wave tag;

[0015] The second interdigital transducer, the first temperature-compensated reflective grating, the first coded reflective grating, the third coded reflective grating, and the fifth coded reflective grating constitute the second sub-region of the surface acoustic wave tag;

[0016] The third interdigital transducer, the second reference reflector, the fourth temperature-compensated reflector, the seventh coded reflector, and the ninth coded reflector constitute the third sub-region of the surface acoustic wave tag.

[0017] The fourth interdigital transducer, the third temperature-compensated reflective grating, the sixth coded reflective grating, the eighth coded reflective grating, and the tenth coded reflective grating constitute the fourth sub-region of the surface acoustic wave tag;

[0018] By designing the finger strip widths of the first interdigital transducer, the second interdigital transducer, the fourth coded reflector, and the fifth coded reflector, and the grating strip widths of the first reference reflector, the first temperature-compensated reflector, the second temperature-compensated reflector, the first coded reflector, the second coded reflector, and the third coded reflector, the center frequency f1 of the first and second sub-regions of the surface acoustic wave (SAW) tag is 922.5 MHz; by designing the finger strip widths of the third interdigital transducer, the fourth interdigital transducer, the ninth coded reflector, and the tenth coded reflector, and the grating strip widths of the second reference reflector, the third temperature-compensated reflector, the fourth temperature-compensated reflector, the sixth coded reflector, the seventh coded reflector, and the eighth coded reflector, the center frequency f2 of the third and fourth sub-regions of the SAW tag is 842.5 MHz.

[0019] The distances between the first reference reflective grating, the second temperature-compensated reflective grating, the second coded reflective grating, the fourth coded reflective grating and the first interdigital transducer, as well as the distances between the first temperature-compensated reflective grating, the first coded reflective grating, the third coded reflective grating, the fifth coded reflective grating and the second interdigital transducer, are all different to ensure that the echo pulse signals corresponding to all reflective gratings in the first sub-region and the second sub-region of the surface acoustic wave tag do not interfere with each other in time.

[0020] The distances between the second reference reflector, the fourth temperature-compensated reflector, the seventh coded reflector, the ninth coded reflector and the third interdigital transducer, as well as the distances between the third temperature-compensated reflector, the sixth coded reflector, the eighth coded reflector, the tenth coded reflector and the fourth interdigital transducer, are all different to ensure that the echo pulse signals corresponding to all reflectors in the third and fourth sub-regions of the surface acoustic wave tag do not interfere with each other in time.

[0021] The first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, and tenth coded reflector gratings are located in ten coded data areas; each coded data area is equally spaced into M time slots, and the coded reflector grating is located in one of these time slots. The coding capacity is then (M... 5 ) 2 The required number of photomasks is (M) 2 +M 3 () ×2; The capacitance values ​​of the first, second, third, and fourth load capacitors each have N possible options, thus further encoding is performed on top of the time slot encoding by connecting external capacitors with different capacitance values, and the encoding capacity can reach (M) ×2; 5 ×N 2 ) 2 The number of photomasks required is still (M) 2 +M 3 )×2. Taking M=5 and N=8 as an example, when only time slot coding is used, the coding capacity is 9,765,625, which is close to 10 million, and the number of masks required is 300; further coding of external capacitors with different capacitance values ​​can reach a capacity of 40 billion, and the number of masks still only needs to be 300.

[0022] Furthermore, the antenna is a dual-band antenna covering two frequency bands: 840–845MHz and 920–925MHz, and is fabricated on a PCB. The first, second, third, and fourth load capacitors are soldered onto the PCB on which the antenna is fabricated. The first, second, third, and fourth sub-regions of the surface acoustic wave (SAW) tag are fabricated using four corresponding photomasks, encapsulated, and then soldered onto the PCB on which the antenna is fabricated. The busbars at both ends of the first, second, third, and fourth interdigital transducers are connected to the antenna on the PCB via pads on the package. The busbars at both ends of the fourth, fifth, ninth, and tenth coded reflector gratings are connected to the first, second, third, and fourth load capacitors on the PCB via pads on the package, respectively, thereby integrating the SAW tag onto the PCB.

[0023] This invention also includes the following technical solution: a method for identifying and measuring temperature of a surface acoustic wave tag structure with radio frequency identification and temperature measurement functions, comprising the following steps: wherein step A is the encoding stage:

[0024] Step A: For surface acoustic wave (SAW) tags with different time slot codes, select the corresponding first, second, third, and fourth mask plates and use these four mask plates to splice together to make the tags; for SAW tags with different external capacitance values, further encode them by soldering four load capacitors of corresponding capacitance values ​​at the corresponding positions on the PCB and attaching the PCB to the item to be identified and temperature measured.

[0025] Step B: The reader transmits an excitation pulse signal with a carrier frequency of f1, which is radiated outward in the form of electromagnetic waves through the reader antenna; the surface acoustic wave tag receives the excitation pulse signal through the antenna, and the first sub-region and the second sub-region, whose center frequency is the same as the carrier frequency of the excitation pulse signal, respond to the excitation pulse signal. The first interdigital transducer and the second interdigital transducer convert the excitation pulse signal into surface acoustic waves through the inverse piezoelectric effect, which propagate along the piezoelectric substrate surface of the first sub-region and the second sub-region, respectively;

[0026] Step C: The surface acoustic wave propagating along the first sub-region sequentially encounters the first reference reflection grating, the second temperature-compensated reflection grating, the second coded reflection grating, and the fourth coded reflection grating, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the first interdigital transducer. The surface acoustic wave propagating along the second sub-region sequentially encounters the first temperature-compensated reflection grating, the first coded reflection grating, the third coded reflection grating, and the fifth coded reflection grating, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the second interdigital transducer. The first and second interdigital transducers convert the above 8 reflected signals into a first echo pulse train including 8 echo pulse signals through the positive piezoelectric effect. The timing sequence of the 8 echo pulse signals has a one-to-one correspondence with the positions of the above 8 reflection gratings. The first echo pulse train is transmitted back to the reader antenna through the antenna.

[0027] Step D: The reader processes the first echo pulse train. Based on the time difference between the echo pulse signals of the first, second, third, fourth, and fifth coded reflective gratings and the echo pulse signal of the first reference reflective grating, the time slot codes of the first and second sub-regions are obtained. Since the reflectivity of the interdigitated grating corresponds to its external load capacitance, the codes of the first and second sub-regions with different external capacitance values ​​are obtained based on the amplitude ratio of the echo pulse signals of the fourth and fifth coded reflective gratings and the echo pulse signal of the first reference reflective grating. The first temperature compensation... The time difference between the echo pulse signals of the first reference reflector and the second temperature-compensated reflector is used as the reference time delay. Based on the known relationship between the distances between the first reference reflector, the first temperature-compensated reflector, the second temperature-compensated reflector, the first coded reflector, the second coded reflector, the third coded reflector, the fourth coded reflector, and the fifth coded reflector at the reference temperature, the unambiguous phase change of the reference time delay caused by temperature is gradually extrapolated to the unambiguous phase difference of the echo pulse signals of the two farthest reflectors among the above eight reflectors, namely the first reference reflector and the fifth coded reflector, in a proportional extrapolation manner from near to far. This achieves high-precision temperature measurement.

[0028] Step E: The reader transmits an excitation pulse signal with a carrier frequency of f2, which is radiated outward in the form of electromagnetic waves through the reader antenna; the surface acoustic wave tag receives the excitation pulse signal through the antenna, and the third and fourth sub-regions, whose center frequencies are consistent with the carrier frequency of the excitation pulse signal, respond to the excitation pulse signal. The third and fourth interdigital transducers convert the excitation pulse signal into surface acoustic waves through the inverse piezoelectric effect, which propagate along the piezoelectric substrate surface of the third and fourth sub-regions, respectively.

[0029] Step F: The surface acoustic wave propagating along the third sub-region encounters the second reference reflector, the fourth temperature-compensated reflector, the seventh coded reflector, and the ninth coded reflector in sequence, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the third interdigital transducer. The surface acoustic wave propagating along the fourth sub-region encounters the third temperature-compensated reflector, the sixth coded reflector, the eighth coded reflector, and the tenth coded reflector in sequence, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the fourth interdigital transducer. The third and fourth interdigital transducers convert the above eight reflected signals into a second echo pulse train including eight echo pulse signals through the positive piezoelectric effect. The timing of the eight echo pulse signals corresponds one-to-one with the positions of the eight reflector gratings. The second echo pulse train is transmitted back to the reader antenna through the antenna.

[0030] Step G: The reader processes the second echo pulse train. Based on the time difference between the echo pulse signals of the sixth, seventh, eighth, ninth, and tenth coded reflective gratings and the echo pulse signal of the second reference reflective grating, it obtains the time slot codes for the third and fourth sub-regions. Based on the amplitude ratio of the echo pulse signals of the ninth and tenth coded reflective gratings to the echo pulse signal of the second reference reflective grating, it obtains the codes for the external capacitors of the third and fourth sub-regions with different capacitance values. The echo pulse signals of the third and fourth temperature-compensated reflective gratings are then compared with the time difference between the echo pulse signals of the sixth, seventh, eighth, ninth, and tenth coded reflective gratings and the echo pulse signal of the second reference reflective grating. Using the time difference of the wave pulse signal as a reference time delay, and based on the known relationship between the distances between the second reference reflection grating, the third temperature-compensated reflection grating, the fourth temperature-compensated reflection grating, the sixth coded reflection grating, the seventh coded reflection grating, the eighth coded reflection grating, the ninth coded reflection grating, and the tenth coded reflection grating at the reference temperature, the unambiguous phase change of the reference time delay caused by temperature is gradually extrapolated to the unambiguous phase difference of the echo pulse signal of the two farthest reflection gratings among the above eight reflection gratings, namely the second reference reflection grating and the tenth coded reflection grating, in a proportional extrapolation manner from near to far, thereby achieving high-precision temperature measurement;

[0031] Step H: Combine the codes of the first and second sub-regions measured in step D with the codes of the third and fourth sub-regions measured in step G to obtain the code of the surface acoustic wave tag; take the average of the temperatures measured in step D and step G to obtain the temperature of the surface acoustic wave tag.

[0032] The present invention has the following beneficial effects:

[0033] 1. All coded surface acoustic wave (SAW) tags are made by splicing four mask plates and further encoded by external capacitors of different capacitance values. This not only results in a huge encoding capacity but also requires very few mask plates, thus enabling large-scale food safety applications with high-capacity encoding and breaking through the current bottleneck faced by integrated SAW RFID and wireless sensing tags.

[0034] 2. By fully utilizing the reusable feature of the mask, the overall cost of the integrated surface acoustic wave radio frequency identification and temperature sensing system is reduced, enabling its practical application.

[0035] 3. While ensuring the reader's recognition performance, the encoding capacity can be dynamically expanded by subdividing the selectable capacitance value of the load capacitor, and the original tags can continue to be used.

[0036] 4. For interdigitated coded reflective gratings with external capacitors, the encoding of external capacitors with different capacitance values ​​is obtained by the ratio of the echo pulse signal amplitude corresponding to the interdigitated reflective grating and the reference reflective grating, thereby eliminating the influence of distance on the recognition result.

[0037] 5. The tag uses a combination of time slot coding and external capacitors with different capacitance values ​​for coding. Compared with the existing coding scheme that combines time slots and phase slots, the recognition result is not affected by temperature, so the tag design and recognition algorithm are relatively simple.

[0038] 6. By transmitting two excitation pulse signals of different frequencies, measuring the temperature twice, and then averaging the results, the accuracy of temperature measurement is further improved. Attached image description:

[0039] Figure 1 This is a schematic diagram of the surface acoustic wave label structure of the present invention, which is made by splicing together four mask plates.

[0040] Figure 2 This is a schematic diagram of the surface acoustic wave tag of the present invention integrated on a PCB.

[0041] Figure 3 This is a schematic diagram of the echo pulse signals (first echo pulse train) corresponding to all the reflection gratings in the first and second sub-regions of the surface acoustic wave tag of the present invention.

[0042] Figure 4 This is a schematic diagram of the echo pulse signals (second echo pulse train) corresponding to all the reflection gratings in the third and fourth sub-regions of the surface acoustic wave tag of the present invention.

[0043] The labels in the above figures are as follows: 01. Piezoelectric substrate, 02. First interdigital transducer, 03. Second interdigital transducer, 04. Third interdigital transducer, 05. Fourth interdigital transducer, 06. First reference reflector, 07. Second reference reflector, 08. First temperature-compensated reflector, 09. Second temperature-compensated reflector, 10. Third temperature-compensated reflector, 11. Fourth temperature-compensated reflector, 12. First coded reflector, 13. Second coded reflector, 14. Third coded reflector, 15. Fourth coded reflector, 16. Fifth coded reflector, 17. Sixth coded reflector, 18. Seventh coded reflector, 19. Eighth coded reflector, 20. Ninth coded reflector, 21. Tenth coded reflector, 22. First load capacitor, 23. Second load capacitor, 24. Third load capacitor, 25. Fourth load capacitor, 26. Antenna. Detailed implementation method:

[0044] The invention will now be further described with reference to the accompanying drawings.

[0045] Please refer to Figure 1 Combination Figure 2As shown, the surface acoustic wave (SAW) tag structure of the present invention includes a piezoelectric substrate 01, a first interdigital transducer 02, a second interdigital transducer 03, a third interdigital transducer 04, a fourth interdigital transducer 05, a first reference reflector grating 06, a second reference reflector grating 07, a first temperature-compensated reflector grating 08, a second temperature-compensated reflector grating 09, a third temperature-compensated reflector grating 10, a fourth temperature-compensated reflector grating 11, a first coded reflector grating 12, a second coded reflector grating 13, a third coded reflector grating 14, a fourth coded reflector grating 15, a fifth coded reflector grating 16, a sixth coded reflector grating 17, a seventh coded reflector grating 18, an eighth coded reflector grating 19, a ninth coded reflector grating 20, a tenth coded reflector grating 21, a first load capacitor 22, a second load capacitor 23, a third load capacitor 24, a fourth load capacitor 25, and an antenna 26.

[0046] The fourth coding reflective grating 15, the fifth coding reflective grating 16, the ninth coding reflective grating 20, and the tenth coding reflective grating 21 are interdigitated grating structures, and are respectively connected to the first load capacitor 22, the second load capacitor 23, the third load capacitor 24, and the fourth load capacitor 25. The other reflective gratings are all open-circuit grating structures.

[0047] The surface acoustic wave (SAW) tag is divided into four sub-regions, namely the first sub-region, the second sub-region, the third sub-region, and the fourth sub-region, from the top to the bottom of the piezoelectric substrate 01. The four sub-regions correspond one-to-one with four photomasks, that is, the first sub-region corresponds to the first photomask, the second sub-region corresponds to the second photomask, the third sub-region corresponds to the third photomask, and the fourth sub-region corresponds to the fourth photomask. Thus, the SAW tag can be fabricated by splicing four photomasks together to reduce costs.

[0048] The first interdigital transducer 02, the first reference reflector 06, the second temperature-compensated reflector 09, the second coded reflector 13, and the fourth coded reflector 15 constitute the first sub-region of the surface acoustic wave (SAW) tag; the second interdigital transducer 03, the first temperature-compensated reflector 08, the first coded reflector 12, the third coded reflector 14, and the fifth coded reflector 16 constitute the second sub-region of the SAW tag; the third interdigital transducer 04, the second reference reflector 07, the fourth temperature-compensated reflector 11, the seventh coded reflector 18, and the ninth coded reflector 20 constitute the third sub-region of the SAW tag; and the fourth interdigital transducer 05, the third temperature-compensated reflector 10, the sixth coded reflector 17, the eighth coded reflector 19, and the tenth coded reflector 21 constitute the fourth sub-region of the SAW tag.

[0049] Based on the center frequency f = v / λ, where v is the propagation speed of the surface acoustic wave, which depends on the shear shape of the piezoelectric substrate 01, and λ is the wavelength of the surface acoustic wave, it has a corresponding relationship with the finger strip width of the interdigital transducer and the interdigital reflector grating, and the grating strip width of the open-circuit reflector grating and the short-circuit reflector grating. Considering the actual situation of dividing the 800 / 900MHz frequency band into two independent frequency bands, 840–845MHz and 920–925MHz, according to Chinese standards, the finger strip widths of the first interdigital transducer 02, the second interdigital transducer 03, the fourth coded reflector grating 15, and the fifth coded reflector grating 16, and the first reference reflector grating 06, the first temperature-compensated reflector grating 08, and the second temperature-compensated reflector grating are designed. 09. The grating widths of the first coded reflective grating 12, the second coded reflective grating 13, and the third coded reflective grating 14 are such that the center frequency f1 of the first and second sub-regions of the surface acoustic wave (SAW) tag is 922.5MHz. By designing the finger strip widths of the third interdigital transducer 04, the fourth interdigital transducer 05, the ninth coded reflective grating 20, and the tenth coded reflective grating 21, and the grating strip widths of the second reference reflective grating 07, the third temperature-compensated reflective grating 10, the fourth temperature-compensated reflective grating 11, the sixth coded reflective grating 17, the seventh coded reflective grating 18, and the eighth coded reflective grating 19, the center frequency f2 of the third and fourth sub-regions of the SAW tag is 842.5MHz.

[0050] Ten coded reflector grids are located in ten coded data regions. Each coded data region is divided into M time slots at equal intervals, and the coded reflector grid is located in one of these time slots, for example... Figure 1 The first coded reflector 12, the second coded reflector 13, the third coded reflector 14, the fourth coded reflector 15, the fifth coded reflector 16, the sixth coded reflector 17, the seventh coded reflector 18, the eighth coded reflector 19, the ninth coded reflector 20, and the tenth coded reflector 21 are located in the 1st, 1st, 2nd, 2nd, 1st, 2nd, Mth, Mth, and 2nd time slots of their respective coded data areas. At this time, the coding capacity is (M... 5 ) 2 The required number of photomasks is (M) 2 +M 3 )×2. The capacitance values ​​of the four load capacitors each have N possible options, for example... Figure 1 The capacitance values ​​of the first load capacitor 22, the second load capacitor 23, the third load capacitor 24, and the fourth load capacitor 25 are the 1st, 2nd, 2nd, and Nth optional values, respectively. Based on the time slot encoding, further encoding is performed on external capacitors with different capacitance values, achieving an encoding capacity of up to (M... 5 ×N 2 ) 2 The number of photomasks required is still (M) 2 +M 3)×2. Taking M=5 and N=8 as an example, when only time slot coding is used, the coding capacity is 9,765,625, which is close to 10 million, and the number of masks required is 300; further coding of external capacitors with different capacitance values ​​can reach a capacity of 40 billion, and the number of masks still only needs to be 300.

[0051] Antenna 26 is a dual-band antenna covering two frequency bands: 840–845MHz and 920–925MHz, and is fabricated on a PCB. The first load capacitor 22, the second load capacitor 23, the third load capacitor 24, and the fourth load capacitor 25 are soldered onto the PCB on which antenna 26 is fabricated. The first, second, third, and fourth sub-regions of the surface acoustic wave (SAW) tag are fabricated by splicing together four corresponding photomasks, packaged, and then soldered onto the PCB on which antenna 26 is fabricated. The busbars at both ends of the first interdigital transducer 02, the second interdigital transducer 03, the third interdigital transducer 04, and the fourth interdigital transducer 05 are connected to the antenna 26 on the PCB via pads on the package. The busbars at both ends of the fourth coded reflector grating 15, the fifth coded reflector grating 16, the ninth coded reflector grating 20, and the tenth coded reflector grating 21 are connected to the first load capacitor 22, the second load capacitor 23, the third load capacitor 24, and the fourth load capacitor 25 on the PCB via pads on the package, thereby integrating the SAW tag onto the PCB.

[0052] Please refer to Figure 1 , Figure 3 As shown, the distances between the first reference reflector grating 06, the second temperature-compensated reflector grating 09, the second coded reflector grating 13, the fourth coded reflector grating 15 and the first interdigital transducer 02, and the distances between the first temperature-compensated reflector grating 08, the first coded reflector grating 12, the third coded reflector grating 14, the fifth coded reflector grating 16 and the second interdigital transducer 03 are all different, so that the echo pulse signals (first echo pulse train) corresponding to all reflector gratings in the first sub-region and the second sub-region of the surface acoustic wave label do not interfere with each other in time.

[0053] Please refer to Figure 1 , Figure 4 As shown, the distances between the second reference reflector grating 07, the fourth temperature-compensated reflector grating 11, the seventh coded reflector grating 18, the ninth coded reflector grating 20 and the third interdigital transducer 04, and the distances between the third temperature-compensated reflector grating 10, the sixth coded reflector grating 17, the eighth coded reflector grating 19, the tenth coded reflector grating 21 and the fourth interdigital transducer 05 are all different, so that the echo pulse signals (second echo pulse trains) corresponding to all reflector gratings in the third and fourth sub-regions of the surface acoustic wave tag do not interfere with each other in time.

[0054] Please refer to Figure 1 , Figure 3 , Figure 4As shown, since the center frequency f1 of the first and second sub-regions of the surface acoustic wave label is 922.5MHz, while the center frequency f2 of the third and fourth sub-regions is 842.5MHz, according to the attenuation characteristics of electromagnetic waves, under the premise of the same distance, the amplitude of the second echo pulse train is slightly larger than that of the first echo pulse train.

[0055] Please refer to Figures 1 to 4 As shown, the identification and temperature measurement method of the integrated surface acoustic wave radio frequency identification and temperature measurement tag structure of the present invention includes the following steps, wherein step A is the encoding stage:

[0056] Step A: For surface acoustic wave (SAW) tags with different time slot codes, select the corresponding first, second, third, and fourth mask plates and use these four mask plates to splice together to make the tags; for SAW tags with different external capacitance values, further encode them by soldering four load capacitors of corresponding capacitance values ​​at the corresponding positions on the PCB and attaching the PCB to the item to be identified and temperature measured.

[0057] Step B: The reader transmits an excitation pulse signal with a carrier frequency of f1, which is radiated outward in the form of electromagnetic waves through the reader antenna; the surface acoustic wave tag receives the excitation pulse signal through antenna 26. The first sub-region and the second sub-region, whose center frequency is the same as the carrier frequency of the excitation pulse signal, respond to the excitation pulse signal. The first interdigital transducer 02 and the second interdigital transducer 03 convert the excitation pulse signal into surface acoustic waves through the inverse piezoelectric effect, which propagate along the piezoelectric substrate surface of the first sub-region and the second sub-region, respectively.

[0058] Step C: The surface acoustic wave propagating along the first sub-region sequentially encounters the first reference reflection grating 06, the second temperature-compensated reflection grating 09, the second coded reflection grating 13, and the fourth coded reflection grating 15, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the first interdigital transducer 02. The surface acoustic wave propagating along the second sub-region sequentially encounters the first temperature-compensated reflection grating 08, the first coded reflection grating 12, the third coded reflection grating 14, and the fifth coded reflection grating 16, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the second interdigital transducer 03. The first interdigital transducer 02 and the second interdigital transducer 03 convert the above 8 reflected signals into a first echo pulse train including 8 echo pulse signals through the positive piezoelectric effect. The timing sequence of the 8 echo pulse signals has a one-to-one correspondence with the positions of the above 8 reflection gratings. The first echo pulse train is transmitted back to the reader antenna through the antenna 26.

[0059] Step D: The reader processes the first echo pulse train. Based on the time difference between the echo pulse signals of the first coded reflective grating 12, the second coded reflective grating 13, the third coded reflective grating 14, the fourth coded reflective grating 15, and the fifth coded reflective grating 16 and the echo pulse signal of the first reference reflective grating 06, the time slot codes of the first sub-region and the second sub-region are obtained. Since there is a correspondence between the reflectivity of the interdigitated grating and its external load capacitance, the codes of the first sub-region and the second sub-region with different external capacitance values ​​are obtained based on the amplitude ratio of the echo pulse signals of the fourth coded reflective grating 15 and the fifth coded reflective grating 16 and the echo pulse signal of the first reference reflective grating 06. The time difference between the echo pulse signals of the first reference reflector 08 and the second temperature-compensated reflector 09 is used as the reference time delay. Based on the known relationship between the distances between the first reference reflector 06, the first temperature-compensated reflector 08, the second temperature-compensated reflector 09, the first coded reflector 12, the second coded reflector 13, the third coded reflector 14, the fourth coded reflector 15, and the fifth coded reflector 16 at the reference temperature, the reference time delay is gradually extrapolated to the unambiguous phase difference of the echo pulse signals of the two farthest reflectors among the above eight reflectors, namely the first reference reflector 06 and the fifth coded reflector 16, through a proportional extrapolation method from near to far. This achieves high-precision temperature measurement.

[0060] Step E: The reader transmits an excitation pulse signal with a carrier frequency of f2, which is radiated outward in the form of electromagnetic waves through the reader antenna; the surface acoustic wave tag receives the excitation pulse signal through antenna 26. The third sub-region and the fourth sub-region, whose center frequency is the same as the carrier frequency of the excitation pulse signal, respond to the excitation pulse signal. The third interdigital transducer 04 and the fourth interdigital transducer 05 convert the excitation pulse signal into surface acoustic waves through the inverse piezoelectric effect, which propagate along the piezoelectric substrate surface of the third sub-region and the fourth sub-region, respectively.

[0061] Step F: The surface acoustic wave propagating along the third sub-region encounters the second reference reflection grating 07, the fourth temperature-compensated reflection grating 11, the seventh coded reflection grating 18, and the ninth coded reflection grating 20 in sequence, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the third interdigital transducer 04. The surface acoustic wave propagating along the fourth sub-region encounters the third temperature-compensated reflection grating 10, the sixth coded reflection grating 17, the eighth coded reflection grating 19, and the tenth coded reflection grating 21 in sequence, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the fourth interdigital transducer 05. The third interdigital transducer 04 and the fourth interdigital transducer 05 convert the above 8 reflected signals into a second echo pulse train including 8 echo pulse signals through the positive piezoelectric effect. The timing sequence of the 8 echo pulse signals has a one-to-one correspondence with the positions of the above 8 reflection gratings. The second echo pulse train is transmitted back to the reader antenna through the antenna 26.

[0062] Step G: The reader processes the second echo pulse train. Based on the time difference between the echo pulse signals of the sixth coded reflector 17, the seventh coded reflector 18, the eighth coded reflector 19, the ninth coded reflector 20, and the tenth coded reflector 21 and the echo pulse signal of the second reference reflector 07, the time slot codes of the third and fourth sub-regions are obtained. Based on the amplitude ratio of the echo pulse signals of the ninth coded reflector 20 and the tenth coded reflector 21 and the echo pulse signal of the second reference reflector 07, the codes of the external capacitors of the third and fourth sub-regions with different capacitance values ​​are obtained. The third temperature-compensated reflector 10 and the fourth temperature-compensated reflector 11... Using the time difference of the echo pulse signal as a reference time delay, and based on the known relationship between the distances between the second reference reflector grating 07, the third temperature-compensated reflector grating 10, the fourth temperature-compensated reflector grating 11, the sixth coded reflector grating 17, the seventh coded reflector grating 18, the eighth coded reflector grating 19, the ninth coded reflector grating 20, and the tenth coded reflector grating 21 at the reference temperature, the unambiguous phase change of the reference time delay caused by temperature is gradually extrapolated to the unambiguous phase difference of the echo pulse signals of the two farthest reflectors among the above eight reflectors, namely the second reference reflector grating 07 and the tenth coded reflector grating 21, through a proportional extrapolation method from near to far, thereby achieving high-precision temperature measurement;

[0063] Step H: Combine the codes of the first and second sub-regions measured in step D with the codes of the third and fourth sub-regions measured in step G to obtain the code of the surface acoustic wave tag; take the average of the temperatures measured in step D and step G to obtain the temperature of the surface acoustic wave tag.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A surface acoustic wave tag structure with radio frequency identification and temperature measurement functions, characterized in that: All coded surface acoustic wave tags are made by splicing together four mask plates and connecting them with capacitors of different capacitance values. The surface acoustic wave (SAW) tag structure includes a piezoelectric substrate (01), a first interdigital transducer (02), a second interdigital transducer (03), a third interdigital transducer (04), a fourth interdigital transducer (05), a first reference reflector (06), a second reference reflector (07), a first temperature-compensated reflector (08), a second temperature-compensated reflector (09), a third temperature-compensated reflector (10), a fourth temperature-compensated reflector (11), a first coded reflector (12), a second coded reflector (13), a third coded reflector (14), a fourth coded reflector (15), a fifth coded reflector (16), a sixth coded reflector (17), and a seventh coded reflector (18). The coded reflector (18), the eighth coded reflector (19), the ninth coded reflector (20), the tenth coded reflector (21), the first load capacitor (22), the second load capacitor (23), the third load capacitor (24), the fourth load capacitor (25), and the antenna (26); among them, the fourth coded reflector (15), the fifth coded reflector (16), the ninth coded reflector (20), and the tenth coded reflector (21) are interdigitated grid structures, which are respectively connected to the first load capacitor (22), the second load capacitor (23), the third load capacitor (24), and the fourth load capacitor (25), while the other reflectors are open-circuit grid structures; The surface acoustic wave (SAW) tag is divided into four sub-regions, namely the first sub-region, the second sub-region, the third sub-region, and the fourth sub-region, from the top to the bottom of the piezoelectric substrate (01). The four sub-regions correspond one-to-one with the four masks used in the fabrication of the SAW tag, namely the first sub-region corresponds to the first mask, the second sub-region corresponds to the second mask, the third sub-region corresponds to the third mask, and the fourth sub-region corresponds to the fourth mask. The first interdigital transducer (02), the first reference reflector (06), the second temperature-compensated reflector (09), the second coded reflector (13), and the fourth coded reflector (15) constitute the first sub-region of the surface acoustic wave tag; The second interdigital transducer (03), the first temperature-compensated reflective grating (08), the first coded reflective grating (12), the third coded reflective grating (14), and the fifth coded reflective grating (16) constitute the second sub-region of the surface acoustic wave tag; The third interdigital transducer (04), the second reference reflector (07), the fourth temperature-compensated reflector (11), the seventh coded reflector (18), and the ninth coded reflector (20) constitute the third sub-region of the surface acoustic wave tag; The fourth interdigital transducer (05), the third temperature-compensated reflective grating (10), the sixth coded reflective grating (17), the eighth coded reflective grating (19), and the tenth coded reflective grating (21) constitute the fourth sub-region of the surface acoustic wave tag; By designing the finger strip widths of the first interdigital transducer (02), the second interdigital transducer (03), the fourth coded reflector (15), and the fifth coded reflector (16), and the grating strip widths of the first reference reflector (06), the first temperature-compensated reflector (08), the second temperature-compensated reflector (09), the first coded reflector (12), the second coded reflector (13), and the third coded reflector (14), the center frequencies of the first and second sub-regions of the surface acoustic wave label are made possible. f 1 is 922.5MHz; by designing the finger strip widths of the third interdigital transducer (04), the fourth interdigital transducer (05), the ninth coded reflector (20), the tenth coded reflector (21), and the grating strip widths of the second reference reflector (07), the third temperature-compensated reflector (10), the fourth temperature-compensated reflector (11), the sixth coded reflector (17), the seventh coded reflector (18), and the eighth coded reflector (19), the center frequencies of the third and fourth sub-regions of the surface acoustic wave label are made so that... f 2 is 842.5MHz; The distances between the first reference reflector (06), the second temperature-compensated reflector (09), the second coded reflector (13), the fourth coded reflector (15) and the first interdigital transducer (02), as well as the distances between the first temperature-compensated reflector (08), the first coded reflector (12), the third coded reflector (14), the fifth coded reflector (16) and the second interdigital transducer (03), are all different, to ensure that the echo pulse signals corresponding to all reflectors in the first sub-region and the second sub-region of the surface acoustic wave label do not interfere with each other in time; The distances between the second reference reflector (07), the fourth temperature-compensated reflector (11), the seventh coded reflector (18), the ninth coded reflector (20) and the third interdigital transducer (04), as well as the distances between the third temperature-compensated reflector (10), the sixth coded reflector (17), the eighth coded reflector (19), the tenth coded reflector (21) and the fourth interdigital transducer (05), are all different to ensure that the echo pulse signals corresponding to all reflectors in the third and fourth sub-regions of the surface acoustic wave label do not interfere with each other in time. The first coded reflective grating (12), the second coded reflective grating (13), the third coded reflective grating (14), the fourth coded reflective grating (15), the fifth coded reflective grating (16), the sixth coded reflective grating (17), the seventh coded reflective grating (18), the eighth coded reflective grating (19), the ninth coded reflective grating (20), and the tenth coded reflective grating (21) are located in ten coded data areas; each coded data area is divided into equal intervals. M There are 10 time slots, and the coded reflector is located in one of them. The coding capacity is ( ). M 5 ) 2 The number of photomasks required is ( M 2 + M 3 )×2; The capacitance values ​​of the first load capacitor (22), the second load capacitor (23), the third load capacitor (24), and the fourth load capacitor (25) are all . N This allows for further encoding of external capacitors with different capacitance values ​​on top of time slot encoding, resulting in an encoding capacity of up to ( ). M 5 × N 2 ) 2 The number of photomasks required is still ( M 2 + M 3 )×2; Using the time difference between the echo pulse signals of the first temperature-compensated reflective grating (08) and the second temperature-compensated reflective grating (09) as the reference time delay, and based on the known relationship between the distances between the first reference reflective grating (06), the first temperature-compensated reflective grating (08), the second temperature-compensated reflective grating (09), the first coded reflective grating (12), the second coded reflective grating (13), the third coded reflective grating (14), the fourth coded reflective grating (15), and the fifth coded reflective grating (16) at the reference temperature, the reference time delay is gradually pushed to the unambiguous phase difference between the echo pulse signals of the two farthest reflective gratings among the above eight reflective gratings, namely the first reference reflective grating (06) and the fifth coded reflective grating (16), in a proportional and progressive manner from near to far, thereby achieving high-precision temperature measurement; Using the time difference between the echo pulse signals of the third temperature-compensated reflector (10) and the fourth temperature-compensated reflector (11) as the reference time delay, and based on the known relationship between the distances between the second reference reflector (07), the third temperature-compensated reflector (10), the fourth temperature-compensated reflector (11), the sixth coded reflector (17), the seventh coded reflector (18), the eighth coded reflector (19), the ninth coded reflector (20), and the tenth coded reflector (21) at the reference temperature, the reference time delay is gradually pushed to the unambiguous phase difference between the echo pulse signals of the two farthest reflectors among the above eight reflectors, namely the second reference reflector (07) and the tenth coded reflector (21), by means of proportional recursion from near to far, thereby realizing high-precision temperature measurement.

2. The surface acoustic wave tag structure with radio frequency identification and temperature measurement functions according to claim 1, characterized in that: The antenna (26) is a dual-band antenna covering two frequency bands: 840~845MHz and 920~925MHz, and is fabricated on a PCB. The first load capacitor (22), the second load capacitor (23), the third load capacitor (24), and the fourth load capacitor (25) are soldered onto the PCB on which the antenna (26) is fabricated. The first sub-region, the second sub-region, the third sub-region, and the fourth sub-region of the surface acoustic wave label are fabricated by splicing together four corresponding photomasks, then packaged, and then soldered onto the PCB on which the antenna (26) is fabricated. The first interdigital transducer (02) The busbars at both ends of the second interdigital transducer (03), the third interdigital transducer (04), and the fourth interdigital transducer (05) are connected to the antenna (26) on the PCB through the pads on the package. The busbars at both ends of the fourth coded reflector (15), the fifth coded reflector (16), the ninth coded reflector (20), and the tenth coded reflector (21) are connected to the first load capacitor (22), the second load capacitor (23), the third load capacitor (24), and the fourth load capacitor (25) on the PCB through the pads on the package, thereby integrating the surface acoustic wave tag on the PCB.

3. A method for identifying and measuring temperature using a surface acoustic wave tag structure with radio frequency identification and temperature measurement functions as described in claim 1 or 2, characterized in that: The process includes the following steps: Step A is the encoding stage: Step A: For surface acoustic wave (SAW) tags with different time slot codes, select the corresponding first, second, third, and fourth mask plates and use these four mask plates to splice together to make the tags; for SAW tags with different external capacitance values, further encode them by soldering four load capacitors of corresponding capacitance values ​​at the corresponding positions on the PCB and attaching the PCB to the item to be identified and temperature measured. Step B: The reader transmits a carrier frequency of... f The excitation pulse signal of 1 is radiated outward in the form of electromagnetic waves through the reader antenna; the surface acoustic wave tag receives the excitation pulse signal through the antenna (26), and the first sub-region and the second sub-region, whose center frequency is the same as the carrier frequency of the excitation pulse signal, respond to the excitation pulse signal. The first interdigital transducer (02) and the second interdigital transducer (03) convert the excitation pulse signal into surface acoustic waves through the inverse piezoelectric effect, which propagate along the piezoelectric substrate surface of the first sub-region and the second sub-region, respectively. Step C: The surface acoustic wave propagating along the first sub-region encounters the first reference reflection grating (06), the second temperature-compensated reflection grating (09), the second coded reflection grating (13), and the fourth coded reflection grating (15) in sequence, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the first interdigital transducer (02); the surface acoustic wave propagating along the second sub-region encounters the first temperature-compensated reflection grating (08), the first coded reflection grating (12), the third coded reflection grating (14), and the fifth coded reflection grating (16) in sequence, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the second interdigital transducer (03); the first interdigital transducer (02) and the second interdigital transducer (03) convert the above 8 reflected signals into a first echo pulse train including 8 echo pulse signals through the positive piezoelectric effect, wherein the timing sequence of the 8 echo pulse signals has a one-to-one correspondence with the positions of the above 8 reflection gratings; the first echo pulse train is transmitted back to the reader antenna through the antenna (26); Step D: The reader processes the first echo pulse train and obtains the time slot codes of the first sub-region and the second sub-region based on the time difference between the echo pulse signals of the first coded reflective grating (12), the second coded reflective grating (13), the third coded reflective grating (14), the fourth coded reflective grating (15), and the fifth coded reflective grating (16) and the echo pulse signal of the first reference reflective grating (06). Since there is a corresponding relationship between the reflectivity of the interdigitated grating and its external load capacitance, the encoding of the first sub-region and the second sub-region with different external capacitance values ​​is obtained based on the amplitude ratio of the echo pulse signals of the fourth coded reflective grating (15) and the fifth coded reflective grating (16) and the echo pulse signal of the first reference reflective grating (06). Using the time difference between the echo pulse signals of the first temperature-compensated reflective grating (08) and the second temperature-compensated reflective grating (09) as the reference time delay, and based on the known relationship between the distances between the first reference reflective grating (06), the first temperature-compensated reflective grating (08), the second temperature-compensated reflective grating (09), the first coded reflective grating (12), the second coded reflective grating (13), the third coded reflective grating (14), the fourth coded reflective grating (15), and the fifth coded reflective grating (16) at the reference temperature, the reference time delay is gradually pushed to the unambiguous phase difference between the echo pulse signals of the two farthest reflective gratings among the above eight reflective gratings, namely the first reference reflective grating (06) and the fifth coded reflective grating (16), in a proportional and progressive manner from near to far, thereby achieving high-precision temperature measurement; Step E: The reader transmits a carrier frequency of... f The excitation pulse signal of 2 is radiated outward in the form of electromagnetic waves through the reader antenna; the surface acoustic wave tag receives the excitation pulse signal through the antenna (26), and the third sub-region and the fourth sub-region, whose center frequency is consistent with the carrier frequency of the excitation pulse signal, respond to the excitation pulse signal. The third interdigital transducer (04) and the fourth interdigital transducer (05) convert the excitation pulse signal into surface acoustic waves through the inverse piezoelectric effect, which propagate along the piezoelectric substrate surface of the third sub-region and the fourth sub-region, respectively. Step F: The surface acoustic wave propagating along the third sub-region encounters the second reference reflection grating (07), the fourth temperature-compensated reflection grating (11), the seventh coded reflection grating (18), and the ninth coded reflection grating (20) in sequence, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the third interdigital transducer (04); the surface acoustic wave propagating along the fourth sub-region encounters the third temperature-compensated reflection grating (10), the sixth coded reflection grating (17), the eighth coded reflection grating (19), and the tenth coded reflection grating (21) in sequence, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the fourth interdigital transducer (05); the third interdigital transducer (04) and the fourth interdigital transducer (05) convert the above 8 reflected signals into a second echo pulse train including 8 echo pulse signals through the positive piezoelectric effect, wherein the timing sequence of the 8 echo pulse signals has a one-to-one correspondence with the positions of the above 8 reflection gratings; the second echo pulse train is transmitted back to the reader antenna through the antenna (26); Step G: The reader processes the second echo pulse train and obtains the time slot codes of the third and fourth sub-regions based on the time difference between the echo pulse signals of the sixth coded reflector (17), the seventh coded reflector (18), the eighth coded reflector (19), the ninth coded reflector (20), and the tenth coded reflector (21) and the echo pulse signal of the second reference reflector (07). Based on the amplitude ratio of the echo pulse signals of the ninth coded reflector (20) and the tenth coded reflector (21) and the echo pulse signal of the second reference reflector (07), the codes of the third and fourth sub-regions with external capacitors of different values ​​are obtained. Using the time difference between the echo pulse signals of the third temperature-compensated reflector (10) and the fourth temperature-compensated reflector (11) as the reference time delay, and based on the known relationship between the distances between the second reference reflector (07), the third temperature-compensated reflector (10), the fourth temperature-compensated reflector (11), the sixth coded reflector (17), the seventh coded reflector (18), the eighth coded reflector (19), the ninth coded reflector (20), and the tenth coded reflector (21) at the reference temperature, the reference time delay is gradually pushed to the unambiguous phase difference between the echo pulse signals of the two farthest reflectors among the above eight reflectors, namely the second reference reflector (07) and the tenth coded reflector (21), by means of proportional extension from near to far. This achieves high-precision temperature measurement. Step H: Combine the codes of the first and second sub-regions measured in step D with the codes of the third and fourth sub-regions measured in step G to obtain the code of the surface acoustic wave tag; take the average of the temperatures measured in step D and step G to obtain the temperature of the surface acoustic wave tag.

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