A passive wireless sensing tag with multi-axis sensing function

Abstract

The application discloses a passive wireless sensing label with multi-axis sensing function and belongs to the technical field of sensing; the device comprises a film layer, a first antenna layer, a piezoelectric layer and a second antenna layer which are sequentially stacked from top to bottom; an RFID chip and an RFID antenna are installed in the first antenna layer; the RFID chip is in signal connection with the RFID antenna; the piezoelectric layer is in signal connection with the RFID chip; the RFID chip is connected with a sensing structure, and the sensing structure is installed on the first antenna layer or the second antenna layer; the number of the sensing structure is two, the two sensing structures are horizontally arranged on the same plane, and the two sensing structures are perpendicular to each other. The passive wireless sensing label has the advantages of convenient manufacturing, low cost, flexible size, high starting sensitivity, flexible adjustment of sensing parameters and the like.

Description

Technical Field

[0001] This invention relates to the field of sensing technology, and more specifically to a passive wireless sensing tag with multi-axis sensing capabilities. Background Technology

[0002] Passive wireless sensor tags, with their advantage of requiring no built-in power supply and relying on external radio frequency energy coupling for power, are widely used in various monitoring scenarios. Their core advantages lie in easy installation, low maintenance costs, and long service life, avoiding the battery life problems and safety hazards such as battery leakage associated with active devices. Currently, existing RFID passive wireless sensor tags have significant limitations: without adding chips or changing existing processes (CMOS process + printed antenna process + flip-chip process + composite process), they can only achieve a very limited range of sensing functions, such as temperature, that are achievable with CMOS technology. For sensing functions based on MEMS and other process technologies, they cannot be implemented using a single CMOS chip. Therefore, with current technology, only two solutions can be used to combine CMOS passive wireless sensor chip technology with other sensor technologies.

[0003] Existing technical solution 1: Utilizing multi-chip SiP co-packaging technology, the sensor is combined with other functional circuits such as power acquisition, communication, ADC, and control onto a single package or die, and then the chip is soldered to the antenna. This solution has two major drawbacks: First, the technical path is narrow, with only a few sensors suitable for SiP packaging with other chips; second, the implementation process is high-risk and high-cost, as the final chip sensing parameters cannot be readjusted, requiring a completely new SiP package to achieve sensing for each parameter, resulting in high technical costs and risks; third, power consumption is high.

[0004] Existing technical solution two: Utilizing PCB soldering technology, multiple chips (including sensor chips, power acquisition chips, communication chips, ADC chips, etc.) are integrated and soldered onto the same circuit board, which is then soldered to the antenna. This solution also has two major drawbacks: First, the soldering process is complex and cumbersome, and more chips result in a larger footprint and higher cost; second, global power consumption optimization is difficult, as different functional chips come from different manufacturers, making it difficult to coordinate and optimize power consumption. In passive wireless sensor tags where ultra-low power consumption is a prerequisite, their startup sensitivity performance faces a significant bottleneck.

[0005] For example, in the current field of multi-axis force sensing, existing products, whether wired or wireless, have significant limitations: Wired systems suffer from susceptibility to electromagnetic interference, are fragile and easily damaged, have high costs, are complex to operate and deploy, and all require dedicated demodulation equipment. Long-term deployment of such equipment is extremely costly; periodic temporary deployments result in a huge amount of repetitive work, but consistency of test results is difficult to guarantee. Wireless systems require periodic replacement of the energy storage batteries supporting wireless operation, and the cost remains high. As for passive wireless multi-axis force sensing, a mature solution has yet to be found.

[0006] Therefore, developing a sensing tag that can achieve multi-axis sensing, has a compact structure, high measurement consistency, strong anti-interference ability, conforms to the passive wireless working mode, and is compatible with existing RFID tag production processes has become an urgent technical problem to be solved. Summary of the Invention

[0007] The purpose of this invention is to provide a passive wireless sensing tag with multi-axis sensing capabilities. This tag achieves three-axis passive wireless sensing with the same parameters or three different parameters without adding a chip (i.e., one chip) or changing existing tag manufacturing processes (CMOS process + printed antenna process + flip-chip process + composite process). This passive wireless sensing tag has significant advantages such as ease of manufacturing, low cost, flexible size, high activation sensitivity, and flexible adjustment of sensing parameters. It also features a compact structure, convenient installation, and strong anti-interference capabilities. In fields where maintenance is difficult or mass deployment is required (such as large-scale equipment in conventional bridge construction, mining, power generation, metallurgy, and refining industries), it can significantly replace existing high-cost, complex-operation, and single-function sensing devices.

[0008] To solve the above-mentioned technical problems, the present invention provides a passive wireless sensing tag with multi-axis sensing function, comprising a thin film layer, a first antenna layer, a piezoelectric layer and a second antenna layer stacked from top to bottom; An RFID chip and an RFID antenna are installed in the first antenna layer; the RFID chip is signal-connected to the RFID antenna. The piezoelectric layer is connected to the RFID chip signal; The RFID chip is connected to the sensing structure, which is installed on the first antenna layer or the second antenna layer. The number of the sensing structures is two, and the two sensing structures are horizontally arranged on the same plane and oriented perpendicularly to each other.

[0009] Preferably, the sensing structure is a bent circuit structure or an interdigitated electrode structure.

[0010] Preferably, the bent circuit structure is a continuous U-shaped bend design, with 5-25 bends and a bend spacing of 0.05-2mm.

[0011] Preferably, the interdigitated electrode structure consists of two interlaced and spaced electrode finger groups with a spacing of 0.05-2 mm.

[0012] Preferably, the thin film layer is a sensitive material thin film layer.

[0013] Preferably, the sensitive material film layer is made of polydimethylsiloxane stress-sensitive composite material, with 10% to 30% carbon nanotubes added as conductive filler, and the thickness is 0.25-0.4 mm.

[0014] Preferably, the piezoelectric layer is made of piezoelectric ceramic and has a thickness of 0.2-3 mm.

[0015] Preferably, the RFID chip is connected to the ground plane of the second antenna layer through a sensing structure and a vertical metallized via.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Compatible with existing processes, no need to add chips, and extremely low cost: It is fully compatible with existing RFID tag manufacturing processes, uses 100% CMOS process to produce single RFID chips, uses printed circuit and composite process to produce antennas, and uses flip packaging, SMT surface mount or bonding process to connect the chip and antenna. No need to add sensor chips, power chips, etc., and no need to change existing mass production processes. It can achieve mass production under the same process, and the marginal cost is almost the same as existing RFID tags, solving the defects of high cost and complex process of existing integrated solutions.

[0017] (2) Achieve multi-axis force, displacement sensing, or multi-parameter sensing to expand application scenarios: Based on a single tag and a single chip, achieve multi-axis force, displacement sensing, or multi-parameter sensing, solving the problem that existing single-chip RFID tags can only achieve single-parameter sensing such as temperature. There is no need to install two different sensing devices separately, reducing installation costs and space occupation, and adapting to scenarios that require multi-parameter monitoring, such as structural health monitoring and industrial equipment inspection; at the same time, the sensing parameters can be flexibly designed. Only by changing the type of sensitive material, temperature, stress, pressure, and gas content sensing of different ranges and accuracies can be achieved, adapting to a variety of application needs.

[0018] (3) Compact structure and flexible size: The integrated layered structure is adopted, and each functional layer is closely attached without any extra splicing parts. The overall thickness of the label is ≤5mm, and the size can be adjusted between 5×5mm-300×300mm. It has good flexibility and can fit the curved surface structure of the object being tested. It can follow the deformation of the object being tested without being damaged, thus solving the defects of existing integrated solutions that have large area and complex structure.

[0019] (4) High sensing accuracy and strong anti-interference ability: The sensing parameter tags are collected locally, which can effectively avoid electromagnetic interference on the acquisition line; (5) High startup sensitivity and low power consumption: The chip integrates ultra-low power sensor signal isolation, conditioning and amplification circuits, eliminating the need for additional independent circuits, optimizing global power consumption, and the tag startup sensitivity is comparable to the typical sensitivity of traditional RFID tags at -18dBm, which is far superior to existing integrated solutions and is suitable for passive wireless monitoring needs.

[0020] (6) High reliability and long service life: The passive wireless design eliminates the need for a built-in battery, avoiding the battery life problem and battery leakage risk of active devices. The tag has a service life of several years and extremely low maintenance costs. The structure of each layer is fixed by a high-strength insulating adhesive, which makes the connection tight and there is no relative displacement. It is suitable for working environments of -40℃ to 85℃ and can operate stably in complex industrial environments. Attached Figure Description

[0021] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0022] Figure 1 This is a schematic diagram of the three-dimensional structure of the first type of passive wireless sensor tag: the X-axis sensor and Y-axis sensor are bent linear structures and are arranged in the first antenna layer; Figure 2 This is a schematic diagram of the three-dimensional structure of the second type of passive wireless sensor tag: the X-axis sensor and Y-axis sensor are interdigitated electrode type structures, arranged on the first antenna layer; Figure 3 This is a schematic diagram of the three-dimensional structure of the third type of passive wireless sensor tag: the X-axis sensor and Y-axis sensor are interdigitated electrode structures, arranged on the second antenna layer; Figure 4 This is a schematic diagram of the three-dimensional structure of the fourth type of passive wireless sensor tag: the X-axis sensor and Y-axis sensor are bent linear structures, arranged on the second antenna layer; Figure 5 This is the front view of the passive wireless sensor tag; Figure 6 This explains the working principle of RFID chips. In the picture: 1-Thin film layer; 2-First antenna layer; 21-RFID chip; 22-Sensing structure; 23-First RFID antenna; 3-Piezoelectric layer; 4-Second antenna layer. Detailed Implementation

[0023] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0024] The terminology used in one or more embodiments of this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the one or more embodiments of this specification. The singular forms “a,” “described,” and “the” as used in one or more embodiments of this specification and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in one or more embodiments of this specification refers to and includes any or all possible combinations of one or more associated listed items.

[0025] It should be understood that although the terms first, second, etc., may be used to describe various information in one or more embodiments of this specification, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first may also be referred to as second without departing from the scope of one or more embodiments of this specification, and similarly, second may also be referred to as first. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to a determination."

[0026] The present invention will now be described in further detail with reference to the accompanying drawings: To better illustrate the technical effects of the present invention, the present invention provides the following specific embodiments to illustrate the above technical process: Example 1: A passive wireless sensing tag with multi-axis sensing function: In the printed antenna layer, the bent circuit structure and electrode structure (the bent circuit structure and electrode structure constitute the sensing structure 22) required for X-axis and Y-axis sensing are pre-designed at specific locations in the first antenna layer 2. These locations include blank areas on the antenna substrate and the middle of the antenna radiating surface. The bent circuit structure and electrode structure are directly connected to the corresponding pins of the RFID chip 21 via conductive printed layer traces or vias. The electrode structure required for Z-axis sensing is respectively disposed in the first antenna layer 2 and the second antenna layer 4, and a piezoelectric layer 3 is added between the first antenna layer 2 and the second antenna layer 4. The piezoelectric layer 3 not only generates a piezoelectric response to forces in the Z-axis direction, but also provides support for the first antenna layer 2 in the XY plane, thus protecting the X-axis and Y-axis sensing structures 22 of the first antenna layer 2 from interference by force components in the Z-axis direction. If a force-resistance sensitive material is laminated onto the upper surface of the antenna layer through a composite process to form a thin film layer 1, the X-axis and Y-axis sensing can be made more sensitive.

[0027] The specific structure and working principle are as follows: A passive wireless sensing tag with multi-axis sensing function includes, from top to bottom, a thin film layer 1: a sensitive material thin film layer, a first antenna layer 2: a sensing structure 22 (interdigitated electrodes, bent circuits, etc.) and a first RFID antenna 23, a piezoelectric layer 3: piezoelectric ceramic, and a second antenna layer 4: a sensing structure 22 (interdigitated electrodes, bent circuits, etc.) and a second RFID antenna 23.

[0028] The RFID chip 21 is fixed at a predetermined position on the antenna layer using flip-chip packaging, SMT surface mount technology, or bonding technology, and is electrically connected to the conductive printed layer, bent circuit structure, and electrode structure of the antenna layer. The antenna layer is used to receive radio frequency signals transmitted by an external reader, realizing power coupling and wireless transmission of sensing signals. Simultaneously, the first antenna layer 2, through its integrated bent circuit structure, achieves X-axis and Y-axis sensing parameter measurement. The first antenna layer 2 can also integrate an interdigitated electrode structure, working in conjunction with the sensitive film of the thin film layer 1, to achieve X-axis and Y-axis sensing parameter measurement. The first antenna layer 2 and the second antenna layer 4, through their electrode structures, measure the electrode charge voltage from the piezoelectric layer 3 after being subjected to a Z-axis force, achieving Z-axis force sensing parameter measurement. The second antenna layer 4 can integrate a bent circuit structure to achieve X-axis and Y-axis sensing parameter measurement; the second antenna layer 4 can also integrate an interdigitated electrode structure, working in conjunction with the sensitive film of the thin film layer 1, to achieve X-axis and Y-axis sensing parameter measurement.

[0029] The first antenna layer 2 of the sensor tag also contains an antenna structure. To ensure antenna performance, the sensor tag is typically installed by attaching it tightly to the surface of the object being measured via the second antenna layer 4. The first antenna layer 2 naturally extends above the surface of the object by the height of a piezoelectric layer 3. Therefore, when the surface of the object undergoes deformation in the x and y axes, if the sensing structure 22 (interdigitated electrodes, bent circuits, etc.) is installed on the second antenna layer 4, its ability to track deformation is better than that of the first antenna layer 2. However, when the parameter to be sensed is not from the surface of the object being measured, but rather from the environment, such as the concentration of a specific gas, the sensing structure of the second antenna layer 4 becomes less sensitive due to being obscured by the object being measured. In this case, the sensing structure 22 of the first antenna layer 2 can more sensitively follow changes in the measured parameter. In summary, the sensing structures 22 of the first antenna layer 2 and the second antenna layer 4 are almost homogeneous from a structural topology perspective. In practice, the choice between the two or both depends on their ability to track the target's physical parameters.

[0030] One end of the sensing structure 22 is connected to the RFID chip 21, and the other end is connected to the second antenna layer 4 through a vertical metallized via. The wiring of the second antenna layer 4 is then connected to the Avss (ground pin) of the chip.

[0031] in: RFID Chip 21: Manufactured using CMOS technology, it features a single-chip structure, eliminating the need for additional sensor chips, energy harvesting chips, etc. The chip integrates an RF energy rectification and regulation module, a wireless communication module, a temperature sensing module, and an ultra-low power sensing signal isolation, conditioning, amplification, and acquisition module. The chip pins include at least RFIN and AVSS pins. The chip is fixed to the central blank area of ​​the antenna layer using a flip-chip packaging process. The chip pins are electrically connected to the antenna feed terminals, the two ends of the bent circuit structure, and the two leads of the electrode layer via conductive silver paste or bonding wires, enabling energy reception, signal transmission, and sensing signal processing. The chip thickness is 0.05-0.5mm, and the dimensions are 1-3mm × 1-3mm, not exceeding the range of the antenna layer, ensuring a compact overall tag structure.

[0032] Antenna and sensing electrode (or sensing circuit) layer: Formed using flexible conductive material through a printing process, preferably conductive silver paste printing or copper foil etching (compatible with existing printed antenna processes); the antenna type is a microstrip antenna or dipole antenna, operating at ultra-high frequency 860-960MHz, with a conductive printed layer thickness of 10-50μm; the antenna layer integrates bent circuit structures and sensing signal lead-out structures such as electrodes. The bent circuit structure adopts a continuous U-shaped bend design, with 5-25 bends and a bend spacing of 0.05-2mm, located in the middle or edge area of ​​the antenna radiating surface. The two ends of the structure are directly connected to the signal connection pins of the RFID chip 21 via traces on the same layer. The electrode lead-out structure is either an interdigitated electrode on the same layer or two plates distributed on the first antenna layer 2 and the second antenna layer 4 respectively, directly connected to the signal connection pins of the RFID chip 21. The interdigitated electrode structure consists of two interlaced and spaced electrode finger groups with a spacing of 0.05-2mm. The upper surface of the first antenna layer 2 is tightly bonded to the lower surface of the sensitive material thin film layer 1, and the lower surface of the first antenna layer 2 is tightly bonded to the upper surface of the dielectric (or pressure-sensitive, stress-sensitive, and gas adsorption-sensitive) piezoelectric layer 3. A total of two sensing structures 22 (bent circuit structure or interdigitated electrode structure) are designed. These two sensing structures 22 are horizontally arranged on the same plane (first antenna layer 2 or second antenna layer 4) and oriented perpendicularly to each other. They are used to detect the deformation of the X and Y axes respectively, and the spacing between the sensing structures 22 is in the range of 0.05-2mm.

[0033] When the sensor tag deforms along with the object being measured, both the first antenna layer 2 and the piezoelectric layer 3 deform accordingly. The planar tensile deformation of the first antenna layer 2 changes the inductance and resistance values ​​of the bent circuits in the first antenna layer 2. These values ​​are detected by the RFID chip 21, which then calculates the X and Y axis force and displacement changes. The vertical compression of the piezoelectric layer 3 in the thickness direction changes the charge voltage of the electrode between the first antenna layer 2 and the second antenna layer 4. The charge voltage at both ends of the electrode is detected by the RFID chip 21, which can then calculate the corresponding Z axis force or displacement change.

[0034] The charge voltage signal of piezoelectric layer 3 is first fed into a charge amplifier, which amplifies the weak charge voltage and converts it into a voltage signal with a certain load-carrying capacity and a voltage range between 0-1V. This signal is then fed into the RFID chip 21. This charge amplifier can also be implemented within the RFID chip 21. The voltage magnitude and the Z-axis force magnitude generally have a positive linear relationship; measurement errors need to be eliminated through calibration and fitting during the calibration process.

[0035] Specific materials for thin film layer 1 are listed below: Polydimethylsiloxane (PDMS) based stress-sensitive composite material, with 10%-30% carbon nanotubes (CNTs) added as conductive filler, has a thickness of 0.25-0.4 mm and is formed by coating process. Its resistance value changes linearly with stress deformation, with a resistance change rate of 0.02-0.05 / MPa, and has good elastic recovery performance. Specific materials for the first antenna layer 2: Piezoelectric ceramics (PZT), with a thickness of 0.2-3mm, are formed by sputtering and have an insulating surface to prevent short circuits with the antenna layer. Their piezoelectric coefficient d33 is 200-300pC / N, which can convert pressure deformation into voltage. In conjunction with the electrode structure of the first antenna layer 2 and the second antenna layer 4, the voltage signal is input to the RFID chip 21. The high dielectric properties of piezoelectric ceramics also facilitate the miniaturization of passive wireless sensing antennas, thereby contributing to the overall miniaturization of passive wireless sensing tags.

[0036] Clearly, this sensing structure 22 is not limited to force and displacement measurement. By replacing the sensing material of the thin film layer 1 or the piezoelectric layer 3 to change its specific response type, it can achieve a wide range of sensing parameters such as humidity, stress, VOCs, and H2 gas content.

[0037] The present invention has the following advantages: 1. Compatible with existing processes, requires no new chips, and has low cost. It adopts a single CMOS RFID chip, which is fully compatible with the existing RFID tag's CMOS + printed antenna + flip packaging + composite mass production process. No additional sensing / energy harvesting chip is required, and the marginal cost is the same as that of ordinary RFID tags. It abandons the high-cost solution of existing multi-chip SIP packaging / PCB soldering.

[0038] 2. Enable multi-axis / multi-parameter sensing and expand application scenarios. Triaxial sensing is achieved by using two perpendicular sensing structures (X / Y axes) on the same plane, plus a piezoelectric layer and a dual antenna layer (Z axis); by replacing the thin film / piezoelectric layer sensitive material, multi-parameter detection such as stress, gas, and humidity can be realized, breaking through the limitations of single-chip single-parameter sensing and adapting to multi-parameter monitoring scenarios.

[0039] 3. Compact structure and flexible size Correspondingly: It adopts an integrated stacked structure of thin film layer - first antenna layer - piezoelectric layer - second antenna layer, with no redundant components; the overall thickness is ≤5mm, and the planar size is adjustable from 5×5 to 300×300mm. The antenna layer uses flexible conductive material, which can fit curved surfaces and deform with shape.

[0040] 4. High sensing accuracy and strong anti-interference capabilities Sensing parameters are acquired locally, avoiding electromagnetic interference from external circuits; the piezoelectric layer provides support for X / Y axis sensing, avoiding interference from Z-axis force components; the chip has built-in signal isolation / conditioning / amplification circuits to process signals locally and reduce transmission loss.

[0041] 5. High startup sensitivity and low power consumption The single chip integrates full functions of RF power harvesting, communication, and signal processing without additional independent circuits, and optimizes global power consumption; the start-up sensitivity reaches the level of traditional RFID tags at -18dBm, which is far superior to existing integrated solutions.

[0042] 6. High reliability and long service life The passive wireless design eliminates the need for a built-in battery, avoiding battery life / leakage issues; each layer is fixed with a high-strength insulating adhesive, preventing relative displacement; it is adaptable to working environments from -40℃ to 85℃, can operate stably in complex industrial environments, has a service life of several years, and low maintenance costs.

[0043] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A passive wireless sensing tag with multi-axis sensing function, characterized in that: It includes a thin film layer, a first antenna layer, a piezoelectric layer, and a second antenna layer, which are stacked sequentially from top to bottom; An RFID chip and an RFID antenna are installed in the first antenna layer; the RFID chip is signal-connected to the RFID antenna. The piezoelectric layer is connected to the RFID chip signal; The RFID chip is connected to the sensing structure, which is installed on the first antenna layer or the second antenna layer. The number of the sensing structures is two, and the two sensing structures are horizontally arranged on the same plane and oriented perpendicularly to each other.

2. The passive wireless sensing tag with multi-axis sensing function according to claim 1, characterized in that: The sensing structure is a bent circuit structure or an interdigitated electrode structure.

3. The passive wireless sensing tag with multi-axis sensing function according to claim 2, characterized in that: The bent circuit structure is a continuous U-shaped bend design with 5-25 bends and a bend spacing of 0.05-2mm.

4. The passive wireless sensing tag with multi-axis sensing function according to claim 2, characterized in that: The interdigitated electrode structure consists of two interlaced and spaced electrode finger groups with a spacing of 0.05-2 mm.

5. The passive wireless sensing tag with multi-axis sensing function according to claim 1, characterized in that: The thin film layer is a sensitive material thin film layer.

6. The passive wireless sensing tag with multi-axis sensing function according to claim 5, characterized in that: The sensitive material thin film layer is made of polydimethylsiloxane stress-sensitive composite material with 10% to 30% carbon nanotubes added as conductive filler, and has a thickness of 0.25-0.4 mm.

7. The passive wireless sensing tag with multi-axis sensing function according to claim 6, characterized in that: The piezoelectric layer is made of piezoelectric ceramic and has a thickness of 0.2-3 mm.

8. The passive wireless sensing tag with multi-axis sensing function according to claim 6, characterized in that: The RFID chip is connected to the ground plane of the second antenna layer through a sensing structure and a vertical metallized via.

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