Impedance load based surface acoustic wave identification and sensing tag structure and method

Abstract

The application discloses a surface acoustic wave identification and multi-parameter sensing label based on impedance load principle and a working method thereof. The label is a double-frequency multi-channel structure, the center frequency of the first channel is 922.5 MHz, and the center frequencies of the other channels are all 842.5 MHz. A load capacitor is connected to each coding reflection grating, and a load reactance is connected to each sensing reflection grating through a matching circuit. The phase of the corresponding reflection grating is measured to obtain the code, and the temperature and other parameters of the environment where the surface acoustic wave label is located are sensed. The application has the characteristics that all the coded labels are made by using the same mask, and the integration of radio frequency identification and multi-parameter sensing can be realized. The application can not only detect the temperature, but also eliminate the influence of the temperature on the coding identification and the sensing of other parameters. The other parameters except the temperature act on the load reactance, do not affect the packaging and working stability of the label, and expand the application scene of the surface acoustic wave label as a sensor.

Description

Technical fields:

[0001] This invention relates to a surface acoustic wave identification and sensing tag structure and method based on the impedance load principle, belonging to the fields of radio frequency identification and wireless sensing. Background technology:

[0002] The Internet of Things (IoT) is an inevitable trend in information development. Its essence lies in achieving automatic identification of objects and the interconnection and sharing of perceived information through technologies such as radio frequency identification (RFID), sensors, and the internet. As core technologies of the IoT, RFID and sensing technologies are at the forefront of its development.

[0003] Tags and readers are the most important components of a radio frequency identification (RFID) system. Surface acoustic wave (SAW) tags encode echo signals by modulating their amplitude, position, and phase. They mainly consist of a piezoelectric substrate, interdigital transducers, a reflector grating, and an antenna. Utilizing the piezoelectric effect, the interdigital transducers excite surface acoustic waves on the surface of the piezoelectric substrate, with the frequency matching the excitation signal received by the antenna. The reader demodulates and processes the echo pulse train reflected back from the reflector grating to complete tag identification. Due to its unique working principle, SAW tags offer advantages over IC tags, including stronger anti-interference capabilities, longer reading distances, and a completely passive operation, making RFID systems suitable for more complex scenarios. Furthermore, the echo signals of SAW tags are affected by environmental factors such as temperature, humidity, pressure, and magnetic fields, thus enabling simultaneous RFID and wireless sensing functions, providing significant characteristics and advantages for applications in the Internet of Things (IoT) field.

[0004] Existing surface acoustic wave (SAW) identification and sensing tags have the following problems:

[0005] (1) Regardless of whether pulse amplitude, pulse delay, or pulse delay combined with phase encoding is used, different encoding tags require different masks. For surface acoustic wave tags manufactured by photolithography, the cost is extremely high and it is difficult to put them into practical use.

[0006] (2) The propagation characteristics of surface acoustic waves on the piezoelectric substrate determine that applying the parameter to be sensed directly to its propagation path is the best choice, such as surface acoustic wave tags used for temperature detection. However, many parameters to be measured are not suitable to be applied directly to the piezoelectric substrate surface, and the direct application of the measured parameters to the propagation path will also cause inconvenience to the tag packaging, thereby affecting the working stability of the tag, such as the detection of parameters such as humidity, pressure, and magnetic field. Summary of the Invention:

[0007] This invention addresses the problems existing in existing surface acoustic wave (SAW) identification and sensing tags by proposing a SAW identification and sensing tag structure and method based on the impedance load principle. Not only are all coded tags made using the same mask, but it also achieves integrated functions of radio frequency identification and multi-parameter sensing.

[0008] The present invention adopts the following technical solution: a surface acoustic wave identification and sensing tag structure based on impedance load, wherein the surface acoustic wave tag is made using the same mask, and the encoding of the surface acoustic wave tag is determined by connecting an external load capacitor and load reactance and measuring the phase of the corresponding reflective grating, and the temperature and other n (n≥1) parameters of the environment in which the surface acoustic wave tag is located are sensed.

[0009] The surface acoustic wave (SAW) tag has a dual-frequency, multi-channel structure with n+1 channels. It includes a piezoelectric substrate, a first interdigital transducer, a second interdigital transducer, a first reference reflector, a second reference reflector, a first temperature-compensated reflector, a second temperature-compensated reflector, a first coded reflector, a second coded reflector, ..., an m-th coded reflector, a first load capacitor, a second load capacitor, ..., an m-th load capacitor, a first sensing reflector, a second sensing reflector, a third sensing reflector, ..., an n-th sensing reflector, a first matching circuit, a second matching circuit, a third matching circuit, ..., an n-th matching circuit, a first load reactance, a second load reactance, a third load reactance, ..., an n-th load reactance, and an antenna. The two reference reflectors and two temperature-compensated reflectors are open-circuit structures, while the m coded reflectors and n sensing reflectors are interdigital grid structures. Each coded reflector is externally connected to a load capacitor, and each sensing reflector is externally connected to a load reactance through a matching circuit.

[0010] The capacitance values ​​of the first load capacitor, the second load capacitor, ..., the m-th load capacitor each have q possible options, corresponding to q possible codes for each coded reflector, denoted as 1, 2, ..., q; the codes of the first coded reflector, the second coded reflector, ..., the m-th coded reflector are denoted as x1, x2, ..., x... m The corresponding codes for surface acoustic wave (SAW) tags are denoted as x1-x2-…-x m Thus, the coding capacity of the surface acoustic wave tag, which includes m coded reflector gratings, is q. m ;

[0011] Each matching circuit consists of capacitors and inductors connected in series or parallel; each load reactance is either a capacitor or an inductor.

[0012] The first interdigital transducer is deposited on the upper left side of the piezoelectric substrate, located in the first propagation channel of the surface acoustic wave;

[0013] The second interdigital transducer is deposited on the left side of the piezoelectric substrate and located directly below the first interdigital transducer, occupying the second to (n+1)th propagation channels of surface acoustic waves;

[0014] The first interdigital transducer, together with the first reference reflector, the first temperature-compensated reflector, the first coded reflector, the second coded reflector, ..., the m-th coded reflector, constitutes the first propagation channel of surface acoustic waves;

[0015] A portion of the second interdigital transducer, together with the second reference reflector, the second temperature-compensated reflector, and the first sensing reflector, constitutes the second propagation channel for surface acoustic waves.

[0016] A portion of the second interdigital transducer, together with the second sensing reflector, forms the third propagation channel of the surface acoustic wave; a portion of the second interdigital transducer, together with the third sensing reflector, forms the fourth propagation channel of the surface acoustic wave; ...; a portion of the second interdigital transducer, together with the nth sensing reflector, forms the (n+1)th propagation channel of the surface acoustic wave.

[0017] By designing the finger strip widths of the first interdigital transducer, the first coded reflective grating, the second coded reflective grating, ..., the m-th coded reflective grating, and the grating strip widths of the first reference reflective grating and the first temperature-compensated reflective grating, the center frequency f1 of the first propagation channel of the surface acoustic wave is made 922.5MHz; by designing the finger strip widths of the second interdigital transducer, the first sensing reflective grating, the second sensing reflective grating, the third sensing reflective grating, ..., the n-th sensing reflective grating, and the grating strip widths of the second reference reflective grating and the second temperature-compensated reflective grating, the center frequency f2 of the second, third, fourth, ..., (n+1)-th propagation channels of the surface acoustic wave is made 842.5MHz;

[0018] The distances between the second reference reflector, the second temperature-compensated reflector, the first sensing reflector, the second sensing reflector, the third sensing reflector, ..., the nth sensing reflector and the second interdigital transducer are all different, so as to ensure that the echo pulse signals corresponding to all reflectors in the second propagation channel, the third propagation channel, the fourth propagation channel, ..., the (n+1)th propagation channel of the surface acoustic wave tag do not interfere with each other in time.

[0019] Furthermore, the antenna is a dual-band antenna covering two frequency bands: 840–845MHz and 920–925MHz, and is fabricated on a PCB. The m load capacitors and n matching circuits are soldered onto the PCB on which the antenna is fabricated. The piezoelectric substrate, two interdigital transducers, two reference reflectors, two temperature-compensated reflectors, m coded reflectors, and n sensing reflectors 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 first and second interdigital transducers are connected to the antenna on the PCB via pads on the package. The busbars at both ends of each coded reflector are connected to one of the load capacitors on the PCB via pads on the package. The busbars at both ends of each sensing reflector are connected to one of the matching circuits on the PCB via pads on the package. Each load reactance is connected to the corresponding matching circuit on the PCB.

[0020] This invention also employs the following technical solution: a surface acoustic wave identification and sensing tag structure based on impedance load, comprising the following steps: wherein step A is the encoding stage and step B is the optimization stage of load reactance and matching circuit:

[0021] 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;

[0022] Step B: Based on the specific parameters of the environment of the object to be detected by each sensing reflector, and in combination with the working principle of the reactance sensor, determine whether each load reactance is a capacitor or an inductor, the sensing mechanism of the load reactance, its relative position with the object, and its installation form. Based on the measurement range, sensitivity, and linearity index, optimize the load reactance value itself and the series and parallel capacitance and inductance values ​​of the corresponding matching circuit.

[0023] Step C: 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;

[0024] Step D: The surface acoustic wave tag receives the excitation pulse signal through the antenna. The first propagation channel, whose center frequency is the same as the carrier frequency of the excitation pulse signal, responds to the excitation pulse signal. The first interdigital transducer converts the excitation pulse signal into a surface acoustic wave through the inverse piezoelectric effect, which propagates along the piezoelectric substrate surface of the first propagation channel.

[0025] Step E: The surface acoustic wave propagating along the first propagation channel encounters the first reference reflection grating, the first temperature-compensated reflection grating, the first coded reflection grating, the second coded reflection grating, ..., the m-th coded reflection grating in sequence, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the first interdigital transducer. The first interdigital transducer converts the reflected signal into a first echo pulse train containing (m+2) echo pulse signals through the positive piezoelectric effect. The timing of the echo pulse signals corresponds one-to-one with the positions of the aforementioned (m+2) reflection gratings, and changes in the capacitance of the load capacitor connected to the coded reflection grating will cause a change in the phase of the corresponding echo pulse signal. The first echo pulse train is transmitted back to the reader antenna through the antenna.

[0026] Step F: The reader processes the first echo pulse train, directly calculating the phases of (m+2) echo pulse signals through orthogonal demodulation. Then, a reference time delay is constructed using the distance between the first temperature-compensated reflector and the first reference reflector. Based on the phase change of the reference time delay and the positional relationship between the (m+2) reflectors, the initial phase of the echo pulse signals corresponding to the m coded reflectors at the reference temperature is deduced. This initial phase eliminates the temperature effect and has a one-to-one correspondence with the capacitance values ​​of the corresponding m load capacitors, thus obtaining the surface acoustic wave tag encoding x1-x2-…-x m ;

[0027] Step G: The phase calculated directly by orthogonal demodulation minus the initial phase at the reference temperature is the phase change caused by temperature. Under the premise of realizing the recognition function, based on the known relationship between the distances between (m+2) reflective gratings at the reference temperature, the phase change caused by temperature with reference time delay is gradually extrapolated to the phase change between the two farthest reflective gratings among (m+2) reflective gratings, namely the first reference reflective grating and the m-th coded reflective grating, in a proportional extrapolation manner from near to far. The ambient temperature value is detected based on the relationship between temperature change and phase change.

[0028] Step H: 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;

[0029] Step 1: The surface acoustic wave tag receives the excitation pulse signal through the antenna. The second propagation channel, the third propagation channel, the fourth propagation channel, ..., the (n+1)th propagation channel, whose center frequency is the same as the carrier frequency of the excitation pulse signal, respond to the excitation pulse signal. The second interdigital transducer converts the excitation pulse signal into a surface acoustic wave through the inverse piezoelectric effect, which propagates along the piezoelectric substrate surface of the second propagation channel, the third propagation channel, the fourth propagation channel, ..., the (n+1)th propagation channel, respectively.

[0030] Step J: Surface acoustic waves propagating along the second propagation channel sequentially encounter the second reference reflection grating, the second temperature-compensated reflection grating, and the first sensing reflection grating, resulting in partial reflection and partial transmission. The reflected signals are transmitted back to the second interdigital transducer. Surface acoustic waves propagating along the third, fourth, ..., (n+1)th propagation channels encounter the second, third, ..., nth sensing reflection grating, resulting in partial reflection and partial transmission. The reflected signals are transmitted back to the second interdigital transducer. The second interdigital transducer converts the reflected signals into a second echo pulse train comprising (n+2) echo pulse signals through the positive piezoelectric effect. The timing of the echo pulse signals corresponds one-to-one with the positions of the (n+2) reflection gratings. A change in a parameter value to be sensed causes a change in the capacitance or inductance of the load reactance, further causing a change in the phase of the echo pulse signal corresponding to the relevant sensing reflection grating. The second echo pulse train is transmitted back to the reader antenna via the antenna.

[0031] Step K: The reader processes the second echo pulse train, directly calculates the phase of (n+2) echo pulse signals through orthogonal demodulation, constructs a reference time delay by using the distance between the second temperature-compensated reflective grating and the second reference reflective grating, and deduces the initial phase of the echo pulse signals corresponding to the n sensing reflective gratings at the reference temperature based on the phase change of the reference time delay and the positional relationship between the (n+2) reflective gratings; based on the initial phase of the first sensing reflective grating, the second sensing reflective grating, the third sensing reflective grating, ..., the nth sensing reflective grating at the reference temperature, the values ​​of the 1st, 2nd, 3rd, ..., nth sensing parameters, after eliminating the influence of temperature, are obtained.

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

[0033] 1. All coded surface acoustic wave tags require only one mask, which is low-cost and enables large-scale IoT applications.

[0034] 2. It can integrate radio frequency identification and multi-parameter sensing. Theoretically, all parameters that can be detected by reactive sensors can be sensed in parallel by the surface acoustic wave tag of this invention.

[0035] 3. It can not only detect temperature, but also eliminate the influence of temperature in encoding recognition and sensing of multiple other parameters.

[0036] 4. Apart from temperature directly affecting the propagation path of surface acoustic waves, other parameters to be sensed act on the external load reactance, thus not affecting the tag's packaging and operational stability, and greatly expanding the application scenarios of surface acoustic wave tags as sensors.

[0037] 5. Identification and sensing functions are achieved by connecting an external load impedance and measuring the phase of the corresponding reflective grating. Compared with measuring the amplitude of the corresponding reflective grating, the tag structure is not only simpler, but also more accurate and less affected by environmental interference such as noise. Attached image description:

[0038] Figure 1 This is a schematic diagram of the surface acoustic wave identification and sensing tag structure based on impedance load of the present invention.

[0039] Figure 2 This is a schematic diagram of the surface acoustic wave tag of the present invention integrated on a PCB.

[0040] Figure 3 This is a schematic diagram of the echo pulse signals (first echo pulse train) corresponding to all the reflection gratings of the first propagation channel on the surface acoustic wave tag of the present invention.

[0041] Figure 4 This is a schematic diagram of the echo pulse signals (second echo pulse train) corresponding to all the reflection gratings of the second, third, fourth, ..., (n+1)th propagation channels on the surface acoustic wave tag of the present invention.

[0042] The labels in the above figures are as follows: 01. Piezoelectric substrate, 02. First interdigital transducer, 03. Second interdigital transducer, 04. First reference reflector, 05. Second reference reflector, 06. First temperature-compensated reflector, 07. Second temperature-compensated reflector, 08. First coded reflector, 09. Second coded reflector, 10. nth coded reflector, 11. First load capacitor, 12. Second load capacitor, 13. mth load capacitor, 14. First sensing reflector, 15. Second sensing reflector, 16. Third sensing reflector, 17. nth sensing reflector, 18. First matching circuit, 19. Second matching circuit, 20. Third matching circuit, 21. nth matching circuit, 22. First load impedance, 23. Second load impedance, 24. Third load impedance, 25. nth load impedance, 26. Antenna. Detailed implementation method:

[0043] The invention will now be further described with reference to the accompanying drawings:

[0044] 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 first reference reflector grating 04, a second reference reflector grating 05, a first temperature-compensated reflector grating 06, a second temperature-compensated reflector grating 07, a first coded reflector grating 08, a second coded reflector grating 09, ..., an m-th coded reflector grating 10, a first load capacitor 11, a second load capacitor 12, ..., an m-th load capacitor 13, a first sensing reflector grating 14, a second sensing reflector grating 15, a third sensing reflector grating 16, ..., an n-th sensing reflector grating 17, a first matching circuit 18, a second matching circuit 19, a third matching circuit 20, ..., an n-th matching circuit 21, a first load reactance 22, a second load reactance 23, a third load reactance 24, ..., an n-th load reactance 25, and an antenna 26. The two reference reflectors and the two temperature-compensated reflectors are open-circuit grating structures, while the m coded reflectors and the n sensing reflectors are interdigital grating structures. Each coded reflector is connected to an external load capacitor, and each sensing reflector is connected to an external load reactance through a matching circuit. Each matching circuit consists of a capacitor and an inductor connected in series or parallel, and each load reactance is either a capacitor or an inductor.

[0045] The capacitance values ​​of the first load capacitor 11, the second load capacitor 12, ..., the m-th load capacitor 13 each have q options, corresponding to the q possible codes for each coded reflector, denoted as 1, 2, ..., q. For example... Figure 1 The capacitance values ​​of the first load capacitor 11, the second load capacitor 12, and the m-th load capacitor 13 are the 2nd, 1st, and qth optional values, respectively. The corresponding codes for the first coded reflective grating 08, the second coded reflective grating 09, and the m-th coded reflective grating 10 are 2, 1, and q, respectively. The codes for the first coded reflective grating 08, the second coded reflective grating 09, ..., the m-th coded reflective grating 10 are denoted as x1, x2, ..., x... m The corresponding codes for surface acoustic wave (SAW) tags are denoted as x1-x2-…-x m Thus, the coding capacity of the surface acoustic wave tag, which includes m coded reflector gratings, is q. m Taking q=12 and m=8 as an example, the encoding capacity can reach 12. 8 >400 million.

[0046] The first interdigital transducer 02 is deposited on the upper left side of the piezoelectric substrate 01, located in the first propagation channel of surface acoustic waves; the second interdigital transducer 03 is deposited on the left side of the piezoelectric substrate 01 and located directly below the first interdigital transducer 02, occupying the second to (n+1)th propagation channels of surface acoustic waves.

[0047] The first interdigital transducer 02, together with the first reference reflector grating 04, the first temperature-compensated reflector grating 06, the first coded reflector grating 08, the second coded reflector grating 09, ..., the m-th coded reflector grating 10, constitutes the first propagation channel of surface acoustic waves; a portion of the second interdigital transducer 03, together with the second reference reflector grating 05, the second temperature-compensated reflector grating 07, and the first sensing reflector grating 14, constitutes the second propagation channel of surface acoustic waves; a portion of the second interdigital transducer 03, together with the second sensing reflector grating 15, constitutes the third propagation channel of surface acoustic waves; a portion of the second interdigital transducer 03, together with the third sensing reflector grating 16, constitutes the fourth propagation channel of surface acoustic waves; ...; a portion of the second interdigital transducer 03, together with the n-th sensing reflector grating 17, constitutes the (n+1)-th propagation channel of surface acoustic waves.

[0048] 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 width of the interdigital transducer and the bar width of the interdigital reflector and the bar width of the open-circuit reflector and the short-circuit reflector. Furthermore, considering the actual situation in my country where the 800 / 900MHz frequency band is divided into two independent frequency bands, 840–845MHz and 920–925MHz, the finger widths of the first interdigital transducer 02, the first coded reflector 08, the second coded reflector 09, ..., the m-th coded reflector 10 are designed... By adjusting the width of the grating bars of the first reference reflector 04 and the first temperature-compensated reflector 06, the center frequency f1 of the first propagation channel of the surface acoustic wave is made to be 922.5MHz. By designing the width of the finger bars of the second interdigital transducer 03, the first sensing reflector 14, the second sensing reflector 15, the third sensing reflector 16, ..., the nth sensing reflector 17, and the grating bars of the second reference reflector 05 and the second temperature-compensated reflector 07, the center frequency f2 of the second, third, fourth, ..., (n+1)th propagation channels of the surface acoustic wave is made to be 842.5MHz.

[0049] Antenna 26 is a dual-band antenna covering two frequency bands: 840–845MHz and 920–925MHz, and is fabricated on a PCB. m load capacitors and n matching circuits are soldered onto the PCB containing antenna 26. The piezoelectric substrate 01, two interdigital transducers, two reference reflectors, two temperature-compensated reflectors, m coded reflectors, and n sensing reflectors are fabricated using a single mask, packaged, and then soldered onto the PCB containing antenna 26. The busbars at both ends of the first interdigital transducer 02 and the second interdigital transducer 03 are connected to antenna 26 on the PCB via pads on the package. The busbars at both ends of each coded reflector are connected to one of the load capacitors on the PCB via pads on the package. The busbars at both ends of each sensing reflector are connected to one of the matching circuits on the PCB via pads on the package. Each load reactance is connected to its corresponding matching circuit on the PCB.

[0050] Please refer to Figure 1 , Figure 3 As shown, the distances between the first reference reflector grating 04, the first temperature-compensated reflector grating 06, the first coded reflector grating 08, the second coded reflector grating 09, ..., the m-th coded reflector grating 10 and the first interdigital transducer 02 are all different, so as to ensure that the echo pulse signals (first echo pulse train) corresponding to all reflectors in the first propagation channel of surface acoustic wave do not interfere with each other in time.

[0051] Please refer to Figure 1 , Figure 4 As shown, the distances between the second reference reflector grating 05, the second temperature-compensated reflector grating 07, the first sensing reflector grating 14, the second sensing reflector grating 15, the third sensing reflector grating 16, ..., the nth sensing reflector grating 17 and the second interdigital transducer 03 are all different, so as to ensure that the echo pulse signals (second echo pulse trains) corresponding to all reflector gratings in the second propagation channel, the third propagation channel, the fourth propagation channel, ..., the (n+1)th propagation channel of the surface acoustic wave do not interfere with each other in time.

[0052] Please refer to Figures 1 to 4 As shown, the present invention provides a surface acoustic wave identification and sensing method based on impedance load and a sensing tag structure, comprising the following steps, wherein step A is the encoding stage and step B is the optimization stage of load reactance and matching circuit:

[0053] 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;

[0054] Step B: Based on the specific parameters of the environment of the object to be detected by each sensing reflector, and in combination with the working principle of the reactance sensor, determine whether each load reactance is a capacitor or an inductor, the sensing mechanism of the load reactance, its relative position with the object, and its installation form. Based on the measurement range, sensitivity, and linearity index, optimize the load reactance value itself and the series and parallel capacitance and inductance values ​​of the corresponding matching circuit.

[0055] Step C: 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;

[0056] Step D: The surface acoustic wave tag receives the excitation pulse signal through the antenna 26. The first propagation channel, whose center frequency is the same as the carrier frequency of the excitation pulse signal, responds to the excitation pulse signal. The first interdigital transducer 02 converts the excitation pulse signal into a surface acoustic wave through the inverse piezoelectric effect, which propagates along the surface of the piezoelectric substrate 01 of the first propagation channel.

[0057] Step E: The surface acoustic wave propagating along the first propagation channel sequentially encounters the first reference reflection grating 04, the first temperature-compensated reflection grating 06, the first coded reflection grating 08, the second coded reflection grating 09, ..., the m-th coded reflection grating 10, resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the first interdigital transducer 02. The first interdigital transducer 02 converts the reflected signal into a first echo pulse train containing (m+2) echo pulse signals through the positive piezoelectric effect. The echo pulse signals are denoted as e. r1 e t1 e c1 e c2 ..., e cm Their timing corresponds one-to-one with the positions of the (m+2) reflective gratings mentioned above, and the change in the capacitance of the load capacitor connected to the coded reflective grating will cause a change in the phase of the corresponding echo pulse signal; the first echo pulse train is transmitted back to the reader antenna through antenna 26;

[0058] Step F: The reader processes the first echo pulse train, directly calculating the phases of (m+2) echo pulse signals through quadrature demodulation. Then, a reference time delay is constructed using the distance between the first temperature-compensated reflector 06 and the first reference reflector 04. Based on the phase change of the reference time delay and the positional relationship between the (m+2) reflectors, the initial phase of the echo pulse signals corresponding to the m coded reflectors at the reference temperature is deduced. This initial phase eliminates the temperature effect and has a one-to-one correspondence with the capacitance values ​​of the corresponding m load capacitors, thus obtaining the surface acoustic wave tag encoding x1-x2-…-x m ;

[0059] Step G: The phase change caused by temperature is obtained by subtracting the initial phase at the reference temperature from the phase directly calculated by orthogonal demodulation. Under the premise of realizing the recognition function, based on the known relationship between the distances between (m+2) reflective gratings at the reference temperature, the phase change caused by temperature with reference time delay is gradually extrapolated to the phase change between the two farthest reflective gratings in (m+2) of the reflective gratings, namely the first reference reflective grating 04 and the m-th coded reflective grating 10, in a proportional extrapolation manner from near to far. The ambient temperature value is detected based on the relationship between temperature change and phase change.

[0060] Step H: 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;

[0061] Step 1: The surface acoustic wave tag receives the excitation pulse signal through the antenna 26. The second propagation channel, the third propagation channel, the fourth propagation channel, ..., the (n+1)th propagation channel, whose center frequency is the same as the carrier frequency of the excitation pulse signal, respond to the excitation pulse signal. The second interdigital transducer 03 converts the excitation pulse signal into a surface acoustic wave through the inverse piezoelectric effect, which propagates along the piezoelectric substrate 01 surface of the second propagation channel, the third propagation channel, the fourth propagation channel, ..., the (n+1)th propagation channel, respectively.

[0062] Step J: The surface acoustic wave propagating along the second propagation channel sequentially encounters the second reference reflection grating 05, the second temperature-compensated reflection grating 07, and the first sensing reflection grating 14, resulting in partial reflection and partial transmission. The reflected signals are transmitted back to the second interdigital transducer 03. The surface acoustic waves propagating along the third, fourth, ..., (n+1)th propagation channels encounter the second sensing reflection grating 15, the third sensing reflection grating 16, ..., the nth sensing reflection grating 17, respectively, resulting in partial reflection and partial transmission. The reflected signals are transmitted back to the second interdigital transducer 03. The second interdigital transducer 03 converts the above reflected signals into a second echo pulse train including (n+2) echo pulse signals through the positive piezoelectric effect. These echo pulse signals are denoted as e. r2 e t2 e s1 e s2 e s3 ..., e sn Their timing has a one-to-one correspondence with the positions of the (n+2) reflective gratings mentioned above; a change in a certain parameter value to be sensed will cause a change in the capacitance or inductance value of the load reactance, and further cause a change in the phase of the echo pulse signal corresponding to the corresponding sensing reflective grating; the second echo pulse train is transmitted back to the reader antenna through antenna 26.

[0063] Step K: The reader processes the second echo pulse train, directly calculates the phase of (n+2) echo pulse signals through quadrature demodulation, constructs a reference time delay through the distance between the second temperature-compensated reflective grating 07 and the second reference reflective grating 05, and deduces the initial phase of the echo pulse signals corresponding to the n sensing reflective gratings at the reference temperature based on the phase change of the reference time delay and the positional relationship between the (n+2) reflective gratings; based on the initial phase of the first sensing reflective grating 14, the second sensing reflective grating 15, the third sensing reflective grating 16, ..., the nth sensing reflective grating 17 at the reference temperature, the values ​​of the 1st, 2nd, 3rd, ..., nth sensing parameters, after eliminating the influence of temperature, are obtained.

[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 identification and sensing tag structure based on impedance load, characterized in that: The surface acoustic wave (SAW) tags are fabricated using the same mask. The encoding of the SAW tag is determined by connecting an external load capacitor and load reactance, and measuring the phase of the corresponding reflective grating. The temperature and other environmental factors of the SAW tag's environment are also considered. n Sensing parameters, among which n ≥1; The surface acoustic wave tag has a dual-frequency, multi-channel structure with the following number of channels: n +1, including a piezoelectric substrate (01), a first interdigital transducer (02), a second interdigital transducer (03), a first reference reflector (04), a second reference reflector (05), a first temperature-compensated reflector (06), a second temperature-compensated reflector (07), a first coded reflector (08), a second coded reflector (09), ..., the first... m Encoded reflective grating (10), first load capacitor (11), second load capacitor (12), ..., the first load capacitor (13) m Load capacitor (13), first sensing reflector (14), second sensing reflector (15), third sensing reflector (16), ..., the first n Sensing reflective grid (17), first matching circuit (18), second matching circuit (19), third matching circuit (20), ..., the first n Matching circuit (21), first load reactance (22), second load reactance (23), third load reactance (24), ..., the first load reactance (25) n Load reactance (25) and antenna (26); wherein, the two reference reflector grids and the two temperature-compensated reflector grids are open-circuit grid structures. m A coded reflective grating and n Each sensing reflector is an interdigitated grid structure; each coded reflector is connected to an external load capacitor, and each sensing reflector is connected to an external load reactance through a matching circuit; The first load capacitor (11), the second load capacitor (12), ..., the first m The capacitance values ​​of the load capacitor (13) are all q There are several options, corresponding to the possible occurrences of each coded reflective grating. q The codes are denoted as 1, 2, ... q ; First coded reflective grating (08), second coded reflective grating (09), ..., the m The encoding of the coded reflective grating (10) is denoted as follows: x 1. x 2、…、 x m The corresponding code for the surface acoustic wave label is denoted as: x 1- x 2-…- x m Thus including m The coding capacity of the surface acoustic wave tag for each coded reflector grating is q m ; Each matching circuit consists of capacitors and inductors connected in series or parallel; each load reactance is either a capacitor or an inductor. The first interdigital transducer (02) is deposited on the upper left side of the piezoelectric substrate (01), located in the first propagation channel of surface acoustic waves; The second interdigital transducer (03) is deposited on the left side of the piezoelectric substrate (01) and located directly below the first interdigital transducer (02), occupying the second propagation channel of the surface acoustic wave. n +1) Transmission channels; The first interdigital transducer (02) is connected to the first reference reflector (04), the first temperature-compensated reflector (06), the first coded reflector (08), the second coded reflector (09), ..., the first... m Together with the coded reflective grating (10), they form the first propagation channel for surface acoustic waves; A portion of the second interdigital transducer (03), together with the second reference reflector (05), the second temperature-compensated reflector (07), and the first sensing reflector (14), constitutes the second propagation channel of surface acoustic waves; A portion of the second interdigital transducer (03), together with the second sensing reflector (15), constitutes the third propagation channel of the surface acoustic wave; a portion of the second interdigital transducer (03), together with the third sensing reflector (16), constitutes the fourth propagation channel of the surface acoustic wave; ...; a portion of the second interdigital transducer (03), together with the third sensing reflector (15), constitutes the fourth propagation channel of the surface acoustic wave; ...; a portion of the second interdigital transducer (03), together with the third sensing reflector (16), constitutes the fourth propagation channel of the surface acoustic wave; n Together with the sensing reflection grating (17), they constitute the first ( ) of the surface acoustic wave. n +1) Transmission channels; By designing the first interdigital transducer (02), the first coded reflector (08), the second coded reflector (09), ..., the ... m The width of the finger strips of the coded reflective grating (10) and the grating strip widths of the first reference reflective grating (04) and the first temperature-compensated reflective grating (06) make the center frequency of the first propagation channel of the surface acoustic wave equal to the width of the finger strips of the first reference reflective grating (04) and the width of the grating strips of the first temperature-compensated reflective grating (06). f 1 is 922.5MHz; by designing a second interdigital transducer (03), a first sensing reflector (14), a second sensing reflector (15), a third sensing reflector (16), ..., the first n The width of the finger strip of the sensing reflective grating (17) and the width of the grating strips of the second reference reflective grating (05) and the second temperature-compensated reflective grating (07) enable the second, third, fourth, ..., fourth propagation channels of the surface acoustic wave to be connected. n +1) Center frequency of the propagation channel f 2 is 842.5MHz; The second reference reflective grating (05), the second temperature-compensated reflective grating (07), the first sensing reflective grating (14), the second sensing reflective grating (15), the third sensing reflective grating (16), ..., the second... n The distances between the sensing reflection grating (17) and the second interdigital transducer (03) are all different to ensure that the second, third, fourth, ..., and ( ) propagation channels of the surface acoustic wave tag are all different. n +1) The echo pulse signals corresponding to all the reflection gratings in the propagation channel do not interfere with each other in time.

2. The surface acoustic wave identification and sensing tag structure based on impedance load 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 m One load capacitor, n A matching circuit is soldered onto the PCB on which the antenna (26) is fabricated; The piezoelectric substrate (01), two interdigital transducers, two reference reflective gratings, and two temperature-compensated reflective gratings are described. m A coded reflective grid, n Each sensing reflector is fabricated using a mask, packaged, and then soldered onto a PCB on which the antenna (26) is fabricated. The busbars at both ends of the first interdigital transducer (02) and the second interdigital transducer (03) are connected to the antenna (26) on the PCB via pads on the package. The busbars at both ends of each coded reflector are connected to one of the load capacitors on the PCB via pads on the package. The busbars at both ends of each sensing reflector are connected to one of the matching circuits on the PCB via pads on the package. Each load reactance is connected to the corresponding matching circuit on the PCB.

3. A method for identifying and sensing surface acoustic wave (SAW) tag structures based on impedance load as described in claim 1 or 2, characterized in that: The process includes the following steps: Step A is the encoding stage, and Step B is the optimization stage of the load reactance and matching circuit. 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: Based on the specific parameters of the environment of the object to be detected by each sensing reflector, and in combination with the working principle of the reactance sensor, determine whether each load reactance is a capacitor or an inductor, the sensing mechanism of the load reactance, its relative position with the object, and the installation form. Based on the measurement range, sensitivity, and linearity index, optimize the load reactance value itself and the series and parallel capacitance and inductance values ​​of the corresponding matching circuit. Step C: 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; Step D: The surface acoustic wave tag receives the excitation pulse signal through the antenna (26). The first propagation channel, whose center frequency is consistent with the carrier frequency of the excitation pulse signal, responds to the excitation pulse signal. The first interdigital transducer (02) converts the excitation pulse signal into a surface acoustic wave through the inverse piezoelectric effect, which propagates along the surface of the piezoelectric substrate (01) of the first propagation channel. Step E: The surface acoustic wave propagating along the first propagation channel sequentially encounters the first reference reflection grating (04), the first temperature-compensated reflection grating (06), the first coded reflection grating (08), the second coded reflection grating (09), ..., the first... m The coded reflective grating (10) generates partial reflection and partial transmission, and its reflected signal is transmitted back to the first interdigital transducer (02); the first interdigital transducer (02) converts the reflected signal into a signal including ( m The first echo pulse train of +2) echo pulse signals has an echo pulse signal timing sequence similar to the above ( m +2) The positions of the reflective gratings have a one-to-one correspondence, and the change in the capacitance of the load capacitor connected to the coded reflective grating will cause a change in the phase of the corresponding echo pulse signal; The first echo pulse train is transmitted back to the reader antenna through the antenna (26); Step F: The reader processes the first echo pulse train and directly calculates the signal after quadrature demodulation. m +2) phase of echo pulse signals, and then construct a reference time delay by means of the distance between the first temperature-compensated reflective grating (06) and the first reference reflective grating (04), and based on the phase change of the reference time delay and ( m The positional relationship between the +2) reflectors can be deduced from this. m The initial phase of the echo pulse signal corresponding to each coded reflector at the reference temperature, which eliminates the temperature effect, is consistent with the corresponding... m The capacitance values ​​of the load capacitors have a one-to-one correspondence, thus obtaining the encoding of the surface acoustic wave tag. x 1- x 2-…- x m ; Step G: The phase directly calculated by orthogonal demodulation minus the initial phase at the reference temperature is the phase change caused by temperature. Under the premise of achieving the recognition function, according to ( m The known relationship between the distances between the +2) reflective gratings at the reference temperature is used to progressively extrapolate the phase change of the reference time delay due to temperature by working from near to far in a proportional manner. m The two farthest reflectors among the +2) reflectors are the first reference reflector (04) and the second. m The phase change between the echo pulse signals corresponding to the coded reflective grating (10) is used to detect the ambient temperature value based on the relationship between temperature change and phase change. Step H: 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; Step I: The surface acoustic wave tag receives the excitation pulse signal through the antenna (26). The second propagation channel, the third propagation channel, the fourth propagation channel, ..., the ( ) channel, whose center frequency is consistent with the carrier frequency of the excitation pulse signal. n +1) The propagation channel responds to the excitation pulse signal, and the second interdigital transducer (03) converts the excitation pulse signal into a surface acoustic wave through the inverse piezoelectric effect, propagating along the second propagation channel, the third propagation channel, the fourth propagation channel, ..., the ( ) n +1) Propagation of the piezoelectric substrate (01) surface in the propagation channel; Step J: The surface acoustic wave propagating along the second propagation channel sequentially encounters the second reference reflection grating (05), the second temperature-compensated reflection grating (07), and the first sensing reflection grating (14), resulting in partial reflection and partial transmission. The reflected signal is transmitted back to the second interdigital transducer (03); along the third propagation channel, the fourth propagation channel, ..., the ( n +1) The surface acoustic wave propagating in the propagation channel encounters the second sensing reflector grating (15), the third sensing reflector grating (16), ..., the ... n The sensing reflection grating (17) generates partial reflection and partial transmission, and its reflected signal is transmitted back to the second interdigital transducer (03); the second interdigital transducer (03) converts the above reflected signal into a signal including ( n The second echo pulse train of +2) echo pulse signals has an echo pulse signal timing sequence similar to the above ( n +2) The positions of the reflective gratings have a one-to-one correspondence; a change in a certain parameter value to be sensed will cause a change in the capacitance or inductance value of the load reactance, and further cause a change in the phase of the echo pulse signal corresponding to the corresponding sensing reflective grating; The second echo pulse train is transmitted back to the reader antenna via antenna (26); Step K: The reader processes the second echo pulse train and directly calculates the signal after quadrature demodulation. n +2) phase of echo pulse signals, and then construct a reference time delay by means of the distance between the second temperature-compensated reflective grating (07) and the second reference reflective grating (05), and based on the phase change of the reference time delay and ( n The positional relationship between the +2) reflectors can be deduced from this. n The initial phase of the echo pulse signal corresponding to each sensing reflector at the reference temperature; based on the first sensing reflector (14), the second sensing reflector (15), the third sensing reflector (16), ..., the first n The initial phase of the sensing reflector (17) at the reference temperature is obtained, and the first, second, third, ..., second phases are obtained after eliminating the influence of temperature. n One parameter value to be sensed.

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