An electromagnetic tag ranging system and method based on phase-coded metasurface

Abstract

The application discloses an electromagnetic tag ranging system and method based on a phase coding intelligent metasurface, which comprises a phase coding intelligent metasurface composed of a receiving array, a rectifier circuit and a reflecting array, and an FPGA control module; the receiving array is used for receiving radio frequency signals emitted by a transmitting end, and the radio frequency signals are transmitted to the rectifier circuit after being synthesized; the rectifier circuit outputs corresponding direct current voltage according to the power of the input radio frequency signals; a load phase shifter containing a PIN diode is loaded on the bottom layer of each reflecting unit in the reflecting array, and two discrete phase states of the reflecting unit are generated by controlling the on-off state of the PIN diode; the FPGA control module controls the on-off state and the change frequency of the PIN diode of each reflecting unit according to the size of the direct current voltage, and the receiving end determines the distance between the transmitting end and the electromagnetic tag according to the reflected echo frequency. The application has the characteristics of high noise resistance, ranging capability and integration, and has a wide range of application scenarios.

Description

Technical Field

[0001] This invention relates to the fields of wireless identification and electromagnetic sensing technology, and in particular to an electromagnetic tag ranging system and method based on a phase-coded smart metasurface. Background Technology

[0002] In the context of the intelligent trend of deep integration of sensing, communication, and control technologies, traditional identification technologies such as barcodes and QR codes are no longer sufficient to meet the performance and adaptability requirements of complex application environments due to limitations in recognition distance, susceptibility to dirt, and inability to penetrate obstacles. Against this backdrop, electromagnetic tags have emerged as a new wireless identification technology. Based on electromagnetic metasurface design, these tags encode target information into their electromagnetic response by performing feature modulation on incident electromagnetic waves. Electromagnetic tags require no chip or power supply, offering significant advantages such as low cost, high durability, and concealable integration, making them particularly suitable for identification and sensing applications on metal surfaces and in complex electromagnetic environments.

[0003] Currently, electromagnetic tags have demonstrated broad application potential in the fields of identification and sensing. Reference 1 (X. Wang, MS Tong and L. Zhao, "Pseudorandom Noise Sequence Time-Modulated Reflective Metasurfaces for Target Recognition," in...) IEEE Transactions on Microwave Theory and Techniques Reference 2 (P. Lopez-Iturri) proposes a target recognition method based on a time-modulated reflective metasurface of pseudo-random noise sequence. By covering the target to be identified with a metasurface, the metasurface scatters the interrogative harmonics into a binary pseudo-random noise modulated wave. Therefore, a radar detector with predictable modulation pseudo-random noise sequence can identify the target by performing cross-correlation operations on the modulation PN sequence, utilizing the strong autocorrelation and weak cross-correlation characteristics of the pseudo-random noise sequence. et al ., "Implementation of a Low-Cost Chipless RFID System With Paper-Based Substrates Printed Tags for Traceability Applications in the Packaging Sector," in IEEE Sensors Journal(Vol. 23, no. 13, pp. 14923-14937, 1 July 1, 2023.) proposes a low-power, chipless RFID system based on frequency response. This system uses conductive ink to print two-dimensional geometric patterns resembling transmissive or reflective surfaces on a paper substrate, and combines this with a portable, low-cost reader to construct a tag system that can be embedded in cardboard materials for traceability applications in the packaging industry. Reference 3 (S. Rodini, S. Genovesi, G. Manara and F. Costa, "Wireless mm-Wave Chipless Pressure Sensor," in...) IEEE Transactions on Microwave Theory and Techniques (Vol. 72, no. 7, pp. 4163-4173, July 2024.) This paper further expands the application of electromagnetic tags in the field of sensing, proposing a millimeter-wave passive wireless pressure sensor operating in the Ka-band. The sensor consists of a tag formed by frequency-selective surface printing on a dielectric support substrate, encapsulated with a dielectric capping layer. Applying pressure causes deformation of the grounding layer, which in turn induces a change in the effective dielectric constant of the dielectric layer, shifting the resonant peak and thus enabling wireless sensing of the pressure value.

[0004] Despite the significant progress made in the field of electromagnetic tag identification and sensing, the following limitations still exist:

[0005] (1) Insufficient resistance to environmental interference: Existing solutions mostly rely on a single dimension such as amplitude, frequency or time domain correlation for information encoding and extraction. For example, although the correlation detection based on pseudo-random noise sequence in Reference 1 has a certain anti-interference capability, it has strict requirements for system synchronization and prior information, and is prone to bit errors or missed detections in complex electromagnetic environments or dynamic multi-target scenarios; References 2 and 3 mainly utilize frequency characteristics (such as resonance peaks and frequency response coding), which are easily affected by multipath effects, background noise and changes in the dielectric properties of materials, resulting in a decrease in measurement stability and reliability.

[0006] (2) Lack of ranging function or limited accuracy: The above technologies mainly focus on target recognition or single physical quantity sensing, lacking the ability to perceive target distance with high precision. For example, Reference 1 only achieves target recognition and does not involve distance measurement; Reference 3 can sense pressure, but cannot simultaneously obtain the relative position information between the tag and the reader. In practical applications, distance information is often a key parameter for environmental perception and target localization, and existing methods are difficult to meet this requirement.

[0007] (3) Low system integration and loose structure: Existing electromagnetic tag systems usually adopt an architecture that separates the tag and the reader. The modules rely on external interconnection and signal transmission, which not only increases the system size and complexity, but also introduces additional transmission loss and error. For example, although Reference 2 designed a portable reader, the tag and the reader still need to be arranged independently; the sensor and the reading device in Reference 3 are also arranged separately, without physical integration, which limits its applicability in scenarios with limited space or high concealment requirements.

[0008] In summary, existing technologies still have significant shortcomings in terms of noise resistance, ranging capability, and system integration, making it difficult to meet the demands for high-precision, high-reliability, and compact wireless sensing in complex environments. Summary of the Invention

[0009] The purpose of this invention is to provide an electromagnetic tag ranging system and method based on a phase-encoded smart metasurface, which combines high noise immunity, ranging capability, and integration features.

[0010] The technical solution for achieving the objective of this invention is: an electromagnetic tag ranging system based on a phase-coded smart metasurface, comprising a phase-coded smart metasurface consisting of a receiving array, a rectifier circuit, and a reflective array, and an FPGA control module, wherein:

[0011] The receiving array is composed of several receiving units arranged together to receive radio frequency signals emitted by the transmitting end, and to synthesize the received radio frequency signals and transmit them to the rectifier circuit.

[0012] The rectifier circuit is used to convert the received radio frequency signal into a DC signal and output a corresponding DC voltage according to the power of the input radio frequency signal.

[0013] The reflective array includes multiple reflective units. Each reflective unit has a load phase shifter containing PIN diodes at its bottom layer. By controlling the on and off of the PIN diodes, the reflective unit can generate two discrete phase states, and the two phase states are 180° apart.

[0014] The FPGA control module is connected to the rectifier circuit and the reflector array. It is used to control the on / off state and frequency of the PIN diodes of each reflector unit according to the magnitude of the DC voltage output by the rectifier circuit, so that the frequency of the reflected echo changes. The receiver determines the distance between the transmitter and the electromagnetic tag based on the frequency of the received reflected echo.

[0015] An electromagnetic tag ranging method based on a phase-encoded smart metasurface is disclosed. This method is based on the aforementioned electromagnetic tag ranging system using a phase-encoded smart metasurface, and the specific steps of the method are as follows:

[0016] Step 1: Pre-store the encoded file in the FPGA control module;

[0017] Step 2: The transmitter sends out a signal, the receiving array receives the signal and synthesizes it before transmitting it to the rectifier circuit. The rectifier circuit outputs the corresponding DC voltage to the FPGA control module according to the power of the input signal.

[0018] Step 3: The FPGA control module retrieves the corresponding encoding file based on the input DC voltage and outputs the corresponding voltage change signal through the digital I / O port;

[0019] Step 4: The voltage change signal output from the digital I / O port controls the on / off state and state change frequency of the PIN diodes in each reflective unit of the reflective array through the power supply network, thereby changing the frequency of the reflected echo; the receiving end determines the distance between the transmitting end and the electromagnetic tag based on the received reflected echo frequency.

[0020] Compared with the prior art, the significant advantages of this invention are:

[0021] (1) High noise resistance: Based on the phase-frequency conversion ranging mechanism, the distance information of the target is encoded into the phase change of the reflected echo by dynamically adjusting the scattering phase state (0° / 180°) of the metasurface unit, thereby realizing the conversion of energy information to spectrum information; This mechanism maps the distance to be measured to the frequency dimension, and utilizes the strong anti-interference characteristics of frequency signals in complex electromagnetic environments to effectively avoid the influence of environmental noise, multipath fading and other factors on the measurement accuracy, and significantly improves the reliability and environmental adaptability of the system;

[0022] (2) High-precision distance sensing capability: Based on the recognition function, the ranging function is further integrated; by dynamically adjusting the phase encoding frequency of the reflection unit according to the received signal power (DC voltage) through the FPGA module, the distance information is converted into the frequency change of the reflected echo, realizing wireless and passive sensing of distance information; This design breaks through the limitation of existing technologies that can only identify or sense a single parameter, and provides a brand-new solution for target positioning and ranging in complex environments.

[0023] (3) Highly integrated design: The receiving array, reflecting array, rectifier circuit and FPGA control module are highly integrated on the same physical platform. The receiving array is embedded in the center of the reflecting array, and the power supply network bypasses the central area and is connected to the pin header, realizing the integrated design at the physical level. This integrated architecture not only makes the system structure compact and significantly reduces the size, but also reduces the additional losses and errors introduced by the interconnection between modules and signal transmission, and improves the overall efficiency and stability of the system. It is especially suitable for application scenarios with limited space and high concealment requirements. Attached Figure Description

[0024] Figure 1 This is an application scenario diagram of the electromagnetic tag ranging system based on phase-encoded smart metasurface of this invention.

[0025] Figure 2a This is a schematic diagram of the medium structure of the receiving unit.

[0026] Figure 2b This is a schematic diagram of the dipole metal patch of the receiving unit.

[0027] Figure 2c This is a schematic diagram of the Wilkinson power divider at the lower layer of the receiver array.

[0028] Figure 3a This is a simulation result of the transmission coefficient of the TE wave incident on the upper layer of the receiving unit.

[0029] Figure 3b This is a simulation result of the reflection coefficient of the TE wave incident on the upper layer of the receiving unit.

[0030] Figure 3c This is a simulation result of the transmission coefficient of the TM wave incident on the upper layer of the receiving unit.

[0031] Figure 3d This is a simulation result of the reflection coefficient of the TM wave incident on the upper layer of the receiving unit.

[0032] Figure 4a This is a simulation curve of the reflection coefficient of the Wilkinson power divider in the lower layer of the receiver array.

[0033] Figure 4b This is a simulation curve of the isolation of the Wilkinson power divider in the lower layer of the receiver array.

[0034] Figure 5 This is a schematic diagram of the rectifier circuit.

[0035] Figure 6a This is a simulation curve of the output voltage of the rectifier circuit changing with the input power.

[0036] Figure 6b This is a simulation curve showing the rectifier efficiency of the rectifier circuit as a function of input power.

[0037] Figure 7 It is a graph showing the relationship between the distance between the transmitter and the electromagnetic tag and the DC voltage output by the rectifier circuit.

[0038] Figure 8a This is a schematic diagram of the dielectric structure of the reflective unit.

[0039] Figure 8b This is a schematic diagram of the load phase shifter for the first type of feeding layout in a reflective array.

[0040] Figure 8cThis is a schematic diagram of the load phase shifter in the second type of feeding layout of the reflective array.

[0041] Figure 8d This is a schematic diagram of the load phase shifter in the third type of feeding layout in the reflective array.

[0042] Figure 9a This is a phase curve of the reflection coefficient of the reflective element when the PIN diode is on and off.

[0043] Figure 9b This is a graph showing the amplitude of the reflection coefficient of the reflective element when the PIN diode is on and off.

[0044] Figure 10 This is a schematic diagram of the overall structure of the phase-encoded smart metasurface array. Detailed Implementation

[0045] To more clearly illustrate the objectives, technical solutions, and advantages of this invention, the following detailed description will be provided in conjunction with the accompanying drawings and embodiments. It is readily understood that, based on the technical solutions of this invention, those skilled in the art can conceive of various embodiments of the invention without altering its essential spirit. Therefore, the following specific embodiments and accompanying drawings are merely illustrative examples of the technical solutions of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solutions of this invention.

[0046] This invention provides an electromagnetic tag ranging system based on a phase-coded smart metasurface, comprising a phase-coded smart metasurface consisting of a receiving array, a rectifier circuit, and a reflective array, and an FPGA control module, wherein:

[0047] The receiving array is composed of several receiving units arranged together to receive radio frequency signals emitted by the transmitting end, and to synthesize the received radio frequency signals and transmit them to the rectifier circuit.

[0048] The rectifier circuit is used to convert the received radio frequency signal into a DC signal and output a corresponding DC voltage according to the power of the input radio frequency signal.

[0049] The reflective array includes multiple reflective units. Each reflective unit has a load phase shifter containing PIN diodes at its bottom layer. By controlling the on and off of the PIN diodes, the reflective unit can generate two discrete phase states, and the two phase states are 180° apart.

[0050] The FPGA control module is connected to the rectifier circuit and the reflector array. It is used to control the on / off state and frequency of the PIN diodes of each reflector unit according to the magnitude of the DC voltage output by the rectifier circuit, so that the frequency of the reflected echo changes. The receiver determines the distance between the transmitter and the electromagnetic tag based on the frequency of the received reflected echo.

[0051] As a specific example, the reflective array is An array of reflective units, , All are positive integers, and the receiving array is embedded in the central region of the reflecting array; for example, the receiving array is composed of Composed of basic unit arrangements, it exhibits angular stability and dual-polarization characteristics in the 9.5-10.5 GHz range; the reflective array consists of... The array is composed of a series of reflective units arranged in a way that the central region of the reflective array is hollowed out to embed the receiving array.

[0052] The phase-encoded smart metasurface also includes a power feed pin header, with the rectifier circuit and the power feed pin header arranged on both sides of the reflective array. The power feed pin header controls the power feed interface of each column of reflective units through multiple power feed lines. The multiple power feed lines form a power feed network for the reflective array. The power feed network bypasses the receiving array on one hand and the connection line between the receiving array and the rectifier circuit on the other hand.

[0053] As a specific example, each receiving unit of the receiving array has a multi-layer dielectric structure, comprising, from top to bottom:

[0054] The first cover layer serves as a wide-angle impedance matching layer to broaden the bandwidth;

[0055] The second substrate layer has multiple mutually orthogonal dipole metal patches on the top. Below the intersection area of ​​four adjacent dipole metal patches, there are conductive vias and a circular metal plate with short-circuit vias. The circular metal plate and the conductive via structure are configured to introduce additional capacitance between the four adjacent dipole metal patches to enhance the capacitive coupling between dipole elements and suppress common-mode resonance caused by structural asymmetry or unbalanced power supply.

[0056] The third support layer has a grounding metal printed on its bottom;

[0057] The fourth circuit board layer, due to the limitation of unit size, has a miniaturized Wilkinson power divider made of bent microstrip lines at its bottom, which is used to combine the multiple radio frequency signals collected by the receiving unit in phase and impedance match them before transmitting them to the rectifier circuit.

[0058] As a specific example, the upper structure of the reflecting unit is the same as that of the receiving unit, except that the bottom layer is loaded with a load phase shifter containing PIN diodes. By switching the on and off states of the PIN diodes, each reflecting unit can achieve two scattering states: 0° and 180° phase, respectively, and has electrically adjustable scattering state characteristics. The load phase shifter is also connected to a feed line, on which a fan-shaped patch is provided as a quarter-wavelength microstrip line to isolate AC signals and conduct DC signals.

[0059] As a specific example, the rectifier circuit adopts a parallel topology, the matching structure uses a simple parallel stub to avoid additional losses, and uses Schottky diodes to realize the conversion of radio frequency signals to DC signals. It can maintain high rectification efficiency over a wide range of input power and output a corresponding DC voltage according to the power of the input radio frequency signal.

[0060] As a specific example, the FPGA control module includes digital I / O ports, and the module is equipped with symbol frequencies and encoding files for each feeder line under different input voltages;

[0061] The encoded file stores the encoded values ​​corresponding to the digital I / O ports. The digital I / O ports will output different voltages according to the encoded values; when the encoding is 1, the digital I / O port outputs a high level; when the encoding is 0, the digital I / O port outputs a low level.

[0062] The digital I / O port is connected to the power supply network of the reflective array. The FPGA control module retrieves the corresponding encoding file according to the magnitude of the input DC voltage and outputs a high or low level to the power supply network of the reflective array through the digital I / O port to control the on / off state and frequency of the PIN diode.

[0063] As a specific example, the reflective array is composed of The receiving array consists of an arrangement of reflective units and is composed of... The receiver unit is arranged in a row; there are 2 power supply pins, each power supply pin controls 12 power supply lines, and each power supply line controls the power supply interface of a row of reflective units.

[0064] The receiving unit and the reflecting unit both use F4B dielectric material, with a dielectric constant of 2.2 and a dielectric loss tangent of 0.003. The thickness of the first cover layer of the receiving unit is 3.5 mm, the thickness of the second substrate layer is 0.254 mm, the thickness of the third support layer is 2.9 mm, and the thickness of the fourth circuit board layer is 0.1 mm.

[0065] The miniaturized Wilkinson power divider at the bottom of the fourth circuit board layer performs in-phase synthesis and impedance matching of the eight radio frequency signals collected by the four receiving units in the receiving array.

[0066] This invention also provides an electromagnetic tag ranging method based on a phase-encoded smart metasurface. This method is based on the aforementioned electromagnetic tag ranging system using a phase-encoded smart metasurface, and the specific steps of the method are as follows:

[0067] Step 1: Pre-store the encoded file in the FPGA control module;

[0068] Step 2: The transmitter sends out a signal, the receiving array receives the signal and synthesizes it before transmitting it to the rectifier circuit. The rectifier circuit outputs the corresponding DC voltage to the FPGA control module according to the power of the input signal.

[0069] Step 3: The FPGA control module retrieves the corresponding encoding file based on the input DC voltage and outputs the corresponding voltage change signal through the digital I / O port;

[0070] Step 4: The voltage change signal output from the digital I / O port controls the on / off state and state change frequency of the PIN diodes in each reflective unit of the reflective array through the power supply network, thereby changing the frequency of the reflected echo; the receiving end determines the distance between the transmitting end and the electromagnetic tag based on the received reflected echo frequency.

[0071] As a specific example, in step 1, the host computer pre-sets the encoding file and symbol frequency in the FPGA control module through the I / O port. The encoding file contains 24 channel codes.

[0072] As a specific example, in step 2, the signal transmission link consists of three stages: transmission, propagation, and reception. When the signal emitted by the transmitter propagates in free space, it is affected by free space loss, causing the signal strength to decrease with increasing distance. The relationship between the power of the radio frequency signal input to the receiver and the distance between the transmitter and the electromagnetic tag is calculated using the Friis formula and transmission loss.

[0073] The relationship between the power of the radio frequency signal input to the receiver and the distance between the transmitter and the electromagnetic tag satisfies the following formula:

[0074] (1)

[0075] in The power of the radio frequency signal input to the receiving end. The power of the radio frequency signal output by the transmitter. For transmitter gain, For receiver gain, Indicates the operating frequency. This indicates the distance between the transmitter and receiver;

[0076] During the transmission of radio frequency (RF) signals to the rectifier circuit, there are two stages of transmission loss. The power of the RF signal input to the rectifier circuit... The power of the radio frequency signal input at the receiving end The following conditions must be met:

[0077] (2)

[0078] in This represents the loss of the radio frequency signal during transmission from the upper-layer receiver array to the lower-layer Wilkinson power divider. This represents the loss during the transmission of the synthesized signal from the lower-level Wilkinson power divider to the rectifier circuit.

[0079] The relationship between the distance between the transmitter and receiver and the power input to the rectifier circuit is calculated based on equations (1) and (2).

[0080] During operation, rectifier circuits inevitably experience various forms of energy loss. These losses primarily stem from the non-ideal characteristics of semiconductor devices and the parasitic parameters of passive components. To mitigate their impact, it is necessary to optimize the circuit structure and achieve efficient conversion between AC and DC signals.

[0081] Rectification efficiency of rectifier circuit Defined as:

[0082] (3)

[0083] in This refers to the internal losses of the diode. This represents the DC power output to the load. Represented as:

[0084] (4)

[0085] in Represents the output voltage. This represents the circuit load. Because the junction resistance and junction capacitance of a Schottky diode change with the input power, its input impedance exhibits nonlinearity in the dynamic range. For different input powers, the conversion efficiency of the rectifier circuit will change accordingly, thereby outputting a DC signal that matches the input power.

[0086] The correspondence between the distance between the transmitter and receiver and the DC voltage output by the rectifier circuit is established by equations (1) to (4).

[0087] As a specific example, in step 3, the encoding file stores the encoded values ​​of each digital I / O port. Under different input DC voltage conditions, the FPGA will read the corresponding encoding configuration file. When the encoded value is read as 1, the digital I / O port outputs a high level; when the encoded value is read as 0, the digital I / O port outputs a low level. In summary, the FPGA control module reads the corresponding encoding file according to the magnitude of the input DC voltage and outputs the corresponding high and low level voltages for each digital I / O port.

[0088] As a specific example, step 4 involves controlling the on / off state and state change frequency of the PIN diodes in each reflective element of the reflective array via a power supply network, thereby changing the frequency of the reflected echo. The receiving end determines the distance between the transmitting end and the electromagnetic tag based on the received reflected echo frequency, as detailed below:

[0089] Assume the phase-coded smart metasurface lies in the xoy plane, with the x-axis horizontal, the y-axis vertical, and the z-axis the normal direction of the metasurface's array plane; the phase-coded smart metasurface in Direction divided Column of reflective elements, the spacing between reflective elements is Each column of reflective units is along Expanding directions, in They have the same response in the same direction; a center frequency is signal Irradiation onto the phase-encoded smart metasurface Represents the range, Representing a moment, Represents the imaginary unit;

[0090] By controlling the on / off state of the PIN diodes in the reflective unit, phase modulation is generated in the reflective array, and the modulation frequency is set to... Assuming far below The reflected echo signal after phase modulation The expression is:

[0091] (5)

[0092] in, Represents wave number, and ; Indicates the incident angle at the transmitting end, the first Reflection coefficient of a column of reflective units For the period is The time-varying function is expressed as:

[0093] (6)

[0094] Within a modulation period, the phase Switching between two discrete states, with values ​​{0°, 180°}, i.e.:

[0095] (7)

[0096] in It is an integer. The duration of the 0° phase within one period;

[0097] Performing a Fourier series expansion on equation (5), the reflected echo signal contains frequencies of... The harmonic components are detected by the receiver by detecting the main frequency offset of the reflected echo. By combining the pre-calibrated mapping relationship between DC voltage and distance, the distance between the transmitter and the electromagnetic tag can be deduced.

[0098] According to the analysis of equation (5), when the signal is incident on the metasurface array at an oblique angle, its reflection amplitude will introduce a phase factor compared to the normal observation. This leads to a decrease in array reflection performance, specifically manifested as attenuation of the target harmonic amplitude. To address this issue, a corresponding delay compensation mechanism can be introduced between different modulation units to correct the aforementioned phase deviation.

[0099] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0100] Example

[0101] Combination Figure 1 This embodiment provides an application scenario and component modules of an electromagnetic tag ranging system. The electromagnetic tag ranging system includes a receiving array, a rectifier circuit, a reflective array, and an FPGA control module. The receiving array outputs the array signal through a Wilkinson power divider; the wide-power rectifier circuit converts the radio frequency signal into a DC signal for transmission to the FPGA; the phase-encoded reflective unit loads a phase shifter containing PIN diodes, and by controlling the on / off state of the PIN diodes, the reflected echo can generate two phase states; the FPGA controls the on / off state of the PIN diodes according to the DC signal, realizing real-time changes in the metasurface scattering state and altering the frequency of the reflected wave.

[0102] In practical applications, when the distance between the signal transmitter and the ranging tag changes, the power of the received signal changes accordingly. After signal processing, the signal receiver will detect the change in the frequency of the reflected wave. This achieves the goal of converting distance information into reflected echo frequency information, effectively avoiding interference from environmental noise caused by multipath effects, for example... Figure 1 The image shows reflected waves from the wall.

[0103] Combination Figure 2a This embodiment provides a receiving unit with an operating frequency of 9.5-10.5 GHz and a unit period of 7.58 mm. The receiving unit comprises four dielectric layers from top to bottom, all using F4B dielectric material with a dielectric constant of 2.2 and a dielectric loss tangent of 0.003.

[0104] The first layer is a capping layer, 3.5 mm thick, which serves as a wide-angle impedance matching layer to broaden the bandwidth; the second layer is a substrate layer, 0.254 mm thick. Figure 2bThe top of the structure features horizontal and vertical dipole patches that intersect. At its bottom, a circular metal plate is printed to provide the necessary capacitive coupling for broadband operation. Load vias are implemented below the cross-sections of the four adjacent dipole elements, via circular metal plates with short-circuit vias. This structure enhances the capacitive coupling between the dipole elements while addressing common-mode resonance. The third layer is a support layer, 2.9 mm thick, with a ground metal plate printed at the bottom. The fourth layer is a circuit board layer, 0.1 mm thick. Figure 2c A three-stage Wilkinson circuit with a bent structure at the bottom is presented to synthesize 8 signals.

[0105] Simulate the receiving unit and the power divider separately. Figures 3a-3d The reflection and transmission coefficients of the receiving unit under periodic boundary conditions are given for incident dual-polarized plane waves at different angles. Figure 3a , Figure 3b The demonstration shows that when the incident angle is 0°~50°, the TE reflectance is less than 15 dB and the TE transmittance is greater than 0.3 dB. Figure 3c , Figure 3d The results show that when the incident angle is 0° to 50°, the TM reflection coefficient is less than 20 dB and the TM transmission coefficient is greater than 0.2 dB.

[0106] Figure 4a , Figure 4b The results show that the power divider has a reflection coefficient of less than 12 dB and a port isolation of less than 18 dB in the 9.5–10.5 GHz frequency band. By integrating these two components, a compact, highly integrated, low-loss, and wide-angle receiving dual-polarized receiver array module is realized.

[0107] The rectifier circuit is the core component that converts captured radio frequency energy into DC energy. Considering that in real-world scenarios, the receiver signal power dynamically varies with distance, environment, and other factors, and is often in a low power range (e.g., microwatts to milliwatts), combined with... Figure 5 This embodiment provides a wide-power rectifier circuit with low input power. Its design goal is not to achieve maximum efficiency at a specific input power point, but rather to achieve high rectification efficiency within a target power bandwidth. A parallel rectifier topology is employed, using a Schottky diode MA4E1317 suitable for the X-band. A simple parallel stub matching structure is chosen to avoid additional losses. A 100 pF capacitor is added at the front end of the circuit to isolate DC current, and a 3 KOhm resistor is added at the rear end as a load to maximize rectification efficiency.

[0108] The simulation results of the rectifier circuit are as follows: Figure 6a , Figure 6bAs shown, within a center frequency of 10 GHz and an input power dynamic range of -3 dBm to 10 dBm, the rectifier circuit achieves an output voltage of over 1 V and a rectification efficiency of over 40%. The output voltage reaches its maximum value of 3.91 V when the input power is 10 dBm. The rectification efficiency reaches its maximum value of 51.26% when the input power is 9 dBm.

[0109] For the entire receiving system, a 10 GHz signal is analyzed as an example. The theoretical propagation loss in free space is calculated using the Friis transmission formula. Then, the actual RF power at the rectifier circuit input port is obtained by subtracting the transmission losses introduced by the upper-layer receiving array and the lower-layer Wilkinson power divider from the obtained input power. According to... Figure 6a The curve showing the relationship between the rectifier circuit output voltage and input power converts the input power into a corresponding DC output voltage. This ultimately yields the relationship between the distance between the transmitter and the electromagnetic tag and the rectifier circuit output DC voltage, as shown below. Figure 7 As shown.

[0110] Combination Figures 8a-8d This embodiment provides the design of a 1-bit phase-coded reflective array unit. The selected diode is MADP-000907-14020 (when on, it is a resistor and inductor in series, with a resistance of 7.8 Ohms and an inductance of 25 pH; when off, it is a capacitor and inductor in series, with a capacitance of 0.025 pF and an inductance of 25 pH). By controlling the on / off state of the PIN diode in the control unit, it can generate two discrete phase responses to the incident wave, thereby achieving digital control of the reflected wave phase. A quarter-wavelength microstrip line is used to prevent RF energy leakage into the control network.

[0111] Because the power supply network needs to bypass the central receiving array, there are three layouts for the feed lines at the bottom of the reflector unit to bypass the circuitry connecting the power divider and the rectifier circuit. Figure 8b , Figure 8c , Figure 8d Three arrangements were shown.

[0112] Figure 9a , Figure 9b The reflection of a 1-bit reflection unit in two states is presented, with the phase difference remaining stable within 180°±20°, and the reflection amplitude loss in both states being less than 1.5 dB. This unit achieves switchable unit performance with low loss and high phase contrast.

[0113] Combination Figure 10 Phase-encoded smart metasurface arrays are composed of Reflective unit array, The system consists of a receiver array, a rectifier circuit, and two feed headers. Each header controls 12 feed lines, and each feed line controls one row of reflector units. The receiver array is placed in the center of the reflector array, with the rectifier circuit and feed headers placed on either side. The Wilkinson power divider of the receiver array is connected to the rectifier circuit outside the array, and the feed network is connected to the headers on the other side. Because the feed network needs to bypass the central receiver array, there are three different layouts for the feed lines at the bottom of the reflector units, with the corresponding units located at different positions in the array.

[0114] This invention achieves the goal of converting distance information into reflected echo frequency information, effectively avoiding interference from multipath effects and broadening the application scenarios of phase-coded metasurfaces.

[0115] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. An electromagnetic tag ranging system based on a phase-encoded smart metasurface, characterized in that, It includes a phase-coded smart metasurface consisting of a receiving array, a rectifier circuit, and a reflector array, as well as an FPGA control module, wherein: The receiving array is composed of several receiving units arranged together to receive radio frequency signals emitted by the transmitting end, and to synthesize the received radio frequency signals and transmit them to the rectifier circuit. The rectifier circuit is used to convert the received radio frequency signal into a DC signal and output a corresponding DC voltage according to the power of the input radio frequency signal. The reflective array includes multiple reflective units. Each reflective unit has a load phase shifter containing PIN diodes at its bottom layer. By controlling the on and off of the PIN diodes, the reflective unit can generate two discrete phase states, and the two phase states are 180° apart. The FPGA control module is connected to the rectifier circuit and the reflector array. It is used to control the on / off state and frequency of the PIN diodes of each reflector unit according to the magnitude of the DC voltage output by the rectifier circuit, so that the frequency of the reflected echo changes. The receiver determines the distance between the transmitter and the electromagnetic tag based on the frequency of the received reflected echo. The reflective array is An array of reflective units, , All are positive integers, and the receiving array is embedded in the central region of the reflecting array; The phase-encoded smart metasurface also includes a power feed pin header, with the rectifier circuit and the power feed pin header arranged on both sides of the reflective array. The power feed pin header controls the power feed interface of each column of reflective units through multiple power feed lines. The multiple power feed lines form a power feed network for the reflective array. The power feed network bypasses the receiving array on one hand and the connection line between the receiving array and the rectifier circuit on the other hand. The FPGA control module includes digital I / O ports, and the module contains symbol frequencies and encoding files for each feeder line under different input voltages. The encoded file stores the encoded values ​​corresponding to the digital I / O ports. The digital I / O ports will output different voltages according to the encoded values; when the encoding is 1, the digital I / O port outputs a high level; when the encoding is 0, the digital I / O port outputs a low level. The digital I / O port is connected to the power supply network of the reflective array. The FPGA control module retrieves the corresponding encoding file according to the magnitude of the input DC voltage and outputs a high or low level to the power supply network of the reflective array through the digital I / O port to control the on / off state and frequency of the PIN diode.

2. The electromagnetic tag ranging system based on a phase-encoded intelligent metasurface according to claim 1, characterized in that, Each receiving unit of the receiving array has a multi-layer dielectric structure, comprising, from top to bottom: The first cover layer serves as a wide-angle impedance matching layer to broaden the bandwidth; The second substrate layer has multiple mutually orthogonal dipole metal patches on the top. Below the intersection area of ​​four adjacent dipole metal patches, there are conductive vias and a circular metal plate with short-circuit vias. The circular metal plate and the conductive via structure are configured to introduce additional capacitance between the four adjacent dipole metal patches to enhance the capacitive coupling between dipole elements and suppress common-mode resonance caused by structural asymmetry or unbalanced power supply. The third support layer has a grounding metal printed on its bottom; The fourth circuit board layer has a miniaturized Wilkinson power divider made of bent microstrip lines at its bottom, which is used to combine the multiple radio frequency signals collected by the receiving unit in phase and impedance match them before transmitting them to the rectifier circuit.

3. The electromagnetic tag ranging system based on a phase-encoded intelligent metasurface according to claim 2, characterized in that, The upper structure of the reflecting unit is the same as that of the receiving unit. The bottom layer is loaded with a load phase shifter containing PIN diodes. By switching the on and off states of the PIN diodes, each reflecting unit can achieve two scattering states: 0° and 180° phase. The load phase shifter is also connected to a feed line. The feed line is equipped with a fan-shaped patch as a quarter-wavelength microstrip line, which is used to isolate AC signals and conduct DC signals.

4. The electromagnetic tag ranging system based on a phase-encoded smart metasurface according to claim 3, characterized in that, The rectifier circuit adopts a parallel topology, the matching structure uses parallel short stubs, and Schottky diodes are used to convert radio frequency signals to DC signals.

5. The electromagnetic tag ranging system based on a phase-encoded intelligent metasurface according to claim 4, characterized in that, The reflective array is composed of The receiving array consists of an arrangement of reflective units and is composed of... The receiving units are arranged in an array; there are two power supply pins, each power supply pin controls 12 power supply lines, and each power supply line controls the power supply interface of a column of reflective units. The receiving unit and the reflecting unit both use F4B dielectric material, with a dielectric constant of 2.2 and a dielectric loss tangent of 0.

003. The thickness of the first cover layer of the receiving unit is 3.5 mm, the thickness of the second substrate layer is 0.254 mm, the thickness of the third support layer is 2.9 mm, and the thickness of the fourth circuit board layer is 0.1 mm. The miniaturized Wilkinson power divider at the bottom of the fourth circuit board layer performs in-phase synthesis and impedance matching of the eight radio frequency signals collected by the four receiving units in the receiving array.

6. A ranging method based on phase-encoded smart metasurfaces using electromagnetic tags, characterized in that, This method is based on the electromagnetic tag ranging system based on phase-encoded smart metasurfaces as described in any one of claims 1 to 5, and the specific steps of the method are as follows: Step 1: Pre-store the encoded file in the FPGA control module; Step 2: The transmitter sends out a signal, the receiving array receives the signal and synthesizes it before transmitting it to the rectifier circuit. The rectifier circuit outputs the corresponding DC voltage to the FPGA control module according to the power of the input signal. Step 3: The FPGA control module retrieves the corresponding encoding file based on the input DC voltage and outputs the corresponding voltage change signal through the digital I / O port; Step 4: The voltage change signal output from the digital I / O port controls the on / off state and state change frequency of the PIN diodes in each reflective unit of the reflective array through the power supply network, thereby changing the frequency of the reflected echo; the receiving end determines the distance between the transmitting end and the electromagnetic tag based on the received reflected echo frequency.

7. The electromagnetic tag ranging method based on phase-encoded smart metasurfaces according to claim 6, characterized in that, In step 2, the relationship between the power of the radio frequency signal input to the receiver and the distance between the transmitter and the electromagnetic tag satisfies the following formula: （1） in The power of the radio frequency signal input to the receiving end. The power of the radio frequency signal output by the transmitter. For transmitter gain, For receiver gain, Indicates the operating frequency. This indicates the distance between the transmitter and receiver; During the transmission of radio frequency (RF) signals to the rectifier circuit, there are two stages of transmission loss. The power of the RF signal input to the rectifier circuit... The power of the radio frequency signal input at the receiving end The following conditions must be met: （2） in This represents the loss of the radio frequency signal during transmission from the upper-layer receiver array to the lower-layer Wilkinson power divider. This represents the loss during the transmission of the synthesized signal from the lower-level Wilkinson power divider to the rectifier circuit. Rectification efficiency of rectifier circuit Defined as: （3） in This refers to the internal losses of the diode. This represents the DC power output to the load. Represented as: （4） in Represents the output voltage. Represents circuit load; The correspondence between the distance between the transmitter and receiver and the DC voltage output by the rectifier circuit is established by equations (1) to (4).

8. The electromagnetic tag ranging method based on phase-encoded smart metasurfaces according to claim 7, characterized in that, Step 4 describes controlling the on / off state and state change frequency of the PIN diodes in each reflective element of the reflective array via the feed network, thereby changing the frequency of the reflected echo. The receiving end determines the distance between the transmitting end and the electromagnetic tag based on the received reflected echo frequency, as detailed below: Assume the phase-coded smart metasurface lies in the xoy plane, with the x-axis horizontal, the y-axis vertical, and the z-axis the normal direction of the metasurface's array plane; the phase-coded smart metasurface in Direction divided Column of reflective elements, the spacing between reflective elements is Each column of reflective units is along Expanding directions, in They have the same response in the same direction; a center frequency is signal Irradiation onto the phase-encoded smart metasurface Represents the range, Representing a moment, Represents the imaginary unit; By controlling the on / off state of the PIN diodes in the reflective unit, phase modulation is generated in the reflective array, and the modulation frequency is set to... Assuming far below The reflected echo signal after phase modulation The expression is: （5） in, Represents wave number, and ; Indicates the incident angle at the transmitting end, the first Reflection coefficient of a column of reflective units For the period is The time-varying function is expressed as: （6） Within a modulation period, the phase Switching between two discrete states, with values ​​{0°, 180°}, i.e.: （7） in It is an integer. The duration of the 0° phase within one period; Performing a Fourier series expansion on equation (5), the reflected echo signal contains frequencies of... The harmonic components are detected by the receiver by detecting the main frequency offset of the reflected echo. By combining the pre-calibrated mapping relationship between DC voltage and distance, the distance between the transmitter and the electromagnetic tag can be deduced.

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