Rfid force sensing and localization tag, system, and method based on biomimetic fingerprint structure

Abstract

This invention discloses an RFID force sensing and positioning tag based on a biomimetic fingerprint structure, belonging to the field of wireless sensing technology. The tag includes an antenna layer, a skin-like structure layer as a substrate, a fingerprint-like ridge structure layer, and an RFID chip. The skin-like structure layer is located between the antenna and the fingerprint-like ridge structure layer, and the antenna layer is attached to the lower surface of the skin-like structure layer; multiple structural breakpoints are distributed on the antenna layer. When an external surface force is applied, the fingerprint-like ridge structure layer generates a micro-lever effect, amplifying the force and transmitting it to the antenna layer, causing a change in the overall impedance of the antenna to encode the magnitude of the force; simultaneously, local deformation at specific structural breakpoints tends towards an open-circuit state, causing a shift in the radiation pattern to encode the position of the force. This invention achieves high-precision two-dimensional surface force synchronous sensing and positioning with zero power consumption and low cost, without the need for doping with force-sensitive materials, and has significant application prospects and promotional value.

Description

Technical Field

[0001] This invention belongs to the field of wireless sensing technology and relates to an RFID force sensing and positioning tag, system and method based on a biomimetic fingerprint structure. Background Technology

[0002] Accurate sensing and localization of surface forces are crucial in a variety of applications, including muscle rehabilitation, robotic manipulation of fragile objects, and finger rehabilitation training. However, existing technologies struggle to achieve high-precision and continuous force sensing due to crosstalk interference from dense sensor arrays, ambient light interference from optical sensors, and reliance on batteries and high-power components. Current force sensing methods primarily rely on electrical components (such as piezoresistors or piezoceles) or optical devices. Specifically, electrical sensors depend on discrete transducer arrays for force localization, fundamentally increasing hardware complexity and power consumption. The spatial resolution of force localization is limited by sensor density, and increasing density amplifies crosstalk interference between adjacent cells, thus reducing sensing accuracy. While optical methods utilize reflected or scattered light signals to determine horizontal force distribution without requiring large arrays, their performance is susceptible to ambient light interference, which also reduces sensing accuracy.

[0003] In recent years, passive sensing using radio frequency identification (RFID) technology has become a research hotspot. Commercial RFID tags are typically built on thin, flexible PET substrates, possessing inherent flexibility. When an external force is applied to the tag antenna, the antenna deforms, causing a change in its impedance, which in turn leads to changes in phase and received signal strength (RSS). However, this physical flexibility does not naturally translate into force sensing capability or provide quantifiable force feedback because the impedance changes in standard commercial tags are not optimized for sensitivity to minute forces. To address this issue, some studies have attempted to achieve force sensing by embedding force-sensitive materials into RFID tags. However, these doping processes introduce material heterogeneity, leading to irreversible structural deformation, which slows down the sensor's response time. Furthermore, the fabrication of these specialized materials requires complex manufacturing equipment and labor-intensive procedures, significantly increasing deployment costs, and most existing research lacks force localization capabilities. Summary of the Invention

[0004] The purpose of this invention is to provide an RFID force sensing and positioning tag, system, and method based on a biomimetic fingerprint structure, which solves the problems of existing surface force sensing devices relying on high-power arrays, being susceptible to environmental interference, and existing RFID force sensing tags requiring the doping of force-sensitive materials, resulting in response lag and high cost.

[0005] To achieve the above objectives, the present invention employs the following technical solution:

[0006] A passive wireless surface force sensing and positioning tag with biomimetic fingerprints includes an antenna layer, a skin-like structure layer, and a fingerprint-like ridge structure layer arranged sequentially from bottom to top, as well as a radio frequency identification (RFID) chip mounted on the antenna layer. The antenna layer includes a feed matching part and a fingerprint-like nested radiating part that are interconnected and located on the same horizontal plane. The antenna layer has multiple structural breaks, and the RFID chip is connected to the feed matching part. The antenna layer is attached to the lower surface of the skin-like structure layer, and the fingerprint-like ridge structure layer is attached to the upper surface of the skin-like structure layer.

[0007] Preferably, the power supply matching section includes a power supply port and a matching ring located on the same horizontal plane and interconnected, and the fingerprint-like nested radiation section includes a rectangular load, two outer ring radiation arms and two sets of inner nested arc arms located on the same horizontal plane; the rectangular load is located on the side of the center of symmetry closer to the power supply matching section; Two peripheral annular radiating arms are arranged symmetrically along the circumference. Each peripheral annular radiating arm is composed of two concentric semicircular rings connected end to end, and the end of the outer semicircular ring of each peripheral annular radiating arm is connected to the end of its adjacent matching ring. Two sets of inner nested arc-shaped arms are arranged symmetrically along the circumference. Each set of inner nested arc-shaped arms is composed of multiple arc-shaped arms that are connected end to end and nested sequentially inside the outer annular radiating arms from the outside to the inside. Each outer arc-shaped arm is connected to the end of the inner semicircular ring of the adjacent peripheral annular radiating arm, and the ends of both inner arc-shaped arms are connected to a rectangular load.

[0008] Preferably, the number of structural breakpoints is eight, located at characteristic positions with high current density on the antenna layer surface, as follows: Breakpoint 1: Located at the center of symmetry at the top of the outer annular radial arm; Breakpoints 2 and 3: symmetrically distributed at the arc-shaped bends of the outermost annular radial arm; Breakpoint 4: Located at the top of the straight segment on the upper part of the inner nested arc arm; Breakpoints 5 and 6: symmetrically distributed on the straight extension segments of the innermost nested arc-shaped arms on the outermost side; Breakpoint 7: Located at the center of the rectangular load; Breakpoint 8: Located at the bottom symmetrical center of the matching ring.

[0009] Preferably, the length of the power supply port is 10.6 mm, and the arc length of the matching ring is 10.5 mm; the length of the rectangular load is 9 mm and the width is 3.3 mm; the outer radius of the outer ring of the outer ring radiating arm is 13.7 mm, the outer radius of the inner ring is 11.5 mm, and the line width is 0.8 mm; the line widths of the inner nested arc arms from the outside to the inside are 1.6 mm, 1.4 mm, and 1.3 mm respectively, and the corresponding outer radii are 9.5 mm, 6.4 mm, and 3.8 mm respectively.

[0010] Preferably, the contact surface between the fingerprint-like ridge structure layer and the skin-like structure layer is provided with annular protrusions, and the annular protrusions match the geometry of the antenna layer.

[0011] Preferably, the thickness of the skin-like structure layer is 100 μm and the radius is 14 mm; the thickness of the fingerprint-like ridge structure layer is 1 mm and the radius is 14 mm; and the protrusion height of the annular protrusion is 0.7 mm.

[0012] Preferably, the antenna layer is made of silver nanowires, the skin-like structure layer is a flexible and stretchable polydimethylsiloxane film, and the fingerprint-like ridge structure layer is made of polydimethylsiloxane.

[0013] A passive wireless surface force sensing and positioning system based on biomimetic fingerprints includes a surface force sensing and positioning tag, an RFID reader, a reader antenna, and a back-end server; wherein, the surface force sensing and positioning tag adopts the passive wireless surface force sensing and positioning tag based on biomimetic fingerprints disclosed in this application; the RFID reader is connected to the reader antenna via an RFID feeder.

[0014] A method for force sensing using the biomimetic fingerprint-based passive wireless surface force sensing and positioning system disclosed in this application includes the following steps: Step 1: Deploy a passive wireless surface force sensing and positioning system based on biomimetic fingerprints in the area to be monitored; Step 2: The backend server sends a collection command to the RFID reader, and the RFID reader transmits a UHF radio frequency signal through the reader antenna; the antenna layer of the surface force sensor and positioning tag receives the UHF radio frequency signal and captures energy, activating the RFID chip; Step 3: When an external surface force is applied to the fingerprint-like ridge structure layer, the structure layer transmits the force to the antenna layer; causing a change in the overall impedance of the antenna to encode the magnitude of the force, and at the same time causing a change in the state of the structural breakpoints to cause a shift in the radiation pattern to encode the location of the force; Step 4: The RFID chip uses the energy captured by the antenna layer to modulate data containing its own ID onto the reflected RF signal, and then transmits it back to the reader antenna through backscattering; Step 5: The reader antenna receives the echo signal and transmits it to the RFID reader; the RFID reader obtains the feature data through demodulation and transmits the feature data to the backend server; Feature data includes Received Signal Strength (RSSI) and Phase; Step 6: The backend server preprocesses the received feature data, and then feeds the preprocessed feature data as input features into the pre-trained multi-task deep learning model. The model outputs the magnitude and two-dimensional position of the surface force in real time.

[0015] Preferably, step 1 includes the following operations: Step 11: Connect the UHF RFID reader compliant with the EPCGen2 protocol to the backend server and connect it to the reader antenna via an RF feeder; Step 12: Fix the reader antenna in front of the area to be monitored; Step 13: Fix the surface force sensor and positioning tag to the surface to be measured, and align the main radiation directions of the reader antenna and the tag antenna in space.

[0016] The present invention has the following advantages and beneficial effects: (1) High-sensitivity micro-lever amplification effect: This invention innovatively introduces a biomimetic fingerprint ridge structure layer, which can act as a micro lever to concentrate and amplify the applied minute surface force. This amplification mechanism of a purely physical structure eliminates the need to dope force-sensitive materials such as piezoresistive or piezoelectric materials in the antenna substrate, completely avoiding the irreversible structural deformation and response hysteresis problems caused by heterogeneous material doping, and achieving extremely high force sensing resolution (up to 4mN level).

[0017] (2) Ingenious Decoupling of Two-Parameter Sensing of Force Magnitude and Location: This invention cleverly utilizes the principle of antenna radiation mode reconstruction by precisely deploying eight structural breakpoints at characteristic locations with high current density on the antenna surface. When a surface force is applied, the change in overall impedance is used to encode the magnitude of the force, while the local deformation at a specific breakpoint (tending towards an open circuit state) causes a sudden change in the radiation pattern, which is used to encode the location of the force. This design breaks the limitation of traditional sensing devices that must rely on dense sensor arrays for positioning, achieving precise synchronous sensing and positioning of 2D surface forces with extremely low cost and hardware complexity.

[0018] (3) Passive wireless and long-term continuous monitoring: The sensing tag of this invention works entirely based on the backscattering principle of radio frequency identification (RFID) and does not rely on any high-power components such as onboard batteries, microcontrollers or analog-to-digital converters. Its skin-like flexible structure is not only comfortable to wear, but also enables long-term, continuous surface force monitoring in a zero-power state.

[0019] (4) Easy to manufacture and low cost: The present invention uses photopolymerization 3D printing technology to make molds and combines electro-hydraulic power (EHD) inkjet printing technology to directly deposit silver nanowires. The manufacturing process is simple, highly repeatable and low cost (extremely low cost per piece), which is very suitable for large-scale mass production. Attached Figure Description

[0020] Figure 1 This is an exploded view of the overall structure of a passive wireless surface force sensing and positioning tag for biomimetic fingerprints according to the present invention. Figure 2 This is a schematic diagram illustrating the biomimetic principle of the three-layer fingerprint structure in this invention; Figure 3 This is a schematic diagram of the overall structure of the antenna layer (1) and the distribution of structural breakpoints (13) in this invention; Figure 4 This is a schematic diagram showing the structural composition of the antenna layer (1) in this invention. Figure 5 This is a schematic diagram of the fingerprint-like ridge structure layer (3) in this invention; Figure 6 This is a schematic diagram of the manufacturing process of the sensing and positioning tag described in this invention; Figure 7 This is a schematic diagram of the architecture of the passive wireless surface force sensing and positioning system based on a biomimetic fingerprint antenna of the present invention. Figure 8 This is a cumulative error distribution curve for force estimation in a specific embodiment of the present invention; Figure 9 This is a cumulative error distribution curve for force position estimation in a specific embodiment of the present invention.

[0021] The meanings of the labels in the diagram are as follows: 1-Antenna layer, 11-Feed matching section, 111-Feed port, 112-Matching ring, 12-Fingerprint-like nested radiator, 121-Rectangular load, 122-Outer ring radiating arm, 123-Inner nested arc arm, 13-Structural breakpoint; 2-Type skin structural layer; 3- Fingerprint-like ridge structure layer, 31- Annular protrusion; 4-Radio frequency identification chip. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments. The following embodiments are used to explain the present invention, rather than to limit the scope of protection of the present invention. Those skilled in the art can reproduce the technical solution of the present invention, solve its technical problems, and achieve the expected technical effects based on the content disclosed in this specification without creative effort.

[0023] Example 1 This embodiment discloses a biomimetic fingerprint passive wireless surface force sensing and positioning tag. The tag has an overall axisymmetric circular flexible structure with a radius of 14mm, allowing it to conform to any surface to be measured, achieving passive wireless synchronous surface force sensing and two-dimensional positioning. Figure 1As shown in the exploded view of the overall structure, the tag in this embodiment is an integrated flexible structure with three stacked layers. From top to bottom, it consists of a fingerprint-like ridge structure layer 3, a skin-like structure layer 2, and an antenna layer 1. It also includes a radio frequency identification chip 4 mounted on the antenna layer 1. The skin-like structure layer 2 is located between the antenna layer 1 and the fingerprint-like ridge structure layer 3. The antenna layer 1 is directly deposited and attached to the lower surface of the skin-like structure layer 2, so that the skin-like structure layer 2 and the antenna layer 1 form an integrated flexible sensor body.

[0024] 1.1 Antenna Layer 1 like Figure 3 , Figure 4 As shown, the material of antenna layer 1 is high-concentration silver nanowires (AgNW) with a thickness of 0.017 mm. It has an overall axisymmetric near-circular planar structure, including a power matching part 11, a fingerprint-like nested radiating part 12, and eight structural breakpoints 13. The radio frequency identification chip 4 forms a stable electrical connection with the power matching part 11.

[0025] Power supply matching unit 11: such as Figure 4 As shown, the power supply matching section 11 includes a power supply port 111 and a matching ring 112, wherein the length of the power supply port 111 is 10.6 mm and the arc length of the matching ring 112 is 10.5 mm. The RFID chip 4 selected in this embodiment is an LXMS21ACMD-220 type ultra-high frequency RFID chip, whose port exhibits strong capacitive impedance. The matching ring 112 can form a parallel inductor branch in the power supply network. By coordinating the adjustment of the arc length of the matching ring 112 and the width of the power supply port 111, the real and imaginary parts of the antenna input impedance can be finely adjusted, achieving conjugate matching between the antenna and the chip in the 915MHz ultra-high frequency band. Verified by HFSS full-wave electromagnetic simulation, the antenna in this embodiment achieves a reflection coefficient S11 of -29.59 dB at the target frequency of 915 MHz, demonstrating excellent energy transmission efficiency.

[0026] Imitation fingerprint nested radiating part 12: such as Figure 4As shown, the fingerprint-simulated nested radiating part 12 includes a rectangular load 121, an outer annular radiating arm 122, and three sets of inner nested arc-shaped arms 123. The rectangular load 121 is located below the center of symmetry of the tag, with a length of 9 mm and a width of 3.3 mm. It is used to introduce additional capacitors at the end of the antenna to reduce the overall resonant frequency of the antenna and realize the miniaturization design of the tag. The outer annular radiating arm 122 is composed of two concentric rings connected together. The outer ring has an outer radius of 13.7 mm, the inner ring has an outer radius of 11.5 mm, and the line width is 0.8 mm. It is the main radiating body of the antenna. The three sets of inner nested arc-shaped arms 123 are nested from the outside to the inside in an inverted U-shape. The line widths from the outside to the inside are 1.6 mm, 1.4 mm, and 1.3 mm, respectively, and the corresponding outer radii are 9.5 mm, 6.4 mm, and 3.8 mm, respectively. This fingerprint-like nested wiring structure provides omnidirectional radiation characteristics, and its wiring geometry is completely consistent with the raised trajectory of the fingerprint-like ridge structure layer 3, which can ensure the vertical and precise transmission of stress.

[0027] Eight structural breakpoints 13: such as Figure 3 As shown, the eight structural breakpoints 13 are the core structure for force positioning of the tag, and are respectively set at characteristic locations with high current density on the antenna surface. Specifically, the distribution is as follows: breakpoint 1 is located at the top symmetrical center of the outer ring radiating arm 122; breakpoints 2 and 3 are symmetrically distributed on the left and right arc bends of the outermost outer ring radiating arm 122; breakpoint 4 is located at the top of the narrow straight segment of the upper part of the inner nested arc arm 123; breakpoints 5 and 6 are symmetrically distributed on the right and left straight extension segments of the outermost inner nested arc arm 123; breakpoint 7 is located at the center of the rectangular load 121; and breakpoint 8 is located at the bottom symmetrical center of the matching ring 112. When a surface force is applied to any breakpoint, local mechanical deformation occurs at the breakpoint, tending towards an open circuit state, cutting off the high-density current path, triggering a unique reconstruction of the antenna radiation pattern, forming an electromagnetic fingerprint of the corresponding location, providing a unique and identifiable feature basis for two-dimensional force positioning.

[0028] 1.2 Skin structural layer 2 like Figure 1 , Figure 2 As shown, the skin-like structure layer 2 is a flexible and stretchable polydimethylsiloxane (PDMS) flat film with a thickness of 100 μm and a radius of 14 mm, located between the antenna layer 1 and the fingerprint-like ridge structure layer 3. The antenna layer 1 is directly deposited and attached to the lower surface of the skin-like structure layer 2, forming an integrated flexible sensor body. In this embodiment, the dielectric constant of the skin-like structure layer 2 at 100 kHz is 2.7, and the dielectric loss is 0.001, which allows the amplified deformation force of the fingerprint-like ridge structure layer 3 to be transmitted vertically to the antenna layer 1 without loss.

[0029] 1.3 Imitation fingerprint ridge structure layer 3 like Figure 1 , Figure 2 , Figure 5 As shown, the fingerprint-like ridge structure layer 3 is made of polydimethylsiloxane (PDMS), with an overall thickness of 1 mm and a radius of 14 mm. Multiple annular protrusions 31 with a height of 0.7 mm are provided on its surface. In this embodiment, the fingerprint-like ridge structure layer 3 has a dielectric constant of 2.7 and a dielectric loss of 0.001 at 100 kHz, consistent with the skin-like structure layer 2, thus avoiding electromagnetic losses caused by dielectric constant mismatch. The planar extension trajectory of the annular protrusions 31 is completely identical to the trace trajectory of the fingerprint-like nested radiating part 12 and the feed matching part 11 of the antenna layer 1. Each protrusion structure corresponds one-to-one with the orthographic projection of the traces of the antenna layer 1 in the vertical direction, ensuring that the surface force acting on the fingerprint-like ridge structure layer 3 can be accurately transmitted vertically to the corresponding traces and structural breakpoints 13 of the antenna layer 1. Figure 2 As shown in the schematic diagram of the biomimetic principle of the three-layer fingerprint structure, the three-layer structure of this embodiment replicates the human fingerprint-skin-tactile sensor perception mechanism. The annular protrusion 31 corresponds to the ridge of the human fingerprint, the skin-like structure layer 2 corresponds to the human dermis, and the antenna layer 1 corresponds to the human tactile sensor. The annular protrusion 31 can form a micro-lever structure, which concentrates and amplifies the applied small surface force through the micro-lever effect. Through simulation and experimental verification, the deformation displacement generated at the bottom of the 0.7mm protrusion height structure in this embodiment can reach 4.3 times that of the planar structure without protrusions, which greatly improves the sensitivity of the tag to small forces.

[0030] 1.4 Radio Frequency Identification Chip 4 This embodiment uses an LXMS21ACMD-220 ultra-high frequency RFID chip that conforms to the EPCGen2 communication protocol. It is fixed to the feed port 111 of the antenna layer 1 with epoxy conductive adhesive, forming a stable electrical connection with the feed matching part 11, and is used to complete the modulation and backscatter transmission of radio frequency signals.

[0031] Example 2 This embodiment discloses a method for fabricating a passive wireless surface force sensing and positioning tag based on a biomimetic fingerprint, which can mass-produce the sensing and positioning tag described in Embodiment 1. The fabrication process is as follows: Figure 6 As shown, the specific steps are as follows: Step 1: The fingerprint mold is prepared using stereolithography (SLA) additive manufacturing technology. Based on the raised structure drawing of the fingerprint ridge structure layer 3, a high-precision fingerprint mold is prepared. The cavity structure of the mold is completely matched with the structure of the annular raised 31, and the molding accuracy is controlled within ±10μm.

[0032] Step 2: Preparation of the fingerprint-like ridge structure layer 3. The polydimethylsiloxane (PDMS) matrix and curing agent are thoroughly mixed at a mass ratio of 10:1. After stirring evenly, the mixture is poured into the fingerprint mold prepared in Step 1. The mold is placed in a vacuum chamber and degassed for 15 minutes to completely remove air bubbles from the mixture. Then, the mold is placed in a constant temperature oven and heat-cured at 80°C for 2 hours. After curing, the mold is demolded to obtain a PDMS film with annular protrusions 31 on the surface, which is the fingerprint-like ridge structure layer 3. The overall thickness is 1 mm, and the protrusion height of the annular protrusions 31 is 0.7 mm with a radius of 14 mm.

[0033] Step 3: Preparation of Skin-like Structure Layer 2 On a flat PET substrate without fingerprint patterns, a layer of PDMS mixture (matrix to curing agent mass ratio 10:1) is spin-coated at a speed of 1000 rpm for 30 s to form a uniform PDMS film with a thickness of 100 μm. Then, the substrate is placed in a constant temperature oven and heat-cured at 80°C for 2 hours to form a flat flexible substrate, namely the skin-like structure layer 2.

[0034] Step 4: Antenna layer 1 is prepared using an electro-hydraulic power (EHD) jet printer. A high-concentration silver nanowire mesh is directly deposited on the lower surface of the skin-like structure layer 2 prepared in step 3. The mesh is then printed according to a preset antenna pattern to form a patterned conductive layer, i.e., antenna layer 1. The thickness of the printed antenna layer is 0.017 mm. Subsequently, the printed substrate is placed in a constant temperature oven and dried at 60°C for 60 minutes to enhance the adhesion between the silver nanowire conductive layer and the PDMS substrate. After drying, the integrated structure of the skin-like structure layer 2 and antenna layer 1 is peeled off from the PET carrier through a fine demolding process, completing the manufacturing of the main label structure.

[0035] Step 5: At the designated connection point of the feed port 111 of the antenna layer 1, precisely apply a uniform layer of epoxy conductive adhesive to ensure that the conductive adhesive completely covers the silver nanowire conductive mesh area; gently press the LXMS21ACMD-220 RFID chip 4 onto the adhesive-coated area to ensure that the chip pins are in full contact with the conductive adhesive, and then let it stand for 8 hours in a dust-free environment at room temperature until the conductive adhesive is completely cured, thus completing the overall assembly of the tag.

[0036] Example 3 This embodiment discloses a passive wireless surface force sensing and positioning system based on a biomimetic fingerprint antenna. The system architecture is as follows: Figure 7 As shown, it includes surface force sensing and positioning tags, RFID readers, reader antennas, and back-end servers.

[0037] The surface force sensing and positioning tag adopts the passive wireless surface force sensing and positioning tag with bionic fingerprint as described in Example 1, which conforms to the EPC Gen2 UHF RFID protocol; the RFID reader adopts the ImpinjR420 UHF RFID reader, which supports UHF band communication of 902-928MHz, and is connected to the circularly polarized reader antenna with a gain of 6dBi through a 50Ω impedance-matched RF feed line; the back-end server is a computer with Windows / Linux operating system, with built-in data preprocessing module and pre-trained multi-task deep learning model, and establishes a communication connection with the RFID reader through Ethernet to complete command issuance, data reception and processing.

[0038] Example 4 This embodiment discloses a passive wireless surface force sensing and positioning method based on a biomimetic fingerprint antenna, implemented using the system described in Embodiment 3. The working principle is as follows: Figure 7 As shown, the specific steps are as follows: Step 1: System Deployment Step 11: Connect the ImpinjR420 UHF RFID reader conforming to the EPCGen2 protocol to the backend server via Ethernet, and connect it to its matching circularly polarized reader antenna via an RF feeder; Step 12: Fix the reader antenna at a position 1m in front of the area to be monitored, with the main radiation direction of the antenna facing the area to be monitored; Step 13: Flatly fix the surface force sensing and positioning tag described in Example 1 to the surface to be measured. During deployment, ensure that the main radiation directions of the reader antenna and the tag antenna are spatially aligned to ensure stable transmission of RF signals.

[0039] Step 2: Tag activation and power supply. The backend server sends a collection command to the RFID reader. The RFID reader transmits a 915MHz UHF radio frequency signal through the reader antenna. The signal propagates in space to the surface force sensing and positioning tag. The tag's antenna layer 1 receives and couples the incident UHF radio frequency signal, completing the capture of radio frequency energy, powering the RFID chip 4, and activating the RFID chip 4 to enter the working state.

[0040] Step 3: Dual-parameter encoding of mechanical-electromagnetic characteristics. When an external surface force is applied to the tag surface and causes structural deformation, dual-parameter encoding of the force magnitude and position is completed simultaneously: On the one hand, the annular protrusion 31 of the fingerprint-like ridge structure layer 3 amplifies the surface force through a micro-lever effect and accurately transmits it to the antenna layer 1, causing the antenna layer 1 to deform as a whole, resulting in a change in the overall equivalent input impedance of the antenna; according to the reflection coefficient formula Γ=(Zc-Za ) / (Zc+Za (Where Zc is the chip impedance, Za) (where Γ is the conjugate value of the antenna input impedance). Impedance mismatch causes a change in the reflection coefficient Γ, which in turn causes an overall shift in the RSSI and phase of the backscattered signal received at the reader end. This overall shift encodes the magnitude of the applied surface force. On the other hand, the structural breakpoint 13 corresponding to the location where the surface force is applied undergoes local deformation, tending towards an open circuit state, cutting off the high-density current path on the antenna surface, resulting in a specific shift in the antenna radiation pattern, producing RSSI and phase abrupt changes that are different from other breakpoint locations. This specific feature encodes the two-dimensional location where the surface force is applied.

[0041] Step 4: Radio Frequency Signal Backscattering and Data Transmission. The RFID chip 4 uses the radio frequency energy captured by the antenna layer 1 to modulate the data containing its unique ID information onto the reflected radio frequency signal. Through backscattering communication, the modulated radio frequency signal is transmitted back to the reader antenna.

[0042] Step 5: Signal Reception and Feature Extraction. After the reader antenna receives the echo signal returned by the tag, it transmits it to the RFID reader. The RFID reader demodulates the echo signal, extracts the tag's unique ID, received signal strength (RSSI), and phase feature data, and transmits this feature data to the back-end server in real time via Ethernet.

[0043] Step 6: Multi-task decoupling and result output. The backend server first preprocesses the received feature data, including moving average filtering to remove environmental noise and data normalization. Then, the preprocessed feature data is used as input features and fed into a pre-trained multi-task deep learning model. In this embodiment, the multi-task deep learning model is an MLP model with three hidden layers. The number of neurons in the hidden layers is 64, 32, and 16 respectively. The activation function is the ReLU function. The output layer contains two branches: a force magnitude output branch based on continuous regression and a force position output branch based on two-dimensional coordinate regression. The model decouples the output of the magnitude of the surface force and the two-dimensional coordinates of the action position in real time and synchronously through the pre-learned nonlinear mapping relationship between impedance gradient and radiation mutation.

[0044] Example 5 This embodiment uses the system described in Embodiment 3 and the method described in Embodiment 4 to test and verify the sensing and positioning performance of the tag. The test platform is built using a commercial high-precision force gauge (accuracy ±0.1mN) and a high-precision two-dimensional displacement stage (positioning accuracy ±0.05mm). The test process is as follows: The tag is fixed on the test platform of the two-dimensional displacement stage. The distance between the reader antenna and the tag is 1m. A standard force in the range of 0~1N is applied to the tag surface through a high-precision force gauge. At the same time, the position of the force is adjusted by the two-dimensional displacement stage to cover all the breakpoints and non-breakpoints on the tag surface. The tag RSSI and phase data under different force magnitudes and different application positions are collected and fed into a multi-task deep learning model for calculation. The error between the force magnitude estimation and the position estimation is statistically analyzed.

[0045] The test results are as follows: (1) Force magnitude detection performance: such as Figure 8 As shown in the cumulative error distribution curve of force estimation, under test conditions where the magnitude and location of the force are unknown, the median error of force estimation by this system is only 1.6mN, and the error of 90% of the measurement samples is controlled within 9.3mN. The force sensing resolution can reach the 4mN level. It does not require the doping of any force-sensitive material, and completely avoids the problems of irreversible structural deformation and response hysteresis caused by the doping of heterogeneous materials. (2) Force positioning performance: such as Figure 9 As shown in the cumulative error distribution curve of force position estimation, under test conditions where the magnitude and position of the force are unknown, the median error of the force position estimation of this system is only 0.3 mm, and the position error of 90% of the measurement samples is controlled within 0.9 mm, achieving sub-millimeter level two-dimensional force positioning accuracy. It does not rely on a dense sensor array, which greatly reduces hardware complexity and deployment cost.

[0046] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A passive wireless surface force sensing and positioning tag based on biomimetic fingerprints, characterized in that, It includes an antenna layer (1), a skin-like structure layer (2) and a fingerprint-like ridge structure layer (3) arranged sequentially from bottom to top, and a radio frequency identification chip (4) mounted on the antenna layer (1). The antenna layer (1) includes a power matching part (11) and a fingerprint-like nested radiating part (12) that are interconnected and located on the same horizontal plane. The antenna layer (1) is provided with multiple structural breakpoints (13). The radio frequency identification chip (4) is connected to the power matching part (11). The antenna layer (1) is attached to the lower surface of the skin-like structure layer (2); The fingerprint-like ridge structure layer (3) is attached to the upper surface of the skin-like structure layer (2).

2. The passive wireless surface force sensing and positioning tag for biomimetic fingerprints as described in claim 1, characterized in that, The power supply matching part (11) includes a power supply port (111) and a matching ring (112) located on the same horizontal plane and connected to each other. The fingerprint-like nested radiation part (12) includes a rectangular load (121) located on the same horizontal plane, two outer ring radiation arms (122) and two sets of inner nested arc arms (123). The rectangular load (121) is located on the side of the center of symmetry closer to the power supply matching part (11); Two peripheral annular radiating arms (122) are arranged symmetrically along the circumference. Each peripheral annular radiating arm (122) is composed of two concentric semicircular rings connected end to end, and the end of the outer semicircular ring of each peripheral annular radiating arm (122) is connected to the end of its adjacent matching ring (112). Two sets of inner nested arc arms (123) are arranged symmetrically along the circumference. Each set of inner nested arc arms (123) consists of multiple arc arms that are connected end to end and nested in the inner side of the outer ring radiating arm (122) from the outside to the inside. Any outer arc arm is connected to the end of the inner semi-circular ring of the adjacent outer ring radiating arm (122). The ends of the two inner arc arms are connected to the rectangular load (121).

3. The passive wireless surface force sensing and positioning tag for biomimetic fingerprints as described in claim 2, characterized in that, The number of structural breakpoints (13) is eight, located at characteristic locations with high current density on the surface of the antenna layer (1), and their specific distribution is as follows: Breakpoint 1: Located at the top symmetry center of the outer annular radial arm (122); Breakpoints 2 and 3: symmetrically distributed at the arc-shaped bends of the outermost annular radial arm (122); Breakpoint 4: Located at the top of the straight segment on the upper part of the inner nested arc arm (123); Breakpoints 5 and 6: symmetrically distributed on the straight extension segments of the outermost inner nested arc arm (123); Breakpoint 7: Located at the center of the rectangular load (121); Breakpoint 8: Located at the bottom symmetry center of the matching ring (112).

4. The passive wireless surface force sensing and positioning tag for biomimetic fingerprints as described in claim 3, characterized in that, The length of the power supply port (111) is 10.6 mm, and the arc length of the matching ring (112) is 10.5 mm; the length of the rectangular load (121) is 9 mm and the width is 3.3 mm; the outer radius of the outer ring of the outer ring of the peripheral annular radiating arm (122) is 13.7 mm, the outer radius of the inner ring is 11.5 mm, and the line width is 0.8 mm; the line width of the inner nested arc arm (123) from the outside to the inside is 1.6 mm, 1.4 mm and 1.3 mm respectively, and the corresponding outer radii are 9.5 mm, 6.4 mm and 3.8 mm respectively.

5. The passive wireless surface force sensing and positioning tag for biomimetic fingerprints as described in claim 1, characterized in that, The contact surface between the fingerprint-like ridge structure layer (3) and the skin-like structure layer (2) is provided with an annular protrusion (31), which matches the geometry of the antenna layer (1).

6. The passive wireless surface force sensing and positioning tag for biomimetic fingerprints as described in claim 5, characterized in that, The passive wireless surface force sensing and positioning tag for biomimetic fingerprints as described in claim 3 is characterized in that the thickness of the skin-like structure layer (2) is 100 μm and the radius is 14 mm; the thickness of the fingerprint-like ridge structure layer (3) is 1 mm and the radius is 14 mm; and the protrusion height of the annular protrusion (31) is 0.7 mm.

7. The passive wireless surface force sensing and positioning tag for biomimetic fingerprints as described in any one of claims 1-6, characterized in that, The antenna layer (1) is made of silver nanowires, the skin-like structure layer (2) is a flexible and stretchable polydimethylsiloxane film, and the fingerprint-like ridge structure layer (3) is made of polydimethylsiloxane.

8. A passive wireless surface force sensing and positioning system based on biomimetic fingerprints, characterized in that, It includes a surface force sensing and positioning tag, an RFID reader, a reader antenna, and a back-end server; wherein, the surface force sensing and positioning tag adopts the passive wireless surface force sensing and positioning tag with bionic fingerprint as described in any one of claims 1 to 7; the RFID reader is connected to the reader antenna through an RF feed line.

9. A method for force sensing using the passive wireless surface force sensing and positioning system based on biomimetic fingerprints as described in claim 8, characterized in that, Includes the following steps: Step 1: Deploy the passive wireless surface force sensing and positioning system based on bionic fingerprint in the area to be monitored; Step 2: The backend server sends a collection command to the RFID reader, and the RFID reader transmits a UHF radio frequency signal through the reader antenna; the antenna layer (1) of the surface force sensing and positioning tag receives the UHF radio frequency signal and captures energy, activating the radio frequency identification chip (4). Step 3: When an external surface force is applied to the fingerprint-like ridge structure layer (3), the structure layer transmits the force to the antenna layer (1); causing a change in the overall impedance of the antenna to encode the magnitude of the force, and at the same time causing a change in the state of the structural breakpoint (13) to cause a shift in the radiation pattern to encode the position of the force; Step 4: The radio frequency identification chip (4) uses the energy captured by the antenna layer (1) to modulate the data containing its own ID onto the reflected radio frequency signal, and transmits it back to the reader antenna through backscattering; Step 5: The reader antenna receives the echo signal and transmits it to the RFID reader; the RFID reader obtains the feature data through demodulation and transmits the feature data to the backend server; The characteristic data includes received signal strength RSSI and phase; Step 6: The backend server preprocesses the received feature data, and then feeds the preprocessed feature data as input features into the pre-trained multi-task deep learning model. The model outputs the magnitude and two-dimensional position of the surface force in real time.

10. The method for force sensing using the passive wireless surface force sensing and positioning system based on biomimetic fingerprints as described in claim 8, as described in claim 9, is characterized in that... Step 1 includes the following operations: Step 11: Connect the UHF RFID reader compliant with the EPCGen2 protocol to the backend server and connect it to the reader antenna via an RF feeder; Step 12: Fix the reader antenna in front of the area to be monitored; Step 13: Fix the surface force sensor and positioning tag to the surface to be measured, and align the main radiation directions of the reader antenna and the tag antenna in space.

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