A three-dimensional positioning and identification system and method using surface acoustic wave tags

Abstract

The present invention discloses a three-dimensional positioning and identification system and method using surface acoustic wave tags. The reader includes four antennas, and uses the carrier signal generated by the transmitting module as the local oscillator signal of the receiving module. Before positioning and identification, the fitting curves of the phase difference and intensity of the echo signals of each tag are calibrated. The time delay of the echo signals measured by the reader is averaged to identify the code of the tag, and then the unambiguous phase difference is obtained by interpolating on the fitting curve according to the phase and intensity of the echo signals, and the distances from each reader antenna to the tag are obtained therefrom. Finally, on the basis of designing the placement positions of the four reader antennas, the three-dimensional coordinates of the tag are obtained through the cosine formula of a triangle, line segment projection and trilateral positioning algorithm. The characteristics of the present invention are that it can avoid the influence of other factors than distance on the phase of the echo signal, and only one set of readers can realize the three-dimensional positioning and identification functions, and the proposed three-dimensional positioning method is simple, easy to implement and has high accuracy.

Description

Technical Field:

[0001] The present invention relates to a three-dimensional positioning and identification system and method using surface acoustic wave tags, belonging to the field of radio frequency identification positioning. Background Art:

[0002] In modern life, people spend about 70-90% of their time indoors on average. In recent years, due to the growing demand for location-based services, indoor positioning has become a research hotspot in both the industrial and academic fields. Currently, in many scenarios, it is also very necessary to clearly know the identity of the positioning point, that is, to achieve the identification function while realizing positioning. In addition, two-dimensional positioning can no longer meet the application requirements of some indoor positioning scenarios, and three-dimensional positioning has gradually become the future development trend in the field of indoor positioning.

[0003] Current indoor positioning technologies can be classified into ultra-wideband positioning, infrared positioning, WIFI positioning, Bluetooth positioning, radio frequency identification (RFID) positioning and other solutions according to different working principles. The indoor positioning solution based on surface acoustic wave (SAW) technology belongs to the category of RFID positioning. Its unique advantage is that the surface acoustic wave tags used for positioning are passive devices and do not require batteries or power supplies, thus being applicable to harsh environments with explosion and fire risks such as underground mines, expanding the application scenarios of indoor positioning. At the same time, using surface acoustic wave tags can achieve both positioning and identification functions.

[0004] The invention patent "An Indoor Positioning and Identification System and Its Positioning and Identification Method Based on Surface Acoustic Wave Technology" (Application No.: 201811508828.2, Application Date: December 11, 2018) uses a positioning reflection grating and a coding reflection grating to achieve positioning and identification functions, and the two types of reflection gratings each perform their own functions. Due to the large number of reflection gratings (4 reflection gratings on each propagation channel and a total of 8 reflection gratings on the surface acoustic wave tag), the reflectivity is low, thus affecting the effective range of positioning and identification. In addition, considering that the received signal strength indicator (RSSI) information is used for positioning, the positioning accuracy is low and the positioning result is greatly affected by the environment.

[0005] The invention patent "A surface acoustic wave positioning system and positioning method integrating intensity and phase information" (application number: 202010855133.2, application date: 2020.08.24) combines RSSI and received signal phase (Received SignalPhase, RSP) for positioning, and its positioning accuracy has been greatly improved, but it can only achieve positioning and does not have identification function. In addition, although the structure of the reader is mentioned in the patent, the specific composition of the transmitting module and the receiving module is not described in detail. In fact, the existing readers that match the surface acoustic wave tags usually adopt a superheterodyne structure, and the local oscillator of the receiving module usually adopts an independent local oscillator that is unrelated to the transmitting module. The transmitting module uses a single-pole single-throw switch to generate an excitation pulse signal of a fixed duration, such as Figure 1 As shown. Assume that the signal source of the transmitter module generates a frequency of f and an initial phase of Carrier signal The excitation pulse signal after modulation by the single-pole single-throw switch is where t on is the moment when the switch is closed, t off is the moment when the switch is turned off; the echo pulse signal responded by the surface acoustic wave tag is in the receiving module with a frequency of f' (not equal to f, the difference between the two is Δf=f-f'≠0) and an initial phase of The local oscillator signal Mixing, the intermediate frequency signal after mixing is Where D is the distance between the reader antenna and the SAW tag, and c is the propagation speed of electromagnetic waves in space. From the last formula above, we can see that the phase of the intermediate frequency signal is not only related to D, but also to t on 、 Due to the limitation of the MCU's maximum operating frequency, the MCU cannot accurately control the time of the single-pole single-throw switch, which results in the switch closing time t on becomes an uncertain value, and the independent local oscillator of the receiving module causes It also has uncertain values, making it impossible to establish a clear functional relationship between phase and distance, making it impossible for the positioning system to truly achieve effective fusion of phase and intensity information during positioning. At the same time, the patent uses a fingerprint positioning method to determine sub-areas without phase ambiguity, but only sets fingerprint points at the geometric centroid of each sub-area and establishes a fingerprint library. Due to the small number of fingerprint points in the fingerprint library, the system is affected in terms of both positioning stability and positioning accuracy.

[0006] Traditional 3D positioning methods such as trilateration often require solving the spherical equation. Due to the existence of ranging errors, there are often cases where the system of three quadratic equations for solving 3D coordinates has no solution, resulting in unstable solutions and further reducing the stability of positioning. Although some new 3D indoor positioning methods have emerged currently, they all have corresponding problems. Taking the well-known VLM (Virtual LandMarks) algorithm in RFID indoor 3D positioning algorithm as an example, it uses the compatibility constraint and exclusivity constraint between tags and readers to obtain a set of tags for positioning. However, this method requires a large number of readers and a complex reader layout, making it difficult to build a positioning system. Summary of the Invention:

[0007] In view of the problems existing in the existing positioning and identification system based on surface acoustic wave technology and the existing 3D positioning methods, the present invention proposes a 3D positioning and identification system and method using surface acoustic wave tags. The system uses surface acoustic wave tags with a dual-frequency, dual-channel, single-ended delay line structure. The reader includes four omnidirectional antennas with exactly the same performance indicators, namely the first reader antenna, the second reader antenna, the third reader antenna, and the fourth reader antenna. Moreover, the reader uses the carrier signal generated by the transmitting module as the local oscillator signal of the receiving module. Before positioning and identification, the relationship between the phase difference and intensity of the echo pulse signals of each surface acoustic wave tag is calibrated to obtain its fitting curve. During the positioning and identification process, first, the time delay of the echo pulse signals measured by the reader is averaged to identify the code of the tag. Then, based on the measured signal phase and intensity, an unambiguous phase difference is obtained by interpolating on the fitting curve, and further the distances from each reader antenna to the tag are obtained. Finally, the coordinate z of the tag is obtained by the cosine formula of a triangle, and further the coordinates x and y of the tag are obtained through line segment projection and trilateral positioning algorithm, realizing the 3D positioning and identification of the tag.

[0008] The present invention adopts the following technical solution: A 3D positioning and identification system using surface acoustic wave tags, which consists of surface acoustic wave tags and a reader; the reader includes four omnidirectional antennas with exactly the same performance indicators, namely the first reader antenna, the second reader antenna, the third reader antenna, and the fourth reader antenna; among them, the first reader antenna, the second reader antenna, and the third reader antenna are all placed in the same plane perpendicular to the z-axis of the positioning coordinate system and at a distance of z0 from the origin O; the distance between the fourth reader antenna and the first reader antenna is d, and the line connecting the positions of these two reader antennas is parallel to the z-axis of the positioning coordinate system.

[0009] Further, the surface acoustic wave tag has a dual - frequency dual - channel single - ended delay line structure, including a piezoelectric substrate, a first interdigital transducer, a second interdigital transducer, a first reflection grating, a second reflection grating, and a tag antenna. Among them, the first interdigital transducer and the first reflection grating are deposited on the upper half of the piezoelectric substrate to form the first propagation channel of the surface acoustic wave; the second interdigital transducer and the second reflection grating are deposited on the lower half of the piezoelectric substrate to form the second propagation channel of the surface acoustic wave. The aperture of the interdigital transducers and the aperture of the reflection gratings in the two propagation channels are equal, and the two propagation channels are independent of each other. By designing the finger width of the first interdigital transducer and the grating bar width of the first reflection grating, the center frequency f1 of the first propagation channel is 842.5 MHz; by designing the finger width of the second interdigital transducer and the grating bar width of the second reflection grating, the center frequency f2 of the second propagation channel is 922.5 MHz. The first interdigital transducer and the second interdigital transducer are deposited on the left side of the piezoelectric substrate and are connected to the tag antenna in parallel. The tag antenna is a dual - frequency omnidirectional antenna covering two frequency bands of 840 - 845 MHz and 920 - 925 MHz. The center - to - center distance L1 from the first reflection grating to the first interdigital transducer and the center - to - center distance L2 from the second reflection grating to the second interdigital transducer satisfy the proportional relationship of L1 / L2 = f2 / f1. Surface acoustic wave tags with different encodings have different L1 and L2 values. The surface acoustic wave tags are encoded according to the different time delays of the echo pulses corresponding to different positions of the reflection gratings. In the order from near to far of the distance between the second reflection grating and the second interdigital transducer on the surface acoustic wave tag, the encoding values of each surface acoustic wave tag are 1, 2, …, n.

[0010] Further, the reader includes a transmitting module, a signal link selection module, a receiving module, a signal processing module, a first reader antenna, a second reader antenna, a third reader antenna, and a fourth reader antenna;

[0011] The transmitting module consists of a signal source, a one - to - two power splitter, and a single - pole single - throw switch;

[0012] The signal link selection module consists of a single - pole triple - throw switch and a single - pole quadruple - throw switch;

[0013] The receiving module consists of a first RF front - end, a second RF front - end, a single - pole double - throw switch, an IQ demodulator, a first intermediate - frequency filtering and amplification circuit, a second intermediate - frequency filtering and amplification circuit, a first ADC, and a second ADC;

[0014] The signal processing module consists of an MCU;

[0015] The input port of the one - to - two power splitter is connected to the signal source, one output port is connected to the input port of the single - pole single - throw switch, and the other output port is connected to the local oscillator input terminal of the IQ demodulator;

[0016] The first port of the single-pole triple-throw switch is connected to the first port of the single-pole four-throw switch. The second port of the single-pole triple-throw switch is connected to the output port of the single-pole single-throw switch. The third port of the single-pole triple-throw switch is connected to the input port of the first RF front-end. The fourth port of the single-pole triple-throw switch is connected to the input port of the second RF front-end;

[0017] The second port of the single-pole four-throw switch is connected to the first reader antenna. The third port of the single-pole four-throw switch is connected to the second reader antenna. The fourth port of the single-pole four-throw switch is connected to the third reader antenna. The fifth port of the single-pole four-throw switch is connected to the fourth reader antenna;

[0018] The first port of the single-pole double-throw switch is connected to the signal input terminal of the IQ demodulator. The second port of the single-pole double-throw switch is connected to the output port of the first RF front-end. The third port of the single-pole double-throw switch is connected to the output port of the second RF front-end;

[0019] The two output terminals of the IQ demodulator are respectively connected to the input terminals of the first intermediate-frequency filtering and amplification circuit and the second intermediate-frequency filtering and amplification circuit. The output terminals of the first intermediate-frequency filtering and amplification circuit and the second intermediate-frequency filtering and amplification circuit are respectively connected to the input terminals of the first ADC and the second ADC. The output terminals of the first ADC and the second ADC are both connected to the MCU.

[0020] The present invention further includes the following technical solution: A positioning and identification method for a three-dimensional positioning and identification system using surface acoustic wave tags, including the following steps: Among them, step A is the offline stage:

[0021] Step A: Within the ranging range that the system can reach, calibrate the relationship between the phase difference and intensity of the echo pulse signals of each surface acoustic wave tag;

[0022] Step B: The reader transmitting module generates an excitation pulse signal with a carrier frequency of f1;

[0023] Step C: The single-pole triple-throw switch of the reader signal link selection module is thrown to the second port, and the single-pole four-throw switch is thrown to the second port;

[0024] Step D: The excitation pulse signal enters the single-pole four-throw switch through the second and first ports of the single-pole three-throw switch, and then enters the corresponding reader antenna through the corresponding port of the single-pole four-throw switch. The excitation pulse signal is transmitted through this reader antenna; the tag antenna of the surface acoustic wave tag receives the excitation pulse signal, and only the propagation channel whose center frequency is consistent with the carrier frequency of the excitation pulse signal responds to this excitation pulse signal. The interdigital transducer of this propagation channel converts the excitation pulse signal into a surface acoustic wave through the inverse piezoelectric effect and propagates along the surface of the piezoelectric substrate. When the surface acoustic wave encounters the reflection grating of this propagation channel, partial reflection and partial transmission occur. Its reflected signal is transmitted back to the interdigital transducer, and the interdigital transducer then converts the reflected signal into an echo pulse signal through the direct piezoelectric effect. The echo pulse signal is transmitted back to the corresponding reader antenna through the tag antenna;

[0025] Step E: The single-pole three-throw switch of the reader signal link selection module is thrown to the third port;

[0026] Step F: The echo pulse signal enters the single-pole three-throw switch through the corresponding port of the single-pole four-throw switch, and then enters the receiving module and the signal processing module through the corresponding port of the single-pole three-throw switch;

[0027] Step G: The signal processing module obtains the intensity value S 11 、time delay value t 11 、phase value

[0028] Step H: The single-pole three-throw switch of the reader signal link selection module is thrown to the second port, and the single-pole four-throw switch is sequentially thrown to the third port, the fourth port, and the fifth port, and steps D and E are repeated each time. Then step F is repeated, and the signal processing module sequentially obtains the intensity value S 12 、time delay value t 12 、phase value intensity value S 13 、time delay value t 13 、phase value intensity value S 14 、time delay value t 14 \(、phase value

[0029] Step I: The reader transmitting module generates an excitation pulse signal with a carrier frequency of f2, repeats steps C and D, the single-pole three-throw switch of the reader signal link selection module is thrown to the fourth port, and then step F is repeated;

[0030] Step J: The signal processing module obtains the phase value of the echo pulse signal

[0031] Step K: The single-pole triple-throw switch of the reader signal link selection module is thrown to the second port, and the single-pole four-throw switch is successively thrown to the third port, the fourth port, and the fifth port, and step D is repeated each time. The single-pole triple-throw switch of the reader signal link selection module is thrown to the fourth port, and then step F is repeated. The signal processing module successively obtains the phase values of the echo pulse signals.

[0032] Step L: Take the average of the time delay values t 11 , t 12 , t 13 , t 14 , that is, t = (t 11 + t 12 + t 13 + t 14 ) / 4; Calculate the position of the reflection grating on the SAW tag according to the average time delay t and the wave velocity of the surface acoustic wave, so as to identify the coding value n' of the SAW tag, and further select the fitting curve between the phase difference and the intensity of the echo pulse signal of the SAW tag with the coding value n' through step A;

[0033] Step M: By interpolating the intensity value S 11 on the fitting curve, obtain the corresponding phase difference of the echo pulse signal Combine the integer part 2π(x' - 1) of the phase ranging of the interpolation result with the phase difference to obtain the distance d1 from the first reader antenna to the SAW tag according to .

[0034] Step N: Adopt the same method as step M, and obtain the distance d2 from the second reader antenna to the SAW tag through the intensity value S 12 , the phase value and ; Obtain the distance d3 from the third reader antenna to the SAW tag through the intensity value S 13 , the phase value and ; Obtain the distance d4 from the fourth reader antenna to the SAW tag through the intensity value S 14 , the phase value and ;

[0035] Step O: From the distances d1 and d4 from the first reader antenna and the fourth reader antenna to the SAW tag obtained in steps M and N, combined with the cosine formula of a triangle, the coordinate z of the SAW tag is obtained as:

[0036] Step P: Project the distances d1, d2, and d3 from the first reader antenna, the second reader antenna, and the third reader antenna to the surface acoustic wave tag onto the plane formed by the positions of the first reader antenna, the second reader antenna, and the third reader antenna, and obtain three projected distances x1, x2, and x3 respectively as follows:

[0037] Step Q: From x1, x2, and x3 obtained in Step P, use the trilateration algorithm to obtain the two-dimensional coordinates (x, y) of the surface acoustic wave tag; combine with the coordinate z obtained in Step O to obtain the three-dimensional coordinates (x, y, z) of the surface acoustic wave tag, and realize the three-dimensional positioning of the surface acoustic wave tag; further combine with the surface acoustic wave tag coding value n' obtained in Step L to complete the three-dimensional positioning and identification of the surface acoustic wave tag.

[0038] Further, Step A is specifically divided into the following steps:

[0039] Step a: According to the center frequency difference Δf = f2 - f1 of the two propagation channels of the surface acoustic wave tag, calculate the non-phase-ambiguity ranging length when using the phase difference information of the echo pulse signal for ranging, so as to divide the ranging range that the system can reach into x sub-regions without phase ambiguity problems. The integer parts of the phase difference ranging for each sub-region from near to far are 0, 1,..., (x - 1), and y calibration points are equally spaced within each sub-region, and the first reader antenna is selected for calibration;

[0040] Step b: Place the surface acoustic wave tag with a coding value of 1 at the first calibration point in the first sub-region;

[0041] Step c: According to the same steps as Steps B, C, D, E, and F in Claim 4, the signal processing module obtains the intensity value S c11 and the phase value Then, according to the same step as Step I in Claim 4, obtain the phase value of this calibration point

[0042] Step d: Obtain the phase difference of the echo pulse signal when the surface acoustic wave tag with a coding value of 1 is placed at the first calibration point in the first sub-region and record the calibration result at this calibration point

[0043] Step e: Place the surface acoustic wave tag with a coding value of 1 at the 2nd,..., yth calibration points in the first sub-region respectively, and further place it at the calibration points of the 2nd, 3rd,..., (x - 1)th, and xth sub-regions respectively. According to the same steps as Step c, until the phase differences of the echo pulse signals of the calibration points in the xth sub-region are obtained Record the calibration results at all calibration points Obtain the fitting curve between the phase difference and intensity of the echo pulse signal of the surface acoustic wave tag with a coding value of 1 by means of curve fitting;

[0044] Step f: Place the surface acoustic wave tags with coding values of 2, 3, …, (n - 1), and n at each calibration point in each sub-region in sequence. According to the same steps as in step e, finally obtain the fitting curves between the phase differences and intensities of the echo pulse signals of all coded surface acoustic wave tags.

[0045] The present invention has the following beneficial effects:

[0046] 1. When using a surface acoustic wave positioning tag for identification, there is no need to additionally increase a coding reflection grating. The identification function can be realized by measuring the distance between the existing positioning reflection grating and the interdigital transducer. Thus, the reflection grating can have a higher reflectivity, thereby ensuring the effective range of positioning and identification, and can also realize the simultaneous positioning and identification of multiple different coded surface acoustic wave tags.

[0047] 2. The reader uses the carrier signal generated by the transmitting module as the local oscillator signal of the receiving module, which not only simplifies the circuit structure, but more importantly, avoids the influence of the uncertainty of the modulation switch closing moment and the randomness of the initial phase of the local oscillator signal on the phase of the measured echo signal. Thus, a clear functional relationship between the phase and the distance can be established, enabling the positioning system to truly realize the effective fusion of the phase and intensity information during positioning.

[0048] 3. The system calibrates the relationship between the phase differences and intensities of the echo pulse signals of all coded surface acoustic wave tags, and equidistantly sets multiple calibration points in each sub-region without the problem of phase ambiguity. In actual application, the unambiguous phase difference is obtained by interpolating the fitting curve. Compared with the fingerprint positioning method that only sets fingerprint points at the geometric centroids of each sub-region and establishes a fingerprint database, it not only ensures the stability of positioning, but also improves the positioning accuracy.

[0049] 4. By reasonably designing the signal link selection module of the reader and the placement position of the reader antenna, a set of readers can realize the three-dimensional positioning and identification functions. This not only expands the application scenarios of indoor positioning, but also reduces the complexity and cost of the system.

[0050] 5. A new three-dimensional positioning method is proposed. First, the z coordinate is obtained, and then the x and y coordinates are obtained, avoiding the requirement of the traditional three-dimensional positioning algorithm to solve the spherical equation, simplifying the calculation process, and avoiding the occurrence of no-solution situations. This method only needs to use simple cosine formulas of triangles, line segment projections, and trilateration algorithms, and the calculation method is simple and easy to implement. Description of the drawings:

[0051] Figure 1 It is a schematic diagram of the existing reader frame structure matching the surface acoustic wave tag.

[0052] Figure 2 It is a schematic diagram of the three-dimensional positioning and identification system structure of the present invention.

[0053] Figure 3(a) and 3(b) It is a schematic diagram of the placement position of the reader antenna of the present invention.

[0054] Figure 4 It is a schematic diagram of the surface acoustic wave tag structure.

[0055] Figure 5 It is a schematic diagram of the surface acoustic wave tag coding of the present invention.

[0056] Figure 6 It is a schematic diagram of the reader frame structure of the present invention.

[0057] Figure 7(a) , 7(b) , 7(c), 7(d) are schematic diagrams of the positional relationship between the surface acoustic wave tag of the present invention and the first reader antenna and the fourth reader antenna.

[0058] Figure 8 It is a schematic diagram of the triangular relationship when the distance from the first reader antenna of the present invention to the surface acoustic wave tag is projected onto the plane formed by the positions of the first reader antenna, the second reader antenna, and the third reader antenna. Specific embodiments:

[0059] The present invention will be further described below with reference to the accompanying drawings.

[0060] Please refer to Figure 2 Combined with Figure 3(a) , 3(b) As shown, the three-dimensional positioning and identification system of the present invention is composed of a surface acoustic wave tag and a reader; the reader includes four omnidirectional antennas with exactly the same performance indicators, namely the first reader antenna, the second reader antenna, the third reader antenna, and the fourth reader antenna; the positions where the surface acoustic wave tag, the first reader antenna, the second reader antenna, the third reader antenna, and the fourth reader antenna are located are respectively marked as T, A, B, C, D; the first reader antenna, the second reader antenna, and the third reader antenna are all placed on the same plane perpendicular to the z-axis of the positioning coordinate system and at a distance of z0 from the origin O; the distance between the fourth reader antenna and the first reader antenna is d, and the connection line of the positions where the two reader antennas are located is parallel to the z-axis of the positioning coordinate system.

[0061] Please refer to Figure 4As shown in the figure, the surface acoustic wave tag has a dual-frequency, dual-channel, single-ended delay line structure, including a piezoelectric substrate, a first interdigital transducer, a second interdigital transducer, a first reflection grating, a second reflection grating, and a tag antenna. The first interdigital transducer and the first reflection grating are deposited on the upper half of the piezoelectric substrate to form the first propagation channel of the surface acoustic wave. The second interdigital transducer and the second reflection grating are deposited on the lower half of the piezoelectric substrate to form the second propagation channel of the surface acoustic wave. The aperture of the interdigital transducers and the aperture of the reflection gratings in the two propagation channels are equal, and the two propagation channels are independent of each other. By designing the finger width of the first interdigital transducer and the grating width of the first reflection grating, the center frequency f1 of the first propagation channel is 842.5 MHz. By designing the finger width of the second interdigital transducer and the grating width of the second reflection grating, the center frequency f2 of the second propagation channel is 922.5 MHz. The first interdigital transducer and the second interdigital transducer are deposited on the left side of the piezoelectric substrate and are connected to the tag antenna in parallel. The tag antenna is a dual-frequency omnidirectional antenna covering two frequency bands of 840 - 845 MHz and 920 - 925 MHz. The center distance L1 from the first reflection grating to the first interdigital transducer and the center distance L2 from the second reflection grating to the second interdigital transducer satisfy the proportional relationship of L1 / L2 = f2 / f1.

[0062] Please refer to Figure 5 in combination with Figure 4 As shown in the figure, the surface acoustic wave tags with different encodings of the present invention have different L1 and L2 values. The surface acoustic wave tags are encoded according to the different time delays of the echo pulses corresponding to the different positions of the reflection gratings. According to the order from near to far of the distance between the second reflection grating and the second interdigital transducer on the surface acoustic wave tags, the encoding values of each surface acoustic wave tag are 1, 2,..., n respectively.

[0063] Please refer to Figure 6 As shown in the figure, the reader of the present invention includes a transmitting module, a signal link selection module, a receiving module, a signal processing module, a first reader antenna, a second reader antenna, a third reader antenna, and a fourth reader antenna. The transmitting module consists of a signal source, a one-to-two power divider, and a single-pole single-throw switch. The signal link selection module consists of a single-pole triple-throw switch and a single-pole quadruple-throw switch. The receiving module consists of a first RF front end, a second RF front end, a single-pole double-throw switch, an IQ demodulator, a first intermediate frequency filtering and amplifying circuit, a second intermediate frequency filtering and amplifying circuit, a first ADC, and a second ADC. The signal processing module consists of an MCU.

[0064] In the transmitting module, the input port of the one-to-two power divider is connected to the signal source. One of the output ports is connected to the input port of the single-pole single-throw switch, and the other output port is connected to the local oscillator input of the IQ demodulator in the receiving module. That is, a one-to-two power divider is used to divide the carrier signal generated by the signal source into two signals with equal amplitude and in-phase. One of the signals is down-converted with the echo pulse signal carrying the tag information, making the receiving module a zero-intermediate-frequency coherent structure. This not only eliminates the influence of the uncertainty at the moment of switch closure on the phase of the echo pulse signal, but also the initial phase of the local oscillator signal in the receiving module is no longer a random value. Thus, a clear functional relationship between phase and distance can be established, enabling the positioning system to truly achieve the effective fusion of phase and intensity information during positioning.

[0065] In the signal link selection module, the first port of the single-pole triple-throw switch is connected to the first port of the single-pole four-throw switch. The second port of the single-pole triple-throw switch is connected to the output port of the single-pole single-throw switch in the transmitting module. The third port of the single-pole triple-throw switch is connected to the input port of the first RF front-end in the receiving module. The fourth port of the single-pole triple-throw switch is connected to the input port of the second RF front-end in the receiving module. The second port of the single-pole four-throw switch is connected to the first reader antenna. The third port of the single-pole four-throw switch is connected to the second reader antenna. The fourth port of the single-pole four-throw switch is connected to the third reader antenna. The fifth port of the single-pole four-throw switch is connected to the fourth reader antenna.

[0066] The RF front-ends of the receiving module adopt two parallel RF filtering and amplification circuits, namely the first RF front-end and the second RF front-end. In the receiving module, the first port of the single-pole double-throw switch is connected to the signal input of the IQ demodulator. The second port of the single-pole double-throw switch is connected to the output port of the first RF front-end. The third port of the single-pole double-throw switch is connected to the output port of the second RF front-end. The two output ends of the IQ demodulator are respectively connected to the input ends of the first intermediate-frequency filtering and amplification circuit and the second intermediate-frequency filtering and amplification circuit. The output ends of the first intermediate-frequency filtering and amplification circuit and the second intermediate-frequency filtering and amplification circuit are respectively connected to the input ends of the first ADC and the second ADC. The output ends of the first ADC and the second ADC are both connected to the MCU.

[0067] Please refer to Figures 2 to 8 As shown, the positioning and identification method of the three-dimensional positioning and identification system using surface acoustic wave tags in the present invention includes the following steps, where step A is the offline stage:

[0068] Step A: Calibrate the relationship between the phase difference and intensity of the echo pulse signals of each surface acoustic wave tag within the ranging range that the system can reach.

[0069] Step B: The reader transmitting module generates an excitation pulse signal with a carrier frequency of f1.

[0070] Step C: The single-pole triple-throw switch of the reader signal link selection module is thrown to the second port, and the single-pole four-throw switch is thrown to the second port;

[0071] Step D: The excitation pulse signal enters the single-pole four-throw switch through the second port and the first port of the single-pole triple-throw switch, and then enters the corresponding reader antenna through the corresponding port of the single-pole four-throw switch. The excitation pulse signal is transmitted through the reader antenna. The tag antenna of the surface acoustic wave tag receives the excitation pulse signal, and only the propagation channel whose center frequency is consistent with the carrier frequency of the excitation pulse signal responds to the excitation pulse signal. The interdigital transducer of this propagation channel converts the excitation pulse signal into a surface acoustic wave through the inverse piezoelectric effect and propagates along the surface of the piezoelectric substrate. When the surface acoustic wave encounters the reflection grating of this propagation channel, partial reflection and partial transmission occur. The reflected signal is transmitted back to the interdigital transducer, and the interdigital transducer then converts the reflected signal into an echo pulse signal through the direct piezoelectric effect. The echo pulse signal is transmitted back to the corresponding reader antenna through the tag antenna;

[0072] Step E: The single-pole triple-throw switch of the reader signal link selection module is thrown to the third port;

[0073] Step F: The echo pulse signal enters the single-pole triple-throw switch through the corresponding port of the single-pole four-throw switch, and then enters the receiving module and the signal processing module through the corresponding port of the single-pole triple-throw switch;

[0074] Step G: The signal processing module obtains the intensity value S of the echo pulse signal when the single-pole four-throw switch is thrown to the second port 11 , time delay value t 11 , phase value

[0075] Step H: The single-pole triple-throw switch of the reader signal link selection module is thrown to the second port, and the single-pole four-throw switch is successively thrown to the third port, the fourth port, and the fifth port, and steps D, E, and F are repeated each time. The signal processing module successively obtains the intensity value S of the echo pulse signal 12 , time delay value t 12 , phase value Intensity value S 13 , time delay value t 13 , phase value Intensity value S 14 , time delay value t 14 , phase value

[0076] Step I: The reader transmitter module generates an excitation pulse signal with a carrier frequency of f2, repeats steps C and D, the single-pole triple-throw switch of the reader signal link selection module is thrown to the fourth port, and then step F is repeated;

[0077] Step J: The signal processing module obtains the phase value of the echo pulse signal

[0078] Step K: The single-pole triple-throw switch of the reader signal link selection module is thrown to the second port, and the single-pole four-throw switch is successively thrown to the third port, the fourth port, and the fifth port, and Step D is repeated each time. The single-pole triple-throw switch of the reader signal link selection module is thrown to the fourth port, and then Step F is repeated. The signal processing module successively obtains the phase values of the echo pulse signal

[0079] Step L: Take the average of the delay values t 11 、t 12 、t 13 、t 14 , that is, t = (t 11 +t 12 +t 13 +t 14 ) / 4; Calculate the position of the reflection grating on the surface acoustic wave tag according to the average delay t and the wave velocity of the surface acoustic wave, so as to identify the encoded value n' of the surface acoustic wave tag, and further select the fitting curve between the phase difference and the intensity of the echo pulse signal of the surface acoustic wave tag with the encoded value n' through Step A;

[0080] Step M: By interpolating the intensity value S 11 on the fitting curve, obtain the corresponding phase difference of the echo pulse signal Take the integer part 2π(x'-1) of the phase ranging of the interpolation result and combine it with the phase difference According to obtain the distance from the first reader antenna to the surface acoustic wave tag where c is the propagation speed of electromagnetic waves in space;

[0081] Step N: Adopt the same method as in Step M, and obtain the distance d2 from the second reader antenna to the surface acoustic wave tag through the intensity value S 12 and the phase value and ; Obtain the distance d3 from the third reader antenna to the surface acoustic wave tag through the intensity value S 13 and the phase value and ; Obtain the distance d4 from the fourth reader antenna to the surface acoustic wave tag through the intensity value S 14 and the phase value and ;

[0082] Step O: From the distances d1 and d4 from the first reader antenna and the fourth reader antenna to the surface acoustic wave tag obtained in Steps M and N, combined with the triangle cosine formula, obtain the coordinates z of the surface acoustic wave tag

[0083] The positional relationships between the surface acoustic wave tag and the first reader antenna and the fourth reader antenna are as follows Figure 7(a) , 7(b) , 7(c), and 7(d) show four cases; taking Fig. 7(a) as an example, TA = d1, TD = d4, O'A = z0, AD = d, ∠TDA = α, where O' is the intersection of the line connecting the positions A and D of the first reader antenna and the fourth reader antenna and the xoy plane when the positioning coordinate system is z = 0; draw a perpendicular line from point T to the line segment AD or its extension, and let the foot of the perpendicular be E, and record the line segment DE = l; in the right triangle TDE, there is In triangle TDA, there is From this, it can be obtained that: Furthermore, it can be obtained that z = O'E = O'A + AE = O'A + (AD - DE), that is Figure 7(b) , 7(c) , 7(d) although has different positional relationships with Fig. 7(a), the derived results are the same, which is It will not be elaborated here;

[0084] Step P: Project the distances d1, d2, and d3 from the first reader antenna, the second reader antenna, and the third reader antenna to the surface acoustic wave tag onto the plane formed by the positions of the first reader antenna, the second reader antenna, and the third reader antenna, and obtain three projected distances x1, x2, and x3;

[0085] The triangular relationship of the distance d1 from the first reader antenna to the surface acoustic wave tag projected onto the plane formed by the positions of the first reader antenna, the second reader antenna, and the third reader antenna is as Figure 8 shown; from Figure 8 it can be seen that According to the same triangular relationship, it can be obtained that:

[0086] Step Q: From x1, x2, and x3 obtained in step P, use the trilateration algorithm to obtain the two-dimensional coordinates (x, y) of the surface acoustic wave tag; combine the coordinate z obtained in step O to obtain the three-dimensional coordinates (x, y, z) of the surface acoustic wave tag, and realize the three-dimensional positioning of the surface acoustic wave tag; further combine the surface acoustic wave tag coding value n' obtained in step L, and thus complete the three-dimensional positioning and identification of the surface acoustic wave tag.

[0087] Among them, step A is specifically divided into the following steps:

[0088] Step a: According to the center frequency difference Δf = f2 - f1 between the two propagation channels of the surface acoustic wave tag, calculate the non-phase-ambiguity ranging length when using the phase difference information of the echo pulse signal for ranging, so as to divide the ranging range that the system can reach into x sub-regions without phase ambiguity problems. The integer parts of the phase difference ranging for each sub-region from near to far are 0, 1, …, (x - 1) respectively, and y calibration points are equally spaced within each sub-region, and the first reader antenna is selected for calibration;

[0089] Step b: Place the surface acoustic wave tag with a coding value of 1 at the first calibration point in the first sub-region;

[0090] Step c: According to the same steps as steps B, C, D, E, and F in claim 4, the signal processing module obtains the intensity value S c11 and the phase value Then, according to the same steps as step I in claim 4, obtain the phase value of this calibration point

[0091] Step d: Obtain the phase difference of the echo pulse signal when the surface acoustic wave tag with a coding value of 1 is placed at the first calibration point in the first sub-region And record the calibration result at this calibration point

[0092] Step e: Place the surface acoustic wave tag with a coding value of 1 at the 2nd, …, yth calibration points in the first sub-region respectively, and further place it at the calibration points in the 2nd, 3rd, …, (x - 1)th, and xth sub-regions respectively. According to the same steps as step c, until the phase differences of the echo pulse signals at the calibration points in the xth sub-region are obtained Record the calibration results at all calibration points Obtain the fitting curve between the phase difference and the intensity of the echo pulse signal of the surface acoustic wave tag with a coding value of 1 by means of curve fitting;

[0093] Step f: Place the surface acoustic wave tags with coding values of 2, 3, …, (n - 1), and n at the calibration points in each sub-region respectively. According to the same steps as step e, finally obtain the fitting curves between the phase differences and the intensities of the echo pulse signals of all coded surface acoustic wave tags.

[0094] The above is only the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, several improvements can be made without departing from the principle of the present invention, and these improvements should also be regarded as the protection scope of the present invention.

Claims

1. A three-dimensional positioning and identification system using surface acoustic wave tags, which consists of surface acoustic wave tags and a reader, is characterized in that: The reader includes four omnidirectional antennas with exactly the same performance indicators, namely the first reader antenna, the second reader antenna, the third reader antenna, and the fourth reader antenna. Among them, the first reader antenna, the second reader antenna, and the third reader antenna are all placed on the same plane perpendicular to the z-axis of the positioning coordinate system and at a distance of z0 from the origin O. The distance between the fourth reader antenna and the first reader antenna is d, and the line connecting the positions of the two reader antennas is parallel to the z-axis of the positioning coordinate system. The surface acoustic wave tag has a dual-frequency, dual-channel, single-ended delay line structure, and includes a piezoelectric substrate, a first interdigital transducer, a second interdigital transducer, a first reflection grating, a second reflection grating, and a tag antenna. Among them, the first interdigital transducer and the first reflection grating are deposited on the upper half of the piezoelectric substrate to form the first propagation channel of the surface acoustic wave. The second interdigital transducer and the second reflection grating are deposited on the lower half of the piezoelectric substrate to form the second propagation channel of the surface acoustic wave. The aperture of the interdigital transducer and the aperture of the reflection grating in the two propagation channels are equal, and the two propagation channels are independent of each other. By designing the finger width of the first interdigital transducer and the grating width of the first reflection grating, the center frequency f1 of the first propagation channel is 842.5 MHz. By designing the finger width of the second interdigital transducer and the grating width of the second reflection grating, the center frequency f2 of the second propagation channel is 922.5 MHz. The first interdigital transducer and the second interdigital transducer are deposited on the left side of the piezoelectric substrate and are connected to the tag antenna in parallel. The tag antenna is a dual-frequency omnidirectional antenna covering two frequency bands of 840 - 845 MHz and 920 - 925 MHz. The center distance L1 from the first reflection grating to the first interdigital transducer and the center distance L2 from the second reflection grating to the second interdigital transducer satisfy the proportional relationship of L1 / L2 = f2 / f1. Its feature is that surface acoustic wave tags with different encodings have different L1 and L2 values. The surface acoustic wave tags are encoded according to the different time delays of the echo pulses corresponding to different positions of the reflection gratings. In the order from near to far of the distance between the second reflection grating and the second interdigital transducer on the surface acoustic wave tag, the encoding values of each surface acoustic wave tag are 1, 2,..., n. The reader includes a transmitting module, a signal link selection module, a receiving module, a signal processing module, a first reader antenna, a second reader antenna, a third reader antenna, and a fourth reader antenna. The transmitting module consists of a signal source, a one-to-two power divider, and a single-pole single-throw switch. The signal link selection module consists of a single-pole triple-throw switch and a single-pole four-throw switch. The receiving module consists of a first RF front-end, a second RF front-end, a single-pole double-throw switch, an IQ demodulator, a first intermediate-frequency filtering and amplifying circuit, a second intermediate-frequency filtering and amplifying circuit, a first ADC, and a second ADC. The signal processing module consists of an MCU. The input port of the one-to-two power divider is connected to the signal source, one output port is connected to the input port of the single-pole single-throw switch, and the other output port is connected to the local oscillator input terminal of the IQ demodulator. The first port of the single-pole triple-throw switch is connected to the first port of the single-pole four-throw switch. The second port of the single-pole triple-throw switch is connected to the output port of the single-pole single-throw switch. The third port of the single-pole triple-throw switch is connected to the input port of the first RF front-end. The fourth port of the single-pole triple-throw switch is connected to the input port of the second RF front-end. The second port of the single-pole four-throw switch is connected to the first reader antenna. The third port of the single-pole four-throw switch is connected to the second reader antenna. The fourth port of the single-pole four-throw switch is connected to the third reader antenna. The fifth port of the single-pole four-throw switch is connected to the fourth reader antenna. The first port of the single-pole double-throw switch is connected to the signal input terminal of the IQ demodulator. The second port of the single-pole double-throw switch is connected to the output port of the first RF front-end. The third port of the single-pole double-throw switch is connected to the output port of the second RF front-end. The two output terminals of the IQ demodulator are respectively connected to the input terminals of the first intermediate-frequency filtering and amplifying circuit and the second intermediate-frequency filtering and amplifying circuit. The output terminals of the first intermediate-frequency filtering and amplifying circuit and the second intermediate-frequency filtering and amplifying circuit are respectively connected to the input terminals of the first ADC and the second ADC. The output terminals of the first ADC and the second ADC are both connected to the MCU.

2. A positioning and identification method for a three-dimensional positioning and identification system using surface acoustic wave tags as described in claim 1, characterized in that: It includes the following steps: Among them, step A is the offline stage: Step A: Within the ranging range that the system can reach, calibrate the relationship between the phase difference and intensity of the echo pulse signals of each SAW tag. Step B: The reader transmitting module generates an excitation pulse signal with a carrier frequency of f1. Step C: The single-pole triple-throw switch of the reader signal link selection module is thrown to the second port, and the single-pole four-throw switch is thrown to the second port. Step D: The excitation pulse signal enters the single-pole four-throw switch through the second port and the first port of the single-pole triple-throw switch, and then enters the corresponding reader antenna through the corresponding port of the single-pole four-throw switch. The excitation pulse signal is transmitted through the reader antenna. The tag antenna of the SAW tag receives the excitation pulse signal, and only the propagation channel with the center frequency consistent with the carrier frequency of the excitation pulse signal responds to the excitation pulse signal. The interdigital transducer of this propagation channel converts the excitation pulse signal into a surface acoustic wave through the inverse piezoelectric effect and propagates along the surface of the piezoelectric substrate. When the surface acoustic wave encounters the reflection grating of this propagation channel, partial reflection and partial transmission occur. Its reflected signal is transmitted back to the interdigital transducer, and the interdigital transducer then converts the reflected signal into an echo pulse signal through the direct piezoelectric effect. The echo pulse signal is transmitted back to the corresponding reader antenna through the tag antenna. Step E: The single-pole triple-throw switch of the reader signal link selection module is thrown to the third port. Step F: The echo pulse signal enters the single-pole triple-throw switch through the corresponding port of the single-pole four-throw switch, and then enters the receiving module and the signal processing module through the corresponding port of the single-pole triple-throw switch. Step G: The signal processing module obtains the intensity value S of the echo pulse signal when the single-pole four-throw switch is thrown to the second port 11 , the time delay value t 11 , the phase value Step H: The single-pole triple-throw switch of the reader signal link selection module is thrown to the second port, and the single-pole four-throw switch is successively thrown to the third port, the fourth port, and the fifth port, and Steps D, E, and F are repeated each time. The signal processing module successively obtains the intensity value S of the echo pulse signal 12 , time delay value t 12 , phase value Intensity value S 13 , time delay value t 13 , phase value Intensity value S 14 , time delay value t 14 , phase value Step I: The reader transmitting module generates an excitation pulse signal with a carrier frequency of f2, repeats step C and step D. The single-pole triple-throw switch of the reader signal link selection module is thrown to the fourth port, and then repeats step F. Step J: The signal processing module obtains the phase value of the echo pulse signal Step K: The single-pole triple-throw switch of the reader signal link selection module is thrown to the second port, the single-pole four-throw switch is sequentially thrown to the third port, the fourth port, and the fifth port, and Step D is repeated each time. The single-pole triple-throw switch of the reader signal link selection module is thrown to the fourth port, and then Step F is repeated. The signal processing module sequentially obtains the phase values of the echo pulse signals Step L: Take the average of the delay values t 11 , t 12 , t 13 , t 14 , i.e., t = (t 11 + t 12 + t 13 + t 14 ) / 4; Calculate the position of the reflection grating on the surface acoustic wave tag based on the average delay t and the wave velocity of the surface acoustic wave, thereby identifying the encoded value n' of the surface acoustic wave tag, and further select the fitting curve between the phase difference and the intensity of the echo pulse signal of the surface acoustic wave tag with the encoded value n' through Step A; Step M: By interpolating the intensity value S on the fitting curve 11 to obtain the corresponding phase difference of the echo pulse signal Take the integer part 2π(x'-1) of the phase ranging of the interpolation result and the phase difference Combine them. According to obtain the distance d1 from the first reader antenna to the surface acoustic wave tag; Step N: Using the same method as in Step M, through the intensity value S 12 , the phase value and obtain the distance d2 from the second reader antenna to the surface acoustic wave tag; through the intensity value S 13 , the phase value and obtain the distance d3 from the third reader antenna to the surface acoustic wave tag; through the intensity value S 14 , the phase value and obtain the distance d4 from the fourth reader antenna to the surface acoustic wave tag; Step O: Based on the distances d1 and d4 from the first reader antenna and the fourth reader antenna obtained in Steps M and N to the surface acoustic wave tag, and by combining with the cosine formula of a triangle, the coordinate z of the surface acoustic wave tag is obtained as follows: Step P: Project the distances d1, d2, and d3 from the first reader antenna, the second reader antenna, and the third reader antenna to the SAW tag onto the plane formed by the positions of the first reader antenna, the second reader antenna, and the third reader antenna, and obtain three projected distances x1, x2, and x3 respectively as follows: Step Q: For x1, x2, and x3 obtained in Step P, use the trilateration algorithm to obtain the two-dimensional coordinates (x, y) of the surface acoustic wave tag; combine with the coordinate z obtained in Step O to obtain the three-dimensional coordinates (x, y, z) of the surface acoustic wave tag, realizing the three-dimensional positioning of the surface acoustic wave tag; further combine with the surface acoustic wave tag coding value n' obtained in Step L to complete the three-dimensional positioning and identification of the surface acoustic wave tag.

3. The positioning and identification method of the three-dimensional positioning and identification system using surface acoustic wave tags according to claim 2, characterized in that: Step A is specifically divided into the following steps: Step a: According to the center frequency difference Δf = f2 - f1 of the two propagation channels of the surface acoustic wave tag, calculate the non-phase-ambiguity ranging length when using the phase difference information of the echo pulse signal for ranging, so as to divide the ranging range that the system can reach into x sub-regions without phase ambiguity problems. The integer part of the phase difference ranging for each sub-region from near to far is 0, 1,..., (x - 1), and y calibration points are equally spaced within each sub-region, and the first reader antenna is selected for calibration; Step b: Place the surface acoustic wave tag with a coding value of 1 at the first calibration point in the first sub-region; Step c: According to the same steps as steps B, C, D, E, and F in claim 2, the signal processing module obtains the intensity value S of this calibration point c11 , phase value Then, according to the same steps as step I in claim 2, the phase value of this calibration point is obtained Step d: When the SAW tag with a coding value of 1 is placed at the first calibration point in the first sub-region, the phase difference of the echo pulse signal and record the calibration result at this calibration point Step e: Place the surface acoustic wave tags with a coding value of 1 at the 2nd, …, yth calibration points in the 1st sub-region, and further place them at the calibration points in the 2nd, 3rd, …, (x - 1)th, and xth sub-regions respectively. Follow the same steps as in step c until the phase differences of the echo pulse signals at the calibration points in the xth sub-region are obtained. Record the calibration results at all calibration points. Obtain the fitting curve between the phase difference and the intensity of the echo pulse signal of the surface acoustic wave tag with a coding value of 1 by means of curve fitting. Step f: Sequentially place the surface acoustic wave tags with coding values of 2, 3,..., (n - 1), and n at the respective calibration points in each sub-region. According to the same steps as in Step e, finally obtain the fitting curve between the phase difference and intensity of the echo pulse signals of all coded surface acoustic wave tags.

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