A mask-based surface acoustic wave (SAW) tag structure and its encoding and recognition method are employed.

Abstract

This invention discloses a surface acoustic wave (SAW) tag structure using a single mask and its encoding and recognition method. All coded tags are made using the same mask, and the tag is encoded by different external capacitors. The SAW tag includes multiple pairs of reflective gratings. Each pair consists of a reference reflective grating and a load reflective grating with an external load capacitor. The capacitance value of the load capacitor has multiple options, corresponding to the possible codes for each reflective grating pair. Since the reflectivity of the load reflective grating changes with the external capacitor, the encoding value of the reflective grating pair is obtained by the amplitude ratio of the two echo pulse signals corresponding to the load reflective grating and the reference reflective grating, and the encoding of the SAW tag is finally identified. The advantages of this invention are that it requires only one mask and can dynamically expand the encoding capacity. Its recognition method not only eliminates the influence of distance but also avoids the coupling effect between the encodings of different reflective grating pairs.

Description

Technical fields:

[0001] This invention relates to a surface acoustic wave tag structure and its encoding and identification method, belonging to the field of radio frequency identification. Background technology:

[0002] In recent years, the Internet of Things (IoT) technology has developed rapidly, and various industries have seen a demand for network connectivity between people, between people and things, and between things. Accurate, efficient, and low-cost RFID systems are an essential foundation for the IoT, and tags and readers are indispensable components of these systems.

[0003] Surface acoustic wave (SAW) tags are a new type of coded tag that uses piezoelectric material as a substrate. Utilizing the piezoelectric effect, surface acoustic waves are excited on the substrate through interdigital transducers. Identification is primarily based on the characteristic that the tag's echo characteristics change with its encoding. With the cooperation of a reader and antenna, SAW tags do not require a power source, offering the advantages of passive and wireless operation. They are also small in size and easy to integrate. Compared to IC tags, SAW tags have better anti-interference capabilities in complex environments such as those with electromagnetic interference.

[0004] Existing surface acoustic wave (SAW) tags typically employ encoding schemes such as pulse amplitude, pulse delay, or a combination of pulse delay and phase, which have the following problems:

[0005] (1) The encoding capacity of the pulse amplitude scheme is extremely small, and the number of reflective gratings of different coded tags is different, making it difficult to achieve a consistent design of tag echoes, which also brings difficulties to the subsequent reader design and recognition algorithm. Although the number of reflective gratings of all tags in the pulse delay scheme is the same, the encoding capacity is improved to a certain extent, but the capacity is still limited. Compared with pulse amplitude and pulse delay, the encoding capacity of the pulse delay combined with phase scheme is greatly improved, but phase encoding is significantly affected by temperature, so temperature needs to be specifically corrected during recognition. In addition, the phase itself has a 360° ambiguity problem, which makes the tag design and recognition algorithm more complicated.

[0006] (2) To achieve different pulse amplitudes, delays, or phases in the tag echoes, different tags, although similar in structure, are not identical. Surface acoustic wave (SAW) tags are typically fabricated using photolithography. For SAW tags with different codes, the three existing schemes all require different masks, which is extremely expensive. Therefore, due to cost reasons, it is almost impossible to achieve large-scale IoT applications with large-capacity coding, except for small-capacity coding. This is precisely the bottleneck currently faced by SAW RFID technology.

[0007] (3) In the manufacturing process of surface acoustic wave (SAW) tags, the expensive mask itself is reusable, which can reduce the overall cost of the SAW RFID system and make it more practical. However, in the existing three coding schemes, each mask corresponds to each code, which cannot give full play to the reusable feature of the mask.

[0008] (4) The coding capacity of the surface acoustic wave (SAW) tags in the three existing schemes is determined by the design rules. Once the design and manufacturing work is completed, the coding capacity cannot be changed. When the application scenario is upgraded and the coding capacity is insufficient, it is usually necessary to change the design rules and remake the tags. All the original tags will be unusable, and dynamic expansion of the coding capacity cannot be achieved. Summary of the Invention:

[0009] This invention addresses the problems existing in current surface acoustic wave (SAW) tag encoding schemes by proposing a SAW tag structure using a mask and its encoding and recognition method. This method can overcome the current bottlenecks faced by SAW radio frequency identification technology to a certain extent and has an open expansion function for encoding capacity.

[0010] The present invention adopts the following technical solution: a surface acoustic wave tag structure using a mask, wherein all coded surface acoustic wave tags are made using the same mask, and the encoding of the surface acoustic wave tag is determined by the difference of the external capacitor;

[0011] The surface acoustic wave (SAW) tag structure includes a piezoelectric substrate, interdigital transducers, m pairs of reflective gratings, m load capacitors, and an antenna. The interdigital transducers are deposited on the left side of the piezoelectric substrate surface. The first, second, ..., mth pairs of reflective gratings are deposited on the right side of the piezoelectric substrate surface in order of increasing distance from the interdigital transducers. Each reflective grating pair consists of a reference reflective grating and a load reflective grating. The reference reflective grating uses an open-circuit grating structure, and the load reflective grating uses an interdigital grating structure. The number of load capacitors is equal to the number of reflective grating pairs, and each load reflective grating is externally connected to a load capacitor.

[0012] Each load capacitor has n possible values, corresponding to n possible codes for each reflector pair, denoted as 1, 2, ..., n; the codes for the 1st, 2nd, ..., mth reflector pairs are denoted as x1, x2, ..., xm, respectively. m The corresponding codes for surface acoustic wave (SAW) tags are denoted as x1-x2-…-x m Thus, the encoding capacity of a surface acoustic wave tag comprising m pairs of reflectors is n. m .

[0013] Furthermore, the antenna is fabricated on a PCB; the m load capacitors are soldered onto the PCB on which the antenna is fabricated; the piezoelectric substrate, interdigital transducer, and m reflective gratings are fabricated using a mask, packaged, and then soldered onto the PCB on which the antenna is fabricated; the busbars at both ends of the interdigital transducer are connected to the antenna on the PCB via pads on the package, and the busbars at both ends of each load reflective grating are connected to one of the capacitors on the PCB via pads on the package, thereby integrating the surface acoustic wave tag onto the PCB.

[0014] This invention also includes the following technical solution: an encoding and recognition method using a mask-based surface acoustic wave tag structure, comprising the following steps: wherein step A is the encoding stage:

[0015] Step A: For surface acoustic wave tags with different codes, solder load capacitors of corresponding values ​​at the corresponding positions on the PCB, and attach the PCB to the item to be identified;

[0016] Step B: The reader transmits an excitation pulse signal, which is received by the antenna of the surface acoustic wave tag and enters the interdigital transducer. The excitation pulse signal is converted into a surface acoustic wave through the inverse piezoelectric effect and propagates along the surface of the piezoelectric substrate to m pairs of reflective gratings.

[0017] Step C: The surface acoustic wave (SAW) undergoes partial reflection and transmission after passing through the first reference reflector of the first reflector pair. The transmitted signal then undergoes partial reflection and transmission again after passing through the first load reflector of the first reflector pair. The two SAW reflection signals corresponding to the first reference reflector and the first load reflector are transmitted back to the interdigital transducer, where the two SAW reflection signals are converted into two echo pulse signals, denoted as e, through the positive piezoelectric effect. 11 e 12 ;

[0018] Step D: The surface acoustic wave transmission signal generated by the first load reflector continues to propagate along the surface of the piezoelectric substrate. The reflection and transmission process of the generated signal through the second reflector is the same as in step C. The two echo pulse signals corresponding to the second reference reflector and the second load reflector are denoted as e. 21 e 22 ;

[0019] Step E: The reflection and transmission process of the surface acoustic wave signal generated by the 3rd reflection grating pair, ..., the mth reflection grating pair is the same as in step C; consistent with steps C and D, the two echo pulse signals corresponding to the 3rd reference reflection grating and the 3rd load reflection grating are denoted as e. 31 e 32 The two echo pulse signals corresponding to the m-th reference reflector and the m-th load reflector are denoted as e. m1 e m2 ;

[0020] Step F: The 2m echo pulse signals corresponding to the m reflector pairs are transmitted back to the reader via the antenna, forming the echo of the surface acoustic wave tag; the two echo pulse signals of the first reflector pair are processed to obtain the two pulse signals e corresponding to the first load reflector and the first reference reflector. 12 e 11 The amplitude ratio is denoted as p1. Since there is a corresponding relationship between the reflectivity of the load grating and its external load capacitance, the code x1 of the first grating pair is obtained based on p1. Using the same signal processing and analysis method, the codes x2, ..., xm of the second grating pair are obtained. m This allows for the identification of the surface acoustic wave (SAW) tag's encoding x1-x2-…-x m .

[0021] The present invention has the following beneficial effects:

[0022] 1. Compared with pulse amplitude and pulse delay coding schemes, the coding capacity is greatly improved; compared with the pulse delay combined with phase coding scheme, the coding is less affected by temperature, and no specific temperature correction is required during recognition. The label design and recognition algorithm are relatively simple.

[0023] 2. All encoded surface acoustic wave (SAW) tags require only one mask, enabling large-scale IoT applications with high-capacity encoding, thus overcoming the current bottlenecks faced by SAW RFID technology.

[0024] 3. By fully utilizing the reusable feature of the mask, the overall cost of the surface acoustic wave radio frequency identification system is reduced, enabling its practical application.

[0025] 4. 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.

[0026] 5. Each reflector pair includes not only a load reflector but also a corresponding reference reflector. The encoding of the reflector pair is obtained by the ratio of the echo pulse signal amplitudes corresponding to the two reflectors, thereby identifying the encoding of the surface acoustic wave tag. This not only eliminates the influence of distance but also eliminates the influence of the capacitance change of the external capacitor of the preceding load reflector on the subsequent load reflector. Attached image description:

[0027] Figure 1 This is a schematic diagram of the surface acoustic wave tag structure using a mask plate according to the present invention.

[0028] Figure 2 This is a schematic diagram of the surface acoustic wave tag of the present invention integrated on a PCB.

[0029] Figure 3 This is a schematic diagram of the echo of the surface acoustic wave tag of the present invention.

[0030] Figure 4(a) , 4(b) 4(c) is the change in the echo pulse signal when the load reflector of the y-th reflector pair of the surface acoustic wave tag of the present invention is connected to a capacitor of different capacitance value under the premise that the recognition distance remains unchanged.

[0031] Figure 5(a) and 5(b) This is a schematic diagram of the echoes of the surface acoustic wave tag of the present invention when the identification distance is relatively close and relatively far, provided that the capacitance value of the external capacitor of all load reflective grids remains unchanged. Detailed implementation method:

[0032] The invention will now be further described with reference to the accompanying drawings.

[0033] Please refer to Figure 1 Combination Figure 2 As shown, the surface acoustic wave (SAW) tag structure of the present invention includes a piezoelectric substrate, interdigital transducers, m pairs of reflective gratings, m load capacitors, and an antenna. The interdigital transducers are deposited on the left side of the piezoelectric substrate surface. The first pair of reflective gratings, the second pair of reflective gratings, ..., the mth pair of reflective gratings are deposited on the right side of the piezoelectric substrate surface in order of increasing distance from the interdigital transducers. Each reflective grating pair consists of a reference reflective grating and a load reflective grating. The reference reflective grating adopts an open-circuit grating structure, and the load reflective grating adopts an interdigital grating structure. The number of load capacitors is equal to the number of reflective grating pairs, and each load reflective grating is externally connected to a load capacitor. The antenna is fabricated on a printed circuit board (PCB). On a PCB (Printed Circuit Board); m load capacitors are soldered onto the PCB on which the antenna is fabricated; the piezoelectric substrate, interdigital transducers, and m reflector pairs are fabricated using a mask, packaged, and then soldered onto the PCB on which the antenna is fabricated; the busbars at both ends of the interdigital transducers are connected to the antenna on the PCB via pads on the package, and the busbars at both ends of each load reflector are connected to one of the capacitors on the PCB via pads on the package, thereby integrating the surface acoustic wave (SAW) tag onto the PCB; all coded SAW tags of this invention are fabricated using the same mask, and the coding of the SAW tag is determined by the different external capacitors; each load capacitor has n possible values, corresponding to the n possible codes for each reflector pair, denoted as 1, 2, ..., n; the codes for the 1st reflector pair, the 2nd reflector pair, ..., the mth reflector pair are denoted as x1, x2, ..., xm, respectively. m The corresponding codes for surface acoustic wave (SAW) tags are denoted as x1-x2-…-x m Thus, the encoding capacity of a surface acoustic wave tag comprising m pairs of reflectors is n. mTaking m=8 and n=10 as an example, the encoding capacity can reach 10. 8 =100 million.

[0034] Please refer to Figure 3 Combination Figure 1 As shown, the reader transmits an excitation pulse signal, and the received surface acoustic wave tag echo includes 2m echo pulse signals, corresponding to m pairs of reflector grids. The two echo pulse signals corresponding to the first reference reflector grid and the first load reflector grid of the first reflector grid pair are e 11 e 12 The two echo pulse signals corresponding to the second reference reflector and the second load reflector of the second reflector pair are e, respectively. 21 e 22 ...; The two echo pulse signals corresponding to the m-th reference reflector and the m-th load reflector of the m-th reflector pair are e m1 e m2 The time delay between each echo pulse signal corresponds one-to-one with the distance between each reflector grating, and the amplitude of each echo pulse signal is related to the reflectivity of each reflector grating.

[0035] Please refer to Figure 4(a) , 4(b) As shown in 4(c), since the reflectivity of the load reflector changes with the capacitance of the external capacitor, when the capacitance of a certain load capacitor changes, the amplitude of the echo pulse signal corresponding to the load reflector changes; at the same time, the load capacitor does not affect the amplitude of the echo pulse signal corresponding to the reference reflector. Taking the y-th reflector pair of the surface acoustic wave tag as an example, when the y-th load reflector is connected to capacitors of different capacitance values, the echo pulse signal e y2 The amplitude changes, but e y1 constant.

[0036] Please refer to Figure 5(a) , 5(b)As shown, with the increase of the recognition distance, the amplitude of the echo pulse signal corresponding to all reflective gratings, whether reference or load, decreases, meaning the echo pulse signal amplitude is inversely proportional to the recognition distance. However, for all reflective grating pairs, the ratio of the echo pulse signal amplitudes corresponding to the load and reference reflective gratings within the same pair is independent of the recognition distance. This means the amplitude ratio of the two echo pulse signals within a reflective grating pair can eliminate the influence of the recognition distance and corresponds to the capacitance value of the external capacitor connected to the load reflective grating. Simultaneously, since the surface acoustic wave propagates on the piezoelectric substrate sequentially through the first, second, ..., mth reflective grating pairs, the reflectivity changes of the preceding grating pairs affect the reflectivity of all subsequent grating pairs. This causes changes in the amplitude of the echo pulse signal corresponding to both the reference and load reflective gratings in all subsequent grating pairs. However, by using the echo pulse signal amplitude ratio, not only is the influence of the recognition distance eliminated, but the influence of the capacitance changes of the external capacitor of the preceding load reflective grating on the subsequent load reflective gratings is also eliminated.

[0037] Please refer to Figure 1 As shown in Figure 5, the encoding and recognition method of the surface acoustic wave tag structure using a mask plate of the present invention includes the following steps, wherein step A is the encoding stage:

[0038] Step A: For surface acoustic wave tags with different codes, solder load capacitors of corresponding values ​​at the corresponding positions on the PCB, and attach the PCB to the item to be identified;

[0039] Step B: The reader transmits an excitation pulse signal, which is received by the antenna of the surface acoustic wave tag and enters the interdigital transducer. The excitation pulse signal is converted into a surface acoustic wave through the inverse piezoelectric effect and propagates along the surface of the piezoelectric substrate to m pairs of reflective gratings.

[0040] Step C: The surface acoustic wave (SAW) undergoes partial reflection and transmission after passing through the first reference reflector of the first reflector pair. The transmitted signal then undergoes partial reflection and transmission again after passing through the first load reflector of the first reflector pair. The two SAW reflection signals corresponding to the first reference reflector and the first load reflector are transmitted back to the interdigital transducer, where they are converted into two echo pulse signals e through the positive piezoelectric effect. 11 e 12 ;

[0041] Step D: The surface acoustic wave transmission signal generated by the first load reflector continues to propagate along the surface of the piezoelectric substrate. The reflection and transmission process of the generated signal through the second reflector is the same as in step C. The two echo pulse signals corresponding to the second reference reflector and the second load reflector are e, respectively. 21 e 22 ;

[0042] Step E: The reflection and transmission process of the surface acoustic wave signal generated by the 3rd reflection grating pair, ..., the mth reflection grating pair is the same as in step C; consistent with steps C and D, the two echo pulse signals corresponding to the 3rd reference reflection grating and the 3rd load reflection grating are e respectively. 31 e 32 The two echo pulse signals corresponding to the m-th reference reflector and the m-th load reflector are e, respectively. m1 e m2 ;

[0043] Step F: The 2m echo pulse signals corresponding to the m reflector pairs are transmitted back to the reader via the antenna, forming the echo of the surface acoustic wave tag; the two echo pulse signals of the first reflector pair are processed to obtain the two pulse signals e corresponding to the first load reflector and the first reference reflector. 12 e 11 The amplitude ratio is denoted as p1. Since there is a corresponding relationship between the reflectivity of the load grating and its external load capacitance, the code x1 of the first grating pair is obtained based on p1. Using the same signal processing and analysis method, the codes x2, ..., xm of the second grating pair are obtained. m This allows for the identification of the surface acoustic wave (SAW) tag's encoding x1-x2-…-x m .

[0044] 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 employing a mask, characterized in that: All coded surface acoustic wave (SAW) tags are made using the same mask, and the coding of the SAW tag is determined by the difference in the external capacitor. The surface acoustic wave (SAW) tag structure includes a piezoelectric substrate, interdigital transducers, m pairs of reflective gratings, m load capacitors, and an antenna. The interdigital transducers are deposited on the left side of the piezoelectric substrate surface. The first, second, ..., mth pairs of reflective gratings are deposited on the right side of the piezoelectric substrate surface in order of increasing distance from the interdigital transducers. Each reflective grating pair consists of a reference reflective grating and a load reflective grating. The reference reflective grating uses an open-circuit grating structure, and the load reflective grating uses an interdigital grating structure. The number of load capacitors is equal to the number of reflective grating pairs, and each load reflective grating is externally connected to a load capacitor. Each load capacitor has n possible values, corresponding to n possible codes for each reflector pair, denoted as 1, 2, ..., n; the codes for the 1st, 2nd, ..., mth reflector pairs are denoted as x1, x2, ..., xm, respectively. m The corresponding codes for surface acoustic wave (SAW) tags are denoted as x1-x2-…-x m Thus, the encoding capacity of a surface acoustic wave tag comprising m pairs of reflectors is n. m .

2. The surface acoustic wave tag structure using a mask as described in claim 1, characterized in that: The antenna is fabricated on a PCB; the m load capacitors are soldered onto the PCB on which the antenna is fabricated. The piezoelectric substrate, interdigital transducer, and m reflective gratings are fabricated using a mask, packaged, and then soldered onto a PCB on which the antenna is fabricated. The busbars at both ends of the interdigital transducer are connected to the antenna on the PCB via pads on the package. The busbars at both ends of each load reflective grating are connected to one of the capacitors on the PCB via pads on the package, thereby integrating the surface acoustic wave label onto the PCB.

3. A coding and identification method for a surface acoustic wave tag structure using a mask 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 tags with different codes, solder load capacitors of corresponding values ​​at the corresponding positions on the PCB, and attach the PCB to the item to be identified; Step B: The reader transmits an excitation pulse signal, which is received by the antenna of the surface acoustic wave tag and enters the interdigital transducer. The excitation pulse signal is converted into a surface acoustic wave through the inverse piezoelectric effect and propagates along the surface of the piezoelectric substrate to m pairs of reflective gratings. Step C: The surface acoustic wave (SAW) undergoes partial reflection and transmission after passing through the first reference reflector of the first reflector pair. The transmitted signal then undergoes partial reflection and transmission again after passing through the first load reflector of the first reflector pair. The two SAW reflection signals corresponding to the first reference reflector and the first load reflector are transmitted back to the interdigital transducer, where the two SAW reflection signals are converted into two echo pulse signals, denoted as e, through the positive piezoelectric effect. 11 e 12 ; Step D: The surface acoustic wave transmission signal generated by the first load reflector continues to propagate along the surface of the piezoelectric substrate. The reflection and transmission process of the generated signal through the second reflector is the same as in step C. The two echo pulse signals corresponding to the second reference reflector and the second load reflector are denoted as e. 21 e 22 ; Step E: The reflection and transmission process of the surface acoustic wave signal generated by the 3rd reflection grating pair, ..., the mth reflection grating pair is the same as in step C; consistent with steps C and D, the two echo pulse signals corresponding to the 3rd reference reflection grating and the 3rd load reflection grating are denoted as e. 31 e 32 The two echo pulse signals corresponding to the m-th reference reflector and the m-th load reflector are denoted as e. m1 e m2 ; Step F: The 2m echo pulse signals corresponding to the m reflector pairs are transmitted back to the reader via the antenna, forming the echo of the surface acoustic wave tag; the two echo pulse signals of the first reflector pair are processed to obtain the two pulse signals e corresponding to the first load reflector and the first reference reflector. 12 e 11 The amplitude ratio is denoted as p1. Since there is a corresponding relationship between the reflectivity of the load grating and its external load capacitance, the code x1 of the first grating pair is obtained based on p1. Using the same signal processing and analysis method, the codes x2, ..., xm of the second grating pair are obtained. m This allows for the identification of the surface acoustic wave (SAW) tag's encoding x1-x2-…-x m .

Images